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Sample records for drag reduction effect

  1. Effects of Polymer Parameters on Drag Reduction.

    Science.gov (United States)

    Safieddine, Abbas Mohammad

    The effects of polymer parameters on fluid drag reduction using polyethylene oxide (PEO), polyacrylamide (PAM), guar gum (GG) and hydroxyethyl cellulose (HEC) were investigated. Due to the unavailability of high molecular weight (MW) water-soluble polymers having narrow molecular weight distribution (MWD), an aqueous preparative size exclusion chromatography (SEC) system capable of fractionating over wide MW ranges was constructed. An online low shear viscometer, coupled to the SEC, measured the instantaneous intrinsic viscosity of the eluting polymer solution and, therefore, served as a MW detector since Mark-Houwink "K" and "a" values for all four polymers were known. With the aid of the viscometer, the SEC system was calibrated. The preparative nature of the chromatography system allowed the collection of large volumes of nearly monodisperse fractions (MWD SEC approach allowed drag reduction (DR) experiments using well-characterized, narrowly dispersed polymer solutions under controlled tube flow conditions. Correlations of drag reduction performance with primary polymer parameters (i.e., concentration, intrinsic viscosity ((eta)), volume fraction (c(eta)), number of chain links (N), and combinations thereof) were used to test the validity of several theoretical DR models. Walsh's energy model, as well as the Deborah argument, did not completely account for drag reduction behavior under all experimental conditions. Within each of the flexible or rigid polymer groups, the extensional viscosity model was successful in correlating c(eta) N with DR under all turbulent conditions. However, it failed to account for the differences in chemical structure between the two polymer groups. However, when the cellulosic repeat unit was used instead of the carbon-carbon bond as the chain link for the rigid polymers (GG and HEC), all DR versus c (eta) N curves under all turbulent conditions collapsed into a single function. This has been predicted by the recent "yo-yo" model of

  2. DRAG REDUCTION EFFECT OF COUPLING FLEXIBLE TUBES WITH TURBULENT FLOW

    Institute of Scientific and Technical Information of China (English)

    CAI Shu-peng; JIN Guo-yu; LI Da-mei; Yang Lin

    2008-01-01

    To analyze the mechanism of drag reducing effect by coupling flexible tubes with turbulent flow, based on experimental examination of more obvious turbulent drag reduction effect in flexible tubes than in rigid tubes, experimental investigation was performed on the effect of turbulent drag reduction, fluctuating vibration characteristics of flexible tube and the correlations by using a double-tube system and laser displacement sensor. The results are as follows: with the decrease of the thickness of the flexible tubes, the root mean square of fluctuating amplitude of the outer wall of the tubes increases, and the non-dimensional burst period increases, resulting in the increase of the reduction rate of drag coefficient by coupling flexible tubes with turbulent flow. At applied pressure-balanced air on the outer wall and the Reynolds number of about 1.75 104, the non-dimensional burst periods of the flexible tubes with the thickness of 2 mm, 3 mm, 4 mm are 141, 126, 105, respectively.

  3. Synthetic Effect of Vivid Shark Skin and Polymer Additive on Drag Reduction Reinforcement

    Directory of Open Access Journals (Sweden)

    Huawei Chen

    2014-06-01

    Full Text Available Natural shark skin has a well-demonstrated drag reduction function, which is mainly owing to its microscopic structure and mucus on the body surface. In order to improve drag reduction, it is necessary to integrate microscopic drag reduction structure and drag reduction agent. In this study, two hybrid approaches to synthetically combine vivid shark skin and polymer additive, namely, long-chain grafting and controllable polymer diffusion, were proposed and attempted to mimic such hierarchical topography of shark skin without waste of polymer additive. Grafting mechanism and optimization of diffusion port were investigated to improve the efficiency of the polymer additive. Superior drag reduction effects were validated, and the combined effect was also clarified through comparison between drag reduction experiments.

  4. Effect of Polymer Type and Mixing of Polymers on Drag Reduction in Turbulent Pipe Flow

    Directory of Open Access Journals (Sweden)

    Salam Hadi Hussein

    2017-05-01

    Full Text Available The paper reports on studies on effect of the type of polymer on drag reduction. The study conducted through circular pipe using Carboxy Methyl Cellulose (CMC, Xanthan gum (XG and their mixing in equal ratios as additives in pipe of diameter 0.0381m. The study covered range of parameters like concentration, mean velocity and angle of inclination of pipe. The maximum drag reduction observed was about 58%, 46% and 46% for the three polymers respectively. It is found that the drag reduction for the mixture is close to the drag reduction for XG polymer. The SPSS program has been used for correlate the data that have been obtained. The drag reduction percentage is correlated in terms of Reynolds number Re, additive concentration C (ppm and angle of inclination of pipe (deg, and the relations obtained is mentioned.

  5. Drag Reduction of Bacterial Cellulose Suspensions

    Directory of Open Access Journals (Sweden)

    Satoshi Ogata

    2011-01-01

    Full Text Available Drag reduction due to bacterial cellulose suspensions with small environmental loading was investigated. Experiments were carried out by measuring the pressure drop in pipe flow. It was found that bacterial cellulose suspensions give rise to drag reduction in the turbulent flow range. We observed a maximum drag reduction ratio of 11% and found that it increased with the concentration of the bacterial cellulose suspension. However, the drag reduction effect decreased in the presence of mechanical shear.

  6. Turbulent Taylor-Couette flow over riblets: drag reduction and the effect of bulk fluid rotation

    Science.gov (United States)

    Greidanus, A. J.; Delfos, R.; Tokgoz, S.; Westerweel, J.

    2015-05-01

    A Taylor-Couette facility was used to measure the drag reduction of a riblet surface on the inner cylinder. The drag on the surfaces of the inner and outer cylinders is determined from the measured torque when the cylinders are in exact counter-rotation. The three velocity components in the instantaneous flow field were obtained by tomographic PIV and indicate that the friction coefficients are strongly influenced by the flow regimes and structures. The riblet surface changes the friction at the inner-cylinder wall, which generates an average bulk fluid rotation. A simple model is proposed to distinguish drag changes due to the rotation effect and the riblet effect, as a function of the measured drag change and shear Reynolds number . An uncorrected maximum drag reduction of 5.3 % was found at that corresponds to riblet spacing Reynolds number . For these conditions, the model predicts an azimuthal bulk velocity shift of 1.4 %, which is confirmed by PIV measurements. This shift indicates a drag change due to a rotation effect of -1.9 %, resulting in a net maximum drag reduction of 3.4 %. The results correspond well with earlier reported results and demonstrate that the Taylor-Couette facility is a suitable and accurate measurement tool to characterize the drag performance of surfaces.

  7. Drag Reduction by Microvortexes in Transverse Microgrooves

    Directory of Open Access Journals (Sweden)

    Bao Wang

    2014-07-01

    Full Text Available A transverse microgrooved surface was employed here to reduce the surface drag force by creating a slippage in bottom layer in turbulent boundary layer. A detailed simulation and experimental investigation on drag reduction by transverse microgrooves were given. The computational fluid dynamics simulation, using RNG k-ε turbulent model, showed that the vortexes were formed in the grooves and they were a main reason for the drag reduction. On the upside of the vortex, the revolving direction was consistent with the main flow, which decreased the flow shear stress by declining the velocity gradient. The experiments were carried out in a high-speed water tunnel with flow velocity varying from 17 to 19 m/s. The experimental results showed that the drag reduction was about 13%. Therefore, the computational and experimental results were cross-checked and consistent with each other to prove that the presented approach achieved effective drag reduction underwater.

  8. The Effect of Sodium Hydroxide on Drag Reduction using a Biopolymer.

    Directory of Open Access Journals (Sweden)

    Singh Harvin Kaur A/P Gurchran

    2014-07-01

    Full Text Available Drag reduction is observed as reduced frictional pressure losses under turbulent flow conditions and hence, substantially increases the flowrate of the fluid. Practical application includes water flooding system, pipeline transport and drainage system. Drag reduction agent, such as polymers, can be introduced to increase the flowrate of water flowing, reducing the water accumulation in the system and subsequently lesser possibility of heavy flooding. Currently used polymer as drag reduction agents is carboxymethylcellulose, to name one. This is a synthetic polymer which will seep into the ground and further harm our environment in excessive use of accumulation. A more environmentally-friendly drag reduction agent, such as the polymer derived from natural sources or biopolymer, is then required for such purpose. As opposed to the synthetic polymers, the potential of biopolymers as drag reduction agents, especially those derived from a local plant source, are not extensively explored. The drag reduction of a polymer produced from a local plant source within the turbulent regime will be explored and assessed in this study using a rheometer where a reduced a torque produced can be perceived as a reduction of drag. The cellulose powder was converted to carboxymethylcellulose (CMC by etherification process using sodium monochloroacetate and sodium hydroxide. The carboxymethylation reaction then was optimized against concentration of NaOH. The research is structured to focus on producing the biopolymer and also assess the drag reduction ability of the biopolymer produced against concentration of sodium hydroxide.

  9. "Fluid bearing" effect of enclosed liquids in grooves on drag reduction in microchannels

    Science.gov (United States)

    Chen, Haosheng; Gao, Yang; Stone, Howard A.; Li, Jiang

    2016-12-01

    We report details of the fluid motion formed within and above grooves when a laminar continuous phase fluid flows over a second immiscible fluid enclosed in a grooved microchannel. Vortical structures within the transverse grooves were caused by a slip velocity at the fluid-fluid interface and act as "fluid bearings" on the boundary to lubricate the flow of the continuous phase. We investigated the drag reduction in the laminar flow in the microchannel by measuring slip at the boundaries and calculating an effective slip length, taking into account the influence of the effect of the viscosity ratio of the two fluids on the effective slip length. The "fluid bearing" effect can be used to transport high viscosity fluids using low viscosity fluids trapped in cavities to reduce drag.

  10. Drag Reduction by Leidenfrost Vapor Layers

    Science.gov (United States)

    Vakarelski, Ivan U.; Marston, Jeremy O.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2011-05-01

    We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.

  11. Drag Reduction by Leidenfrost Vapor Layers

    KAUST Repository

    Vakarelski, Ivan Uriev

    2011-05-23

    We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.

  12. Drag reduction effects facilitated by microridges inside the mouthparts of honeybee workers and drones.

    Science.gov (United States)

    Li, Chu-Chu; Wu, Jia-Ning; Yang, Yun-Qiang; Zhu, Ren-Gao; Yan, Shao-Ze

    2016-01-21

    The mouthpart of a honeybee is a natural well-designed micropump that uses a reciprocating glossa through a temporary tube comprising a pair of galeae and labial palpi for loading nectar. The shapes and sizes of mouthparts differ among castes of honeybees, but the diversities of the functional microstructures inside the mouthparts of honeybee workers and drones remain poorly understood. Through scanning electron microscopy, we found the dimensional difference of uniformly distributed microridges on the inner galeae walls of Apis mellifera ligustica workers and drones. Subsequently, we recorded the feeding process of live honeybees by using a specially designed high-speed camera system. Considering the microridges and kinematics of the glossa, we constructed a hydrodynamic model to calculate the friction coefficient of the mouthpart. In addition, we test the drag reduction through the dimensional variations of the microridges on the inner walls of mouthparts. Theoretical estimations of the friction coefficient with respect to dipping frequency show that inner microridges can reduce friction during the feeding process of honeybees. The effects of drag reduction regulated by specific microridges were then compared. The friction coefficients of the workers and drones were found to be 0.011±0.007 (mean±s.d.) and 0.045±0.010, respectively. These results indicate that the mouthparts of workers are more capable of drag reduction compared with those of drones. The difference was analyzed by comparing the foraging behavior of the workers and drones. Workers are equipped with well-developed hypopharyngeal, and their dipping frequency is higher than that of drones. Our research establishes a critical link between microridge dimensions and drag reduction capability during the nectar feeding of honeybees. Our results reveal that microridges inside the mouthparts of honeybee workers and drones reflect the caste-related life cycles of honeybees.

  13. Effects of solids loading on drag reduction in polymeric drilling fluids through straight and coiled tubings

    Energy Technology Data Exchange (ETDEWEB)

    Shah, S.N.; Tareen, M. [Oklahoma Univ., Norman, OK (United States); Clark, D. [Baker Hughes INTEQ, Calgary, AB (Canada)

    2000-06-01

    The effects of solids loading on drag reduction characteristics of commonly used polymeric drilling fluid flowing through straight and coiled tubing was studied. Energy is wasted to friction losses when fluids flow through pipes, whether it be for crude oil transportation, drilling, hydraulic fracturing or gas injection. This is seen in the form of pressure drop along the pipe. This is remedied by adding polymers to the fluid stream to help reduce pressure losses. In this study, polymeric fluids flowing through straight pipe without solids were first examined. The polymers investigated were partially hydrolyzed polyacrylamide (PHPA) and polysaccharide gum (XCD). They were dissolved in brines which were prepared by mixing potassium chloride and sodium formate in water. The fluid system which provided the least resistance to the flow was then determined and the study was extended by increasing solids and determining the effects on the flow of the polymeric fluid through straight and coiled tubing. The PHPA/potassium chloride solution was selected for this study because it exhibited the best drag resistance. The solution was then loaded with barite and bentonite to simulate solid cuttings. It was observed that when clear polymeric solutions were loaded with solids, drag reduction decreased significantly. The effect of curvature on the flow of solid-laden fluids was also studied. Frictional losses in coiled tubing was found to be nearly doubled that of straight tubing. 15 refs., 2 tabs., 15 figs.

  14. Bubble Drag Reduction Requires Large Bubbles

    Science.gov (United States)

    Verschoof, Ruben A.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef

    2016-09-01

    In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.

  15. Bubble drag reduction requires large bubbles

    CERN Document Server

    Verschoof, Ruben A; Sun, Chao; Lohse, Detlef

    2016-01-01

    In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.

  16. Turbulent drag reduction by polymers

    Energy Technology Data Exchange (ETDEWEB)

    Bonn, Daniel [Van der Waals-Zeeman Instituut, University of Amsterdam, Valckenierstraat 65 1018, XE Amsterdam (Netherlands); Amarouchene, Yacine [CPMOH, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence cedex (France); Wagner, Christian [Institut fuer Experimentalphysik, Universitaet des Saarlandes, Saarbruecken (Germany); Douady, Stephane [Laboratoire de Physique Statistique de l' ENS, 24 rue Lhomond, 75231 Paris cedex 05 (France); Cadot, Olivier [ENSTA, Chemin de la Huniere, 91761 Palaiseau cedex (France)

    2005-04-13

    The reduction of turbulent energy dissipation by addition of polymers is studied experimentally. We first address the question of where the action of the polymers is taking place. Subsequently, we show that there is a direct correlation of drag reduction with the elongational viscosity of the polymers. For this, the reduction of turbulent energy dissipation by addition of the biopolymer DNA is studied. These results open the way for a direct visualization study of the polymer conformation in a turbulent boundary layer.

  17. Bioinspired surfaces for turbulent drag reduction.

    Science.gov (United States)

    Golovin, Kevin B; Gose, James W; Perlin, Marc; Ceccio, Steven L; Tuteja, Anish

    2016-08-06

    In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.

  18. Global effect of local skin friction drag reduction in spatially developing turbulent boundary layer

    CERN Document Server

    Stroh, A; Schlatter, P; Frohnapfel, B

    2016-01-01

    A numerical investigation of two locally applied drag reducing control schemes is carried out in the configuration of a spatially developing turbulent boundary layer (TBL). One control is designed to damp near-wall turbulence and the other induces constant mass flux in the wall-normal direction. Both control schemes yield similar local drag reduction rates within the control region. However, the flow development downstream of the control significantly differs: persistent drag reduction is found for the uniform blowing case whereas drag increase is found for the turbulence damping case. In order to account for this difference the formulation of a global drag reduction rate is suggested. It represents the reduction of the streamwise force exerted by the fluid on a finite length plate. Furthermore, it is shown that the far downstream development of the TBL after the control region can be described by a single quantity, namely a streamwise shift of the uncontrolled boundary layer, i.e. a changed virtual origin. B...

  19. Effect of Off-Body Laser Discharge on Drag Reduction of Hemisphere Cylinder in Supersonic Flow

    Science.gov (United States)

    Kianvashrad, Nadia; Knight, Doyle; Wilkinson, Stephen P.; Chou, Amanda; Horne, Robert A.; Herring, Gregory C.; Beeler, George B.; Jangda, Moazzam

    2017-01-01

    The interaction of an off-body laser discharge with a hemisphere cylinder in supersonic flow is investigated. The objectives are 1) experimental determination of the drag reduction and energetic efficiency of the laser discharge, and 2) assessment of the capability for accurate simulation of the interaction. The combined computational and experimental study comprises two phases. In the first phase, laser discharge in quiescent air was examined. The temporal behavior of the shock wave formed by the laser discharge was compared between experiment and simulation and good agreement is observed. In the second phase, the interaction of the laser discharge with a hemisphere cylinder was investigated numerically. Details of the pressure drag reduction and the physics of the interaction of the heated region with the bow shock are included. The drag reduction due to this interaction persisted for about five characteristic times where one characteristic time represents the time for the flow to move a distance equal to the hemisphere radius. The energetic efficiency of laser discharge for the case with 50 mJ energy absorbed by the gas is calculated as 3.22.

  20. Improvement of water-repellent and hydrodynamic drag reduction properties on bio-inspired surface and exploring sharkskin effect mechanism

    Science.gov (United States)

    Luo, Yuehao; Liu, Yufei; Anderson, James; Li, Xiang; Li, Yuanyue

    2015-07-01

    Bio-inspired/biomimetic surface technologies focusing on sharkskin, lotus leaf, gecko feet, and others have attracted so lots of attentions from all over the world; meanwhile, they have also brought great advantages and profits for mankind. Sharkskin drag-reducing/low-resistance surface is the imperative consequence of nature selection and self-evolution in the long history, which can enable itself accommodate the living environments perfectly. Generally speaking, sharkskin effect can become transparent only in some certain velocity scope. How to expand its application range and enhance the drag reduction function further has developed into the urgent issue. In this article, the water-repellent and hydrodynamic drag-reducing effects are improved by adjusting sharkskin texture. The experimental results show that contact angle of more than 150° is achieved, and drag-reducing property is improved to some extent. In addition, the drag-reducing mechanism is explored and generalized from different aspects adopting the numerical simulation, which has important significance to comprehend sharkskin effect.

  1. Innovative Flow Control Concepts for Drag Reduction

    Science.gov (United States)

    Lin, John C.; Whalen, Edward A.; Eppink, Jenna L.; Siochi, Emilie J.; Alexander, Michael G.; Andino, Marlyn Y.

    2016-01-01

    This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wing's leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs

  2. Bionic Research on Bird Feather for Drag Reduction

    Directory of Open Access Journals (Sweden)

    Beibei Feng

    2015-02-01

    Full Text Available To reduce friction drag with bionic method in a more feasible way, the surface microstructure of bird feather was analyzed attempting to reveal the biologic features responding to skin friction drag reduction. Then comparative bionic surface mimicking bird feather was fabricated through hot-rolling technology for drag reduction. The microriblet film was formed on a PVC substrate through a self-developed hot-rolling equipment. The bionic surface with micron-scale riblets formed spontaneously due to the elastic-plastic deformation of PVC in high temperature and high pressure environment. Comparative experiments between micro-structured bionic surface and smooth surface were performed in a wind tunnel to evaluate the effect of bionic surface on drag reduction, and significant drag reduction efficiency was obtained. Numerical simulation results show that microvortex induced in the solid-gas interface of bionic surface has the effect of shear stress reduction and the small level of an additional pressure drag resulting from pressure distribution deviation on bird feather like surface, hence reducing the skin friction drag significantly. Therefore, with remarkable drag reduction performance and simple fabrication technology, the proposed drag reduction technique shows the promise for practical applications.

  3. Polymer flexibility and turbulent drag reduction

    NARCIS (Netherlands)

    Gillissen, J.J.J.

    2008-01-01

    Polymer-induced drag reduction is the phenomenon by which the friction factor of a turbulent flow is reduced by the addition of small amounts of high-molecular-weight linear polymers, which conformation in solution at rest can vary between randomly coiled and rodlike. It is well known that drag redu

  4. Bionic Research on Fish Scales for Drag Reduction

    Institute of Scientific and Technical Information of China (English)

    Zhaoliang Dou; Jiadao Wang; Darong Chen

    2012-01-01

    To reduce friction drag with bionic method in a more feasible way,the surface microstructure of fish scales was analyzed attempting to reveal the biologic features responding to skin friction drag reduction.Then comparable bionic surface mimicking fish scales was fabricated through coating technology for drag reduction.The paint mixture was coated on a substrate through a self-developed spray-painting apparatus.The bionic surface with micron-scale caves formed spontaneously due to the interfacial convection and deformation driven by interfacial tension gradient in the presence of solvent evaporation.Comparative experiments between bionic surface and smooth surface were performed in a water tunnel to evaluate the effect of bionic surface on drag reduction,and visible drag reduction efficiency was obtained.Numerical simulation results show that gas phase develops in solid-liquid interface of bionic surface with the effect of surface topography and partially replaces the solid-liquid shear force with gas-liquid shear force,hence reducing the skin friction drag effectively.Therefore,with remarkable drag reduction performance and simple fabrication technology,the proposed drag reduction technique shows the promise for practical applications.

  5. Drag reduction through self-texturing compliant bionic materials

    Science.gov (United States)

    Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

    2017-01-01

    Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction.

  6. Riblet drag reduction and the effect of bulk fluid rotation in a fully turbulent Taylor-Couette flow

    NARCIS (Netherlands)

    Greidanus, A.J.; Delfos, R.; Tokgoez, S.; Westerweel, J.

    2015-01-01

    Low drag surfaces are often desired in many industries with applications in open and closed channel flows, such as ship hulls and pipe flows. Drag reduction is a phenomenon that can have substantial energy savings, resulting in ecological and economical benefits. We use a Taylor-Couette facility as

  7. Experimental study of drag reduction in flumes and spillway tunnels

    Institute of Scientific and Technical Information of China (English)

    Ying-kui WANG; Chun-bo JIANG

    2010-01-01

    Experiments in an open flume model and spillway tunnel model were carried out using drag reduction techniques.Two drag reduction techniques were adopted in the experiments:polymer addition and coating.The drag reduction effect of a polyacrylamide(PAM)solution and dimethyl silicone oil coating were studied in the flume model experiments,and the results were analyzed.Experiments were then carried out with a model of the Xiluodu Hydropower Station,the second largest dam in China.In order to reduce the resistance,the spillway tunnels were internally coated with dimethyl silicone oil.This is the first time that these drag reduction techniques have been applied to so large a hydraulic model.The experimental results show that the coating technique can effectively increase flood discharge.The outlet velocity and the jet trajectory distance are also increased,which enhances the energy dissipation of the spillway tunnel.

  8. Effect of Catalyst Film Thickness on Growth Morphology, Surface Wettability and Drag Reduction Property of Carbon Nanotubes

    Science.gov (United States)

    Ma, Weiwei; Zhou, Zhiping; Li, Gang; Li, Ping

    2016-10-01

    Nickel films were deposited on silicon substrates using magnetron sputtering method. The pretreatment process of nickel films under high temperature and ammonia atmosphere was investigated. The thickness of nickel film has a great influence on growth morphology of carbon nanotubes (CNTs). Too large or too small thickness would do harm to the orientated growth of CNTs. The inner structure, elements composition and growth mechanism have been confirmed by TEM and EDX characterization. The surface wettability and drag reduction property of CNTs were investigated. This paper can provide a new, effective method to further develop the practical application in micro/nano devices field.

  9. Induce Drag Reduction of an Airplane Wing

    Directory of Open Access Journals (Sweden)

    Md. Fazle Rabbi

    2015-06-01

    Full Text Available This work describes the aerodynamic characteristics for aircraft wing model with and without slotted winglet. When an aircraft moves forward with a high speed then a small circulatory motion of air is created at the wingtip due to the pressure difference between the upper and lower surface of the wing is called vortices. This circulatory fluid tends to leak from lower to upper surface of wing which causes downward motion is called “downwash” and generates a component of the local lift force in the direction of the free stream called induced drag. Downwash causes reduction of lift and contribute induced drag to the total drag. Drag reduction for aerial vehicles has a range of positive ramifications: reduced fuel consumption, larger operational range, greater endurance and higher achievable speeds. An experimental study is conducted to examine the potentiality of slotted winglet for the reduction of induced drag, and for the improvement of lift coefficient without increasing the span of aircraft wing. The model composed of a swept wing built from NACA 0012 airfoil. The test conducted in subsonic wind tunnel of 1m×1m rectangular test section at flow speed 25m/s placing the wing without winglet, wing with winglet at 30° inclination, wing with winglet at 60° inclination, and wing with winglet at 70° inclination at angle of attack ranging from 0 to 16 degree. The test result shows 20- 25% reduction in drag coefficient and 10-20% increase in lift coefficient by using slotted winglet.

  10. Turbulent drag reduction in dilute polymer solutions

    Science.gov (United States)

    Sreenivasan, K. R.; White, Christopher M.

    1998-11-01

    It is well known that the addition of small amounts of flexible polymers reduces drag in turbulent pipe flows. However, the underlying physics is still poorly understood. This paper will consider two aspects: The dependence of the onset of drag reduction on polymer concentration, and the so-called maximum drag reduction asymptote. The latter defines the maximum drag reduction possible for any polymer at a given Reynolds number, independent of the polymer concentration and detailed polymeric structure [1]. It is shown tentatively that a modest reworking of de Gennes' theory [2] is compatible with available experimental data. The principal element of the theory is that the polymers do not get stretched fully, but that the partially extended polymers store elastic energy and interfere with cascade mechanisms in turbulence. A conclusive understanding requires experiments in which the polymer properties that go into the theory are directly measured. [1] P.S. Virk, AIChE J., 21, 625 (1975) [2] P.G. de Gennes, Introduction to Polymer Dynamics, University of Cambridge (1990)

  11. Drag reduction using slippery liquid infused surfaces

    Science.gov (United States)

    Hultmark, Marcus; Stone, Howard; Smits, Alexander; Jacobi, Ian; Samaha, Mohamed; Wexler, Jason; Shang, Jessica; Rosenberg, Brian; Hellström, Leo; Fan, Yuyang

    2013-11-01

    A new method for passive drag reduction is introduced. A surface treatment inspired by the Nepenthes pitcher plant, previously developed by Wong et al. (2011), is utilized and its design parameters are studied for increased drag reduction and durability. Nano- and micro-structured surfaces infused with a lubricant allow for mobility within the lubricant itself when the surface is exposed to flow. The mobility causes slip at the fluid-fluid interface, which drastically reduces the viscous friction. These new surfaces are fundamentally different from the more conventional superhydrophobic surfaces previously used in drag reduction studies, which rely on a gas-liquid interface. The main advantage of the liquid infused surfaces over the conventional surfaces is that the lubricant adheres more strongly to the surface, decreasing the risk of failure when exposed to turbulence and other high-shear flows. We have shown that these surfaces can reduce viscous drag up to 20% in both Taylor-Couette flow and in a parallel plate rheometer. Supported under ONR Grants N00014-12-1-0875 and N00014-12-1-0962 (program manager Ki-Han Kim).

  12. Turbulent drag reduction through oscillating discs

    CERN Document Server

    Wise, Daniel J

    2014-01-01

    The changes of a turbulent channel flow subjected to oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations. The Reynolds number is $R_\\tau$=$180$, based on the friction velocity of the stationary-wall case and the half channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20%. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim to identify the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, computed by taking into account the power spent to actuate the discs. This may be positive and reaches 6%. The Rosenblat viscous pump flow is used to predict the power spent for disc motion in the turbulent channel flow and to estimate localized and transient regions over the disc surface subjected to the turbulent regenerative braking effect, for which the wall turbulence exerts work on the discs. The...

  13. Agitator tank device and drag reduction agent evaluation

    Institute of Scientific and Technical Information of China (English)

    张帆; 肖博元; 汤养浩; 罗旗荣

    2008-01-01

    The device that consists of tank and disk agitator for evaluation drag reduction agents(DRA) was established.The effect of DRA was defined by testing the changes of agitator torque that drives the disk rotation.The HG-DRA for oil pipeline from Linyi to Puyang was studied by agitator tank device.The relationships between the drag reduction rate and Reynolds number,concentration,balance time were studied.The best concentration and the highest Renords number for the best drag reduction rate were confirmed.The results show that the drag reduction rate tested in agitator tank is close to that in pipeline.The maximum error of drag reduction rate between pipeline and agitator tank is 18.3%,which indicates that the agitator tank device is available to evaluate the effect of DRA for pipeline and it also has the advantages of simple,easy to be operated and using small volume of oil.Those are very helpful for operaters to know the properties of DRA and operate pipeline well.

  14. Numerical Research on Drag Reduction Characteristics of Supercavitating Body of Revolution

    Institute of Scientific and Technical Information of China (English)

    FUHui-ping; LUChuan-jing; LIJie

    2004-01-01

    Drag reduction characteristics of supercavitating body of revolution was researched numerically with a bubble two-phase flow model embodied in commercial CFD code Fluent 6.0.The work included the effects of body shape on drag coefficient and supercavity sizes; supercavity control; drag coefficient Cd as a function of cavitation number; and the effect of the ratio of length L to diameter D on drag reduction rate. Research on drag reduction mechanism of supercavitation shows that supercavitation can reduce not only the friction drag coefficient but also the pressure drag coefficient. There may be a best combination among body shape, the ratio L/D, cavitation number, engineering feasibility and so on, which makes the drag reduction ratehighest.

  15. Investigation into the Mechanism of Polymer Thread Drag Reduction

    Science.gov (United States)

    1990-01-01

    drag reducers than polyacrylamides of equal molecular weight. The drag reduction increases as the Re or Cm increases. The concentrations of polymer...wall region, 10 < y’ < 100, for drag reduction to occur. The normalized distance from the wall is defined as y* = yut/v; u, is the friction velocity...AP 30, a polyacrylamide solution, with a 5000 ppm concentration on the centerline of a water flow in a glass tube, they achieved drag reduction up to

  16. Drag reduction in electro-osmosis of polymer solutions

    Science.gov (United States)

    Chang, Feng-Ming; Tsao, Heng-Kwong

    2007-05-01

    Electro-osmosis is the preferred transport mechanism in microfluidic systems. Drag reduction in electro-osmosis of polymer solutions is observed due to polymer depletion in the electric double layer (EDL). The well-known Helmholtz-Smoluchowski (HS) equation indicates that the electro-osmosis mobility is inversely proportional to the solution viscosity. For low molecular weight the polymer size (R) is smaller than the EDL thickness (λ) and the HS equation is valid. For high molecular weight (R>λ) the chains in the EDL are partially sheared and the effective viscosity is smaller than the solution viscosity. Salt addition reduces λ and can enhance drag reduction substantially.

  17. Drag Reduction by Polymeric and Nonpolymeric Additives

    Science.gov (United States)

    White, Christopher; Sreenivasan, K. R.

    1997-11-01

    To investigate the ``self-healing'' property of drag reducing surfactant micelles we have conducted a comparative study between high polymers and surfactants in six turbulent pipe flows (Reynolds numbers between 2000 and 90,000) with varying intensities o f secondary flow. Friction factor values are measured in a straight pipe of 185 diameters; three pipes, each turning through four 90 degree elbows, of lengths 1085 diameters, 875 diameters, and 600 diameters; and a twice-turned coiled pipe, radius of curv ature of 24 diameters and length of 290 diameters. All the flows are gravity driven to prevent degradation effects caused by pump impellers. The large stresses set up by the secondary flows degrade the fragile polymers, thus reducing their effectivness as a drag reducer. The ``self-healing'' of the micelles enables the surfactant to maintain its effectivness. We will present the ``self-healing'' characteristics of the surfactant micelles using the polymer data as the datum.

  18. Dynamics of propagating turbulent pipe flow structures. Part I: Effect of drag reduction by spanwise wall oscillation

    CERN Document Server

    Duggleby, A; Paul, M R

    2006-01-01

    The results of a comparative analysis between turbulent pipe flow and drag reduced turbulent pipe flow by spanwise wall oscillation based upon a Karhunen-Loeve expansion are presented. The turbulent flow is generated by a direct numerical simulation at a Reynolds number Re_\\tau = 150. The spanwise wall oscillation is imposed as a velocity boundary condition with an amplitude of A^+ = 20 and a period of T^+ = 50. The flow is driven by a constant pressure gradient, resulting in a 27% mean velocity increase with wall oscillation. The peaks of the Reynolds stress and root-mean-squared velocities shift away from the wall and the Karhunen-Loeve dimension of the turbulent attractor is reduced from 2453 to 102. The coherent vorticity structures are pushed away from the wall into higher speed flow, causing an increase of their advection speed of 34% as determined by a normal speed locus. The mechanism of drag reduction by spanwise wall oscillation is discussed.

  19. Effect of Interface Curvature on Turbulent Skin-Friction Drag Reduction with Super-Hydrophobic Micro-Grooves

    Science.gov (United States)

    Akhavan, Rayhaneh; Rastegari, Amirreza

    2016-11-01

    Effect of interface curvature on Drag Reduction (DR) with Super-Hydrophobic (SH) Micro-Grooves (MGs) was investigated by DNS with lattice Boltzmann methods. The liquid/gas interfaces in the SH MGs were modeled as curved, stationary, shear-free boundaries, with the interface shape determined from the Young-Laplace equation. The full range of interface protrusion angles, ranging from 0° to -90o , were investigated. DRs of 35% to 63% were realized in DNS, in turbulent channel flows at a Rebulk = 7200 (Reτ0 222) with longitudinal MGs of size 14 <=g+0 <= 56 & g+0 /w+0 = 7 on both walls, where g+0 and w+0 denote the widths and spacings of the MGs, in wall units of the base flow, respectively. The presence of interface curvature led to increases of 2.3% to 4.5% in the magnitude of DR, and drops of -3.5% to -13.5% in the slip velocity, at low protrusion angles, and drops of -2.2% to -12.5% in the magnitude of DR, and either drops of up to -16.5% or increases of up to 6% in the slip velocity, at high protrusion angles, compared to flat interfaces. In addition, the instantaneous pressure fluctuations on curved SH interfaces at low protrusion angles were significantly lower (by a factor of 2) than those on flat interfaces.

  20. Drag reduction of flow boiling with polymer additives

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The drag-reducing effect of polymer additive aqueous solution was investigated in flow boiling, and the polymer additives were two kinds of polyacrylamide (PAM) with relative molecular mass about 2.56×106 and 8.55×106. The frictional pressure drop was calculated according to the measured total pressure drop. The results show that the flow drag of flow boiling is reduced by adding a small amount of PAM to water when heat flux is in the range of 15.1 kW*m-2 to 47.0 kW*m-2, when the mass fraction of PAM is higher than 2.0×10-5, the drag-reducing effect is obvious. Drag-reducing effect of PAM, whose relative molecular mass is 8.55×106, is slightly better than that of 2.56×106 at the same mass fraction, and the greater the flow rate of the additive solution, the better the effect of the drag reduction.

  1. Superhydrophobic drag reduction in laminar flows: a critical review

    Science.gov (United States)

    Lee, Choongyeop; Choi, Chang-Hwan; Kim, Chang-Jin

    2016-12-01

    A gas in between micro- or nanostructures on a submerged superhydrophobic (SHPo) surface allows the liquid on the structures to flow with an effective slip. If large enough, this slippage may entail a drag reduction appreciable for many flow systems. However, the large discrepancies among the slippage levels reported in the literature have led to a widespread misunderstanding on the drag-reducing ability of SHPo surfaces. Today we know that the amount of slip, generally quantified with a slip length, is mainly determined by the structural features of SHPo surfaces, such as the pitch, solid fraction, and pattern type, and further affected by secondary factors, such as the state of the liquid-gas interface. Reviewing the experimental data of laminar flows in the literature comprehensively and comparing them with the theoretical predictions, we provide a global picture of the liquid slip on structured surfaces to assist in rational design of SHPo surfaces for drag reduction. Because the trapped gas, called plastron, vanishes along with its slippage effect in most application conditions, lastly we discuss the recent efforts to prevent its loss. This review is limited to laminar flows, for which the SHPo drag reduction is reasonably well understood.

  2. Nacelle drag reduction: An analytically-guided experimental program

    Science.gov (United States)

    Smetana, F. O.

    1975-01-01

    Modifications are proposed to standard estimating procedures, as well as the BODY computer program, which predict that the drag of two nacelles will equal the drag of the fuselage. A preliminary computer analysis that considers increased dimensions for the nacelle forebody so that the noise is relatively less blunt indicates a reduction in form drag much greater than the increase in skin friction drag attributable to increased surface area.

  3. Navier slip model of drag reduction by Leidenfrost vapour layers

    OpenAIRE

    Berry, Joseph D; Vakarelski, Ivan U.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2016-01-01

    Recent experiments found that a hot solid sphere that is able to sustain a stable Leidenfrost vapour layer in a liquid exhibits significant drag reduction during free fall. The variation of the drag coefficient with Reynolds number shows substantial deviation from the characteristic drag crisis behavior at high Reynolds numbers. Results obtained with liqiuds of different viscosities show that onset of the drag crisis depends on the viscosity ratio of the vapor to the liquid. The key feature o...

  4. Drag reduction properties of superhydrophobic mesh pipes

    Science.gov (United States)

    Geraldi, Nicasio R.; Dodd, Linzi E.; Xu, Ben B.; Wells, Gary G.; Wood, David; Newton, Michael I.; McHale, Glen

    2017-09-01

    Even with the recent extensive study into superhydrophobic surfaces, the fabrication of such surfaces on the inside walls of a pipe remains challenging. In this work we report a convenient bi-layered pipe design using a thin superhydrophobic metallic mesh formed into a tube, supported inside another pipe. A flow system was constructed to test the fabricated bi-layer pipeline, which allowed for different constant flow rates of water to be passed through the pipe, whilst the differential pressure was measured, from which the drag coefficient (ƒ) and Reynolds numbers (Re) were calculated. Expected values of ƒ were found for smooth glass pipes for the Reynolds number (Re) range 750-10 000, in both the laminar and part of the turbulent regimes. Flow through plain meshes without the superhydrophobic coating were also measured over a similar range (750  superhydrophobic coating, ƒ was found for 4000  superhydrophobic mesh can support a plastron and provide a drag reduction compared to a plain mesh, however, the plastron is progressively destroyed with use and in particular at higher flow rates.

  5. Drag reduction in turbulent MHD pipe flows

    Science.gov (United States)

    Orlandi, P.

    1996-01-01

    This is a preliminary study devoted to verifying whether or not direct simulations of turbulent Magneto-Hydro-Dynamic (MHD) flows in liquid metals reproduce experimental observations of drag reduction. Two different cases have been simulated by a finite difference scheme which is second order accurate in space and time. In the first case, an external azimuthal magnetic field is imposed. In this case, the magnetic field acts on the mean axial velocity and complete laminarization of the flow at N(sub a) = 30 has been achieved. In the second case, an axial magnetic field is imposed which affects only fluctuating velocities, and thus the action is less efficient. This second case is more practical, but comparison between numerical and experimental results is only qualitative.

  6. Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

    Directory of Open Access Journals (Sweden)

    Bharat Bhushan

    2011-02-01

    Full Text Available The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as lotus (Nelumbo nucifera leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical surface roughness and presence of a wax layer. In addition to a self-cleaning effect, these surfaces with a high contact angle and low contact angle hysteresis also exhibit low adhesion and drag reduction for fluid flow. An aquatic animal, such as a shark, is another model from nature for the reduction of drag in fluid flow. The artificial surfaces inspired from the shark skin and lotus leaf have been created, and in this article the influence of structure on drag reduction efficiency is reviewed. Biomimetic-inspired oleophobic surfaces can be used to prevent contamination of the underwater parts of ships by biological and organic contaminants, including oil. The article also reviews the wetting behavior of oil droplets on various superoleophobic surfaces created in the lab.

  7. Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity.

    Science.gov (United States)

    Bhushan, Bharat

    2011-01-01

    The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as lotus (Nelumbo nucifera) leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical surface roughness and presence of a wax layer. In addition to a self-cleaning effect, these surfaces with a high contact angle and low contact angle hysteresis also exhibit low adhesion and drag reduction for fluid flow. An aquatic animal, such as a shark, is another model from nature for the reduction of drag in fluid flow. The artificial surfaces inspired from the shark skin and lotus leaf have been created, and in this article the influence of structure on drag reduction efficiency is reviewed. Biomimetic-inspired oleophobic surfaces can be used to prevent contamination of the underwater parts of ships by biological and organic contaminants, including oil. The article also reviews the wetting behavior of oil droplets on various superoleophobic surfaces created in the lab.

  8. Drag reduction in turbulent flows over superhydrophobic surfaces

    Science.gov (United States)

    Daniello, Robert J.; Waterhouse, Nicholas E.; Rothstein, Jonathan P.

    2009-08-01

    In this paper, we demonstrate that periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime. Superhydrophobic surfaces contain micro- or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to drag reductions approaching 50%. At a given Reynolds number, drag reduction is found to increase with increasing feature size and spacing, as in laminar flows. No observable drag reduction was noted in the laminar regime, consistent with previous experimental results for the channel geometry considered. The onset of drag reduction occurs at a critical Reynolds number where the viscous sublayer thickness approaches the scale of the superhydrophobic microfeatures and performance is seen to increase with further reduction in viscous sublayer height. These results indicate superhydrophobic surfaces may provide a significant drag reducing mechanism for marine vessels.

  9. Hypersonic wave drag reduction performance of cylinders with repetitive laser energy depositions

    Energy Technology Data Exchange (ETDEWEB)

    Fang, J; Hong, Y J; Li, Q; Huang, H, E-mail: fangjuan314@163.com [Academy of Equipment Command and Technology, Post Box 3380-86, Huairou Dis. Beijing 101416 (China)

    2011-02-01

    It has been widely research that wave drag reduction on hypersonic vehicle by laser energy depositions. Using laser energy to reduce wave drag can improve vehicle performance. A second order accurate scheme based on finite-difference method and domain decomposition of structural grid is used to compute the drag performance of cylinders in a hypersonic flow of Mach number 2 at altitude of 15km with repetitive energy depositions. The effects of frequency on drag reduction are studied. The calculated results show: the recirculation zone is generated due to the interaction between bow shock over the cylinder and blast wave produced by energy deposition, and a virtual spike which is supported by an axis-symmetric recirculation, is formed in front of the cylinder. By increasing the repetitive frequency, the drag is reduced and the oscillation of the drag is decreased; however, the energy efficiency decreases by increasing the frequency.

  10. TURBULENCE TRANSPORT OF SURFACTANT SOLUTION FLOW DURING DRAG REDUCTION DEGENERATION

    Institute of Scientific and Technical Information of China (English)

    GU Wei-guo; WANG De-zhong

    2012-01-01

    Turbulence transport of surfactant solution flow during drag reduction degeneration is investigated experimentally in a two-dimensional channel.Particle Image Velocimetry (P1V) system is used to take two-dimensional velocity frames in the streamwise and wall-normal plane.The additive of surfactant is cetyltrimethyl ammonium chloride (CTAC) with the mass concentration of 25 ppm.Drag reduction degeneration happens in the CTAC solution flow,exhibiting the maximal drag reduction at Re =25000and losing drag reduction completely at Re =40 000.The velocity frames are statistically analyzed in four quadrants which are divided by the u -axis and v-axis.It is found that the phenomenon of“Zero Reynolds shear stress” is caused by the decrease of wallnormal fluctuations and its symmetrical distribution in quadrants.The increase of Reynolds number leads to the enhancement of turbulence burst phenomenon.During thc drag reduction degeneration,the CTAC solution flow contains both high turbulence intensity and drag reduction states.

  11. Drag Effects in Charm Photoproduction

    CERN Document Server

    Norrbin, E

    1999-01-01

    We have refined a model for charm fragmentation at hadron colliders. This model can also be applied to the photoproduction of charm. We investigate the effect of fragmentation on the distribution of produced charm quarks. The drag effect is seen to produce charm hadrons that are shifted in rapidity in the direction of the beam remnant. We also study the importance of different production mechanisms such as charm in the photon and from parton showers.

  12. Investigation on Drag Reduction of Trucks

    Institute of Scientific and Technical Information of China (English)

    QI Xiao-ni; LIU Zhen-yan

    2008-01-01

    A study of the mechanism of fences was given to reduce drag by means of theoretical analysis, numerical simulation and experimental research. A 3D mathematical model has been developed based on computational fluid dynamics software Phoenics that was capable of handling steady state, 3D flow to simulate the flow field around the truck. The experiment made in a low speed wind tunnel is used as references for validation. By analyzing the results of calculation and experiment, the flowing mechanism of the flow field around the container truck and the drag-reducing mechanism of #-shaped fences on the truck are unveiled, which provides theoretical guidance to the aerodynamic formation designing and amelioration.

  13. Drag Reduction, from Bending to Pruning

    CERN Document Server

    Lopez, Diego; Michelin, Sébastien; de Langre, Emmanuel

    2013-01-01

    Most plants and benthic organisms have evolved efficient reconfiguration mechanisms to resist flow-induced loads. These mechanisms can be divided into bending, in which plants reduce their sail area through elastic deformation, and pruning, in which the loads are decreased through partial breakage of the structure. In this work, we show by using idealized models that these two mechanisms or, in fact, any combination of the two, are equally efficient to reduce the drag experienced by terrestrial and aquatic vegetation.

  14. Drag reduction by means of dimpled surfaces in turbulent boundary layers

    Science.gov (United States)

    van Nesselrooij, M.; Veldhuis, L. L. M.; van Oudheusden, B. W.; Schrijer, F. F. J.

    2016-09-01

    Direct force measurements and particle image velocimetry (PIV) were used to investigate the drag and flow structure caused by surfaces with patterns of shallow spherical dimples with rounded edges subject to turbulent boundary layers. Drag reduction of up to 4 % is found compared to a flat surface. The largest drag reduction was found at the highest tested Reynolds number of 40,000 (based on dimple diameter). A favorable trend promises further improvements at higher Reynolds numbers. PIV revealed the absence of significant separation inside the dimples but did show the existence of a converging/diverging flow in the upstream and downstream dimple half, respectively. This leads to the rejection of theories proposed by other authors concerning the mechanism responsible for drag reduction. Instead, a fundamental dependence on pattern orientation is observed. Furthermore, preliminary Reynolds-averaged Navier-Stokes (RANS) simulations have been compared with the PIV data. Although the large-scale mean flows show good agreement, the numerical simulation predicts no drag reduction. As the RANS approach is inherently incapable of resolving effects on the behavior of small-scale turbulence structure, the origin of drag reduction is attributed to effects on the small-scale turbulence, which is not resolved in the simulations. It is argued that dimples, when placed in well-designed patterns to create the necessary large-scale flow structure, lead to drag reduction by affecting the turbulent structures in the boundary layer, possibly in a way similar to spanwise oscillations of the wall.

  15. Drag reduction through wave-current interactions with a marine hydrofoil

    Science.gov (United States)

    Tully, Susan; Viola, Ignazio Maria; Ingram, David

    2015-11-01

    A hydrofoil exposed to oscillating flow experiences a reduction in drag due to the Knoller-Betz effect. This is experimentally identifiable by an increasingly inverted von Kármán wake and a corresponding thrust force on the foil. The rate of drag reduction, dependent on plunge amplitude and frequency, reduces with unsteady flow phenomena at higher reduced frequencies. For experimental ease, investigations of this effect have relied on actively plunging/pitching a foil within a steady current. However, one potential application is to drag reduction in high-speed ships adopting submerged foils. In this case the foil is travelling through wave-current induced oscillatory flow, resulting in an additional dynamic variation of hydrostatic pressure across the chord; a phenomena not fully addressed in previous experiments. Here we investigate the effects of this pressure gradient on drag reduction for a stationary foil in combined waves and current, through a combination of force measurements and particle image velocimetry.

  16. Numerical Simulation of High Drag Reduction in a Turbulent Channel Flow with Polymer Additives

    Science.gov (United States)

    Dubief, Yves

    2003-01-01

    The addition of small amounts of long chain polymer molecules to wall-bounded flows can lead to dramatic drag reduction. Although this phenomenon has been known for about fifty years, the action of the polymers and its effect on turbulent structures are still unclear. Detailed experiments have characterized two distinct regimes (Warholic et al. 1999), which are referred to as low drag reduction (LDR) and high drag reduction (HDR). The first regime exhibits similar statistical trends as Newtonian flow: the log-law region of the mean velocity profile remains parallel to that of the Newtonian ow but its lower bound moves away from the wall and the upward shift of the log-region is a function of drag reduction, DR. Although streamwise fluctuations are increased and transverse ones are reduced, the shape of the rms velocity profiles is not qualitatively modified. At higher drag reductions, of the order of 40-50%, the ow enters the HDR regime for which the slope of the log-law is dramatically augmented and the Reynolds shear stress is small (Warholic et al. 1999; Ptasinski et al. 2001). The drag reduction is eventually bounded by a maximum drag reduction (MDR) (Virk & Mickley 1970) which is a function of the Reynolds number. While several experiments report mean velocity profiles very close to the empirical profile of Virk & Mickley (1970) for MDR conditions, the observations regarding the structure of turbulence can differ significantly. For instance, Warholic et al. (1999) measured a near-zero Reynolds shear stress, whereas a recent experiment (Ptasinski et al. 2001) shows evidence of non-negligible Reynolds stress in their MDR flow. To the knowledge of the authors, only the LDR regime has been documented in numerical simulations (Sureshkumar et al. 1997; Dimitropoulos et al. 1998; Min et al. 2001; Dubief & Lele 2001; Sibilla & Baron 2002). This paper discusses the simulation of polymer drag reduced channel ow at HDR using the FENE-P (Finite Elastic non

  17. Investigation of drag reduction through a flapping mechanism on circular cylinder

    Science.gov (United States)

    Asif, Md. Asafuddoula; Gupta, Avijit Das; Rana, M. D. Juwel; Ahmed, Dewan Hasan

    2016-07-01

    During flapping wing, a bird develops sufficient lift force as well as counteracts drag and increases its speed through different orientations of feathers on the flapping wings. Differently oriented feathers play a significant role in drag reduction during flying of a bird. With an objective to investigate the effect of installation of such flapping mechanism as a mean of drag reduction in case of flow over circular cylinder, this concept has been implemented through installation of continuous and mini flaps, made of MS sheet metal, where flaps are oriented at different angles as like feathers of flapping wings. The experiments are carried out in a subsonic wind tunnel. After validation and comparison with conventional result of drag analysis of a single cylinder, effects of flapping with Reynolds number variation, implementation of different orientations of mini flaps and variation of different interspacing distance between mini flaps are studied to find the most effective angle of attack of drag reduction on the body of circular cylinder. This research show that, installation of continuous flap reduces value of drag co-efficient, CD up to 66%, where as mini flaps are found more effective by reducing it up to 73%. Mini flaps of L/s=6.25, all angled at 30O, at the 30O angular position on the body of circular cylinder has been found the most effective angle of attack for drag reduction in case of flow over circular cylinder.

  18. Experimental Investigation of Tunnel Discharge Ability by Using Drag Reduction Techniques

    Directory of Open Access Journals (Sweden)

    Ying-kui WANG

    2010-06-01

    Full Text Available The experiments in an open flume model and in the spillway tunnel models were carried out by using drag reduction technique. The drag reduction experiments in open channel model adopted two techniques: polymer addition and coating. The drag reduction effect of polyacrylamide (PAM solution and the dimethyl silicone oil coating were studied by the flume model experiments, and the results were satisfied. Then the experiments were carried out in the model of a Hydropower station, which is the second largest dam in China. In order to reduce the resistance, the spillway tunnel models were coated inside with the dimethyl silicone oil. It is the first time that applying the drag reduction technique in the large hydraulic model. The experimental results show that the coating technique can effectively increase the ability of flood discharge. The outlet velocity and the jet trajectory distance were also increased, which is beneficial to the energy dissipation of the spillway tunnel.

  19. Biomimetic Drag Reduction Study on Herringbone Riblets of Bird Feather

    Institute of Scientific and Technical Information of China (English)

    Huawei Chen; Fugang Rao; Xiaopeng Shang; Deyuan Zhang; Ichiro Hagiwara

    2013-01-01

    Birds have gradually formed various excellent structures such as streamlined shape and hollow shaft of feather to improve their flying performance by millions of years of natural selection.As typical property of bird feather,herringbone riblets align along the shaft of each feather,which is caused by perfect link of barbs,especially for the primary and secondary feathers of wings.Such herringbone riblets of feather are assumed to have great impact on drag reduction.In this paper,microstructures of secondary feathers of adult pigeons are investigated by SEM,and their structural parameters are statistically obtained.Based on quantitative analysis of feather structure,novel biomimetic herringbone riblets with narrow smooth edge are proposed to reduce surface drag.In comparison with traditional microgroove riblets and other drag reduction structures,the drag reduction rate of the proposed biomimetic herringbone riblets is experimentally clarified up to 16%,much higher than others.Moreover,the drag reduction mechanism of herringbone riblets are also confirmed and exploited by CFD.

  20. Large-eddy simulation of a turbulent flow over a heavy vehicle with drag reduction devices

    Science.gov (United States)

    Lee, Sangseung; Kim, Myeongkyun; You, Donghyun

    2015-11-01

    Aerodynamic drag contributes to a considerable amount of energy loss of heavy vehicles. To reduce the energy loss, drag reduction devices such as side skirts and boat tails, are often installed to the side and the rear of a heavy vehicle. In the present study, turbulent flow around a heavy vehicle with realistic geometric details is simulated using large-eddy simulation (LES), which is capable of providing unsteady flow physics responsible for aerodynamic in sufficient detail. Flow over a heavy vehicle with and without a boat tail and side skirts as drag reduction devices is simulated. The simulation results are validated against accompanying in-house experimental measurements. Effects of a boat tail and side skirts on drag reduction are discussed in detail. Supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) Grant NTIS 1615007940.

  1. Drag reduction by reconfiguration of a full tree in a wind tunnel

    Science.gov (United States)

    de Langre, Emmanuel; Tadrist, Loic; Leclercq, Tristan; Hemon, Pascal; Amandolese, Xavier; Saudreau, Marc; Marquier, Andre; Knapp, Graham; Flamand, Olivier

    2015-11-01

    The results of drag measurements performed on a full 3 m-tall cherry tree in an atmospheric wind tunnel are presented. The drag on the trunk alone is shown to increase quadratically with the velocity of the flow, as expected, but the drag on the whole tree with branches and leaves follows a smaller power law with velocity, after the reconfiguration of most leaves. The transition from the quadratic law to a linear increase of the drag of the leaves with the magnitude of the flow is observed. Data is also obtained on moment loading on the base of the tree showing also an effect of the reconfiguration. Finally, these results are compared with current models of drag reduction by reconfiguration.

  2. Rheological and drag reduction properties of hydroxypropyl xanthan gum solutions☆

    Institute of Scientific and Technical Information of China (English)

    Meng Tian; Bo Fang; Leiping Jin; Yongjun Lu; Xiaohui Qiu; Hao Jin; Kejing Li

    2015-01-01

    Hydroxypropyl xanthan gum (HXG) was prepared from xanthan gum (XG) and propylene oxide under alkaline condition. Rheological and drag reduction properties of different concentrations of aqueous HXG and XG solution were studied. The micro-structure network of HXG and XG solutions was investigated by Cryo-FESEM. The re-sults showed that HXG and XG solutions could exhibit shear thinning property. The apparent viscosity of 6 g·L−1 HXG solution was 1.25 times more than that of 6 g·L−1 XG solution. The storage modulus G′and the loss modulus G″of HXG solutions were greater than those of XG solutions, and thixotropic and viscoelastic prop-erties were more significant in HXG solutions. The HXG and XG solutions reduced the pressure drop of straight pipe, and the maximum drag reduction of 1 g·L−1 HXG and XG in smooth tube reached 72.8%and 68.1%, respec-tively. Drag reduction rate was increased as the concentration increased. The HXG solution may become a new polymeric drag reducer.

  3. Laminar Drag Reduction in Microchannels Using Ultrahydrophobic Surfaces

    Science.gov (United States)

    Ou, Jia; Perot, Blair; Rothstein, Jonathan

    2003-11-01

    In devices where the fluid flow is laminar, there are currently no methods for reducing drag. We will present a series of experiments which demonstrate a 20-30% drag reduction for the flow of water through microchannels using hydrophobic surfaces with micron sized roughness. These 'ultrahydrophobic' surfaces are fabricated using photolithography to etch microposts and microridges with specific size, spacing and arrangement into silicon. The surfaces are then reacted with an organosilane to make them hydrophobic. The resulting surfaces have contact angles greater than 150 degrees. Pressure drop measurements are made for a series of ultrahydrophobic surface patterns, flow rates and microchannel heights. Pressure drop measurements across hydrophobic smooth surfaces are found to correlate precisely with theory while the drag reduction observed for the flow across these ultrahydrophobic surfaces is found to increase with increasing micropost spacing and decreasing micropost area. A physical model will be presented which explains the drag reduction in terms of a shear-free air-water interface between microposts supported by surface tension. Confirmation of the model will be presented with optical measurements of the displacement of the air-water interface under flow.

  4. Self-burrowing seeds: drag reduction in granular media

    Science.gov (United States)

    Jung, Wonjong; Choi, Sung Mok; Kim, Wonjung; Kim, Ho-Young

    2014-11-01

    We present the results of a combined experimental and theoretical investigation of drag reduction of self-burrowing seeds in granular media. In response to environmental changes in humidity, the awn (a tail-like appendage of seed) of Pelargonium carnosum exhibits coiling-uncoiling deformation which induces the thrust and rotary motions of the head of the seed against the surface of the soil. Using various sizes of glass beads that mimic the granular soil, we measure the thrust forces required for the seed of Pelargonium carnosum to penetrate into granular media with and without rotation. Our quantitative measurements show that the rotation of the seed remarkably reduces the granular drag as compared to the drag against the non-spinning seed. This leads us to conclude that the hygroscopically active awns of Pelargonium carnosum enables its seed to dig into the relatively coarse granular soils.

  5. Numerical simulation on drag reduction of revolution body through bionic riblet surface

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Numerical simulations of flow fields on the bionic riblet and the smooth revolution bodies were performed based on the SST k-ω turbulence model in order to explain the mechanisms of the skin friction drag reduction, base drag reduction on the riblet surface, and flow control behaviors of riblet surface near the wall. The simulation results show that the riblet surface arranged on the rearward of the revolution body can reduce the skin friction drag by 8.27%, the base drag by 9.91% and the total drag by 8.59% at Ma number 0.8. The riblet surface reduces the skin friction drag by reducing the velocity gradient and turbulent intensity, and reduces the base drag by weakening the pumping action on the dead water region which behind the body of revolution caused by the external flow. The flow control behavior on boundary layer shows that the riblet surface can cut the low-speed flow near the wall effectively, and restrain the low-speed flow concentrating in span direction, thus weaken the instability of the low speed steaks produced by turbulent flow bursting.

  6. Numerical simulation for the influence of injected laser power on plasma drag reduction

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Z; Fang, J [Department of Postgraduates, Academy of Equipment Command and Technology, 3380 Post box, Huairou Beijing 101416 (China); Dou, Z G; Huang, H, E-mail: liuzhun0@gmail.com [Department of Basic Theories, Academy of Equipment Command and Technology, 3380 Post box, Huairou Beijing 101416 (China)

    2011-02-01

    Laser plasma drag reduction is a new method to reduce the wave drag of hypersonic flight. Inject laser power is an important parameter. An appropriate laser power should be chosen when laser power was injected to achieve the best drag reduction effect via the minimum laser power. The effect of inject laser power on the performance of laser plasma drag reduction when incoming flight Mach number is 6.5 and at 30km altitude was simulated numerically. The result indicates that the drag can be effectively reduced by energy injection in the upstream flow. The larger the inject power is, the smaller the drag of the blunt body obtained. The energy injection can also influence the pressure and temperature on the surface of blunt body. When laser energy injected, high pressure region on the surface moves to the back of the hemisphere, the pressure of stagnation point decreased. There are two peaks of temperature on the blunt surface, one is the stagnation point and the other is the high pressure region. Temperature of the surface after high pressure region is lower comparison to the condition that no energy injected.

  7. Drag reduction and improvement of material transport in creeping films

    Energy Technology Data Exchange (ETDEWEB)

    Scholle, M.; Rund, A.; Aksel, N. [University of Bayreuth, Department of Applied Mechanics and Fluid Dynamics, Bayreuth (Germany)

    2006-01-01

    It is widely accepted that for bodies in turbulent flows a reduction of skin friction can be reached if the surface of the body is provided with small ridges aligned in the local flow direction. This surprising and counterintuitive phenomenon is called the shark-skin effect, motivated from the dermal surface morphology of sharks. In the present article we examine the possibility of resistance reduction due to a rippled surface topography in Stokes flow. We especially analyse the influence of wall riblets perpendicular to the flow direction on the mean transport velocity in gravity-driven creeping film flows following the idea that eddies generated in the valleys of the riblets act like fluid roller bearings and hence may reduce drag. Using a theoretical treatment of the Stokes equations with complex function theory, parameter studies with varying flow rate, bottom amplitude and bottom shape are presented. For the given bottom shapes the maximum enhancement of transport velocity is found by optimising the film thickness. (orig.)

