Effect of wearing a swimsuit on hydrodynamic drag of swimmer
Directory of Open Access Journals (Sweden)
Daniel Almeida Marinho
2012-12-01
Full Text Available The purpose of this study was to analyse the effect of wearing a swimsuit on swimmer's passive drag. A computational fluid dynamics analysis was carried out to determine the hydrodynamic drag of a female swimmer's model (i wearing a standard swimsuit; (ii wearing a last generation swimsuit and; (iii with no swimsuit, wearing light underwear. The three-dimensional surface geometry of a female swimmer's model with different swimsuit/underwear was acquired through standard commercial laser scanner. Passive drag force and drag coefficient were computed with the swimmer in a prone position. Higher hydrodynamic drag values were determined when the swimmer was with no swimsuit in comparison with the situation when the swimmer was wearing a swimsuit. The last generation swimsuit presented lower hydrodynamic drag values, although very similar to standard swimsuit. In conclusion, wearing a swimsuit could positively influence the swimmer's hydrodynamics, especially reducing the pressure drag component.
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
Hydrodynamic Drag on Streamlined Projectiles and Cavities
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.
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.
Influence of hydrodynamic stress on the frictional drag of biofouling communities.
Hunsucker, J Travis; Hunsucker, Kelli Z; Gardner, Harrison; Swain, Geoffrey
2016-11-01
The role of hydrodynamic wall shear stresses on the development of the fouling community structure and resulting frictional drag were examined using a commercially available fouling release coating. Immersed test panels were exposed to three different hydrodynamic treatments, one static and two dynamic (corresponding to an estimated wall shear stress of 7.0 and 25.5 Pa). The drag of the panels was measured in a hydrodynamic test chamber at discrete time intervals over 35 days. The fouling community composition on the static panels was significantly different from the organisms observed on the dynamic panels. Despite different fouling community composition, the drag forces measured on the panels were very similar. This suggests that the frictional drag of low form and soft fouling communities are similar and that there may be a stepwise increase in frictional drag associated with the presence of mature calcareous organisms.
O'Neill, F. G.; Summerbell, K. J.
2016-12-01
The hydrodynamic drag of towed fishing gears leads to direct impacts on the benthic environment, and can play a major role in the overall economic efficiency of the fishing operation and emissions of nitrogen oxides, sulphur oxides and greenhouse gases such as CO2. Here we investigate some of the underpinning processes which govern these issues and make direct hydrodynamic drag measurements and calculate the hydrodynamic drag coefficients for a range of well-defined gear components that, when fished, are in contact with the seabed. We measure the concentration and particle size distribution of the sediment mobilised into the water column in the wake of these gear elements, at a range of towing speeds, and demonstrate that as the hydrodynamic drag increases the amount of sediment mobilised also increases. We also vary the weight of the elements and show that this does not influence the amount of sediment put into the water column. These results provide a better understanding of the physical and mechanical processes that take place when a towed fishing gear interacts with the seabed. They will permit the development of more fuel efficient gears and gears of reduced benthic impact and will improve the empirical modelling of the sediment mobilised into the turbulent wake behind towed fishing gears which will lead to better assessments of the environmental and ecological impact of fishing gears.
Drag Reducing and Cavitation Resistant Coatings
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Pease, Leonard F.
2016-12-28
Client, Green Building Systems (GBS), presented PNNL a coating reported to reduce drag and prevent cavitation damage on marine vessels, turbines and pumps. The composition of the coating remains proprietary but has as constituents including silicon oxides, aliphatic carbon chains, and fluorine rich particles. The coating is spray applied to surfaces. Prior GBS testing and experiments suggest reduction of both drag and cavitation on industrial scale propellers, but the underlying mechanism for these effects remains unclear. Yet, the application is compelling because even modest reductions in drag to marine vessels and cavitation to propellers and turbines present a significant economic and environmental opportunity. To discern among possible mechanisms, PNNL considered possible mechanisms with the client, executed multiple experiments, and completed one theoretical analysis (see appendix). The remainder of this report first considers image analysis to gain insight into drag reduction mechanisms and then exposes the coating to cavitation to explore its response to an intensely cavitating environment. Although further efforts may be warranted to confirm mechanisms, this report presents a first investigation into these coatings within the scope and resources of the technology assistance program (TAP).
Hydrodynamic flows of non-Fermi liquids: Magnetotransport and bilayer drag
Patel, Aavishkar A.; Davison, Richard A.; Levchenko, Alex
2017-11-01
We consider a hydrodynamic description of transport for generic two-dimensional electron systems that lack Galilean invariance and do not fall into the category of Fermi liquids. We study magnetoresistance and show that it is governed only by the electronic viscosity provided that the wavelength of the underlying disorder potential is large compared to the microscopic equilibration length. We also derive the Coulomb drag transresistance for double-layer non-Fermi-liquid systems in the hydrodynamic regime. As an example, we consider frictional drag between two quantum Hall states with half-filled lowest Landau levels, each described by a Fermi surface of composite fermions coupled to a U (1 ) gauge field. We contrast our results to prior calculations of drag of Chern-Simons composite particles and place our findings in the context of available experimental data.
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.
Parameters of Drag Reducing Polymers and Drag Reduction Performance in Single-Phase Water Flow
Directory of Open Access Journals (Sweden)
A. Abubakar
2014-07-01
Full Text Available This study presents experimental investigation about the effect of polymer parameters on the performance of the drag reducing polymers in single-phase water flowing in a horizontal pipe of 30.6 mm ID. Master solutions (1000 ppm of ten high-molecular weight polymers were injected at different flow rates to achieve polymer concentrations in the range of 2–40 ppm in the test section. The drag reduction increased with polymer concentration up to 10 ppm, above which it reached a plateau value. While the drag reduction at the plateau value increases with polymer molecular weight, the maximum drag reduction was not affected by the increase in polymer charge density up to 13%. For instance, the maximum drag reduction for anionic polymers with molecular weight 6–8 million Da. and charge density between 5 and 13% was around 60%, which decreased to around 38% for the polymer with charge density of 25%. Ionic polymers provided more drag reduction than nonionic ones. The overall conclusion is that drag reduction depends on polymer ability to form intermolecular associations and/or its flexibility, which can be enhanced by increasing molecular weight, decreasing charge density, and selecting smaller side groups in the main polymer backbone.
Anchor Dragging Analysis of Rock-Berm Using Smoothed Particle Hydrodynamics Method
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Jinho Woo
2015-01-01
Full Text Available This study presents dynamic responses of rock-berm structural system under anchor dragging and accordingly provides the characteristics of the stresses and displacements obtained. For the purpose, first, a rock-berm was modeled by the SPH (smoothed particle hydrodynamics method and piecewise Drucker-Prager material model by facilitating the associated software package—ANSYS-AUTODYN. Second, 2-ton stockless anchor was modeled as a rigid body and eventually dragging external force was obtained. Then, the dragging velocity (1 and 2 m/s was considered as a parameter to investigate the effect of its variation on the responses. Finally, the dragging tensile forces of the anchor cable were obtained and compared according to the dragging velocities. It is shown that the four-layer rock-berm gives the safety margin to the submarine power cable according to the unaffected gauge points near the cable. This safety is accomplished by the four layers (related to rock-berm height and the number of rock particles at each layer (related to rock-berm widths.
Surface modification of clutch plates to reduce disengaged drag torque
Aphale, Chinar R.
2005-11-01
Viscous drag torque in disengaged clutches is a significant source of power loss in modern transportation. The main way to reduce this drag torque is to introduce air between the plates when disengaged without reducing the transmission fluid flow eventually needed for reengagement. Six different groove patterns are tested experimentally to determine which have the lowest drag characteristics. Our computations using Fluent showed that the contact angle made by oil with the stationary plate is critical in determining aeration initiation. Experiments coating the stationary plate with an oleophobic substance like Teflon, confirmed these simulations. We will show torque comparisons and visualization through a quartz disk acting as one of the clutch plates.
Jiang, ChenXing; Li, FengChen
2015-09-01
In this study, a new control strategy for turbulent drag reduction involving ventilated cavitation is proposed. The configurational and hydrodynamic characteristics of ventilated cavities influenced by turbulent drag-reducing additives were experimentally studied in water tunnel. The test model was fixed in the water tunnel by a strut in the aft-part. Aqueous solutions of CTAC/NaSal (cetyltrimethyl ammonium chloride/sodium salicylate) with weight concentrations of 100, 200, 400 and 600 ppm (part per million), respectively, were injected into the ventilated air cavity from the edge of the cavitator with accurate control by an injection pump. The cavity configurations were recorded by a high-speed CCD camera. The hydrodynamic characteristics of the test model were measured by a six-component balance. Experimental results show that, within the presently tested cases, the lengths of cavity influenced by drag-reducing solution are smaller than normal condition (ventilated cavity) in water, but the asymmetry of the cavity is improved. The drag resisted by the test model is reduced dramatically (the maximum drag reduction can reach to 80%) and the re-entrant jet is more complex after the CTAC solution is injected into the cavity. Turbulent drag-reducing additives have the potential in enhancement of supercavitating asymmetry and further drag reduction.