  8. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow

    Science.gov (United States)

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  9. 5th Drag Reduction in Engineering Flows Meeting

    CERN Document Server

    1991-01-01

    The European Drag Reduction Meeting has been held on 15th and 16th November 1990 in London. This was the fifth of the annual European meetings on drag reduction in engineering flows. The main objective of this meeting was to discuss up-to-date results of drag reduction research carried out in Europe. The organiser has adopted the philosophy of discussing the yesterday's results rather than the last year's results. No written material has therefore been requested for the meeting. It was only after the meeting the submission of papers was requested to the participants, from which 16 papers were selected for this proceedings volume. The meeting has attracted a record number of participants with a total of 52 researchers from seven European countries, U. K. , France, Germany, the Netherlands, Italy, Switzerland and U. S. S. R. as well as from Japan, Canada and Australia. The subjects covered in this proceedings volume include riblets, LEBUs (Large Eddy Break-Up device), surface roughness, compliant surfaces and p...

  10. Lubricant-impregnated surfaces for drag reduction in viscous laminar flow

    Science.gov (United States)

    Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team

    2013-11-01

    For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).

  11. Thermal lift generation and drag reduction in rarefied aerodynamics

    Science.gov (United States)

    Pekardan, Cem; Alexeenko, Alina

    2016-11-01

    With the advent of the new technologies in low pressure environments such as Hyperloop and helicopters designed for Martian applications, understanding the aerodynamic behavior of airfoils in rarefied environments are becoming more crucial. In this paper, verification of rarefied ES-BGK solver and ideas such as prediction of the thermally induced lift and drag reduction in rarefied aerodynamics are investigated. Validation of the rarefied ES-BGK solver with Runge-Kutta discontinous Galerkin method with experiments in transonic regime with a Reynolds number of 73 showed that ES-BGK solver is the most suitable solver in near slip transonic regime. For the quantification of lift generation, A NACA 0012 airfoil is studied with a high temperature surface on the bottom for the lift creation for different Knudsen numbers. It was seen that for lower velocities, continuum solver under predicts the lift generation when the Knudsen number is 0.00129 due to local velocity gradients reaching slip regime although lift coefficient is higher with the Boltzmann ES-BGK solutions. In the second part, the feasibility of using thermal transpiration for drag reduction is studied. Initial study in drag reduction includes an application of a thermal gradient at the upper surface of a NACA 0012 airfoil near trailing edge at a 12-degree angle of attack and 5 Pa pressure. It was seen that drag is reduced by 4 percent and vortex shedding frequency is reduced due to asymmetry introduced in the flow due to temperature gradient causing reverse flow due to thermal transpiration phenomena.

  12. Mechanically Robust Superhydrophobic Surfaces for Turbulent Drag Reduction

    Science.gov (United States)

    Golovin, Kevin; Boban, Mathew; Xia, Charlotte; Tuteja, Anish

    2014-11-01

    Superhydrophobic surfaces (SHS) resist wetting by keeping a thin air layer within their texture. Such surfaces have been shown to reduce skin friction during laminar and transitional flows. However, turbulent boundary layer flows exhibit high shear stresses that damage the fragile microstructure of most SHS, and it is yet unclear to what extent these surfaces can reduce drag. Moreover, the increasing pressure fluctuations and decreasing wall unit length experienced during turbulent flow makes designing mechanically robust SHS with the correct roughness scales a challenge. In this work we evaluate many different SHS in terms of their hydrophobicity, mechanical durability and roughness. Whereas even commercially available SHS lose their superhydrophobic properties after slight mechanical abrasion, our novel coatings survive up to 200x longer. Moreover, we evaluate how the roughness of such surfaces changes with mechanical abrasion, and we design SHS with the correct roughness to display optimal drag reduction in turbulent boundary layer flows. Funding from ONR.

  13. AN INVESTIGATION OF FLOW CHARACTERISTIC OF AERATED DRAG REDUCTION IN TUBE

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Under the aerated conditions of wall and top intube, the turbulent flow in the tube was measured by usingLDA. The turbulent structure of the flow field and the mech-anism of aerating drag reduction in the tube were discussed. It is shown that the energy dissipations of turbulence flow andmean flow will reduce and the flow velocity (or flow rate) willincrease by injecting mini-bubbles to the wall or top of tube,namely the effect of aerating drag reduction is attained.

  14. Influence of Nonionic Surfactant Addition on Drag Reduction of Water Based Nanofluid in a Small Diameter Pipe

    Institute of Scientific and Technical Information of China (English)

    Micha(l) Drzazga; Andrzej Gierczycki; Grzegorz Dzido; Marcin Lemanowicz

    2013-01-01

    The goal of this research was to determine the impact of nonionic surfactants on drag reduction effect in water and metal oxide nanofluid.Two nonionic surfactants (Rokacet O7 and Rokanol K7) and copper(Ⅱ) oxide water-based nanofluid were examined.Friction factors in a 4 mm diameter pipe for the Reynolds number between 8000 and 50000 were determined.Results showed that addition of nonionic surfactants caused the decrease of friction factor in water and nanofluid.The drag reduction effect was similar in both cases.Presence of nanoparticles in the system has no great influence on drag reduction effect.

  15. Investigations on drag reduction in turbulent pipe flows by addition of ionic and nonionic high polymers

    Science.gov (United States)

    Graeger, Helmut

    Drag reduction in turbulent pipe flow is obtained by addition of polymeric flow accelerator. Turbulent flow pattern is described on the basis of existing theories and reduction of loss of pressure heads is discussed. A turbulence rheometer is developed permitting the measurement of friction reduction for Reynolds numbers 1100 to 90,000. Effectiveness of water soluble polymer systems like polyacrylamide and coacrylate is studied in dependence of concentration, chemical composition, product aging and polymer chain deformation.

  16. Reynolds-dependence of turbulent skin-friction drag reduction induced by spanwise forcing

    CERN Document Server

    Gatti, Davide

    2015-01-01

    This paper examines how increasing the value of the Reynolds number $Re$ affects the ability of spanwise-forcing techniques to yield turbulent skin-friction drag reduction. The control strategy is the streamwise-travelling waves of spanwise wall velocity (Quadrio {\\em et al. J. Fluid Mech.}, vol. 627, 2009, pp. 161--178). The study builds upon an extensive drag-reduction database created with Direct Numerical Simulation of a turbulent channel flow for two, 5-fold separated values of $Re$, namely $Re_\\tau=200$ and $Re_\\tau=1000$. The sheer size of the database, which for the first time systematically addresses the amplitude of the forcing, allows a comprehensive view of the drag-reducing characteristics of the traveling waves, and enables a detailed description of the changes occurring when $Re$ increases. The effect of using a viscous scaling based on the friction velocity of either the non-controlled flow or the drag-reduced flow is described. In analogy with other wall-based drag reduction techniques, like ...

  17. Studies of compressible shear flows and turbulent drag reduction

    Science.gov (United States)

    Orszag, S. A.

    1981-04-01

    Compressible shear flows and drag reduction were examined and three methods are addressed: (1) the analytical and numerical aspects of conformal mapping were summarized and a new method for computation of these maps is presented; (2) the computer code SPECFD for solution of the three dimensional time dependent Navier-Stokes equations for compressible flow on the CYBER 203 computer is described; (3) results of two equation turbulence modeling of turbulent flow over wavy walls are presented. A modified Jones-Launder model is used in two dimensional spectral code for flow in general wavy geometries.

  18. Drag reduction of high altitude airships by active boundary layer control. Effect of a cusp on the reduction; Nodo kyokaiso seigyo ni yoru koso hikosen no teiko teigen. Cusp ni yoru teigen koka

    Energy Technology Data Exchange (ETDEWEB)

    Yamamura, N. [Nissan Motor Co. Ltd., Tokyo (Japan); Matsuuchi, K.; Yamazaki, S.; Sasaki, A. [University of Tsukuba, Tsukuba (Japan); Onda, M. [Mechanical Engineering Lab., Tokyo (Japan)

    1998-02-25

    The aerodynamic character of station-keeping airships at high Reynolds numbers is examined. The boundary layer developing on the surface is sucked by an axial flow fan through a slot located at the rear part of the airship and the sucked gas is blown out as a jet. To know the effect of the cusp two models with and without a cusp attached to the inlet of the suction slot were used. The flow field near the inlet, in particular the pressure on the surface, was measured as the suction discharge was varied. We obtained the form drag by integrating the pressure distribution in a wide range of Reynolds number and of suction discharge. Taking into account the jet thrust and the calculated friction drag, we finally determined the total drag and evaluated the role of the cusp. It was found that the cusp plays an efficient role in reducing the drag. 7 refs., 12 figs.

  19. Simulation of drag reduction in superhydrophobic microchannels based on parabolic gas-liquid interfaces

    Science.gov (United States)

    Li, Chunxi; Zhang, Shuo; Xue, Quanxi; Ye, Xuemin

    2016-10-01

    Based on the given parabolic gas-liquid interfaces, a two-dimensional fluid flow in superhydrophobic microchannels is numerically simulated with the steady volume of fluid model in the laminar regime. The influence of several crucial parameters on drag reduction effect is discussed. The results indicate that the superhydrophobic microchannel containing rectangular cavities displays significant drag reduction effect. With increasing inlet velocity, the pressure drop reduction decreases slightly. Augments in the pressure drop reduction tend to be large with the increase of the cavity fraction or the decrease of the channel height. The results also reveal that the variation of the normalized slip length with the cavity fraction tends to be more dramatic when the channel height is smaller. As the parabolic height of the gas-liquid interface is enlarged, both the pressure drop reduction and the normalized slip length decrease linearly, while fRe increases linearly. The impact of the cavity depth on the normalized slip length, fRe, and the pressure drop reduction is minimal supposing the depth of the cavity is greater than 40% of its width. The drag reduction effect corresponding to the dovetail cavity model is the best, and the consequence of the rectangular, trapezoidal, and triangular cavity models sequentially worsens.

  20. Turbulent drag reduction with liquid-infused surfaces

    Science.gov (United States)

    Smits, Alexander; van Buren, Tyler

    2016-11-01

    We present turbulent skin friction reduction over liquid-impregnated surfaces in Taylor-Couette flow. The surface of the inner cylinder of the facility contains square grooves, with widths from 100 μm to 800 μm and a fixed liquid area of half the total area. Alkane liquids are infused in the surface with viscosities from 1/3 to 2 times that of water. For Reynolds numbers up to Red =10,500 corresponding to a flow shear of τ=50 Pa, we achieve drag reduction exceeding 30%, three times higher than ever reported for liquid-infused surfaces. Supported by the ONR through MURI Grant Nos. N00014-12-1-0875 and N00014-12-1-0962.

  1. 壁面湍流流动中高分子减阻等效粘度模型的验证%Validation of Effective Viscosity Model for Polymer Drag Reduction in Wall-Bounded Turbulent Flow

    Institute of Scientific and Technical Information of China (English)

    王瑞; 李昌烽; 吴桂芬; 胡自成; 王迎慧

    2011-01-01

    In recent studies of drag reduction in wall turbulence it was proposed that the streching polymer produces a self-consistent effective viscosity that increases with the distance from the wall. This linear effective viscosity theory for drag reduction in the wall-bounded turbulent flow was examined by introducing such linear viscosity profile to Navier-Stokes equation, and computing with Reynolds stress model. It shows that the linear effective viscosity model demonstrates drag reducing properties, and the percentage of the drag reduction increases up to the drag reduction saturation with the slope of viscosity profile increasing. The level of drag reduction up to about 75% , approaching the maximum drag reduction extent was obtained. The turbulence important characteristics including mean velocity profile, root-mean-square velocity fluctuations, Reynolds stress and viscous stress profiles are in agreement with the direct numerical simulation results and experimental data. It is universal and reasonable in some content for the linear viscosity profile model to explain drag reduction mechanism.%近来在壁面湍流高分子减阻研究中,一种拉伸的高分子产生自相一致的等效粘度的理论提了出来,这个等效粘度随离开壁面的距离而增长。本文将此线性分布等效粘度置入Navier-Stokes方程,运用雷诺应力模型计算在壁面湍流中的减阻情况,检验这种等效粘度的可行性。可以发现,此模型可以得到湍流减阻的效果,所得到的减阻率随着等效粘度线性分布斜率的增加增大到一个饱和值。本文得到了接近最大减阻极限的减阻率(75%)。且由此模型计算得到的减阻湍流特征值包括平均速度分布、速度脉动均方根、雷诺应力及粘性应力分布都与实验数据和直接数值模拟结果相符。该线性分布等效粘度减阻模型大致上把握了高分子湍流减阻特性,给出了在一定程度上对湍流减阻机理普适和合理的解释。

  2. Preparation, anti-biofouling and drag-reduction properties of a biomimetic shark skin surface

    Directory of Open Access Journals (Sweden)

    Xia Pu

    2016-04-01

    Full Text Available Shark skin surfaces show non-smoothness characteristics due to the presence of a riblet structure. In this study, biomimetic shark skin was prepared by using the polydimethylsiloxane (PDMS-embedded elastomeric stamping (PEES method. Scanning electron microscopy (SEM was used to examine the surface microstructure and fine structure of shark skin and biomimetic shark skin. To analyse the hydrophobic mechanism of the shark skin surface microstructure, the effect of biomimetic shark skin surface microstructure on surface wettability was evaluated by recording water contact angle. Additionally, protein adhesion experiments and anti-algae adhesion performance testing experiments were used to investigate and evaluate the anti-biofouling properties of the surface microstructure of biomimetic shark skin. The recorded values of the water contact angle of differently microstructured surfaces revealed that specific microstructures have certain effects on surface wettability. The anti-biofouling properties of the biomimetic shark skin surface with microstructures were superior to a smooth surface using the same polymers as substrates. Moreover, the air layer fixed on the surface of the biomimetic shark skin was found to play a key role in their antibiont adhesion property. An experiment into drag reduction was also conducted. Based on the experimental results, the microstructured surface of the prepared biomimetic shark skin played a significant role in reducing drag. The maximum of drag reduction rate is 12.5%, which is higher than the corresponding maximum drag reduction rate of membrane material with a smooth surface.

  3. Cotunneling Drag Effect in Coulomb-Coupled Quantum Dots

    Science.gov (United States)

    Keller, A. J.; Lim, J. S.; Sánchez, David; López, Rosa; Amasha, S.; Katine, J. A.; Shtrikman, Hadas; Goldhaber-Gordon, D.

    2016-08-01

    In Coulomb drag, a current flowing in one conductor can induce a voltage across an adjacent conductor via the Coulomb interaction. The mechanisms yielding drag effects are not always understood, even though drag effects are sufficiently general to be seen in many low-dimensional systems. In this Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot and, through both experimental and theoretical arguments, identify cotunneling as essential to obtaining a correct qualitative understanding of the drag behavior.

  4. Drag reduction by linear viscosity model in turbulent channel flow of polymer solution

    Institute of Scientific and Technical Information of China (English)

    吴桂芬; 李昌烽; 黄东升; 赵作广; 冯晓东; 王瑞

    2008-01-01

    A further numerical study of the theory that the drag reduction in the turbulence is related to the viscosity profile growing linearly with the distance from the wall was performed.The constant viscosity in the Navier-Stokes equations was replaced using this viscosity model.Some drag reduction characteristics were shown comparing with Virk’s phenomenology.The mean velocity and Reynolds stress profiles are consistent with the experimental and direct numerical simulation results.A drag reduction level of 45% was obtained.It is reasonable for this linear viscosity model to explain the mechanism of turbulence drag reduction in some aspects.

  5. Computational analysis of methods for reduction of induced drag

    Science.gov (United States)

    Janus, J. M.; Chatterjee, Animesh; Cave, Chris

    1993-01-01

    The purpose of this effort was to perform a computational flow analysis of a design concept centered around induced drag reduction and tip-vortex energy recovery. The flow model solves the unsteady three-dimensional Euler equations, discretized as a finite-volume method, utilizing a high-resolution approximate Riemann solver for cell interface flux definitions. The numerical scheme is an approximately-factored block LU implicit Newton iterative-refinement method. Multiblock domain decomposition is used to partition the field into an ordered arrangement of blocks. Three configurations are analyzed: a baseline fuselage-wing, a fuselage-wing-nacelle, and a fuselage-wing-nacelle-propfan. Aerodynamic force coefficients, propfan performance coefficients, and flowfield maps are used to qualitatively access design efficacy. Where appropriate, comparisons are made with available experimental data.

  6. Fluid Mechanics, Drag Reduction and Advanced Configuration Aeronautics

    Science.gov (United States)

    Bushnell, Dennis M.

    2000-01-01

    This paper discusses Advanced Aircraft configurational approaches across the speed range, which are either enabled, or greatly enhanced, by clever Flow Control. Configurations considered include Channel Wings with circulation control for VTOL (but non-hovering) operation with high cruise speed, strut-braced CTOL transports with wingtip engines and extensive ('natural') laminar flow control, a midwing double fuselage CTOL approach utilizing several synergistic methods for drag-due-to-lift reduction, a supersonic strut-braced configuration with order of twice the L/D of current approaches and a very advanced, highly engine flow-path-integrated hypersonic cruise machine. This paper indicates both the promise of synergistic flow control approaches as enablers for 'Revolutions' in aircraft performance and fluid mechanic 'areas of ignorance' which impede their realization and provide 'target-rich' opportunities for Fluids Research.

  7. Spatially distributed control for optimal drag reduction of the flow past a circular cylinder

    Science.gov (United States)

    Poncet, Philippe; Hildebrand, Roland; Cottet, Georges-Henri; Koumoutsakos, Petros

    We report high drag reduction in direct numerical simulations of controlled flows past circular cylinders at Reynolds numbers of 300 and 1000. The flow is controlled by the azimuthal component of the tangential velocity of the cylinder surface. Starting from a spanwise-uniform velocity profile that leads to high drag reduction, the optimization procedure identifies, for the same energy input, spanwise-varying velocity profiles that lead to higher drag reduction. The three-dimensional variations of the velocity field, corresponding to modes A and B of three-dimensional wake instabilities, are largely responsible for this drag reduction. The spanwise wall velocity variations introduce streamwise vortex braids in the wake that are responsible for reducing the drag induced by the primary spanwise vortices shed by the cylinder. The results demonstrate that extending two-dimensional controllers to three-dimensional flows is not optimal as three-dimensional control strategies can lead efficiently to higher drag reduction.

  8. Development of FDR-AF (Frictional Drag Reduction Anti-Fouling) Marine Coating

    Science.gov (United States)

    Lee, Inwon; Park, Hyun; Chun, Ho Hwan; GCRC-SOP Team

    2013-11-01

    In this study, a novel skin-friction reducing marine paint has been developed by mixing fine powder of PEO(PolyEthyleneOxide) with SPC (Self-Polishing Copolymer) AF (Anti-Fouling) paint. The PEO is well known as one of drag reducing agent to exhibit Toms effect, the attenuation of turbulent flows by long chain polymer molecules in the near wall region. The frictional drag reduction has been implemented by injecting such polymer solutions to liquid flows. However, the injection holes have been a significant obstacle to marine application. The present PEO-containing marine paint is proposed as an alternative to realize Toms effect without any hole on the ship surface. The erosion mechanism of SPC paint resin and the subsequent dissolution of PEO enable the controlled release of PEO solution from the coating. Various tests such as towing tank drag measurement of flat plate and turbulence measurement in circulating water tunnel demonstrated over 10% frictional drag reduction compared with conventional AF paint. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) through GCRC-SOP(No. 2011-0030013).

  9. A design and analysis approach for drag reduction on aircraft with adaptive lifting surfaces

    Science.gov (United States)

    Cusher, Aaron Anthony

    Adaptive lifting surfaces, which can be tailored for different flight conditions, have been shown to be beneficial for drag reduction when compared with conventional non-adaptive surfaces. Applying multiple trailing-edge flaps along the wing span allows for the redistribution of lift to suit different flight conditions. The current approach uses the trailing-edge flap distribution to reduce both induced- and profile- components of drag with a trim constraint. Induced drag is reduced by optimally redistributing the lift between the lifting surfaces and along the span of each surface. Profile drag is reduced through the use of natural laminar flow airfoils, which maintain distinct low-drag-ranges (drag buckets) surrounding design lift values. The low-drag-ranges can be extended to include off-design values through small flap deflections, similar to cruise flaps. Trim is constrained for a given static margin by considering longitudinal pitching moment contributions from changes in airfoil section due to individual flap deflections, and from the redistribution of fore-and-aft lift due to combination of flap deflections. The approach uses the concept of basic and additional lift to linearlize the problem, which allows for standard constrained-minimization theory to be employed for determining optimal flap-angle solutions. The resulting expressions for optimal flap-angle solutions are presented as simple matrix equations. This work presents a design and analysis approach which is used to produce flap-angle solutions that independently reduce induced, profile, and total drag. Total drag is defined to be the sum of the induced- and profile-components of drag. The general drag reduction approach is adapted for each specific situation to develop specific drag reduction schemes that are applied to single- and multiple-surface configurations. Successful results show that, for the application of the induced drag reduction schemes on a tailless aircraft, near-elliptical lift

  10. Feature-resolved computational and analytical study of laminar drag reduction by superhydrophobic surfaces

    Science.gov (United States)

    Li, Yixuan; Alame, Karim; Mahesh, Krishnan

    2017-05-01

    Direct numerical simulations are used to study the drag reduction by superhydrophobic surfaces in laminar channel flow. Resolved multiphase simulations using the volume of fluid methodology are performed to study the effects of groove geometry, interface shear rate, and meniscus penetration independently. An analytical solution for the flow in a laminar channel with a grooved surface with a gas pocket within is obtained. The solution accounts for both the groove geometry and the trapped fluid properties, and shows good agreement with simulation results. The solution is used to propose a scaling law that collapses data across fully wetted to fully gas-filled regimes. The trapped gas is simulated as both flat and meniscal interfaces. The drag reduction initially increases with interface deflection into the groove and then decreases for large deflections as the interface velocity approaches zero due to the proximity to the bottom of the groove.

  11. Drag reduction in reservoir rock surface: Hydrophobic modification by SiO2 nanofluids

    Science.gov (United States)

    Yan, Yong-Li; Cui, Ming-Yue; Jiang, Wei-Dong; He, An-Le; Liang, Chong

    2017-02-01

    Based on the adsorption behavior of modified silica nanoparticles in the sandstone core surface, the hydrophobic surface was constructed, which consists of micro-nanoscale hierarchical structure. This modified core surface presents a property of drag reduction and meets the challenge of high injection pressure and low injection rate in low or ultra-low permeability reservoir. The modification effects on the surface of silica nanoparticles and reservoir cores, mainly concerning hydrophobicity and fine structure, were determined by measurements of contact angle and scanning electron microscopy. Experimental results indicate that after successful modification, the contact angle of silica nanoparticles varies from 19.5° to 141.7°, exhibiting remarkable hydrophobic properties. These modified hydrophobic silica nanoparticles display a good adsorption behavior at the core surface to form micro-nanobinary structure. As for the wettability of these modified core surfaces, a reversal has happened from hydrophilic into hydrophobic and its contact angle increases from 59.1° to 105.9°. The core displacement experiments show that the relative permeability for water has significantly increased by an average of 40.3% via core surface modification, with the effects of reducing injection pressure and improving injection performance of water flooding. Meanwhile, the mechanisms of drag reduction and improving water injection operation induced from the modified core surface were uncovered. The present study will establish a fundamental understanding on the drag reduction at the core surface modified by nanofluids and its applications in more industries.

  12. Drag reduction by the introduction of shear-free surfaces in a turbulent channel flow

    Indian Academy of Sciences (India)

    AJAY KUMAR SOOD; MURALI R CHOLEMARI; BALAJI SRINIVASAN

    2017-03-01

    In this paper, a novel technique for drag reduction in turbulent flows is presented. The technique involves the modification of the large scales of turbulent flows and is a passive approach. The lateral transport of momentum, which is a dominant mechanism in turbulence, is attenuated by the introduction of moving shearfree surfaces (SFSes). This brings about a reduction in the drag. 2D simulations have been carried out for aturbulent channel flow using shear stress transport (SST) Reynolds-averaged Navier–Stokes (RANS) model and validated with the available experimental results. The interaction between the plates and the fluid is two way,and is enforced either by the use of a rigid body solver with moving mesh, or by considering the SFSes to befixed at particular locations and then updating the velocities of the plates at those locations. The latter is equivalent to solving a fully developed flow in the moving mesh case. The number, shape, size and placement of the SFSes strongly influence the amount of drag reduction. The phenomenon is confirmed to be governed by a ‘slow’ turbulent time scale. Further, the efficacy of the method is seen to depend on the ratio of two time scales – an advection time scale indicating the ‘resident time’ near an SFS, and the turbulent time scale. In addition, the effectiveness of the approach is improved by judicious placement of multiple SFSes in the flow.

  13. Influence of rheological parameters in all drag reduction regimes of turbulent channel flow with polymer additives

    Institute of Scientific and Technical Information of China (English)

    李昌烽; 赵作广; 吴桂芬; 冯晓东

    2008-01-01

    The influence of rheological parameters on vortex dynamics and the extent of drag reduction(DR) were deciphered via extensively analyzing the hi-fidelity direct numerical simulation results of the turbulent channel flow with polymer solutions.It has been observed that in all drag reduction regimes from the onset of DR to maximum drag reduction(MDR) limit,the Deborah number is defined as the product of an effective Weissenberg number,and the root mean square streamwise vorticity fluctuation remains O(1) in the near wall region.The ratio of the average lifetime of axial vortices to the vortex rotating duration decreases with increasing DR,and MDR is achieved when these time scales become nearly equal.Based on these observations a simple framework is proposed adequately to describe the influence of polymer additives on the extent of DR from onset to MDR as well as the universality of the MDR in flow systems with polymer additives.

  14. An Experimental Study of Drag Reduction in a Pipe with Superhydrophobic Coating at Moderate Reynolds Numbers

    Directory of Open Access Journals (Sweden)

    Kuo L.

    2010-06-01

    Full Text Available This paper experimentally investigates drag reduction, durability for operations and effects for preventing microorganism from adhering to the surface when the superhydrophobic coating is applied on a solid surface. The experiments are divided into two parts. In the first part, a pipe flow system was established to measure the drag and to test the durability of the micro-structure of superhydrophobic coating at average speeds varying from 1m/sec to 6m/sec. In the second part, we tested the effect for preventing microorganism from adhering to the surface by putting the coated steel plates into sea water. There are four different superhydrophobic coatings in the present study. The experimental results were compared to those applied by ship paint usually used at CSBC.

  15. Experimental Study on Physical Mechanism of Drag Reduction of Hydrophobic Materials in Laminar Flow

    Institute of Scientific and Technical Information of China (English)

    YU Yong-Sheng; WEI Qin-Ding

    2006-01-01

    We experimentally study the physical mechanism of the drag reduction of hydrophobic materials in the macroscopic scale. The experiment includes the drag and velocity measurements of laminar boundary layer Sow over flat plates, and the observation of air bubbles on the surfaces. The plate surfaces have different wetting and roughness properties. In the drag measurements, the plates with bubbles on the surfaces lead to drag reduction, but not for those without bubbles. Velocity measurement confirms that the flow is laminar and gives apparent fluid slip on the plate wall with bubbles. In observation, air bubbles in macroscopic size emerge and enlarge on hydrophobic surfaces but not on hydrophilic surfaces. Therefore, the drag reduction of hydrophobic materials is explained by the generation of air bubbles of macroscopic size that cause the apparent velocity slip.

  16. Drag reduction in turbulent channel flow laden with finite-size oblate spheroids

    CERN Document Server

    Ardekani, M Niazi; Breugem, W -P; Picano, F; Brandt, L

    2016-01-01

    We study suspensions of oblate rigid particles in a viscous fluid for different values of the particle volume fractions. Direct numerical simulations have been performed using a direct-forcing immersed boundary method to account for the dispersed phase, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. We show that the drag is reduced and the turbulent fluctuations attenuated in flows laden with oblate spheroids not only when compared to suspensions of perfect spheres but also to the single phase turbulent flow. In particular, the turbulence activity decreases to lower values than those obtained by only accounting for the effective suspension viscosity. To explain the observed drag reduction we consider the particle dynamics and the interactions of the particles with the turbulent velocity field. We report the lack of the particle layer at the wall observed for spherical particles, which was found to be responsible for inc...

  17. A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces

    Science.gov (United States)

    Fukagata, Koji; Kasagi, Nobuhide; Koumoutsakos, Petros

    2006-05-01

    We present a theoretical prediction for the drag reduction rate achieved by superhydrophobic surfaces in a turbulent channel flow. The predicted drag reduction rate is in good agreement with results obtained from direct numerical simulations at Reτ≃180 and 400. The present theory suggests that large drag reduction is possible also at Reynolds numbers of practical interest (Reτ˜105-106) by employing a hydrophobic surface, which induces a slip length on the order of ten wall units or more.

  18. Experimental Measurements of Turbulent Drag Reduction Using Ultrahydrophobic Surfaces with Periodic Microfeatures

    Science.gov (United States)

    Daniello, Robert; Rothstein, Jonathan P.

    2007-11-01

    The experimental results of fully-developed turbulent channel flow past a series of ultrahydrophobic surfaces will be presented. We have shown previously that these surfaces can produce significant drag reduction in laminar channel flow by supporting a shear-free air-water interface between hydrophobic microridges or microposts. In this talk, we will experimentally demonstrate that it is possible to utilize these micropatterned surfaces as a passive technique for achieving significant drag reduction in fully-developed turbulent flows. Two-dimensional velocity profiles as well as shear and Reynolds stress fields generated from particle image velocimetry will be presented. These measurements clearly demonstrate a reduction in drag along the ultrahydrophobic wall when compared to a smooth surface. Pressure drop measurements along the channel will also be presented. Discussion will include the influence of Reynolds number and surface geometry on the velocity profiles, Reynolds stresses and the resulting drag reduction.

  19. Aerodynamic Drag Reduction for a Generic Truck Using Geometrically Optimized Rear Cabin Bumps

    Directory of Open Access Journals (Sweden)

    Abdellah Ait Moussa

    2015-01-01

    Full Text Available The continuous surge in gas prices has raised major concerns about vehicle fuel efficiency, and drag reduction devices offer a promising strategy. In this paper, we investigate the mechanisms by which geometrically optimized bumps, placed on the rear end of the cabin roof of a generic truck, reduce aerodynamic drag. The incorporation of these devices requires proper choices of the size, location, and overall geometry. In the following analysis we identify these factors using a novel methodology. The numerical technique combines automatic modeling of the add-ons, computational fluid dynamics and optimization using orthogonal arrays, and probabilistic restarts. Numerical results showed reduction in aerodynamic drag between 6% and 10%.

  20. Superhydrophobic copper tubes with possible flow enhancement and drag reduction.

    Science.gov (United States)

    Shirtcliffe, Neil J; McHale, Glen; Newton, Michael I; Zhang, Yong

    2009-06-01

    The transport of a Newtonian liquid through a smooth pipe or tube is dominated by the frictional drag on the liquid against the walls. The resistance to flow against a solid can, however, be reduced by introducing a layer of gas at or near the boundary between the solid and liquid. This can occur by the vaporization of liquid at a surface at a temperature above the Leidenfrost point, by a cushion of air (e.g. below a hovercraft), or by producing bubbles at the interface. These methods require a continuous energy input, but a more recent discovery is the possibility of using a superhydrophobic surface. Most reported research uses small sections of lithographically patterned surfaces and rarely considers pressure differences or varying flow rates. In this work we present a method for creating a uniform superhydrophobic nanoribbon layer on the inside of round copper tubes of millimetric internal radius. Two types of experiments are described, with the first involving a simultaneous comparison of four tubes with different surface finishes (as received, as received with hydrophobic coating, nanoribbon, and nanoribbon with a hydrophobic coating) under constant flow rate conditions using water and water-glycerol mixtures. The results show that the superhydrophobic nanoribbon with a hydrophobic coating surface finish allows greater flow at low pressure differences but that the effect disappears as the pressure at the inlet of the tube is increased. The second experiment is a simple visual demonstration of the low-pressure behavior using two nominally identical tubes in terms of length and cross-section, but with one tube possessing a superhydrophobic internal surface finish. In this experiment a reservoir is allowed to feed the two tubes with open ends via a T-piece and it is observed that, once flow commences, it preferentially occurs down the superhydrophobic tube.

  1. Experiment about Drag Reduction of Bionic Non-smooth Surface in Low Speed Wind Tunnel

    Institute of Scientific and Technical Information of China (English)

    Tian Li-mei; Ren Lu-quan; Han Zhi-wu; Zhang Shi-cun

    2005-01-01

    The body surface of some organisms has non-smooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a non-smooth surface were made. In order to find a relationship be tween drag reduction and the non-smooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the non-smooth surface causes drag reduction and the distribution of non-smooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the non-smooth structure on the tail of the experimental model, the configuration of riblets, diameter/bottom width of 1 mm, height/depth of 0.5 mm, arranged in a rhombic formation. At the optimal combination mentioned above, the 99% confidence interval for drag reduction was 11.13 % to 22.30%.

  2. Boundary layer drag reduction research hypotheses derived from bio-inspired surface and recent advanced applications.

    Science.gov (United States)

    Luo, Yuehao; Yuan, Lu; Li, Jianhua; Wang, Jianshe

    2015-12-01

    Nature has supplied the inexhaustible resources for mankind, and at the same time, it has also progressively developed into the school for scientists and engineers. Through more than four billions years of rigorous and stringent evolution, different creatures in nature gradually exhibit their own special and fascinating biological functional surfaces. For example, sharkskin has the potential drag-reducing effect in turbulence, lotus leaf possesses the self-cleaning and anti-foiling function, gecko feet have the controllable super-adhesion surfaces, the flexible skin of dolphin can accelerate its swimming velocity. Great profits of applying biological functional surfaces in daily life, industry, transportation and agriculture have been achieved so far, and much attention from all over the world has been attracted and focused on this field. In this overview, the bio-inspired drag-reducing mechanism derived from sharkskin is explained and explored comprehensively from different aspects, and then the main applications in different fluid engineering are demonstrated in brief. This overview will inevitably improve the comprehension of the drag reduction mechanism of sharkskin surface and better understand the recent applications in fluid engineering.

  3. Micro-bubble Drag Reduction on a High Speed Vessel Model

    Institute of Scientific and Technical Information of China (English)

    Yanuar; Gunawan; Sunaryo; A. Jamaluddin

    2012-01-01

    Ship hull form of the underwater area strongly influences the resistance of the ship.The major factor in ship resistance is skin friction resistance.Bulbous bows,polymer paint,water repellent paint (highly water-repellent wall),air injection,and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships.Micro-bubble injection is a promising technique for lowering frictional resistance.The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction.The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat (FPB) 57 m type model with the following main dimensions:L=2 450 mm,B=400 mm,and T=190 mm.The influence of the location of micro bubble injection and bubble velocity was also investigated.The ship model was pulled by an electric motor whose speed could be varied and adjusted.The ship model resistance was precisely measured by a load cell transducer.Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number.It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction,and the drag reduction caused by the micro-bubbles can reach 6%-9%.

  4. Wetting behavior and drag reduction of superhydrophobic layered double hydroxides films on aluminum

    Science.gov (United States)

    Zhang, Haifeng; Yin, Liang; Liu, Xiaowei; Weng, Rui; Wang, Yang; Wu, Zhiwen

    2016-09-01

    We present a novel method to fabricate Zn-Al LDH (layered double hydroxides) film with 3D flower-like micro-and nanostructure on the aluminum foil. The wettability of the Zn-Al LDH film can be easily changed from superhydrophilic to superhydrophobic with a simple chemical modification. The as-prepared superhydrophobic surfaces have water CAs (contact angles) of 165 ± 2°. In order to estimate the drag reduction property of the surface with different adhesion properties, the experimental setup of the liquid/solid friction drag is proposed. The drag reduction ratio for the as-prepared superhydrophobic sample is 20-30% at low velocity. Bearing this in mind, we construct superhydrophobic surfaces that have numerous technical applications in drag reduction field.

  5. Turbulent Drag Reduction: Studies of Feedback Control and Flow Over Riblets

    Science.gov (United States)

    Choi, Haecheon

    The objective of this study is to explore concepts for control of turbulent boundary layers leading to skin -friction reduction using the direct numerical simulation technique. This report is divided into three parts where three different control methods are investigated; a passive control by longitudinal riblets, an active control by sensing and perturbing structures near the wall, and a feedback control procedure guided by control theory. In PART I significant drag reduction is achieved when the surface boundary condition is modified to suppress the dynamically significant coherent structures present in the wall region. The drag reduction is accompanied with significant reduction in the intensity of the wall -layer structures and reductions in the magnitude of Reynolds shear stress throughout the flow. Two essential drag reduction mechanisms are presented. In PART II mathematical methods of control theory are applied to the problem of control of fluid flow. The procedure of how to cast the problem of controlling turbulence into a problem in optimal control theory is presented through the formalism and language of control theory. Then a suboptimal control and feedback procedure are presented using methods of calculus of variations through the adjoint state and gradient algorithms. This suboptimal feedback control procedure is applied to the distributed and boundary controls of the stochastic Burgers equation. Most cases considered show significant reductions of the costs. In PART III direct numerical simulation is performed to analyze turbulent flow over longitudinal riblets, and to educe the mechanism of drag reduction by riblets. The computed drags on the riblet surfaces are in good agreement with the existing experimental data. Differences in the mean-velocity profile and turbulence quantities are found to be limited to the inner region of the boundary layer. Velocity and vorticity fluctuations as well as the Reynolds shear stresses above the riblets are

  6. Drag reduction by wing tip slots in a gliding Harris' hawk, Parabuteo unicinctus

    Science.gov (United States)

    Tucker

    1995-01-01

    The anterior-most primary feathers of many birds that soar over land bend upwards and separate vertically to form slotted wing tips during flight. The slots are thought to reduce aerodynamic drag, although drag reduction has never been demonstrated in living birds. Wing theory explains how the feathers that form the tip slots can reduce induced drag by spreading vorticity horizontally along the wing and by acting as winglets, which are used on aircraft to make wings non-planar and to spread vorticity vertically. This study uses the induced drag factor to measure the induced drag of a wing relative to that of a standard planar wing with the same span, lift and speed. An induced drag factor of less than 1 indicates that the wing is non-planar. The minimum drag of a Harris' hawk gliding freely in a wind tunnel was measured before and after removing the slots by clipping the tip feathers. The unclipped hawk had 70­90 % of the drag of the clipped hawk at speeds between 7.3 and 15.0 m s-1. At a wing span of 0.8 m, the unclipped hawk had a mean induced drag factor of 0.56, compared with the value of 1.10 assumed for the clipped hawk. A Monte Carlo simulation of error propagation and a sensitivity analysis to possible errors in measured and assumed values showed that the true mean value of the induced drag factor for the unclipped hawk was unlikely to be more than 0.93. These results for a living bird support the conclusions from a previous study of a feathered tip on a model wing in a wind tunnel: the feathers that form the slotted tips reduce induced drag by acting as winglets that make the wings non-planar and spread vorticity both horizontally and vertically.

  7. Flow characteristics of the two tandem wavy cylinders and drag reduction phe-nomenon

    Institute of Scientific and Technical Information of China (English)

    邹琳; 郭丛波; 熊灿

    2013-01-01

    This paper presents an extensive numerical study of 3-D laminar flow around two wavy cylinders in the tandem arrangement for spacing ratios (L/Dm ) ranging from 1.5 to 5.5 at a low Reynolds number of 100. The investigation focuses on the effects of spacing ratio (L/Dm ) and wavy surface on the 3-D near wake flow patterns, the force and pressure coefficients and the vortex shedding frequency for the two tandem wavy cylinders. Flows around the two tandem circular cylinders are also obtained for comparison. With the spacing ratio in the range of L/Dm=1.5-5.5 , unlike two tandem circular cylinders, the wavy cylinders in the tandem arrangement do not have the wake interference behaviour of three basic types. The vortex shedding behind the upstream wavy cylinder occurs at a further downstream position as compared with that of the upstream circular cylinder. This leads to the weakening of the effect of the vibration of the cylinders as well as a distinct drag reduction. The effects of the drag reduction and the control of the vibration of the two wavy cylinders in tandem become more and more evident when L/Dm³4.0, with a distinct vortex shedding in the upstream cylinder regime for the two circular cylinders in tandem.

  8. Effect of The Swimmer's Head Position on Passive Drag.

    Science.gov (United States)

    Cortesi, Matteo; Gatta, Giorgio

    2015-12-22

    The aim of this study was to investigate the effect of the head position on passive drag with a towing-line experiment in a swimming pool. The tests were performed on ten male swimmers with regional level swimming skills and at least 10 years of competitive swimming experience. They were towed underwater (at a depth of 60 cm) at three speeds (1.5, 1.7 and 1.9 m/s) and in two body positions (arms above the swimmer's head and arms alongside the body). These two body positions were repeated while the swimmer's head was positioned in three different ways: head-up, head-middle and head-down in relation to the body's horizontal alignment. The results showed a reduction of 4-5.2% in the average passive drag at all speeds when the head was down or aligned to the swimmer's arms alongside the body, in comparison to the head-up position. A major significant decrease of 10.4-10.9% (p < 0.05) was shown when the head was down or aligned at the swimmer's arms above the swimmer's head. The passive drag tended to decrease significantly by a mean of 17.6% (p < 0.001) for all speeds examined with the arms alongside the body position rather than with the arms above the head position. The swimmer's head location may play an important role in reducing hydrodynamic resistance during passive underwater gliding.

  9. Compliant Materials for Drag Reduction of High-speed Submerged Bodies

    Directory of Open Access Journals (Sweden)

    N. Bane Jee

    2005-01-01

    Full Text Available This paper briefly discusses the possibility of employing the compliant materials on underwater bodies for the drag reduction. Recent studies in the area of hydrobionics all-over the world have drawn the attention of hydrodynamicists for using the compliant materials on underwater body surfaces, similar to that found in fast aquatic animals like dolphins, towards achieving drag reduction and increased speeds of underwater vehicles and weapons'. Some basic principles of hydrohionics in drag reduction have been presented with special emphasis on the control of turbulent boundary layer characteristics of flow over the compliant material surfaces and induce delay in transition. Various researchers have estimated that the use of such compliantmaterial surfaces can lead to an overall drag reductton of the order of 10-12 per cent over drag of the rigid surface. This is a considerable drag reduction and should arouse keen interest among the underwater weapon and vehicle designers as the next stage of technological advancement in underwater hydrodynamic technology.

  10. Drag reduction for external and internal boundary layers using riblets and polymers

    Science.gov (United States)

    Reidy, Laurel W.; Anderson, Greg W.

    1988-01-01

    The efficiency of riblets and a drag-reducing polymer solution (a polyacrylamide slurry) in high-speed water tunnels for reducing drag in turbulent boundary layers was investigated in two experiments. One was an external flow experiment, in which riblets were applied to a flat plate in a high-speed water tunnel and the skin friction drag was calculated from velocity profile data. The second was an internal flow experiment, in which riblets were applied to the inside of a 6-in diameter pipe and the friction factor was calculated from mass flow rate and pressure drop measurements. Both experiments used adhesive-backed vinyl riblet film with 0.003-in height and spacing of the symmetric V-grooves. For the flat plate test, free stream velocity and Re data indicated a maximum drag reduction of about 8.1 percent. With riblets in the pipe, however, there was about three times as much friction reduction. When the polymer slurry was used in conjunction with riblets in the pipe flow, the total drag reduction was approximately equal to the sum of the drag reductions of the two techniques used separately, with some dependence on Reynolds number.

  11. Buoyancy increase and drag-reduction through a simple superhydrophobic coating.

    Science.gov (United States)

    Hwang, Gi Byoung; Patir, Adnan; Page, Kristopher; Lu, Yao; Allan, Elaine; Parkin, Ivan P

    2017-06-08

    A superhydrophobic paint was fabricated using 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES), TiO2 nanoparticles and ethanol. The paint has potential for aquatic application of a superhydrophobic coating as it induces increased buoyancy and drag reduction. Buoyance testing showed that the reduction of surface energy by superhydrophobic coating made it feasible that glass, a high density material, was supported by the surface tension of water. In a miniature boat sailing test, it was shown that the low energy surface treatment decreased the adhesion of water molecules to the surface of the boat resulting in a reduction of the drag force. Additionally, a robust superhydrophobic surface was fabricated through layer-by-layer coating using adhesive double side tape and the paint, and after a 100 cm abrasion test with sand paper, the surface still retained its water repellency, enhanced buoyancy and drag reduction.

  12. The Mechanism of Drag Reduction around Bodies of Revolution Using Bionic Non-Smooth Surfaces

    Institute of Scientific and Technical Information of China (English)

    Li-mei Tian; Lu-quan Ren; Qing-ping Liu; Zhi-wu Han; Xiao Jiang

    2007-01-01

    Bionic non-smooth surfaces (BNSS) can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been, well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.

  13. WATER TUNNEL EXPERIMENTAL INVESTIGATION ON THE DRAG REDUCTION CHARACTERISTICS OF THE TRAVELING WAVY WALL

    Institute of Scientific and Technical Information of China (English)

    YAO Yan; LU Chuan-jing; SI Ting; ZHU Kun

    2011-01-01

    Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted. A suit of traveling wavy wall device is developed. The drag forces of the traveling wavy wall with various wave speeds ( c ) are measured under different water speeds (U) in the K15 cavitation water tunnel and are compared with that of the flat plate. The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed.Under different flow speeds, when traveling wave wall reached to the minimum of drag force, the corresponding the ratio of the wall motion phase speed c to flow speed U, c/U is slightly different. Within the parameters of the experiment, when c/U reaches a certain value, the drag force of the traveling wavy wall can be less than that of the flat plate. The drag reduction can be up to 42%.Furthermore, as the value of c / U increases, the traveling wavy wall can restrain the separation and improve the quality of flow field.

  14. Re-examination of compliant wall experiments in air with water substrates. [for drag reduction

    Science.gov (United States)

    Hefner, J. N.; Weinstein, L. M.

    1976-01-01

    A possible alternative explanation is proposed for compliant wall drag reductions measured in previous investigations. Standing waves were observed to form on the surfaces of compliant wall models in air with water substrates as the freestream velocity was increased from 15 to 30 m/s. These waves resembled sine waves with half of the wave protruding over the upstream portion of the model and the other half being recessed over the downstream end of the model. These data coupled with results of recent drag reduction experiments suggest that standing waves could have caused a shift in the model center of gravity creating a bending moment that was interpreted as a reduction in the skin friction drag.

  15. Drag reduction in ultrahydrophobic channels with micro-nano structured surfaces

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experiments,the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale.For the drag reduction in macro-scale channels few reports are available.Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes.The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces.The micro-PIV was used to measure the flow velocity in channels.Compared with the traditional no-slip theory at walls,a significant slip velocity was observed on the ultrahydrophobic surfaces.

  16. Experimental investigation on drag and heat flux reduction in supersonic/hypersonic flows: A survey

    Science.gov (United States)

    Wang, Zhen-guo; Sun, Xi-wan; Huang, Wei; Li, Shi-bin; Yan, Li

    2016-12-01

    The drag and heat reduction problem of hypersonic vehicles has always attracted the attention worldwide, and the experimental test approach is the basis of theoretical analysis and numerical simulation. In the current study, research progress of experimental investigations on drag and heat reduction are summarized by several kinds of mechanism, namely the forward-facing cavity, the opposing jet, the aerospike, the energy deposition and their combinational configurations, and the combinational configurations include the combinational opposing jet and forward-facing cavity concept and the combinational opposing jet and aerospike concept. The geometric models and flow conditions are emphasized, especially for the basic principle for the drag and heat flux reduction of each device. The measurement results of aerodynamic and aerothermodynamic are compared and analyzed as well, which can be a reference for assessing the accuracy of numerical results.

  17. Surfactant aggregation and its application to drag reduction

    Energy Technology Data Exchange (ETDEWEB)

    Harwigsson, I.

    1995-09-01

    A number of different drag-reducing (DR) surfactants: nonionics, zwitterionics and ampholytics suitable for use in both cool and hot water solution are described. These surfactants have been tested under various conditions common in district energy distribution. The surfactants described are environmentally more acceptable than the organic salts of quaternary ammonium compounds which have so far dominated as DR surfactants. The micellar phase formed in water by the surfactant system cetylpyridinium chloride/sodium salicylate has been investigated with surfactant self-diffusion (NMR) measurements and cryo-transmission electron microscopy. Results from this study support the hypothesis that worm-like micellar systems form a network before the phase boundary, when the first liquid crystalline phase formed is a bicontinuous cubic phase. A series of surfactants similar to the one used in the DR experiments has been examined in dilute solutions. Critical micellar concentration and the size of these micelles are investigated as a function of the amphiphile concentration, the pH and salt concentration. Adsorption properties on silica of zwitterionic dodecyl-N,N-dimethylammonio alkanoates, with polymethylene interchange arms of different lengths, have been investigated with an in situ ellipsometry technique. The use of two-tone frequency modulation spectroscopy as a general method for the determination of water activity has been initiated. 173 refs, 6 figs

  18. Experimental Research on Air Film Drag Reduction Effect of Van Body at Different Jet Velocity%不同喷射速度下厢体气膜减阻效果的实验研究

    Institute of Scientific and Technical Information of China (English)

    谢小鹏; 曾建豪; 曹立峰

    2015-01-01

    The effect on the air film drag reduction effect of van body by jet velocity of seeping air flow on van body sur⁃face was studied.Film air jet velocity of van experimental model with air film was controlled by air film generation system to carry out resistance measurement contrast experiments of models with and without air film in variable⁃speed laminar flow wind generator with an air flowing speed of 30 m/s.The resistances of experimental models in the different ejection velocity were compared.Experimental result shows that in a condition of constant speed of laminar flow wind,seeping air flow on van body surface can effectively reduce wind resistance on van body.In a certain range,the drag reduction rate is increased with increasing of jet velocity as approximately linear growth.%研究厢体表面渗透空气流的喷射速度对气膜在空气中的减阻效果的影响。通过气膜发生系统控制有气膜厢式车实验模型的气膜空气喷射速度,在30 m/s的流动空气速度下,于可调速拟层流风力发生装置中开展与无气膜厢式车实验模型的对比测阻实验,比较不同喷射速度下,有气膜厢式车实验模型的受阻情况。实验结果表明,在流速恒定的拟层流空气流体环境下,厢体表面渗透空气流有效地降低了厢体所受的空气阻力,且在一定范围内,减阻率随喷射速度的增大近似呈线性增长。

  19. Rotating systems, universal features in dragging and anti-dragging effects, and bounds onto angular momentum

    CERN Document Server

    Karkowski, Janusz; Malec, Edward; Pirog, Michal; Xie, Naqing

    2016-01-01

    We consider stationary, axially symmetric toroids rotating around spinless black holes, assuming the general-relativistic Keplerian rotation law, in the first post-Newtonian approximation. Numerical investigation shows that the angular momentum accumulates almost exclusively within toroids. It appears that various types of dragging (anti-dragging) effects are positively correlated with the ratio $M_\\mathrm{D}/m$ ($M_\\mathrm{D}$ is the mass of a toroid and $m$ is the mass of the black hole) - moreover, their maxima are proportional to $M_\\mathrm{D}/m$. The horizontal sizes of investigated toroids range from c. 50 to c. 450 of Schwarzschild radii $R_\\mathrm{S}$ of the central black hole; their mass $M_\\mathrm{D} \\in (10^{-4}m, 40m)$ and the radial size of the system is c. 500 $R_\\mathrm{S}$. We found that the relative strength of various dragging (anti-dragging) effects does not change with the mass ratio, but it depends on the size of toroids. Several isoperimetric inequalities involving angular momentum are s...

  20. Aerodynamic Drag Reduction for A Generic Sport Utility Vehicle Using Rear Suction

    Directory of Open Access Journals (Sweden)

    Abdellah Ait Moussa

    2014-08-01

    Full Text Available The high demand for new and improved aerodynamic drag reduction devices has led to the invention of flow control mechanisms and continuous suction is a promising strategy that does not have major impact on vehicle geometry. The implementation of this technique on sport utility vehicles (SUV requires adequate choice of the size and location of the opening as well as the magnitude of the boundary suction velocity. In this paper we introduce a new methodology to identifying these parameters for maximum reduction in aerodynamic drag. The technique combines automatic modeling of the suction slit, computational fluid dynamics (CFD and a global search method using orthogonal arrays. It is shown that a properly designed suction mechanism can reduce drag by up to 9%..

  1. Elasto-Inertial Turbulence: From Subcritical Turbulence to Maximum Drag Reduction

    Science.gov (United States)

    Dubief, Yves; Sid, Samir; Egan, Raphael; Terrapon, Vincent

    2015-11-01

    Elasto Inertial Turbulence (EIT) is a turbulence state found so far in polymer solutions. Upon the appropriate initial perturbation, an autonomous regeneration cycle emerges between polymer dynamics, pressure and velocity fluctuations. This cycle is best explained by the Poisson equation derived from viscoelastic flow models such as FENE-P (used in this study). This presentation provides an overview of the structure of EIT in 2D channel flows for Reynolds numbers ranging from Reτ = 10 to 100 and for 3D simulations up to Ret au = 300 . For flows below the Newtonian critical Reynolds number, EIT increases the drag. For higher Reynolds numbers, EIT is surmised to be the energetic bound of Maximum Drag Reduction (MDR), the asymptotic state of drag reduction in polymer solutions. The very existence of EIT at low Reynolds numbers (Reτ FNRS grant No.2.5020.11), the PRACE infrastructure, and the Vermont Advanced Computing Core.

  2. Heavy Class Helicopter Fuselage Model Drag Reduction by Active Flow Control Systems

    Science.gov (United States)

    De Gregorio, F.

    2017-08-01

    A comprehensive experimental investigation of helicopter blunt fuselage drag reduction using active flow control is being carried out within the European Clean Sky program. The objective is to demonstrate the capability of several active flow technologies to decrease fuselage drag by alleviating the flow separation occurring in the rear area of some helicopters. The work is performed on a simplified blunt fuselage at model-scale. Two different flow control actuators are considered for evaluation: steady blowing, unsteady blowing (or pulsed jets). Laboratory tests of each individual actuator are first performed to assess their performance and properties. The fuselage model is then equipped with these actuators distributed in 3 slots located on the ramp bottom edge. This paper addresses the promising results obtained during the wind-tunnel campaign, since significant drag reductions are achieved for a wide range of fuselage angles of attack and yaw angles without detriment of the other aerodynamic characteristics.

  3. Modeling of drag reduction in turbulent channel flow with hydrophobic walls by FVM method and weakly-compressible flow equations

    Institute of Scientific and Technical Information of China (English)

    Ling Li; Ming-Shun Yuan

    2011-01-01

    In this paper the effects of hydrophobic wall on skin-friction drag in the channel flow are investigated through large eddy simulation on the basis of weaklycompressible flow equations with the MacCormack's scheme on collocated mesh in the FVM framework. The slip length model is adopted to describe the behavior of the slip velocities in the streamwise and spanwise directions at the interface between the hydrophobic wall and turbulent channel flow. Simulation results are presented by analyzing flow behaviors over hydrophobic wall with the Smagorinky subgrid-scale model and a dynamic model on computational meshes of different resolutions. Comparison and analysis are made on the distributions of timeaveraged velocity, velocity fluctuations, Reynolds stress as well as the skin-friction drag. Excellent agreement between the present study and previous results demonstrates the accuracy of the simple classical second-order scheme in representing turbulent vertox near hydrophobic wall. In addition, the relation of drag reduction efficiency versus time-averaged slip velocity is established. It is also found that the decrease of velocity gradient in the close wall region is responsible for the drag reduction. Considering its advantages of high calculation precision and efficiency, the present method has good prospect in its application to practical projects.

  4. Frictional Drag Reduction - A Literature Survey of Progress from Summer 1976 to Fall 1977,

    Science.gov (United States)

    1978-03-01

    of Cambridge (1977). 112. Stenberg , L.-G., 1. Lagerstedt, and E.R. Lindgren , “Polymer Additive Mixing and Turbulent Drag Reduction ,” Physics of...Fluids , Vol . 20, No. 10, Part 2, pp. S276-S278 (Oct 1977). 113. Stenberg , L.-G., 1. Lagerstedt, 0. Sehl~n, and E.R. Lindgren , “Mechanical Mixing of

  5. What happens to turbulent skin-friction drag reduction at high $Re$?

    CERN Document Server

    Gatti, Davide

    2012-01-01

    We address one of the capital problems in the field of turbulent skin-friction drag reduction, i.e. the performance of the known techniques at high values of the Reynolds number $Re$. We limit ourselves to considering open-loop techniques based on spanwise forcing (oscillating wall, streamwise-travelling waves), and explore via Direct Numerical Simulations (DNS) how quickly the drag reduction and net energy savings decrease when the friction Reynolds number is increased. We suggest an unexpected and interesting scenario where the performance of the drag-reduction technique degrade with $Re$ with a markedly different rate depending on the parameters. In particular, the known optimal region turns out to be such at low-$Re$ only, since there drag reduction degrades quite fast with $Re$, in line with available results. However, other regions are much less sensitive to $Re$, or insensitive at all. If one considers that the energy required to create the forcing presents a slightly favorable trend with $Re$, the pos...

  6. Drag reduction by surface treatment in turbulent Taylor-Couette flow

    Science.gov (United States)

    Greidanus, A. J.; Delfos, R.; Westerweel, J.

    2011-12-01

    We use a Taylor-Couette facility to study the drag reducing effects of commercial surface products at high shear Reynolds numbers (Res) under perfect couter-rotating conditions (riwi = -rowo). The correlation between torque contribution of the von Kármán flow and shear Reynolds number is investigated. At this moment no significant drag changes are found for the commercial products. However, further research is needed to exclude uncertainties and errors from the torque measurements.

  7. Drag measurements in laterally confined 2D canopies: Reconfiguration and sheltering effect

    Science.gov (United States)

    Barsu, Sylvie; Doppler, Delphine; Jerome, J. John Soundar; Rivière, Nicolas; Lance, Michel

    2016-10-01

    Plants in aquatic canopies deform when subjected to a water flow and so, unlike a rigid bluff body, the resulting drag force FD grows sub-quadratically with the flow velocity U ¯ . In this article, the effect of density on the canopy reconfiguration and the corresponding drag reduction is experimentally investigated for simple 2D synthetic canopies in an inclinable, narrow water channel. The drag acting on the canopy, and also on individual sheets, is systematically measured via two independent techniques. Simultaneous drag and reconfiguration measurements demonstrate that data for different Reynolds numbers (400-2200), irrespective of sheet width (w) and canopy spacing (ℓ), collapse on a unique curve given by a bending beam model which relates the reconfiguration number and a properly rescaled Cauchy number. Strikingly, the measured Vogel exponent V and hence the drag reduction via reconfiguration is found to be independent of the spacing between sheets and the lateral confinement; only the drag coefficient decreases linearly with the sheet spacing since a strong sheltering effect exists as long as the spacing is smaller than a critical value depending on the sheet width.

  8. Phonon-drag effects on thermoelectric power

    OpenAIRE

    Wu, M. W.; Horing, N. J. M.; Cui, H. L.

    1995-01-01

    We carry out a calculation of the phonon-drag contribution $S_g$ to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to the weakly nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation times due to phonon-phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at hi...

  9. A bio-inspired device for drag reduction on a three-dimensional model vehicle.

    Science.gov (United States)

    Kim, Dongri; Lee, Hoon; Yi, Wook; Choi, Haecheon

    2016-03-10

    In this paper, we introduce a bio-mimetic device for the reduction of the drag force on a three-dimensional model vehicle, the Ahmed body (Ahmed et al 1984 SAE Technical Paper 840300). The device, called automatic moving deflector (AMD), is designed inspired by the movement of secondary feathers on bird's wing suction surface: i.e., secondary feathers pop up when massive separation occurs on bird's wing suction surface at high angles of attack, which increases the lift force at landing. The AMD is applied to the rear slanted surface of the Ahmed body to control the flow separation there. The angle of the slanted surface considered is 25° at which the drag coefficient on the Ahmed body is highest. The wind tunnel experiment is conducted at Re H  = 1.0 × 10(5)-3.8 × 10(5), based on the height of the Ahmed body (H) and the free-stream velocity (U ∞). Several AMDs of different sizes and materials are tested by measuring the drag force on the Ahmed body, and showed drag reductions up to 19%. The velocity and surface-pressure measurements show that AMD starts to pop up when the pressure in the thin gap between the slanted surface and AMD is much larger than that on the upper surface of AMD. We also derive an empirical formula that predicts the critical free-stream velocity at which AMD starts to operate. Finally, it is shown that the drag reduction by AMD is mainly attributed to a pressure recovery on the slanted surface by delaying the flow separation and suppressing the strength of the longitudinal vortices emanating from the lateral edges of the slanted surface.