Basu, Jaydeep; Begam, Nafisa; Chandran, Sivasurender; Sprung, Michael
2015-03-01
One of the central dogma of fluid physics is the no-slip boundary condition whose validity has come under intense scrutiny, especially in the fields of micro and nanofluidics. Although various studies show the violation of the no-slip condition its effect on flow of colloidal particles in viscous media has been rarely explored. Here we report unusually large reduction of effective drag experienced by polymer grafted nanoparticles moving through a highly viscous film of polymer, well above its glass transition temperature. The extent of drag reduction increases with decreasing temperature and polymer film thickness. We also observe apparent divergence of the wave vector dependent hydrodynamic interaction function of these nanoparticles with an anomalous power law exponent of ~ 2 at the lowest temperatures and film thickness. Such strong hydrodynamic interactions are not expected in polymer melts where these interactions are known to be screened to molecular dimensions. We provide evidence for the presence of large hydrodynamic slip at the nanoparticle-polymer interface and demonstrate its tunability with temperature and confinement. Our study suggests novel physics emerging in dynamics nanoparticles due to confinement and interface wettability in thin films of polymer nanocomposites.
Directory of Open Access Journals (Sweden)
Maziar Gholami Korzani
2017-04-01
Full Text Available Simulations of two-dimensional (2D flow past a circular cylinder with the smoothed particle hydrodynamics (SPH method were conducted in order to accurately determine the drag coefficient. The fluid was modeled as a viscous liquid with weak compressibility. Boundary conditions, such as a no-slip solid wall, inflow and outflow, and periodic boundaries, were employed to resemble the physical problem. A sensitivity analysis, which has been rarely addressed in previous studies, was conducted on several SPH parameters. Hence, the effects of distinct parameters, such as the kernel choices and the domain dimensions, were investigated with the goal of obtaining highly accurate results. A range of Reynolds numbers (1–500 was simulated, and the results were compared with existing experimental data. It was observed that the domain dimensions and the resolution of SPH particles, in comparison to the obstacle size, affected the obtained drag coefficient significantly. Other parameters, such as the background pressure, influenced the transient condition, but did not influence the steady state at which the drag coefficient was determined.
Why fibers are better turbulent drag reducing agents than polymers
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.
Oral cavity hydrodynamics and drag production in Balaenid whale suspension feeding.
Potvin, Jean; Werth, Alexander J
2017-01-01
Balaenid whales feed on large aggregates of small and slow-moving prey (predominantly copepods) through a filtration process enabled by baleen. These whales exhibit continuous filtration, namely, with the mouth kept partially opened and the baleen exposed to oncoming prey-laden waters while fluking. The process is an example of crossflow filtration (CFF) in which most of the particulates (prey) are separated from the substrate (water) without ever coming into contact with the filtering surface (baleen). This paper discusses the simulation of baleen filtration hydrodynamics based on a type of hydraulic circuit modeling commonly used in microfluidics, but adapted to the much higher Reynolds number flows typical of whale hydrodynamics. This so-called Baleen Hydraulic Circuit (BHC) model uses as input the basic characteristics of the flows moving through a section of baleen observed in a previous flume study by the authors. The model has low-spatial resolution but incorporates the effects of fluid viscosity, which doubles or more a whale's total body drag in comparison to non-feeding travel. Modeling viscous friction is crucial here since exposing the baleen system to the open ocean ends up tripling a whale's total wetted surface area. Among other findings, the BHC shows how CFF is enhanced by a large filtration surface and hence large body size; how it is carried out via the establishment of rapid anteroposterior flows transporting most of the prey-water slurry towards the oropharyngeal wall; how slower intra-baleen flows manage to transfer most of the substrate out of the mouth, all the while contributing only a fraction to overall oral cavity drag; and how these anteroposterior and intra-baleen flows lose speed as they approach the oropharyngeal wall.
Reducing drag of a commuter train, using engine exhaust momentum
Ha, Dong Keun
The objective of this thesis was to perform numerical investigations of two different methods of injecting fluid momentum into the air flow above a commuter train to reduce its drag. Based on previous aerodynamic modifications of heavy duty trucks in improving fuel efficiency, two structural modifications were designed and applied to a Metrolink Services commuter train in the Los Angeles (LA) County area to reduce its drag and subsequently improve fuel efficiency. The first modification was an L-shaped channel, added to the exhaust cooling fan above the locomotive roof to divert and align the exhaust gases in the axial direction. The second modification was adding an airfoil shaped lid over the L-shape channel, to minimize the drag of the perturbed structure, and thus reduce the overall drag. The computational fluid dynamic (CFD) software CCM+ from CD-Adapco with the ?-? turbulence model was used for the simulations. A single train set which consists of three vehicles: one locomotive, one trailer car and one cab car were used. All the vehicles were modeled based on the standard Metrolink fleet train size. The wind speed was at 90 miles per hour (mph), which is the maximum speed for the Orange County Metrolink line. Air was used as the exhaust gas in the simulation. The temperature of the exhausting air emitting out of the cooling fan on the roof was 150 F and the average fan speed was 120 mph. Results showed that with the addition of the lid, momentum injection results in reduced flow separation and pressure recovery behind the locomotive, which reduces the overall drag by at least 30%.
Hydrodynamic Characteristics of a Low-drag, Planing-tail Flying-boat Hull
Suydam, Henry B
1948-01-01
The hydrodynamic characteristics of a flying-boat incorporating a low-drag, planing-tail hull were determined from model tests made in Langley tank number 2 and compared with tests of the same flying boat incorporating a conventional-type hull. The planing-tail model, with which stable take-offs were possible for a large range of elevator positions at all center-of-gravity locations tested, had more take-off stability than the conventional model. No upper-limit porpoising was encountered by the planing-tail model. The maximum changes in rise during landings were lower for the planing-tail model than for the conventional model at most contact trims, an indication of improved landing stability for the planing-tail model. The hydrodynamic resistance of the planing-tail hull was lower than the conventional hull at all speeds, and the load-resistance ratio was higher for the planing-tail hull, being especially high at the hump. The static trim of the planing-tail hull was much higher than the conventional hull, but the variation of trim with speed during take-off was smaller.
A coating of passively oscillating flexible cilia to reduce drag
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.
Shen, Chongyang; Jin, Yan; Li, Baoguo; Zheng, Wenjuan; Huang, Yuanfang
2014-01-01
This study investigated effects of flow velocity on attachment of nanoparticles at primary minima in the presence of surface roughness under unfavorable chemical conditions. Saturated sand-packed column experiments were conducted at 0.1 and 0.2M NaCl using 30 nm polystyrene latex nanoparticles as model colloids. Particle attachment at primary minima was unambiguously determined by removing particles attached at secondary minima through introducing deionized water and excavating the packed beds. The calculated primary-minimum attachment efficiency was found to decrease with increasing flow velocity, indicating that the fraction of a collector surface that is available for attachment at primary minima decreases with increasing flow velocity. The torque analysis, however, showed that the adhesive torque that the particle experiences at primary minima is much larger than the maximum hydrodynamic drags of a porous medium for the flow velocities used. We attributed the discrepancy to the reason that the sand surface is very rough and the roughness mainly causes the attachment in primary minima under the experimental conditions used in this study. By considering influence of surface roughness in the torque analysis, our calculations show that while particle attachment in primary minima is favored atop of nanoasperities under unfavorable conditions, the adhesive torque that the particle experiences can be greatly reduced and, thus, the attachment is susceptible to flow drag. Whereas the increase of adhesive torque by surface roughness has been widely recognized in the literature, our study indicates that the rough asperities can also decrease adhesive torques for particles attached atop of them. © 2013.
Impact of the Microstructure of Polymer Drag Reducer on Slick-Water Fracturing
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Zhi-yu Liu
2017-01-01
Full Text Available Many studies have focused on the drag reduction performance of slick-water, but the microdrag reduction mechanism remains unclear since the microstructure of the drag reducer and its effect on this mechanism have not been well studied. In this study, the microstructure of the drag reducer in slick-water was effectively characterized by transmission electron microscopy. The viscoelasticity and drag reduction performance of the drag reducer with different microstructures were then investigated. Further, the effects of the microstructure of the drag reducer on the viscoelasticity and drag reduction performance of slick-water were analyzed. The results demonstrated that the viscoelasticity of slick-water is governed by the microstructure of the drag reducer, which exhibits a network structure. In addition, the drag reduction performance is related to the viscoelasticity. At low flow rates, the drag reduction performance is dominantly influenced by viscosity, whereas, at high flow rates, it is governed mainly by elasticity. Furthermore, the drag reducer with a uniformly distributed network structure exhibits the most stable drag reduction performance. This drag reducer was used in a field test and the obtained results were consistent with those of a laboratory experiment.
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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.