  10. On Nature of Plasmonic Drag Effect

    CERN Document Server

    Durach, Maxim

    2016-01-01

    Light-matter momentum transfer in plasmonic materials is theoretically discussed in context of the modified plasmonic pressure mechanism, taking into account electron thermalization process. We show that our approach explains the observed in experiments relationship between the photoinduced electromotive force and absorption, emphasizes the quantum nature of plasmon-electron interaction, and allows one to correctly calculate the magnitude of the plasmon drag emf in flat metal films for the first time. We extend our theory on the films with modulated profiles and show that simple relationship between plasmonic energy and momentum transfer holds for the case of laminar electron drift and relatively small amplitudes of height modulation.

  11. Biomimetic structures for fluid drag reduction in laminar and turbulent flows

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Yong Chae; Bhushan, Bharat, E-mail: Bhushan.2@osu.ed [Nanoprobe Laboratory for Bio- and Nanotechnology and Biomimetics (NLB2), Ohio State University, 201 West 19th Avenue, Columbus, OH 43210-1142 (United States)

    2010-01-27

    Biomimetics allows one to mimic nature to develop materials and devices of commercial interest for engineers. Drag reduction in fluid flow is one of the examples found in nature. In this study, nano, micro, and hierarchical structures found in lotus plant surfaces, as well as shark skin replica and a rib patterned surface to simulate shark skin structure were fabricated. Drag reduction efficiency studies on the surfaces were systematically carried out using water flow. An experimental flow channel was used to measure the pressure drop in laminar and turbulent flows, and the trends were explained in terms of the measured and predicted values by using fluid dynamics models. The slip length for various surfaces in laminar flow was also investigated based on the measured pressure drop. For comparison, the pressure drop for various surfaces was also measured using air flow.

  12. Sustained drag reduction in a turbulent flow using a low-temperature Leidenfrost surface

    Science.gov (United States)

    Saranadhi, Dhananjai; Chen, Dayong; Kleingartner, Justin A.; Srinivasan, Siddarth; Cohen, Robert E.; McKinley, Gareth H.

    2016-01-01

    Skin friction drag contributes a major portion of the total drag for small and large water vehicles at high Reynolds number (Re). One emerging approach to reducing drag is to use superhydrophobic surfaces to promote slip boundary conditions. However, the air layer or “plastron” trapped on submerged superhydrophobic surfaces often diminishes quickly under hydrostatic pressure and/or turbulent pressure fluctuations. We use active heating on a superhydrophobic surface to establish a stable vapor layer or “Leidenfrost” state at a relatively low superheat temperature. The continuous film of water vapor lubricates the interface, and the resulting slip boundary condition leads to skin friction drag reduction on the inner rotor of a custom Taylor-Couette apparatus. We find that skin friction can be reduced by 80 to 90% relative to an unheated superhydrophobic surface for Re in the range 26,100 ≤ Re ≤ 52,000. We derive a boundary layer and slip theory to describe the hydrodynamics in the system and show that the plastron thickness is h = 44 ± 11 μm, in agreement with expectations for a Leidenfrost surface. PMID:27757417

  13. Drag reduction on the 25 slant angle Ahmed reference body using pulsed jets

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, Pierric [CNAM, Institut AeroTechnique (IAT), Saint Cyr l' Ecole (France); Amandolese, Xavier [CNAM, Aerodynamics Department, Saint Cyr l' Ecole (France); Aider, Jean-Luc [UMR 7636, CNRS, ESPCI ParisTech, PMMH Laboratory, Paris (France)

    2012-05-15

    This paper highlights steady and unsteady measurements and flow control results obtained on an Ahmed model with slant angle of 25 in wind tunnel. On this high-drag configuration characterized by a large separation bubble along with energetic streamwise vortices, time-averaged and time-dependent results without control are first presented. The influence of rear-end periodic forcing on the drag coefficient is then investigated using electrically operated magnetic valves in an open-loop control scheme. Four distinct configurations of flow control have been tested: rectangular pulsed jets aligned with the spanwise direction or in winglets configuration on the roof end and rectangular jets or a large open slot at the top of the rear slant. For each configuration, the influence of the forcing parameters (non-dimensional frequency, injected momentum) on the drag coefficient has been studied, along with their impact on the static pressure on both the rear slant and vertical base of the model. Depending on the type and location of pulsed jets actuation, the maximum drag reduction is obtained for increasing injected momentum or well-defined optimal pulsation frequencies. (orig.)

  14. Application of reduced-order controller to turbulent flows for drag reduction

    Science.gov (United States)

    Lee, Keun H.; Cortelezzi, Luca; Kim, John; Speyer, Jason

    2001-05-01

    A reduced-order linear feedback controller is designed and applied to turbulent channel flow for drag reduction. From the linearized two-dimensional Navier-Stokes equations a distributed feedback controller, which produces blowing/suction at the wall based on the measured turbulent streamwise wall-shear stress, is derived using model reduction techniques and linearquadratic-Gaussian/loop-transfer-recovery control synthesis. The quadratic cost criterion used for synthesis is composed of the streamwise wall-shear stress, which includes the control effort of blowing/suction. This distributed two-dimensional controller developed from a linear system theory is shown to reduce the skin friction by 10% in direct numerical simulations of a low-Reynolds number turbulent nonlinear channel flow. Spanwise shear-stress variation, not captured by the distributed two-dimensional controller, is suppressed by augmentation of a simple spanwise ad hoc control scheme. This augmented three-dimensional controller, which requires only the turbulent streamwise velocity gradient, results in a further reduction in the skin-friction drag. It is shown that the input power requirement is significantly less than the power saved by reduced drag. Other turbulence characteristics affected by these controllers are also discussed.

  15. Drag Reduction and Performance Improvement of Hydraulic Torque Converters with Multiple Biological Characteristics

    Science.gov (United States)

    Chunbao, Liu; Changsuo, Liu; Yubo, Zhang

    2016-01-01

    Fish-like, dolphin-like, and bionic nonsmooth surfaces were employed in a hydraulic torque converter to achieve drag reduction and performance improvement, which were aimed at reducing profile loss, impacting loss and friction loss, respectively. YJSW335, a twin turbine torque converter, was bionically designed delicately. The biological characteristics consisted of fish-like blades in all four wheels, dolphin-like structure in the first turbine and the stator, and nonsmooth surfaces in the pump. The prediction performance of bionic YJSW335, obtained by computational fluid dynamics simulation, was improved compared with that of the original model, and then it could be proved that drag reduction had been achieved. The mechanism accounting for drag reduction of three factors was also investigated. After bionic design, the torque ratio and the highest efficiencies of YJSW335 were both advanced, which were very difficult to achieve through traditional design method. Moreover, the highest efficiency of the low speed area and high speed area is 85.65% and 86.32%, respectively. By economic matching analysis of the original and bionic powertrains, the latter can significantly reduce the fuel consumption and improve the operating economy of the loader. PMID:27752220

  16. Drag Reduction and Performance Improvement of Hydraulic Torque Converters with Multiple Biological Characteristics

    Directory of Open Access Journals (Sweden)

    Liu Chunbao

    2016-01-01

    Full Text Available Fish-like, dolphin-like, and bionic nonsmooth surfaces were employed in a hydraulic torque converter to achieve drag reduction and performance improvement, which were aimed at reducing profile loss, impacting loss and friction loss, respectively. YJSW335, a twin turbine torque converter, was bionically designed delicately. The biological characteristics consisted of fish-like blades in all four wheels, dolphin-like structure in the first turbine and the stator, and nonsmooth surfaces in the pump. The prediction performance of bionic YJSW335, obtained by computational fluid dynamics simulation, was improved compared with that of the original model, and then it could be proved that drag reduction had been achieved. The mechanism accounting for drag reduction of three factors was also investigated. After bionic design, the torque ratio and the highest efficiencies of YJSW335 were both advanced, which were very difficult to achieve through traditional design method. Moreover, the highest efficiency of the low speed area and high speed area is 85.65% and 86.32%, respectively. By economic matching analysis of the original and bionic powertrains, the latter can significantly reduce the fuel consumption and improve the operating economy of the loader.

  17. Drag reduction in turbulent channel laden with finite-size oblate spheroids

    Science.gov (United States)

    Niazi Ardekani, Mehdi; Pedro Costa Collaboration; Wim-Paul Breugem Collaboration; Francesco Picano Collaboration; Luca Brandt Collaboration

    2016-11-01

    Suspensions of oblate rigid particles in a turbulent plane channel flow are investigated for different values of the particle volume fraction. We perform direct numerical simulations (DNS), using a direct-forcing immersed boundary method to account for the particle-fluid interactions, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. We show a clear drag reduction and turbulence attenuation in flows laden with oblate spheroids, both with respect to the single phase turbulent flow and to suspensions of rigid spheres. We explain the drag reduction by the lack of the particle layer at the wall, observed before for spherical particles. In addition, the special shape of the oblate particles creates a tendency to stay parallel to the wall in its vicinity, forming a shield of particles that prevents strong fluctuations in the outer layer to reach the wall and vice versa. Detailed statistics of the fluid and particle phase will be presented at the conference to explain the observed drag reduction. Supported by the European Research Council Grant No. ERC-2013-CoG-616186, TRITOS. The authors acknowledge computer time provided by SNIC (Swedish National Infrastructure for Computing) and the support from the COST Action MP1305: Flowing matter.

  18. Influence of hydrogen concentration on Fe2O3 particle reduction in fluidized beds under constant drag force

    Institute of Scientific and Technical Information of China (English)

    Lei Guo; Han Gao; Jin-tao Yu; Zong-liang Zhang; Zhan-cheng Guo

    2015-01-01

    The fixed-gas drag force from a model calculation method that stabilizes the agitation capabilities of different gas ratios was used to explore the influence of temperature and hydrogen concentration on fluidizing duration, metallization ratio, utilization rate of reduction gas, and sticking behavior. Different hydrogen concentrations from 5vol%to 100vol%at 1073 and 1273 K were used while the drag force with the flow of N2 and H2 (N2:2 L·min−1;H2:2 L·min−1) at 1073 K was chosen as the standard drag force. The metallization ratio, mean reduc-tion rate, and utilization rate of reduction gas were observed to generally increase with increasing hydrogen concentration. Faster reduction rates and higher metallization ratios were obtained when the reduction temperature decreased from 1273 to 1073 K. A numerical relation among particle diameter, particle drag force, and fluidization state was plotted in a diagram by this model.

  19. A Preliminary Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

    Science.gov (United States)

    Pahle, Joe; Berger, Dave; Venti, Michael W.; Faber, James J.; Duggan, Chris; Cardinal, Kyle

    2012-01-01

    Many theoretical and experimental studies have shown that aircraft flying in formation could experience significant reductions in fuel use compared to solo flight. To date, formation flight for aerodynamic benefit has not been thoroughly explored in flight for large transport-class vehicles. This paper summarizes flight data gathered during several two ship, C-17 formation flights at a single flight condition of 275 knots, at 25,000 ft MSL. Stabilized test points were flown with the trail aircraft at 1,000 and 3,000 ft aft of the lead aircraft at selected crosstrack and vertical offset locations within the estimated area of influence of the vortex generated by the lead aircraft. Flight data recorded at test points within the vortex from the lead aircraft are compared to data recorded at tare flight test points outside of the influence of the vortex. Since drag was not measured directly, reductions in fuel flow and thrust for level flight are used as a proxy for drag reduction. Estimated thrust and measured fuel flow reductions were documented at several trail test point locations within the area of influence of the leads vortex. The maximum average fuel flow reduction was approximately 7-8%, compared to the tare points flown before and after the test points. Although incomplete, the data suggests that regions with fuel flow and thrust reduction greater than 10% compared to the tare test points exist within the vortex area of influence.

  20. Drag reduction by surface treatment in turbulent Taylor-Couette flow

    NARCIS (Netherlands)

    Greidanus, A.J.; Delfos, R.; Westerweel, J.

    2011-01-01

    We use a Taylor-Couette facility to study the drag reducing effects of commercial surface products at high shear Reynolds numbers (Res) under perfect couter-rotating conditions (riwi=rowo). The correlation between torque contribution of the von Karman flow and shear Reynolds number is investigated.

  1. Significant and stable drag reduction with air rings confined by alternated superhydrophobic and hydrophilic strips

    Science.gov (United States)

    Hu, Haibao; Wen, Jun; Bao, Luyao; Jia, Laibing; Song, Dong; Song, Baowei; Pan, Guang; Scaraggi, Michele; Dini, Daniele; Xue, Qunji; Zhou, Feng

    2017-01-01

    Superhydrophobic surfaces have the potential to reduce the viscous drag of liquids by significantly decreasing friction at a solid-liquid interface due to the formation of air layers between solid walls and interacting liquids. However, the trapped air usually becomes unstable due to the finite nature of the domain over which it forms. We demonstrate for the first time that a large surface energy barrier can be formed to strongly pin the three-phase contact line of air/water/solid by covering the inner rotor of a Taylor-Couette flow apparatus with alternating superhydrophobic and hydrophilic circumferential strips. This prevents the disruption of the air layer, which forms stable and continuous air rings. The drag reduction measured at the inner rotor could be as much as 77.2%. Moreover, the air layers not only significantly reduce the strength of Taylor vortexes but also influence the number and position of the Taylor vortex pairs. This has strong implications in terms of energy efficiency maximization for marine applications and reduction of drag losses in, for example, fluid transport in pipelines and carriers. PMID:28879234

  2. Transonic Drag Reduction Through Trailing-Edge Blowing on the FAST-MAC Circulation Control Model

    Science.gov (United States)

    Chan, David T.; Jones, Gregory S.; Milholen, William E., II; Goodliff, Scott L.

    2017-01-01

    A third wind tunnel test of the FAST-MAC circulation control semi-span model was completed in the National Transonic Facility at the NASA Langley Research Center where the model was configured for transonic testing of the cruise configuration with 0deg flap detection to determine the potential for transonic drag reduction with the circulation control blowing. The model allowed independent control of four circulation control plenums producing a high momentum jet from a blowing slot near the wing trailing edge that was directed over a 15% chord simple-hinged ap. Recent upgrades to transonic semi-span flow control testing at the NTF have demonstrated an improvement to overall data repeatability, particularly for the drag measurement, that allows for increased confidence in the data results. The static thrust generated by the blowing slot was removed from the wind-on data using force and moment balance data from wind-o thrust tares. This paper discusses the impact of the trailing-edge blowing to the transonic aerodynamics of the FAST-MAC model in the cruise configuration, where at flight Reynolds numbers, the thrust-removed corrected data showed that an overall drag reduction and increased aerodynamic efficiency was realized as a consequence of the blowing.

  3. Stability of two-layer Couette flow with application to drag reduction

    Science.gov (United States)

    Mohammadi, Alireza; Smits, Alexander J.

    2016-11-01

    We consider the linear stability of flows composed of two superposed fluids in Couette flow in order to improve our understanding of the longevity and performance of superhydrophobic surfaces (SHS) or liquid-infused surfaces (LIS) which are important for drag reduction. Here, we assume that the fluids are immiscible, incompressible, and Newtonian with constant properties. Single-fluid Couette flow is known to be linearly stable for any Reynolds number. However, inclusion of the second layer of fluid enriches the problem and introduces five new parameters: viscosity ratio, density ratio, thickness ratio, Froude number and Weber number. Two kinds of instability can appear: an unstable interfacial mode, and a Tollmein-Schlichting mode. In this work we parametrically study the flow stability with specific emphasis on the effects of viscosity ratio, interfacial tension, and thickness ratio. Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Office of Naval Research (ONR) through MURI Grants N00014-12-1-0875 and N00014-12-1-0962 (Program Manager Dr. Ki-Han Kim).

  4. EFFECT OF AERATOR ON HYDRAULIC DRAG ACTING ON A CHUTE

    Institute of Scientific and Technical Information of China (English)

    NI Han-gen; LI Xin; ZHOU Jing; JIN Qiao

    2005-01-01

    The formulae used to calculate the friction in the non-uniform flow chute were examined with the experimental data, and the results show that the accuracy of the formula is enough for engineering applications. A comparison between the results of friction respectively from the uniform flow assumption and the non-uniform flow approximation indicates that the former is an order of magnitude larger than the latter in the case of steep chute. The hydraulic drag on a steep chute with aerators was measured on the hydraulic model directly and the coefficient of the aerator effect on the drag was obtained. The variation patterns of the wall shear just downstream of the aerators were investigated and the mechanism of the increase in the drag by aerator were analyzed qualitatively with the measured water-depths just downstream the aerators.

  5. Drag and heat reduction mechanism induced by a combinational novel cavity and counterflowing jet concept in hypersonic flows

    Science.gov (United States)

    Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li

    2016-09-01

    The drag and heat reduction problem of hypersonic reentry vehicles has always attracted the attention worldwide, and many novel schemes have been proposed recently. In the current study, the research progress of the combinational configuration of the forward-facing cavity and the counterflowing jet has been reviewed, and the conventional cavity configuration has been substituted by an approximate maximum thrust nozzle contour for better heat and surface pressure reduction efficiency. The Reynolds-average of Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flow fields. A validation metric and the grid convergence index (GCI) have been employed to conduct the turbulence model assessment and the grid independence analysis respectively. The axisymmetric assumption has been verified by three-dimensional computational results as well. The obtained results show that the SST k-ω model is more suitable for the novel drag and heat flux reduction scheme proposed in this article, and the axisymmetric assumption is approximately reasonable. After investigating the influence of jet pressure ratio, the novel combinational configuration has been verified to be more effective in heat and surface pressure reduction, and this is because the approximate maximum thrust nozzle contour contributes to better expansion and avoids total pressure loss of the jet.

  6. Effect of Radiation Drag on Hoyle-Lyttleton Accretion

    CERN Document Server

    Nio, T; Fukue, J; Nio, Tomomi; Matsuda, Takuya; Fukue, Jun

    1998-01-01

    Hoyle-Lyttleton type accretion is investigated, by taking account of not only the effect of radiation pressure but the effect of radiation drag. We calculate the trajectories of particles for three cases: only the effect of gravity is considered (case A); the effect of radiation pressure is taken into account (case B); the effect of radiation drag as well as radiation pressure is taken into account (case C). The accretion radii for former two cases are $2GM/v_{\\infty}^2$ for case A and $2GM(1-\\Gamma)/v_{\\infty}^2$ for case B, where M is the mass of the accreted object, $v_{\\infty}$ the relative velocity, and Gamma the normalized luminosity of the accreted object. We found that the accretion radius for case C is in between those of cases A and B under the present approximation; i.e., the accretion radius decreases due to radiation pressure while it increases due to radiation drag. In addition, the accretion radius for case C becomes larger as the incident velocity becomes fast. The effect of radiation drag bec...

  7. Drag Reduction of a Turbulent Boundary Layer over an Oscillating Wall and Its Variation with Reynolds Number

    Directory of Open Access Journals (Sweden)

    Martin Skote

    2015-01-01

    Full Text Available Spanwise oscillation applied on the wall under a spatially developing turbulent boundary layer flow is investigated using direct numerical simulation. The temporal wall forcing produces a considerable drag reduction over the region where oscillation occurs. Downstream development of drag reduction is investigated from Reynolds number dependency perspective. An alternative to the previously suggested power-law relation between Reynolds number and peak drag reduction values, which is valid for channel flow as well, is proposed. Considerable deviation in the variation of drag reduction with Reynolds number between different previous investigations of channel flow is found. The shift in velocity profile, which has been used in the past for explaining the diminishing drag reduction at higher Reynolds number for riblets, is investigated. A new predictive formula is derived, replacing the ones found in the literature. Furthermore, unlike for the case of riblets, the shift is varying downstream in the case of wall oscillations, which is a manifestation of the fact that the boundary layer has not reached a new equilibrium over the limited downstream distance in the simulations. Taking this into account, the predictive model agrees well with DNS data. On the other hand, the growth of the boundary layer does not influence the drag reduction prediction.

  8. The Mercury-Drag Effect, a Demonstration of Transport Phenomena

    Science.gov (United States)

    Martin, D. H.; Teese, R. B

    1969-01-01

    The mercury-drag effect is demonstrated when mercury vapor diffuses through nitrogen gas at low pressure, passing through tubes of different radii to liquid nitrogen-cooled cold traps. The pressure changes of the nitrogen gas on the mercury-deficient side of the cold traps are observed and compared with theoretical and experimental valves from the…

  9. Novel mussel-inspired Ti-6Al-4V surfaces with biocompatibility, blood ultra-drag reduction and superior durability.

    Science.gov (United States)

    Li, Qi; Tang, Fei; Wang, Chunze; Wang, Xiaohao

    2017-07-01

    In order to develop new Ti-based biomaterials with biocompatibility, blood ultra-drag reduction and superior durability, a novel fabrication combining simple electrochemical and chemical processes was proposed. After being modified by C14H19F13O3Si (FAS), a biocompatible TiO2-SiO2-polydopamine composite surface on Ti-6Al-4V substrate was obtained. The biocompatibility was evaluated using a series of in vitro test, revealing that compared with Ti-6Al-4V alloys, the surfaces exhibited a number of bio-advantages such as anti-platelet aggregation, anti-bovine serum albumin protein adsorption, a lower hemolysis rate (~0.7%) and non-cytotoxicity (the cell viability >88%). The test of human microvascular endothelial cells (HMEC) cultured on the specimens for 48h showed better cell proliferation of the surface. Moreover, we explored the blood dynamic characteristics of titanium alloy substrate biomaterial for the first time, with a focus on the effects of dopamine-reactant concentration on blood flow resistance. The results showed that, compared to titanium alloy material, the TiO2-SiO2 surface modified by 4mg·mL(-1) dopamine solution displayed the optimal blood drag reduction characteristics, reaching a 76% drag reduction. After a 2m (800 meshes, 3500Pa) sandpaper abrasion test, the surface still maintained a superior repellency of blood (contact angles>150°, sliding angles<10°). This practical method may expand the applications of biomedical implantation materials. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. 槽道纤维悬浮流动转捩阶段稳定性与减阻研究%Stability and drag reduction in transient channel flow of fibre suspension

    Institute of Scientific and Technical Information of China (English)

    游振江; 林建忠; 邵雪明; 张卫峰

    2004-01-01

    Drag reduction features in the transition regime of channel flow with fibre suspension were analyzed in terms of the linear stability theory.The modified stability equation was obtained based on the slender-body theory and natural closure approximation.Results of the stability analysis show attenuating effects of fibre additives to the flow instability.For the cases leading to transition,drag reduction rate increases with the characteristic parameter H of fibres.The mechanism of drag reduction by fibres is revealed through the variation of velocity profile and the decrease of wall shear stress.The theoretical results are qualitatively consistent with some typical experiments.

  11. Effect of swim cap model on passive drag.

    Science.gov (United States)

    Gatta, Giorgio; Zamparo, Paola; Cortesi, Matteo

    2013-10-01

    Hydrodynamics plays an important role in swimming because even small decreases in a swimmer's drag can lead to performance improvements. During the gliding phases of a race, the head of a swimmer is an important point of impact with the fluid, and the swim cap, even if it covers only a small portion of the swimmer's body, can have an influence on drag. The purpose of this study was to investigate the effects on passive drag (Dp) of wearing 3 different types of swim caps (LSC: a lycra cap; CSC: a silicone cap; HSC: a silicone helmet cap without seams). Sixteen swimmers were tested at 3 velocities (1.5, 1.7, 1.9 m·s), and the Dp measurements were repeated at each condition 5 times. A statistical analysis revealed significant differences in drag (p swim cap is the most rigid, the most adherent to the swimmer's head, and does not allow the formation of wrinkles compared with the other 2 investigated swim caps. Therefore, the following conclusions can be made: (a) swimmers should take care when selecting their swim cap if they want to improve the fluid dynamics at the "leading edge" of their body and (b) because Dp is affected by the swim cap model, care should be taken when comparing data from different studies, especially at faster investigated speeds.

  12. On the parameterization scheme of gravity wave drag effect on the mean zonal flow of mesosphere

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Based on McFarlane's parameterization scheme of gravity wave drag, a refined gravity-wave-drag scheme is presented. Both the drag effect of the momentum flux and the dissipation effect of gravity wave breaking on the mean zonal flow are included in the refined parameterization scheme. The dissipation effect can be formulated with the gravity wave numbers and the mean quantities. The refined parameterization scheme may represent a complete drag effect of stationary gravity wave breaking on the mean zonal flow.

  13. Razor clam to RoboClam: burrowing drag reduction mechanisms and their robotic adaptation.

    Science.gov (United States)

    Winter, A G; V; Deits, R L H; Dorsch, D S; Slocum, A H; Hosoi, A E

    2014-09-01

    Estimates based on the strength, size, and shape of the Atlantic razor clam (Ensis directus) indicate that the animal's burrow depth should be physically limited to a few centimeters; yet razor clams can dig as deep as 70 cm. By measuring soil deformations around burrowing E. directus, we have found the animal reduces drag by contracting its valves to initially fail, and then fluidize, the surrounding substrate. The characteristic contraction time to achieve fluidization can be calculated directly from soil properties. The geometry of the fluidized zone is dictated by two commonly-measured geotechnical parameters: coefficient of lateral earth pressure and friction angle. Calculations using full ranges for both parameters indicate that the fluidized zone is a local effect, occurring between 1-5 body radii away from the animal. The energy associated with motion through fluidized substrate-characterized by a depth-independent density and viscosity-scales linearly with depth. In contrast, moving through static soil requires energy that scales with depth squared. For E. directus, this translates to a 10X reduction in the energy required to reach observed burrow depths. For engineers, localized fluidization offers a mechanically simple and purely kinematic method to dramatically reduce energy costs associated with digging. This concept is demonstrated with RoboClam, an E. directus-inspired robot. Using a genetic algorithm to find optimal digging kinematics, RoboClam has achieved localized fluidization burrowing performance comparable to that of the animal, with a linear energy-depth relationship, in both idealized granular glass beads and E. directus' native cohesive mudflat habitat.

  14. Model-based design of transverse wall oscillations for turbulent drag reduction

    CERN Document Server

    Moarref, Rashad

    2012-01-01

    Over the last two decades, both experiments and simulations have demonstrated that transverse wall oscillations with properly selected amplitude and frequency can reduce turbulent drag by as much as 40%. In this paper, we develop a model-based approach for designing oscillations that suppress turbulence in a channel flow. We utilize eddy-viscosity-enhanced linearization of the turbulent flow with control in conjunction with turbulence modeling to determine skin-friction drag in a simulation-free manner. The Boussinesq eddy viscosity hypothesis is used to quantify the effect of fluctuations on the mean velocity in the flow subject to control. In contrast to the traditional approach that relies on numerical simulations, we determine the turbulent viscosity from the second order statistics of the linearized model driven by white-in-time stochastic forcing. The spatial power spectrum of the forcing is selected to ensure that the linearized model for the uncontrolled flow reproduces the turbulent energy spectrum. ...

  15. Drag reduction of a car model by linear genetic programming control

    Science.gov (United States)

    Li, Ruiying; Noack, Bernd R.; Cordier, Laurent; Borée, Jacques; Harambat, Fabien

    2017-08-01

    We investigate open- and closed-loop active control for aerodynamic drag reduction of a car model. Turbulent flow around a blunt-edged Ahmed body is examined at ReH≈ 3× 105 based on body height. The actuation is performed with pulsed jets at all trailing edges (multiple inputs) combined with a Coanda deflection surface. The flow is monitored with 16 pressure sensors distributed at the rear side (multiple outputs). We apply a recently developed model-free control strategy building on genetic programming in Dracopoulos and Kent (Neural Comput Appl 6:214-228, 1997) and Gautier et al. (J Fluid Mech 770:424-441, 2015). The optimized control laws comprise periodic forcing, multi-frequency forcing and sensor-based feedback including also time-history information feedback and combinations thereof. Key enabler is linear genetic programming (LGP) as powerful regression technique for optimizing the multiple-input multiple-output control laws. The proposed LGP control can select the best open- or closed-loop control in an unsupervised manner. Approximately 33% base pressure recovery associated with 22% drag reduction is achieved in all considered classes of control laws. Intriguingly, the feedback actuation emulates periodic high-frequency forcing. In addition, the control identified automatically the only sensor which listens to high-frequency flow components with good signal to noise ratio. Our control strategy is, in principle, applicable to all multiple actuators and sensors experiments.

  16. Stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection

    Science.gov (United States)

    Qin, Shijie; Chu, Ning; Yao, Yan; Liu, Jingting; Huang, Bin; Wu, Dazhuan

    2017-03-01

    To investigate the stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection, both experiments and simulations of bubble drag reduction (BDR) have been conducted in this paper. Drag reductions at various flow speeds and air injection rates have been tested in cavitation tunnel experiments. Visualization of bubble flow pattern is implemented synchronously. The computational fluid dynamics (CFD) method, in the framework of Eulerian-Eulerian two fluid modeling, coupled with population balance model (PBM) is used to simulate the bubbly flow along the flat plate. A wide range of bubble sizes considering bubble breakup and coalescence is modeled based on experimental bubble distribution images. Drag and lift forces are fully modeled based on applicable closure models. Both predicted drag reductions and bubble distributions are in reasonable concordance with experimental results. Stream-wise distribution of BDR is revealed based on CFD-PBM numerical results. In particular, four distinct regions with different BDR characteristics are first identified and discussed in this study. Thresholds between regions are extracted and discussed. And it is highly necessary to fully understand the stream-wise distribution of BDR in order to establish a universal scaling law. Moreover, mechanism of stream-wise distribution of BDR is analysed based on the near-wall flow parameters. The local drag reduction is a direct result of near-wall max void fraction. And the near-wall velocity gradient modified by the presence of bubbles is considered as another important factor for bubble drag reduction.

  17. Drag Reduction in a Swimming Humboldt Penguin, Spheniscus Humboldti, when the Boundary Layer is Turbulent

    Institute of Scientific and Technical Information of China (English)

    Alex R. Parfitt; Julian F.V. Vincent

    2005-01-01

    An area of protruding feathers found around the beak of many penguin species is thought to induce a turbulent boundary layer whilst swimming. Hydrodynamic tests on a model Humboldt penguin, Spheniscus humboldti, suggest that induced turbulence causes a significant reduction in boundary layer height, flow separation, and an average of 31% reduction in drag (1.0 m/s to 4.5 m/s). Visualisation of surface flow showed it to follow the body profile, over the feet and tail, before separating. Movement of the feet in swimming penguins correlates with steering of the bird. Induced turbulence may therefore further increase swimming efficiency by reducing the amount of foot movement required to direct the swimming bird.

  18. Evaluation of polymers with drag reduction potential used in drilling fluids; Avaliacao de polimeros com potencial de reducao de arraste usado em fluidos de perfuracao

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Marcus V.D.; Costa, Francileide G. da [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES)]. E-mail: mvferreira.puc@petrobras.com.br; Lopes, Lea; Figueiredo, Marcos S.; Lucas, Elizabete F. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Macromoleculas]. E-mail: elucas@ima.ufrj.br

    2005-07-01

    The employment of linear chain polymers with high molecular weight in fluids as drag reducers became a current practice in the chemical industry. The petroleum industry presents several potential applications for drag reducers. Although some commercial products are available for specific applications, the major drag reduction mechanisms are, still unknown nowadays, despite of several theories about the phenomena. The aim of this work is to evaluate the rheological behavior of partially hydrolyzed polyacrylamide (PHPA) and xanthan and diu tan gums solutions that have drag reduction characteristics. It is expected that these polymers present a good drag reduction potential. All these polymers will be evaluated as drag reducers in a pressure drop flow loop. The final step is to correlate drag reduction tendency with rheological properties and molecular structure. (author)

  19. Drag reduction in oil flows; Reducao da perda de carga durante o escoamento de petroleo

    Energy Technology Data Exchange (ETDEWEB)

    Rocha, Nelson de Oliveira; Carvalho, Carlos Henrique M. de; Ziglio, Claudio Marcos [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas; Noronha, Francisco de Assis; Silva, Aldo Manoel Borburema da [PETROBRAS S.A., Natal, RN (Brazil). Unidade de Negocio RN/CE; Santos, Anderson Oliveira; Rizzo, Rodrigo Gouveia de O.; Sanatana, Marcos Antonio de Oliveira [PETROBRAS S.A., Aracaju, SE (Brazil). Unidade de Negocio SE/AL

    2008-07-01

    The strong world demand for petroleum has increased interest in optimizing the production from mature fields. To do this, it is necessary to use recovery methods that are associated with others that generally use water and/or steam injection, aimed at increasing the production. In parallel with the increase in water production from mature fields, it is evident that there is an increase in viscosity of the liquid phase. This is due to the formation of an emulsion during the lift and flow processes, principally caused by the agitation and shearing, which in turn provoke less oil mobility and high pressure in the production systems. For this reason the oil flow has become a challenge to the production and this is highlighted in the technological innovation scenario in the petroleum industry. Different situations are observed in the production scenario where the following are found: oil production with high BSW, low BSW and /or stable emulsions. The study of the phenomenon to reduce the drag during the turbulent flow, through the injection of polymeric type chemical additives with high molecular weight has been the subject of various surveys over the past few years. The employment of chemical additives containing a drag-reducing agent known as DRA (Drag-Reducing Agents), in turbulent flows, allows for a lower pressure to maintain or to even increase the production capacity. In this study, a mathematic equation of the problem will be presented and the operational methods employed. The performance of different multi functional chemical additives are shown, which are capable of maintaining the flow, either by breaking the emulsion, or by modifying the flow regime, culminating in the reduction of the loss of load during the production flow. (author)

  20. Substructure drag effects and recrystallization textures in aluminium

    Energy Technology Data Exchange (ETDEWEB)

    Higginson, R. [Univ. of Sheffield (United Kingdom). Dept. of Engineering Materials; Bate, P. [Doncasters plc, Melbourne (United Kingdom)

    1999-03-10

    Many important recrystallization texture components in metals such as aluminium originate from nuclei in which the mobile high-angle boundary exists prior to, or is formed in the early stages of, annealing. Nucleation can then occur by a process known as strain-induced boundary migration (SIBM). It is possible that this process will involve several growing subgrains, and the drag from that substructure can then have a significant effect. A simple model is used to demonstrate how changes in the overall driving force for recrystallization and Zener drag can affect recrystallization textures when SIBM is involved. This is discussed in relation to experimental observations and the evidence for this process is reviewed.

  1. A unified view of energetic efficiency in active drag reduction, thrust generation and self-propulsion through a loss coefficient with some applications

    Science.gov (United States)

    Arakeri, Jaywant H.; Shukla, Ratnesh K.

    2013-08-01

    An analysis of the energy budget for the general case of a body translating in a stationary fluid under the action of an external force is used to define a power loss coefficient. This universal definition of power loss coefficient gives a measure of the energy lost in the wake of the translating body and, in general, is applicable to a variety of flow configurations including active drag reduction, self-propulsion and thrust generation. The utility of the power loss coefficient is demonstrated on a model bluff body flow problem concerning a two-dimensional elliptical cylinder in a uniform cross-flow. The upper and lower boundaries of the elliptic cylinder undergo continuous motion due to a prescribed reflectionally symmetric constant tangential surface velocity. It is shown that a decrease in drag resulting from an increase in the strength of tangential surface velocity leads to an initial reduction and eventual rise in the power loss coefficient. A maximum in energetic efficiency is attained for a drag reducing tangential surface velocity which minimizes the power loss coefficient. The effect of the tangential surface velocity on drag reduction and self-propulsion of both bluff and streamlined bodies is explored through a variation in the thickness ratio (ratio of the minor and major axes) of the elliptical cylinders.

  2. A study of performance parameters on drag and heat flux reduction efficiency of combinational novel cavity and opposing jet concept in hypersonic flows

    Science.gov (United States)

    Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li

    2017-02-01

    The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.

  3. Vapor layers reduce drag without the crisis

    Science.gov (United States)

    Vakarelski, Ivan; Berry, Joseph; Chan, Derek; Thoroddsen, Sigurdur

    2016-11-01

    The drag of a solid sphere moving in fluid is known to be only a function of the Reynolds number, Re and diminishes rapidly at the drag crisis around Re 3 ×105. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect, can occur over a wide range of Re, from as low as 600. The Navier slip model with a viscosity dependent slip length captures the observed drag reduction and wake shape.

  4. The Common Mechanism of Turbulent Skin-Friction Drag Reduction with Super-Hydrophobic Micro-Grooves and Riblets

    Science.gov (United States)

    Rastegari, Amirreza; Akhavan, Rayhaneh

    2016-11-01

    Drag Reduction (DR) with Super-Hydrophobic (SH) longitudinal Micro-Grooves (MGs) and riblets was investigated by DNS using lattice Boltzmann methods. The liquid/gas interfaces on the SH MGs were modeled as curved, stationary, shear-free boundaries, with the meniscus shape determined from the Young-Laplace equation. For comparison, the same geometries were also studied as riblets. DRs of 35% to 63% with SH MGs, and 10% to -17% with riblets, were realized in DNS in turbulent channel flow at Reb = 7200 , with MGs of size 14 <=g+0 <= 56 g+0 /w+0 = 7 , and protrusion angles of 0° to 90°, where g+0 and w+0 denote the widths and spacings of the MGs in base flow wall units. It was found that 100% of the DR with riblets, and 95% to 100% of the DR with SH MGs, arises from the effective slip on the walls and the resultant drop in the friction Reynolds number of the flow due to this effective slip. Modifications to the turbulence dynamics were always drag enhancing (DE) with riblets and generally DE with SH MGs. Increasing the riblet wall curvature significantly increased the wall slip velocity at the riblet tips. But this translated to an increase in DR only for g+0 14 , due to significant enhancement of turbulence production at larger MG widths.

  5. Frame-dragging Effect in Strong Gravity Regime

    CERN Document Server

    Chakraborty, Chandrachur

    2016-01-01

    The exact frame-dragging (or Lense-Thirring (LT) precession) rates for Kerr, Kerr-Taub-NUT (KTN) and Taub-NUT spacetimes have been derived. Remarkably, in the case of the `zero angular momentum' Taub-NUT spacetime, the frame-dragging effect is shown not to vanish, when considered for spinning test gyroscope. In the case of the interior of the pulsars, the exact frame-dragging rate monotonically decreases from the center to the surface along the pole and but it shows an `anomaly' along the equator. Moving from the equator to the pole, it is observed that this `anomaly' disappears after crossing a critical angle. The `same' anomaly can also be found in the KTN spacetime. The resemblance of the anomalous LT precessions in the KTN spacetimes and the spacetime of the pulsars could be used to identify a role of Taub-NUT solutions in the astrophysical observations or equivalently, a signature of the existence of NUT charge in the pulsars.

  6. Effects of drag factor on physiological aspects of rowing.

    Science.gov (United States)

    Kane, D A; Jensen, R L; Williams, S E; Watts, P B

    2008-05-01

    This study examined the effects of two resistances, or "drag factors" on selected physiological variables during incremental progressive rowing tests (seven 3-min stages) on a Concept2 ergometer. Subjects were seven male and seven female university club rowers. Their mean age, body mass and height were 19.6 +/- 1.5 years, 72.7 +/- 8.0 kg, and 172.2 +/- 7.5 cm, respectively. Progressive tests were conducted using drag factors 100 (D100) and 150 (D150) before the spring racing season. Values were determined for the following physiological variables: ventilation (V.E), oxygen uptake (V.O2), heart rate (HR), blood lactate concentration (BLC), respiratory exchange ratio (R) and rowing economy (W/V.O2). Comparisons across all six submaximal stages showed no significant difference between D(100) and D(150) for any of the variables measured (p > .05). Maximal V.E(max) was significantly greater at D100 than D150 (p D100 than at D150, though not significantly so. The mean D100-D150 differences in V.E and SR for each stage were significantly correlated (r = 0.76, p < .01), suggesting drag factor may affect V.E via SR.

  7. Experimental demonstration of a new concept of drag reduction and thermal protection for hypersonic vehicles

    Institute of Scientific and Technical Information of China (English)

    Zonglin Jiang; Yunfeng Liu; Guilai Han; Wei Zhao

    2009-01-01

    A new idea of drag reduction and thermal protection for hypersonic vehicles is proposed based on the combination of a physical spike and lateral jets for shock-reconstruction. The spike recasts the bow shock in front of a blunt body into a conical shock, and the lateral jets work to protect the spike tip from overheating and to push the conical shock away from the blunt body when a pitching angle exists during flight. Experiments are conducted in a hypersonic wind tunnel at a nominal Math number of 6. It is demonstrated that the shock/shock interaction on the blunt body is avoided due to injection and the peak pressure at the reattachment point is reduced by 70% under a 4°attack angle.

  8. Experimental Investigation of the Fresnel Drag Effect in RF Coaxial Cables

    Directory of Open Access Journals (Sweden)

    Brotherton D.

    2011-01-01

    Full Text Available An experiment that confirms the Fresnel drag formalism in RF coaxial cables is reported. The Fresnel "drag" in bulk dielectrics and in optical fibers has previously been well established. An explanation for this formalism is given, and it is shown that there is no actual drag phenomenon, rather that the Fresnel drag effect is merely the consequence of a simplified description of EM scattering within a dielectric in motion wrt the dynamical 3-space. The Fresnel drag effect plays a critical role in the design of various light-speed anisotropy detectors.

  9. Giant Surface-Plasmon-Induced Drag Effect in Metal Nanowires

    Science.gov (United States)

    Durach, Maxim; Rusina, Anastasia; Stockman, Mark I.

    2009-10-01

    Here, for the first time we predict a giant surface-plasmon-induced drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. In nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ˜105-106V/cm. The giant SPIDER is an ultrafast effect whose bandwidth for nanometric wires is ˜20THz. It opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.

  10. Giant surface plasmon induced drag effect (SPIDEr) in metal nanowires

    Science.gov (United States)

    Durach, Maxim; Rusina, Anastasia; Stockman, Mark I.

    2009-08-01

    Here, for the first time we predict a giant surface plasmon-induced drag effect (SPIDEr), which exists under conditions of the extreme nanoplasmonic confinement. Under realistic conditions, in nanowires, this giant SPIDEr generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ~ 105 ~ 106 V/cm. The SPIDEr is an ultrafast effect whose bandwidth for nanometric wires is ~ 20 THz. The giant SPIDEr opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.

  11. Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

    Science.gov (United States)

    Littlewood, R. P.; Passmore, M. A.

    2012-08-01

    A large contribution to the aerodynamic drag of a vehicle arises from the failure to fully recover pressure in the wake region, especially on squareback configurations. A degree of base pressure recovery can be achieved through careful shape optimisation, but the freedom of an automotive aerodynamicist to implement significant shape changes is limited by a variety of additional factors such styling, ergonomics and loading capacity. Active flow control technologies present the potential to create flow field modifications without the need for external shape changes and have received much attention in previous years within the aeronautical industry and, more recently, within the automotive industry. In this work the influence of steady blowing applied at a variety of angles on the roof trailing edge of a simplified ¼ scale squareback style vehicle has been investigated. Hot-wire anemometry, force balance measurements, surface pressure measurements and PIV have been used to investigate the effects of the steady blowing on the vehicle wake structures and the resulting body forces. The energy consumption of the steady jet is calculated and is used to deduce an aerodynamic drag power change. Results show that overall gains can be achieved; however, the large mass flow rate required restricts the applicability of the technique to road vehicles. Means by which the mass flow rate requirements of the jet may be reduced are discussed and suggestions for further work put forward.

  12. Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

    Energy Technology Data Exchange (ETDEWEB)

    Littlewood, R.P. [LaVisionUK Ltd, Grove, Oxon (United Kingdom); Passmore, M.A. [Loughborough University, Department of Aeronautical and Automotive Engineering, Loughborough (United Kingdom)

    2012-08-15

    A large contribution to the aerodynamic drag of a vehicle arises from the failure to fully recover pressure in the wake region, especially on squareback configurations. A degree of base pressure recovery can be achieved through careful shape optimisation, but the freedom of an automotive aerodynamicist to implement significant shape changes is limited by a variety of additional factors such styling, ergonomics and loading capacity. Active flow control technologies present the potential to create flow field modifications without the need for external shape changes and have received much attention in previous years within the aeronautical industry and, more recently, within the automotive industry. In this work the influence of steady blowing applied at a variety of angles on the roof trailing edge of a simplified 1/4 scale squareback style vehicle has been investigated. Hot-wire anemometry, force balance measurements, surface pressure measurements and PIV have been used to investigate the effects of the steady blowing on the vehicle wake structures and the resulting body forces. The energy consumption of the steady jet is calculated and is used to deduce an aerodynamic drag power change. Results show that overall gains can be achieved; however, the large mass flow rate required restricts the applicability of the technique to road vehicles. Means by which the mass flow rate requirements of the jet may be reduced are discussed and suggestions for further work put forward. (orig.)

  13. The Use of Biobased Surfactant Obtained by Enzymatic Syntheses for Wax Deposition Inhibition and Drag Reduction in Crude Oil Pipelines

    Directory of Open Access Journals (Sweden)

    Zhihua Wang

    2016-04-01

    Full Text Available Crude oil plays an important role in providing the energy supply of the world, and pipelines have long been recognized as the safest and most efficient means of transporting oil and its products. However, the transportation process also faces the challenges of asphaltene-paraffin structural interactions, pipeline pressure losses and energy consumption. In order to determine the role of drag-reducing surfactant additives in the transportation of crude oils, experiments of wax deposition inhibition and drag reduction of different oil in pipelines with a biobased surfactant obtained by enzymatic syntheses were carried out. The results indicated that heavy oil transportation in the pipeline is remarkably enhanced by creating stable oil-in-water (O/W emulsion with the surfactant additive. The wax appearance temperature (WAT and pour point were modified, and the formation of a space-filling network of interlocking wax crystals was prevented at low temperature by adding a small concentration of the surfactant additive. A maximum viscosity reduction of 70% and a drag reduction of 40% for light crude oil flows in pipelines were obtained with the surfactant additive at a concentration of 100 mg/L. Furthermore, a successful field application of the drag-reducing surfactant in a light crude oil pipeline in Daqing Oilfield was demonstrated. Hence, the use of biobased surfactant obtained by enzymatic syntheses in oil transportation is a potential method to address the current challenges, which could result in a significant energy savings and a considerable reduction of the operating cost.

  14. Aerodynamic drag reduction tests on a full-scale tractor-trailer combination with several add-on devices

    Energy Technology Data Exchange (ETDEWEB)

    Montoya, L.C.; Steers, L.L.

    1974-12-01

    Aerodynamic drag tests were performed on a conventional cab-over-engine tractor with a 45-foot trailer and five commercially available or potentially available add-on devices using the coast-down method. The tests ranged in velocity from approximately 30 miles per hour to 65 miles per hour and included some flow visualization. A smooth, level runway at Edwards Air Force Base was used for the tests, and deceleration measurements were taken with both accelerometers and stopwatches. An evaluation of the drag reduction results obtained with each of the five add-on devices is presented.

  15. Bluff body drag manipulation using pulsed jets and Coanda effect

    CERN Document Server

    Barros, Diogo; Noack, Bernd R; Spohn, Andreas; Ruiz, Tony

    2015-01-01

    We analyze the effects of unsteady forcing on the wake and drag of a square back blunt body. In combination with a Coanda effect, shear-layer forcing by periodic blowing of wall bounded jets allows to recover over 30 % of the base pressure. The actuation frequency is an order of magnitude higher than the natural shear-layer instabilities. High frequency Coanda blowing leads to a thinner time-averaged wake. The effect of this form shaping is analyzed by pressure taps on the rear side of the model in combination with PIV measurements. Velocity components of the mean field indicate a pressure recovery and favorable mean curvature effects across the separated shear layers in the region close to the rear end of the blunt body when actuation is applied. The wake dynamics further downstream, however, remains very similar to the unforced oscillatory wake mode.

  16. 螺旋式翼梢小翼减阻技术研究%The Study on the Spiroid Winglets Drag-reduction Technic

    Institute of Scientific and Technical Information of China (English)

    吕飞; 陈迎春; 张彬乾; 李亚林; 王元元

    2012-01-01

    In this paper,taking DLR-F4 wing as a base wing,two types of spiroid winglets have been designed to decrease the induced drag.The drag-reduction capability and flow mechanism of spiroid winglets has been simulated by CFD method which is based on N-S equations.The results show that the spiroid winglets have much potential in the aspect of reducing induced drag and enhancing lift.The spiroid winglets can raise the lift coefficient by 12% and the span efficiency factor by 37.5% comparing with the initial geometry without winglets.The spiroid winglets reduce the induced drag by preventing the concentrated wingtip vortex from bringing effectively,it is a promising wingtip drag-reduction technic,which is worthy of further study.%以减小诱导阻力为目标,以DLR-F4机翼为基本机翼,自行设计了两种外形的螺旋式翼梢小翼,采用CFD方法研究螺旋式翼梢小翼减阻的能力和流动机理。研究结果表明:螺旋式翼梢小翼具有显著的减阻增升能力,升力系数最大增量可达到12%以上,诱导阻力效率因子提高了37.5%。螺旋式翼梢小翼通过有效阻止翼梢集中涡的形成,减小诱导阻力,是一种很有发展前景的翼梢减阻技术。

  17. Flight and wind-tunnel measurements showing base drag reduction provided by a trailing disk for high Reynolds number turbulent flow for subsonic and transonic Mach numbers

    Science.gov (United States)

    Powers, Sheryll Goecke; Huffman, Jarrett K.; Fox, Charles H., Jr.

    1986-01-01

    The effectiveness of a trailing disk, or trapped vortex concept, in reducing the base drag of a large body of revolution was studied from measurements made both in flight and in a wind tunnel. Pressure data obtained for the flight experiment, and both pressure and force balance data were obtained for the wind tunnel experiment. The flight test also included data obtained from a hemispherical base. The experiment demonstrated the significant base drag reduction capability of the trailing disk to Mach 0.93 and to Reynolds numbers up to 80 times greater than for earlier studies. For the trailing disk data from the flight experiment, the maximum decrease in base drag ranged form 0.08 to 0.07 as Mach number increased from 0.70 to 0.93. Aircraft angles of attack ranged from 3.9 to 6.6 deg for the flight data. For the trailing disk data from the wind tunnel experiment, the maximum decrease in base and total drag ranged from 0.08 to 0.05 for the approximately 0 deg angle of attack data as Mach number increased from 0.30 to 0.82.

  18. Biomimetic bluff body drag reduction by self-adaptive porous flaps

    CERN Document Server

    Mazellier, Nicolas; Kourta, Azeddine

    2011-01-01

    The performances of an original passive control system based on a biomimetic approach are assessed by investigating the flow over a bluff-body. This control device consists in a couple of flaps made from the combination of a rigid plastic skeleton coated with a porous fabric mimicking the shaft and the vane of the bird's feathers, respectively. The sides of a square cylinder have been fitted with this system so as to enable the flaps to freely rotate around their leading edge. This feature allows the movable flaps to self-adapt to the flow conditions. Comparing both the uncontrolled and the controlled flow, a significant drag reduction (up to 22%) has been obtained over a broad range of Reynolds number. The investigation of the mean flow reveals a noticeable modification of the flow topology at large scale in the vicinity of the controlled cylinder accounting for the increase of the pressure base in comparison with the natural flow. Meanwhile, the study of the relative motion of both flaps points out that the...

  19. Drag Reduction of Turbulence Air Channel Flow with Distributed Micro Sensors and Actuators

    Science.gov (United States)

    Yoshino, Takashi; Suzuki, Yuji; Kasagi, Nobuhide

    A prototype system for feedback control of wall turbulence is developed, and its performance is evaluated in a physical experiment. Arrayed micro hot-film sensors with a spanwise spacing of 1 mm are employed for the measurement of streamwise shear stress fluctuations, while arrayed magnetic actuators of 2.4 mm in spanwise width are used to introduce control input through wall deformation. A digital signal processor with a time delay of 0.1 ms is employed to drive the actuators based on the sensor signals. The driving voltage of each actuator is determined with a linear combination of the wall shear stress fluctuations at three sensors located upstream of the actuator, and a noise-tolerant genetic algorithm is employed to optimize the control parameters. Feedback control experiments are conducted in a fully-developed turbulent air channel flow at the Reynolds number of Reτ=300. It is found that about 6% drag reduction has been achieved in a physical experiment for the first time. Through turbulent statistics measurements with LDV, it is also found that the Reynolds shear stress close to the wall is decreased by the present control scheme. A conditional average of a DNS database is also made to extract coherent structures associated with the present control input. It is shown that the wall-deformation actuators induce a wall-normal velocity away from the wall when the high-speed region is located above the actuator.

  20. Role of on-board discharge in shock wave drag reduction and plasma cloaking

    Institute of Scientific and Technical Information of China (English)

    Qiu Xiao-Ming; Tang De-Li; Sun Ai-Ping; Liu Wan-Dong; Zeng Xue-Jun

    2007-01-01

    In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance between the magnetic pressure and gas pressure of plane shock of a partially ionized gas consisting of the environmental gas around the nose of the vehicle and the on-board discharge-produced plasma. The relation between the shock strength and the discharge-induced magnetic pressure is studied by means of a set of one-fluid, hydromagnetic equations reformed for the present purpose, where the discharge-induced magnetic field consists of the electron current (produced by the discharge)-induced magnetic field and the partially ionized gas flow-induced one. A formula for the relation between the above parameters is derived. It shows that the discharge-induced magnetic pressure can minimize the shock strength,successfully explaining the two recent experimental observations on attached bow shock mitigation and elimination in a supersonic flow during on-board discharge [Phys. Plasmas 9 (2002) 721 and Phys. Plasmas 7 (2000) 1345]. In addition,the formula implies that the shock elimination leaves room for a layer of higher-density plasma rampart moving around the nose of the vehicle, being favourable to the plasma radar cloaking of the vehicle. The reason for it is expounded.

  1. Drag reduction of a car model by linear genetic programming control

    CERN Document Server

    Li, Ruiying; Cordier, Laurent; Borée, Jacques; Harambat, Fabien; Kaiser, Eurika; Duriez, Thomas

    2016-01-01

    We investigate open- and closed-loop active control for aerodynamic drag reduction of a car model. Turbulent flow around a blunt-edged Ahmed body is examined at $Re_{H}\\approx3\\times10^{5}$ based on body height. The actuation is performed with pulsed jets at all trailing edges combined with a Coanda deflection surface. The flow is monitored with pressure sensors distributed at the rear side. We apply a model-free control strategy building on Dracopoulos & Kent (Neural Comput. & Applic., vol. 6, 1997, pp. 214-228) and Gautier et al. (J. Fluid Mech., vol. 770, 2015, pp. 442-457). The optimized control laws comprise periodic forcing, multi-frequency forcing and sensor-based feedback including also time-history information feedback and combination thereof. Key enabler is linear genetic programming as simple and efficient framework for multiple inputs (actuators) and multiple outputs (sensors). The proposed linear genetic programming control can select the best open- or closed-loop control in an unsupervis...

  2. Effect of Gravitational Frame Dragging on Orbiting Qubits

    CERN Document Server

    Lanzagorta, Marco

    2012-01-01

    In this paper we discuss the effect of gravitational frame dragging on orbiting qubits. In particular, we consider the Kerr spacetime geometry and spin-1/2 qubits moving in an equatorial radial fall with zero angular momentum and equatorial circular orbits. We ignore the ${\\cal O}(\\hbar)$ order effects due to spin-curvature coupling, which allows us to consider the motion of the spin-1/2 particles as Kerr geometry geodesics. We derive analytical expressions for the infinitesimal Wigner rotation and numerical results for their integration across the length of the particle's trajectory. To this end, we consider the bounds on the finite Wigner rotation imposed by Penrose's cosmic censorship hypothesis.

  3. EFFECTIVE DIFFUSION AND EFFECTIVE DRAG COEFFICIENT OF A BROWNIAN PARTICLE IN A PERIODIC POTENTIAL

    Institute of Scientific and Technical Information of China (English)

    Hongyun Wang

    2011-01-01

    We study the stochastic motion of a Brownian particle driven by a constant force over a static periodic potential.We show that both the effective diffusion and the effective drag coefficient are mathematically well-defined and we derive analytic expressions for these two quantities.We then investigate the asymptotic behaviors of the effective diffusion and the effective drag coefficient,respectively,for small driving force and for large driving force.In the case of small driving force,the effective diffusion is reduced from its Brownian value by a factor that increases exponentially with the amplitude of the potential.The effective drag coefficient is increased by approximately the same factor.As a result,the Einstein relation between the diffusion coefficient and the drag coefficient is approximately valid when the driving force is small.For moderately large driving force,both the effective diffusion and the effective drag coefficient are increased from their Brownian values,and the Einstein relation breaks down. In the limit of very large driving force,both the effective diffusion and the effective drag coefficient converge to their Brownian values and the Einstein relation is once again valid.

  4. Experimental Investigation of the Fresnel Drag Effect in RF Coaxial Cables

    Directory of Open Access Journals (Sweden)

    Cahill R. T.

    2011-01-01

    Full Text Available An experiment that confirms the Fresnel drag formalism in RF coaxial cables is re- ported. The Fresnel ‘drag’ in bulk dielectrics and in optical fibers has previously been well established. An explanation for this formalism is given, and it is shown that there is no actual drag phenomenon, rather that the Fresnel drag effect is merely the conse- quence of a simplified description of EM scattering within a dielectric in motion wrt the dynamical 3-space. The Fresnel drag effect plays a critical role in the design of various light-speed anisotropy detectors.

  5. Collisional Effects on Nonlinear Ion Drag Force for Small Grains

    CERN Document Server

    Hutchinson, I H

    2013-01-01

    The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

  6. Principles of operation and data reduction techniques for the loft drag disc turbine transducer

    Energy Technology Data Exchange (ETDEWEB)

    Silverman, S.

    1977-09-01

    An analysis of the single- and two-phase flow data applicable to the loss-of-fluid test (LOFT) is presented for the LOFT drag turbine transducer. Analytical models which were employed to correlate the experimental data are presented.

  7. Effect of Swim Cap Surface Roughness on Passive Drag.

    Science.gov (United States)

    Gatta, Giorgio; Cortesi, Matteo; Zamparo, Paola

    2015-11-01

    In the last decade, great attention has been given to the improvements in swimming performance that can be obtained by wearing "technical swimsuits"; the technological evolution of these materials only marginally involved swim caps production, even if several studies have pointed out the important role of the head (as main impact point with the fluid) on hydrodynamics. The aim of this study was to compare the effects on passive drag (Dp) of 3 swim cap models: a smooth silicon helmet cap (usually used during swimming competitions), a silicon helmet cap with "dimples," and a silicon helmet cap with "wrinkles." Experiments were performed on 10 swimmers who were towed underwater (at a depth of 60 cm) at 3 speeds (1.5, 1.7, and 1.9 m·s) and in 2 body positions: LA (arms above the swimmer's head) and SA (arms alongside the body). The Dp values obtained in each trial were divided by the square of the corresponding speed to obtain the speed-specific drag (the k coefficient = Dp/v). No differences in k were observed among swim caps in the LA position. No differences in k were observed between the smooth and dimpled helmets also in the SA position; however, the wrinkled swim cap helmet showed a significant larger k (4.4%) in comparison with the model with dimples, when the swimmers kept their arms alongside the body (in the SA position). These data suggest that wearing a wrinkled swim cap helmet can be detrimental to performance at least in this specific position.

  8. A survey of drag and heat reduction in supersonic flows by a counterflowing jet and its combinations

    Institute of Scientific and Technical Information of China (English)

    Wei HUANG

    2015-01-01

    题目:逆向喷流及其组合体在超声速气流中减阻防热功效研究进展  概总结归纳国内外逆向喷流及其组合体在超声速气流中减阻防热功效的研究进展,并给出逆向喷流在某些应用领域的建议,特别是喷流的不稳定性保护、减阻与热防护之间的权衡以及流动模态转换的工作参数和结构参数临界点选取等。%Drag reduction and thermal protection is very important for hypersonic vehicles, and a counterflowing jet and its combinations is one of the most promising drag and heat release reduction strategies. In the current survey, research progress on the drag and heat release reduction induced by a counterflowing jet and its combinations is summarized. Three combinatorial configurations are considered, namely the combination of the counterflowing jet and a forward-facing cavity, the combination of the counterflowing jet and an aerospike, and the combination of the counterflowing jet and energy deposition. In conclusion, some recommendations are provided, especially for jet instability protection, for the tradeoff between drag and heat release re-ductions, and for the critical points for the operational and geometric parameters in the flow mode transition.

  9. Optimally amplified large-scale streaks and drag reduction in turbulent pipe flow.

    Science.gov (United States)

    Willis, Ashley P; Hwang, Yongyun; Cossu, Carlo

    2010-09-01

    The optimal amplifications of small coherent perturbations within turbulent pipe flow are computed for Reynolds numbers up to one million. Three standard frameworks are considered: the optimal growth of an initial condition, the response to harmonic forcing and the Karhunen-Loève (proper orthogonal decomposition) analysis of the response to stochastic forcing. Similar to analyses of the turbulent plane channel flow and boundary layer, it is found that streaks elongated in the streamwise direction can be greatly amplified from quasistreamwise vortices, despite linear stability of the mean flow profile. The most responsive perturbations are streamwise uniform and, for sufficiently large Reynolds number, the most responsive azimuthal mode is of wave number m=1 . The response of this mode increases with the Reynolds number. A secondary peak, where m corresponds to azimuthal wavelengths λ_{θ}^{+}≈70-90 in wall units, also exists in the amplification of initial conditions and in premultiplied response curves for the forced problems. Direct numerical simulations at Re=5300 confirm that the forcing of m=1,2 and m=4 optimal structures results in the large response of coherent large-scale streaks. For moderate amplitudes of the forcing, low-speed streaks become narrower and more energetic, whereas high-speed streaks become more spread. It is further shown that drag reduction can be achieved by forcing steady large-scale structures, as anticipated from earlier investigations. Here the energy balance is calculated. At Re=5300 it is shown that, due to the small power required by the forcing of optimal structures, a net power saving of the order of 10% can be achieved following this approach, which could be relevant for practical applications.

  10. Shape Optimization for Drag Reduction in Linked Bodies using Evolution Strategies and the Hybrid Wavelet Collocation - Brinkman Penalization Method

    Science.gov (United States)

    Vasilyev, Oleg V.; Gazzola, Mattia; Koumoutsakos, Petros

    2010-11-01

    In this talk we discuss preliminary results for the use of hybrid wavelet collocation - Brinkman penalization approach for shape optimization for drag reduction in flows past linked bodies. This optimization relies on Adaptive Wavelet Collocation Method along with the Brinkman penalization technique and the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). Adaptive wavelet collocation method tackles the problem of efficiently resolving a fluid flow on a dynamically adaptive computational grid, while a level set approach is used to describe the body shape and the Brinkman volume penalization allows for an easy variation of flow geometry without requiring body-fitted meshes. We perform 2D simulations of linked bodies in order to investigate whether flat geometries are optimal for drag reduction. In order to accelerate the costly cost function evaluations we exploit the inherent parallelism of ES and we extend the CMA-ES implementation to a multi-host framework. This framework allows for an easy distribution of the cost function evaluations across several parallel architectures and it is not limited to only one computing facility. The resulting optimal shapes are geometrically consistent with the shapes that have been obtained in the pioneering wind tunnel experiments for drag reduction using Evolution Strategies by Ingo Rechenberg.

  11. Evaluation of Drag Reduction via Superhydrophobic Surfaces and Active Gas Replenishment in a Fully-developed Turbulent Flow

    Science.gov (United States)

    Gose, James W.; Golovin, Kevin; Ceccio, Steven L.; Perlin, Marc; Tuteja, Anish

    2014-11-01

    The development of superhydrophobic surfaces (SHS) for skin-friction drag reduction in the laminar regime has shown great promise. A team led by the University of Michigan is examining the potential of similar SHS in high-speed naval applications. Specifically, we have developed a recirculating facility to investigate the reduction of drag along robustly engineered SHS in a fully-developed turbulent boundary layer flow. The facility can accommodate both small and large SHS samples in a test section 7 mm (depth) × 100 mm (span) × 1200 mm (length). Coupled with an 11.2 kilowatt pump and a 30:1 contraction, the facility is capable of producing an average flow velocity of 20 m/s, yielding a height based (7 mm) Reynolds number of 140,000. The SHS tested were designed for large-scale application. The present investigation shows skin-friction drag reduction for various sprayable and chemically developed SHS that were applied over a 100 mm (span) × 1100 mm (length) area. The drag measurement methods include pressure drop across the test specimen and PIV measured boundary layers. Additional SHS investigations include the implementation of active gas replenishment, providing an opportunity to replace gas-pockets that would otherwise be disrupted in traditional passive SHS due to high shear stress and turbulent pressure fluctuations. Gas is evenly distributed through a 90 mm (span) × 600 mm (length) sintered porous media with pore sizes of 10 to 100 microns. The impact of the active gas replenishment is being evaluated with and without SHS.

  12. Effects of surface drag on low-level frontogenesis within baroclinic waves

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yi; TAN ZheMin

    2007-01-01

    Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope especially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection dominates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are reduced.

  13. Effects of surface drag on low-level frontogenesis within baroclinic waves

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope espe- cially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection domi- nates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are re- duced.

  14. The drag reduction research of the additives in the heating network%添加剂在供热管网中的减阻研究

    Institute of Scientific and Technical Information of China (English)

    韦节廷; 倪兵

    2011-01-01

    This paper mainly studies the drag reduction characteristics of the heating system at various temperatures,and compares the characteristics of water with additives cetyltrimethyl ammonium chloride(CTAC) and polyacrylamide(PAM).Ac-cording to experimental data,we can see that in 30 ℃ heating network system,the effect of adding polyacrylamide is the best.The drag reduction of additive is gradually reduced with the increasing of temprature.In 60 ℃,the polyacrylamide loses the drag reduction,and pressure loss of heating network system increased.The highest friction reduction efficiency with 20ppmCTAC can reach 25.7%,and the highest friction reduction efficiency with polyacrylamide could reach 40.68%.%主要进行了供热系统在不同温度时的清水、添入十六烷基三甲基氯化铵(CTAC)和聚丙烯酰胺(PAM)时减阻特性的比较研究,通过实验数据可以得出,30℃时在供热管网系统中添入聚丙烯酰胺减阻效果最佳,随着温度升高减租剂减阻性能逐渐降低,聚丙烯酰胺到60℃时丧失减阻性能并使热网压损增大。CTAC最大减阻效果达到25.7%,聚丙烯酰胺最高达到40.68%。

  15. Optimization of Mass Bleed Control for Base Drag Reduction of Supersonic Flight Bodies

    Institute of Scientific and Technical Information of China (English)

    Y.-K.Lee; H.-D.Kim

    2006-01-01

    The minimization of base drag using mass bleed control is examined in consideration of various base to orifice exit area ratios for a body of revolution in the Mach 2.47 freestream. Axisymmtric, compressible, mass-averaged Navier-Stokes equations are solved using the standard k-ω turbulence model, a fully implicit finite volume scheme, and a second order upwind scheme. Base flow characteristics are explained regarding the base configuration as well as the injection parameter which is defined as the mass flow rate of bleed jet non-dimensionalized by the product of the base area and freestream mass flux. The results obtained through the present study show that for a smaller base area, the optimum mass bleed condition leading to minimum base drag occurs at relatively larger mass bleed, and a larger orifice exit can offer better drag control.

  16. Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium

    CERN Document Server

    Kuan, Pei-Chen; Chan, Wei Sheng; Kosen, Sandoko; Lan, Shau-Yu

    2016-01-01

    As one of the most influential experiments on the development of modern macroscopic theory from Newtonian mechanics to Einstein's special theory of relativity, the phenomenon of light dragging in a moving medium has been discussed and observed extensively in different types of systems. To have a significant dragging effect, the long duration of light travelling in the medium is preferred. Here we demonstrate a light-dragging experiment in an electromagnetically induced transparent cold atomic ensemble and enhance the dragging effect by at least three orders of magnitude compared with the previous experiments. With a large enhancement of the dragging effect, we realize an atom-based velocimeter that has a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. Such a demonstration could pave the way for motional sensing using the collective state of atoms in a room temperature vapour cell or solid state material.

  17. Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium

    Science.gov (United States)

    Kuan, Pei-Chen; Huang, Chang; Chan, Wei Sheng; Kosen, Sandoko; Lan, Shau-Yu

    2016-10-01

    As one of the most influential experiments on the development of modern macroscopic theory from Newtonian mechanics to Einstein's special theory of relativity, the phenomenon of light dragging in a moving medium has been discussed and observed extensively in different types of systems. To have a significant dragging effect, the long duration of light travelling in the medium is preferred. Here we demonstrate a light-dragging experiment in an electromagnetically induced transparent cold atomic ensemble and enhance the dragging effect by at least three orders of magnitude compared with the previous experiments. With a large enhancement of the dragging effect, we realize an atom-based velocimeter that has a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. Such a demonstration could pave the way for motional sensing using the collective state of atoms in a room temperature vapour cell or solid state material.

  18. Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium.

    Science.gov (United States)

    Kuan, Pei-Chen; Huang, Chang; Chan, Wei Sheng; Kosen, Sandoko; Lan, Shau-Yu

    2016-10-03

    As one of the most influential experiments on the development of modern macroscopic theory from Newtonian mechanics to Einstein's special theory of relativity, the phenomenon of light dragging in a moving medium has been discussed and observed extensively in different types of systems. To have a significant dragging effect, the long duration of light travelling in the medium is preferred. Here we demonstrate a light-dragging experiment in an electromagnetically induced transparent cold atomic ensemble and enhance the dragging effect by at least three orders of magnitude compared with the previous experiments. With a large enhancement of the dragging effect, we realize an atom-based velocimeter that has a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. Such a demonstration could pave the way for motional sensing using the collective state of atoms in a room temperature vapour cell or solid state material.

  19. Aeroelastic tailoring using lamination parameters: drag reduction of a Formula One rear wing

    NARCIS (Netherlands)

    Thuwis, G.A.A.; De Breuker, R.; Abdalla, M.M.; Gürdal, Z.

    2009-01-01

    The aim of the present work is to passively reduce the induced drag of the rear wing of a Formula One car at high velocity through aeroelastic tailoring. The angle-of-attack of the rear wing is fixed and is determined by the required downforce needed to get around a turn. As a result, at higher velo

  20. Phenomena of drag reduction on saltating sediment in shallow, supercritical flows

    Science.gov (United States)

    ABSTRACT: When a group of objects move through a fluid, it often exhibits coordinated behavior in which bodies in the wake of a leader generally experience reduced drag. Locomotion provides well known examples including the maneuvering and clustering of racing automobiles and bicyclists and queuing...

  1. Hydrodynamic sensing does not facilitate active drag reduction in the golden shiner (Notemigonus crysoleucas)

    NARCIS (Netherlands)

    McHenry, M. J.; Michel, K. B.; Stewart, W.; Mueller, U. K.

    2010-01-01

    The lateral line system detects water flow, which allows fish to orient their swimming with respect to hydrodynamic cues. However, it is unclear whether this sense plays a role in the control of propulsion. Hydrodynamic theory suggests that fish could reduce drag by coordinating the motion of the

  2. Fabrication Development and Flow Testing of Underwater Superhydrophobic Films for Drag Reduction

    Science.gov (United States)

    2017-03-21

    SHPo samples each in meters is unreasonable • We hope to sense the drag of a surface sample ~5 cm in size (made from 4” wafer ) placed on a desired...of passive SHPo surfaces observed up to Re > 1.59 x 107 • At high speeds, the floating plate was found vibrating excessively and bumping into the

  3. Phonon-drag effect in FeGa3

    Science.gov (United States)

    Wagner-Reetz, Maik; Kasinathan, Deepa; Schnelle, Walter; Cardoso-Gil, Raul; Rosner, Helge; Grin, Yuri; Gille, Peter

    2014-11-01

    The thermoelectric properties of single-crystalline and polycrystalline FeGa3 are systematically investigated over a wide temperature range. At low temperatures, below 20 K, previously not known pronounced peaks in the thermal conductivity (400 -800 WK-1 m-1) with corresponding maxima in the thermopower (in the order of -16000 μ V K-1) were found in single-crystalline samples. Measurements in single crystals along [100] and [001] directions indicate only a slight anisotropy in both the electrical and thermal transports. From susceptibility and heat-capacity measurements, a magnetic or structural phase transition was excluded. Using density functional theory based calculations, we have revisited the electronic structure of FeGa3 and compared the magnetic (including correlations) and nonmagnetic electronic densities of states. Thermopower at fixed carrier concentrations is calculated using semiclassical Boltzmann transport theory, and the calculated results match fairly with our experimental data. The inclusion of strong electron correlations treated in a mean field manner (by LSDA + U ) does not improve this comparison, rendering strong correlations as the sole explanation for the low-temperature enhancement unlikely. Eventually, after a careful review, we assign the peaks in the thermopower as a manifestation of the phonon-drag effect, which is supported by thermopower measurements in a magnetic field.

  4. Drag reduction by polymer addition in single and two-phase gas-liquid flows in pipelines

    Energy Technology Data Exchange (ETDEWEB)

    Bizotto, Vanessa Cristina; Paes, Diogo Melo; Franca, Fernando de Almeida [Universidade Estadual de Campinas, SP (Brazil). Centro de Estudos de Petroleo. LabPetro]. E-mails: vanessa@cepetro.unicamp.br; diogopaes10@hotmail.com; Sabadini, Edvaldo [Universidade Estadual de Campinas, SP (Brazil). Inst. de Quimica]. E-mails: sabadini@iqm.unicamp.br; ffranca@fem.unicamp.br

    2008-07-01

    Turbulence mechanisms, as the eddies formation frequency and size, promote energy dissipation that appears as pressure drop in pipe flows. Adding minute amounts of polymers - ppm - of high molecular weight to the solution can lead to the reduction of the viscous dissipation. The formed macromolecules interact with the eddies, cause the eddies coherence breakdown, damp the energy transport and reduces the pressure drop. This phenomenon is known as the hydrodynamic drag reduction (DR, for short). Thus, for a given pipe flow rate there is decrease in pressure head, which is a desired operating strategy when transporting liquids. Studies on the hydrodynamic drag reduction in polymeric systems have been carried out in collaboration by the Chemistry Institute and the Petroleum Laboratory - LabPetro, UNICAMP. These studies have allowed microscopic approaches to the engineering scales, tackling the most usual processes - single phase flows, as well as gas-liquid two-phase flows in pipelines, which are quite common in the chemical and the petroleum industries. Tests conducted in the Chemistry Institute comprised over-the-bench experimentations made with a rotational double-gap type rheometer. These quick performed tests used small amount of polymers, and provided information on the additive concentration, the drag reduction and the solution mechanical stability along a turbulent shearing process. The results indicated that 17% is the limiting drag reduction achieved when a 2 ppm aqueous solution of polyacrylamide - PAM - was tested. These tests, besides giving preliminary estimations, are limited in terms of engineering application due to the low shearing rates applied by the viscometer. The tests performed at LabPetro comprised pressure drop measurements in actual pipe flows, both water single and air-water two-phase flows, using the previous knowledge acquired with the viscometer tests. In the former case, the Prandtl-von Karman map has been drawn to show the %DR in terms

  5. Study and Application of Internal Coating Technique to Drag Reduction of the Trunk Pipeline for the West-East Gas Pipeline

    Institute of Scientific and Technical Information of China (English)

    HuShixin; QuShenyang; LinZhu

    2004-01-01

    Coverage layer coated in the internal wall of pipeline enables the friction drag to be reduced, the throughput and the gas transmission efficiency to be increased, the frequency of pigging and the number of the intermediate compressor station to be reduced, and the power consumption of the compressor to be decreased etc. The drag reduction is a high advanced scientific technique with outstanding economical benefit. The study and application of internal coating technique for drag reduction of 4000km trunk pipeline in West-East gas transmission pipeline (WEGTP) project are described, in which the main points are the drag reduction principle, coating process and the indoor study of this technique with own-decided knowledge property right at home.

  6. Effective Medium Theory for Drag Reducing Micro-patterned Surfaces in Turbulent Flows

    CERN Document Server

    Battiato, Ilenia

    2013-01-01

    Inspired by the lotus effect, many studies in the last decade have focused on micro- and nano-patterned surfaces. They revealed that patterns at the micro-scale combined with high contact angles can significantly reduce skin drag. However, the mechanisms and parameters that control drag reduction, e.g. Reynolds number and pattern geometry, are still unclear. We propose an effective medium representation of the micro-features, that treats the latter as a porous medium, and provides a framework to model flow over patterned surfaces in both Cassie and Wenzel states. Our key result is a closed-form expression for the skin friction coefficient in terms of frictional Reynolds (or K\\'arm\\'an) number in turbulent regime, the viscosity ratio between the fluid in and above the features, and their geometrical properties. We apply the proposed model to turbulent flows over superhydrophobic ridged surfaces. The model predictions agree with laboratory experiments for Reynolds numbers ranging from 3000 to 10000.

  7. Effect of The Swimmer’s Head Position on Passive Drag

    Directory of Open Access Journals (Sweden)

    Cortesi Matteo

    2015-12-01

    Full Text Available The aim of this study was to investigate the effect of the head position on passive drag with a towing-line experiment in a swimming pool. The tests were performed on ten male swimmers with regional level swimming skills and at least 10 years of competitive swimming experience. They were towed underwater (at a depth of 60 cm at three speeds (1.5, 1.7 and 1.9 m/s and in two body positions (arms above the swimmer’s head and arms alongside the body. These two body positions were repeated while the swimmer’s head was positioned in three different ways: head-up, head-middle and head-down in relation to the body’s horizontal alignment. The results showed a reduction of 4-5.2% in the average passive drag at all speeds when the head was down or aligned to the swimmer’s arms alongside the body, in comparison to the head-up position. A major significant decrease of 10.4-10.9% (p < 0.05 was shown when the head was down or aligned at the swimmer’s arms above the swimmer’s head. The passive drag tended to decrease significantly by a mean of 17.6% (p < 0.001 for all speeds examined with the arms alongside the body position rather than with the arms above the head position. The swimmer’s head location may play an important role in reducing hydrodynamic resistance during passive underwater gliding.

  8. Effect of The Swimmer’s Head Position on Passive Drag

    Science.gov (United States)

    Cortesi, Matteo; Gatta, Giorgio

    2015-01-01

    The aim of this study was to investigate the effect of the head position on passive drag with a towing-line experiment in a swimming pool. The tests were performed on ten male swimmers with regional level swimming skills and at least 10 years of competitive swimming experience. They were towed underwater (at a depth of 60 cm) at three speeds (1.5, 1.7 and 1.9 m/s) and in two body positions (arms above the swimmer’s head and arms alongside the body). These two body positions were repeated while the swimmer’s head was positioned in three different ways: head-up, head-middle and head-down in relation to the body’s horizontal alignment. The results showed a reduction of 4–5.2% in the average passive drag at all speeds when the head was down or aligned to the swimmer’s arms alongside the body, in comparison to the head-up position. A major significant decrease of 10.4–10.9% (p < 0.05) was shown when the head was down or aligned at the swimmer’s arms above the swimmer’s head. The passive drag tended to decrease significantly by a mean of 17.6% (p < 0.001) for all speeds examined with the arms alongside the body position rather than with the arms above the head position. The swimmer’s head location may play an important role in reducing hydrodynamic resistance during passive underwater gliding. PMID:26839604

  9. The photon drag effect: A fast FIR detector

    Energy Technology Data Exchange (ETDEWEB)

    Sigg, H.C. [Paul Scherrer Institut, Zuerich (Switzerland); Son, P.C. van; Wenckebach, W.Th. [Delft Univ. of Technology (Netherlands)

    1995-12-31

    The photon drag (PD) effect in solids is the electrical current generated along the path of the absorbed photons. It is a very direct transducer which is also very fast because the momentum relaxation times of the electrons are involved. We studied the PD effect in the 2D electron gas (2DEG) of a GaAs/AlGaAs multi-quantum well system using the free-electron laser source FELIX. The temporal response on a ps timescale has been observed, and the continuous spectral response through the intersubband resonance (ISR) is investigated. For high excitation intensities we observe saturation of both the PD effect and the ISR absorption. The experiments are performed on an MBE grown GaAs/AlGaAs sample with 30 8-nm-wide quantum wells, each containing 0.8 10{sup 12} electrons/cm{sup 2}. The light is coupled to the 2DEG through a single-pass internal reflection in a Ge prism pressed onto the sample surface, and the electrical signal is capacitively coupled out to a microstrip line. The measured temporal response to the 2-ps-long infrared micropulses is limited by the 34 GHz bandwidth of the sampling oscilloscope. The spectral response (ISR at 120 meV) and the saturation of the PD effect and of the optical absorption are measured real-time on the timescale of the FELIX macropulse (typically 2 {mu}). Two contributions to the PD signal an be distinguished in the spectral response: One is proportional to the absorption and the other is proportional to its derivative with respect to frequency. The relative strength of the contributions is related to the momentum relaxation times of the electrons in the lowest and first excited subbands. At high excitation intensities, the relative strength of the two contributions stays surprisingly constant, despite the strongly increased ISR linewidth and the saturation of the signal. This indicates that the limiting relaxation time relevant for the saturation of the PD effect is longer than the sub-picosecond momentum relaxation times.

  10. Kevlar/PMR-15 polyimide matrix composite for a complex shaped DC-9 drag reduction fairing

    Science.gov (United States)

    Kawai, R. T.; Mccarthy, R. F.; Willer, M. S.; Hrach, F. J.

    1982-01-01

    The Aircraft Energy Efficiency (ACEE) Program was established by NASA to improve the fuel efficiency of commercial transport aircraft and thereby to reduce the amount of fuel consumed by the air transportation industry. One of the final items developed by the program is an improved fairing which is the aft closure for the thrust reverser actuators on the JT8D nacelles on DC-9 aircraft. The reduced-drag fairing uses, in the interest of weight savings, an advanced composite construction. The composite material contains Kevlar 49 fibers in a PMR-15 matrix. Attention is given to the aerodynamic configuration, the material system, and aspects of fabrication development.

  11. Drag reduction by air release promotes fast ascent in jumping emperor penguins—a novel hypothesis

    DEFF Research Database (Denmark)

    Davenport, J.; Hughes, R.N.; Shorten, M

    2011-01-01

    (mean ± SD: 5.3 ± 1.01 m s–1), prior to jumps. Here we show evidence that penguins dive to 15 to 20 m with air in their plumage and that this compressed air is released as the birds subsequently ascend whilst maintaining depressed feathers. Fine bubbles emerge continuously from the entire plumage...... presented, we hypothesize that a significant proportion of the enhanced ascent speed is due to air lubrication reducing frictional and form drag, that ­buoyancy forces alone cannot explain the observed speeds, and that cavitation plays no part in ­bubble formation....

  12. Measuring the Effects of Lift and Drag on Projectile Motion

    Science.gov (United States)

    Cross, Rod

    2012-01-01

    The trajectory of a projectile through the air is affected both by gravity and by aerodynamic forces. The latter forces can conveniently be ignored in many situations, even when they are comparatively large. For example, if a 145-g, 74-mm diameter baseball is pitched at 40 ms[superscript -1] (89.5 mph), it experiences a drag force of about 1.5 N.…

  13. Phonon and magnon heat transport and drag effects

    Science.gov (United States)

    Heremans, Joseph P.

    2014-03-01

    Thermoelectric generators and coolers constitute today's solid-state energy converters. The two goals in thermoelectrics research are to enhance the thermopower while simultaneously maintaining a high electrical conductivity of the same material, and to minimize its lattice thermal conductivity without affecting its electronic properties. Up to now the lattice thermal conductivity has been minimized by using alloy scattering and, more recently, nanostructuring. In the first part of the talk, a new approach to minimize the lattice thermal conductivity is described that affects phonon scattering much more than electron scattering. This can be done by selecting potential thermoelectric materials that have a very high anharmonicity, because this property governs phonon-phonon interaction probability. Several possible types of chemical bonds will be described that exhibit such high anharmonicity, and particular emphasis will be put on solids with highly-polarizable lone-pair electrons, such as the rock salt I-V-VI2 compounds (e.g. NaSbSe2). The second part of the talk will give an introduction to a completely new class of solid-state thermal energy converters based on spin transport. One configuration for such energy converters is based on the recently discovered spin-Seebeck effect (SSE). This quantity is expressed in the same units as the conventional thermopower, and we have recently shown that it can be of the same order of magnitude. The main advantage of SSE converters is that the problem of optimization is now distributed over two different materials, a ferromagnet in which a flux of magnetization is generated by a thermal gradient, and a normal metal where the flux of magnetization is converted into electrical power. The talk will focus on the basic physics behind the spin-Seebeck effect. Recent developments will then be described based on phonon-drag of spin polarized electrons. This mechanism has made it possible to reach magnitudes of SSE that are comparable

  14. Fluid flow field synergy principle and its application to drag reduction

    Institute of Scientific and Technical Information of China (English)

    CHEN Qun; REN JianXun; GUO ZengYuan

    2008-01-01

    The concept of field synergy for fluid flow is introduced, which refers to the synergy of the velocity field and the velocity gradient field in an entire flow domain. Analyses show that the flow drag depends not only on the velocity and the velocity gradient fields but also on their synergy. The principle of minimum dissipation of mechanical energy is developed, which may be stated as follows: the worse the synergy between the velocity and velocity gradient fields is, the smaller the resistance becomes. Furthermore, based on the principle of minimum dissipation of mechanical energy together with conservation equations, a field synergy equation with a set of specified constraints has been established for optimizing flow processes. The optimal flow field can be obtained by solving the field synergy equation, which leads to the minimum resistance to fluid flow in the fixed flow domain. Finally, as an example, the field synergy analysis for duct flow with two parallel branches is presented. The optimized velocity distributor nearby the fork, which was designed based on the principle of minimum dissipation of mechanical energy, may reduce the drag of duct flow with two parallel branches.

  15. DOE Project on Heavy Vehicle Aerodynamic Drag

    Energy Technology Data Exchange (ETDEWEB)

    McCallen, R; Salari, K; Ortega, J; Castellucci, P; Pointer, D; Browand, F; Ross, J; Storms, B

    2007-01-04

    Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At highway speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; (2) Develop innovative drag reducing concepts that are operationally and economically sound; and (3) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices. The studies described herein provide a demonstration of the applicability of the experience developed in the analysis of the standard configuration of the Generic Conventional Model. The modeling practices and procedures developed in prior efforts have been applied directly to the assessment of new configurations including a variety of geometric modifications and add-on devices. Application to the low-drag 'GTS' configuration of the GCM has confirmed that the error in predicted drag coefficients increases as the relative contribution of the base drag resulting from the vehicle wake to the total drag increases and it is recommended that more advanced turbulence modeling strategies be applied under those circumstances. Application to a commercially-developed boat tail device has confirmed that this restriction does not apply to geometries where the relative contribution of the base drag to the total drag is reduced by modifying the geometry in that region. Application to a modified GCM geometry with an open grille and radiator has confirmed that the underbody flow, while important for underhood cooling, has little impact on the drag

  16. Effect of plasma actuator and splitter plate on drag coefficient of a circular cylinder

    Directory of Open Access Journals (Sweden)

    Akbıyık Hürrem

    2016-01-01

    Full Text Available In this paper, an experimental study on flow control around a circular cylinder with splitter plate and plasma actuator is investigated. The study is performed in wind tunnel for Reynolds numbers at 4000 and 8000. The wake region of circular cylinder with a splitter plate is analyzed at different angles between 0 and 180 degrees. In this the study, not only plasma actuators are activated but also splitter plate is placed behind the cylinder. A couple electrodes are mounted on circular cylinder at ±90 degrees. Also, flow visualization is achieved by using smoke wire method. Drag coefficient of the circular cylinder with splitter plate and the plasma actuator are obtained for different angles and compared with the plain circular cylinder. While attack angle is 0 degree, drag coefficient is decreased about 20% by using the splitter plate behind the circular cylinder. However, when the plasma actuators are activated, the improvement of the drag reduction is measured to be 50%.

  17. COMPUTATIONAL FLUID DYNAMICS (CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

    Institute of Scientific and Technical Information of China (English)

    LI Gang; ZHOU Ming; WU Bo; YE Xia; CAI Lan

    2008-01-01

    Computational fluid dynamics(CFD) simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 μm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.

  18. Experimental investigation of drag reduction by forward facing high speed gas jet for a large angle blunt cone at Mach 8

    Indian Academy of Sciences (India)

    Balla Venukumar; K P J Reddy

    2007-02-01

    Substantial aerodynamic drag, while flying at hypersonic Mach number, due to the presence of strong standing shock wave ahead of a large-angle bluntcone configuration, is a matter of great design concern. Preliminary experimental results for the drag reduction by a forward-facing supersonic air jet for a 60° apex-angle blunt cone at a flow Mach number of 8 are presented in this paper. The measurements are carried out using an accelerometer-based balance system in the hypersonic shock tunnel HST2 of the Indian Institute of Science, Bangalore. About 29% reduction in the drag coefficient has been observed with the injection of a supersonic gas jet.

  19. Effects of surface drag on upper-level frontogenesis within a developing baroclinic wave

    Science.gov (United States)

    Zhang, Yi; Tan, Zhemin; Chu, Kekuan

    2016-08-01

    This paper investigates the effects of surface drag on upper-level front with a three-dimensional nonhydrostatic mesoscale numerical model (MM5). To this end, a new and simple potential vorticity intrusion (PVI) index is proposed to quantitatively describe the extent and path that surface drag affects upper-level front. From a PV perspective, the formation of the upper-level front is illustrated as the tropopause folding happens from the stratosphere. The PVI index shows a good correlation with the minimum surface pressure, and tends to increase with the deepening of the surface cyclone and upper-level front. The surface drag acts to damp and delay the development of upper-level front, which could reduce the growth rate of the PVI index. However, the damping presents different effects in different development stages. It is the most significant during the rapid development stage of the surface cyclone. Compared with no surface drag cases, the tropopause is less inclined to intrude into the troposphere due to the surface drag. Positive feedback between the surface cyclone and upper-level front could accelerate the development of the frontal system.

  20. The effect of finger spreading on drag of the hand in human swimming

    CERN Document Server

    van Houwelingen, Josje; Kunnen, Rudie P J; van Heijst, GertJan F; Grift, Ernst Jan; Breugem, Wim Paul; Delfos, Rene; Westerweel, Jerry; Clercx, Herman J H; van de Water, Willem

    2016-01-01

    The effect of finger spreading on hydrodynamic drag in swimming is studied both with a numerical simulation and with laboratory experiments. Both approaches are based on the exact same 3D model of the hand with attached forearm. The virtual version of the hand with forearm was implemented in a numerical code by means of an immersed boundary method and the physical version was studied in a wind tunnel experiment. An enhancement of the drag coefficient of 2 and 5% compared to the case with closed fingers was found for the numerical simulation and experiment, respectively. A 5 and 8% favourable effect on the (dimensionless) force moment at an optimal finger spreading of 10 degrees was found, which indicates that the difference is more outspoken in the force moment. Also an analytical model is proposed, using scaling arguments similar to the Betz actuator disk model, to explain the drag coefficient as a function of finger spacing.

  1. Simulation of Motion of Satellite under the Effect of Oblateness of Earth and Atmospheric Drag

    CERN Document Server

    Sharma, Jaita; Pirzada, U M; Shah, Vishant

    2016-01-01

    The equations governing motion of the satellite under the effect of oblateness of Earth and atmospheric drag have been simulated, for a fixed initial position and three different initial velocities, till satellite collapses on Earth. Simulation of motion of artificial Earth satellite subject to the combined effects of oblate Earth and atmospheric drag is presented. The atmospheric model considered here takes in to account of exponential variation of the density with initial distance of Satellite from Earth's surface, scale height and radial distance. The minimum and maximum values of orbital elements and their variation over a time for different initial velocities have been reported.

  2. A study of optimum cowl shapes and flow port locations for minimum drag with effective engine cooling, volume 1

    Science.gov (United States)

    Fox, S. R.; Smetana, F. O.

    1980-01-01

    The contributions to the cruise drag of light aircraft arising from the shape of the engine cowl and the forward fuselage area and also that resulting from the cooling air mass flow through intake and exhaust sites on the nacelle were analyzed. The methods employed for the calculation of the potential flow about an arbitrary three dimensional body are described with modifications to include the effects of boundary layer displacement thickness, a nonuniform onset flow field (such as that due to a rotating propeller), and the presence of air intakes and exhausts. A simple, reliable, largely automated scheme to better define or change the shape of a body is also presented. A technique was developed which can yield physically acceptable skin friction and pressure drag coefficients for isolated light aircraft bodies. For test cases on a blunt nose Cessna 182 fuselage, the technique predicted drag reductions as much as 28.5% by body recontouring and proper placements and sizing of the cooling air intakes and exhausts.

  3. Numerical investigation of the effect of sphere dimples on the drag crisis and the Magnus effect

    Science.gov (United States)

    Li, Jing; Tsubokura, Makoto; Tsunoda, Masaya

    2015-11-01

    The present study investigates the flow over a golf ball and a smooth sphere around the critical Reynolds numbers under both stationary and self-spinning conditions by conducting Large-eddy simulations (LES) based on high resolution unstructured grids. For the stationary cases, the present calculation results validate the promotion of the drag crisis at a relatively lower Reynolds number due to the golf ball dimples. It also shows that the golf ball dimples have a limited effect on the time-dependent lateral force development in the subcritical regime, whereas the dimples are beneficial in suppressing the lateral force oscillations in the supercritical regimes. With spin parameter Γ = 0.1, the drag coefficients for the spinning smooth sphere increase slightly in all Reynolds number regimes when compared to the stationary cases, whereas for the spinning golf ball, the drag force decreases in the critical regime and increases in the supercritical regime. For both spinning models, the inverse Magnus effect was reproduced in the critical regime, whereas in the supercritical regime the ordinary Magnus force was generated. Relatively weaker lift forces were also observed in the cases of the spinning golf balls when compared to the spinning smooth spheres.

  4. Effect of the Size Distribution of Nanoscale Dispersed Particles on the Zener Drag Pressure

    Science.gov (United States)

    Eivani, A. R.; Valipour, S.; Ahmed, H.; Zhou, J.; Duszczyk, J.

    2011-04-01

    In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction, which have been incorporated in the existing relationships. Microstructural observations indicated a clear correlation between the size distribution of dispersed particles and recrystallized grain sizes in the AA7020 aluminum alloy. However, the existing relationship to calculate the Zener drag pressure yielded a negligible difference of 0.016 pct between the two structures homogenized at different conditions resulting in totally different size distributions of nanoscale dispersed particles and, consequently, recrystallized grain sizes. The difference in the Zener drag pressure calculated by the application of the new relationship was 5.1 pct, being in line with the experimental observations of the recrystallized grain sizes. Mathematical investigations showed that the ratio of the Zener drag pressure from the new equation to that from the existing equation is maximized when the number densities of all the particles with different sizes are equal. This finding indicates that in the two structures with identical parameters except the size distribution of nanoscale dispersed particles, the one that possesses a broader size distribution of particles, i.e., the number densities of particles with different sizes being equal, gives rise to a larger Zener drag pressure than that having a narrow size distribution of nanoscale dispersed particles, i.e., most of the particles being in the same size range.

  5. Effect of wind-induced drag on leaf shapes

    Science.gov (United States)

    Louf, Jean-Francois; Ntoh Song, Pierre; Zehnbauer, Tim; Jung, Sunghwan

    2016-11-01

    Under windy conditions everyone can see leaves bending and twisting. From a geometrical point of view, a leaf is composed of two parts: a large flat plate called the lamina, and a small beam called the petiole, connecting the lamina to the branch/stem. While the wind is exerting forces (e.g. drag) on the lamina, the petiole undergoes twisting and bending stresses. To survive in harsh abiotic conditions, leaves might have evolved to form in many different shapes, resulting from a coupling between the lamina and the petiole. In this study we measure the twisting modulus (G) of the petiole using a twisting setup, and its Young modulus (E) by performing tensile tests. Micro-CT scan is used to precisely measure the cross section of the petiole allowing us to calculate the second moment of inertia (I) and the second moment of area (J). We then use the non-dimensional number EI/GJ and compare it to a geometrical non-dimensional number (Lpetiole +Llamina/2)/W, where Lpetiole is the length of the petiole, Llamina the length of the lamina, and W the width of the lamina. We found a linear relation between the ratio of the bending to twisting rigidity and the leaf geometry.

  6. Effects of Boattail Area Contouring and Simulated Turbojet Exhaust on the Loading and Fuselage-tail Component Drag of a Twin-engine Fighter-type Airplane Model

    Science.gov (United States)

    Foss, Willard E , Jr; Runckel, Jack F; Lee, Edwin E , Jr

    1958-01-01

    An investigation of a twin-engine fighter-type airplane model has been conducted in the Langley 16-foot transonic tunnel to determine the effect on drag of a fuselage volume addition incorporating streamline contouring and more extensive boattailing of the engine shrouds. The effect of hot exhausts from the turbojet engines was simulated with hydrogen peroxide gas generators using scaled nonafterburning engine nozzles. Afterbody pressure distributions, base drag coefficients, and forces on the fuselage-tail configurations are presented at Mach numbers from 0.80 to 1.05 angles of attack of 0 degree and 4 degrees for jet pressure ratios from 1 to 7. The effect of jet operation on both the basic and modified models was generally to decrease base pressures but to increase most other afterbody pressures and, therefore, to result in an overall decrease in fuselage-tail component drag. The addition of volume to the basic model reduced the base drag coefficient by 0.0010 with the jets off and 0.0018 at a typical cruise operating condition of a jet pressure ratio of 3, a Mach number of 0.85, and an angle of attack of 4 degrees. The overall jet-off reduction in fuselage-tail component drag due to the volume addition was a maximum of 0.0040 at a Mach number of 0.90 for an angle of attack of 4 degrees.

  7. Effects of turbulence on the drag force on a golf ball

    Science.gov (United States)

    Cross, Rod

    2016-09-01

    Measurements are presented of the drag force on a golf ball dropped vertically into a tank of water. As observed previously in air, the drag coefficient drops sharply when the flow becomes turbulent. The experiment would be suitable for undergraduate students since it can be undertaken at low ball speeds and since the effects of turbulence are easily observed on video film. A modified golf ball was used to show how a ball with a smooth and a rough side, such as a cricket ball, is subject to a side force when the ball surface itself is asymmetrical in the transverse direction.

  8. Effect of the size distribution of nanoscale dispersed particles on the Zener drag pressure

    NARCIS (Netherlands)

    Eivani, A.R.; Valipour, S.; Ahmed, H.; Zhou, J.; Duszczyk, J.

    2010-01-01

    In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction, which have been incorporated in the existing relati

  9. Effects of Winglets on the Drag of a Low-Aspect-Ratio Configuration

    Science.gov (United States)

    Smith, Leigh Ann; Campbell, Richard L.

    1996-01-01

    A wind-tunnel investigation has been performed to determine the effect of winglets on the induced drag of a low-aspect-ratio wing configuration at Mach numbers between 0.30 and 0.85 and a nominal angle-of-attack range from -2 deg to 20 deg. Results of the tests at the cruise lift coefficient showed significant increases in lift-drag ratio for the winglet configuration relative to a wing-alone configuration designed for the same lift coefficient and Mach number. Further, even larger increases in lift-drag ratio were observed at lift coefficients above the design value at all Mach numbers tested. The addition of these winglets had a negligible effect on the static lateral-directional stability characteristics of the configuration. No tests were made to determine the effect of these winglets at supersonic Mach numbers, where increases in drag caused by winglets might be more significant. Computational analyses were also performed for the two configurations studied. Linear and small-disturbance formulations were used. The codes were found to give reasonable performance estimates sufficient for predicting changes of this magnitude.

  10. Effect of ambient flow inhomogeneity on drag forces on a sphere at finite Reynolds numbers

    Science.gov (United States)

    Kim, Jungwoo; Balachandar, S.; Lee, Hyungoo

    2013-11-01

    For studies on particle-laden flows involving particle transport and dispersion, the prediction capability of hydrodynamic forces on the particle in a non-uniform flow is one of the central issues. However, existing analytical expressions and empirical correlations are mainly made based on the homogeneous flow conditions such as uniform or uniform shear flows. Therefore, the objective of this study is to investigate the effect of flow inhomogeneity on drag forces on a sphere at finite Reynolds numbers. To do so, we perform direct numerical simulations of flow over a sphere in an inhomogeneous flow. In this study, we consider three different kinds of the inhomogeneous flows: cosine, hyperbolic cosine and hyperbolic secant profiles. The Reynolds number of the sphere based on the freestream velocity and sphere diameter is 100. The present simulations show that the quasi-steady drag forces in inhomogeneous flows are reasonably estimated by standard drag law based on the relative velocity if the fluid velocity seen by the particle is evaluated by surface average. The results support Loth and Dorgan (2009)'s proposed formula. In the final presentation, the effect of ambient flow inhomogeneity on drag forces would be presented in more detail.

  11. The rigid bi-functional sail, new concept concerning the reduction of the drag of ships

    Science.gov (United States)

    Țicu, I.; Popa, I.; Ristea, M.

    2015-11-01

    The policy of the European Union in the energy field, for the period to follow until 2020, is based on three fundamental objectives: sustainability, competitiveness and safety in energy supply. The “Energy - Climate Changes” program sets out a number of objectives for the EU for the year 2020, known as the “20-20-20 objectives”, namely: the reduction of greenhouse gas emissions by at least 20% from the level of those of 1990, a 20% increase in the share of renewable energy sources out of the total energy consumption as well as a target of 10% biofuels in the transports energy consumption. In this context, in order to produce or save a part of the propulsive power produced by the main propulsion machinery, by burning fossil fuels, we suggest the equipping of vessels designed for maritime transport with a bi-functional rigid sail. We consider that this device may have both the role of trapping wind energy and the role of acting as a deflector for reducing the resistance of the vessel's proceeding through the water by conveniently using the bow air current, as a result of the vessel's heading through the water with significant advantage in reducing the energy consumption for propulsion insurance.

  12. Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids

    Science.gov (United States)

    Vakarelski, Ivan U.; Berry, Joseph D.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2016-09-01

    The drag coefficient CD of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re ˜3 ×1 05 . A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ˜600 to 1 05. The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape.

  13. Austenite grain growth simulation considering the solute-drag effect and pinning effect

    Science.gov (United States)

    Fujiyama, Naoto; Nishibata, Toshinobu; Seki, Akira; Hirata, Hiroyuki; Kojima, Kazuhiro; Ogawa, Kazuhiro

    2017-01-01

    Abstract The pinning effect is useful for restraining austenite grain growth in low alloy steel and improving heat affected zone toughness in welded joints. We propose a new calculation model for predicting austenite grain growth behavior. The model is mainly comprised of two theories: the solute-drag effect and the pinning effect of TiN precipitates. The calculation of the solute-drag effect is based on the hypothesis that the width of each austenite grain boundary is constant and that the element content maintains equilibrium segregation at the austenite grain boundaries. We used Hillert’s law under the assumption that the austenite grain boundary phase is a liquid so that we could estimate the equilibrium solute concentration at the austenite grain boundaries. The equilibrium solute concentration was calculated using the Thermo-Calc software. Pinning effect was estimated by Nishizawa’s equation. The calculated austenite grain growth at 1473–1673 K showed excellent correspondence with the experimental results. PMID:28179962

  14. Biomimetic Approaches to Functional Surfaces, Surface Wetting and Fluids Drag Reduction

    Institute of Scientific and Technical Information of China (English)

    Yuying Yan; Jianqiao Li; Khellil Sefiane

    2009-01-01

    @@ In the natural world, plants and animals have evolved over time to best adapt to the environment. They interact very effectively with the surrounding environment by exchanging energies and mass flow across their cuticles of specific micro structures and functions to achieve perfect energy balance.

  15. Drag Reduction Control for Flow over a Hump with Surface-Mounted Thermoacoustic Actuator

    Science.gov (United States)

    2015-01-01

    fabricating graphene/ carbon nanotube -based surface compliant loud speakers, the effectiveness of thermoacoustic actuators that locally introduce high...as a flow control actuator. A membrane of carbon nanotubes /graphene laid on a backing material such as paper under AC power has been shown to produce...propagated through the fluid field as high-intensity acoustic waves.7,8 One of the attractive characteristics of this carbon -based sound-emitting device

  16. Electroviscous effect on fluid drag in a microchannel with large zeta potential.

    Science.gov (United States)

    Jing, Dalei; Bhushan, Bharat

    2015-01-01

    The electroviscous effect has been widely studied to investigate the effect of surface charge-induced electric double layers (EDL) on the pressure-driven flow in a micro/nano channel. EDL has been reported to reduce the velocity of fluid flow and increase the fluid drag. Nevertheless, the study on the combined effect of EDL with large zeta potential up to several hundred millivolts and surface charge depenedent-slip on the micro/nano flow is still needed. In this paper, the nonlinear Poisson-Boltzmann equation for electrical potential and ion distribution in non-overlapping EDL is first analytically solved. Then, the modified Navier-Stokes equation for the flow considering the effect of surface charge on the electrical conductivity of the electrolyte and slip length is analytically solved. This analysis is used to study the effect of non-overlapping EDL with large zeta potential on the pressure-driven flow in a microchannel with no-slip and charge-dependent slip conditions. The results show that the EDL leads to an increase in the fluid drag, but that slip can reduce the fluid drag. When the zeta potential is large enough, the electroviscous effect disappears for flow in the microchannel under a no-slip condition. However, the retardation of EDL on the flow and the enhancement of slip on the flow counteract each other under a slip condition. The underlying mechanisms of the effect of EDL with large zeta potential on fluid drag are the high net ionic concentration near the channel wall and the fast decay of electrical potential in the EDL when the zeta potential is large enough.

  17. CFD modeling of liquid-solid fluidization: Effect of drag correlation and added mass force

    Institute of Scientific and Technical Information of China (English)

    Xiao yan Huang

    2011-01-01

    Computational fluid dynamics (CFD) has been widely used to study the hydrodynamics of gas-solid fluidization; however,its applications in liquid-solid fluidization are relatively rare.In this study,CFD simulations of a liquid-solid fluidized bed are carried out,focusing on the effect of drag correlation and added mass force on the hydrodynamics of liquid-solid fluidization.It is shown that drag correlation has a significant effect on the simulation results and the correlation proposed by Beetstra et al.(2007) gives the best agreement with experimental data.We further show that the added mass force does play an important role in CFD simulation of liquid-solid fluidization,and therefore should not be ignored in CFD simulations.

  18. The Machian contribution of the Universe to geodetic precession, frame dragging and gravitational clock effect

    CERN Document Server

    Christillin, Paolo

    2012-01-01

    Gravitomagnetism resulting from SR has been applied to geodetic precession and frame dragging. The substantial contribution of the "fictitious" Coriolis force, due to the relative rotation of the rest of the Universe in the non inertial frame of the free falling but rotating satellite, has to be taken into account, giving another quantitative confirmation of Mach's arguments and of the black hole nature of our Universe. Also the gravitational clock effect has an elementary prediction in the present post Newtonian formulation.

  19. Effect of the size distribution of nanoscale dispersed particles on the Zener drag pressure

    OpenAIRE

    Eivani, A.R.; Valipour, S.; Ahmed, H.; Zhou, J; Duszczyk, J.

    2010-01-01

    In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction, which have been incorporated in the existing relationships. Microstructural observations indicated a clear correlation between the size distribution of dispersed particles and recrystallized grain sizes in the AA7020 aluminum alloy. However, the ex...

  20. Drag sails for space debris mitigation

    Science.gov (United States)

    Visagie, Lourens; Lappas, Vaios; Erb, Sven

    2015-04-01

    The prudence for satellites to have a mitigation or deorbiting strategy has been brought about by the ever increasing amount of debris in Earth orbit. Drag augmentation is a potentially passive method for de-orbiting in LEO but its collision risk mitigation efficiency is sometimes underestimated by not taking all the relevant factors into account. This paper shows that using drag augmentation from a deployable drag-sail to de-orbit a satellite in LEO will lead to a reduction in collision risk. In order to support this finding, the models that are needed in order to evaluate the collision risk of a decaying object under drag conditions are presented. A comparison is performed between the simpler Area-Time-Product (ATP) and more precise collision risk analysis, and the effects that are overlooked in the simple ATP calculation are explained.

  1. A perturbative model for predicting the high-Reynolds-number behaviour of the streamwise travelling waves technique in turbulent drag reduction

    CERN Document Server

    Belan, Marco

    2013-01-01

    The background of this work is the problem of reducing the aerodynamic turbulent friction drag, which is an important source of energy waste in innumerable technological fields. We develop a theoretical framework aimed at predicting the behaviour of existing drag reduction techniques when used at the large values of Re which are typical of applications. We focus on one recently proposed and very promising technique, which consists in creating at the wall streamwise-travelling waves of spanwise velocity. A perturbation analysis of the Navier-Stokes equations that govern the fluid motion is carried out, for the simplest wall-bounded flow geometry, i.e. the plane channel flow. The streamwise base flow is perturbed by the spanwise time-varying base flow induced by the travelling waves. An asymptotic expansion is then carried out with respect to the velocity amplitude of the travelling wave. The analysis, although based on several assumptions, leads to predictions of drag reduction that agree well with the measure...

  2. Effects of Geopotential and Atmospheric Drag Effects on Frozen Orbits Using Nonsingular Variables

    Directory of Open Access Journals (Sweden)

    Paula Cristiane Pinto Mesquita Pardal

    2014-01-01

    Full Text Available The concept of frozen orbit has been applied in space missions mainly for orbital tracking and control purposes. This type of orbit is important for orbit design because it is characterized by keeping the argument of perigee and eccentricity constant on average, so that, for a given latitude, the satellite always passes at the same altitude, benefiting the users through this regularity. Here, the system of nonlinear differential equations describing the motion is studied, and the effects of geopotential and atmospheric drag perturbations on frozen orbits are taken into account. Explicit analytical expressions for secular and long period perturbations terms are obtained for the eccentricity and the argument of perigee. The classical equations of Brouwer and Brouwer and Hori theories are used. Nonsingular variables approach is used, which allows obtaining more precise previsions for CBERS (China Brazil Earth Resources Satellite satellites family and similar satellites (SPOT, Landsat, ERS, and IRS orbital evolution.

  3. Invariant Type-B characteristics of drag-reducing microalgal biopolymer solutions

    Science.gov (United States)

    Gasljevic, K.; Hall, K.; Chapman, D.; Matthys, E. F.

    2017-05-01

    The drag-reducing properties of polysaccharides from marine microalgae were investigated. They were compared to two drag-reducing additives studied extensively in the past, synthetic poly(ethylene) oxide, one of the most effective drag-reducing additives; and Xanthan Gum, another biopolymer often considered a model polymer for chemical and rheological research. Compared to Xanthan Gum, the most effective polymers from our microalgae show a higher drag-reducing efficiency in terms of necessary concentration to achieve a given level of drag reduction. In addition, they show a striking Type-B drag reduction behavior, which may be a very useful quality in most drag reduction applications, thanks to the independence of the drag reduction level on flow conditions such as velocity, shear stress, and tube diameter. With these polymers from microalgae we did not see evidence of Type-A behavior over the wide range of conditions studied (including pipe diameters up to 52 mm). Importantly, this suggests that the Drag Reduction coefficient in pipe flow for ideal drag-reducing solutions such as the polysaccharides investigated here is invariant at a given additive concentration of flow or solution parameters like ionic strength and can be used as a solution property to predict its drag reduction effectiveness over a wide range of conditions. On the contrary, Xanthan Gum showed evidence of both Type-A behavior in large diameter pipes and Type-B behavior in smaller ones. The polymers from microalgae also showed high resistance to degradation. Considering that these microalgae are very effective producers of polysaccharides (both extracellular and intracellular), they appear to be very promising additives for drag reduction applications.

  4. Hydrodynamic Drag on Streamlined Projectiles and Cavities

    KAUST Repository

    Jetly, Aditya

    2016-04-19

    The air cavity formation resulting from the water-entry of solid objects has been the subject of extensive research due to its application in various fields such as biology, marine vehicles, sports and oil and gas industries. Recently we demonstrated that at certain conditions following the closing of the air cavity formed by the initial impact of a superhydrophobic sphere on a free water surface a stable streamlined shape air cavity can remain attached to the sphere. The formation of superhydrophobic sphere and attached air cavity reaches a steady state during the free fall. In this thesis we further explore this novel phenomenon to quantify the drag on streamlined shape cavities. The drag on the sphere-cavity formation is then compared with the drag on solid projectile which were designed to have self-similar shape to that of the cavity. The solid projectiles of adjustable weight were produced using 3D printing technique. In a set of experiments on the free fall of projectile we determined the variation of projectiles drag coefficient as a function of the projectiles length to diameter ratio and the projectiles specific weight, covering a range of intermediate Reynolds number, Re ~ 104 – 105 which are characteristic for our streamlined cavity experiments. Parallel free fall experiment with sphere attached streamlined air cavity and projectile of the same shape and effective weight clearly demonstrated the drag reduction effect due to the stress-free boundary condition at cavity liquid interface. The streamlined cavity experiments can be used as the upper bound estimate of the drag reduction by air layers naturally sustained on superhydrophobic surfaces in contact with water. In the final part of the thesis we design an experiment to test the drag reduction capacity of robust superhydrophobic coatings deposited on the surface of various model vessels.

  5. Numerical simulation of microbubble drag reduction in a plate and factors in fluencing its practicality process%平板微气泡减阻数值模拟及影响因素分析

    Institute of Scientific and Technical Information of China (English)

    傅慧萍

    2015-01-01

    为了进一步揭示微气泡减阻机理,并探讨其实用化进程的影响因素,采用混合物多相流模型对平板微气泡减阻( BDR)问题进行了二维数值模拟,讨论了重力及底部和顶部2种通气方式的影响,对微气泡减阻机理进行了分析. 利用相群平衡模型( population balance model)三维数值模拟了平板底部通气和侧壁通气,对平板三维效应进行了研究. 结果表明:重力对大气泡影响较大;对于顶部通气方式,重力使气泡停留在边界层,从而使减阻效果得到改善;减阻率与气层厚度之间存在一定的关系. 侧壁通气的减阻效果不佳,三维效应也降低减阻效果.%In order to further reveal the microbubble drag reduction ( BDR) mechanism, and ascertain the factors influencing the practicality process of BDR, the two-dimensional numerical simulation was done to solve the plate BDR problem, using the mixture′s multi-phase flow model. The effects of gravity and the bottom and top ventilating modes were discussed, and the BDR mechanism was analyzed. Based on the population balance model, the ventila-ting on the bottom and on the side of the plate was respectively simulated with the three-dimensional model, and the plate′s 3D effects were analyzed. It is shown that the effect of gravity on big bubbles is larger. For the plate-on-top ventilating mode, gravity is beneficial to retaining the bubbles in the boundary layer and therefore BDR is improved. The drag reduction levels are related to the thickness of the gas layer near the plate. The drag reduction levels with plate vertical are discounted. The 3D effect also reduces the drag reduction effect.

  6. Effect of Electron Drag on Performances of Carbon Nanotubes as Flow Sensors

    Institute of Scientific and Technical Information of China (English)

    L(ü) Jian-wei; WANG Wan-lu; LIAO Ke-jun; CAO Chun-lan; LIU Cang-lin; ZENG Qing-gao

    2004-01-01

    Experimentally, the electron drag effect on carbon nanotube surface in flowing liquids was investigated. It was found that electric current could be generated in metallic carbon nanotubes immersed in the liquids. Carbon nanotubes were synthesized on Si substrate by hot filament chemical vapor deposition. The experimental results showed that the flow-induced current on the surface of carbon nanotube films was closely depended on the flow rate, concentration, properties and temperature of liquids. The flow-induced current was increased with the increasing of flow rate, concentration and temperature of liquids. The obtained results were discussed in detail.

  7. Frame Dragging Effect on Properties of Rotating Neutron Stars with Strong Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    GUO Yu-Wu; WEN De-Hua; HU Jian-Xun

    2008-01-01

    The general relativistic frame dragging effect on the properties, such as the moments of inertia and the radii of gyration of fast rotating neutron stars with a uniform strong magnetic field, is calculated accurate to the first order in the uniform angular velocity. The results show that compared with the corresponding non-rotating static spherical symmetric neutron star with a weaker magnetic field, a fast rotating neutron star (millisecond pulsar) with a stronger magnetic field has a relative smaller moment of inertia and radius of gyration.

  8. The 'W' prawn-trawl with emphasised drag-force transfer to its centre line to reduce overall system drag.

    Directory of Open Access Journals (Sweden)

    Cheslav Balash

    Full Text Available For prawn trawling systems, drag reduction is a high priority as the trawling process is energy intensive. Large benefits have occurred through the use of multiple-net rigs and thin twine in the netting. An additional positive effect of these successful twine-area reduction strategies is the reduced amount of otter board area required to spread the trawl systems, which leads to further drag reduction. The present work investigated the potential of redirecting the drag-strain within a prawn trawl away from the wings and the otter boards to the centre line of the trawl, where top and bottom tongues have been installed, with an aim to minimise the loading/size of the otter boards required to spread the trawl. In the system containing the new 'W' trawl, the drag redirected to the centre-line tongues is transferred forward through a connected sled and towing wires to the trawler. To establish the extent of drag redirection to the centre-line tongues and the relative drag benefits of the new trawl system, conventional and 'W' trawls of 3.65 m headline length were tested firstly over a range of spread ratios in the flume tank, and subsequently at optimum spread ratio in the field. The developed 'W' trawl effectively directed 64% of netting-drag off the wings and onto the centre tongues, which resulted in drag savings in the field of ∼20% for the associated 'W' trawl/otter-board/sled system compared to the traditional trawl/otter-board arrangement in a single trawl or twin rig configuration. Furthermore, based on previously published data, the new trawl when used in a twin rig system is expected to provide approximately 12% drag reduction compared to quad rig. The twin 'W' trawl system also has benefits over quad rig in that a reduced number of cod-end/By-catch Reduction Device units need to be installed and attended each tow.

  9. The flash-lag effect and the flash-drag effect in the same display.

    Science.gov (United States)

    Murai, Yuki; Murakami, Ikuya

    2016-09-01

    Visual motion distorts the perceived position of a stimulus. In the flash-drag effect (FDE), the perceived position of a flash appears to be shifted in the direction of nearby motion. In the flash-lag effect (FLE), a flash adjacent to a moving stimulus appears to lag behind. The FLE has been explained by several models, including the differential latency hypothesis, that a moving stimulus has a shorter processing latency than a flash does. The FDE even occurs when the flash is presented earlier than the moving stimulus, and it has been discussed whether this temporal property can be explained by the differential latency model. In the present study, we simultaneously quantified the FDE and FLE using the random jump technique (Murakami, 2001b) and compared their temporal properties. While the positional offset between a randomly jumping stimulus and a flashed stimulus determined the FLE, a drifting grating appeared next to the flash at various stimulus-onset asynchronies to induce the FDE. The grating presented up to 200 ms after the flash onset induced the FDE, whose temporal tuning was explained by a simple convolution model incorporating stochastic fluctuations of differential latency estimated from the FLE data and a transient-sustained temporal profile of motion signals. Thus, a common temporal mechanism to compute the stimulus position in reference to surrounding stimuli governs both the FDE and the FLE.

  10. La eficacia del efecto látigo en el drag flick en el hockey hierba The effectiveness of the bullwhip effect in the Drag-flick in field hockey

    Directory of Open Access Journals (Sweden)

    C. López de Subijana

    2010-09-01

    whipping effect of the stick before an explosive movement of hips, shoulders and a maximum acceleration of the stick.
    Key Words: Biomechanics, drag-flick, field hockey, kinematics.

  11. Simulation of the Clustering Phenomenon in a Fast Fluidized Bed: The Importance of Drag Correlation

    Institute of Scientific and Technical Information of China (English)

    李佑楚

    2004-01-01

    Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has, however, not been thoroughly investigated. In this article, a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization, including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles. Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation. The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds. This drag force correlation, based on a simple averaging assumption, could give some basic insights about the magnitude of the drag reduction.

  12. Research on the drag reduction performance induced by the counterflowing jet for waverider with variable blunt radii

    Science.gov (United States)

    Li, Shi-bin; Wang, Zhen-guo; Barakos, George N.; Huang, Wei; Steijl, Rene

    2016-10-01

    Waverider will endure the huge aero-heating in the hypersonic flow, thus, it need be blunt for the leading edge. However, the aerodynamic performance will decrease for the blunt waverider because of the drag hoik. How to improve the aerodynamic performance and reduce the drag and aero-heating is very important. The variable blunt radii method will improve the aerodynamic performance, however, the huge aero-heating and bow shock wave at the head is still serious. In the current study, opposing jet is used in the waverider with variable blunt radii to improve its performance. The three-dimensional coupled implicit Reynolds-averaged Navier-Stokes(RANS) equation and the two equation SST k-ω turbulence model have been utilized to obtain the flow field properties. The numerical method has been validated against the available experimental data in the open literature. The obtained results show that the L/D will drop 7-8% when R changes from 2 to 8. The lift coefficient will increase, and the drag coefficient almost keeps the same when the variable blunt radii method is adopted, and the L/D will increase. The variable blunt radii method is very useful to improve the whole characteristics of blunt waverider and the L/D can improve 3%. The combination of the variable blunt radii method and opposing jet is a novel way to improve the whole performance of blunt waverider, and L/D can improve 4-5%. The aperture as a novel way of opposing jet is suitable for blunt waverider and also useful to improve the aerodynamic and aerothermodynamic characteristics of waverider in the hypersonic flow. There is the optimal P0in/P0 that can make the detached shock wave reattach the lower surface again so that the blunt waverider can get the better aerodynamic performance.