Riblets show most promise for reducing drag in pipelines
Energy Technology Data Exchange (ETDEWEB)
May, R. [HR Wallingford, Oxfordshire (United Kingdom)
1996-08-01
Flow resistance in pipes and conduits is a fundamental factor governing the design of any pipeline system and the economics of its operation. If the hydraulic resistance can be reduced, savings can be made in the size of pipes used, in pumping costs or in the gradients at which gravity pipes need to be laid. According to the well-established Colebrook-White equation, the drag exerted by pipe walls consists of two components: that due to the viscosity of the fluid, which tends to dominate at low velocity; and that due to the surface texture of walls which is dominant at high velocity. For this reason, most manufacturers aim to maximize the flow capacity of their pipes by producing the smoothest possible surface finish consistent with the materials and manufacturing techniques being used. The paper describes hydraulic roughness in pipes and reducing drag resistance with the use of riblets, which are small, longitudinal grooves formed on the internal walls of the pipe.
Truscott, Starr; Parkinson, J B; Ebert, John W , Jr; Valentine, E Floyd
1938-01-01
The present tests illustrate how the aerodynamic drag of a flying boat hull may be reduced by following closely the form of a low drag aerodynamic body and the manner in which the extent of the aerodynamic refinement is limited by poorer hydrodynamic performance. This limit is not sharply defined but is first evidenced by an abnormal flow of water over certain parts of the form accompanied by a sharp increase in resistance. In the case of models 74-A and 75, the resistance (sticking) occurs only at certain combinations of speed, load, and trim and can be avoided by proper control of the trim at high water speeds. Model 75 has higher water resistance at very high speeds than does model 74-A. With constant speed propellers and high takeoff speeds, it appears that the form of model 75 would give slightly better takeoff performance. Model 74-A, however, has lower aerodynamic drag than does model 75 for the same volume of hull.
2016-12-01
resiliency of this surface treatment . 14. SUBJECT TERMS superhydrophobic, superhydrophilic, Femto-second laser surface processing , skin friction drag...and Y. Kunitake, Frictional drag reduction with air lubricant over a super- water -repellent surface, Journal of Marine Science and Technology , vol...properties being extended to a variety of metallic substrates through the process of ablation due to femto-second laser surface processing (FLSP), it is
Reducing turbulent boundary layer drag by a sustainable thin-air film
Wang, Cong; Jeon, David; Gharib, Morteza
2017-11-01
Reduction of hydrodynamic frictional drag through introduction of air bubbles or films at the wall regions has been tried by several groups in the past. The main challenge for these approaches has been to sustain the air bubble or film under high turbulent velocity fluctuations. We will report a novel technique that allows maintaining stable oscillating air films over solid surface in order to obtain large drag reduction effect. Based on our DPIV results, we will present a potential mechanism for the Reynolds stress suppression in the near wall region. This work is supported by the Office of Naval Research under Grant No. N00014-15-1-2479.
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.
Grafted natural polymer as new drag reducing agent: An experimental approach
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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.
Analysis of Zero Reynolds Shear Stress Appearing in Dilute Surfactant Drag-Reducing Flow
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Weiguo Gu
2011-01-01
Full Text Available Dilute surfactant solution of 25 ppm in the two-dimensional channel is investigated experimentally compared with water flow. Particle image velocimetry (PIV system is used to take 2D velocity frames in the streamwise and wall-normal plane. Based on the frames of instantaneous vectors and statistical results, the phenomenon of zero Reynolds shear stress appearing in the drag-reducing flow is discussed. It is found that 25 ppm CTAC solution exhibits the highest drag reduction at Re = 25000 and loses drag reduction completely at Re = 40000. When drag reduction lies in the highest, Reynolds shear stress disappears and reaches zero although the RMS of the velocity fluctuations is not zero. By the categorization in four quadrants, the fluctuations of 25 ppm CTAC solution are distributed in all four quadrants equally at Re = 25000, which indicates that turnaround transportation happens in drag-reducing flow besides Reynolds shear stress transportation. Moreover, the contour distribution of streamwise velocity and the fluctuations suggests that turbulence transportation is depressed in drag-reducing flow. The viscoelasticity is possible to decrease the turbulence transportation and cause the turnaround transportation.
Drag-based 'hovering' in ducks: the hydrodynamics and energetic cost of bottom feeding.
Directory of Open Access Journals (Sweden)
Gal Ribak
Full Text Available Diving ducks use their webbed feet to provide the propulsive force that moves them underwater. To hold position near the bottom while feeding, ducks paddle constantly to resist the buoyant force of the body. Using video sequences from two orthogonal cameras we reconstructed the 3-dimensional motion of the feet through water and estimated the forces involved with a quasi-steady blade-element model. We found that during station holding, near the bottom, ducks use drag based propulsion with the webbed area of the foot moving perpendicular to the trajectory of the foot. The body was pitched at 76+/-3.47 degrees below the horizon and the propulsive force was directed 26+/-1.9 degrees ventral to the body so that 98% of the propulsive force in the sagittal plane of the duck worked to oppose buoyancy. The mechanical work done by moving both feet through a paddling cycle was 1.1+/-0.2 J which was equivalent to an energy expenditure of 3.7+/-0.5 W to hold position while feeding at 1.5 m depth. We conclude that in shallow water the high energetic cost of feeding in ducks is due to the need to paddle constantly against buoyancy even after reaching the bottom. The mechanical energy spent on holding position near the bottom, while feeding, is approximately 2 fold higher than previous estimates that were made for similar bottom depths but based on the presumed motion of the body instead of motion of the feet.
Directory of Open Access Journals (Sweden)
Li Dong Qing
2016-01-01
Full Text Available The breeze vibration duration of conductors is long, the vibration amplitude is strong and the frequency range is wide for electric power transmission lines in strong wind areas, which seriously affects the safe and stable operation of transmission lines. There are two design schemes of conductors which can achieve the purpose of reducing wind-induced disaster. One is enhancing the structural strength of conductors to withstand wind load, but the investment is enormous and the effect is limited. The other is developing drag reduced conductors to reduce wind load by changing conductor structure. This paper started from application feasibility analysis of drag reduced conductors and designed four drag reduced conductors by structure optimization of the conventional aluminium conductor steel reinforced JL/G1A-630/45-45/7, denoted as DFY630/45(45°-R3.5, DFY630/45(60°-R3.5, DFY630/45(45°–R3.2 and DFY630/45(60°-R3.2, respectively. The wind tunnel test was performed and the wind resistance coefficients in unit length of five conductors were compared. Result showed that the wind resistance coefficients in unit length of four drag reduced conductors were obviously lower than that of the conventional conductor. By controlling the manufacturing process, popularization and application of drag reduced conductors for transmission lines in strong wind areas can be realized.
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Chen-Xing Jiang
2014-04-01
Full Text Available The configurational and dynamic characteristics of water entry supercavities influenced by turbulent drag-reducing additives were studied through supercavitating projectile approach, experimentally and numerically. The projectile was projected vertically into water and aqueous solution of CTAC with weight concentrations of 100, 500, and 1000 ppm, respectively, using a pneumatic nail gun. The trajectories of the projectile and the supercavity configuration were recorded by a high-speed CCD camera. Besides, water entry supercavities in water and CTAC solution were numerically simulated based on unsteady RANS scheme, together with application of VOF multiphase model. The Cross viscosity model was adopted to represent the fluid property of CTAC solution. It was obtained that the numerical simulation results are in consistence with experimental data. Numerical and experimental results all show that the length and diameter of supercavity in drag-reducing solution are larger than those in water, and the drag coefficient is smaller than that in water; the maintaining time of supercavity is longer in solution as well. The surface tension plays an important role in maintaining the cavity. Turbulent drag-reducing additives have the potential in enhancement of supercavitation and drag reduction.
Directory of Open Access Journals (Sweden)
Anaïs Ramos-Fuertes
2013-12-01
Full Text Available Doñana National Park wetlands are located in southwest Spain, on the right bank of the Guadalquivir River, near the Atlantic Ocean coast. The wetlands dry out completely every summer and progressively flood again throughout the fall and winter seasons. Given the flatness of Doñana’s topography, the wind drag action can induce the flooding or emergence of extensive areas, detectable in remote sensing images. Envisat/ASAR scenes acquired before and during strong and persistent wind episodes enabled the spatial delineation of the wind-induced water displacement. A two-dimensional hydrodynamic model of Doñana wetlands was built in 2006 with the aim to predict the effect of proposed hydrologic restoration actions within Doñana’s basin. In this work, on-site wind records and concurrent ASAR scenes are used for the calibration of the wind-drag modeling by assessing different formulations. Results show a good adjustment between the modeled and observed wind drag effect. Displacements of up to 2 km in the wind direction are satisfactorily reproduced by the hydrodynamic model, while including an atmospheric stability parameter led to no significant improvement of the results. Such evidence will contribute to a more accurate simulation of hypothetic or design scenarios, when no information is available for the atmospheric stability assessment.