  13. Drag balance Cubesat attitude motion effects on in-situ thermosphere density measurements

    Science.gov (United States)

    Felicetti, Leonard; Santoni, Fabio

    2014-08-01

    The dynamics of Cubesats carrying a drag balance instrument (DBI) for in situ atmosphere density measurements is analyzed. Atmospheric drag force is measured by the displacement of two light plates exposed to the incoming particle flow. This system is well suited for a distributed sensor network in orbit, to get simultaneous in situ local (non orbit averaged) measurements in multiple positions and orbit heights, contributing to the development and validation of global atmosphere models. The implementation of the DBI leads to orbit normal pointing spinning two body system. The use of a spin-magnetic attitude control system is suggested, based only on magnetometer readings, contributing to making the system simple, inexpensive, and reliable. It is shown, by an averaging technique, that this system provides for orbit normal spin axis pointing. The effect of the coupling between the attitude dynamics and the DBI is evaluated, analyzing its frequency content and showing that no frequency components arise, affecting the DBI performance. The analysis is confirmed by Monte Carlo numerical simulation results.

  14. Drag on Sessile Drops

    Science.gov (United States)

    Milne, Andrew J. B.; Fleck, Brian; Nobes, David; Sen, Debjyoti; Amirfazli, Alidad; University of Alberta Mechanical Engineering Collaboration

    2013-11-01

    We present the first ever direct measurements of the coefficient of drag on sessile drops at Reynolds numbers from the creeping flow regime up to the point of incipient motion, made using a newly developed floating element differential drag sensor. Surfaces of different wettabilities (PMMA, Teflon, and a superhydrophobic surface (SHS)), wet by water, hexadecane, and various silicone oils, are used to study the effects of drop shape, and fluid properties on drag. The relation between drag coefficient and Reynolds number (scaled by drop height) varies slightly with liquid-solid system and drop volume with results suggesting the drop experiences increased drag compared to similar shaped solid bodies due to drop oscillation influencing the otherwise laminar flow. Drops adopting more spherical shapes are seen to experience the greatest force at any given airspeed. This indicates that the relative exposed areas of drops is an important consideration in terms of force, with implications for the shedding of drops in applications such as airfoil icing and fuel cell flooding. The measurement technique used in this work can be adapted to measure drag force on other deformable, lightly adhered objects such as dust, sand, snow, vesicles, foams, and biofilms. The authours acknowledge NSERC, Alberta Innovates Technology Futures, and the Killam Trusts.

  15. Effect of Drag Reducing Polymer and Suspended Solid on the Rate of Diffusion Controlled Corrosion in 90° Copper Elbow

    Science.gov (United States)

    Fouad, Mohamed Ahmed; Zewail, Taghreed Mohamed; Amine, Nieven Kamal Abbes

    2016-06-01

    Rate of diffusion controlled corrosion in 90° Copper Elbow acidified dichromate has been investigated in relation to the following parameters: effect of solution velocity in the absence and presence of drag- reducing polymer on the rate of diffusion controlled corrosion, and effect of the presence of suspended solids on the rate of diffusion controlled corrosion. It was found that the presence of drag reducing polymer inhibited the rate of mass transfer, while the presence of suspended solid increased significantly the rate of mass transfer.

  16. Research for Application of Vibration Drag Reduction Technology to the Design of Soil Tillage Equipment%振动减阻技术应用于土壤耕作机具的研究

    Institute of Scientific and Technical Information of China (English)

    庄凯; 郭志军

    2014-01-01

    近年来,振动理论作为减阻技术应用于土壤耕作愈来愈受到人们重视,如何有效地减小工作阻力和降低能源功耗是其亟需解决的两大难题。为此,以应用比较广泛的振动深松铲为重点,阐述了振动耕作方式二维切削的减阻机理。同时,介绍了目前国内外的研究现状,研究表明合理选择振动方式和性能参数是使机具达到最佳减阻效果的关键。通过对比分析强迫和自激两种主要振动型式的优缺点,列举了几种振动关键机构的设计及应用;指出了振动参数对工作阻力影响程度的研究有待于进一步完善等问题。最后展望了振动控制方式向人工智能化方向转变的前景。%As a new emerging technology applied to the field , the vibration theory of soil cultivation and mining has be-come increasingly important in recent years .However , how to reduce the drag and energy consumption remain to be two major problems .This paper elaborates the theory of how to reduce the drag of the mechanism of drag reduction of two -di-mensional by using the vibrating subsoiler which is widely used in vibration subsoil as an example , and presents the re-search status both here and abroad , in which shows that the reasonable selection of vibration mode and performance pa-rameters is the key to implement the best drag reduction effect .Also describes the design and application of key institu-tions of several vibrations through analyzing the advantages and disadvantages of two main types of forced and self -excited vibration , points out some issues such as the vibration parameters of traction force is not enough .And forecasts the future of vibration theory is applied in conjunction with the artificial intelligence technology .

  17. The effect of shape on drag: a physics exercise inspired by biology

    Science.gov (United States)

    Fingerut, Jonathan; Johnson, Nicholas; Mongeau, Eric; Habdas, Piotr

    2017-07-01

    As part of a biomechanics course aimed at upper-division biology and physics majors, but applicable to a range of student learning levels, this laboratory exercise provides an insight into the effect of shape on hydrodynamic performance, as well an introduction to computer aided design (CAD) and 3D printing. Students use hydrodynamic modeling software and simple CAD programs to design a shape with the least amount of drag based on strategies gleaned from the study of natural forms. Students then print the shapes using a 3D printer and test their shapes against their classmates in a friendly competition. From this exercise, students gain a more intuitive sense of the challenges that organisms face when moving through fluid environments, the physical phenomena involved in moving through fluids at high Reynolds numbers and observe how and why certain morphologies, such as streamlining, are common answers to the challenge of swimming at high speeds.

  18. Modeling atmospheric drag effect on Mangalyaan Mars orbiter during geocentric, heliocentric and areocentric trajectories

    Science.gov (United States)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip Kumar

    2016-07-01

    Interplanetary missions are susceptible to gravitational and non-gravitational perturbing forces at every trajectory phase, assuming that the man made rockets and thrusters work as expected. These forces are mainly due to planetary and solar-forcing-induced perturbations during geocentric, heliocentric and Martian trajectories, and before orbit insertion. In this study, we analyzed perturbing forces and their possible effects on interplanetary and/or Mars mission satellites, before Orbit Insertion. We also model the significance of atmospheric drag force on Mangalyaan Mars orbiter mission, as a function of appropriate space environmental parameters during its 28 days in Earth's orbit (around and during perigee passage), 300 days of heliocentric and 100 days of Martian trajectory based on Earth-Mars atmosphere density ratio.

  19. Large photon drag effect of intrinsic graphene induced by plasmonic evanescent field

    Science.gov (United States)

    Luo, Ma; Li, Zhibing

    2016-12-01

    A large photon drag effect of the massless Dirac fermions in intrinsic graphene is predicted for a graphene-on-plasmonic-layer system. The surface plasmons in the plasmonic layer enlarge the wave number of the photon hundreds times more than in vacuum. The evanescent field of the surface plasmons generates a directional motion of carriers in the intrinsic graphene because of the large momentum transfer from the surface plasmon to the excited carriers. A model Hamiltonian is developed on the assumption that the in-plane wavelength of the surface plasmons is much smaller than the mean free path of the carriers. The time evolution of the density matrix is solved by perturbation method as well as numerical integration. The nondiagonal density matrix elements with momentum transfer lead to a gauge current, which is an optically driven macroscopic direct current. The dependence of the macroscopic direct current on the incident direction and intensity of the laser field is studied.

  20. Studying the rheological properties and the influence of drag reduction on a waxy crude oil in pipeline flow

    Directory of Open Access Journals (Sweden)

    M.H. Hassanean

    2016-03-01

    The rheological behaviors of tested waxy crude oil were studied at different temperatures (varies from 67 to 102 °F and different DRA concentrations (10, 20, 30, 40, and 50 ppm. The results showed that at all constant DRA concentrations, the viscosity highly decreased until 80 °F (above pour point by 15 °F. However, by increasing the DRA concentration, the viscosity is increased at temperatures lower than 80 °F. This is because the DRA is a high molecular weight polymer which participates in increasing viscosity by increasing its concentration. After 80 °F, the DRA concentration has an insignificant effect on viscosity. So the effect of the DRA is not in reducing viscosity but mainly in reducing the degree of turbulence energy. The field studies were performed at a normal temperature of tested pipeline sections (100 °F. The tested DRA has an improving effect on reducing the pressure drop of pipeline which leads to reduction in crude oil pumping energy or an increase in the pipeline capacity with a high efficiency of the DRA.

  1. Coulomb drag in quantum circuits

    OpenAIRE

    Levchenko, Alex; Kamenev, Alex

    2008-01-01

    We study drag effect in a system of two electrically isolated quantum point contacts (QPC), coupled by Coulomb interactions. Drag current exhibits maxima as a function of QPC gate voltages when the latter are tuned to the transitions between quantized conductance plateaus. In the linear regime this behavior is due to enhanced electron-hole asymmetry near an opening of a new conductance channel. In the non-linear regime the drag current is proportional to the shot noise of the driving circuit,...

  2. Optimal design of bodies of revolution of annular jet flow surface and analysis of the drag reduction mechanism%旋成体环形射流表面优化设计与减阻机理分析

    Institute of Scientific and Technical Information of China (English)

    赵刚; 李芳; 臧东阳

    2014-01-01

    With a focus on the problem of bionic jet drag reduction , a bionic jet surface model is presented by using the jet flow of shark cheeks as the prototype .Based on the orthogonal test design method , this paper goes into detail about numerical simulations by making a comparison between bodies of revolution of a bionic annular jet flow sur -face ( BRBAJFS ) and smooth bodies of revolution with the SST k-ωturbulence model .The results prove that BRBAJFS has obvious drag-reduction and energy-saving effects .The highest energy saving efficiency can be 262 and the corresponding rate of drag reduction is 27.74%.The jet velocity has the most important impact on energy saving efficiency and it has a linear relation with the energy saving efficiency , i.e., the energy saving efficiency will decrease with an increase in the jet velocity .Furthermore, the position of the jet hole has the greatest impact on the total resistance .When the jet hole is far away from the bottom of the bodies of revolution , the drag reduction effi-ciency will increase and BRBAJFS decreases the viscous friction resistance by decreasing the velocity gradient of the wall and increasing the area of counterblows .There can also be a decrease in the pressure drag resulting from the jet fluid complementing the bottom of the bodies of revolution fluid .%针对仿生射流表面减阻问题,以鲨鱼鳃部射流为原型,建立仿生射流表面模型,采用正交试验设计法,利用SST k-ω湍流模型对仿生环形射流表面旋成体与光滑旋成体进行数值模拟。结果表明:旋成体环形射流表面具有减阻节能效果,最高节能效率达262,此时的减阻率为27.74%;射流速度对节能效率影响最大,射流速度与节能效率呈线性关系,随着射流速度增大,节能效率减小,射流孔位置对总阻力的影响最大,随着射流孔远离旋成体底部,减阻率增大。旋成体环形射流表面通过减小壁面的速度梯

  3. Drag Moderation by the Melting of an Ice Surface in Contact with Water

    Science.gov (United States)

    Vakarelski, Ivan U.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2015-07-01

    We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re ˜2 ×104- 3 ×105 and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface.

  4. Drag Moderation by the Melting of an Ice Surface in Contact with Water

    KAUST Repository

    Vakarelski, Ivan Uriev

    2015-07-24

    We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re∼2×104–3×105 and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface.

  5. Analytical calculation of the drag force near drag crisis of a falling sphere

    CERN Document Server

    Assis, Armando V D B; Branco, N S

    2010-01-01

    We obtain analitically the $v^2$ dependence of the drag force on a falling sphere close to the drag crisis, as well as the drag coefficient at the drag crisis, with excellent agreement with experiment. We take into account the effects of viscosity in creating a turbulent boundary layer and perform the calculations using the Navier-Stokes equation.

  6. Colossal Seebeck effect enhanced by quasi-ballistic phonons dragging massive electrons in FeSb2

    Science.gov (United States)

    Takahashi, H.; Okazaki, R.; Ishiwata, S.; Taniguchi, H.; Okutani, A.; Hagiwara, M.; Terasaki, I.

    2016-09-01

    Phonon transport is an essential property of thermoelectric materials. Although the phonon carries heat, which reduces the thermoelectric efficiency, it contributes positively to the Seebeck coefficient S through the phonon-drag effect, as typified by the high-purity semiconductors, which show fairly large S at cryogenic temperatures. Although such a large S is attractive in terms of Peltier cooling, a clear guiding principle for designing thermoelectric materials enriched by the phonon-drag effect remains to be established. Here we demonstrate that a correlated semiconductor, FeSb2, is a promising thermoelectric material featuring quasi-ballistic phonons dragging d electrons with large effective mass. By changing the sample size within the sub-millimetre order for high-purity single crystals, we succeed in substantially increasing S to as much as -27 mV K-1 at low temperatures. Our results exemplify a strategy for exploring phonon-drag-based thermoelectric materials, the performance of which can be maximized by combining heavy electrons with ballistic phonons.

  7. Colossal Seebeck effect enhanced by quasi-ballistic phonons dragging massive electrons in FeSb2.

    Science.gov (United States)

    Takahashi, H; Okazaki, R; Ishiwata, S; Taniguchi, H; Okutani, A; Hagiwara, M; Terasaki, I

    2016-09-06

    Phonon transport is an essential property of thermoelectric materials. Although the phonon carries heat, which reduces the thermoelectric efficiency, it contributes positively to the Seebeck coefficient S through the phonon-drag effect, as typified by the high-purity semiconductors, which show fairly large S at cryogenic temperatures. Although such a large S is attractive in terms of Peltier cooling, a clear guiding principle for designing thermoelectric materials enriched by the phonon-drag effect remains to be established. Here we demonstrate that a correlated semiconductor, FeSb2, is a promising thermoelectric material featuring quasi-ballistic phonons dragging d electrons with large effective mass. By changing the sample size within the sub-millimetre order for high-purity single crystals, we succeed in substantially increasing S to as much as -27 mV K(-1) at low temperatures. Our results exemplify a strategy for exploring phonon-drag-based thermoelectric materials, the performance of which can be maximized by combining heavy electrons with ballistic phonons.

  8. Effect of Jet-nozzle-expansion Ratio on Drag of Parabolic Afterbodies

    Science.gov (United States)

    Englert, Gerald W; Vargo, Donald J; Cubbison, Robert W

    1954-01-01

    The interaction of the flow from one convergent and two convergent-divergent nozzles on parabolic afterbodies was studied at free-stream Mach numbers of 2.0, 1.6, and 0.6 over a range of jet pressure ratio. The influence of the jet on boattail and base drag was very pronounced. Study of the total external afterbody drag values at supersonic speeds indicated that, over most of the high-pressure-ratio range, increasing the nozzle design expansion ratio increased the drag even though the boattail area was reduced. Increasing the pressure ratio tended to increase slightly the total-drag increment caused by angle-of-attack operation.

  9. Gastronomiske drags

    DEFF Research Database (Denmark)

    Leer, Jonatan

    2013-01-01

    with Jennifer Parson and Clarissa Dickson Wright (1996-1999). I will argue that the two self-declared fat women can be read as “gastronomic drags” by their transgression of a “recognizable” feminine way of “doing food”. The article is theoretically informed by the reflections on drag as subversive practice...... of appearing either too radical or not radical enough. The article concludes with some reflections on the development of the cooking show as a site for gendered negotiation from the 90’s and today....

  10. Wing Tip Drag Reduction at Nominal Take-Off Mach Number: An Approach to Local Active Flow Control with a Highly Robust Actuator System

    Directory of Open Access Journals (Sweden)

    Matthias Bauer

    2016-10-01

    Full Text Available This paper discusses wind tunnel test results aimed at advancing active flow control technology to increase the aerodynamic efficiency of an aircraft during take-off. A model of the outer section of a representative civil airliner wing was equipped with two-stage fluidic actuators between the slat edge and wing tip, where mechanical high-lift devices fail to integrate. The experiments were conducted at a nominal take-off Mach number of M = 0.2. At this incidence velocity, separation on the wing section, accompanied by increased drag, is triggered by the strong slat edge vortex at high angles of attack. On the basis of global force measurements and local static pressure data, the effect of pulsed blowing on the complex flow is evaluated, considering various momentum coefficients and spanwise distributions of the actuation effort. It is shown that through local intensification of forcing, a momentum coefficient of less than c μ = 0.6 % suffices to offset the stall by 2.4°, increase the maximum lift by more than 10% and reduce the drag by 37% compared to the uncontrolled flow.

  11. Effects of Different Cutting Patterns and Experimental Conditions on the Performance of a Conical Drag Tool

    Science.gov (United States)

    Copur, Hanifi; Bilgin, Nuh; Balci, Cemal; Tumac, Deniz; Avunduk, Emre

    2017-06-01

    This study aims at determining the effects of single-, double-, and triple-spiral cutting patterns; the effects of tool cutting speeds on the experimental scale; and the effects of the method of yield estimation on cutting performance by performing a set of full-scale linear cutting tests with a conical cutting tool. The average and maximum normal, cutting and side forces; specific energy; yield; and coarseness index are measured and compared in each cutting pattern at a 25-mm line spacing, at varying depths of cut per revolution, and using two cutting speeds on five different rock samples. The results indicate that the optimum specific energy decreases by approximately 25% with an increasing number of spirals from the single- to the double-spiral cutting pattern for the hard rocks, whereas generally little effect was observed for the soft- and medium-strength rocks. The double-spiral cutting pattern appeared to be more effective than the single- or triple-spiral cutting pattern and had an advantage of lower side forces. The tool cutting speed had no apparent effect on the cutting performance. The estimation of the specific energy by the yield based on the theoretical swept area was not significantly different from that estimated by the yield based on the muck weighing, especially for the double- and triple-spiral cutting patterns and with the optimum ratio of line spacing to depth of cut per revolution. This study also demonstrated that the cutterhead and mechanical miner designs, semi-theoretical deterministic computer simulations and empirical performance predictions and optimization models should be based on realistic experimental simulations. Studies should be continued to obtain more reliable results by creating a larger database of laboratory tests and field performance records for mechanical miners using drag tools.

  12. Hydrodynamic interaction on large-Reynolds-number aligned bubbles: Drag effects

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez-Munoz, J., E-mail: jrm@correo.azc.uam.mx [Departamento de Energia, Universidad Autonoma Metropolitana-Azcapotzalco, Av. San Pablo 180, Col. Reynosa Tamaulipas, 02200 Mexico D.F. (Mexico); Centro de Investigacion en Polimeros, Marcos Achar Lobaton No. 2, Tepexpan, 55885 Acolman, Edo. de Mexico (Mexico); Salinas-Rodriguez, E.; Soria, A. [Departamento de IPH, Universidad Autonoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Col. Vicentina, Iztapalapa, 09340 Mexico D.F. (Mexico); Gama-Goicochea, A. [Centro de Investigacion en Polimeros, Marcos Achar Lobaton No. 2, Tepexpan, 55885 Acolman, Edo. de Mexico (Mexico)

    2011-07-15

    Graphical abstract: Display Omitted Highlights: > The hydrodynamic interaction of a pair aligned equal-sized bubbles is analyzed. > The leading bubble wake decreases the drag on the trailing bubble. > A new semi-analytical model for the trailing bubble's drag is presented. > The equilibrium distance between bubbles is predicted. - Abstract: The hydrodynamic interaction of two equal-sized spherical gas bubbles rising along a vertical line with a Reynolds number (Re) between 50 and 200 is analyzed. An approach to estimate the trailing bubble drag based on the search of a proper reference fluid velocity is proposed. Our main result is a new, simple semi-analytical model for the trailing bubble drag. Additionally, the equilibrium separation distance between bubbles is predicted. The proposed models agree quantitatively up to small distances between bubbles, with reported data for 50 {<=} Re {<=} 200. The relative average error for the trailing bubble drag, Er, is found to be in the range 1.1 {<=} Er {<=} 1.7, i.e., it is of the same order of the analytical predictions in the literature.

  13. New insights into the microvascular mechanisms of drag reducing polymers: effect on the cell-free layer.

    Directory of Open Access Journals (Sweden)

    Judith Brands

    Full Text Available Drag-reducing polymers (DRPs significantly increase blood flow, tissue perfusion, and tissue oxygenation in various animal models. In rectangular channel microfluidic systems, DRPs were found to significantly reduce the near-wall cell-free layer (CFL as well as modify traffic of red blood cells (RBC into microchannel branches. In the current study we further investigated the mechanism by which DRP enhances microvascular perfusion. We studied the effect of various concentrations of DRP on RBC distribution in more relevant round microchannels and the effect of DRP on CFL in the rat cremaster muscle in vivo. In round microchannels hematocrit was measured in parent and daughter branch at baseline and after addition of DRP. At DRP concentrations of 5 and 10 ppm, the plasma skimming effect in the daughter branch was eliminated, as parent and daughter branch hematocrit were equivalent, compared to a significantly lowered hematocrit in the daughter branch without DRPs. In anesthetized rats (N=11 CFL was measured in the cremaster muscle tissue in arterioles with a diameter of 32.6 ± 1.7 µm. In the control group (saline, N=6 there was a significant increase in CFL in time compared to corresponding baseline. Addition of DRP at 1 ppm (N=5 reduced CFL significantly compared to corresponding baseline and the control group. After DRP administration the CFL reduced to about 85% of baseline at 5, 15, 25 and 35 minutes after DRP infusion was complete. These in vivo and in vitro findings demonstrate that DRPs induce a reduction in CFL width and plasma skimming in the microvasculature. This may lead to an increase of RBC flux into the capillary bed, and thus explain previous observations of a DRP mediated enhancement of capillary perfusion.

  14. The Effects of Drag and Tidal Forces on the Orbits of High-Velocity Clouds

    Science.gov (United States)

    Fernandes, Alexandre; Benjamin, R. A.

    2013-06-01

    Over the past several years, orbital constraints have been obtained for several high velocity cloud complexes surrounding the Milky Way: Complex GCP (Smith Cloud), Complex A, Complex H, Complex GCN, and the Magellanic Stream. We summarize what is known about the orbits of these clouds and and discuss how well each of these complexes fits a balistic trajectory, and discuss how the length of a complex across the sky is related to the inital "fragmentation" and velocity dispersion of the clouds. We then introduce gas drag into the simulation of the orbits of these complexes. We present analytical tests of our numerical method and characterize the departure of the clouds from the ballistic trajectory as a function of drag parameters (ambient gas density and velocity and cloud column density). Using the results of these simulations we comment on the survivability and ultimate fate of HVC in the context of the different models of drag forces.

  15. Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids

    KAUST Repository

    Vakarelski, Ivan Uriev

    2016-09-08

    The drag coefficient CD of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re∼3×105. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ∼600 to 105. The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape. © 2016 American Physical Society.

  16. Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water

    KAUST Repository

    Vakarelski, Ivan Uriev

    2014-01-01

    We investigate the dynamic effects of a Leidenfrost vapour layer sustained on the surface of heated steel spheres during free fall in water. We find that a stable vapour layer sustained on the textured superhydrophobic surface of spheres falling through 95 °C water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory for the Reynolds number between 104 and 106, spanning the drag crisis in the absence of the vapour layer. For hydrophilic spheres under the same conditions, the transition to drag reduction and trajectory stability occurs abruptly at a temperature different from the static Leidenfrost point. The observed drag reduction effects are attributed to the disruption of the viscous boundary layer by the vapour layer whose thickness depends on the water temperature. Both the drag reduction and the trajectory stabilization effects are expected to have significant implications for development of sustainable vapour layer based technologies. © the Partner Organisations 2014.

  17. Seebeck effect in dilute two-dimensional electron systems: temperature dependencies of diffusion and phonon-drag thermoelectric powers

    OpenAIRE

    Liu, S Y; Lei, X. L.; Horing, Norman J. M.

    2011-01-01

    Considering screeening of electron scattering interactions in terms of the finite-temperature STLS theory and solving the linearized Boltzmann equation (with no appeal to a relaxation time approximation), we present a theoretical analysis of the low-temperature Seebeck effect in two-dimensional semiconductors with dilute electron densities. We find that the temperature ($T$) dependencies of the diffusion and phonon-drag thermoelectric powers ($S_d$ and $S_g$) can no longer be described by the...

  18. Three-dimensional Numerical Analysis on Drag Reduction Characteristics of the Riblet Structure for Centrifugal Fan Blades%离心风机叶片脊状结构减阻特性的三维数值分析

    Institute of Scientific and Technical Information of China (English)

    吴正人; 郝晓飞; 戎瑞; 王松岭

    2014-01-01

    The drag reduction characteristics of riblet structure on aerofoil blade in the single channel model of G4-73 centrifugal fan were numerically simulated based on Realizable k-εturbulence model with Fluent. Then the effects of riblet structure on the performance of centrifugal fan were researched. The results are as follows. The total pressure of the model with riblet structure in appropriate size is higher than that with smooth surface blade at the same condition, and the improvement can reach 7.98% at most, which indirectly reflects the reduction effect of flow loss. The riblet structure only has a certain impact on the distributions of boundary layer near the wall. And the wall shear stress on the valleys’ surface could be reduced effectively by the stable secondary vortex formed within the valleys of the riblet structure, verifying the drag reduction effect of riblet structure. The gradients of the normal velocity near the wall in the turbulent boundary layer and the turbulent kinetic energy of the riblet surface are both lower than those of the smooth surface, which verifies the inhibition to the turbulent dissipation and drag reduction effect of the riblet structure. But the shear stress of some areas would increase because of the existence of the equal interval between the valleys, and this has a certain adverse effect on the drag reduction effect. In off-design conditions, the separation of the boundary layer on the pressure side or the suction side of the blade would also affect the drag reduction effect and its position of the riblet structure. The present results can be used to provide a valuable reference for the blade modification and performance improvement of centrifugal fan.%基于 Realizable k-ε紊流模型,采用 Fluent 软件对G4-73型离心风机单流道模型叶片翼型表面脊状结构的减阻特性进行了数值模拟研究,并分析了脊状结构对风机运行特性的影响。结果表明:适当尺寸的脊状结构布置

  19. Light Drag Effect of Vacuum Tube Versus Light Propagation in Stationary Vacuum Tube with Moving Source and Receiver

    CERN Document Server

    Wang, Ruyong; He, Le; Zhang, Wenyan; Zhang, Liang

    2016-01-01

    We presented a new way to examine the principle of relativity of Special Relativity. According to the principle of relativity, the light dragging by moving media and the light propagation in stationary media with moving source and receiver should be two totally equivalent phenomena. We select a vacuum tube with two glass rods at two ends as the optical media. The length of the middle vacuum cell is L and the thicknesses of the glass rods with refractive index n are D1 and D2. The light drag effect of the moving vacuum tube with speed v is a first-order effect, delta t = 2(n-1)(D1+D2)v/c^2, which is independent of L because vacuum does not perform a drag effect. Predicted by the principle of relativity, the change of the light propagation time interval with stationary vacuum tube and moving source and receiver must be the same, i.e., delta tao = delta t = 2(n-1)(D1+D2)v/c^2. However all analyses have shown that the change of the propagation time interval delta tao is caused by the motion of the receiver during...

  20. Effect of the drag force on the orbital motion of the broad-line region clouds

    CERN Document Server

    Khajenabi, Fazeleh

    2016-01-01

    We investigate orbital motion of cold clouds in the broad line region of active galactic nuclei subject to the gravity of a black hole and a force due to a nonisotropic central source and a drag force proportional to the velocity square. The intercloud is described using the standard solutions for the advection-dominated accretion flows. Orbit of a cloud decays because of the drag force, but the typical time scale of falling of clouds onto the central black hole is shorter comparing to the linear drag case. This time scale is calculated when a cloud is moving through a static or rotating intercloud. We show that when the drag force is a quadratic function of the velocity, irrespective of the initial conditions and other input parameters, clouds will generally fall onto the central region much faster than the age of whole system and since cold clouds present in most of the broad line regions, we suggest that mechanisms for continuous creation of the clouds must operate in these systems.

  1. Coupled Vortex-Lattice Flight Dynamic Model with Aeroelastic Finite-Element Model of Flexible Wing Transport Aircraft with Variable Camber Continuous Trailing Edge Flap for Drag Reduction

    Science.gov (United States)

    Nguyen, Nhan; Ting, Eric; Nguyen, Daniel; Dao, Tung; Trinh, Khanh

    2013-01-01

    This paper presents a coupled vortex-lattice flight dynamic model with an aeroelastic finite-element model to predict dynamic characteristics of a flexible wing transport aircraft. The aircraft model is based on NASA Generic Transport Model (GTM) with representative mass and stiffness properties to achieve a wing tip deflection about twice that of a conventional transport aircraft (10% versus 5%). This flexible wing transport aircraft is referred to as an Elastically Shaped Aircraft Concept (ESAC) which is equipped with a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for active wing shaping control for drag reduction. A vortex-lattice aerodynamic model of the ESAC is developed and is coupled with an aeroelastic finite-element model via an automated geometry modeler. This coupled model is used to compute static and dynamic aeroelastic solutions. The deflection information from the finite-element model and the vortex-lattice model is used to compute unsteady contributions to the aerodynamic force and moment coefficients. A coupled aeroelastic-longitudinal flight dynamic model is developed by coupling the finite-element model with the rigid-body flight dynamic model of the GTM.

  2. Effects of Frame-Dragging on X-ray Emission from Black Holes and Neutron Stars

    Science.gov (United States)

    Markovic, D.; Lamb, F. K.

    2000-10-01

    In previous work on the effects of frame-dragging on viscous accretion disks around black holes and neutron stars, we discovered gravitomagnetically precessing global modes localized near the inner edge of the Keplerian flow. The highest-frequency modes of this type precess in the prograde direction with frequencies slightly lower than the Lense-Thirring precession frequency at the mean radius of the mode. Contrary to what had been expected since the pioneering work of Bardeen & Petterson, these modes are very weakly damped (Q ≈ 20--50) and are therefore likely to be excited. We present analytical arguments that shed further light on the nature of these modes and allow a better understanding of the symmetry-breaking pattern of viscous dissipation they create. The two highest-frequency modes tilt the innermost part of the Keplerian flow, redirecting gas crossing the sonic radius. As we discuss, these modes are likely to be the most easily excited and may be excited by magnetoturbulence in the disk or interaction of the disk with a stellar magnetic field. They may modulate X-ray emission from black holes and neutron stars by periodically altering the inspiral of gas from the Keplerian disk, by periodically obscuring emission from the inner disk or star, or by creating a rotating pattern of enhanced emission. This modulation is expected to create power spectral peaks at ~1--10 Hz in black hole sources and at ~10--40 Hz in the kilohertz QPO sources. It may also produce sidebands on the kilohertz QPOs, separated from the main peaks by ~10--40 Hz. Detecting and measuring the frequencies of these modes would provide valuable new information about the strongly curved, twisting spacetime expected near spinning neutron stars and black holes. This research was supported in part by the NSF and NASA.

  3. A study of optimum cowl shapes and flow port locations for minimum drag with effective engine cooling, volume 2

    Science.gov (United States)

    Fox, S. R.; Smetana, F. O.

    1980-01-01

    The listings, user's instructions, sample inputs, and sample outputs of two computer programs which are especially useful in obtaining an approximate solution of the viscous flow over an arbitrary nonlifting three dimensional body are provided. The first program performs a potential flow solution by a well known panel method and readjusts this initial solution to account for the effects of the boundary layer displacement thickness, a nonuniform but unidirectional onset flow field, and the presence of air intakes and exhausts. The second program is effectually a geometry package which allows the user to change or refine the shape of a body to satisfy particular needs without a significant amount of human intervention. An effort to reduce the cruise drag of light aircraft through an analytical study of the contributions to the drag arising from the engine cowl shape and the foward fuselage area and also that resulting from the cooling air mass flowing through intake and exhaust sites on the nacelle is presented. The programs may be effectively used to determine the appropriate body modifications or flow port locations to reduce the cruise drag as well as to provide sufficient air flow for cooling the engine.

  4. Drag reduction in numerical two-phase Taylor–Couette turbulence using an Euler–Lagrange approach

    NARCIS (Netherlands)

    Arza, Vamsi Spandan; Ostilla-Monico, Rodolfo; Verzicco, Roberto; Lohse, Detlef

    2016-01-01

    Two-phase turbulent Taylor–Couette (TC) flow is simulated using an Euler–Lagrange approach to study the effects of a secondary phase dispersed into a turbulent carrier phase (here bubbles dispersed into water). The dynamics of the carrier phase is computed using direct numerical simulations (DNS) in

  5. DOE's effort to reduce truck aerodynamic drag through joint experiments and computations.

    Energy Technology Data Exchange (ETDEWEB)

    Salari, Kambiz (Lawrence Livermore National Laboratory); Browand, Fred (University of Southern California); Sreenivas, Kidambi (University of Tennessee, Chattanooga); Pointer, W. David (Argonne National Laboratory); Taylor, Lafayette (University of Tennessee, Chattanooga); Pankajakshan, Ramesh (University of Tennessee, Chattanooga); Whitfield, David (University of Tennessee, Chattanooga); Plocher, Dennis (University of Southern California); Ortega, Jason M. (Lawrence Livermore National Laboratory); Merzel, Tai (University of Southern California); McCallen, Rose (Lawrence Livermore National Laboratory); Walker, Stephen M (NASA Ames Research Center); Heineck, James T (NASA Ames Research Center); Hassan, Basil; Roy, Christopher John (Auburn University); Storms, B. (NASA Ames Research Center); Ross, James (NASA Ames Research Center); Englar, Robert (Georgia Tech Research Institute); Rubel, Mike (Caltech); Leonard, Anthony (Caltech); Radovich, Charles (University of Southern California); Eastwood, Craig (Lawrence Livermore National Laboratory); Paschkewitz, John (Lawrence Livermore National Laboratory); Castellucci, Paul (Lawrence Livermore National Laboratory); DeChant, Lawrence Justin.

    2005-08-01

    Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million gal/year. Objectives are: (1) In support of DOE's mission, provide guidance to industry in the reduction of aerodynamic drag; (2) To shorten and improve design process, establish a database of experimental, computational, and conceptual design information; (3) Demonstrate new drag-reduction techniques; and (4) Get devices on the road. Some accomplishments are: (1) Concepts developed/tested that exceeded 25% drag reduction goal; (2) Insight and guidelines for drag reduction provided to industry through computations and experiments; (3) Joined with industry in getting devices on the road and providing design concepts through virtual modeling and testing; and (4) International recognition achieved through open documentation and database.

  6. Drag Torque Prediction Model for the Wet Clutches

    Institute of Scientific and Technical Information of China (English)

    HU Jibin; PENG Zengxiong; YUAN Shihua

    2009-01-01

    Reduction of drag torque in disengaged wet clutch is one of important potentials for vehicle transmission improvement. The flow of the oil film in clutch clearance is investigated. A three-dimension Navier-Stokes(N-S) equation based on laminar flow is presented to model the drag torque. Pressure and speed distribution in radial and circumferential directions are deduced. The theoretical analysis reveals that oil flow acceleration in radial direction caused by centrifugal force is the key reason for the shrinking of oil film as constant feeding flow rate. The peak drag torque occurs at the beginning of oil film shrinking. A variable is introduced to describe effective oil film area and drag torque after oil film shrinking is well evaluated with the variable. Under the working condition, tests were made to obtain drag torque curves at different clutch speed and oil viscosity. The tests confirm that simulation results agree with test data. The model performs well in the prediction of drag torque and lays a theoretical foundation to reduce it.

  7. Skin-friction drag analysis from the forced convection modeling in simplified underwater swimming.

    Science.gov (United States)

    Polidori, G; Taïar, R; Fohanno, S; Mai, T H; Lodini, A

    2006-01-01

    This study deals with skin-friction drag analysis in underwater swimming. Although lower than profile drag, skin-friction drag remains significant and is the second and only other contribution to total drag in the case of underwater swimming. The question arises whether varying the thermal gradient between the underwater swimmer and the pool water may modify the surface shear stress distribution and the resulting skin-friction drag acting on a swimmer's body. As far as the authors are aware, such a question has not previously been addressed. Therefore, the purpose of this study was to quantify the effect of this thermal gradient by using the integral formalism applied to the forced convection theory. From a simplified model in a range of pool temperatures (20-30 degrees C) it was demonstrated that, whatever the swimming speeds, a 5.3% reduction in the skin-friction drag would occur with increasing average boundary-layer temperature provided that the flow remained laminar. However, as the majority of the flow is actually turbulent, a turbulent flow analysis leads to the major conclusion that friction drag is a function of underwater speed, leading to a possible 1.5% reduction for fast swimming speeds above 1m/s. Furthermore, simple correlations between the surface shear stress and resulting skin-friction drag are derived in terms of the boundary-layer temperature, which may be readily used in underwater swimming situations.

  8. Stony meteoroid space erosion and drag: Effect on cosmic ray exposure ages

    Science.gov (United States)

    Rubincam, David Parry

    2017-09-01

    Collisions with dust particles in retrograde orbits cause space erosion on stony meteoroids in addition to the particle drag which causes drift toward resonances. The spacing between resonances determines the maximum drift time and sets upper limits on the neon-21 cosmic ray exposure (CRE) ages for meteoroids less than ∼1 m in radius, while space erosion controls the limit for radii greater than ∼1 m; the limits accord well with the measured CRE ages of stony meteorites.

  9. The coupling of surface charge and boundary slip at the solid-liquid interface and their combined effect on fluid drag: A review.

    Science.gov (United States)

    Jing, Dalei; Bhushan, Bharat

    2015-09-15

    Fluid drag of micro/nano fluidic systems has inspired wide scientific interest. Surface charge and boundary slip at the solid-liquid interface are believed to affect fluid drag. This review summarizes the recent studies on the coupling of surface charge and slip, and their combined effect on fluid drag at micro/nano scale. The effect of pH on surface charge of borosilicate glass and silica surfaces in deionized (DI) water and saline solution is discussed using a method based on colloidal probe atomic force microscopy (AFM). The boundary slip of various oil-solid interfaces are discussed for samples with different degrees of oleophobicity prepared by nanoparticle-binder system. By changing the pH of solution or applying an electric field, effect of surface charge on slip of a smooth hydrophobic octadecyltrichlorosilane (OTS) in DI water and saline solution is studied. A theoretical model incorporating the coupling relationship between surface charge and slip is used to discuss the combined effect of surface charge-induced electric double layer (EDL) and slip on fluid drag of pressure-driven flow in a one-dimensional parallel-plates microchannel. A theoretical method is used to reduce the fluid drag. The studies show that the increasing magnitude of surface charge density leads to a decrease in slip length. The surface charge results in a larger fluid drag, and the coupling of surface charge and slip can further increase the fluid drag. Surface charge-induced EDLs with asymmetric zeta potentials can effectively reduce the fluid drag.

  10. Drag Coefficient of Thin Flexible Cylinder

    Science.gov (United States)

    Subramanian, Chelakara; Gurram, Harika

    2015-11-01

    Measurements of drag coefficients of thin flexible cylindrical wires are described for the Reynolds number range between 250 - 1000. Results indicate that the coefficient values are about 20 to 30 percent lower than the reported laminar flow values for rigid cylinders. Possible fluid dynamics mechanism causing the reduction in drag will be discussed.

  11. Aircraft Drag Prediction and Reduction

    Science.gov (United States)

    1985-07-01

    Manual . NASA CR159105, Aug, 1979. 12. Srokowski, A. J. and Orszag, S. A.: Mass Flow Requirements for LFC Wing Design. AIAA Paper No. 77-1222, Aug. 1977. 13...Instituto Superior Tecnico , Lisbon (1984). 51 T.W. Swafford Analytical approximation of two-dimensional separated turbulent boundary-layer profiles

  12. Improving the durability of a drag-reducing nanocoating by enhancing its mechanical stability.

    Science.gov (United States)

    Cheng, Mengjiao; Zhang, Songsong; Dong, Hongyu; Han, Shihui; Wei, Hao; Shi, Feng

    2015-02-25

    The durability of superhydrophobic surface is a major problem to restrict industrial application of superhydrophobic materials from laboratory research, which can be attributed to a more general issue of mechanical stability for superhydrophobic coatings. Therefore, in order to handle this issue, we have fabricated a mechanically stable drag-reducing coating composed of elastic polydimethylsiloxane (PDMS) and hydrophobic copper particles on model ships, which can resist mechanical abrasion and has displayed a durable drag-reducing effect. In comparison with normal Au superhydrophobic coatings, the as-prepared PDMS/copper coatings showed durable drag reduction performance with a similar drag-reducing rate before (26%) and after (24%) mechanical abrasion. The mechanism for the enhanced mechanical stability and maintained drag reduction of the superhydrophobic surfaces was investigated through characterizations of surface morphology, surface wettability, and water adhesive force evaluation before and after abrasion. This is the first demonstration to realize the application of durable drag reduction by improving the mechanical stability of superhydrophobic coatings. We do believe that superhydrophobic surfaces with good resistance to mechanical abrasion or scratching may draw wide attention and gain significant applications with durable drag-reducing properties.

  13. Harnessing the polariton drag effect to design an electrically controlled optical switch.

    Science.gov (United States)

    Berman, Oleg L; Kezerashvili, Roman Ya; Kolmakov, German V

    2014-10-28

    We propose a design of a Y-shaped electrically controlled optical switch based on the studies of propagation of an exciton-polariton condensate in a patterned optical microcavity with an embedded quantum well. The polaritons are driven by a time-independent force due to the microcavity wedge shape and by a time-dependent drag force owing to the interaction of excitons in a quantum well and the electric current running in a neighboring quantum well. It is demonstrated that by applying the drag force one can direct more than 90% of the polariton flow toward the desired branch of the switch with no hysteresis. By considering the transient dynamics of the polariton condensate, we estimate the response speed of the switch as 9.1 GHz. We also propose a design of the polariton switch in a flat microcavity based on the geometrically identical Y-shaped quantum wells where the polariton flow is only induced by the drag force. The latter setup enables one to design a multiway switch that can act as an electrically controlled optical transistor with on and off functions. Finally, we performed the simulations for a microcavity with an embedded gapped graphene layer and demonstrated that in this case the response speed of the switch can be increased up to 14 GHz for the same switch size. The simulations also show that the energy gap in the quasiparticle spectrum in graphene can be utilized as an additional parameter that controls the propagation of the signals in the switch.

  14. Turbulent drag in a rotating frame

    CERN Document Server

    Campagne, Antoine; Gallet, Basile; Cortet, Pierre-Philippe; Moisy, Frédéric

    2016-01-01

    What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at constant angular velocity $\\omega$ in a water tank mounted on a platform rotating at a rate $\\Omega$. We report a dramatic reduction in drag as $\\Omega$ increases, down to values as low as $12$\\% of the non-rotating drag. At small Rossby number $Ro = \\omega/\\Omega$, the decrease in drag coefficient $K$ follows the approximate scaling law $K \\sim Ro$, which is predicted in the framework of nonlinear inertial wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction rather originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.

  15. Biofilm effects on size gradation, drag coefficient and settling velocity of sediment particles

    Institute of Scientific and Technical Information of China (English)

    Qian-qian SHANG; Hong-wei FANG; Hui-ming ZHAO; Guo-jian HE; Zheng-hui CUI

    2014-01-01

    Sediment particles are often colonized by biofilm in a natural aquatic ecological system, especially in eutrophic water body. A series of laboratory experiments on particle size gradation, drag coefficient and settling velocity were conducted after natural sediment was colonized by biofilm for 5, 10, 15 and 20 days. Particle image acquisition, particle tracking techniques of Particle Image Velocimetry and Particle Tracking Velocimetry were utilized to analyze the changes of these properties. The experimental results indicate that the size gradation, the drag force exerted on bio-particles, and the settling velocity of bio-particles underwent significant change due to the growth of biofilm onto the sediment surface. The study proposes a characteristic particle size formula and a bio-particle settling velocity formula based on the regression of experiment results, that the settling velocity is only 50% to 60%as the single particle which has the same diameter and density. However, biofilm growth causes large particle which the settling velocities are approximately 10 times larger than that of primary particles. These results may be specifically used in the low energy reservoir or lake environment.

  16. Oxygen ion uplift and satellite drag effects during the 30 October 2003 daytime superfountain event

    Directory of Open Access Journals (Sweden)

    B. T. Tsurutani

    2007-03-01

    Full Text Available The prompt penetration of interplanetary electric fields (IEFs to the dayside low-latitude ionosphere during the first ~2 h of a superstorm is estimated and applied to a modified NRL SAMI2 code for the 30 October 2003 event. In our simulations, the dayside ionospheric O+ is convected to higher altitudes (~600 km and higher latitudes (~±25° to 30°, forming highly displaced equatorial ionospheric anomaly (EIA peaks. This feature plus others are consistent with previously published CHAMP electron (TEC measurements and with the dayside superfountain model. The rapid upward motion of the O+ ions causes neutral oxygen (O uplift due to ion-neutral drag. It is estimated that above ~400 km altitude the O densities within the displaced EIAs can be increased substantially over quiet time values. The latter feature will cause increased drag for low-altitude satellites. This newly predicted phenomenon is expected to be typical for superstorm/IEF events.

  17. Departure of microscopic friction from macroscopic drag in molecular fluid dynamics

    Science.gov (United States)

    Hanasaki, Itsuo; Fujiwara, Daiki; Kawano, Satoyuki

    2016-03-01

    Friction coefficient of the Langevin equation and drag of spherical macroscopic objects in steady flow at low Reynolds numbers are usually regarded as equivalent. We show that the microscopic friction can be different from the macroscopic drag when the mass is taken into account for particles with comparable scale to the surrounding fluid molecules. We illustrate it numerically by molecular dynamics simulation of chloride ion in water. Friction variation by the atomistic mass effect beyond the Langevin regime can be of use in the drag reduction technology as well as the electro or thermophoresis.

  18. Bio-replicated forming of the biomimetic drag-reducing surfaces in large area based on shark skin

    Institute of Scientific and Technical Information of China (English)

    HAN Xin; ZHANG DeYuan; LI Xiang; LI YuanYue

    2008-01-01

    On the investigation of biomimetic drag-reducing surface, direct replication of the firm scarfskins on low-resistance creatures to form biomimetic drag-reducing surfaces with relatively vivid morphology relative to the living prototype is a new attempt of the bio-replicated forming technology. Taking shark skin as the bio-replication template, the hot embossing method was applied to the micro-replication of its outward morphology. Furthermore, the skins were jointed together to form the drag-reducing sur-face in large area. The results of the resistance measurements in a water tunnel according to the flat-plate sample pieces have shown that the biomimetic shark-skin coating fabricated by the bio-replicated forming method has significant drag reduction effect, and that the drag reduction effi-ciency reached 8.25% in the test conditions.

  19. Why fibers are better turbulent drag reducing agents than polymers

    Science.gov (United States)

    Boelens, Arnout; Muthukumar, Murugappan

    2016-11-01

    It is typically found in literature that fibers are not as effective as drag reducing agents as polymers. However, for low concentrations, when adding charged polymers to either distilled or salt water, it is found that polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. In this study, using hybrid Direct Numerical Simulation with Langevin dynamics, a comparison is performed between polymer and fiber stress tensors in turbulent flow. The stress tensors are found to be similar, suggesting a common drag reducing mechanism in the onset regime. Since fibers do not have an elastic backbone, this must be a viscous effect. Analysis of the viscosity tensor reveals that all terms are negligible, except the off-diagonal shear viscosity associated with rotation. Based on this analysis, we are able to explain why charged polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. Additionally, we identify the rotational orientation time as the unifying time scale setting a new time criterion for drag reduction by both flexible polymers and rigid fibers. This research was supported by NSF Grant No. DMR-1404940 and AFOSR Grant No. FA9550-14-1-0164.

  20. The effects of turbulence on droplet drag and secondary droplet breakup

    Science.gov (United States)

    Song, Y.-H.; Coy, E.; Greenfield, S.; Ondas, M.; Prevish, T.; Spegar, T.; Santavicca, D.

    1994-01-01

    The objective of this research is to obtain an improved understanding of the behavior of droplets in vaporizing sprays, particularly under conditions typical of those in high pressure rocket sprays. Experiments are conducted in a variety of high pressure, high temperature, optically-accessible flow systems, including one which is capable of operation at pressures up to 70 atm, temperatures up to 600 K, gas velocities up to 30 m/sec and turbulence intensities up to 40 percent. Single droplets, 50 to 500 micron in diameter, are produced by an aerodynamic droplet generator and transversely injected into the flow. Measurements are made of the droplet position, size, velocity and temperature and of the droplet's vapor wake from which droplet drag, dispersion, heating, vaporization and breakup are characterized.

  1. Effects of Plasma Drag on Low Earth Orbiting Satellites due to Heating of Earth's Atmosphere by Coronal Mass Ejections

    CERN Document Server

    Nwankwo, Victor U J

    2013-01-01

    Solar events, such as coronal mass ejections (CMEs) and solar flares, heat up the upper atmosphere and near-Earth space environment. Due to this heating and expansion of the outer atmosphere by the energetic ultraviolet, X-ray and particles expelled from the sun, the low Earth-Orbiting satellites (LEOS) become vulnerable to an enhanced drag force by the ions and molecules of the expanded atmosphere. Out of various types of perturbations, Earth directed CMEs play the most significant role. They are more frequent and intense during the active (solar maximum) phase of the sun's approximately 11-year cycle. As we are approaching another solar maximum later in 2013, it may be instructive to analyse the effects of the past solar cycles on the orbiting satellites using the archival data of space environment parameters as indicators. In this paper, we compute the plasma drag on a model LEOS due to the atmospheric heating by CMEs and other solar events as a function of the solar parameters. Using the current forecast ...

  2. Cells in 3D matrices under interstitial flow: effects of extracellular matrix alignment on cell shear stress and drag forces.

    Science.gov (United States)

    Pedersen, John A; Lichter, Seth; Swartz, Melody A

    2010-03-22

    Interstitial flow is an important regulator of various cell behaviors both in vitro and in vivo, yet the forces that fluid flow imposes on cells embedded in a 3D extracellular matrix (ECM), and the effects of matrix architecture on those forces, are not well understood. Here, we demonstrate how fiber alignment can affect the shear and pressure forces on the cell and ECM. Using computational fluid dynamics simulations, we show that while the solutions of the Brinkman equation accurately estimate the average fluid shear stress and the drag forces on a cell within a 3D fibrous medium, the distribution of shear stress on the cellular surface as well as the peak shear stresses remain intimately related to the pericellular fiber architecture and cannot be estimated using bulk-averaged properties. We demonstrate that perpendicular fiber alignment of the ECM yields lower shear stress and pressure forces on the cells and higher stresses on the ECM, leading to decreased permeability, while parallel fiber alignment leads to higher stresses on cells and increased permeability, as compared to a cubic lattice arrangement. The Spielman-Goren permeability relationships for fibrous media agreed well with CFD simulations of flow with explicitly considered fibers. These results suggest that the experimentally observed active remodeling of ECM fibers by fibroblasts under interstitial flow to a perpendicular alignment could serve to decrease the shear and drag forces on the cell.

  3. Effects of biofouling development on drag forces of hull coatings for ocean-going ships: a review

    DEFF Research Database (Denmark)

    Lindholdt, Asger; Dam-Johansen, Kim; Olsen, S. M.;

    2015-01-01

    This review presents a systematic overview of the literature and describes the experimental methods used to quantify the drag of hull coatings. It also summarizes the findings of hull coating's drag performance and identifies the main parameters impacting it. The advantages and disadvantages...... of the reported methods listed in this review provide an assessment of the most efficient methods to quantify the drag performance of hull coatings. This review determines that drag performance of hull coating technology varies depending on whether the coating condition is newly applied, after dynamic or static...

  4. Drag-reducing performance of obliquely aligned superhydrophobic surface in turbulent channel flow

    Science.gov (United States)

    Watanabe, Sho; Mamori, Hiroya; Fukagata, Koji

    2017-04-01

    Friction drag reduction effect by superhydrophobic surfaces in a turbulent channel flow is investigated by means of direct numerical simulation. The simulations are performed under a constant pressure gradient at the friction Reynolds number of 180. A special focus is laid upon the influence of the angle of microridge structure to flow direction, while the gas area fraction on the surface is kept at 50% and the groove width is kept constant at 33.75 wall units. Larger drag reduction effect is observed for a smaller angle: the bulk-mean velocity is increased about 15% when the microridge is parallel to the flow. The drag reduction effect is found to deteriorate rapidly with the microridge angle due to a decrease in the slip velocity. The Reynolds stress budgets show that the modification in each physical effect is qualitatively similar but more pronounced when the microridge is aligned with the stream.

  5. Rice- and butterfly-wing effect inspired self-cleaning and low drag micro/nanopatterned surfaces in water, oil, and air flow.

    Science.gov (United States)

    Bixler, Gregory D; Bhushan, Bharat

    2014-01-01

    In search of new solutions to complex challenges, researchers are turning to living nature for inspiration. For example, special surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we study four microstructured surfaces inspired by rice leaves and fabricated with photolithography techniques. We also present a method of creating such surfaces using a hot embossing procedure for scaled-up manufacturing. Fluid drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of sample geometrical dimensions. Conceptual modeling provides design guidance when developing novel low drag, self-cleaning, and potentially antifouling surfaces for medical, marine, and industrial applications.

  6. FY2003 Annual Report: DOE Project on Heavy Vehicle Aerodynamic Drag

    Energy Technology Data Exchange (ETDEWEB)

    McCallen, R C; Salari, K; Ortega, J; DeChant, L J; Roy, C J; Payne, J J; Hassan, B; Pointer, W D; Browand, F; Hammache, M; Hsu, T; Ross, J; Satran, D; Heineck, J; Walker, S; Yaste, D; Englar, R; Leonard, A; Rubel, M; Chatelain, P

    2003-10-24

    Objective: {sm_bullet} Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles. {sm_bullet} Establish a database of experimental, computational, and conceptual design information, and demonstrate potential of new drag-reduction devices.

  7. The effect of plasma actuator on the depreciation of the aerodynamic drag on box model

    Science.gov (United States)

    Harinaldi, Budiarso, Julian, James; Rabbani M., N.

    2016-06-01

    Recent active control research advances have provided many benefits some of which in the field of transportation by land, sea as well as by air. Flow engineering by using active control has proven advantages in energy saving significantly. One of the active control equipment that is being developed, especially in the 21st century, is a plasma actuator, with the ability to modify the flow of fluid by the approach of ion particles makes these actuators a very powerful and promising tool. This actuator can be said to be better to the previously active control such as suction, blowing and synthetic jets because it is easier to control, more flexible because it has no moving parts, easy to be manufactured and installed, and consumes a small amount of energy with maximum capability. Plasma actuator itself is the composition of a material composed of copper and a dielectric sheet, where the copper sheets act as an electricity conductor and the dielectric sheet as electricity insulator. Products from the plasma actuators are ion wind which is the result of the suction of free air around the actuator to the plasma zone. This study investigates the ability of plasma actuators in lowering aerodynamic drag which is commonly formed in the models of vehicles by varying the shape of geometry models and the flow speed.

  8. Experimental study on flow drag reduction characteristics of xanthan gum solution in smooth pipes with different diameters%不同直径光滑圆管中黄原胶溶液流动减阻特性的实验研究

    Institute of Scientific and Technical Information of China (English)

    禹燕飞; 李明义; 赵文斌; 侯金亮; 李昌烽

    2014-01-01

    采用实验的方法,测试了黄原胶溶液在不同直径的光滑管道流动中的减阻特性和管径效应。其中变化参数为:(1)管道直径,共有3种管径,分别为5、10和20mm;(2)黄原胶溶液的浓度,变化范围为50~550 ppm;(3)流速,用广义雷诺数(ReM)来表征,变化范围为0~50000。实验测量了不同参数下的管道压降Δp和体积流量Q,得到了黄原胶溶液浓度与减阻率的关系,以及ReM 数对沿程阻力系数λ的影响,观测到黄原胶溶液减阻具有很明显的浓度效应,即随着溶液浓度的升高减阻率不断增大,直至达到最佳饱和减阻浓度,减阻率基本保持恒定。还观测到黄原胶溶液在不同管径中高低流速下表现出减阻类型的差异。%Experimental study on drag reduction characteristics of xanthan gum solution in smooth pipes with different diameters has been conducted.The variable parameters are as fol-lows:(1)the pipe diameters,5,10 and 20mm,respectively;(2)the concentration of xanthan gum solution ranging from 50 to 550ppm;(3 )fluid velocity,characterized by flow generalized Reynolds number in the range of 0~50000.The pipe pressure dropΔp and flow volume flux Q under different conditions have been measured.The relationship between drag reduction and con-centration of xanthan gum solution is obtained,and the influence of Reynolds number on friction factorλis also investigated.It is observed that the drag reduction effect of xanthan gum solution relys obviously on the concentration of the solution,percent drag reduction increasing with the increase of xanthan gum solution concentration until it reaches the optimum saturation concentra-tion where the percent drag reduction is mainly keeping constant.The experimental results also show the drag reduction type difference under low and high Reynolds number flow conditions for xanthan gum solution in three pipes with different diameters.

  9. Copolymers for Drag Reduction in Marine Propulsion: New Molecular Structures with Enhanced Effectiveness

    Science.gov (United States)

    1992-05-31

    amido )-2-inethylpropylltrimnethylammonium chloride (AMPTAC) have been prepared by free-radical po- lymerization in a 0.5 M NaCI aqueous solution using...addition of urea. The calorimetric peak in a slightly higher %DR. At a wall shear stress of 143 Pa, the 0.514 M NaCI is higher (AC,> 35) in deionized water

  10. Copolymers for Drag Reduction in Marie Propulsion: New Molecular Structures with Enhanced Effectiveness

    Science.gov (United States)

    1991-05-31

    monomer. Sodium dodecyl sulfate was the surfactant in this acknowledged. 573 References 1. McCormick, C. L. and Johnson, C. B. PMSE , 55, 366 (1986). 2...Preprints, 30(2), 348 (1989). 4. Valint, P. L., Jr.; Bock, J. and Schulz, D. N. PMSE , 482 (1987). 5. McCormick, C. L. and Blackmon, K P. J. Polym. Si. Polym...constant shear rate of 4. Ezzell, S. A.; and McCormick, C. L., Polym. Prepr., 30(2), 6 sc’. 340 (1989). 5. Peer, W. J., PMSE , 57, 492 (1987). AM-APS

  11. A coating of passively oscillating flexible cilia to reduce drag

    Science.gov (United States)

    Revell, Alistair; Harwood, Adrian; O'Connor, Joseph; Sanchez, Jonathan; Favier, Julien

    2016-11-01

    We present results related to the reduction of wake drag by the coordinated action of a layer of passively oscillating flexible cilia. Inspired by the pop-up of bird feathers, this configuration is shown to self-adapt to the surrounding flow, leading to a stabilization of the wake, a reduction of the mean drag and of lift oscillations. The study is performed using Lattice Boltzmann method, coupled to a recent version of the immersed boundary method. We will present the physical analysis of the coupling between multiple beating cilia and an incoming fluid flow. The modal behaviour of the cilia dynamics will be discussed, as well as their effect on an archetype of unsteady separated boundary layer (first the oscillating channel flow and then the circular cylinder). In the latter case results demonstrate an optimal drag occurs for a particular stiffness, compared to the control case where the same cilia are fixed. It appears that the optimal results are due to a reconfiguration of the elastic coating according to the local vorticity of the flow, and a frequency lock-in, which leads to more stable wake and reduced drag. The structural parameters of the layer will be varied. Results from the PEL-SKIN project: funded by EU Grant #334954.

  12. Methods of reducing vehicle aerodynamic drag

    Energy Technology Data Exchange (ETDEWEB)

    Sirenko V.; Rohatgi U.

    2012-07-08

    A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.