Injection of Drag Reducing Additives Into Turbulent Water Flows: Results from Factorial Design
1984-04-01
with edditive Injection was measured. The injection was then terminated and the "without- injsction" pressure drop was reoeitured. Finally the flow...result is of prime impetance in the optimization proceoe . Since the purpose of this studl Is to mazimie the drag- reducing performance of the
McMullen, Ryan; McKeon, Beverley
2017-11-01
It is well-known that small amounts of high-molecular weight polymers can drastically reduce turbulent drag in a liquid (Toms, 1948). Furthermore, recent work has shown that studying polymers in turbulence can shed light on the nature of the self-sustaining mechanisms of wall turbulence (White and Mungal, 2008; Graham, 2014). The focus of this talk is an investigation of the linear mechanisms at play in polymer drag-reduced turbulent channel flow. The resolvent framework introduced by McKeon and Sharma (2010) for Newtonian turbulence is extended to the viscoelastic case in order to study the most-amplified velocity and polymer stretching modes, explored in the case of creeping flow by Jovanović and coworkers (Jovanović and Kumar, 2010; Lieu et al., 2013). Particular attention is given to the role of critical layers, which have been shown to be important in the dynamics of Newtonian turbulence (McKeon and Sharma, 2010). Additionally, comparisons will be made with the lower branch of the P4 family of exact coherent states, which closely reproduce statistical features of polymer drag-reduced turbulence close to maximum drag reduction (Park and Graham, 2015). The support of the Dow Corporation is gratefully acknowledged.
Modification of Flow Structure Over a Van Model By Suction Flow Control to Reduce Aerodynamics Drag
Directory of Open Access Journals (Sweden)
Harinaldi Harinaldi
2012-05-01
Full Text Available Automobile aerodynamic studies are typically undertaken to improve safety and increase fuel efficiency as well as to find new innovation in automobile technology to deal with the problem of energy crisis and global warming. Some car companies have the objective to develop control solutions that enable to reduce the aerodynamic drag of vehicle and significant modification progress is still possible by reducing the mass, rolling friction or aerodynamic drag. Some flow control method provides the possibility to modify the flow separation to reduce the development of the swirling structures around the vehicle. In this study, a family van is modeled with a modified form of Ahmed's body by changing the orientation of the flow from its original form (modified/reversed Ahmed body. This model is equipped with a suction on the rear side to comprehensively examine the pressure field modifications that occur. The investigation combines computational and experimental work. Computational approach used a commercial software with standard k-epsilon flow turbulence model, and the objectives was to determine the characteristics of the flow field and aerodynamic drag reduction that occurred in the test model. Experimental approach used load cell in order to validate the aerodynamic drag reduction obtained by computational approach. The results show that the application of a suction in the rear part of the van model give the effect of reducing the wake and the vortex formation. Futhermore, aerodynamic drag reduction close to 13.86% for the computational approach and 16.32% for the experimental have been obtained.
Bragin, Denis E.; Thomson, Susan; Bragina, Olga; Statom, Gloria; Kameneva, Marina V.; Nemoto, Edwin M.
2016-01-01
Current treatments for traumatic brain injury (TBI) have not focused on improving microvascular perfusion. Drag-reducing polymers (DRP), linear, long-chain, blood soluble non-toxic macromolecules, may offer a new approach to improving cerebral perfusion by primary alteration of the fluid dynamic properties of blood. Nanomolar concentrations of DRP have been shown to improve hemodynamics in animal models of ischemic myocardium and limb, but have not yet been studied in the brain. Recently, we ...
Drag Reduction by Leidenfrost Vapor Layers
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.
Viscosity and Vorticity in Reduced Magneto-Hydrodynamics
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Joseph, Ilon [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2015-08-12
Magneto-hydrodynamics (MHD) critically relies on viscous forces in order for an accurate determination of the electric eld. For each charged particle species, the Braginskii viscous tensor for a magnetized plasma has the decomposition into matrices with special symmetries.
Drag Moderation by the Melting of an Ice Surface in Contact with Water
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.
Energy Technology Data Exchange (ETDEWEB)
McCallen, R; Salari, K; Ortega, J; DeChant, L; Hassan, B; Roy, C; Pointer, W; Browand, F; Hammache, M; Hsu, T; Leonard, A; Rubel, M; Chatalain, P; Englar, R; Ross, J; Satran, D; Heineck, J; Walker, S; Yaste, D; Storms, B
2004-06-17
At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the 'smart' design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments, and discuss our future direction.
Shi, Haifeng; Wang, Yi; Fang, Bo; Talmon, Yeshayahu; Ge, Wu; Raghavan, Srinivasa R; Zakin, Jacques L
2011-05-17
Drag-reducing (DR) surfactant fluids based on threadlike micelles are known to suffer from poor heat-transfer capabilities. Accordingly, the use of these fluids is limited to recirculating systems in which heat exchange is not important. Here, we show for the first time that light-responsive threadlike micelles can offer a potential solution to the above problem. The fluids studied here are composed of the cationic surfactant Ethoquad O/12 PG (EO12) and the sodium salt of trans-ortho-methoxycinnamic acid (OMCA). Initially, these fluids contain numerous threadlike micelles and, in turn, are strongly viscoelastic and effective at reducing drag (up to 75% DR). Upon exposure to UV light, OMCA is photoisomerized from trans to cis. This causes the micelles to shorten considerably, as confirmed by cryo-transmission electron microscopy (cryo-TEM). Because of the absence of long micelles, the UV-irradiated fluid shows lower viscoelasticity and much lower DR properties; however, its heat-transfer properties are considerably superior to the initial fluid. Thus, our study highlights the potential of switching off the DR (and in turn enhancing heat-transfer) at the inlet of a heat exchanger in a recirculating system. While the fluids studied here are not photoreversible, an extension of the above concept would be to subsequently switch on the DR again at the exit of the heat exchanger, thus ensuring an ideal combination of DR and heat-transfer properties.
Li, Bing; Sheng, Xiang; Xing, Wen-guo; Dong, Gui-lin; Liu, Yong-jun; Zhang, Chang-qiao; Chen, Xiang-jun; Zhou, Ning-ning; Qin, Zhan-bo
2010-12-01
The absorbing process in isolating and coating process of α-olefin drag reducing polymer was studied by molecular dynamic simulation method, on basis of coating theory of α-olefin drag reducing polymer particles with polyurethane as coating material. The distributions of sodium laurate, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate on the surface of α-olefin drag reducing polymer particles were almost the same, but the bending degrees of them were obviously different. The bending degree of SLA molecules was greater than those of the other two surfactant molecules. Simulation results of absorbing and accumulating structure showed that, though hydrophobic properties of surfactant molecules were almost the same, water density around long chain sulfonate sodium was bigger than that around alkyl sulfate sodium. This property goes against useful absorbing and accumulating on the surface of α-olefin drag reducing polymer particles; simulation results of interactions of different surfactant and multiple hydroxyl compounds on surface of particles showed that, interactions of different surfactant and one kind of multiple hydroxyl compound were similar to those of one kind of surfactant and different multiple hydroxyl compounds. These two contrast types of interactions also exhibited the differences of absorbing distribution and closing degrees to surface of particles. The sequence of closing degrees was derived from simulation; control step of addition polymerization interaction in coating process was absorbing mass transfer process, so the more closed to surface of particle the multiple hydroxyl compounds were, the easier interactions with isocyanate were. Simulation results represented the compatibility relationship between surfactant and multiple hydroxyl compounds. The isolating and coating processes of α-olefin drag reducing polymer were further understood on molecule and atom level through above simulation research, and based on the simulation, a
Roles of size and kinematics in drag reduction for two tandem flexible foils
Chao, Li-Ming; Zhang, Dong; Pan, Guang
2017-11-01
The effect of size and kinematics difference between two tandem flexible foils on drag reduction have been numerically studied. Compared with single foil, it is found that the kinematics difference between two foils would not play a significant role in reducing drag, while the size difference between two foils significantly affects the drag reduction in this two foil system. For leading foil, it always enjoys drag reduction and the highest drag reduction can be observed at bigger size difference and gap distance between two foil as 22%. For trailing foil, it suffers drag increase when the gap distance between two foils is smaller, while it enjoys drag decrease when the size difference between two foils is bigger enough. The hydrodynamic interaction between such actively undulated foils also has been uncovered and used to explain the mechanisms of drag reduction.
Bushnell, D. M.; Moore, K. J.
1991-01-01
Recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design. Consideration is given to form drag reduction (turbulent flow, vortex generation, mass transfer, and adaptations for body-intersection regions), skin-friction drag reduction (polymers, surfactants, and bubbles as surface 'additives'), reduction of the drag due to lift, drag-reduction studies on porpoises, and drag-reducing animal behavior (e.g., leaping out of the water by porpoises). The need for further research is stressed.
Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids
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.
Hydrodynamics of fossil fishes
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-01-01
From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377
Hydrodynamics of fossil fishes.
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-08-07
From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms.
Effect of drag-reducing polymers on Tubing Performance Curve (TPC) in vertical gas-liquid flows
Shoeibi Omrani, P.; Veltin, J.; Turkenburg, D.H.