  13. 基于抛物线形气-液界面的超疏水微通道减阻特性%Drag reduction of superhydrophobic microchannels based on parabolic gas-liquid interfaces

    Institute of Scientific and Technical Information of China (English)

    李春曦; 张硕; 薛全喜; 叶学民

    2016-01-01

    针对超疏水表面微通道中的流动减阻特性,基于抛物线形气-液界面假设,采用VOF模型模拟了微通道中的二维层流流动,分析了流动和结构参数对减阻效果的影响。结果表明,含矩形微坑的超疏水表面微通道具有显著减阻作用,fRe随Reynolds数增大而略有提高,量纲1压降比随入口速度增大而略有下降。当增大微坑面积比或减小微通道高度时,fRe减小,量纲1压降比增大;且微通道高度越小,微坑面积比对fRe的影响越显著。随抛物线形高度增加,压降比和滑移长度均线性减小,而fRe则线性增加。当微坑深度大于其宽度的40%时,压降比和滑移长度趋于定值。微坑形状对减阻效果的影响依次是燕尾形、矩形、梯形和三角形。%Based on the model of volume of fluid, two-dimensional fluid laminar flow in superhydrophobic microchannels was numerically simulated with given parabolic gas-liquid interfaces. The effects of several flow and structural parameters onfRe, the normalized slip length and pressure drop were investigated. The results show that superhydrophobic microchannels with rectangular microcavities exhibited significant drag reduction in a way thatfRe increased slightly with increase of Reynolds number whereas normalized pressure drop decreased slightly with increase of inlet velocity. When the area ratio of microcavities was increased or the microchannel diameter was decreased,fRe was reduced but normalized pressure drop was enhanced. In case of small microchannel diameter, the area ratio of microcavities significantly affectedfRe. With increase of the parabolic height, the ratio of normalized pressure drop and the normalized slip length decreased linearly, howeverfRe increased linearly. The impact of microcavities on the normalized slip length and the ratio of normalized pressure drop was minimal provided that the microcavity depth was greater than 40% of its width. The

  14. Drag reduction regime by hydrofoil and resistance estimation method for gliding-hydrofoil craft%高速艇水翼减阻方案及翼滑艇阻力估算方法

    Institute of Scientific and Technical Information of China (English)

    唐建飞; 杨帅

    2015-01-01

    This paper presents the drag reduction mechanism and regime by using hydrofoil and its effect for three types of high speed crafts. Resistance prediction method of full scale is given for planning boat with fore hydrofoil. A numerical model, based on nonlinear vortex lattice method, is developed for hydrodynam-ic prediction of single hydrofoil or its assembly. Numerical results are agree well with the test results. The method presented in this paper can be used for initial design of hydrofoil crafts.%文章介绍了高速艇上水翼减阻的原理以及三种不同类型的高速艇上加装水翼的技术方案及其达到的减阻效果,并给出了滑行艇首部加装水翼(即翼滑艇)后整船阻力的估算方法。基于三维非线性涡格法,建立了单独水翼/水翼组合体/多水翼系统的水动力性能理论计算方法,计算结果与试验结果吻合较好,可作为翼滑艇阻力估算中单独水翼水动力性能的计算方法。算例结果表明,文中的方法可用于单独水翼/水翼组合体/多水翼系统和滑行艇加装减阻水翼的初步技术方案设计。

  15. 新型改性脂肪胺固化剂的合成及其在管道减阻耐磨无溶剂涂料中的应用%Synthesis of A New Modified Aliphatic Amine Curing Agent and Its Application in Abrasion Resistant Solventless Coatings for Pipeline Drag Reduction

    Institute of Scientific and Technical Information of China (English)

    粟鹰; 廖有为; 李芳; 丁武斌

    2012-01-01

    合成了一种新型的改性脂肪胺固化剂,并以此制备了用于天然气管道减阻耐磨的无溶剂涂料。该固化剂赋予涂层优良的机械性能、良好的耐盐雾性和耐化学介质浸泡性。通过电化学阻抗谱对该涂层的耐腐蚀性进行了评价,并对其减阻效果进行了研究。%A abrasion resistant solventless coatings for pipeline drag reduction was prepared by the new modified aliphatic amine curing agent, which was synthesized in this article. The film has excellent mechanical properties, salt fog resistance and chemicals resistance. Through electrochemical impedance spectroscopy, its corrosion resistance was evaluated. And its drag reduction effect was also researched.

  16. Wind Tunnel Experiments to Assess the Effect of Back-Mounted Radio Transmitters on Bird Body Drag

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The aerodynamic drag of bird bodies was measured in a wind tunnel, with and without back-mounted dummy radio transmitters. Flight performance estimates indicate that...

  17. The Research of Drag Reduction Anti-corrosion Coating Technology for Marine Natural Gas Condensed Liquid Pipeline%海洋天然气凝析液管道内壁减阻防腐涂层技术研究

    Institute of Scientific and Technical Information of China (English)

    杜宝银; 李京; 陆卫中; 张晓灵; 郭旭; 高英; 张立新; 吴文通; 杨加栋; 史杰智

    2013-01-01

    According to the service characteristics of marine condensate gas pipeline, determine the development of new two types solvent-free coatings of drag reduction, including technological performance index, test method and test standard of coatings. Through the formula optimization design and pilot-plant test, finally the two types of solvent-free epoxy modified coating are suitable for anti-drag natural gas pipeline at room temperature and for anticorrosion gas liquids pipeline at medium temperature. Coatings were tested by the third party inspection agency, its performance indicators meet the design requirements. And through the field production line applied, the anti-drag and anti-corrosion coatings quality and application had met the needs of the mass production.%根据输送海洋天然气管道凝析液的服役特点,确定了研制新型的无溶剂内减阻防腐涂料的涂层类型、性能指标、检验方法和测试标准。通过配方优化设计和工艺试验,最终研制出了适用于非腐蚀性气体管道输送的常温无溶剂改性环氧涂料以及适用于天然气凝析液管道输送的中温无溶剂改性环氧涂料内减阻涂料。涂料经第三方检测机构检测,其性能及指标符合设计的要求。并通过生产线涂覆工艺的现场实施,内减阻防腐涂层质量和施工工艺满足规模化生产的需要。

  18. DRAG REDUCTION IN TURBULENT FLOWS OVER SUPERHYDROPHOBIC SURFACES WITH MICRO-NANO TEXTURES%微纳结构超疏水表面的湍流减阻机理研究

    Institute of Scientific and Technical Information of China (English)

    卢思; 姚朝晖; 郝鹏飞; 傅承诵

    2013-01-01

    超疏水表面的优异性质使其在现代生活和工业生产中具有十分广泛的潜在应用价值.本文采用了碳纳米管缠绕技术和聚氟硅氧烷疏水化处理方法制备了具有二级微纳米结构的超疏水表面.测量了由该超疏水表面构建的槽道中的流动压降,将其与普通表面构建的槽道内的流动压降进行比较,发现在层流情况下,流动阻力减小最多达到了22.8%.在湍流的情况下,超疏水表面的减阻比例约为53.3%,减阻效果比层流更加明显.利用PIV (particle image velocimetry)技术测量了具有超疏水表面的槽道内的速度场,通过超疏水表面速度滑移和湍动脉动场信息,分析了湍流减阻效果比层流更加明显的物理机制.%The superhydrophobic surfaces have a very wide range of potential applications in the modern life and industrial production due to their excellent properties.In this paper,a kind of superhydrophobic surface was fabricated by pasting micro-nano particles onto an aluminium or PMMA (polymethylmethacrylate)substrate.The micro-nano particles were obtained by carbon nanotubes winding technology and hydrophobic processing.The pressure drop measurements were carried out in the channel with superhydrophobic surfaces above.Compared with the common surface channel,the flow resistance decreases by about 22.8% at most in the laminar flow.In the turbulent flow,the drag reduction can reach 53.3%.The velocity field in the channel with such superhydrophobic surfaces was measured by particle image velocimetry (PIV) technology.Through the slip velocities in the superhydrophobic surface and the turbulent fluctuations,the physical mechanism is revealed to show that the turbulent friction reduction effects are apparently better than in cases of laminar flows.

  19. Ultrafast photon drag detector for intersubband spectroscopy

    Science.gov (United States)

    Sigg, Hans; Graf, Stephan; Kwakernaak, Martin H.; Margotte, Bernd; Erni, Daniel; Van Son, Peter; Köhler, Klaus

    1996-03-01

    The photon drag effect of a 2D electron gas is measured using the ps infrared pulses of the wavelength-tunable free electron laser source FELIX. The pulsed photon drag response is found to depend critically on the coupling characteristics of the electrical circuit. We therefore developed an impedance and velocity matched photon drag detector. It consists of a GaAs/AlGaAs multi quantum well sample which forms an integral part of a microstrip line. A Ge-prism enables incoupling at the critical total reflection angle. This novel transmission line integrated photon drag detector (TIP-detector) generates signal transients below 10 ps rise and fall times. Its continuous spectral response through the intersubband resonance is investigated at room temperature and at T=100 K. An analysis of the spectral lineshape of the photon drag current response yields information about the momentum relaxation times of the electrons in the ground and excited subbands.

  20. Drag bias feedback for the analytic drag control entry guidance system. [for the space shuttle orbiter

    Science.gov (United States)

    Kyle, H. C.

    1976-01-01

    The Analytic Drag Control (ADC) entry guidance has been developed and baselined for the space shuttle orbiter entry. A method is presented which corrects the orbiter entry guidance commanded bank angle for biases between navigated drag and guidance computed reference drag. This is accomplished by an integral feedback technique, which uses the drag bias information to adjust the difference between navigated and reference altitude rate used by the ADC guidance. The method improves the capability of the ADC guidance system by compensating for any error source which causes a bias between the navigated drag and reference drag profile. These errors include navigated altitude rate errors, atmosphere dispersions, and roll attitude deadband effects. A discussion of the method and results of digital computer entry simulations is presented.

  1. Aerodynamic Drag and Gyroscopic Stability

    CERN Document Server

    Courtney, Elya R

    2013-01-01

    This paper describes the effects on aerodynamic drag of rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that a bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by the experiments reported here. Measured ballistic coefficients were compared with gyroscopic stabilities computed using the Miller Twist Rule for nearly solid metal bullets with uniform density and computed using the Courtney-Miller formula for plastic-tipped bullets. The experiments reported here also demonstrate a decrease in aerodynamic drag near Sg = 1.23 +/- 0.02. It is hypothesized that this decrease in drag over a narrow band of Sg values is due to a rapid damping of coning motions (precession and nutation). Observation of this drag decrease at a consistent value of Sg demonstrates the relati...

  2. Research on Drag Torque Prediction Model for the Wet Clutches

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equivalent radius is a function of clutch speed and flow rate. The drag torque achieves its peak at a critical speed. Above this speed, drag torque drops due to the shrinking of the oil film. The model also points out that viscosity and flow rate effects on drag torque. Experimental results indicate that the model is reasonable and it performs well for predicting the drag torque peak.

  3. Flow drag and heat transfer characteristics of drag-reducing nanofluids with CuO nanoparticles

    Science.gov (United States)

    Wang, Ping-Yang; Wang, Xue-Jiao; Liu, Zhen-Hua

    2017-02-01

    A new kind of aqueous CuO nanofluid with drag-reducing performance was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CuO nanoparticles added and has both special effects of drag-reducing and heat transfer enhancement. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube with an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag reducing fluid and new drag-reducing nanofluid. However, their heat transfer characteristics were obvious different. The heat transfer characteristics of the new drag-reducing nanofluid significantly depend on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be applied to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.

  4. Flow drag and heat transfer characteristics of drag-reducing nanofluids with CuO nanoparticles

    Science.gov (United States)

    Wang, Ping-Yang; Wang, Xue-Jiao; Liu, Zhen-Hua

    2016-05-01

    A new kind of aqueous CuO nanofluid with drag-reducing performance was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CuO nanoparticles added and has both special effects of drag-reducing and heat transfer enhancement. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube with an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag reducing fluid and new drag-reducing nanofluid. However, their heat transfer characteristics were obvious different. The heat transfer characteristics of the new drag-reducing nanofluid significantly depend on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be applied to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.

  5. Experimental Investigation of the Effects of Various Plasma Actuator Configurations on Lift and Drag Coefficients of a Circular Cylinder Including the Effects of Electrodes

    Institute of Scientific and Technical Information of China (English)

    Siavash TABATABAEIAN; Masoud MIRZAEI; Asghar SADIGHZADEH; Vahid DAMIDEH; Abdollah SHADARAM

    2012-01-01

    In this paper,the effects of the existence of plasma actuator electrodes and also various configurations of the actuator for controlling the flow field around a circular cylinder are experimentally investigated.The cylinder is made of PVC (Polyvinyl Chloride) and considered as a dielectric barrier.Two electrodes are flush-mounted on the surface of the cylinder and are connected to a DC high voltage power supply for generation of electrical discharge.Pressure distribution results show that the existence of the electrodes and also the plasma are able to change the pressure distribution around the cylinder and consequently the lift and drag coefficients.It is found that the effect of the existence of the electrodes is comparable with the effect of plasma actuator in controlling the flow field around the cylinder and this effect is not reported by other researchers.Eventually it is concluded that the existence of the electrodes or any extra objects on the cylinder and also the existence of the plasma are capable of changing the flow field structure around the cylinder so that the behavior of the lift and drag coefficients of the cylinder will be changed significantly.

  6. Simulation of Effective Slip and Drag in Pressure-Driven Flow on Superhydrophobic Surfaces

    Directory of Open Access Journals (Sweden)

    Yuanding Huang

    2016-01-01

    Full Text Available The flow on superhydrophobic surfaces was investigated using finite element modeling (FEM. Surfaces with different textures like grooves, square pillars, and cylinders immersed in liquid forming Cassie state were modeled. Nonslip boundary condition was assumed at solid-liquid interface while slip boundary condition was supposed at gas-liquid interface. It was found that the flow rate can be affected by the shape of the texture, the fraction of the gas-liquid area, the height of the channel, and the driving pressure gradient. By extracting the effective boundary slip from the flow rate based on a model, it was found that the shape of the textures and the fraction of the gas-liquid area affect the effective slip significantly while the height of the channel and the driving pressure gradient have no obvious effect on effective slip.

  7. 输气管道减阻内涂层与减阻剂应用现状及效益分析%Application and economic benefits of internal drag-reduction coating and DRA in gas pipeline

    Institute of Scientific and Technical Information of China (English)

    张兴水; 曹杰

    2013-01-01

    The paper reviews the advantages and disadvantages of internal drag-reduction coating and DRA used to improve pipeline gas transmission as well as their economic benefit and prospects.The internal drag-reduction coating has been used as a proved technique in long-distance gas pipelines at home and abroad with significant economic benefit,but its application is restricted by some handicaps such as large one-off investment,complex procedures,harsh operating conditions and uncertainty of coating service life.The use of DRA has won great favor due to its simple technology and wide applicability.However,as a technique which would be used in the future,it is still in the phase of research and development.(2 Figures,16 References)%综述了提高天然气管输效率的内涂层法和减阻剂法的经济效益、优势、不足以及应用前景.内涂层法已在国内外长输天然气管道中成熟应用,经济效益明显,但存在一次性投资较大、施工程序复杂、施工条件苛刻,涂层寿命尚不确定等问题;减阻剂法因加注工艺简单、适用性广而备受青睐,但作为管道储备技术尚处于开发研究阶段.(图2,参16)

  8. The physics of orographic gravity wave drag

    Directory of Open Access Journals (Sweden)

    Miguel A C Teixeira

    2014-07-01

    Full Text Available The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.

  9. Effective removal of co-purified inhibitors from extracted DNA samples using synchronous coefficient of drag alteration (SCODA) technology.

    Science.gov (United States)

    Schmedes, Sarah; Marshall, Pamela; King, Jonathan L; Budowle, Bruce

    2013-07-01

    Various types of biological samples present challenges for extraction of DNA suitable for subsequent molecular analyses. Commonly used extraction methods, such as silica membrane columns and phenol-chloroform, while highly successful may still fail to provide a sufficiently pure DNA extract with some samples. Synchronous coefficient of drag alteration (SCODA), implemented in Boreal Genomics' Aurora Nucleic Acid Extraction System (Boreal Genomics, Vancouver, BC), is a new technology that offers the potential to remove inhibitors effectively while simultaneously concentrating DNA. In this initial study, SCODA was tested for its ability to remove various concentrations of forensically and medically relevant polymerase chain reaction (PCR) inhibitors naturally found in tissue, hair, blood, plant, and soil samples. SCODA was used to purify and concentrate DNA from intentionally contaminated DNA samples containing known concentrations of hematin, humic acid, melanin, and tannic acid. The internal positive control (IPC) provided in the Quantifiler™ Human DNA Quantification Kit (Life Technologies, Foster City, CA) and short tandem repeat (STR) profiling (AmpFℓSTR® Identifiler® Plus PCR Amplification Kit; Life Technologies, Foster City, CA) were used to measure inhibition effects and hence purification. SCODA methodology yielded overall higher efficiency of purification of highly contaminated samples compared with the QIAquick® PCR Purification Kit (Qiagen, Valencia, CA). SCODA-purified DNA yielded no cycle shift of the IPC for each sample and yielded greater allele percentage recovery and relative fluorescence unit values compared with the QIAquick® purification method. The Aurora provided an automated, minimal-step approach to successfully remove inhibitors and concentrate DNA from challenged samples.

  10. Frame-Dragging from Charged Rotating Body

    CERN Document Server

    Dubey, Anuj Kumar

    2016-01-01

    In the present paper, we have considered the three parameters: mass, charge and rotation to discuss their combined effect on frame dragging for a charged rotating body. If we consider the ray of light which is emitted radially outward from a rotating body then the frame dragging shows a periodic nature with respect to coordinate $\\phi$ (azimuthal angle). It has been found that the value of frame dragging obtains a maximum at, $ \\phi =\\frac{\\pi}{2}$ and a minimum at $ \\phi =\\frac{3 \\pi}{2}$.

  11. Comparative analysis on temperature reduction effectiveness of ...

    African Journals Online (AJOL)

    The process of urbanization causes alterations in the landscape, affects the ... Five ornamental tree species effectiveness on temperature reduction were ... Keywords: Crown, Climate change, Shading, Temperature, Urban environment ...

  12. Study of Geodesics and the Frame-dragging effect in a Rotating Traversable Wormhole

    CERN Document Server

    Pradhan, Parthapratim

    2016-01-01

    The complete equatorial causal geodesic structure of a rotating traversable wormhole is analyzed and it has been shown that the ISCO (Innermost Stable Circular Orbit) coincides at the throat of the wormhole for the retrograde rotation. By studying the effective potential we also find the radius of the circular photon orbit. The Periastron precession frequency and the nodal precession frequency have been derived for both of the direct and retrograde rotation. Moreover, we derive the exact Lense-Thirring precession frequency of a test gyro for the said wormhole and we show that this frequency is inversely proportional to the angular momentum $(a)$ of the wormhole along the pole in a certain range of $r \\,\\, (r < 16a^2)$ whereas it is directly proportional to the angular momentum of the spacetime for the other compact objects like black holes and pulsars.

  13. Consideration of Zener drag effect by introducing a limiting radius for neighbourhood in grain growth simulation

    Science.gov (United States)

    Maazi, N.; Rouag, N.

    2002-08-01

    A model for grain growth simulation, in the presence of preferential particle distribution, is presented. The model predicts two grain size limits due to second-phase particles. Less than the maximal critical radius the grains will shrink. Greater than the minimal critical radius the grains will grow. Between the two limiting radii no grain growth takes place. These critical radii permit us to introduce the effect of the precipitates directly in the simulation procedure, without their assigning sites in the base matrix. In this case, all sites of the matrix are only occupied by grains. The conditions necessary for the development of secondary recrystallization in textured materials such as Fe-3%Si are, first, the stagnation of normal grain growth, second, the presence of special boundaries around the secondary grains. The grain growth simulation is performed until the grain structure was pinned, i.e. when boundaries become pinned.

  14. Effect of a protruding rod-supported disk on the drag of a nose-controlled cylinder

    Science.gov (United States)

    Mikhalev, A. N.; Podlaskin, A. B.; Tomson, S. G.

    2008-04-01

    The drag C x of a cylinder of diameter D with a front protruding disk supported on a rod of length l has been studied as a function of the relative distance l/D under the conditions of high (supersonic) flight velocities. It is established that the optimum (minimum) drug C x exists, the value of which agrees with the results of numerical simulations.

  15. Rotating cylinder drag balance with application to riblets

    Science.gov (United States)

    Hall, T.; Joseph, D.

    2000-12-01

    Experimental results are reported and discussed for a rotating cylinder drag balance designed to predict drag reduction by surfaces like riblets. The apparatus functions by measuring the torque applied to the inner cylinder by a fluid, such as water, that is set in motion by the controlled rotation of the outer cylinder. The instrument was validated by calibration for laminar flow and comparison of turbulent flow results to the those of G. I. Taylor. The ability to predict drag reduction was demonstrated by testing 114 m symmetric sawtooth riblets, which gave a maximum reduction of about 5% and an overall drag reduction range of 5

  16. Welfare Effects of Tariff Reduction Formulas

    DEFF Research Database (Denmark)

    Guldager, Jan G.; Schröder, Philipp J.H.

    . This paper presents a two country intra-industry trade model with heterogeneous firms subject to high and low tariffs. We examine the welfare effects of applying three different tariff reduction formulas proposed in the literature i) a proportional cut, ii) the Swiss formula and iii) a compression formula...

  17. Welfare Effects of Tariff Reduction Formulas

    DEFF Research Database (Denmark)

    Guldager, Jan G.; Schröder, Philipp J.H.

    . This paper presents a two country intra-industry trade model with heterogeneous firms subject to high and low tariffs. We examine the welfare effects of applying three different tariff reduction formulas proposed in the literature i) a proportional cut, ii) the Swiss formula and iii) a compression formula......WTO negotiations rely on tariff reduction formulas. It has been argued that formula approaches are of increasing importance in trade talks, because of the large number of countries involved, the wider dispersion in initial tariffs (e.g. tariff peaks) and gaps between bound and applied tariff rates....... No single formula dominates for all conditions. The ranking of the three tools depends on the degree of product differentiation in the industry, and the achieved reduction in the average tariff....

  18. Study on Mechanism of Drag Reduction by Core-annular Flow in Transportation of Emulsion Matrix%乳胶基质水环输送的机理研究

    Institute of Scientific and Technical Information of China (English)

    杨佳; 刘寿康

    2012-01-01

    对目前广泛应用于乳化炸药混装车上的水环输送乳胶基质的减阻机理进行了理论分析,分别推导出层流同心水环、湍流同心水环的速度分布与流量计算公式,并得到了从层流到湍流的转捩判据.此外,优化了水环润滑装置结构参数,提出了稳定水环输送的相关措施.%The mechanism of drag reduction by core-annular flow in transportation of emulsion matrix was widely used in the existing mixing-loading truck for emulsion explosive. After theoretical analysis, formulas were deduced respectively to calculate the velocity distribution, flow rate of annular water flow in laminar and turbulent flows. The criterion of transition from laminar flow to turbulent flow was obtained. Furthermore, the optimized parameters and some stabilizing measures are also proposed for core-annular flow device.

  19. Development of Drag Reducing Polymer of FDR-SPC

    Science.gov (United States)

    Lee, Inwon; Park, Hyun; Chun, Ho Hwan

    2015-11-01

    In this study, a novel FDR-SPC (Frictional Drag Reduction Self-Polishing Copolymer) is first synthesized in this study. The drag reducing functional radical such as PEGMA (Poly(ethylene) glycol methacrylate) has been utilized to participate in the synthesis process of the SPC. The release mechanism of drag reducing radical is accounted for the hydrolysis reaction between the FDR-SPC and seawater. The types of the baseline SPC monomers, the molecular weight and the mole fraction of PEGMA were varied in the synthesis process. The resulting SPCs were coated to the substrate plates for the subsequent hydrodynamic test for skin friction measurement. A significant reduction in Reynolds stress was observed in a range of specimen, with the maximum drag reduction being 15.9% relative to the smooth surface for PRD3-1.

  20. Alleviation of fuselage form drag using vortex flows: Final report

    Energy Technology Data Exchange (ETDEWEB)

    Wortman, A.

    1987-09-15

    The concept of using vortex generators to reduce the fuselage form drag of transport aircraft combines the outflow from the plane of symmetry which is induced by the rotational component of the vortex flow with the energization of the boundary layer to reduce the momentum thickness and to delay or eliminate flow separation. This idea was first advanced by the author in 1981. Under a DOE grant, the concept was validated in wind tunnel tests of approximately 1:17 scale models of fuselages of Boeing 747 and Lockheed C-5 aircraft. The search for the minimum drag involved three vortex generator configurations with three sizes of each in six locations clustered in the aft regions of the fuselages at the beginning of the tail upsweep. The local Reynolds number, which is referred to the length of boundary layer run from the nose, was approximately 10{sup 7} so that a fully developed turbulent boundary layer was present. Vortex generator planforms ranged from swept tapered, through swept straight, to swept reverse tapered wings whose semi-spans ranged from 50% to 125% of the local boundary layer thickness. Pitch angles of the vortex generators were varied by inboard actuators under the control of an external proportional digital radio controller. It was found that certain combinations of vortex generator parameters increased drag. However, with certain configurations, locations, and pitch angles of vortex generators, the highest drag reductions were 3% for the 747 and about 6% for the C-5, thus confirming the arguments that effectiveness increases with the rate of upsweep of the tail. Greatest gains in performance are therefore expected on aft loading military transports. 10 refs., 11 figs., 1 tab.

  1. Application and numerical simulation research on biomimetic drag-reducing technology for gas pipelining

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Deyuan; Luo Yuehao; Chen Huawei [Beihang Univ., Beijing (China). School of Mechanical Engineering and Automation

    2011-06-15

    For the purpose of increasing the transmission capacity of gas pipelines, the internal coating technology has been vastly put into application, and a remarkable benefit has been achieved so far. However, with the reduction of wall roughness, the small convex parts are all completely submerged in the viscous sublayer, the gas pipeline becomes a 'hydraulic smooth pipe', even by smoothing the coating surface further, it is difficult to reduce wall friction. Therefore, in order to increase the transportation capacity on the basis of internal coating, the new methods and technologies should be researched and investigated, and perhaps, the biomimetic drag-reducing technology is a good approach. In this paper, according to the planning parameters of the second pipeline of the West-to-East gas transmission project, the best drag reducing effect grooves are calculated and designed, and based on the characteristics and properties of internal coating (AW-01 epoxy resin), the Pre-Cured Micro- Rolling Technology (PCMRT) is discussed and presented, the rolling equipment is also designed and analyzed, the rolling process can be easily added on the available production line. Aiming at the field operating parameters of the gas pipeline in China, and the drag-reducing effect of the grooved surface is analyzed and discussed comprehensively. In addition, the economic benefit of adopting the biomimetic drag reduction technology is investigated. (orig.)

  2. Drag Coefficient and Foam in Hurricane Conditions.

    Science.gov (United States)

    Golbraikh, E.; Shtemler, Y.

    2016-12-01

    he present study is motivated by recent findings of saturation and even decrease in the drag coefficient (capping) in hurricane conditions, which is accompanied by the production of a foam layer on the ocean surface. As it is difficult to expect at present a comprehensive numerical modeling of the drag coefficient saturation that is followed by wave breaking and foam production, there is no complete confidence and understanding of the saturation phenomenon. Our semi-empirical model is proposed for the estimation of the foam impact on the variation of the effective drag coefficient, Cd , with the reference wind speed U10 in stormy and hurricane conditions. The proposed model treats the efficient air-sea aerodynamic roughness length as a sum of two weighted aerodynamic roughness lengths for the foam-free and foam-covered conditions. On the available optical and radiometric measurements of the fractional foam coverage,αf, combined with direct wind speed measurements in hurricane conditions, which provide the minimum of the effective drag coefficient, Cd for the sea covered with foam. The present model yields Cd10 versus U10 in fair agreement with that evaluated from both open-ocean and laboratory measurements of the vertical variation of mean wind speed in the range of U10 from low to hurricane speeds. The present approach opens opportunities for drag coefficient modeling in hurricane conditions and hurricane intensity estimation by the foam-coverage value using optical and radiometric measurements.

  3. Coupling effect between film boiling heat transfer and evaporation drag around a hot-particle in cold liquid

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Yan; YANG Yan-Hua; XU Ji-Jun

    2003-01-01

    Extremely rapid evaporation could occur when high-temperature particles contact withlow-temperature liquid. This kind of phenomenon is associated with the engineering safety and the problems inhigh-transient multi-phase fluid and heat transfer. The aim of our study was to design and build an observable ex-periment facility. The first series of experiments were performed by pouring one or six high-temperature particles intoa low saturated temperature liquid pool. The particle's falling-down speed was recorded by a high-speed camera, thuswe can find the special resistant feature of the moving high-temperature particles, which is induced by the high-speedevaporation surrounding the particles. The study has experimentally verified the theory of evaporation drag model.

  4. Sphere Drag and Heat Transfer.

    Science.gov (United States)

    Duan, Zhipeng; He, Boshu; Duan, Yuanyuan

    2015-07-20

    Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.

  5. Tomographic PIV investigation on coherent vortex structures over shark-skin-inspired drag-reducing riblets

    Science.gov (United States)

    Yang, Shao-Qiong; Li, Shan; Tian, Hai-Ping; Wang, Qing-Yi; Jiang, Nan

    2016-04-01

    Nature has shown us that the microstructure of the skin of fast-swimming sharks in the ocean can reduce the skin friction drag due to the well-known shark-skin effect. In the present study, the effect of shark-skin-inspired riblets on coherent vortex structures in a turbulent boundary layer (TBL) is investigated. This is done by means of tomographic particle image velocimetry (TPIV) measurements in channel flows over an acrylic plate of drag-reducing riblets at a friction Reynolds number of 190. The turbulent flows over drag-reducing riblets are verified by a planar time-resolved particle image velocimetry (TRPIV) system initially, and then the TPIV measurements are performed. Two-dimensional (2D) experimental results with a drag-reduction rate of around 4.81 % are clearly visible over triangle riblets with a peak-to-peak spacing s+ of 14, indicating from the drag-reducing performance that the buffer layer within the TBL has thickened; the logarithmic law region has shifted upward and the Reynolds shear stress decreased. A comparison of the spatial topological distributions of the spanwise vorticity of coherent vortex structures extracted at different wall-normal heights through the improved quadrant splitting method shows that riblets weaken the amplitudes of the spanwise vorticity when ejection (Q2) and sweep (Q4) events occur at the near wall, having the greatest effect on Q4 events in particular. The so-called quadrupole statistical model for coherent structures in the whole TBL is verified. Meanwhile, their spatial conditional-averaged topological shapes and the spatial scales of quadrupole coherent vortex structures as a whole in the overlying turbulent flow over riblets are changed, suggesting that the riblets dampen the momentum and energy exchange between the regions of near-wall and outer portion of the TBL by depressing the bursting events (Q2 and Q4), thereby reducing the skin friction drag.

  6. An Analytical Method for Positioning Drag Anchors in Seabed Soils

    Institute of Scientific and Technical Information of China (English)

    张炜; 刘海笑; 李新仲; 李清平; 曹静

    2015-01-01

    Positioning drag anchors in seabed soils are strongly influenced not only by the properties of the anchor and soil, but also by the characteristics of the installation line. The investigation on the previous prediction methods related to anchor positioning demonstrates that the prediction of the anchor position during dragging has inevitably introduced some key and unsubstantiated hypotheses and the applicability of these methods is limited. In the present study, the interactional system between the drag anchor and installation line is firstly introduced for the analysis of anchor positioning. Based on the two mechanical models for embedded lines and drag anchors, the positioning equations for drag anchors have been derived both for cohesive and noncohesive soils. Since the drag angle at the shackle is the most important parameter in the positioning equations, a novel analytical method that can predict both the variation and the exact value of the drag angle at the shackle is proposed. The analytical method for positioning drag anchors which combines the interactional system between the drag anchor and the installation line has provided a reasonable theoretic approach to investigate the anchor behaviors in soils. By comparing with the model flume experiments, the sensitivity, effectiveness and veracity of the positioning method are well verified.

  7. Low-drag events in transitional wall-bounded turbulence

    Science.gov (United States)

    Whalley, Richard D.; Park, Jae Sung; Kushwaha, Anubhav; Dennis, David J. C.; Graham, Michael D.; Poole, Robert J.

    2017-03-01

    Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 - 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.

  8. Drag Reduction in Oil-water Flows

    OpenAIRE

    Edomwonyi-Otu, L. C.

    2015-01-01

    Liquid-liquid flows occur in many chemical and process industries including the petroleum industry where crude oil and its derivatives are transported over long distances often in mixtures with water. Depending on flow conditions and pipe geometry different flow patterns can appear ranging from fully separated to dispersed ones. The addition of small amounts of some polymeric materials to one of the phases has been found to change the flow patterns and their boundaries and reduce the friction...

  9. Turbulence, Turbulence Control, and Drag Reduction.

    Science.gov (United States)

    1987-08-01

    hed - P’ri,vig (. rf )und. first appeared in (’orrs in & Kis.tler 1 195𔃾). And has, .,rce been repro)duc’ed Finaml tirnes The remarkahl -Aharp...e z. .. a cpri ..ar pipe. of parameter space, where the chief governing para- Pipe :laws, far from being well-,undersleo, * an 77e " t nerers are the

  10. Improvements of evaporation drag model

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Yan; XU Ji-Jun

    2004-01-01

    A special visible experiment facility has been designed and built, and an observable experiment is performed by pouring one or several high-temperature particles into a water pool in the facility. The experiment result has verified Yang's evaporation drag model, which holds that the non-symmetric profile of the local evaporation rate and the local density of vapor would bring about a resultant force on the hot particle so as to resist its motion. However, in Yang's evaporation drag model, radiation heat transfer is taken as the only way to transfer heat from hot particle to the vapor-liquid interface, and all of the radiation energy is deposited on the vapor-liquid interface and contributed to the vaporization rate and mass balance of the vapor film. In improved model heat conduction and heat convection are taken into account. This paper presents calculations of the improved model, putting emphasis on the effect of hot particle's temperature on the radiation absorption behavior of water.

  11. Lift and Drag Measurements of Superhydrophobic Hydrofoils

    Science.gov (United States)

    Sur, Samrat; Kim, Jeong-Hyun; Rothstein, Jonathan

    2015-11-01

    For several years, superhydrophobic surfaces which are chemically hydrophobic with micron or nanometer scale surface features have been considered for their ability to reduce drag and produce slip in microfluidic devices. More recently it has been demonstrated that superhydrophobic surfaces reduce friction coefficient in turbulent flows as well. In this talk, we will consider that modifying a hydrofoil's surface to make it superhydrophobic has on the resulting lift and drag measurements over a wide range of angles of attack. Experiments are conducted over the range of Reynolds numbers between 10,000hydrofoil is made superhydrophobic. The hydrofoils are coated Teflon that has been hot embossed with a 325grit stainless steel woven mesh to produce a regular pattern of microposts. In addition to fully superhydrophobic hydrofoils, selectively coated symmetrical hydrofoils will also be examined to study the effect that asymmetries in the surface properties can have on lift and drag. Partially funded by NSF CBET-1334962.

  12. 高速列车气动阻力地板效应数值研究%Numerical study of ground effects on high speed train aerodynamic drag

    Institute of Scientific and Technical Information of China (English)

    周健; 欧平; 刘沛清; 郭昊

    2016-01-01

    Based on wind tunnel tests of aerodynamic drag on two kinds of 1/25th scale CRH2 models,research of aerodynamic drag with different experimental ground planes was carried out by numerical simulation.The reliability of the numerical methods was verified by comparing the results of simulation and tests.By analyzing the variation of the flow field and resistance distribu-tion on the train body with the usage of the wind tunnel wall,the stationary ground plane,and the moving ground plane in simulation,it is found that:ground effects of different planes have a great influence on the drag measurement of the high speed train;the moving ground plane gives the best simulation performance;the results of drag computed with the other two ground planes are less than that with the moving plane and the difference increases with the increase of the body length,therefore,it is almost impossible to simulate the flow field of the real train operation.Fi-nally the mechanism of influence by ground planes is analyzed and references are provided for drag measurement of high speed train on different ground planes.%针对CRH2型动车组外形,在2种1∶25缩比模型风洞试验基础上,展开基于数值模拟的明线情况高速列车不同地板试验条件阻力测量影响研究。通过与风洞试验结果对比,确定数值方法的可靠性;通过数值模拟风洞壁地板、固定地板、移动地板下高速列车流场分布与阻力变化情况表明,不同试验地板的地面效应对高速列车阻力测量结果影响很大,移动地板模拟效果最佳,固定地板与风洞壁地板阻力测量值小于移动地板情况,且差距随车身长度的增加而增加,很难模拟真实列车运行的流场;通过深入分析不同地板条件的影响机理,为高速列车不同地板条件风洞阻力测量结果提供参考意见。

  13. Application of water jet assisted drag bit and pick cutter for the cutting of coal measure rocks. Final technical report. [Tests of combination in different rocks

    Energy Technology Data Exchange (ETDEWEB)

    Ropchan, D.; Wang, F.D.; Wolgamott, J.

    1980-04-01

    A laboratory investigation was made of the effects of high pressure water jets on the cutting forces of drag bit cutters in sedimentary rocks. A hard and soft sandstone, shale and limestone were tested with commercially obtainable conical and plow type drag bits on the EMI linear cutting machine. About 1200 cuts were made at different bit penetration, jet orientation, and water pressure to determine the reduction of cutting forces on the bit from the use of the water jet. Both independent and interactive cutting was used. The greatest reduction in cutting forces were with both of the sandstones; the drag forces were reduced about 30 percent and the normal forces about 60 percent at 5000 psi water pressure with the nozzle behind the bit. The method was less effective in the shale, except at 10,000 psi water pressure the reduction in drag force was about 55 percent. Of the rocks tested, the limestone was least affected by the water jet. The cutting forces for the plow bit showed continuous change with wear so a machined conical bit was used for most of the testing. Tests with the plow bit did show a large reduction in cutting forces by using the water jet with worn bits. An economic analysis of equipping a drag bit tunnel boring machine indicated that the water jet system could reduce costs per foot in sandstone by up to 40 percent.

  14. Fermi surface versus Fermi sea contributions to intrinsic anomalous and spin Hall effects of multiorbital metals in the presence of Coulomb interaction and spin-Coulomb drag

    Science.gov (United States)

    Arakawa, Naoya

    2016-06-01

    Anomalous Hall effect (AHE) and spin Hall effect (SHE) are fundamental phenomena, and their potential for application is great. However, we understand the interaction effects unsatisfactorily, and should have clarified issues about the roles of the Fermi sea term and Fermi surface term of the conductivity of the intrinsic AHE or SHE of an interacting multiorbital metal and about the effects of spin-Coulomb drag on the intrinsic SHE. Here, we resolve the first issue and provide the first step about the second issue by developing a general formalism in the linear response theory with appropriate approximations and using analytic arguments. The most striking result is that even without impurities, the Fermi surface term, a non-Berry-curvature term, plays dominant roles at high or slightly low temperatures. In particular, this Fermi surface term causes the temperature dependence of the dc anomalous Hall or spin Hall conductivity due to the interaction-induced quasiparticle damping and the correction of the dc spin Hall conductivity due to the spin-Coulomb drag. Those results revise our understanding of the intrinsic AHE and SHE. We also find that the differences between the dc anomalous Hall and longitudinal conductivities arise from the difference in the dominant multiband excitations. This not only explains why the Fermi sea term such as the Berry-curvature term becomes important in clean and low-temperature case only for interband transports, but also provides the useful principles on treating the electron-electron interaction in an interacting multiorbital metal for general formalism of transport coefficients. Several correspondences between our results and experiments are finally discussed.

  15. Gravity Tunnel Drag

    CERN Document Server

    Concannon, Thomas

    2016-01-01

    The time it takes to fall down a tunnel through the center of the Earth to the other side takes approximately 42 minutes, but only when given several simplifying assumptions: a uniform density Earth; a gravitational field that varies linearly with radial position; a non-rotating Earth; a tunnel evacuated of air; and zero friction along the sides of the tunnel. Though several papers have singularly relaxed the first three assumptions, in this paper we relax the final two assumptions and analyze the motion of a body experiencing these types of drag forces in the tunnel. Under such drag forces, we calculate the motion of a transport vehicle through a tunnel of the Earth under uniform density, under constant gravitational acceleration, and finally under the more realistic Preliminary Reference Earth Model (PREM) density data. We find the density profile corresponding to a constant gravitational acceleration better models the motion through the tunnel compared to the PREM density profile, and the uniform density m...

  16. DRAG ON SUBMICRON NANOPARTICLE AGGREGATES

    Institute of Scientific and Technical Information of China (English)

    F.; Einar; Kruis

    2005-01-01

    A new procedure was developed for estimating the effective collision diameter of an aggregate composed of primary particles of any size. The coagulation coefficient of two oppositely charged particles was measured experimentally and compared with classic Fuchs theory, including a new method to account for particle non-sphericity. A second set of experiments were performed on well-defined nanoparticle aggregates at different stages of sintering, i.e. from the aggregate to the fully sintered stage. Here, electrical mobility was used to characterize the particle drag. The aggregates are being built from two different size-fractionated nanoparticle aerosols, the non-aggregated particles are discarded by an electrofilter and then they are passed through a furnace at concentrations low enough not to induce coagulation.

  17. Covariance analysis of differential drag-based satellite cluster flight

    Science.gov (United States)

    Ben-Yaacov, Ohad; Ivantsov, Anatoly; Gurfil, Pini

    2016-06-01

    One possibility for satellite cluster flight is to control relative distances using differential drag. The idea is to increase or decrease the drag acceleration on each satellite by changing its attitude, and use the resulting small differential acceleration as a controller. The most significant advantage of the differential drag concept is that it enables cluster flight without consuming fuel. However, any drag-based control algorithm must cope with significant aerodynamical and mechanical uncertainties. The goal of the current paper is to develop a method for examination of the differential drag-based cluster flight performance in the presence of noise and uncertainties. In particular, the differential drag control law is examined under measurement noise, drag uncertainties, and initial condition-related uncertainties. The method used for uncertainty quantification is the Linear Covariance Analysis, which enables us to propagate the augmented state and filter covariance without propagating the state itself. Validation using a Monte-Carlo simulation is provided. The results show that all uncertainties have relatively small effect on the inter-satellite distance, even in the long term, which validates the robustness of the used differential drag controller.

  18. Study on Pipeline Transport Drag Reduction Technology of CPB based on the Fuller Grading Theory%基于Fuller级配理论的膏体管道输送减阻技术研究

    Institute of Scientific and Technical Information of China (English)

    刘晓辉; 苏先锋; 黄明清; 谭伟

    2016-01-01

    针对膏体充填的物料配比问题,通过分析膏体内部结构的物质组成,提出物料密实度越大膏体流动性越好;采用Fuller理论对某铜矿充填物料的级配特性进行分析,考察了级配指数n随物料配比的变化规律;开展膏体塌落度、流变特性实验,采用白金汉公式对膏体管流阻力进行理论计算。结果表明:该铜矿膏体中全尾砂∶水淬渣=3∶2时,物料密实度较大,最利于其管道输送;质量分数72%,管径150 mm,流量60 m3/h的工况条件下,水淬渣掺量40%时的管流阻力为2.46 MPa/km,与全尾砂膏体管流阻力3.65 MPa/km相比,减阻率达32.6%,说明级配优化后膏体管流阻力明显降低。%Aimed at the question of material ratio of cement paste backfilling (CPB),through analyzing the material composition of the internal structure in CPB,it was proposed that the larger aggregate packing degree is,the better paste flow;The Fuller theory was used to analyze the filling material gradation characteristics of a certain copper mine,and explore the rule of grading index n changing with material ratio. The slump test and rheological experiments of CPB were carried out, and Buckingham formula was adopted to calculate the pipe flow resistance. The results showed that the aggregate packing degree is larger and is most favorable for pipeline transport,when the material ratio with unclassified tailings of water quenching slag as 3of 2. The pipe flow resistance was 2. 46 MPa/km under the conditions of mass fraction 72%,pipe diameter of 150 mm,flow rate of 60m3/h and water quenching slag content 40%. By contrast with the pipe flow resistance of unclassified tailings 3. 65 MPa/km,its drag reduction efficiency reached 32. 6% in pipeline transport. That illustrated that the paste pipe flow resistance is reduced obviously after gradation optimization.

  19. Judicial civil procedure dragging out in Kosovo

    Directory of Open Access Journals (Sweden)

    Rrustem Qehaja

    2016-03-01

    Full Text Available This article tends to deal with one of the most worrying issues in the judicial system of Kosovo the problem of judicial civil procedure dragging out. The article analyses the reasons of these dragging outs of the judicial civil procedure focusing on the context of one of the basic procedural principles in civil procedure-the principle of economy or efficiency in the courts. Dragging out of civil procedure in Kosovo has put in question not only the basic principles of civil procedure, but it also challenges the general principles related to human rights and freedoms sanctioned not only by the highest legal act of the country, but also with international treaties. The article tends to give a reflection to the most important reasons that effect and influence in these dragging outs of civil procedure, as well as, at the same time aims to give the necessary alternatives to pass through them by identifying dilemmas within the judicial practice. As a result, the motives of this scientific paper are exactly focused at the same time on identifying the dilemmas, as well as presenting ideas, to overstep them, including the judicial practice of the European Court of Human Rights on Article 6 of the European Convention on Human Rights, by which it is given the possibility to offering people efficient and within a reasonable time legal protection of their rights before national courts. For these reasons, the paper elaborates this issue based on both, the legal theory and judicial practice.

  20. When superfluids are a drag

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, David C [Los Alamos National Laboratory

    2008-01-01

    The article considers the dramatic phenomenon of seemingly frictionless flow of slow-moving superfluids. Specifically the question of whether an object in a superfluid flow experiences any drag force is addressed. A brief account is given of the history of this problem and it is argued that recent advances in ultracold atomic physics can shed much new light on this problem. The article presents the commonly held notion that sufficiently slow-moving superfluids can flow without drag and also discusses research suggesting that scattering quantum fluctuations might cause drag in a superfluid moving at any speed.

  1. Pressure effect on dissimilatory sulfate reduction

    Science.gov (United States)

    Williamson, A. J.; Carlson, H. K.; Coates, J. D.

    2015-12-01

    Biosouring is the production of H2S by sulfate reducing microorganisms (SRM) in-situ or in the produced fluids of oil reservoirs. Sulfide is explosive, toxic and corrosive which can trigger equipment and transportation failure, leading to environmental catastrophe. As oil exploration and reservoir development continue, subsequent enhanced recovery is occurring in progressively deeper formations and typical oil reservoir pressures range from 10-50 MPa. Therefore, an understanding of souring control effects will require an accurate understanding of the influence of pressure on SRM metabolism and the efficacy of souring control treatments at high pressure. Considerable work to date has focussed on souring control at ambient pressure; however, the influence of pressure on biogeochemical processes and souring treatments in oil reservoirs is poorly understood. To explore the impact of pressure on SRM, wild type Desulfovibrio alaskensis G20 (isolated from a producing oil well in Ventura County, California) was grown under a range of pressures (0.1-14 MPa) at 30 °C. Complete sulfate reduction occurred in all pressures tested within 3 days, but microbial growth was inhibited with increasing pressure. Bar-seq identified several genes associated with flagella biosynthesis (including FlhB) and assembly as important for survival at elevated pressure and fitness was confirmed using individual transposon mutants. Flagellar genes have previously been implicated with biofilm formation and confocal microscopy on glass slides incubated with wild type D. alaskensis G20 showed more biomass associated with surfaces under pressure, highlighting the link between pressure, flagellar and biofilm formation. To determine the effect of pressure on the efficacy of SRM inhibitors, IC50 experiments were conducted and D. alaskensis G20 showed a greater resistance to nitrate and the antibiotic chloramphenicol, but a lower resistance to perchlorate. These results will be discussed in the context of

  2. A Clustering Genetic Algorithm for Cylinder Drag Optimization

    Science.gov (United States)

    Milano, Michele; Koumoutsakos, Petros

    2002-01-01

    A real coded genetic algorithm is implemented for the optimization of actuator parameters for cylinder drag minimization. We consider two types of idealized actuators that are allowed either to move steadily and tangentially to the cylinder surface (“belts”) or to steadily blow/suck with a zero net mass constraint. The genetic algorithm we implement has the property of identifying minima basins, rather than single optimum points. The knowledge of the shape of the minimum basin enables further insights into the system properties and provides a sensitivity analysis in a fully automated way. The drag minimization problem is formulated as an optimal regulation problem. By means of the clustering property of the present genetic algorithm, a set of solutions producing drag reduction of up to 50% is identified. A comparison between the two types of actuators, based on the clustering property of the algorithm, indicates that blowing/suction actuation parameters are associated with larger tolerances when compared to optimal parameters for the belt actuators. The possibility of using a few strategically placed actuators to obtain a significant drag reduction is explored using the clustering diagnostics of this method. The optimal belt-actuator parameters obtained by optimizing the two-dimensional case is employed in three-dimensional simulations, by extending the actuators across the span of the cylinder surface. The three-dimensional controlled flow exhibits a strong two-dimensional character near the cylinder surface, resulting in significant drag reduction.

  3. Cyclist drag in team pursuit: influence of cyclist sequence, stature, and arm spacing.

    Science.gov (United States)

    Defraeye, Thijs; Blocken, Bert; Koninckx, Erwin; Hespel, Peter; Verboven, Pieter; Nicolai, Bart; Carmeliet, Jan

    2014-01-01

    In team pursuit, the drag of a group of cyclists riding in a pace line is dependent on several factors, such as anthropometric characteristics (stature) and position of each cyclist as well as the sequence in which they ride. To increase insight in drag reduction mechanisms, the aerodynamic drag of four cyclists riding in a pace line was investigated, using four different cyclists, and for four different sequences. In addition, each sequence was evaluated for two arm spacings. Instead of conventional field or wind tunnel experiments, a validated numerical approach (computational fluid dynamics) was used to evaluate cyclist drag, where the bicycles were not included in the model. The cyclist drag was clearly dependent on his position in the pace line, where second and subsequent positions experienced a drag reduction up to 40%, compared to an individual cyclist. Individual differences in stature and position on the bicycle led to an intercyclist variation of this drag reduction at a specific position in the sequence, but also to a variation of the total drag of the group for different sequences. A larger drag area for the group was found when riding with wider arm spacing. Such numerical studies on cyclists in a pace line are useful for determining the optimal cyclist sequence for team pursuit.

  4. Fabrication of a micro through-hole array by gas-blowing a PDMS-treated polyamide screen for a flexible drag-reducing skin-like device

    Science.gov (United States)

    Li, Yong; Zhou, Kai; Zhao, Xiang; Kong, Quancun

    2017-01-01

    We propose a method for fabricating a flexible skin-like device for generating and trapping micro bubbles with the aim of reducing underwater drag. This low-cost, efficient, high-pressure gas-blow method is used to fabricate a micro through-hole array in a flexible polydimethylsiloxane (PDMS) gel-based skin. The key parameters in the gas-blowing method are investigated, such as the viscosity of PDMS and the blowing pressure in order to optimize the quality of through-hole layer. Deviation of the linear dimensions of the obtained micro holes was less than 4.5%. In addition, multiphase computational fluid dynamics models were built to analyze the drag-reduction performance of bell-shaped holes made by this method. Compared with cylindrical through holes produced by molding, the drag-reduction effect of bell-shaped holes increased as much as 34%.

  5. Effect of tail size reductions on longitudinal aerodynamic characteristics of a three surface F-15 model with nonaxisymmetric nozzles

    Science.gov (United States)

    Frassinelli, Mark C.; Carson, George T., Jr.

    1990-01-01

    An investigation was conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of horizontal and vertical tail size reductions on the longitudinal aerodynamic characteristics of a modified F-15 model with canards and 2-D convergent-divergent nozzles. Quantifying the drag decrease at low angles of attack produced by tail size reductions was the primary focus. The model was tested at Mach numbers of 0.40, 0.90, and 1.20 over an angle of attack of -2 degree to 10 degree. The nozzle exhaust flow was simulated using high pressure air at nozzle pressure ratios varying from 1.0 (jet off) to 7.5. Data were obtained on the baseline configuration with and without tails as well as with reduced horizontal and/or vertical tail sizes that were 75, 50, and 25 percent of the baseline tail areas.

  6. Experimental investigation of drag coefficients of gobi surfaces

    Institute of Scientific and Technical Information of China (English)

    董治宝; 屈建军; 刘小平; 张伟民; 王训明

    2002-01-01

    The response of gobi surfaces to the near-surface air flow can be characterized quantitatively by drag coefficients. By using wind tunnel tests, an attempt is made to define the relationship between the drag coefficients of gobi surfaces and gravel size and coverage. It is concluded that the drag coefficients of gobi surfaces tend to be constants when gravel coverage is over 40%-50%. Consequently, we think that the gobi deflation planes expanding vastly in the arid Northwestern China are aerodynamically stable, at least not the supplying sources of current dust storms, and therefore the emphasis on dust storm control should be paid on the so-called "earth gobi" that has low gravel coverage. The prediction model for drag coefficients of gobi surfaces has been developed by regressing drag coefficients on gravel size and coverage, the predicted results are in reasonably good agreement with wind tunnel results (R 2 = 0.94). The change of drag coefficients with gravel friction Reynolds number implies that the development extent of drag effect increases with gravel size and coverage.

  7. DOE Project on Heavy Vehicle Aerodynamic Drag FY 2005 Annual Report

    Energy Technology Data Exchange (ETDEWEB)

    McCallen, R C; Salari, K; Ortega, J; Castellucci, P; Eastwood, C; Paschkewitz, J; Pointer, W D; DeChant, L J; Hassan, B; Browand, F; Radovich, C; Merzel, T; Plocher, D; Ross, J; Storms, B; Heineck, J T; Walker, S; Roy, C J

    2005-11-14

    Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At high way speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; and (2) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices.

  8. Satellite Formation Control Using Atmospheric Drag

    Science.gov (United States)

    2007-03-01

    all cases tested, and the eccentricity-minimizing control law was able to maintain the position within 4.17 feet. More recently, Wedekind considered...three different formations, in-plane, in-track, and circular, was considered. Wedekind achieved favorable results for these three formations when the...and Kluwer Academic Publishers, 2004. 23. Wedekind , James T. Characterizing and Controlling the Effects of Differential Drag on Satellite Formations

  9. Optical and electrical properties and phonon drag effect in low temperature TEP measurements of AgSbSe2 thin films

    Science.gov (United States)

    Namitha Asokan, T.; Urmila, K. S.; Jacob, Rajani; Reena Philip, Rachel; Okram, G. S.; Ganesan, V.; Pradeep, B.

    2014-05-01

    Polycrystalline thin films of silver antimony selenide have been deposited using a reactive evaporation technique onto an ultrasonically cleaned glass substrate at a vacuum of 10-5 torr. The preparative parameters, like substrate temperature and incident fluxes, have been properly controlled in order to get stoichiometric, good quality and reproducible thin film samples. The samples are characterized by XRD, SEM, AFM and a UV—vis—NIR spectrophotometer. The prepared sample is found to be polycrystalline in nature. From the XRD pattern, the average particle size and lattice constant are calculated. The dislocation density, strain and number of crystallites per unit area are evaluated using the average particle size. The dependence of the electrical conductivity on the temperature has also been studied and the prepared AgSbSe2 samples are semiconducting in nature. The AgSbSe2 thin films exhibited an indirect allowed optical transition with a band gap of 0.64 eV. The compound exhibits promising thermoelectric properties, a large Seebeck coefficient of 30 mV/K at 48 K due to strong phonon electron interaction. It shows a strong temperature dependence on thermoelectric properties, including the inversion of a dominant carrier type from p to n over a low temperature range 9-300 K, which is explained on the basis of a phonon drag effect.

  10. Electromagnetically-Induced Frame-Dragging around Astrophysical Objects

    CERN Document Server

    Ruiz, Andrés F Gutiérrez

    2015-01-01

    Frame dragging (Lense-Thirring effect) is generally associated with rotating astrophysical objects. However, it can also be generated by electromagnetic fields if electric and magnetic fields are simultaneously present. In most models of astrophysical objects, macroscopic charge neutrality is assumed and the entire electromagnetic field is characterized in terms of a magnetic dipole component. Hence, the purely electromagnetic contribution to the frame dragging vanishes. However, strange stars may posses independent electric dipole and neutron stars independent electric quadrupole moments that may lead to the presence of purely electromagnetic contributions to the frame dragging. Moreover, recent observations have shown that in stars with strong electromagnetic fields, the magnetic quadrupole may have a significant contribution to the dynamics of stellar processes. As an attempt to characterized and quantify the effect of electromagnetic frame-dragging in this kind of astrophysical objects, an analytic soluti...

  11. Grafted natural polymer as new drag reducing agent: An experimental approach

    Directory of Open Access Journals (Sweden)

    Abdulbari Hayder A.

    2012-01-01

    Full Text Available The present investigation introduces a new natural drag reducing agent which has the ability to improve the flow in pipelines carrying aqueous or hydrocarbon liquids in turbulent flow. Okra (Abelmoschus esculentus mucilage drag reduction performance was tested in water and hydrocarbon (gas-oil media after grafting. The drag reduction test was conducted in a buildup closed loop liquid circulation system consists of two pipes 0.0127 and 0.0381 m Inside Diameter (ID, four testing sections in each pipe (0.5 to 2.0 m, tank, pump and pressure transmitters. Reynolds number (Re, additive concentration and the transported media type (water and gas-oil, were the major drag reduction variables investigated. The experimental results show that, new additive drag reduction ability is high with maximum percentage of drag reduction (%Dr up to 60% was achieved. The experimental results showed that the drag reduction ability increased by increasing the additive concentration. The %Dr was found to increase by increasing the Re by using the water-soluble additive while it was found to decrease by increasing the Re when using the oil-soluble additive. The %Dr was higher in the 0.0381 m ID pipe. Finally, the grafted and natural mucilage showed high resistance to shear forces when circulated continuously for 200 seconds in the closed-loop system.

  12. Effective Image Database Search via Dimensionality Reduction

    DEFF Research Database (Denmark)

    Dahl, Anders Bjorholm; Aanæs, Henrik

    2008-01-01

    Image search using the bag-of-words image representation is investigated further in this paper. This approach has shown promising results for large scale image collections making it relevant for Internet applications. The steps involved in the bag-of-words approach are feature extraction......, vocabulary building, and searching with a query image. It is important to keep the computational cost low through all steps. In this paper we focus on the efficiency of the technique. To do that we substantially reduce the dimensionality of the features by the use of PCA and addition of color. Building....... In the query step, features from the query image are assigned to the visual vocabulary. The dimensionality reduction enables us to do exact feature labeling using kD-tree, instead of approximate approaches normally used. Despite the dimensionality reduction to between 6 and 15 dimensions we obtain improved...

  13. Prescription grazing and waterfowl nest dragging : Their effects on neotropical birds : A four year report : Audubon Complex

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — In 1990 a ten year monitoring program on Audubon National Wildlife Refuge and Audubon Wetland Management District was initiated to study wildlife effects on the...

  14. Drag/thrust analysis of jet-propelled transonic transport aircraft; definition of physical drag components

    Energy Technology Data Exchange (ETDEWEB)

    Destarac, D. [Office National d' Etudes et de Recherches Aerospatiales (ONERA), 92 - Chatillon (France); Van der Vooren, J. [Senior research scientist, retired, Hoekse Waard (Netherlands)

    2004-09-01

    Drag/thrust analysis of jet-propelled transonic transport aircraft on the basis of calculated viscous flow is discussed. Unique definitions for viscous drag plus wave drag and for induced drag are established. The concept of additive through flow drag is introduced. Drag/thrust bookkeeping is given attention. All drag components can be calculated in the flow region adjacent to the aircraft, where numerical accuracy is expectingly highest. Uniform handling of complex aircraft configurations is brought within reach. Near-field/far-field drag balances are exact. Computational aspects are discussed, in particular the elimination of spurious drag sources. Numerical examples are given for a wing-body and for a wing-body-pylon-nacelle configuration. In either case, the spurious drag sources are eliminated. Acceptable agreement is obtained for the total drag in the first case, and for the installation drag in the second case. Extension of the analysis presented to propeller-driven transport aircraft is straightforward. (author)

  15. Effective randomness, strong reductions and Demuth's theorem

    CERN Document Server

    Bienvenu, Laurent

    2011-01-01

    We study generalizations of Demuth's Theorem, which states that the image of a Martin-L\\"of random real under a tt-reduction is either computable or Turing equivalent to a Martin-L\\"of random real. We show that Demuth's Theorem holds for Schnorr randomness and computable randomness (answering a question of Franklin), but that it cannot be strengthened by replacing the Turing equivalence in the statement of the theorem with wtt-equivalence. We also provide some additional results about the Turing and tt-degrees of reals that are random with respect to some computable measure.

  16. Modelling LARES temperature distribution and thermal drag

    CERN Document Server

    Nguyen, Phuc H

    2015-01-01

    The LARES satellite, a laser-ranged space experiment to contribute to geophysics observation, and to measure the general relatistic Lense-Thirring effect, has been observed to undergo an anomalous along-track orbital acceleration of -$0.4\\ pm/s^2$ (pm := picometer). This "drag" is not surprising; along track drag has previously been observed with the related LAGEOS satellites (-$3.4\\ pm/s^2$). It is hypothesized that the drag is due to anisotropic thermal radiation from the satellite's exterior. We report the results of numerical computations of the along-track orbital decay of the LARES satellite during the first 105 days after launch. The results depend to a significant degree on the visual and IR absorbance $\\alpha$ and emissivity $\\epsilon$ of the fused silica cube-cornered laser retroreflectors (CCRs). We present results for two values of $\\alpha_{IR}$ = $\\epsilon_{IR}$: 0.82, a standard number for "clean" fused silica; and 0.60, a possible value for silica with slight surface contamination subjected to ...