2014-01-01
This paper discusses the effect of drag reducing polymers on the Tubing Performance Curve (TPC) of vertical air-water flows at near atmospheric conditions. The effect of polymer concentration, liquid and gas flow rates on the pressure drop curve (Tubing Performance Curve) was investigated
Bragin, Denis E; Thomson, Susan; Bragina, Olga; Statom, Gloria; Kameneva, Marina V; Nemoto, Edwin M
2016-01-01
Current treatments for traumatic brain injury (TBI) have not focused on improving microvascular perfusion. Drag-reducing polymers (DRP), linear, long-chain, blood-soluble, nontoxic macromolecules, may offer a new approach to improving cerebral perfusion by primary alteration of the fluid dynamic properties of blood. Nanomolar concentrations of DRP have been shown to improve hemodynamics in animal models of ischemic myocardium and ischemic limb, but have not yet been studied in the brain. We recently demonstrated that DRP improved microvascular perfusion and tissue oxygenation in a normal rat brain. We hypothesized that DRP could restore microvascular perfusion in hypertensive brain after TBI. Using in vivo two-photon laser scanning microscopy we examined the effect of DRP on microvascular blood flow and tissue oxygenation in hypertensive rat brains with and without TBI. DRP enhanced and restored capillary flow, decreased microvascular shunt flow, and, as a result, reduced tissue hypoxia in both nontraumatized and traumatized rat brains at high intracranial pressure. Our study suggests that DRP could constitute an effective treatment for improving microvascular flow in brain ischemia caused by high intracranial pressure after TBI.
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Haifeng Shi
2011-01-01
Full Text Available A novel high-efficiency vortex (HEV static mixer was used to locally enhance the heat transfer coefficient of a drag-reducing fluid, Ethoquad O/12 (EO12 (3 mM with sodium salicylate (NaSal (5 mM. Significant enhancement of heat transfer coefficients was observed. The Nusselt numbers were three to five times those of normal drag-reducing flow without mixer and were close to those of water at high Reynolds number with only modest energy penalty. In contrast, a Helix static mixer increased Nusselt number slightly with very high pressure loss. A performance number was used for comparisons among the HEV static mixer, the Helix static mixer, and water without mixer. The HEV static mixer had a performance number comparable to that of water. The enhanced heat transfer by the HEV static mixer resulted from streamwise vortices generated by the inclined tabs, which increased the convective heat transfer in the radial direction.
1987-04-01
Heterogeneous drag reduction in turbulent pipe flow. The Influence of Polymer Additives on Velocity and Temperature Fields, B. Gampert , ed., Springer-Verlag...Temperature Fields, B. Gampert , ed., Springer-Verlag, Berlin. Kim, H.T., S.J. Kline and W.C. Reynolds, 1971. The production of turbulence near a smooth
Miniaturized rotating disc rheometer test for rapid screening of drag reducing marine coatings
Dennington, Simon; Mekkhunthod, Ponkrit; Rides, Martin; Gibbs, David; Salta, Maria; Stoodley, Victoria; Wharton, Julian; Stoodley, Paul
2015-09-01
Frictional drag from the submerged hull surface of a ship is a major component of the resistance experienced when moving through water. Techniques for measuring frictional drag on test surfaces include towing tanks, flow tunnels and rotating discs. These large-scale methods present practical difficulties that hinder their widespread adoption and they are not conducive to rapid throughput. In this study a miniaturized benchtop rotating disc method is described that uses test discs 25 mm in diameter. A highly sensitive analytical rheometer is used to measure the torque acting on the discs rotating in water. Frictional resistance changes are estimated by comparing momentum coefficients. Model rough surfaces were prepared by attaching different grades of sandpaper to the disc surface. Discs with experimental antifouling coatings applied were exposed in the marine environment for the accumulation of microbial fouling, and the rotor was capable of detecting the increased drag due to biofilm formation. The drag due to biofilm was related to an equivalent sand roughness.
Li, Feng-Chen; Wang, Lu; Cai, Wei-Hua
2015-07-01
A mixed subgrid-scale (SGS) model based on coherent structures and temporal approximate deconvolution (MCT) is proposed for turbulent drag-reducing flows of viscoelastic fluids. The main idea of the MCT SGS model is to perform spatial filtering for the momentum equation and temporal filtering for the conformation tensor transport equation of turbulent flow of viscoelastic fluid, respectively. The MCT model is suitable for large eddy simulation (LES) of turbulent drag-reducing flows of viscoelastic fluids in engineering applications since the model parameters can be easily obtained. The LES of forced homogeneous isotropic turbulence (FHIT) with polymer additives and turbulent channel flow with surfactant additives based on MCT SGS model shows excellent agreements with direct numerical simulation (DNS) results. Compared with the LES results using the temporal approximate deconvolution model (TADM) for FHIT with polymer additives, this mixed SGS model MCT behaves better, regarding the enhancement of calculating parameters such as the Reynolds number. For scientific and engineering research, turbulent flows at high Reynolds numbers are expected, so the MCT model can be a more suitable model for the LES of turbulent drag-reducing flows of viscoelastic fluid with polymer or surfactant additives. Project supported by the China Postdoctoral Science Foundation (Grant No. 2011M500652), the National Natural Science Foundation of China (Grant Nos. 51276046 and 51206033), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20112302110020).
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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.
Reducing the pressure drag of a D-shaped bluff body using linear feedback control
Dalla Longa, L.; Morgans, A. S.; Dahan, J. A.
2017-12-01
The pressure drag of blunt bluff bodies is highly relevant in many practical applications, including to the aerodynamic drag of road vehicles. This paper presents theory revealing that a mean drag reduction can be achieved by manipulating wake flow fluctuations. A linear feedback control strategy then exploits this idea, targeting attenuation of the spatially integrated base (back face) pressure fluctuations. Large-eddy simulations of the flow over a D-shaped blunt bluff body are used as a test-bed for this control strategy. The flow response to synthetic jet actuation is characterised using system identification, and controller design is via shaping of the frequency response to achieve fluctuation attenuation. The designed controller successfully attenuates integrated base pressure fluctuations, increasing the time-averaged pressure on the body base by 38%. The effect on the flow field is to push the roll-up of vortices further downstream and increase the extent of the recirculation bubble. This control approach uses only body-mounted sensing/actuation and input-output model identification, meaning that it could be applied experimentally.
Shape optimization of active and passive drag-reducing devices on a D-shaped bluff body
Semaan, Richard
2016-01-01
Shape optimization of an active and a passive drag-reducing device on a two-dimensional D-shaped bluff body is performed. The two devices are: Coanda actuator, and randomly-shaped trailing-edge flap. The optimization sequence is performed by coupling the genetic algorithm software DAKOTA to the mesh generator Pointwise and to the CFD solver OpenFOAM. For the the active device the cost functional is the power ratio, whereas for the passive device it is the drag coefficient. The optimization leads to total power savings of $\\approx 70\\%$ for the optimal Coanda actuator, and a 40\\% drag reduction for the optimal flap. This reduction is mainly achieved through streamlining the base flow and suppressing the vortex shedding. The addition of either an active or a passive device creates two additional smaller recirculation regions in the base cavity that shifts the larger recirculation region away from the body and increases the base pressure. The results are validated against more refined URANS simulations for selec...
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Ding Z
2017-02-01
Full Text Available Zhijie Ding,1,* Marion Joy,1,* Marina V Kameneva,1-3 Partha Roy1,3-6 1Department of Bioengineering, 2Department of Surgery, 3McGowan Institute of Regenerative Medicine, 4Department of Pathology, 5Department of Cell Biology, 6Magee Women’s Research Institute, University of Pittsburgh, Pittsburgh, PA, USA *These authors contributed equally to this work Abstract: Metastasis is the leading cause of cancer mortality. Extravasation of cancer cells is a critical step of metastasis. We report a novel proof-of-concept study that investigated whether non-toxic blood-soluble chemical agents capable of rheological modification of the near-vessel-wall blood flow can reduce extravasation of tumor cells and subsequent development of metastasis. Using an experimental metastasis model, we demonstrated that systemic administration of nanomolar concentrations of so-called drag-reducing polymer dramatically impeded extravasation and development of pulmonary metastasis of breast cancer cells in mice. This is the first proof-of-principle study to directly demonstrate physical/rheological, as opposed to chemical, way to prevent cancer cells from extravasation and developing metastasis and, thus, it opens the possibility of a new direction of adjuvant interventional approach in cancer. Keywords: breast cancer, metastasis, extravasation, hemodynamics, drag-reducing polymer, blood cell traffic, microvessels
Energy Technology Data Exchange (ETDEWEB)
Clark, D. S.; Robey, H. F.; Smalyuk, V. A. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States)
2015-05-15
Encouraging progress is being made in demonstrating control of ablation front hydrodynamic instability growth in inertial confinement fusion implosion experiments on the National Ignition Facility [E. I. Moses, R. N. Boyd, B. A. Remington, C. J. Keane, and R. Al-Ayat, Phys. Plasmas 16, 041006 (2009)]. Even once ablation front stabilities are controlled, however, instability during the stagnation phase of the implosion can still quench ignition. A scheme is proposed to reduce the growth of stagnation phase instabilities through the reverse of the “adiabat shaping” mechanism proposed to control ablation front growth. Two-dimensional radiation hydrodynamics simulations confirm that improved stagnation phase stability should be possible without compromising fuel compression.
Margolis, Stephen B.
1997-01-01
which steady, planar burning is unstable to nonsteady, and/or nonplanar (cellular) modes of burning. These instabilities thus lead to a number of interesting phenomena, such as the sloshing type of waves that have been observed in mixtures of HAN and TriEthanolAmmonium Nitrate (TEAN) with water. Although the Froude number was treated as an O(1) quantity in these studies, the limit of small inverse Froude number corresponding to the microgravity regime is increasingly of interest and can be treated explicitly, leading to various limiting forms of the models, the neutral stability boundaries, and, ultimately, the evolution equations that govern the nonlinear dynamics of the propagating reaction front. In the present work, we formally exploit this limiting parameter regime to compare some of the features of hydrodynamic instability of liquid-propellant combustion at reduced gravity with the same phenomenon at normal gravity.
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Colin Ware
Full Text Available Forces due to propulsion should approximate forces due to hydrodynamic drag for animals horizontally swimming at a constant speed with negligible buoyancy forces. Propulsive forces should also correlate with energy expenditures associated with locomotion-an important cost of foraging. As such, biologging tags containing accelerometers are being used to generate proxies for animal energy expenditures despite being unable to distinguish rotational movements from linear movements. However, recent miniaturizations of gyroscopes offer the possibility of resolving this shortcoming and obtaining better estimates of body accelerations of swimming animals. We derived accelerations using gyroscope data for swimming Steller sea lions (Eumetopias jubatus, and determined how well the measured accelerations correlated with actual swimming speeds and with theoretical drag. We also compared dive averaged dynamic body acceleration estimates that incorporate gyroscope data, with the widely used Overall Dynamic Body Acceleration (ODBA metric, which does not use gyroscope data. Four Steller sea lions equipped with biologging tags were trained to swim alongside a boat cruising at steady speeds in the range of 4 to 10 kph. At each speed, and for each dive, we computed a measure called Gyro-Informed Dynamic Acceleration (GIDA using a method incorporating gyroscope data with accelerometer data. We derived a new metric-Averaged Propulsive Body Acceleration (APBA, which is the average gain in speed per flipper stroke divided by mean stroke cycle duration. Our results show that the gyro-based measure (APBA is a better predictor of speed than ODBA. We also found that APBA can estimate average thrust production during a single stroke-glide cycle, and can be used to estimate energy expended during swimming. The gyroscope-derived methods we describe should be generally applicable in swimming animals where propulsive accelerations can be clearly identified in the signal
Trites, Andrew W.; Rosen, David A. S.; Potvin, Jean
2016-01-01
Forces due to propulsion should approximate forces due to hydrodynamic drag for animals horizontally swimming at a constant speed with negligible buoyancy forces. Propulsive forces should also correlate with energy expenditures associated with locomotion—an important cost of foraging. As such, biologging tags containing accelerometers are being used to generate proxies for animal energy expenditures despite being unable to distinguish rotational movements from linear movements. However, recent miniaturizations of gyroscopes offer the possibility of resolving this shortcoming and obtaining better estimates of body accelerations of swimming animals. We derived accelerations using gyroscope data for swimming Steller sea lions (Eumetopias jubatus), and determined how well the measured accelerations correlated with actual swimming speeds and with theoretical drag. We also compared dive averaged dynamic body acceleration estimates that incorporate gyroscope data, with the widely used Overall Dynamic Body Acceleration (ODBA) metric, which does not use gyroscope data. Four Steller sea lions equipped with biologging tags were trained to swim alongside a boat cruising at steady speeds in the range of 4 to 10 kph. At each speed, and for each dive, we computed a measure called Gyro-Informed Dynamic Acceleration (GIDA) using a method incorporating gyroscope data with accelerometer data. We derived a new metric—Averaged Propulsive Body Acceleration (APBA), which is the average gain in speed per flipper stroke divided by mean stroke cycle duration. Our results show that the gyro-based measure (APBA) is a better predictor of speed than ODBA. We also found that APBA can estimate average thrust production during a single stroke-glide cycle, and can be used to estimate energy expended during swimming. The gyroscope-derived methods we describe should be generally applicable in swimming animals where propulsive accelerations can be clearly identified in the signal—and they should
Numerical Study of Hydrodynamic Forces for AFM Operations in Liquid
Directory of Open Access Journals (Sweden)
Tobias Berthold
2017-01-01
Full Text Available For advanced atomic force microscopy (AFM investigation of chemical surface modifications or very soft organic sample surfaces, the AFM probe tip needs to be operated in a liquid environment because any attractive or repulsive forces influenced by the measurement environment could obscure molecular forces. Due to fluid properties, the mechanical behavior of the AFM cantilever is influenced by the hydrodynamic drag force due to viscous friction with the liquid. This study provides a numerical model based on computational fluid dynamics (CFD and investigates the hydrodynamic drag forces for different cantilever geometries and varying fluid conditions for Peakforce Tapping (PFT in liquids. The developed model was verified by comparing the predicted values with published results of other researchers and the findings confirmed that drag force dependence on tip speed is essentially linear in nature. We observed that triangular cantilever geometry provides significant lower drag forces than rectangular geometry and that short cantilever offers reduced flow resistance. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as a temperature induced variation of the drag force could be demonstrated. The acting forces are lowest in ultrapure water, whereas with increasing ethanol concentrations the drag forces increase.
Numerical Study of Hydrodynamic Forces for AFM Operations in Liquid.
Berthold, Tobias; Benstetter, Guenther; Frammelsberger, Werner; Rodríguez, Rosana; Nafría, Montserrat
2017-01-01
For advanced atomic force microscopy (AFM) investigation of chemical surface modifications or very soft organic sample surfaces, the AFM probe tip needs to be operated in a liquid environment because any attractive or repulsive forces influenced by the measurement environment could obscure molecular forces. Due to fluid properties, the mechanical behavior of the AFM cantilever is influenced by the hydrodynamic drag force due to viscous friction with the liquid. This study provides a numerical model based on computational fluid dynamics (CFD) and investigates the hydrodynamic drag forces for different cantilever geometries and varying fluid conditions for Peakforce Tapping (PFT) in liquids. The developed model was verified by comparing the predicted values with published results of other researchers and the findings confirmed that drag force dependence on tip speed is essentially linear in nature. We observed that triangular cantilever geometry provides significant lower drag forces than rectangular geometry and that short cantilever offers reduced flow resistance. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as a temperature induced variation of the drag force could be demonstrated. The acting forces are lowest in ultrapure water, whereas with increasing ethanol concentrations the drag forces increase.
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.
Vakarelski, Ivan U; Chan, Derek Y C; Thoroddsen, Sigurdur T
2014-08-21
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 10(4) and 10(6), 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.
Effect of wetted surface area on friction, pressure, wave and total drag of a kayak.
Gomes, Beatriz B; Machado, Leandro; Ramos, Nuno V; Conceição, Filipe A V; Sanders, Ross H; Vaz, Mário A P; Vilas-Boas, João Paulo; Pendergast, David R
2017-11-21
Using theoretical principles, the components of drag (friction DF, pressure DPR and wave DW) of a single-seat kayak were analysed. The purpose was to examine the effect of changes in wetted surface area due to changes in kayaker's weight and the relative contribution of DF, DPR and DW to the total passive drag as function of velocity. The total passive drag values were based on experimental data collected in a single-seat kayak. Three different kayaker simulated weights were tested - 65, 75 and 85 kg. DF was the drag component that contributed the greatest percentage (between 60 and 68% at 5.56 m/s the top velocity tested) to the total passive drag for all the velocities tested and simulated weights. DW was the most affected by the increase in kayaker's simulated weight, mainly when comparing 65/75 to 85 kg. Results support the importance of a kayak design selection that minimises the kayak's drag for the individual weight of the kayaker. Also, the results suggest that the path for better hydrodynamic kayak performance should seek changes that can reduce DF, DPR and DW with DF offering the most potential to reduce passive drag.