  17. Drag prediction method of powered-on civil aircraft based on thrust drag bookkeeping

    Directory of Open Access Journals (Sweden)

    Zhang Yufei

    2015-08-01

    Full Text Available A drag prediction method based on thrust drag bookkeeping (TDB is introduced for civil jet propulsion/airframe integration performance analysis. The method is derived from the control volume theory of a powered-on nacelle. Key problem of the TDB is identified to be accurate prediction of velocity coefficient of the powered-on nacelle. Accuracy of CFD solver is validated by test cases of the first AIAA Propulsion Aerodynamics Workshop. Then the TDB method is applied to thrust and drag decomposing of a realistic aircraft. A linear relation between the computations assumed free stream Mach number and the velocity coefficient result is revealed. The thrust losses caused by nozzle internal drag and pylon scrubbing are obtained by the isolated nacelle and mapped on to the in-flight whole configuration analysis. Effects of the powered-on condition are investigated by comparing through-flow configuration with powered-on configuration. The variance on aerodynamic coefficients and pressure distribution is numerically studied.

  18. The Effect of Polar Vortex Disturbances on Mesopause Gravity Wave Drag in Relation to Mesopause Pole-to-Pole Coupling

    Science.gov (United States)

    de Wit, R.; Hibbins, R. E.; Espy, P. J.

    2014-12-01

    Gravity waves (GWs) play an important role in the dynamics of the mesosphere/lower thermosphere (MLT) region, linking the lower to the upper atmosphere. GW filtering by the background zonal wind is furthermore believed to be the fundamental mechanism coupling the winter stratosphere to the summer polar mesopause, in which increased planetary wave (PW) activity in the former is related to enhanced temperatures in the latter through a chain of global MLT temperature anomalies. During major Sudden Stratospheric Warmings (SSWs) the interaction between PWs and the background flow leads to increased polar stratospheric temperatures and a reversal of the climatological winds from eastward to westward. As a result, large changes in GW filtering conditions occur, making SSWs an excellent tool to empirically test the inter-hemispheric coupling mechanism. In this study, mesopause GW forcing derived from meteor radar observations over Trondheim, Norway (63°N, 10°E) during the January 2013 major SSW is discussed in light of the polar vortex strength and selective filtering conditions over the same location to show the coupling between the polar winter stratosphere and MLT. Global temperature observations obtained with the Aura Microwave Limb Sounder (MLS) are subsequently used to study the temperature signature of the SSW in the MLT region over the winter pole in relation to the observed GW forcing. Furthermore, the temperature effect of the SSW throughout the middle atmosphere is tracked, away from the winter pole toward the summer pole, and compared to the temperature structure expected from the inter-hemispheric coupling mechanism.

  19. Time Resolved PIV Investigation on the Skin Friction Reduction Mechanism of Outer-Layer Vertical Blades Array

    Directory of Open Access Journals (Sweden)

    Seong Hyeon Park

    2015-02-01

    Full Text Available The drag reducing efficiency of the outer-layer vertical blades, which were first devised by Hutchins (2003, have been demonstrated by the recent towing tank measurements. From the drag measurement of flat plate with various vertical blades arrays by Park et al. (2011, a maximum 9.6% of reduction of total drag was achieved. The scale of blade geometry is found to be weakly correlated with outer variable of boundary layer. The drag reduction of 2.8% has been also confirmed by the model ship test by An et al. (2014. With a view to enabling the identification of drag reduction mechanism of the outer-layer vertical blades, detailed flow field measurements have been performed using 2D time resolved PIV in this study. It is found that the skin friction reduction effect is varied according to the spanwise position, with 2.73% and 7.95% drag reduction in the blade plane and the blade-in-between plane, respectively. The influence of vertical blades array upon the characteristics of the turbulent coherent structures was analyzed by POD method. It is observed that the vortical structures are cut and deformed by blades array and the skin frictional reduction is closely associated with the subsequent evolution of turbulent structures.

  20. Systemic cost-effectiveness analysis of food hazard reduction

    DEFF Research Database (Denmark)

    Jensen, Jørgen Dejgård; Lawson, Lartey Godwin; Lund, Mogens

    2015-01-01

    stage are considered. Cost analyses are conducted for different risk reduction targets and for three alternative scenarios concerning the acceptable range of interventions. Results demonstrate that using a system-wide policy approach to risk reduction can be more cost-effective than a policy focusing...

  1. Effects of over-expression of the regulatory enzymes DraT and DraG on the ammonium-dependent post-translational regulation of nitrogenase reductase in Azospirillum brasilense.

    Science.gov (United States)

    Huergo, Luciano F; Souza, Emanuel M; Steffens, Maria B R; Yates, M Geoffrey; Pedrosa, Fábio O; Chubatsu, Leda S

    2005-03-01

    Nitrogen fixation in Azospirillum brasilense is regulated at transcriptional and post-translational levels. Post-translational control occurs through the reversible ADP-ribosylation of dinitrogenase reductase (Fe Protein), mediated by the dinitrogenase reductase ADP-ribosyltransferase (DraT) and dinitrogenase reductase glycohydrolase (DraG). Although the DraT and DraG activities are regulated in vivo, the molecules responsible for such regulation remain unknown. We have constructed broad-host-range plasmids capable of over-expressing, upon IPTG induction, the regulatory enzymes DraT and DraG as six-histidine-N-terminal fused proteins (His). Both DraT-His and DraG-His are functional in vivo. We have analyzed the effects of DraT-His and DraG-His over-expression on the post-translational modification of Fe Protein. The DraT-His over-expression led to Fe Protein modification in the absence of ammonium addition, while cells over-expressing DraG-His showed only partial ADP-ribosylation of Fe Protein by adding ammonium. These results suggest that both DraT-His and DraG-His lose their regulation upon over-expression, possible by titrating out negative regulators.

  2. Coulomb drag in the mesoscopic regime

    DEFF Research Database (Denmark)

    Mortensen, N.A.; Flensberg, Karsten; Jauho, Antti-Pekka

    2002-01-01

    We present a theory for Coulomb drag between two mesoscopic systems which expresses the drag in terms of scattering matrices and wave functions. The formalism can be applied to both ballistic and disordered systems and the consequences can be studied either by numerical simulations or analytic...... average drag for chaotic 2D-systems and dominating fluctuations of drag between quasi-ballistic wires with almost ideal transmission....

  3. Drag of a D-shaped bluff body under small amplitude harmonic actuation

    Directory of Open Access Journals (Sweden)

    Yaqing Li

    2015-01-01

    Full Text Available Open-loop flow control method was used to affect the development of a turbulent wake behind a D-shaped bluff body. Loud speakers were embedded inside the bluff body to produce two zero-net-mass-flux jets through 2 mm-wide span-wise slots located along the upper and lower edges on the rear wall. The drag forces for different actuation amplitudes (Cμ, the ratio between the momentum of the actuating jets and the moment deficit caused by the bluff body and frequencies (StA were examined. The effects of the phase difference in the two jets (0 and π were also studied. It was found that when Cμ was 0.1%, a drag reduction up to 5% was achieved when the velocities of the two jets varied in phase at a frequency of StA=0.16. When the velocities of the two jets varied π out of phase, significant drag increase was observed.

  4. On the Zener drag

    Science.gov (United States)

    Nes, E.; Ryum, N.; Hunderi, O.

    1985-01-01

    The interaction between particles and a grain boundary is investigated analytically, with attention given to the interaction between a single particle and a grain boundary and to the calculation of a restraining force from many particles on a grain boundary. The results of the analysis are fully consistent with the estimate of Zener and Smith (1984). It is noted that the effects of particle shape and distribution are more important factors than the effect of the nature of the particle interface and that such effects can strongly influence recrystallization and grain growth behavior.

  5. The flow around a macroscopical body by a colloid solution and the drag crisis

    CERN Document Server

    Iordanski, S V

    2013-01-01

    The motion of colloids in the flow field of a viscous liquid is investigated. The small colloid size compare to the macroscopical scale of the flow allow to calculate their velocity relative to that of the liquid. If the inner colloid density is larger then the density of the liquid the flow field has the domains where the colloid velocity is close to the liquid velocity. But in the domains with a strong braking of the liquid velocity the colloids are accelerated relative to the liquid. This effect is used for the qualitative explanation of the drag reduction in the flow around macroscopical bodies and in the pipes.

  6. Effect of reduction of anticonvulsants on wellbeing.

    Science.gov (United States)

    Fischbacher, E

    1982-01-01

    An attempt was made over a period of a year to reduce the number of anticonvulsants used to treat epilepsy in a hospital for the mentally handicapped. At least one drug was withdrawn for each of 20 patients, without loss of seizure control. Effect on wellbeing was assessed by a behavioural scale completed before and after withdrawal, and in the 20 cases of successful withdrawal wellbeing was significantly improved. PMID:6809110

  7. Coulomb drag in coherent mesoscopic systems

    DEFF Research Database (Denmark)

    Mortensen, Niels Asger; Flensberg, Karsten; Jauho, Antti-Pekka

    2001-01-01

    , such as the random matrix theory, or by numerical simulations. We show that Coulomb drag is sensitive to localized states, which usual transport measurements do not probe. For chaotic 2D systems we find a vanishing average drag, with a nonzero variance. Disordered 1D wires show a finite drag, with a large variance......We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both ballistic and disordered systems. The consequences can be worked out either by analytic means...

  8. Gravitational Capture of Asteroids by Gas Drag

    Directory of Open Access Journals (Sweden)

    E. Vieira Neto

    2009-01-01

    captured by the planet got its velocity reduced and could been trapped as an irregular satellite. It is well known that, depending on the time scale of the gas envelope, an asteroid will spiral and collide with the planet. So, we simulate the passage of the asteroid in the gas envelope with its density decreasing along the time. Using this approach, we found effective captures, and have a better understanding of the whole process. Finally, we conclude that the origin of the irregular satellites cannot be attributed to the gas drag capture mechanism alone.

  9. Study on Rural Poverty Reduction Effect of Traffic Infrastructure

    Institute of Scientific and Technical Information of China (English)

    Junping; GUO; Bin; ZHANG; Xiyan; ZHANG

    2014-01-01

    To systematically comb and explore the rural poverty reduction effect of traffic infrastructure,the author analyzed the mechanism,main channels and actual effect of rural traffic infrastructure on poverty reduction.It revealed that rural traffic infrastructure exerts positive or negative effect on poverty reduction directly or indirectly.The positive channel includes increasing non-agricultural employment opportunities,reducing costs for agricultural production,transportation and labor transfer,increasing availability of social service,and promoting adjustment of agricultural industrial structure and development of rural tourism resources.On the whole,traffic infrastructure has significant positive influence on rural poverty reduction.Finally,it summarized policy recommendations for building pro-poor traffic infrastructure,and came up with vacancy of related research field and future exploration direction.

  10. Effect of Nature of Coal on Carbothermal Reduction of Barites

    Directory of Open Access Journals (Sweden)

    Jyotsna Agarwal

    2014-09-01

    Full Text Available The paper reports the effect of nature of coal on the carbothermal reduction of barite by using different types of coal. Usually in industrial practices, the reductive operations are carried out by using any type of cheap and easily available coal, but the extent of reduction rarely exceeds 35-40%. After admixing the steam coal in matrix, yields have been found to increase to the order of 51 to 53%. The obtained results prove to be quite economical in industrial practices.

  11. Nonlocal Drag of Magnons in a Ferromagnetic Bilayer

    Science.gov (United States)

    Liu, Tianyu; Vignale, G.; Flatté, Michael E.

    2016-06-01

    Quantized spin waves, or magnons, in a magnetic insulator are assumed to interact weakly with the surroundings, and to flow with little dissipation or drag, producing exceptionally long diffusion lengths and relaxation times. In analogy to Coulomb drag in bilayer two-dimensional electron gases, in which the contribution of the Coulomb interaction to the electric resistivity is studied by measuring the interlayer resistivity (transresistivity), we predict a nonlocal drag of magnons in a ferromagnetic bilayer structure based on semiclassical Boltzmann equations. Nonlocal magnon drag depends on magnetic dipolar interactions between the layers and manifests in the magnon current transresistivity and the magnon thermal transresistivity, whereby a magnon current in one layer induces a chemical potential gradient and/or a temperature gradient in the other layer. The largest drag effect occurs when the magnon current flows parallel to the magnetization; however, for oblique magnon currents a large transverse current of magnons emerges. We examine the effect for practical parameters, and find that the predicted induced temperature gradient is readily observable.

  12. Electron and phonon drag in thermoelectric transport through coherent molecular conductors

    DEFF Research Database (Denmark)

    Lü, Jing-Tao; Wang, Jian-Sheng; Hedegård, Per

    2016-01-01

    there are at least two phonon degrees of freedom. After deriving expressions for the linear drag coefficients, obeying the Onsager relation, we further investigate their effect on nonequilibrium transport. We show that the drag effect is closely related to two other phenomena: (1) adiabatic charge pumping through...

  13. Drag characteristics of competitive swimming children and adults.

    Science.gov (United States)

    Kjendlie, Per-Ludvik; Stallman, Robert Keig

    2008-02-01

    The aims of this study were to compare drag in swimming children and adults, quantify technique using the technique drag index (TDI), and use the Froude number (Fr) to study whether children or adults reach hull speed at maximal velocity (vmax). Active and passive drag was measured by the perturbation method and a velocity decay method, respectively, including 9 children aged 11.7+/-0.8 and 13 adults aged 21.4+/-3.7. The children had significantly lower active (kAD) and passive drag factor (kPD) compared with the adults. TDI (kAD/kPD) could not detect any differences in swimming technique between the two groups, owing to the adults swimming maximally at a higher Fr, increasing the wave drag component, and masking the effect of better technique. The children were found not to reach hull speed at vmax, and their Fr were 0.37+/-0.01 vs. the adults 0.42+/-0.01, indicating adults' larger wave-making component of resistance at vmax compared with children. Fr is proposed as an evaluation tool for competitive swimmers.

  14. Summary of the Fourth AIAA CFD Drag Prediction Workshop

    Science.gov (United States)

    Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Rider, Ben; Zickuhr, Tom; Levy, David W.; Brodersen, Olaf P.; Eisfeld, Bernhard; Crippa, Simone; Wahls, Richard A.; Morrison, Joseph H.; Mavriplis, Dimitri J.; Murayama, Mitcuhiro

    2010-01-01

    Results from the Fourth AIAA Drag Prediction Workshop (DPW-IV) are summarized. The workshop focused on the prediction of both absolute and differential drag levels for wing-body and wing-body-horizontal-tail configurations that are representative of transonic transport air- craft. Numerical calculations are performed using industry-relevant test cases that include lift- specific flight conditions, trimmed drag polars, downwash variations, dragrises and Reynolds- number effects. Drag, lift and pitching moment predictions from numerous Reynolds-Averaged Navier-Stokes computational fluid dynamics methods are presented. Solutions are performed on structured, unstructured and hybrid grid systems. The structured-grid sets include point- matched multi-block meshes and over-set grid systems. The unstructured and hybrid grid sets are comprised of tetrahedral, pyramid, prismatic, and hexahedral elements. Effort is made to provide a high-quality and parametrically consistent family of grids for each grid type about each configuration under study. The wing-body-horizontal families are comprised of a coarse, medium and fine grid; an optional extra-fine grid augments several of the grid families. These mesh sequences are utilized to determine asymptotic grid-convergence characteristics of the solution sets, and to estimate grid-converged absolute drag levels of the wing-body-horizontal configuration using Richardson extrapolation.

  15. Estimating the Instantaneous Drag-Wind Relationship for a Horizontally Homogeneous Canopy

    Science.gov (United States)

    Pan, Ying; Chamecki, Marcelo; Nepf, Heidi M.

    2016-07-01

    The mean drag-wind relationship is usually investigated assuming that field data are representative of spatially-averaged metrics of statistically stationary flow within and above a horizontally homogeneous canopy. Even if these conditions are satisfied, large-eddy simulation (LES) data suggest two major issues in the analysis of observational data. Firstly, the streamwise mean pressure gradient is usually neglected in the analysis of data from terrestrial canopies, which compromises the estimates of mean canopy drag and provides misleading information for the dependence of local mean drag coefficients on local velocity scales. Secondly, no standard approach has been proposed to investigate the instantaneous drag-wind relationship, a critical component of canopy representation in LES. Here, a practical approach is proposed to fit the streamwise mean pressure gradient using observed profiles of the mean vertical momentum flux within the canopy. Inclusion of the fitted mean pressure gradient enables reliable estimates of the mean drag-wind relationship. LES data show that a local mean drag coefficient that characterizes the relationship between mean canopy drag and the velocity scale associated with total kinetic energy can be used to identify the dependence of the local instantaneous drag coefficient on instantaneous velocity. Iterative approaches are proposed to fit specific models of velocity-dependent instantaneous drag coefficients that represent the effects of viscous drag and the reconfiguration of flexible canopy elements. LES data are used to verify the assumptions and algorithms employed by these new approaches. The relationship between mean canopy drag and mean velocity, which is needed in models based on the Reynolds-averaged Navier-Stokes equations, is parametrized to account for both the dependence on velocity and the contribution from velocity variances. Finally, velocity-dependent drag coefficients lead to significant variations of the calculated

  16. Harm reduction-a systematic review on effects of alcohol reduction on physical and mental symptoms.

    Science.gov (United States)

    Charlet, Katrin; Heinz, Andreas

    2017-09-01

    Based on the knowledge that alcohol misuse causes a multitude of diseases and increased mortality, this systematic review examines whether a reduction of the individual alcohol consumption can contribute to a minimization of health risks within a harm reduction approach. In fact, the reviewed 63 studies indicate that interventions aiming at alcohol reduction (including total abstinence as one possible therapeutic aim) indeed resulted in or were associated with positive effects in harmful, hazardous or alcohol-dependent drinkers. Major benefits were observed for reducing alcohol-associated injuries, recovery of ventricular heart function in alcoholic cardiomyopathy, blood pressure lowering, normalization of biochemical parameter, body weight reduction, histological improvement in pre-cirrhotic alcohol-related liver disease and slowed progression of an already existing alcohol-attributable liver fibrosis. Furthermore, reduced withdrawal symptoms, prevalence of psychiatric episodes and duration of in-patient hospital days, improvement of anxiety and depression symptoms, self-confidence, physical and mental quality of life, fewer alcohol-related adverse consequences as well as lower psychosocial stress levels and better social functioning can result from reduced alcohol intake. The reviewed literature demonstrated remarkable socioeconomic cost benefits in areas such as the medical health-care system or workforce productivity. Individuals with heightened vulnerability further benefit significantly from alcohol reduction (e.g. hypertension, hepatitis C, psychiatric co-morbidities, pregnancy, but also among adolescents and young adults). Concluding, the reviewed studies strongly support and emphasize the importance and benefits of early initial screening for problematic alcohol use followed by brief and other interventions in first contact medical health-care facilities to reduce alcohol intake. © 2016 Society for the Study of Addiction.

  17. 凹槽形仿生针头优化设计与减阻机理分析%Optimization Design and Drag Reduction Mechanism Research on Groove Shape Bionic Needle

    Institute of Scientific and Technical Information of China (English)

    齐迎春; 丛茜; 王骥月; 齐欣

    2012-01-01

    以蚊子和蝉的口针为原形设计了凹槽形仿生针头,运用试验优化技术,通过显示动力学接触分析,证明凹槽形仿生针头具有明显减阻效果,最高减阻率可达40.94%;分析凹槽针头表面非光滑几何形态参数对注射时针头外壁所受摩擦力的影响规律,凹槽深度对摩擦力影响最大,宽度对摩擦力影响最小,凹槽深度和宽度与摩擦力呈抛物线关系,凹槽条数与摩擦力呈线性关系,随着凹槽条数增加,摩擦力减小;探讨仿生针头减阻机理,针头凹槽结构的存在可减小针头外壁与软组织的接触面积,使软组织与针头表面间存在间隙,产生空气膜,降低摩擦因数,另一方面,可使皮肤中的液体易于逸出,增加了润滑效果.依据国标,对数值分析所用的9种凹槽形仿生针头进行了穿刺试验,试验结果与数值分析结果一致.%Taken the microstructure of mosquitoes and cicada mouthparts as the prototypes, one groove shape bionic needle is design. The conclusion that the groove shape bionic needle has obvious resistance reduction effect is proved through contact dynamic analysis using the method of orthogonal design of experiment. The highest resistance reduction rate can amount to 40.94%; the influence law between the non smooth geometry parameters and the friction on the needle external wall getting in the injecting process is found out. The greatest impact factor of the friction is the groove depth, the minimum width. The relationship between the groove depth, width, and friction is a parabola. The relationship between groove number and friction is linear. The groove number increases, friction decreases. The influence order of factors and optimal levels are determined. The existence of the needle groove structure can reduce the contact area of the needle outer wall and soft tissue and this gap can produce a film of air, reducing the friction coefficient. On the other hand, the liquid can make the skin easy to

  18. 芦荟减阻剂对烧伤休克大鼠微循环的影响%Effects of Drag-reducing polymer derived from Aloe vera on microcirculation in burn rats

    Institute of Scientific and Technical Information of China (English)

    张俊莉; 蔡淑敏; 李涛; 曾振华; 高友光; 陈仲清

    2014-01-01

    Objective To investigate the effects of drag-reducing polymers on microcirculation in 40%total body surface area burn-injured rats. Methods SD rats were randomized into control group, drag-reducing polymer (DRPs) group and normal saline (NS) group (5 minutes after scald, drag-reducing polymer or saline was injected for fluid resuscitation). Wet dry weigh ratio of lung, histopathologic changes and arterial blood gas at 24 hour were respectively measured by wet dry weigh ratio method, hematoxylin-eosin (HE) staining and arterial blood gas analysis. The velocity of flow of red cell in oblique ridge and the survival time of burn-injured rats were observed. Results Compared with control group, rats in NS group exhibit significant lung injury characterized by a high W/D (P < 0.01), accumulation of a large number of neutrophils in HE stain, low partial pressure of oxygen (PO2) and high lactate (Lac) (P<0.05 or P<0.01) in arterial blood. Compared with the NS group, DRPs treatment rats exhibit significantly reduced lung injury characterized by W/D reducing (P < 0.05), the reduction of neutrophil infiltration, increased PO2, decreased Lac (P<0.05, P<0.01). In addition, DRPs treatment obviously increases the burn-induced low velocity of flow of red cell in oblique ridge (P<0.01). Moreover, the survival time of burned rats can be improved by DRPs treatment (P < 0.05). Conclusion DRPs ameliorates burn-induced acute lung injury, the mechanism may be through improving the burn-induced microcirculation disorders.%目的:探讨芦荟减阻剂对大鼠40%体表面积深Ⅱ度烧伤休克模型微循环的影响。方法:SD大鼠随机分为3组:对照组、减阻剂组及盐水组(烫伤后5 min给予减阻剂或者盐水进行补液复苏)。检测烧伤休克后24 h肺湿干重比(W/D)、病理及动脉血气;活体微循环观测技术观察烧伤休克后脊斜肌微动脉红细胞流速;观察动物的存活时间。结果:与对照组比较,盐

  19. Research of low boom and low drag supersonic aircraft design

    Institute of Scientific and Technical Information of China (English)

    Feng Xiaoqiang; Li Zhanke; Song Bifeng

    2014-01-01

    Sonic boom reduction will be an issue of utmost importance in future supersonic trans-port, due to strong regulations on acoustic nuisance. The paper describes a new multi-objective optimization method for supersonic aircraft design. The method is developed by coupling Seebass-George-Darden (SGD) inverse design method and multi-objective genetic algorithm. Based on the method, different codes are developed. Using a computational architecture, a concep-tual supersonic aircraft design environment (CSADE) is constructed. The architecture of CSADE includes inner optimization level and out optimization level. The low boom configuration is gener-ated in inner optimization level by matching the target equivalent area distribution and actual equivalent area distribution. And low boom/low drag configuration is generated in outer optimiza-tion level by using NSGA-II multi-objective genetic algorithm to optimize the control parameters of SGD method and aircraft shape. Two objective functions, low sonic boom and low wave drag, are considered in CSADE. Physically reasonable Pareto solutions are obtained from the present optimization. Some supersonic aircraft configurations are selected from Pareto front and the optimization results indicate that the swept forward wing configuration has benefits in both sonic boom reduction and wave drag reduction. The results are validated by using computational fluid dynamics (CFD) analysis.

  20. Research of low boom and low drag supersonic aircraft design

    Directory of Open Access Journals (Sweden)

    Feng Xiaoqiang

    2014-06-01

    Full Text Available Sonic boom reduction will be an issue of utmost importance in future supersonic transport, due to strong regulations on acoustic nuisance. The paper describes a new multi-objective optimization method for supersonic aircraft design. The method is developed by coupling Seebass–George–Darden (SGD inverse design method and multi-objective genetic algorithm. Based on the method, different codes are developed. Using a computational architecture, a conceptual supersonic aircraft design environment (CSADE is constructed. The architecture of CSADE includes inner optimization level and out optimization level. The low boom configuration is generated in inner optimization level by matching the target equivalent area distribution and actual equivalent area distribution. And low boom/low drag configuration is generated in outer optimization level by using NSGA-II multi-objective genetic algorithm to optimize the control parameters of SGD method and aircraft shape. Two objective functions, low sonic boom and low wave drag, are considered in CSADE. Physically reasonable Pareto solutions are obtained from the present optimization. Some supersonic aircraft configurations are selected from Pareto front and the optimization results indicate that the swept forward wing configuration has benefits in both sonic boom reduction and wave drag reduction. The results are validated by using computational fluid dynamics (CFD analysis.

  1. A numerical simulation analysis of the effect of the interface drag function on cluster evolution in a CFB riser gas-solid flow

    Directory of Open Access Journals (Sweden)

    L. C. Gómez

    2004-12-01

    Full Text Available The dynamics of formation, dissipation and breaking of coherent structures in the riser gas-solid flow of a circulating fluidized bed (CFB are evaluated by numerical simulation. The simulation is performed using the MICEFLOW code, which includes IIT's two-fluid hydrodynamic model B. The methodology for cluster characterization is used from Sharma et al. and is based on determination of four characteristics, average lifetime, average volumetric fraction of solid, existence time fraction and frequency of occurrence. Clusters are identified applying a criterion for the time average value of the volumetric solid fraction. A qualitative analysis of the influence of different drag function correlations on the hydrodynamics of the flow, including the evolution of coherent structures, is performed. The simulation predictions are also compared to experimental results. The results indicate that the choice of a correlation for drag function should be quite judicious. Finally it is shown that the mean clustering criteria of Sharma et al. should be modified to take into account other factors that influence cluster dynamics.

  2. Effectiveness of Schema Therapy on Symptoms Intensity Reduction and Anxiety

    Directory of Open Access Journals (Sweden)

    Mohammad Sadegh Montazeri

    2014-05-01

    Full Text Available The aim of this study was to determine the effectiveness of schema therapy on symptoms intensity reduction and anxiety in a special case with obsessive compulsive personality disorder. In this study a single case method with A-B design was used on a woman with obsessive compulsive personality disorder that was diagnosed by semi-structure interview for axis I and II of DSM-IV-TR (SCID. Martukovich -s obsessive compulsive personality disorder questionnaire and Beck -s anxiety inventory were used to collect data. Schema therapy intervention was effective in symptom reduction of obsessive compulsive personality disorder.

  3. Effect of mindfulness-based stress reduction on sleep quality

    DEFF Research Database (Denmark)

    Andersen, Signe; Würtzen, Hanne; Steding-Jessen, Marianne;

    2013-01-01

    The prevalence of sleep disturbance is high among cancer patients, and the sleep problems tend to last for years after the end of treatment. As part of a large randomized controlled clinical trial (the MICA trial, NCT00990977) of the effect of mindfulness-based stress reduction (MBSR) on psycholo......The prevalence of sleep disturbance is high among cancer patients, and the sleep problems tend to last for years after the end of treatment. As part of a large randomized controlled clinical trial (the MICA trial, NCT00990977) of the effect of mindfulness-based stress reduction (MBSR...

  4. 过渡型艇微气泡减阻喷缝尺度影响数值计算%Numerical Calculation on the Influence of the Slot Size of Air Injection on Micro Bubbles Drag Reduction for Transitional Craft

    Institute of Scientific and Technical Information of China (English)

    王家楣; 张玲

    2011-01-01

    针对一优良过渡型艇,为喷气需要进行船底断阶,采用有限体积法、SIMPLEC算法和k-ε两方程湍流模型,不计自由面影响,计及气泡与水的相对运动,数值求解包含气液两相流的雷诺平均控制方程组.获得不同喷缝宽度、不同傅汝德数和相对喷气速度下的船舶的阻力特性和气泡浓度分布规律并与模型实验结果进行对比分析.结果显示:在获得高减阻率条件下,Cn随Fr增加而呈非线性增加,当Fr=0.779时,Cn达到最大值;在获得25%减阻率的条件下,Fr=0.973时相对喷缝宽度为0.112所需喷气量最小即喷气所消耗功率最小.计算结果可为高速气泡船喷缝参数设计提供参考.%The two-phase flow around a fine transitional with step for injecting air is figured out numerically under the condition of neglecting influences of free-surface. The drag characteristic of the ship and the distribution of the volume fraction of micro bubble are got at different air jet slot size,Fr and relative air injection velocity. The results show that at Cn=25% and Fr=0.973, the air flow rate could reach minimum if non-dimension jet slot size is 0.112. The calculation result will provide reference on the parametric design of air injection slot of High-Speed Air Cavity Craft.

  5. Coulomb drag in the mesoscopic regime

    DEFF Research Database (Denmark)

    Mortensen, N. Asger; Flensberg, Karsten; Jauho, Antti-Pekka

    2002-01-01

    We present a theory for Coulomb drug between two mesoscopic systems which expresses the drag in terms of scattering matrices and wave functions. The formalism can be applied to both ballistic and disordered systems and the consequences can be studied either by numerical simulations or analytic...... average drag for chaotic 2D-systems and dominating fluctuations of drag between quasi-ballistic wires with almost ideal transmission....

  6. Intershell resistance in multiwall carbon nanotubes: A Coulomb drag study

    DEFF Research Database (Denmark)

    Lunde, Anders Mathias; Flensborg, Karsten; Jauho, Antti-Pekka

    2005-01-01

    We calculate the intershell resistance R-21 in a multiwall carbon nanotube as a function of temperature T and Fermi level epsilon(F) (e.g., a gate voltage), varying the chirality of the inner and outer tubes. This is done in a so-called Coulomb drag setup, where a current I-1 in one shell induces...... effects for the Coulomb drag between different tubes due to selection rules combined with mismatching of wave vector and crystal angular momentum conservation near the Fermi level. This gives rise to orders of magnitude changes in R-21 and even the sign of R-21 can change depending on the chirality...

  7. Drag and lift coefficients evolution of a Savonius rotor

    Science.gov (United States)

    Chauvin, A.; Benghrib, D.

    1989-10-01

    The lift and drag coefficients of the rotating Savonius wind machine are determined from the pressure difference measured between the upper plane and the lower plane of a blade. Pressure measurements have been performed for two sets of experiments; the first one for U ∞ = 10 m/s and the second one for U ∞ = 12.5 m/s. In each case it is to be noted that a negative lift effect is present for low values of the tip speed ratio λ. The lift coefficient becomes positive when λ increases. The drag coefficient is of course always negative.

  8. Transformance: reading the gospel in drag.

    Science.gov (United States)

    McCune, Jeffrey Q

    2004-01-01

    Despite the large body of scholarship on drag and its performance of misogyny, mimicry, and masculinity, little attention has been paid to the role of musical genres in Black drag performance and its reception. This essay explores drag performances of gospel music and its relationship with the spectator at the Biology Bar, a Black gay drag site in Chicago. By examining the shift from the club "space" to the church "place," this research locates several possibilities for queer gospel performances. Through the introduction of a theory of transformance, this essay highlights the contradictions, complications, and complexities of the relationship between the Black church and the Black gay community.

  9. Extensibility enables locomotion under isotropic drag

    CERN Document Server

    Pak, On Shun

    2011-01-01

    Anisotropic viscous drag is usually believed to be a requirement for the low Reynolds number locomotion of slender bodies such as flagella and cilia. Here we show that locomotion under isotropic drag is possible for extensible slender bodies. After general considerations, a two-ring swimmer and a model dinoflagellate flagellum are studied analytically to illustrate how extensibility can be exploited for self-propulsion without drag anisotropy. This new degree of freedom could be useful for some complex swimmer geometries and locomotion in complex fluid environments where drag anisotropy is weak or even absent.

  10. Coulomb drag in coherent mesoscopic systems

    DEFF Research Database (Denmark)

    Mortensen, Asger; Flensberg, Karsten; Jauho, Antti-Pekka

    2001-01-01

    We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both ballistic and disordered systems. The consequences can be worked out either by analytic means, such as th......We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both ballistic and disordered systems. The consequences can be worked out either by analytic means...

  11. Effects of windbreak width in wind direction on wind velocity reduction%迎风向防风林带宽对风速减弱的作用

    Institute of Scientific and Technical Information of China (English)

    Mulati Yusaiyin; Norio Tanaka

    2009-01-01

    通过在日本扎晃人学水压力工程实验室开展的埃菲尔型非循环风洞试验,研究了防风林阻尼变化及不同林带宽的整体阻力系数,阐明在迎风向上防风林带宽对风速减弱的作用.以二维雷诺时均N-S方程-k-ε吨扰动闭合模型数字地研究了不同防风林带宽的流量场变化.结果表明,防风林对风的阻力随林带宽增加而增加,但是整体阻尼系数略微降低.整体阻尼系数Cd、防风林带宽W和林高H之间满足方程Cd=kd(W/H)-b(kd,b:常数).数字模拟结果表明,防风林带宽度明显影响最小风速值及其位置.随着防风林带宽度的增加,风速下降15%-22%.%The variations of drag force acting on the windbreak and the bulk drag coefficients for different windbreak widths were studied experimentally in the Eiffel-type non-circulating wind tunnel at the Hydraulic Engineering Laboratory, Saitama University, Japan, to eluci-date the effects of windbreak width in the wind direction on wind velocity reduction behind a windbreak. The variations of flow field for different windbreak widths were studied numerically by using the two-dimensional Reynolds-averaged Navier-Stokes (RANS) equation with a k-ε turbulence closure model. Results show that the total drag force to wind increased with increasing windbreak width, but the bulk drag coefficient decreased slightly. The relationship between the bulk drag coefficient Cd and the windbreak width W and height H can be presented by the equation of Cd=kd (W/H)-b (kd,b: constants). The result of the numerical simulation shows that the windbreak width greatly affects the location and the value of the minimum wind velocity. The wind velocity decreased by 15%-22% as the windbreak width in-creased.

  12. Supervisor control strategy of synchronizer for wet DCT based on online estimation of clutch drag torque

    Science.gov (United States)

    Lu, Tongli; Li, Hongkui; Zhang, Jianwu; Hao, Hongtao

    2016-01-01

    The objective of this paper is to improve the performance of the synchronizer control strategy by considering the effect of clutch drag torque. The research of synchronization process in wet dual clutch transmission is performed in this paper. The significant effect of clutch drag torque is analyzed by adding a complex clutch drag torque module to synchronizer model. This paper focuses on the development of original estimation method of clutch drag torque. The estimation method offers an effective way to obtain accurate clutch drag torque, and it is applied to develop a new supervisor control strategy. Results have demonstrated that the estimation method has satisfied efficiency and accuracy and the control strategy improves the performance of the synchronizer mechanism significantly.

  13. Exponential reduction of finite volume effects with twisted boundary conditions

    CERN Document Server

    Cherman, Aleksey; Wagman, Michael L; Yaffe, Laurence G

    2016-01-01

    Flavor-twisted boundary conditions can be used for exponential reduction of finite volume artifacts in flavor-averaged observables in lattice QCD calculations with $SU(N_f)$ light quark flavor symmetry. Finite volume artifact reduction arises from destructive interference effects in a manner closely related to the phase averaging which leads to large $N_c$ volume independence. With a particular choice of flavor-twisted boundary conditions, finite volume artifacts for flavor-singlet observables in a hypercubic spacetime volume are reduced to the size of finite volume artifacts in a spacetime volume with periodic boundary conditions that is four times larger.

  14. Investigations of Fluid-Structure-Coupling and Turbulence Model Effects on the DLR Results of the Fifth AIAA CFD Drag Prediction Workshop

    Science.gov (United States)

    Keye, Stefan; Togiti, Vamish; Eisfeld, Bernhard; Brodersen, Olaf P.; Rivers, Melissa B.

    2013-01-01

    The accurate calculation of aerodynamic forces and moments is of significant importance during the design phase of an aircraft. Reynolds-averaged Navier-Stokes (RANS) based Computational Fluid Dynamics (CFD) has been strongly developed over the last two decades regarding robustness, efficiency, and capabilities for aerodynamically complex configurations. Incremental aerodynamic coefficients of different designs can be calculated with an acceptable reliability at the cruise design point of transonic aircraft for non-separated flows. But regarding absolute values as well as increments at off-design significant challenges still exist to compute aerodynamic data and the underlying flow physics with the accuracy required. In addition to drag, pitching moments are difficult to predict because small deviations of the pressure distributions, e.g. due to neglecting wing bending and twisting caused by the aerodynamic loads can result in large discrepancies compared to experimental data. Flow separations that start to develop at off-design conditions, e.g. in corner-flows, at trailing edges, or shock induced, can have a strong impact on the predictions of aerodynamic coefficients too. Based on these challenges faced by the CFD community a working group of the AIAA Applied Aerodynamics Technical Committee initiated in 2001 the CFD Drag Prediction Workshop (DPW) series resulting in five international workshops. The results of the participants and the committee are summarized in more than 120 papers. The latest, fifth workshop took place in June 2012 in conjunction with the 30th AIAA Applied Aerodynamics Conference. The results in this paper will evaluate the influence of static aeroelastic wing deformations onto pressure distributions and overall aerodynamic coefficients based on the NASA finite element structural model and the common grids.

  15. A Phenomenological Drag Law in Blast-Soil Interaction

    Science.gov (United States)

    2013-01-16

    mentioned work coming from the sedimentation and fluidization UNCLASSIFIED: Distribution Statement A. Approved for public release 4 studies [Gidaspow, 1994...with Fluidization . Academic Press. [Loth, 2008] Loth, E. (2008). Compressibility and rarefaction effects on drag of a spherical particle. AIAA, 46(9

  16. September 2002 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentations and Summary of Comments and Conclusions

    Energy Technology Data Exchange (ETDEWEB)

    McCallen, R

    2002-09-01

    report. Sid Diamond of DOE discussed the reorganization of the Office of Energy Efficiency and Renewable Energy and that the Office of Heavy Vehicle Technology is now part of the Office of FreedomCAR & Vehicle Technologies. Sid reviewed the FY03 budget and provided information on some plans for FY04. The soon to be posted DOE request for proposals from industry for projects related to parasitic energy losses was discussed. A minimum of 50% cost share by industry will be required and the proposal must be submitted by industry. Collaborative efforts in aerodynamic drag with members of the DOE consortium are encouraged. Sid also mentioned interest in aerodynamic drag contribution due to wheel wells and underbody flow. Sid also mentioned his continued interest in the application of our computational and experimental expertise to the area of locomotive and railcar aerodynamics for the reduction of drag effects and thus, the reduction of fuel consumption by trains. In summary, the technical presentations at the meeting included a review of experimental results and plans by GTRI, USC, and NASA Ames, the computational results from LLNL and SNL for the integrated tractor-trailer benchmark geometry called the Ground Transportation System (GTS) model, and by LLNL for the tractor-trailer gap and trailer wake flow, and turbulence model development and benchmark simulations being investigated by Caltech. USC is also investigating an acoustic drag reduction device that has been named ''Mozart'', GTRI continues their investigation of a blowing device, and LLNL presented their ideas for 2 new base drag reduction devices. ANL presented their plans for a DOE supported Cooperative Research and Development Agreement (CRADA) with Paccar Truck Company utilizing commercial software tools to simulate the flow and drag for an actual tractor and showed the results of some preliminary griding attempts. The attendees also had the opportunity to tour the 12-ft pressure wind tunnel

  17. Some Remarks on CFD Drag Prediction of an Aircraft Model

    Science.gov (United States)

    Peng, S. H.; Eliasson, P.

    Observed in CFD drag predictions for the DLR-F6 aircraft model with various configurations, some issues are addressed. The emphasis is placed on the effect of turbulence modeling and grid resolution. With several different turbulence models, the predicted flow feature around the aircraft is highlighted. It is shown that the prediction of the separation bubble in the wing-body junction is closely related to the inherent modeling mechanism of turbulence production. For the configuration with an additional fairing, which has effectively removed the separation bubble, it is illustrated that the drag prediction may be altered even for attached turbulent boundary layer when different turbulence models are used. Grid sensitivity studies are performed with two groups of subsequently refined grids. It is observed that, in contrast to the lift, the drag prediction is rather sensitive to the grid refinement, as well as to the artificial diffusion added for solving the turbulence transport equation. It is demonstrated that an effective grid refinement should drive the predicted drag components monotonically and linearly converged to a finite value.

  18. Modeling effective viscosity reduction behaviour of solid suspensions

    Institute of Scientific and Technical Information of China (English)

    Wei En-Bo; Ji Yan-Ju; Zhang Jun

    2012-01-01

    Under a simple shearing flow,the effective viscosity of solid suspensions can be reduced by controlling the inclusion particle size or the number of inclusion particles in a unit volume.Based on the Stokes equation,the transformation field method is used to model the reduction behaviour of effective viscosity of solid suspensions theoretically by enlarging the particle size at a given high concentration of particles.With a lot of samples of random cubic particles in a unit cell,our statistical results show that at the same higher concentration,the effective viscosity of solid suspensions can be reduced by increasing the particle size or reducing the number of inclusion particles in a unit volume.This work discloses the viscosity reduction mechanism of increasing particle size,which is observed experimentally.

  19. Determination of the surface drag coefficient

    DEFF Research Database (Denmark)

    Mahrt, L.; Vickers, D.; Sun, J.L.

    2001-01-01

    This study examines the dependence of the surface drag coefficient on stability, wind speed, mesoscale modulation of the turbulent flux and method of calculation of the drag coefficient. Data sets over grassland, sparse grass, heather and two forest sites are analyzed. For significantly unstable ...

  20. [Effects of the reduction of caffeine consumption on tinnitus perception].

    Science.gov (United States)

    Figueiredo, Ricardo Rodrigues; Rates, Marcelo José Abras; Azevedo, Andréia Aparecida de; Moreira, Ronaldo Kennedy de Paula; Penido, Norma de Oliveira

    2014-01-01

    For many years, excessive caffeine consumption has been touted as an aggravating factor for tinnitus. The pathophysiology behind this effect is probably related to the blockage of adenosine receptors by the action of caffeine on the central nervous system. To evaluate the effects of reduction of coffee consumption on tinnitus sensation and to identify subgroups more prone to benefit from this therapeutic strategy. Prospective. Twenty-six tinnitus patients who consumed at least 150 mL of coffee per day were selected. All were asked to reduce their coffee consumption. The Tinnitus Handicap Inventory (THI) questionnaire was completed by the patients before and after the reduction of coffee consumption, as well as a visual-analog scale (VAS) graduated from 1 to 10. THI and VAS scores were significantly reduced (pconsumption between 150 and 300 mL showed a significantly greater reduction of THI and VAS scores. Patients under 60 years of age with bilateral tinnitus and daily coffee consumption between 150 and 300 mL are more prone to benefit from consumption reduction. Thirty-day observation periods may be helpful for a better therapeutical decision. Copyright © 2014 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Published by Elsevier Editora Ltda. All rights reserved.

  1. Impacts of emission reductions on aerosol radiative effects

    Directory of Open Access Journals (Sweden)

    J.-P. Pietikäinen

    2015-05-01

    Full Text Available The global aerosol–climate model ECHAM-HAMMOZ was used to investigate changes in the aerosol burden and aerosol radiative effects in the coming decades. Four different emissions scenarios were applied for 2030 (two of them applied also for 2020 and the results were compared against the reference year 2005. Two of the scenarios are based on current legislation reductions: one shows the maximum potential of reductions that can be achieved by technical measures, and the other is targeted to short-lived climate forcers (SLCFs. We have analyzed the results in terms of global means and additionally focused on eight subregions. Based on our results, aerosol burdens show an overall decreasing trend as they basically follow the changes in primary and precursor emissions. However, in some locations, such as India, the burdens could increase significantly. The declining emissions have an impact on the clear-sky direct aerosol effect (DRE, i.e. the cooling effect. The DRE could decrease globally 0.06–0.4 W m−2 by 2030 with some regional increases, for example, over India (up to 0.84 W m−2. The global changes in the DRE depend on the scenario and are smallest in the targeted SLCF simulation. The aerosol indirect radiative effect could decline 0.25–0.82 W m−2 by 2030. This decrease takes place mostly over the oceans, whereas the DRE changes are greatest over the continents. Our results show that targeted emission reduction measures can be a much better choice for the climate than overall high reductions globally. Our simulations also suggest that more than half of the near-future forcing change is due to the radiative effects associated with aerosol–cloud interactions.

  2. Drag force and surface roughness measurements on freshwater biofouled surfaces.

    Science.gov (United States)

    Andrewartha, J; Perkins, K; Sargison, J; Osborn, J; Walker, G; Henderson, A; Hallegraeff, G

    2010-05-01

    The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m x 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.

  3. The effects of gear reduction on robot dynamics

    Science.gov (United States)

    Chen, J.

    1989-01-01

    The effect of the joint drive system with gear reduction for a generic two-link system is studied. It is done by comparing the kinetic energy of such a system with that of a direct drive two-link system. The only difference are two terms involving the inertia of the motor rotor and gear ratio. Modifications of the equations of motion from a direct drive system are then developed and generalized to various cases encountered in robot manipulators.

  4. Drag coefficient for the air-sea exchange in hurricane conditions

    CERN Document Server

    Golbraikh, E

    2013-01-01

    The physical model is proposed for prediction of the non-monotonic drag coefficient variation with the neutral stability 10-m wind speed, U10. The model is based upon measurements of the foam coverage fraction and characteristic size of foam bubbles with U10, and on the drag coefficient approximation by the linearly weighted averaging over alternating foam-free and foam-covered portions of the ocean surface. The obtained drag coefficient is in fair agreement with that obtained by field measurements of the vertical variation of mean wind speed in Powell et al. (Nature, 2003) which discover reduction of the sea-surface drag with U10 rising to hurricane conditions.

  5. Giant Frictional Drag in Double Bilayer Graphene Heterostructures

    Science.gov (United States)

    Lee, Kayoung; Xue, Jiamin; Dillen, David C.; Watanabe, Kenji; Taniguchi, Takashi; Tutuc, Emanuel

    2016-07-01

    We study the frictional drag between carriers in two bilayer graphene flakes separated by a 2-5 nm thick hexagonal boron nitride dielectric. At temperatures (T ) lower than ˜10 K , we observe a large anomalous negative drag emerging predominantly near the drag layer charge neutrality. The anomalous drag resistivity increases dramatically with reducing T , and becomes comparable to the layer resistivity at the lowest T =1.5 K . At low T the drag resistivity exhibits a breakdown of layer reciprocity. A comparison of the drag resistivity and the drag layer Peltier coefficient suggests a thermoelectric origin of this anomalous drag.

  6. Flat Plate Reduction in a Water Tunnel Using Riblets

    Science.gov (United States)

    1987-05-01

    II ~Ci +c SE- 2 8 0Lg 𔃺 E (D so (wwI) 10 DRAG CALCULATIONS The drag on the flat plate was calculated using D = bpU 20 The drag reduction over the...described in the previous section, are used so that bpU 2. is a constant, and that the drag upstream of the leading edge of the test surface is the same

  7. Spacecraft Re-Entry Impact Point Targeting Using Aerodynamic Drag

    Science.gov (United States)

    Omar, Sanny R.; Bevilacqua, Riccardo

    2017-01-01

    The ability to re-enter the atmosphere at a desired location is important for spacecraft containing components that may survive re-entry. While impact point targeting has traditionally been initiated through impulsive burns with chemical thrusters on large vehicles such as the Space Shuttle, and the Soyuz and Apollo capsules, many small spacecraft do not host thrusters and require an alternative means of impact point targeting to ensure that falling debris do not cause harm to persons or property. This paper discusses the use of solely aerodynamic drag force to perform this targeting. It is shown that by deploying and retracting a drag device to vary the ballistic coefficient of the spacecraft, any desired longitude and latitude on the ground can be targeted provided that the maneuvering begins early enough and the latitude is less than the inclination of the orbit. An analytical solution based on perturbations from a numerically propagated trajectory is developed to map the initial state and ballistic coefficient profile of a spacecraft to its impact point. This allows the ballistic coefficient profile necessary to reach a given target point to be rapidly calculated, making it feasible to generate the guidance for the decay trajectory onboard the spacecraft. The ability to target an impact point using aerodynamic drag will enhance the capabilities of small spacecraft and will enable larger space vehicles containing thrusters to save fuel by more effectively leveraging the available aerodynamic drag.

  8. Interactive point cloud blending by drag-and-drop

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    With the rapid development of 3D digital photography and 3D digital scanning devices, massive amount of point samples can be generated in acquisition of complex, real-world objects, and thus create an urgent need for advanced point-based processing and editing. In this paper, we present an interactive method for blending point-based geometries by dragging-anddropping one point-based model onto another model's surface metaphor. We first calculate a blending region based on the polygon of interest when the user drags-and-drops the model. Radial basis function is used to construct an implicit surface which smoothly interpolates with the transition regions. Continuing the drag-and-drop operation will make the system recalculate the blending regions and reconstruct the transition regions. The drag-and-drop operation can be compound in a constructive solid geometry (CSG) manner to interactively construct a complex point-based model from multiple simple ones. Experimental results showed that our method generates good quality transition regions between two raw point clouds and can effectively reduce the rate of overlapping during the blending.

  9. The effect of Compton drag on the dynamics of dissipative Poynting dominated flows: Implications for the unification of radio loud AGN

    CERN Document Server

    Levinson, Amir

    2016-01-01

    The dynamics of a dissipative Poynting dominated flow subject to a radiation drag due to Compton scattering of ambient photons by relativistic electrons accelerated in reconnecting current sheets is studied. It is found that the efficiency at which magnetic energy is converted to radiation is limited to a maximum value of $\\epsilon_c=3l_{dis}\\,\\sigma_0/4(\\sigma_0+1)$, where $\\sigma_0$ is the initial magnetization of the flow and $l_{dis}\\le1$ the fraction of initial Poynting flux that can dissipate. The asymptotic Lorentz factor satisfies $\\Gamma_\\infty\\ge\\Gamma_0(1+l_{dis}\\,\\sigma_0/4)$, where $\\Gamma_0$ is the initial Lorentz factor. This limit is approached in cases where the cooling time is shorter than the local dissipation time. A somewhat smaller radiative efficiency is expected if radiative losses are dominated by synchrotron and SSC emissions. It is suggested that under certain conditions magnetic field dissipation may occur in two distinct phases: On small scales, asymmetric magnetic fields that are...

  10. Test, Evaluation, and Demonstration of Practical Devices/Systems to Reduce Aerodynamic Drag of Tractor/Semitrailer Combination Unit Trucks

    Energy Technology Data Exchange (ETDEWEB)

    Scott Smith; Karla Younessi; Matt Markstaller; Dan Schlesinger; Bhaskar Bhatnagar; Donald Smith; Bruno Banceu; Ron Schoon; V.K. Sharma; Mark Kachmarsky; Srikant Ghantae; Michael Sorrels; Conal Deedy; Justin Clark; Skip Yeakel; Michael D. Laughlin; Charlotte Seigler; Sidney Diamond

    2007-04-30

    Class 8 heavy-duty trucks account for over three-quarters of the total diesel fuel used by commercial trucks (trucks with GVWRs more than 10,000 pounds) in the United States each year. At the highway speeds at which these trucks travel (i.e., 60 mph or greater), aerodynamic drag is a major part of total horsepower needed to move the truck down the highway, Reductions in aerodynamic drag can yield measurable benefits in fuel economy through the use of relatively inexpensive and simple devices. The goal of this project was to examine a number of aerodynamic drag reduction devices and systems and determine their effectiveness in reducing aerodynamic drag of Class 8 tractor/semitrailer combination-units, thus contributing to DOE's goal of reducing transportation petroleum use. The project team included major heavy truck manufacturers in the United States, along with the management and industry expertise of the Truck Manufacturers Association as the lead investigative organization. The Truck Manufacturers Association (TMA) is the national trade association representing the major North American manufacturers of Class 6-8 trucks (GVWRs over 19,500 lbs). Four major truck manufacturers participated in this project with TMA: Freightliner LLC; International Truck and Engine Corporation; Mack Trucks Inc.; and Volvo Trucks North America, Inc. Together, these manufacturers represent over three-quarters of total Class 8 truck sales in the United States. These four manufacturers pursued complementary research efforts as part of this project. The project work was separated into two phases conducted over a two-year period. In Phase I, candidate aerodynamic devices and systems were screened to focus research and development attention on devices that offered the most potential. This was accomplished using full-size vehicle tests, scale model tests, and computational fluid dynamics analyses. In Phase II, the most promising devices were installed on full-size trucks and their

  11. Mercury and frame-dragging in light of the MESSENGER flybys: conflict with general relativity, poor knowledge of the physical properties of the Sun, data reduction artifact, or still insufficient observations?

    CERN Document Server

    Iorio, Lorenzo

    2011-01-01

    The Lense-Thirring precession of the longitude of perihelion of Mercury, as predicted by general relativity by using the value of the Sun's angular momentum S = 190 x 10^39 kg m^2 s^-1 from helioseismology, is -2.0 milliarcseconds per century, computed in a celestial equatorial reference frame. It disagrees at 4-{\\sigma} level with the correction 0.4 +/- 0.6 milliarcseconds per century to the standard Newtonian/Einsteinian precession. It was recently determined in a global fit with the INPOP10a ephemerides to a long planetary data record (1914-2010) including also 3 data points collected in 2008-2009 from the MESSENGER spacecraft. The INPOP10a models did not include the solar gravitomagnetic field at all, so that its signature might have partly been removed in the data reduction process. On the other hand, the Lense-Thirring precession may have been canceled to a certain extent by the competing precession caused by a small mismodeling in the quadrupole mass moment of the Sun, actually modeled, of the order of...

  12. On the Minimum Induced Drag of Wings

    Science.gov (United States)

    Bowers, Albion H.

    2011-01-01

    Of all the types of drag, induced drag is associated with the creation and generation of lift over wings. Induced drag is directly driven by the span load that the aircraft is flying at. The tools by which to calculate and predict induced drag we use were created by Ludwig Prandtl in 1903. Within a decade after Prandtl created a tool for calculating induced drag, Prandtl and his students had optimized the problem to solve the minimum induced drag for a wing of a given span, formalized and written about in 1920. This solution is quoted in textbooks extensively today. Prandtl did not stop with this first solution, and came to a dramatically different solution in 1932. Subsequent development of this 1932 solution solves several aeronautics design difficulties simultaneously, including maximum performance, minimum structure, minimum drag loss due to control input, and solution to adverse yaw without a vertical tail. This presentation lists that solution by Prandtl, and the refinements by Horten, Jones, Kline, Viswanathan, and Whitcomb.

  13. The role of drag in insect hovering.

    Science.gov (United States)

    Wang, Z Jane

    2004-11-01

    Studies of insect flight have focused on aerodynamic lift, both in quasi-steady and unsteady regimes. This is partly influenced by the choice of hovering motions along a horizontal stroke plane, where aerodynamic drag makes no contribution to the vertical force. In contrast, some of the best hoverers--dragonflies and hoverflies--employ inclined stroke planes, where the drag in the down- and upstrokes does not cancel each other. Here, computation of an idealized dragonfly wing motion shows that a dragonfly uses drag to support about three quarters of its weight. This can explain an anomalous factor of four in previous estimates of dragonfly lift coefficients, where drag was assumed to be small. To investigate force generation and energy cost of hovering flight using different combination of lift and drag, I study a family of wing motion parameterized by the inclined angle of the stroke plane. The lift-to-drag ratio is no longer a measure of efficiency, except in the case of horizontal stroke plane. In addition, because the flow is highly stalled, lift and drag are of comparable magnitude, and the aerodynamic efficiency is roughly the same up to an inclined angle about 60 degrees , which curiously agrees with the angle observed in dragonfly flight. Finally, the lessons from this special family of wing motion suggests a strategy for improving efficiency of normal hovering, and a unifying view of different wing motions employed by insects.

  14. Coulomb drag between helical Luttinger liquids

    Science.gov (United States)

    Kainaris, N.; Gornyi, I. V.; Levchenko, A.; Polyakov, D. G.

    2017-01-01

    We theoretically study Coulomb drag between two helical edges with broken spin-rotational symmetry, such as would occur in two capacitively coupled quantum spin Hall insulators. For the helical edges, Coulomb drag is particularly interesting because it specifically probes the inelastic interactions that break the conductance quantization for a single edge. Using the kinetic equation formalism, supplemented by bosonization, we find that the drag resistivity ρD exhibits a nonmonotonic dependence on the temperature T . In the limit of low T ,ρD vanishes with decreasing T as a power law if intraedge interactions are not too strong. This is in stark contrast to Coulomb drag in conventional quantum wires, where ρD diverges at T →0 irrespective of the strength of repulsive interactions. Another unusual property of Coulomb drag between the helical edges concerns higher T for which, unlike in the Luttinger liquid model, drag is mediated by plasmons. The special type of plasmon-mediated drag can be viewed as a distinguishing feature of the helical liquid—because it requires peculiar umklapp scattering only available in the presence of a Dirac point in the electron spectrum.

  15. Orographic drag uncertainties impact forecast skill

    Science.gov (United States)

    Sandu, Irina; Zadra, Ayrton; Wedi, Nils; Bacmeister, Julio

    2017-04-01

    Despite their importance for the large-scale circulation, to date the representation of drag processes remains a major source of uncertainty in global models. Among the different drag processes the representation of orographic drag is particularly challenging. This has been recently highlighted by the WMO Working Group on Numerical Experimentation (WGNE) 'Drag project' which demonstrated that the main NWP and climate models differ significantly in representation of the total parameterized surface stress and in the partitioning of surface stress among various physical processes, particularly in regions with orography. Here we discuss how uncertain is the representation of orographic drag in models, and we illustrate how this uncertainty affects the skill of medium range weather forecasts. Namely we show how different is the representation of the resolved orography even in models with similar headline horizontal resolution. We also use the results of the WGNE 'Drag project' to illustrate how much models differ in terms of the total parameterized surface stress and its partition among various processes. Finally, we use the Integrated Forecasting System of ECMWF to demonstrate how much these intermodel differences either in the resolved orography or the representation subgrid drag affect the forecast skill.

  16. Multi-Objective Flight Control for Drag Minimization and Load Alleviation of High-Aspect Ratio Flexible Wing Aircraft

    Science.gov (United States)

    Nguyen, Nhan; Ting, Eric; Chaparro, Daniel; Drew, Michael; Swei, Sean

    2017-01-01

    As aircraft wings become much more flexible due to the use of light-weight composites material, adverse aerodynamics at off-design performance can result from changes in wing shapes due to aeroelastic deflections. Increased drag, hence increased fuel burn, is a potential consequence. Without means for aeroelastic compensation, the benefit of weight reduction from the use of light-weight material could be offset by less optimal aerodynamic performance at off-design flight conditions. Performance Adaptive Aeroelastic Wing (PAAW) technology can potentially address these technical challenges for future flexible wing transports. PAAW technology leverages multi-disciplinary solutions to maximize the aerodynamic performance payoff of future adaptive wing design, while addressing simultaneously operational constraints that can prevent the optimal aerodynamic performance from being realized. These operational constraints include reduced flutter margins, increased airframe responses to gust and maneuver loads, pilot handling qualities, and ride qualities. All of these constraints while seeking the optimal aerodynamic performance present themselves as a multi-objective flight control problem. The paper presents a multi-objective flight control approach based on a drag-cognizant optimal control method. A concept of virtual control, which was previously introduced, is implemented to address the pair-wise flap motion constraints imposed by the elastomer material. This method is shown to be able to satisfy the constraints. Real-time drag minimization control is considered to be an important consideration for PAAW technology. Drag minimization control has many technical challenges such as sensing and control. An initial outline of a real-time drag minimization control has already been developed and will be further investigated in the future. A simulation study of a multi-objective flight control for a flight path angle command with aeroelastic mode suppression and drag

  17. Optimizing Geometry Mediated Skin Friction Drag on Riblet-Textured Surfaces

    Science.gov (United States)

    Raayai, Shabnam; McKinley, Gareth

    2016-11-01

    Micro-scale riblets have been shown to modify the skin friction drag on patterned surfaces. Shark skin is widely known as a natural example of this passive drag reduction mechanism and artificial riblet tapes have been previously used in the America's Cups tournament resulting in a 1987 victory. Previous experiments with riblet surfaces in turbulent boundary layer flow have shown 4-8% reduction in the skin friction drag. Our computations with sinusoidal riblet surfaces in high Reynolds number laminar boundary layer flow and experiments with V-grooves in laminar Taylor-Couette flow also show that the reduction in skin friction can be substantial and depends on the spacing and height of the riblets. In the boundary layer setting, this frictional reduction is also a function of the length of the plate in the flow direction, while in the Taylor Couette setting it depends on the gap size. In the current work, we use scaling arguments and conformal mapping to establish a simplified theory for laminar flow over V-groove riblets and explore the self-similarity of the velocity contours near the patterned surface. We combine these arguments with theoretical and numerical calculations using Matlab and OpenFOAM to show that the drag reduction achievable in laminar flow over riblet surfaces depends on a rescaled form of the Reynolds number combined with the aspect ratio of the texture (defined in terms of the ratio of the height to spacing of the riblets). We then use these results to explain the underlying physical mechanisms driving frictional drag reduction and offer recommendations for designing low drag surfaces.