Energy Technology Data Exchange (ETDEWEB)
Paes, Diogo M.; Franca, Fernando A. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Faculdade de Engenharia Mecanica; Bizotto, Vanessa C. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Lab. Kelsen Valente Serra (LABPETRO); Sabadini, Edvaldo [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Inst. de Quimica
2008-07-01
The phenomenon of hydrodynamic drag reduction (DR) takes place when small amounts of polymer with high molecular weight are added to a turbulent flow. This phenomenon is very important in pumping process, mainly in petroleum industries. Studies on DR have been made using high-grade polyacrylamide (PAM) and a commercial polymer (FA920, basically composed by PAM) in water solution, both with a high molecular weight. At first, studies were developed in a double gap type rheometer using small amount of polymer. They provided information on the polymer concentration in which the maximum DR was reached, the amount of drag reduction and the solution mechanical stability along a turbulent shearing process. The results indicated a limiting 17%DR when a 2 ppm aqueous solution of high grade 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-UNICAMP comprised of pressure drop measurements in actual pipe flows, single water and two-phase airwater flows, using the previous knowledge acquired with the viscometer tests. In the former case, the classical Moody diagram, (f vs Re) has been drawn to show the %DR in terms of the friction factor reduction for the Reynolds number in the 2x10{sup 4} to 10{sup 5} range. Single phase flows attained up to 37% DR with commercial PAM (FA 920), depending on the polymer concentration. Preliminary results of DR tests performed with air-water flows, in different flow patterns - stratified-wavy and slug flows, are shown. To infer the air-water flow pattern, high speed filming was used. (author)
Jashnsaz, Hossein; Al Juboori, Mohammed; Weistuch, Corey; Miller, Nicholas; Nguyen, Tyler; Meyerhoff, Viktoria; McCoy, Bryan; Perkins, Stephanie; Wallgren, Ross; Ray, Bruce D; Tsekouras, Konstantinos; Anderson, Gregory G; Pressé, Steve
2017-03-28
The Gram-negative Bdellovibrio bacteriovorus (BV) is a model bacterial predator that hunts other bacteria and may serve as a living antibiotic. Despite over 50 years since its discovery, it is suggested that BV probably collides into its prey at random. It remains unclear to what degree, if any, BV uses chemical cues to target its prey. The targeted search problem by the predator for its prey in three dimensions is a difficult problem: it requires the predator to sensitively detect prey and forecast its mobile prey's future position on the basis of previously detected signal. Here instead we find that rather than chemically detecting prey, hydrodynamics forces BV into regions high in prey density, thereby improving its odds of a chance collision with prey and ultimately reducing BV's search space for prey. We do so by showing that BV's dynamics are strongly influenced by self-generated hydrodynamic flow fields forcing BV onto surfaces and, for large enough defects on surfaces, forcing BV in orbital motion around these defects. Key experimental controls and calculations recapitulate the hydrodynamic origin of these behaviors. While BV's prey (Escherichia coli) are too small to trap BV in hydrodynamic orbit, the prey are also susceptible to their own hydrodynamic fields, substantially confining them to surfaces and defects where mobile predator and prey density is now dramatically enhanced. Colocalization, driven by hydrodynamics, ultimately reduces BV's search space for prey from three to two dimensions (on surfaces) even down to a single dimension (around defects). We conclude that BV's search for individual prey remains random, as suggested in the literature, but confined, however-by generic hydrodynamic forces-to reduced dimensionality. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Anon.
1999-07-01
Research engineers at DaimlerChrysler Aerospace Airbus have developed a new technology which may result in 16 percent fuel savings in big aeroplanes. The aeroplane skin is perforated using laser technology, and the surface air is sucked off for a drastic reduction of drag. [German] Forscher von DaimlerChrysler Aerospace Airbus haben jetzt eine neue Technik entwickelt, mit der sie in Zukunft den Treibstoffverbrauch von grossen Flugzeugen um rund 16 Prozent reduzieren koennten. Der Trick dabei: Mit Lasern perforieren sie die Flugzeughaut, saugen die Luft an deren Oberflaeche ab und senken so drastisch den Luftwiderstand. (orig.)
Hydrodynamic modeling of semi-planing hulls with air cavities
Directory of Open Access Journals (Sweden)
Konstantin I. Matveev
2015-05-01
Full Text Available High-speed heavy loaded monohull ships can benefit from application of drag-reducing air cavities under stepped hull bottoms. The subject of this paper is the steady hydrodynamic modeling of semi-planing air-cavity hulls. The current method is based on a linearized potential-flow theory for surface flows. The mathematical model description and parametric calculation results for a selected configuration with pressurized and open air cavities are presented.
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.
Kim, Kyoungyoun; Sureshkumar, Radhakrishna
2013-06-01
To study the influence of dynamic interactions between turbulent vortical structures and polymer stress on turbulent friction drag reduction, a series of simulations of channel flow is performed. We obtain self-consistent evolution of an initial eddy in the presence of polymer stresses by utilizing the finitely extensible nonlinear elastic-Peterlin (FENE-P) model. The initial eddy is extracted by the conditional averages for the second quadrant event from fully turbulent Newtonian flow, and the initial polymer conformation fields are given by the solutions of the FENE-P model equations corresponding to the mean shear flow in the Newtonian case. At a relatively low Weissenberg number We(τ) (=50), defined as the ratio of the polymer relaxation time to the wall time scale, the generation of new vortices is inhibited by polymer-induced countertorques. Thus fewer vortices are generated in the buffer layer. However, the head of the primary hairpin is unaffected by the polymer stress. At larger We(τ) values (≥100), the hairpin head becomes weaker and vortex autogeneration and Reynolds stress growth are almost entirely suppressed. The temporal evolution of the vortex strength and polymer torque magnitude reveals that polymer extension by the vortical motion results in a polymer torque that increases in magnitude with time until a maximum value is reached over a time scale comparable to the polymer relaxation time. The polymer torque retards the vortical motion and Reynolds stress production, which in turn weakens flow-induced chain extension and torque itself. An analysis of the vortex time scales reveals that with increasing We(τ), vortical motions associated with a broader range of time scales are affected by the polymer stress. This is qualitatively consistent with Lumley's time criterion for the onset of drag reduction.
Daly, Amanda R; Sobajima, Hideo; Olia, Salim E; Takatani, Setsuo; Kameneva, Marina V
2010-01-01
In vitro evaluation of the potential of a circulatory-assist device to damage blood cells has generally been performed using blood from various species. Problems with this approach include the variability of blood sensitivity to mechanical stress in different species, preparation of blood including the adjustment of hematocrit to a standard value, changes in the mechanical properties of blood that occur during storage, and necessity to pool blood samples to obtain an adequate amount of blood for in vitro circulating systems. We investigated whether the mechanical degradation of a drag-reducing polymer (DRP) solution resulting in the loss of drag-reducing ability can indicate the degree of shear-induced blood damage within blood pumps. DRP solution (polyethylene oxide, 4,500 kDa, 1,000 ppm) or porcine blood were driven through a turbulent flow system by a centrifugal pump, either the Bio-Pump BPX-80 (Medtronic, Inc.) or CentriMag (Levitronix LLC) at a constant pressure gradient of 300 mm Hg for 120 minutes. DRP mechanical degradation was evaluated by reduction of flow rate and solution viscosity. A proposed index of DRP mechanical degradation (PDI) is similar to the normalized index of hemolysis (NIH) typically used to quantify the results of in vitro testing of blood pumps. Results indicate that the mechanical degradation of DRP solutions may provide a sensitive standard method for the evaluation of potential blood trauma produced by blood pumps without the use of blood.
Aerodynamic drag on intermodal railcars
Kinghorn, Philip; Maynes, Daniel
2014-11-01
The aerodynamic drag associated with transport of commodities by rail is becoming increasingly important as the cost of diesel fuel increases. This study aims to increase the efficiency of intermodal cargo trains by reducing the aerodynamic drag on the load carrying cars. For intermodal railcars a significant amount of aerodynamic drag is a result of the large distance between loads that often occurs and the resulting pressure drag resulting from the separated flow. In the present study aerodynamic drag data have been obtained through wind tunnel testing on 1/29 scale models to understand the savings that may be realized by judicious modification to the size of the intermodal containers. The experiments were performed in the BYU low speed wind tunnel and the test track utilizes two leading locomotives followed by a set of five articulated well cars with double stacked containers. The drag on a representative mid-train car is measured using an isolated load cell balance and the wind tunnel speed is varied from 20 to 100 mph. We characterize the effect that the gap distance between the containers and the container size has on the aerodynamic drag of this representative rail car and investigate methods to reduce the gap distance.
Shi, Haifeng; Ge, Wu; Oh, Hyuntaek; Pattison, Sean M; Huggins, Jacob T; Talmon, Yeshayahu; Hart, David J; Raghavan, Srinivasa R; Zakin, Jacques L
2013-01-08
A photoresponsive micellar solution is developed as a promising working fluid for district heating/cooling systems (DHCs). It can be reversibly switched between a drag reduction (DR) mode and an efficient heat transfer (EHT) mode by light irradiation. The DR mode is advantageous during fluid transport, and the EHT mode is favored when the fluid passes through heat exchangers. This smart fluid is an aqueous solution of cationic surfactant oleyl bis(2-hydroxyethyl)methyl ammonium chloride (OHAC, 3.4 mM) and the sodium salt of 4-phenylazo benzoic acid (ACA, 2 mM). Initially, ACA is in a trans configuration and the OHAC/ACA solution is viscoelastic and exhibits DR (of up to 80% relative to pure water). At the same time, this solution is not effective for heat transfer. Upon UV irradiation, trans-ACA is converted to cis-ACA, and in turn, the solution is converted to its EHT mode (i.e., it loses its viscoelasticity and DR) but it now has a heat-transfer capability comparable to that of water. Subsequent irradiation with visible light reverts the fluid to its viscoelastic DR mode. The above property changes are connected to photoinduced changes in the nanostructure of the fluid. In the DR mode, the OHAC/trans-ACA molecules assemble into long threadlike micelles that impart viscoelasticity and DR capability to the fluid. Conversely, in the EHT mode the mixture of OHAC and cis-ACA forms much shorter cylindrical micelles that contribute to negligible viscoelasticity and effective heat transfer. These nanostructural changes are confirmed by cryo-transmission electron microscopy (cryo-TEM), and the photoisomerization of trans-ACA and cis-ACA is verified by (1)H NMR.