  18. Effect of ambient-pressure reduction on multibubble sonochemiluminescence

    Science.gov (United States)

    Tuziuti, Toru; Hatanaka, Shin-ichi; Yasui, Kyuichi; Kozuka, Teruyuki; Mitome, Hideto

    2002-04-01

    The effect of ambient-pressure reduction on multibubble sonochemiluminescence (MBSCL) is studied experimentally with a luminol solution through measurements of MBSCL intensity as a function of ultrasound irradiation time, applied voltage to a transducer and ultrasonic frequencies to accomplish high efficiency in chemical reactions. From the measurement of ambient-pressure dependence, it is shown that there is an ambient pressure that produces the maximum intensity of the MBSCL and the maximum intensity appears at higher ambient pressure as the applied voltage to the transducer increases. The highest intensity of MBSCL is obtained by appropriate reduction of ambient pressure both for various applied voltages and frequencies. This is caused by both the number of bubbles induced with supersaturation of the gas in a luminol solution and the variation in bubble dynamics.

  19. 挖掘机仿生斗齿土壤切削试验与减阻机理研究%Experiment and Drag Reduction Mechanism of Bionic Excavator Tooth during Soil Cutting

    Institute of Scientific and Technical Information of China (English)

    张琰; 黄河; 任露泉

    2013-01-01

    模仿蝼蛄爪趾形态设计了挖掘机斗齿.使用多项式拟合方法对爪趾的侧面轮廓线进行拟合,利用快速成型设备制造仿生斗齿样件.通过土壤切削试验,测定了仿生斗齿和JL80斗齿试样的土壤切削阻力.试验结果显示,仿生斗齿切削时受到的土壤阻力较原形斗齿降低约11%.分析表明,仿生斗齿易形成“自刃尖”,保持斗齿整体切削性能,且可在不改变挖掘机设计与工况的条件下,减小切削角,实现减阻.%A bionic excavator tooth was developed, which is bio-inspired and based on the morphology of the toe of mole cricket foreleg claw. The profile line of the mole cricket's toe was fitted by using polynomial fitting method. The bionic tooth specimens were fabricated by a rapid prototyping machine. The cutting resistances of the bionic tooth and JL80 tooth specimens were measured during soil cutting. The experimental results show that the cutting resistances of bionic tooth is about 11 % lower than that of JL80 tooth. The force analysis indicates that the bionic tooth is more likely to form self-sharpening blade so that the cutting performance of the tooth can be maintained. Besides, the bionic tooth is convenient for reducing the cutting angle, which can help for the reduction of cutting resistance, without changing the design and working condition of the excavator.

  20. Analysis of the Wmdmilling Effect to the Drag of Cessna172 during Engine Failure%塞斯纳172型飞机发动机失效后螺旋桨风车状态对飞行阻力的影响分析

    Institute of Scientific and Technical Information of China (English)

    马菲

    2011-01-01

    对于螺旋桨飞机,当发动机空中失效后,螺旋桨的风车状态将改变飞机的飞行阻力,从而影响到飞机下降率以及升阻比的改变.通过对应用范围较广的塞斯纳172型飞机进行实际测试,量化讨论螺旋桨的风车状态对飞机实际下降率及升阻比的影响程度.%For the propeller driven aircraft, when the engine failed during the flight, the windmilling of propeller will change the drag of the aircraft, then the rate of descent and lift over drag will be changed. The effect of windmilling will be discussed to the drag according to the flight test data from Cessna 172.

  1. Drag and Torque on Locked Screw Propeller

    Directory of Open Access Journals (Sweden)

    Tomasz Tabaczek

    2014-09-01

    Full Text Available Few data on drag and torque on locked propeller towed in water are available in literature. Those data refer to propellers of specific geometry (number of blades, blade area, pitch and skew of blades. The estimation of drag and torque of an arbitrary propeller considered in analysis of ship resistance or propulsion is laborious. The authors collected and reviewed test data available in the literature. Based on collected data there were developed the empirical formulae for estimation of hydrodynamic drag and torque acting on locked screw propeller. Supplementary CFD computations were carried out in order to prove the applicability of the formulae to modern moderately skewed screw propellers.

  2. Simulations to demonstrate reduction of the Gordon-Haus effect.

    Science.gov (United States)

    Marcuse, D

    1992-01-01

    The superposition of spontaneous emission noise on a train of soliton pulses produces a random change of the center frequency of the soliton spectrum that causes a change of the group velocity of individual solitons, which in long-light-wave systems translates into a random jitter of the position of the pulses at the receiver. This phenomenon is known as the Gordon-Haus effect. If uncontrolled, the Gordon-Haus effect sets a definite limit on the permissible data rate or on the length of soliton-based light-wave systems. Recently Kodama and Hasegawa [Opt. Lett. 17, 31 (1992)] have shown that the Gordon-Haus effect can be suppressed by placing filters along the fiber that reduce the frequency jitter and the concomitant group-velocity changes. We demonstrate the reduction of the Gordon-Haus effect by computer simulations.

  3. Bioinspired superhydrophobic, self-cleaning and low drag surfaces

    Science.gov (United States)

    Bhushan, Bharat

    2013-09-01

    Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. This article provides an overview of four topics: (1) Lotus Effect used to develop superhydrophobic and self-cleaning/antifouling surfaces with low adhesion, (2) Shark Skin Effect to develop surfaces with low fluid drag and anti-fouling characteristics, and (3-4) Rice Leaf and Butterfly Wing Effect to develop superhydrophobic and self-cleaning surfaces with low drag. Rice Leaf and Butterfly Wings combine the Shark Skin and Lotus Effects.

  4. Quantifying drag on wellbore casings in moving salt sheets

    Science.gov (United States)

    Weijermars, R.; Jackson, M. P. A.; Dooley, T. P.

    2014-08-01

    Frontier hydrocarbon development projects in the deepwater slopes of the Gulf of Mexico Basin, Santos Basin and Lower Congo Basin all require wells to cross ductile layers of autochthonous or allochthonous salt moving at peak rates of 100 mm yr-1. The Couette-Poiseuille number is introduced here to help pinpoint the depth of shear stress reversal in such salt layers. For any well-planned through salt, the probable range of creep forces of moving salt needs to be taken into account when designing safety margins and load-factor tolerance of the well casing. Drag forces increase with wellbore diameter, but more significantly with effective viscosity and speed of the creeping salt layer. The potential drag forces on cased wellbores in moving salt sheets are estimated analytically using a range of salt viscosities (1015-1019 Pa s) and creep rates (0-10 mm yr-1). Drag on perfectly rigid casing of infinite strength may reach up to 13 Giga Newton per meter wellbore length in salt having a viscosity of 1019 Pa s. Well designers may delay stress accumulations due to salt drag when flexible casing accommodates some of the early displacement and strain. However, all creeping salt could displace, fracture and disconnect well casing, eventually. The shear strength of typical heavy duty well casing (about 1000 MPa) can be reached due to drag by moving salt. Internal flow of salt will then fracture the casing near salt entry and exit points, but the structural damage is likely to remain unnoticed early in the well-life when the horizontal shift of the wellbore is still negligibly small (at less than 1 cm yr-1). Disruption of casing and production flow lines within the anticipated service lifetime of a well remains a significant risk factor within distinct zones of low-viscosity salt which may reach ultrafast creep rates of 100 mm yr-1.

  5. Preparation of Nano-Scale Biopolymer Extracted from Coconut Residue and Its Performance as Drag Reducing Agent (DRA

    Directory of Open Access Journals (Sweden)

    Hasan Muhammad Luqman Bin

    2017-01-01

    Full Text Available Drag or frictional force is defined as force that acts opposite to the object’s relative motion through a fluid which then will cause frictional pressure loss in the pipeline. Drag Reducing Agent (DRA is used to solve this issue and most of the DRAs are synthetic polymers but has some environmental issues. Therefore for this study, biopolymer known as Coconut Residue (CR is selected as the candidate to replace synthetic polymers DRA. The objective of this study is to evaluate the effectiveness of Nano-scale biopolymer DRA on the application of water injection system. Carboxymethyl cellulose (CMC is extracted by synthesizing the cellulose extracted from CR under the alkali-catalyzed reaction using monochloroacetic acid. The synthesize process is held in controlled condition whereby the concentration of NaOH is kept at 60%wt, 60 °C temperature and the reaction time is 4 hours. For every 25 g of dried CR used, the mass of synthesized CMC yield is at an average of 23.8 g. The synthesized CMC is then grinded in controlled parameters using the ball milling machine to get the Nano-scale size. The particle size obtained from this is 43.32 Nm which is in range of Nano size. This study proved that Nano-size CMC has higher percentage of drag reduction (%DR and flow increase (%FI if compared to normal-size CMC when tested in high and low flow rate; 44% to 48% increase in %DR and %FI when tested in low flow rate, and 16% to 18% increase in %DR and %FI when tested in high flow rate. The success of this research shows that Nano-scale DRA can be considered to be used to have better performance in reducing drag.

  6. Effect of hydrogen on reduction of burden materials

    Energy Technology Data Exchange (ETDEWEB)

    Hooey, P.L. [Rautaruukki Oy, Raahe (Finland). Raahe Steel

    1996-12-31

    Efficient operation of iron blast furnaces requires that the iron bearing burden material have good reduction, softening and melting characteristics. These characteristics are determined by the physical operation of the blast furnace and the mineralogical composition of the agglomerate. Increasing oil injection rates will increase the hydrogen content of the reducing gas significantly. The aim of this work is to establish how different burden materials react to this change in gas environment, and develop sinters which have optimal properties. The testing of sinter and pellets is broken into two areas: development of the test methods; and determination of sinter and pellet characteristics. The test method requires development because recent testwork has shown that the reducibility of the sinter is now so high that the reduction under load test is no longer sensitive. A new control program and more realistic gas compositions are currently being tested. The softening and melting characteristics of sinters of varying composition, acid pellets and olivine pellets have been tested using the reduction under load test at Rautaruukki Oy Research Centre. The effect of hydrogen in the reducing gas on the different iron ore agglomerates has been evaluated SULA 2 Research Programme; 6 refs.

  7. The Effect of Fertility Reduction on Economic Growth.

    Science.gov (United States)

    Ashraf, Quamrul H; Weil, David N; Wilde, Joshua

    2013-03-01

    We assess quantitatively the effect of exogenous reductions in fertility on output per capita. Our simulation model allows for effects that run through schooling, the size and age structure of the population, capital accumulation, parental time input into child-rearing, and crowding of fixed natural resources. The model is parameterized using a combination of microeconomic estimates, data on demographics and natural resource income in developing countries, and standard components of quantitative macroeconomic theory. We apply the model to examine the effect of a change in fertility from the UN medium-variant to the UN low-variant projection, using Nigerian vital rates as a baseline. For a base case set of parameters, we find that such a change would raise output per capita by 5.6 percent at a horizon of 20 years, and by 11.9 percent at a horizon of 50 years.

  8. Integrated lift/drag controller for aircraft

    Science.gov (United States)

    Olcott, J. W.; Seckel, E.; Ellis, D. R. (Inventor)

    1974-01-01

    A system for altering the lift/drag characteristics of powered aircraft to provide a safe means of glide path control includes a control device integrated for coordination action with the aircraft throttle. Such lift/drag alteration devices as spoilers, dive brakes, and the like are actuated by manual operation of a single lever coupled with the throttle for integrating, blending or coordinating power control. Improper operation of the controller is inhibited by safety mechanisms.

  9. A cooperative reduction model for regional air pollution control in China that considers adverse health effects and pollutant reduction costs.

    Science.gov (United States)

    Xie, Yujing; Zhao, Laijun; Xue, Jian; Hu, Qingmi; Xu, Xiang; Wang, Hongbo

    2016-12-15

    How to effectively control severe regional air pollution has become a focus of global concern recently. The non-cooperative reduction model (NCRM) is still the main air pollution control pattern in China, but it is both ineffective and costly, because each province must independently fight air pollution. Thus, we proposed a cooperative reduction model (CRM), with the goal of maximizing the reduction in adverse health effects (AHEs) at the lowest cost by encouraging neighboring areas to jointly control air pollution. CRM has two parts: a model of optimal pollutant removal rates using two optimization objectives (maximizing the reduction in AHEs and minimizing pollutant reduction cost) while meeting the regional pollution control targets set by the central government, and a model that allocates the cooperation benefits (i.e., health improvement and cost reduction) among the participants according to their contributions using the Shapley value method. We applied CRM to the case of sulfur dioxide (SO2) reduction in Yangtze River Delta region. Based on data from 2003 to 2013, and using mortality due to respiratory and cardiovascular diseases as the health endpoints, CRM saves 437 more lives than NCRM, amounting to 12.1% of the reduction under NCRM. CRM also reduced costs by US $65.8×10(6) compared with NCRM, which is 5.2% of the total cost of NCRM. Thus, CRM performs significantly better than NCRM. Each province obtains significant benefits from cooperation, which can motivate them to actively cooperate in the long term. A sensitivity analysis was performed to quantify the effects of parameter values on the cooperation benefits. Results shown that the CRM is not sensitive to the changes in each province's pollutant carrying capacity and the minimum pollutant removal capacity, but sensitive to the maximum pollutant reduction capacity. Moreover, higher cooperation benefits will be generated when a province's maximum pollutant reduction capacity increases.

  10. development of a new drag coefficient model for oil and gas

    African Journals Online (AJOL)

    eobe

    determination is critical to determination is critical to ensuring effective transportation of the particles. ... the fluid, and an upward diffusion of the particles, caused by a .... drag correction expression in multiphase flows since many particles are ...

  11. Ship Hull Form Optimization by Evolutionary Algorithm in Order to Diminish the Drag

    Institute of Scientific and Technical Information of China (English)

    Hassan Zakerdoost; Hassan Ghassemi; Mahmoud Ghiasi

    2013-01-01

    This study presents a numerical method for optimizing hull form in calm water with respect to total drag which contains a viscous drag and a wave drag.The ITTC 1957 model-ship correlation line was used to predict frictional drag and the corrected linearized thin-ship theory was employed to estimate the wave drag.The evolution strategy (ES) which is a member of the evolutionary algorithms (EAs) family obtains an optimum hull form by considering some design constraints.Standard Wigley hull is considered as an initial hull in optimization procedures for two test cases and new hull forms were achieved at Froude numbers 0.24,0.316 and 0.408.In one case the ES technique was ran for the initial hull form,where the main dimensions were fixed and the only variables were the hull offsets.In the other case in addition to hull offsets,the main dimensions were considered as variables that are optimized simultaneously.The numerical results of optimization procedure demonstrate that the optimized hull forms yield a reduction in total drag.

  12. Monoclonal antibody disulfide reduction during manufacturing: Untangling process effects from product effects.

    Science.gov (United States)

    Hutterer, Katariina M; Hong, Robert W; Lull, Jonathon; Zhao, Xiaoyang; Wang, Tian; Pei, Rex; Le, M Eleanor; Borisov, Oleg; Piper, Rob; Liu, Yaoqing Diana; Petty, Krista; Apostol, Izydor; Flynn, Gregory C

    2013-01-01

    Manufacturing-induced disulfide reduction has recently been reported for monoclonal human immunoglobulin gamma (IgG) antibodies, a widely used modality in the biopharmaceutical industry. This effect has been tied to components of the intracellular thioredoxin reduction system that are released upon cell breakage. Here, we describe the effect of process parameters and intrinsic molecule properties on the extent of reduction. Material taken from cell cultures at the end of production displayed large variations in the extent of antibody reduction between different products, including no reduction, when subjected to the same reduction-promoting harvest conditions. Additionally, in a reconstituted model in which process variables could be isolated from product properties, we found that antibody reduction was dependent on the cell line (clone) and cell culture process. A bench-scale model using a thioredoxin/thioredoxin reductase regeneration system revealed that reduction susceptibility depended on not only antibody class but also light chain type; the model further demonstrates that the trend in reducibility was identical to DTT reduction sensitivity following the order IgG1λ > IgG1κ > IgG2λ > IgG2κ. Thus, both product attributes and process parameters contribute to the extent of antibody reduction during production.

  13. FY 2004 Annual Report: DOE Project on Heavy Vehicle Aerodynamic Drag

    Energy Technology Data Exchange (ETDEWEB)

    McCallen, R C; Salari, K; Ortega, J; Castellucci, P; Eastwood, C; Whittaker, K; DeChant, L J; Roy, C J; Payne, J L; Hassan, B; Pointer, W D; Browand, F; Hammache, M; Hsu, T; Ross, J; Satran, D; Heineck, J T; Walker, S; Yaste, D; Englar, R; Leonard, A; Rubel, M; Chatelain, P

    2004-11-18

    The objective of this report is: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; and (2) Establish a database of experimental, computational, and conceptual design information, and demonstrate potential of new drag-reduction devices. The approaches used were: (1) Develop and demonstrate the ability to simulate and analyze aerodynamic flow around heavy truck vehicles using existing and advanced computational fluid dynamics (CFD) tools; (2) Through an extensive experimental effort, generate an experimental data base for code validation; (3) Using experimental data base, validate computations; (4) Provide industry with design guidance and insight into flow phenomena from experiments and computations; and (5) Investigate aero devices (e.g., base flaps, tractor-trailer gap stabilizer, underbody skirts and wedges, blowing and acoustic devices), provide industry with conceptual designs of drag reducing devices, and demonstrate the full-scale fuel economy potential of these devices.

  14. Direct drag and hot-wire measurements on thin-element riblet arrays

    Science.gov (United States)

    Wilkinson, S. P.; Lazos, B. S.

    1987-01-01

    An experimental study of stream wise, near-wall, thin-element riblet arrays under a turbulent boundary layer has been conducted in low-speed air. Hot-wire data show that a single, isolated thin-element riblet causes formation of counter-rotating vortex-pairs with a spanwise wavelength of 130 viscous lengths. Abrupt shifts in turbulence intensity magnitude and peak location are observed for streamwise riblet arrays as spanwise riblet spacing is varied. Direct drag measurements show net drag reduction (up to 8.5 percent) over a wide range of riblet spacings along with behavior at discrete non-dimensional spacings indicative of vortex activity. Overall, the data suggest that more than one drag reduction mechanism may be involved.

  15. CAN 8-WEEKS OF TRAINING AFFECT ACTIVE DRAG IN YOUNG SWIMMERS?

    Directory of Open Access Journals (Sweden)

    Daniel A. Marinho

    2010-03-01

    Full Text Available The aim of this study was to assess the effects of 8-weeks of training on active drag in young swimmers of both genders. Eight girls and twelve boys' belonging to the same swimming team and with regular competitive participation in national and regional events for the previous two seasons participated in this study. Active drag measurements were conducted in two different evaluation moments: at the beginning of the season and after 8 weeks of training (6.0 ± 0.15 training units per week, 21.00 ± 3.23 km per week and 3.50 ± 0.23 km per training unit. The maximal swimming velocity at the distance of 13 m, active drag and drag coefficient were measured on both trials by the method of small perturbations with the help of an additional hydrodynamic body. After 8 weeks of training, mean active drag (drag force and drag coefficient decreased in girls and boys, although no significant differences were found between the two trials. It seems that 8 weeks of swimming training were not sufficient to allow significant improvements on swimming technique

  16. Drag and Lift Force Acting on a Rotational Spherical Particle in a Logarithmic Boundary Flow

    Institute of Scientific and Technical Information of China (English)

    XU Wei-jiang; CHE De-fu; XU Tong-mo

    2006-01-01

    The drag and lift forces acting on a rotational spherical particle in a logarithmic boundary flow are numerically studied. The effects of the drag velocity and rotational speed of the sphere on the drag force are examined for the particle Reynolds number from 50 to 300 and for the dimensionless rotational angular speed of 0≤Ω≤1.0. The influence of dimensionless roughness height z0of the wall is also evaluated for z0≤10. The results show that the drag forces on a sphere both in a logarithmic flow and in a uniform unsheared flow increase with the increase of the drag velocity. For 50≤Rep≤300, the drag coefficient (-C)D increases with decreased roughness height z0. The time-averaged drag coefficient is also significantly affected by rotational speed of the sphere and roughness height z0 . The lift coefficient -CL increases with increased rotational speed and decreases with increased roughness height.

  17. Photon drag enhancement by a slow-light moving medium via electromagnetically-induced transparency amplification

    Science.gov (United States)

    Iqbal, Azmat; Khan, Naveed; Bacha, Bakht Amin; Rahman, Amin Ur; Ahmad, Afaq

    2017-09-01

    Recently, a considerable enhancement has been observed in the celebrated Fresnel-Fizeau light drag by innovative experimental and theoretical approaches because of its fundamental and practical interest in the emerging technology of quantum optics and photonics. We present a semiclassical density matrix approach on the demonstration of light drag in a slow-light moving medium comprising five-level single tripod atomic configuration. To accomplish this, we introduce Kerr-type nonlinearity that leads to electromagnetically-induced transparency amplification under resonance conditions. By switching ON Kerr-type nonlinearity effect, we observe a prominent transparency window in probe field's absorption spectrum whose width and amplitude can be controlled further by the intensity of Kerr field and control field. The incorporation of Kerr field also switches light propagation from superluminal to subluminal domain. We predict a significant enhancement both in the lateral and the rotary photon drag owing to drag of light linear polarization state subjected to translation and rotation of the host medium, respectively. Consistent with earlier results, light drag considerably depends on both transverse and angular velocity of the host medium. In regime of subluminal propagation, light polarization state drags along the medium motion while in the superluminal propagation region it drags opposite to the medium motion.

  18. Detection of gravitational frame dragging using orbiting qubits

    Science.gov (United States)

    Lanzagorta, Marco; Salgado, Marcelo

    2016-05-01

    In this paper we propose information theoretic and interferometric techniques to detect the effect of gravitational frame dragging on orbiting qubits. In particular, we consider the Kerr spacetime geometry and spin-\\tfrac{1}{2} qubits moving in equatorial circular orbits. We ignore the { O }({\\hslash }) order effects due to spin-curvature coupling, which allows us to consider the motion of the spin-\\tfrac{1}{2} particles as Kerr geometry geodesics. We derive analytical expressions for the infinitesimal Wigner rotation and numerical results for their integration across the length of the particle’s trajectory. To this end, we consider the bounds on the finite Wigner rotation imposed by Penrose’s cosmic censorship hypothesis. Finally we propose how the Wigner rotation strictly due to frame dragging could be observed using interferometry and other quantum metrology techniques.

  19. Ion drag force in plasmas at high electronegativity.

    Science.gov (United States)

    Denysenko, I; Yu, M Y; Stenflo, L; Xu, S

    2005-07-01

    The electric as well as the positive- and negative-ion drag forces on an isolated dust grain in an electronegative plasma are studied for large negative-ion densities, when the negative ions are not Boltzmann distributed. The investigation is carried out for submicrometer dust particles, so that the theory of Coulomb scattering is applicable for describing ion-dust interaction. Among the forces acting on the dust grain, the negative-ion drag force is found to be important. The effects of the negative-ion density, neutral-gas pressure, and dust-grain size on the forces are also considered. It is shown that by increasing the density of the negative ions one can effectively manipulate the dust grains. Our results imply that both dust voids and balls can be formed.

  20. Observation of light dragging in rubidium vapor cell

    CERN Document Server

    Strekalov, D V; Yu, N; Maleki, L; Strekalov, Dmitry; Matsko, Andrey B.; Yu, Nan; Maleki, Lute

    2003-01-01

    We report on the experimental demonstration of light dragging effect due to atomic motion in a rubidium vapor cell. We found that the minimum group velocity is achieved for light red-shifted from the center of the atomic resonance, and that the value of this shift increases with decreasing group velocity, in agreement with the theoretical predictions by Kocharovskaya, Rostovtsev, and Scully [Phys. Rev. Lett. {\\bf 86}, 628 (2001)].

  1. Reducing Aerodynamic Drag on Empty Open Cargo Vehicles

    Science.gov (United States)

    Ross, James C.; Storms, Bruce L.; Dzoan, Dan

    2009-01-01

    Some simple structural modifications have been demonstrated to be effective in reducing aerodynamic drag on vehicles that have empty open cargo bays. The basic idea is to break up the airflow in a large open cargo bay by inserting panels to divide the bay into a series of smaller bays. In the case of a coal car, this involves inserting a small number (typically between two and four) of vertical full-depth or partial-depth panels.

  2. Drag-free Small Satellite Platforms for Future Geodesy Missions

    Science.gov (United States)

    Conklin, J. W.; Hong, S.; Nguyen, A.; Serra, P.; Balakrishnan, K.; Buchman, S.; De Bra, D. B.; Hultgren, E.; Zoellner, A.

    2013-12-01

    Continuous satellite geodesy measurements lasting into the foreseeable future are critical for the understanding of our changing planet. It is therefore imperative that we explore ways to reduce costs, while maintaining science return. Small satellite platforms represent a promising path forward if ways can be found to reduce the size, weight, and power of the necessary instrumentation. One key enabling technology is a precision small-scale drag-free system under development at the University of Florida and Stanford University. A drag-free satellite (a) contains and shields a free-floating test mass from all non-gravitational forces, and (b) precisely measures the position of the test mass inside the satellite. A feedback control system commands thrusters to fly the 'tender' spacecraft with respect to the test mass. Thus, both test mass and spacecraft follow a pure geodesic in spacetime. By tracking the relative positions of low Earth orbiting drag-free satellites, using laser interferometry for example, the detailed shape of geodesics, and through analysis, the higher order harmonics of the Earth's geopotential can be determined. Drag-free systems can be orders of magnitude more accurate that accelerometer-based systems because they fundamentally operate at extremely low acceleration levels, and are therefore not limited by dynamic range like accelerometers. Since no test mass suspension force is required, larger gaps between the test mass and satellite are possible, which reduces the level of unwanted disturbing forces produced by the satellite itself. The small satellite platform also enables cost-effective constellations, which can increase the temporal resolution of gravity field maps by more-frequently observing given locations on the Earth. Mixed-orbit constellations can also markedly enhance observational strength, decorrelate gravity coefficient estimates, and help address the fundamental aliasing problem that exists with previous missions. The

  3. Integrating UAS Flocking Operations with Formation Drag Reduction

    Science.gov (United States)

    2014-03-01

    direction throughout this project. From providing a starting point for my research to introducing me to MATLAB , I could not have accomplished any of...efficiency, range, and endurance. Research Focus The focal point of the research is a simulation constructed using MATLAB . It has been extensively...way to position the aircraft in varying or abnormal flight conditions. Laser-based sensors called “ lidar ” are capable of detecting and measuring

  4. A New Paradigm for Turbulence Control for Drag Reduction

    Science.gov (United States)

    2017-02-27

    neutral and unstable turbulent Ekman layer were conducted. These DNS results were used to evaluate various turbulence and heat transfer models for the...used to determine the proper computational box size for a minimal flow unit (MFU) at Ro_b=0.5. For the neutrally stratified Ekman layer, the higher...order moments of velocity were examined and the accuracy of a kurtosis model was assessed. For the unstable Ekman layer, the analysis of higher-order

  5. Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

    OpenAIRE

    Bharat Bhushan

    2011-01-01

    The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such a...

  6. Development of a Plasma Injector for Supersonic Drag Reduction Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Methods to reduce the turbulent viscous skin friction stand out as paramount to increasing the energy efficiency, and therefore the aerodynamic efficiency of...

  7. Acceleration Noise Considerations for Drag-free Satellite Geodesy Missions

    Science.gov (United States)

    Hong, S. H.; Conklin, J. W.

    2016-12-01

    The GRACE mission, which launched in 2002, opened a new era of satellite geodesy by providing monthly mass variation solutions with spatial resolution of less than 200 km. GRACE proved the usefulness of a low-low satellite-to-satellite tracking formation. Analysis of the GRACE data showed that the K-Band ranging system, which is used to measure the range between the two satellites, is the limiting factor for the precision of the solution. Consequently, the GRACE-FO mission, schedule for launch in 2017, will continue the work of GRACE, but will also test a new, higher precision laser ranging interferometer compared with the K-Band ranging system. Beyond GRACE-FO, drag-free systems are being considered for satellite geodesy missions. GOCE tested a drag-free attitude control system with a gravity gradiometer and showed improvements in the acceleration noise compensation compared to the electrostatic accelerometers used in GRACE. However, a full drag-free control system with a gravitational reference sensor has not yet been applied to satellite geodesy missions. More recently, this type of drag-free system was used in LISA Pathfinder, launched in 2016, with an acceleration noise performance two orders of magnitude better than that of GOCE. We explore the effects of drag-free performance in satellite geodesy missions similar to GRACE-FO by applying three different residual acceleration noises from actual space missions: GRACE, GOCE and LISA Pathfinder. Our solutions are limited to degree 60 spherical harmonic coefficients with biweekly time resolution. Our analysis shows that a drag-free system with acceleration noise performance comparable to GOCE and LISA-Pathfinder would greatly improve the accuracy of gravity solutions. In addition to these results, we also present the covariance shaping process used in the estimation. In the future, we plan to use actual acceleration noise data measured using the UF torsion pendulum. This apparatus is a ground facility at

  8. CHARACTERISTICS OF WIND DEFLECTOR FOR REDUCING AERODYNAMIC DRAG OF VAN-BODY TRUCK

    Institute of Scientific and Technical Information of China (English)

    Du Guang-sheng; Lei Li; Zhou Lian-di

    2003-01-01

    In this paper, the differences in the characteristics of airflow around the van-body truck and of the aerodynamic drag, which were caused by the installation of a wind deflector, were studied by experimentally and numerically. The results show that after the installation of the deflector, the airflow around the top and bottom of the truck becoms smooth, the intensity of tail-vortex is weakened and its contribution area lessened. It also indicates that the aerodynamic characteristics of the airflow are changed distinctly and the aerodynamic drag is reduced considerably. The effect of the thin-wall deflector is better than the solid one in decreasing the drag. It is also concluded that proper design of the gap between the deflector bottom and the top of the driver cab can enhance the effect of the deflector in reducing drag.

  9. Comparative study of the hydrodynamic drag reducer efficiency in petroleum samples; Estudo comparativo da eficiencia de redutores de atrito hidrodinamico comerciais em amostras de petroleo

    Energy Technology Data Exchange (ETDEWEB)

    Sabadini, Edvaldo; Silva, Marcelo Alves da [Universidade Estadual de Campinas (UNICAMP), SP (Brazil); Ziglio, Claudio Marcos; Carvalho, Carlos Henrique Monteiro de; Rocha, Nelson de Oliveira [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES)

    2008-07-01

    In this work the efficiency of five commercial additives which produce drag reduction in petroleum was determined and compared. The studies were carried out in a rheometer using samples of petroleum from Bacia de Campos diluted in 50% of toluene. For such purpose the rheometer acts as a 'torquemeter', in which the magnitude of the drag reduction promoted by the additive is directly proportional to the difference in torque applied to maintain the sample in a specific flow rate. The obtained results have shown excellent capability of the additives to promote drag reduction (up to 20%) and small difference of efficiency among the additives was detectable. (author)

  10. Effect of nozzle lateral spacing on afterbody drag and performance of twin-jet afterbody models with convergent-divergent nozzles at Mach numbers up to 2.2

    Science.gov (United States)

    Pendergraft, O. C., Jr.; Schmeer, J. W.

    1972-01-01

    Twin-jet afterbody models were investigated by using two balances to measure the thrust-minus-total drag and the afterbody drag, separately, at static conditions and at Mach numbers up to 2.2 for an angle of attack of 0 deg. Hinged-flap convergent-divergent nozzles were tested at subsonic-cruise- and maximum-afterburning-power settings with a high-pressure air system used to provide jet-total-pressure ratios up to 20. Two nozzle lateral spacings were studied, using afterbodies with similar interfairing shapes but with different longitudinal cross-sectional area distributions. Alternate, blunter, interfairings with different shapes for the two spacings, which produced afterbodies having identical cross-sectional area progressions corresponding to an axisymmetric minimum wave-drag configuration, were also tested. The results indicate that the wide-spaced configurations improved the flow field around the nozzles, thereby reducing drag on the cruise nozzles; however, the increased surface and projected cross-sectional areas caused an increase in afterbody drag. Except for a slight advantage with cruise nozzles at subsonic speeds, the wide-spaced configurations had the higher total drag at all other test conditions.

  11. Effects of picture size reduction and blurring on emotional engagement.

    Directory of Open Access Journals (Sweden)

    Andrea De Cesarei

    Full Text Available The activity of basic motivational systems is reflected in emotional responses to arousing stimuli, such as natural pictures. The manipulation of picture properties such as size or detail allows for investigation into the extent to which separate emotional reactions are similarly modulated by perceptual changes, or, rather, may subserve different functions. Pursuing this line of research, the present study examined the effects of two types of perceptual degradation, namely picture size reduction and blurring, on emotional responses. Both manipulations reduced picture relevance and dampened affective modulation of skin conductance, possibly because of a reduced action preparation in response to degraded or remote pictures. However, the affective modulation of the startle reflex did not vary with picture degradation, suggesting that the identification of these degraded affective cues activated the neural circuits mediating appetitive or defensive motivation.

  12. Braneworld effective action An alternative to Kaluza-Klein reduction

    CERN Document Server

    Barvinsky, A O; Rathke, A; Kiefer, C; Barvinsky, Andrei; Kamenshchik, Alexander; Rathke, Andreas; Kiefer, Claus

    2003-01-01

    We construct the braneworld effective action in the two-brane Randall-Sundrum model in a setup alternative to Kaluza-Klein reduction: The action is written as a functional of the two metric and radion fields on the branes. In the low-energy spectrum of the model we find two - one massless and one massive - graviton modes, the mass of the massive mode diverging in the limit of merging branes. Our results confirm a recently proposed model of braneworld inflation with diverging branes. They also suggest the possibility of a new mechanism for a repulsive interbrane potential which can underlie the model of colliding "thick" branes in the Big Crunch/Big Bang transitions in cosmology. Mixing of the obtained massless and massive modes can be interpreted as radion-induced graviton oscillations potentially interesting for gravitational wave astronomy.

  13. Is the Clean Development Mechanism Effective for Emission Reductions?

    DEFF Research Database (Denmark)

    Tarp, Finn; Huang, Yongfu; He, Jingjing

    2014-01-01

    The UNFCCC COP 17 Durban conference confirmed the need to reach an all‐party‐inclusive global climate agreement by 2015 as the successor of the Kyoto Protocol. Although this Durban ‘road map’ is promising, the international negotiation process for reaching such a deal is bound to be filled...... with great challenges, given the wide divide between developed and developing nations. Against this background, comprehensive evaluations of the effectiveness of Kyoto market‐based mechanisms such as the Clean Development Mechanism (CDM) in terms of mitigating human‐induced climate change are urgently needed....... Such information is required to assess how the world's collective actions against climate change should proceed after Kyoto. This paper studies whether CDM is achieving its objective of emission reductions in the host countries. Here we empirically investigate the impacts of CDM projects on CO 2 emission...

  14. Development of pollution reduction strategies for Mexico City: Estimating cost and ozone reduction effectiveness

    Energy Technology Data Exchange (ETDEWEB)

    Thayer, G.R.; Hardie, R.W. [Los Alamos National Lab., NM (United States); Barrera-Roldan, A. [Instituto Mexicano de Petroleo, Mexico City (Mexico)

    1993-12-31

    This reports on the collection and preparation of data (costs and air quality improvement) for the strategic evaluation portion of the Mexico City Air Quality Research Initiative (MARI). Reports written for the Mexico City government by various international organizations were used to identify proposed options along with estimates of cost and emission reductions. Information from appropriate options identified by SCAQMD for Southem California were also used in the analysis. A linear optimization method was used to select a group of options or a strategy to be evaluated by decision analysis. However, the reduction of ozone levels is not a linear function of the reduction of hydrocarbon and NO{sub x} emissions. Therefore, a more detailed analysis was required for ozone. An equation for a plane on an isopleth calculated with a trajectory model was obtained using two endpoints that bracket the expected total ozone precursor reductions plus the starting concentrations for hydrocarbons and NO{sub x}. The relationship between ozone levels and the hydrocarbon and NO{sub x} concentrations was assumed to lie on this plane. This relationship was used in the linear optimization program to select the options comprising a strategy.

  15. Numerical simulation on heat transfer characteristics for turbulent drag-reducing flow with additives%添加剂湍流减阻流动的传热特性数值计算

    Institute of Scientific and Technical Information of China (English)

    李昌烽; 许世铎; 冯晓东; 王迎慧

    2009-01-01

    The reynolds stress model and the Cross viscosity equation have been adopted to simulate the turbulent flow and temperature fields of the dilute polyacrylamide (PAM) solution in a two-dimensional axisymmetric circular tube. The effect of flow velocity on drag reduction and heat transfer performance of drag-reducing fluid have been investigated systematically. The results indicate that the drag reduction (DR) and heat transfer reduction (HTR) of drag-reducing fluid increase with increasing flow velocity and approach the asymptotes, and HTR is greater than DR all the time. The comparison between Colburn factor and friction coefficient shows that Colburn analogy is not so much applicable to the drag-reducing fluid,especially for the low bulk flow Reynolds number conditions.%采用雷诺应力模型和Cross粘度方程,对二维轴对称圆管内湍流流动的聚丙烯酰胺稀溶液(PAM)的流场和温度场进行了数值模拟.在数值计算结果的基础上,系统研究了流速对减阻流体的减阻性能和传热特性的影响.结果表明,减阻流体的减阻率和传热降低率随流速的增大逐渐增大到渐进值,而且传热降低率恒大于减阻率. 减阻流体柯尔本(Colburn)因子与摩擦系数的对比结果表明柯尔本比拟,特别是在较低流动雷诺数下有较大偏差.

  16. Solute drag on perfect and extended dislocations

    Science.gov (United States)

    Sills, R. B.; Cai, W.

    2016-04-01

    The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction ?, and the dislocation character angle ?, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.

  17. Drag force of Anisotropic plasma at finite U(1) chemical potential

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Long; Ge, Xian-Hui [Shanghai University, Department of Physics, Shanghai (China); Wu, Shang-Yu [National Chiao Tung University, Department of Electrophysics, Yau Shing Tung Center, Hsinchu (China); National Center for Theoretical Science, Hsinchu (China)

    2016-05-15

    We perform the calculation of the drag force acting on a massive quark moving through an anisotropic N = 4 SU(N) Super Yang-Mills plasma in the presence of a U(1) chemical potential. We present the numerical results for any value of the anisotropy and arbitrary direction of the quark velocity with respect to the direction of the anisotropy. We find the effect of the chemical potential or charge density will enhance the drag force for our charged solution. (orig.)

  18. 3-D Effects Force Reduction of Short-Crested Non-Breaking Waves on Caissons

    DEFF Research Database (Denmark)

    Burcharth, H. F.; Liu, Z.

    1998-01-01

    The effect of wave short-crestedness on the horizontal wave force on a caisson is twofold. The one is the force reduction due to the reduction of point pressure on the caisson, named point-pressure reduction. The other is the force reduction due to the fact that the peak pressures do not occur si...

  19. Effects of Cerium on Reduction of Non-Chromium Iron Based CO Shift Catalyst

    Institute of Scientific and Technical Information of China (English)

    苏运来; 胡捷; 马卓娜; 杜宝石; 郭益群

    2001-01-01

    The effects of Ce on reduction of non-chromium iron based CO shift catalyst were studied by XRD, TPR, SEM and XPS. The results show that Ce refines Fe2O3 grains and riches on the surface of catalyst in the process of reduction, which leads to decrease of the initial reductive temperature and increase of the final reductive temperature.

  20. A Simple Method for Predicting Drag Characteristics of the Wells Turbine

    Institute of Scientific and Technical Information of China (English)

    HUANG Zhong-zhou; YU Zhi; ZHENG Yong-hong

    2006-01-01

    The drag characteristics of the Wells turbine are difficult to be accurately predicted because of the influences of many variables. Detailed analyses about the effects of these variables on the drag characteristics educe that the most sensitive parameters to the drag characteristics are the turbine solidity of the turbine and incidence angle of airflow. In this paper, an experimental research is conducted on the pressure drop across the flat-plate rotor which is used to simulate the Wells turbine. After nondimensionalization and fitting of the experimental data, a common experiential formula is obtained. Compared with the experimental data from literature, the computational results are satisfactory. Thus, this report provides a simple and convenient method for predicting the drag characteristics of the Wells turbine and optimizing the match design between an oscillating water column and a chamber.

  1. Black carbon reduction will weaken the aerosol net cooling effect

    Directory of Open Access Journals (Sweden)

    Z. L. Wang

    2014-12-01

    Full Text Available Black carbon (BC, a distinct type of carbonaceous material formed from the incomplete combustion of fossil and biomass based fuels under certain conditions, can interact with solar radiation and clouds through its strong light-absorption ability, thereby warming the Earth's climate system. Some studies have even suggested that global warming could be slowed down in a short term by eliminating BC emission due to its short lifetime. In this study, we estimate the influence of removing some sources of BC and other co-emitted species on the aerosol radiative effect by using an aerosol-climate coupled model BCC_AGCM2.0.1_CUACE/Aero, in combination with the aerosol emissions from the Representative Concentration Pathways (RCPs scenarios. We find that the global annual mean aerosol net cooling effect at the top of the atmosphere (TOA will be enhanced by 0.12 W m−2 compared with present-day conditions if the BC emission is reduced exclusively to the level projected for 2100 based on the RCP2.6 scenario. This will be beneficial for the mitigation of global warming. However, the global annual mean aerosol net cooling effect at the TOA will be weakened by 1.7–2.0 W m−2 relative to present-day conditions if emissions of BC and co-emitted sulfur dioxide and organic carbon are simultaneously reduced as the most close conditions to the actual situation to the level projected for 2100 in different ways based on the RCP2.6, RCP4.5, and RCP8.5 scenarios. Because there are no effective ways to remove the BC exclusively without influencing the other co-emitted components, our results therefore indicate that a reduction in BC emission can lead to an unexpected warming on the Earth's climate system in the future.

  2. Balancing acts: drag queens, gender and faith.

    Science.gov (United States)

    Sullivan-Blum, Constance R

    2004-01-01

    While engaged in research on the same-sex marriage debate in mainline denominations, I interviewed 23 LGBT Christians, four of whom were drag queens. While it is not possible to generalize from such a small sample, the drag queens in this study insist on maintaining their identity as Christians despite the hegemonic discourse that renders faith and LGBT identities mutually exclusive. They developed innovative approaches to reconciling their gender and sexual identities with their spirituality. Their innovations are potentially liberating not just for them personally, but for LGBT people generally because they challenge Christianity's rigid dichotomies of gender and sexuality.

  3. New drag laws for flapping flight

    Science.gov (United States)

    Agre, Natalie; Zhang, Jun; Ristroph, Leif

    2014-11-01

    Classical aerodynamic theory predicts that a steadily-moving wing experiences fluid forces proportional to the square of its speed. For bird and insect flight, however, there is currently no model for how drag is affected by flapping motions of the wings. By considering simple wings driven to oscillate while progressing through the air, we discover that flapping significantly changes the magnitude of drag and fundamentally alters its scaling with speed. These measurements motivate a new aerodynamic force law that could help to understand the free-flight dynamics, control, and stability of insects and flapping-wing robots.

  4. Drag, but not buoyancy, affects swim speed in captive Steller sea lions

    Directory of Open Access Journals (Sweden)

    Ippei Suzuki

    2014-04-01

    Full Text Available Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (∼12–26% subcutaneous fat. Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag showed that swim speed was best predicted by two variables, drag and dive phase (AIC = −139. Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy.

  5. Experimental study on the minimum drag coefficient of supercritical pressure water in horizontal tubes

    Energy Technology Data Exchange (ETDEWEB)

    Lei, Xianliang, E-mail: xianlianglei@mail.xjtu.edu.cn; Li, Huixiong; Guo, YuMeng; Zhang, Qing; Zhang, Weiqiang; Zhang, Qian

    2016-05-15

    Highlights: • The minimum drag coefficient phenomenon (MDC) has been observed and further investigated. • Effects of heat flux, mass flux and pressure to MDC have been discussed. • A series of comparisons between existing correlations and data have been conducted. • Two correlations of drag coefficient are proposed for isothermal and nonisothermal flow. - Abstract: Hydraulic resistance and its components are of great importance for understanding the turbulence nature of supercritical fluid and establishing prediction methods. Under supercritical pressures, the hydraulic resistance of the fluid exhibits a “pit” in the regions near its pseudo-critical point, which is hereafter called the minimum drag coefficient phenomenon. However, this special phenomenon was paid a little attention before. Hence systematical experiments have been carried out to investigate the hydraulic resistance of supercritical pressure water in both adiabatic and heated horizontal tubes. Parametric effects of heat flux, pressure and mass fluxes to drag coefficient are further compared. It is found that almost all of the existing correlations don’t agree well with the experimental data due to the insufficient consideration of thermal-properties near the pseudocritical point. Two correlations of the drag coefficients are finally proposed by introducing the new variable of the derivative of density with respect to temperature or Prandtl number, which can better predict the drag coefficient of isothermal and nonisothermal flow respectively.

  6. Drag measurements on a laminar-flow body of revolution in the 13-inch magnetic suspension and balance system

    Science.gov (United States)

    Dress, David A.

    1989-01-01

    Low speed wind tunnel drag force measurements were taken on a laminar flow body of revolution free of support interference. This body was tested at zero incidence in the NASA Langley 13 in. Magnetic Suspension and Balance System (MSBS). The primary objective of these tests was to substantiate the drag force measuring capabilities of the 13 in. MSBS. The drag force calibrations and wind-on repeatability data provide a means of assessing these capabilities. Additional investigations include: (1) the effects of fixing transition; (2) the effects of fins installed in the tail; and (3) surface flow visualization using both liquid crystals and oil flow. Also two simple drag prediction codes were used to assess their usefulness in estimating overall body drag.

  7. Development of a Kevlar/PMR-15 reduced drag DC-9 nacelle fairing

    Science.gov (United States)

    Kawai, R. T.; Hrach, F. J.

    1980-01-01

    The paper describes an advanced composite fairing designed to reduce drag on DC-9 nacelles as a part of the NASA Engine Component Improvement Program. This fairing is the aft enclosure for the thrust reverser actuator system on JT8D engine nacelles and is subjected to a 500 F exhaust flow during the reverse thrust. A reduced-drag configuration was developed by using in-flight tuft surveys for flow visualization in order to identify areas with low-quality flow, and then modifying the aerodynamic lines to improve the flow. A fabrication method for molding the part in an autoclave was developed; this material system is suitable for 500 F. The resultant composite fairing reduces the overall aircraft drag 1% with a weight reduction of 40% when compared with a metal component.

  8. Pipeline cost reduction through effective project management and applied technology

    Energy Technology Data Exchange (ETDEWEB)

    Jenkins, A. [TransCanada Pipeline Ltd., Alberta (Canada); Babuk, T. [Empress International Inc., Westwood, NJ (United States); Mohitpour, M. [Tempsys Pipeline Solutions Inc., Vancouver, BC (Canada); Murray, M.A. [National Energy Board of Canada (Canada)

    2005-07-01

    Pipelines are regarded by many as passive structures with the technology involved in their construction and operation being viewed as relatively simple and stable. If such is the case how can there be much room for cost improvement? In reality, there have been many technological and regulatory innovations required within the pipeline industry to meet the challenges posed by ever increasing consumer demand for hydrocarbons, the effects of aging infrastructure and a need to control operating and maintenance expenditures. The importance of technology management, as a subset of overall project management, is a key element of life cycle cost control. Assurance of public safety and the integrity of the system are other key elements in ensuring a successful pipeline project. The essentials of best practise project management from an owner/ operator's perspective are set out in the paper. Particular attention is paid to the appropriate introduction of new technology, strategic procurement practice and material selection, indicating that capital cost savings of up to 15% are achievable without harming life cycle cost. The value of partnering leading to technical innovation, cost savings and improved profitability for all the participants is described. Partnering also helps avoid duplicated effort through the use of common tools for design, planning schedule tracking and reporting. Investing in appropriate technology development has been a major source of cost reduction in recent years and the impact of a number of these recently introduced technologies in the areas of materials, construction processes and operation and maintenance are discussed in the paper. (author)

  9. Recruitment-of-loudness effects of attenuative noise reduction algorithms

    Science.gov (United States)

    Whitmal, Nathaniel; Vosoughi, Azadeh

    2002-05-01

    Hearing-impaired listeners have greater difficulty understanding speech in noise than normal-hearing listeners do. As a result, hearing aid users are often challenged by the inability of their hearing aids to improve intelligibility in noise. Several investigators have addressed this problem by using well-known signal processing methods (e.g., spectral subtraction, Wiener filtering) to enhance noise-corrupted speech. Unfortunately, these methods have failed to provide significant improvements in intelligibility. One possible explanation is the level-dependent nature of the attenuation that the algorithms impose on the speech. In the cases described above, this attenuation resembles the piecewise-linear input-output characteristic observed in certain recruitment-of-loudness simulators. The purpose of this study was to compare the intelligibility of processed speech with that expected for recruitment-of-loudness simulation. Trials of the CUNY Nonsense Syllable Test were conducted with 12 normal-hearing listeners, using syllables that were mixed with additive noise at SNRs of 6, 12, and 18 dB. Input-output characteristics for the signals were measured and used to determine the effective threshold shift imposed by the algorithms. Comparisons of measured intelligibility scores with articulation index-based intelligibility predictions indicate that the behavior of such noise reduction algorithms can be successfully modeled as a form of mild sensorineural hearing loss.

  10. Effects of noise reduction on AM and FM perception.

    Science.gov (United States)

    Ives, D Timothy; Calcus, Axelle; Kalluri, Sridhar; Strelcyk, Olaf; Sheft, Stanley; Lorenzi, Christian

    2013-02-01

    The goal of noise reduction (NR) algorithms in digital hearing aid devices is to reduce background noise whilst preserving as much of the original signal as possible. These algorithms may increase the signal-to-noise ratio (SNR) in an ideal case, but they generally fail to improve speech intelligibility. However, due to the complex nature of speech, it is difficult to disentangle the numerous low- and high-level effects of NR that may underlie the lack of speech perception benefits. The goal of this study was to better understand why NR algorithms do not improve speech intelligibility by investigating the effects of NR on the ability to discriminate two basic acoustic features, namely amplitude modulation (AM) and frequency modulation (FM) cues, known to be crucial for speech identification in quiet and in noise. Here, discrimination of complex, non-linguistic AM and FM patterns was measured for normal hearing listeners using a same/different task. The stimuli were generated by modulating 1-kHz pure tones by either a two-component AM or FM modulator with patterns changed by manipulating component phases. Modulation rates were centered on 3 Hz. Discrimination of AM and FM patterns was measured in quiet and in the presence of a white noise that had been passed through a gammatone filter centered on 1 kHz. The noise was presented at SNRs ranging from -6 to +12 dB. Stimuli were left as such or processed via an NR algorithm based on the spectral subtraction method. NR was found to yield small but systematic improvements in discrimination for the AM conditions at favorable SNRs but had little effect, if any, on FM discrimination. A computational model of early auditory processing was developed to quantify the fidelity of AM and FM transmission. The model captured the improvement in discrimination performance for AM stimuli at high SNRs with NR. However, the model also predicted a relatively small detrimental effect of NR for FM stimuli in contrast with the average

  11. Effect of certain structural features of coal on Its tendency towards reduction

    Energy Technology Data Exchange (ETDEWEB)

    Grigor' yeva, Ye. A.; Bakirova, Ye.V.; Dzhalyabova, L.V.; Larina, N.K.; Lesnikova, Ye.B.; Zharova, M.N.,

    1981-01-01

    A study is made of the effect of easily destroyed ether groupings and organic-mineral bonds in coal structure on the tendency towards reduction with the help of hydrolytic destruction of coals and subsequent selective reduction by sodium borohydride.

  12. ABM Drag_Pass Report Generator

    Science.gov (United States)

    Fisher, Forest; Gladden, Roy; Khanampornpan, Teerapat

    2008-01-01

    dragREPORT software was developed in parallel with abmREPORT, which is described in the preceding article. Both programs were built on the capabilities created during that process. This tool generates a drag_pass report that summarizes vital information from the MRO aerobreaking drag_pass build process to facilitate both sequence reviews and provide a high-level summarization of the sequence for mission management. The script extracts information from the ENV, SSF, FRF, SCMFmax, and OPTG files, presenting them in a single, easy-to-check report providing the majority of parameters needed for cross check and verification as part of the sequence review process. Prior to dragReport, all the needed information was spread across a number of different files, each in a different format. This software is a Perl script that extracts vital summarization information and build-process details from a number of source files into a single, concise report format used to aid the MPST sequence review process and to provide a high-level summarization of the sequence for mission management reference. This software could be adapted for future aerobraking missions to provide similar reports, review and summarization information.

  13. Wind speed scaling and the drag coefficient

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Wind speed scaling in similarity law in wind-generated waves and the drag coefficient are studied. In analyzing the data in the wind wave channel, it is found that the u. scaling greatly reduces the scatter in the U10 scaling. The u. scaling has much less scatter than the scaling using other wind speeds. The friction velocity seems to play a distinctive role in wave growth. The result is important in the applications of the similarity law and in wave modeling. In theory it gives an insight into the mechanism of wind wave interaction. It is found that wave steepness is important in influencing the drag coefficient. The variability of the coefficients in the currently widely used drag form can be explained by the differences in wave steepness in the observations. A drag coefficient model with wind speed and wave steepness as parameters is proposed. An explanation for Kahma' s result that the u. scaling does not reduce the scatter in the U10 scaling is given.

  14. Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

    Science.gov (United States)

    Koplik, Joel; Maldarelli, Charles

    2017-02-01

    Measurements of the surface diffusivity of colloidal spheres translating along a vapor-liquid interface show an unexpected decrease in diffusivity, or increase in surface drag (from the Stokes-Einstein relation), when the particles situate further into the vapor phase. However, direct measurements of the surface drag from the colloid velocity due to an external force find the expected decrease with deeper immersion into the vapor. We perform molecular dynamics simulations of the diffusivity and force experiments for a nanoparticle with a small surface roughness at a vapor-liquid interface to examine the effect of contact line fluctuations. The drag calculated from both calculations agree and decrease as the particle positions further into the vapor. The surface drag is smaller than the bulk liquid drag due to the partial submersion into the liquid and the finite thickness of the interfacial zone relative to the nanoparticle size. We observe weak contact line fluctuations and transient pinning events, but these do not give rise to an anomalous increase in drag in this system.

  15. Summary of Data from the First AIAA CFD Drag Prediction Workshop

    Science.gov (United States)

    Levy, David W.; Zickuhr, Tom; Vassberg, John; Agrawal, Shreekant; Wahls, Richard A.; Pirzadeh, Shahyar; Hemsch, Michael J.

    2002-01-01

    The results from the first AIAA CFD Drag Prediction Workshop are summarized. The workshop was designed specifically to assess the state-of-the-art of computational fluid dynamics methods for force and moment prediction. An impartial forum was provided to evaluate the effectiveness of existing computer codes and modeling techniques, and to identify areas needing additional research and development. The subject of the study was the DLR-F4 wing-body configuration, which is representative of transport aircraft designed for transonic flight. Specific test cases were required so that valid comparisons could be made. Optional test cases included constant-C(sub L) drag-rise predictions typically used in airplane design by industry. Results are compared to experimental data from three wind tunnel tests. A total of 18 international participants using 14 different codes submitted data to the workshop. No particular grid type or turbulence model was more accurate, when compared to each other, or to wind tunnel data. Most of the results overpredicted C(sub Lo) and C(sub Do), but induced drag (dC(sub D)/dC(sub L)(exp 2)) agreed fairly well. Drag rise at high Mach number was underpredicted, however, especially at high C(sub L). On average, the drag data were fairly accurate, but the scatter was greater than desired. The results show that well-validated Reynolds-Averaged Navier-Stokes CFD methods are sufficiently accurate to make design decisions based on predicted drag.

  16. A new technique for investigating the induced and profile drag coefficients of a smooth wing and a tubercled wing

    Directory of Open Access Journals (Sweden)

    Bolzon Michael

    2016-01-01

    Full Text Available The induced and profile drag coefficients of a wing are typically determined through a complex experimental technique, such as wake surveying. Such a technique requires measurement of all three orthogonal components of the downstream velocity to find the components of drag, which results in the necessary usage of a sophisticated and costly measurement device, such as multi-hole pressure probe. However, in this paper data is presented which demonstrate that the relative changes in the induced and profile drag coefficients can largely be determined through the sole measurement of the downstream, streamwise velocity. To demonstrate this, the induced and profile drags of two NACA 0021 wings, one with a smooth leading edge and the other wing a tubercled leading edge for comparison, are determined through the measurement of the three orthogonal velocities. The downstream, streamwise velocity distribution of each wing is then constructed and relationships can be determined. The wings were surveyed at 3°, 9°, and 12°. It has been found that the relative magnitude of the profile drag coefficient can be found for all considered angles of attack, while the relative magnitude of the induced drag coefficient can be found at 9° and 12°. These findings produce an innovative, simpler, and more cost effective experimental technique in determining the components of drag of a wing, and reduces the burdensome requirement of a sophisticated measurement device for such an experiment. Further investigation is required to determine the induced drag at 3°.

  17. Side-effects of fluticasone in asthmatic children : no effects after dose reduction

    NARCIS (Netherlands)

    Visser, MJ; van der Veer, E; Postma, DS; Arends, LR; de Vries, TW; Brand, PLP; Duiverman, EJ

    2004-01-01

    To assess long-term effects and side-effects of fluticasone propionate (FP), a 2-yr study was performed, comparing a step-down dose approach (1,000 mug.day(-1), with reductions every 2 months to 500, 200 and 100 mug.day(-1) for the remainder of the study) versus a constant dose (200 mug.day(-1)). In

  18. Significance of relative velocity in drag force or drag power estimation for a tethered float

    Digital Repository Service at National Institute of Oceanography (India)

    Vethamony, P.; Sastry, J.S.

    There is difference in opinion regarding the use of relative velocity instead of particle velocity alone in the estimation of drag force or power. In the present study, a tethered spherical float which undergoes oscillatory motion in regular waves...

  19. Drag measurements on a laminar flow body of revolution in Langley's 13 inch magnetic suspension and balance system. M.S. Thesis

    Science.gov (United States)

    Dress, David A.

    1988-01-01

    Low-speed wind tunnel drag force measurements were taken on a laminar flow body of revolution free of support interference. This body was tested at zero incidence in the NASA Langley 13 inch Magnetic Suspension and Balance System (MSBS). The primary objective of these tests was to substantiate the drag force measuring capabilities of the 13 inch MSBS. A secondary objective was to obtain support interference free drag measurements on an axisymmetric body of interest. Both objectives were met. The drag force calibrations and wind-on repeatability data provide a means of assessing the drag force measuring capabilities of the 13 inch MSBS. The measured drag coefficients for this body are of interest to researchers actively involved in designing minimum drag fuselage shapes. Additional investigations included: the effects of fixing transition; the effects of fins installed in the tail; surface flow visualizations using both liquid crystals and oil flow; and base pressure measurements using a one-channel telemetry system. Two drag prediction codes were used to assess their usefulness in estimating overall body drag. These theoretical results did not compare well with the measured values because of the following: incorrect or non-existent modeling of a laminar separation bubble on the body and incorrect of non-existent estimates of base pressure drag.

  20. Calculation of the drag and heat transfer from a sphere in the gas flow in a cylindrical channel

    Science.gov (United States)

    Simakov, N. N.

    2016-09-01

    A numerical experiment on the simulation of heat transfer from a sphere to a gas flow in a cylindrical channel in the Stokes and transient flow regimes has been described. Radial and axial profiles of the gas temperature and the dependences of drag coefficient C d of the body and Nusselt number Nu on Reynolds number Re have been calculated and analyzed. The problem of the influence of the early drag crisis for a sphere on its heat transfer to the gas flow has been considered. The estimation of this phenomenon has shown that the early drag crisis of the sphere in a strongly turbulent flow causes a reduction in heat transfer from the sphere to the gas by three to six times (in approximately the same proportion as for its drag coefficient).