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
Zheng, Tianyu; Cherubin, Patrick; Cilenti, Lucia; Teter, Ken; Huo, Qun
2016-02-07
The hydrodynamic dimension of a protein is a reflection of both its molecular weight and its tertiary structures. Studying the hydrodynamic dimensions of proteins in solutions can help elucidate the structural properties of proteins. Here we report a simple and fast method to measure the hydrodyamic size of a relatively small protein, protein disulfide isomerase (PDI), using gold nanoparticle probes combined with dynamic light scattering. Proteins can readily adsorb to citrate-capped gold nanoparticles to form a protein corona. By measuring the average diameter of the gold nanoparticles before and after protein corona formation, the hydrodynamic diameter of the protein can be deduced from the net particle size increase of the assay solution. This study found that when the disulfide bonds in PDI are reduced to thiols, the reduced PDI exhibits a smaller hydrodynamic diameter than the oxided PDI. This finding is in good agreement with the X-ray diffraction analysis of PDI in single crystals. In comparison with other techniques that are used for protein hydrodynamic size analysis, the current method is easy to use, requires a trace amount of protein samples, with results obtained in minutes instead of hours.
Progress in Frictional Drag Reduction Summer 1971 to Summer 1972
1973-01-01
additives, indicates equally significant drag reduction. One high polymer that shows extreme promise as a drag reducing additive in blood flow is okra ...1972. 9 Lindeman, L. F., "Polymer Injection for Drag Reduction," M.S. thesis , Department of Civil Engineering, Colorado State University, Fort Collins...K.-S., "Measurement of Complex Viscosity in Solutions at Finite Shear Strains," Ph.D. Thesis , University of Missouri - Rolla, 1971. 16 6. Drag
Hill, D. Christopher
1994-12-01
previously a description was given of an active control scheme using wall transpiration that leads to a 15% reduction in surface skin friction beneath a turbulent boundary layer, according to direct numerical simulation. In this research brief further details of that scheme and its variants are given together with some suggestions as to how sensor/actuator arrays could be configured to reduce surface drag. The research which is summarized here was performed during the first half of 1994. This research is motivated by the need to understand better how the dynamics of near-wall turbulent flow can be modified so that skin friction is reduced. The reduction of turbulent skin friction is highly desirable in many engineering applications. Experiments and direct numerical simulations have led to an increased understanding of the cycle of turbulence production and transport in the boundary layer and raised awareness of the possibility of disrupting the process with a subsequent reduction in turbulent skin friction. The implementation of active feedback control in a computational setting is a viable approach for the investigation of the modifications to the flow physics that can be achieved. Bewley et al. and Hill describe how ideas from optimal control theory are employed to give 'sub-optimal' drag reduction schemes. The objectives of the work reported here is to investigate in greater detail the assumptions implicit within such schemes and their limitations. It is also our objective to describe how an array of sensors and actuators could be arranged and interconnected to form a 'smart' surface which has low skin friction.
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.
Vertical variations of coral reef drag forces
Asher, Shai; Niewerth, Stephan; Koll, Katinka; Shavit, Uri; LWI Collaboration; Technion Collaboration
2017-11-01
Corals rely on water flow for the supply of nutrients, particles and energy. Therefore, modeling of processes that take place inside the reef, such as respiration and photosynthesis, relies on models that describe the flow and concentration fields. Due to the high spatial heterogeneity of branched coral reefs, depth average models are usually applied. Such an average approach is insufficient when the flow spatial variation inside the reef is of interest. We report on measurements of vertical variations of drag force that are needed for developing 3D flow models. Coral skeletons were densely arranged along a laboratory flume. Two corals were CT-scanned and replaced with horizontally sliced 3D printed replicates. Drag profiles were measured by connecting the slices to costume drag sensors and velocity profiles were measured using a LDV. The measured drag of whole colonies was in excellent agreement with previous studies; however, these studies never showed how drag varies inside the reef. In addition, these distributions of drag force showed an excellent agreement with momentum balance calculations. Based on the results, we propose a new drag model that includes the dispersive stresses, and consequently displays reduced vertical variations of the drag coefficient.
Dassele, M. A.; Fairall, H.
1978-01-01
Wire-drag system improves wire profile and applies consistent drag to wire. Wire drag is continuously adjustable from zero drag to tensile strength of wire. No-sag wire drag is easier to thread than former system and requires minimal downtime for cleaning and maintenance.
Roskam, J.
1975-01-01
A discussion of data of and methods for predicting trim drag is presented. Specifically the following subjects are discussed: (1) economic impact of trim drag; (2) the trim drag problem in propeller driven airplanes and the effect of propeller and nacelle location; (3) theoretical procedures for predicting trim drag; and (4) research needs in the area of trim drag.
The Hamiltonian approach in classification and integrability of hydrodynamic chains
Pavlov, Maxim V.
2006-01-01
New approach in classification of integrable hydrodynamic chains is established. This is the method of the Hamiltonian hydrodynamic reductions. Simultaneously, this approach yields explicit Hamiltonian hydrodynamic reductions of the Hamiltonian hydrodynamic chains. The concept of reducible Poisson brackets is established. Also this approach is useful for non-Hamiltonian hydrodynamic chains. The deformed Benney hydrodynamic chain is considered.
Some comments on fuselage drag
Roskam, J.
1975-01-01
The following areas relating to fuselage drag are considered: (1) fuselage fineness - ratio and why and how this can be selected during preliminary design; (2) windshield drag; (3) skin roughness; and (4) research needs in the area of fuselage drag.
Bubble drag reduction requires large bubbles
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.
Margolis, Stephen B.
1998-01-01
The classical Landau/Levich models of liquid-propellant combustion, despite their relative simplicity, serve as seminal examples that correctly describe the onset of hydrodynamic instability in reactive systems. Recently, these two separate models have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed either numerically or analytically in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity and other parameters on the hydrodynamic instability of the propagating liquid/gas interface. In particular, an analytical expression is derived for the neutral stability boundary A(sub p)(k), where A(sub p) is the pressure sensitivity of the burning rate and k is the wavenumber of the disturbance. The results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity (both liquid and gas) and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limiting case of weak gravity, it is shown that hydrodynamic instability in liquid-propellant combustion is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumber disturbances. It is also demonstrated that, in general, surface tension and the viscosity of both the liquid and gas phases each produce comparable stabilizing effects in the large-wavenumber regime, thereby providing important modifications to previous analyses in which one or more of these effects were neglected.
The Minimum Induced Drag of Aerofoils
Munk, M. M.
1979-01-01
Equations are derived to demonstrate which distribution of lifting elements result in a minimum amount of aerodynamic drag. The lifting elements were arranged (1) in one line, (2) parallel lying in a transverse plane, and (3) in any direction in a transverse plane. It was shown that the distribution of lift which causes the least drag is reduced to the solution of the problem for systems of airfoils which are situated in a plane perpendicular to the direction of flight.
Drag reduction in riblet-lined pipes
Energy Technology Data Exchange (ETDEWEB)
Enyutin, G.V.; Lashkov, Yu.A.; Samoilova, N.V.
1995-07-01
The possibilities of reducing the drag in pipes with a circular cross section by lining them with riblets have been investigated experimentally for developed turbulent air flow. The maximum drag reduction of 6-7% in the riblet-lined as compared with the smooth pipe was obtained for a dimensionless riblet pitch, expressed in law-of-the-wall parameters, s{sup +} = 14-18.
Measurements of drag and flow over biofilm
Hartenberger, Joel; Gose, James W.; Perlin, Marc; Ceccio, Steven L.
2017-11-01
Microbial `slime' biofilms detrimentally affect the performance of every day systems from medical devices to large ocean-going vessels. In flow applications, the presence of biofilm typically results in a drag increase and may alter the turbulence in the adjacent boundary layer. Recent studies emphasize the severity of the drag penalty associated with soft biofouling and suggest potential mechanisms underlying the increase; yet, fundamental questions remain-such as the role played by compliance and the contribution of form drag to the overall resistance experienced by a fouled system. Experiments conducted on live biofilm and 3D printed rigid replicas in the Skin-Friction Flow Facility at the University of Michigan seek to examine these factors. The hydrodynamic performance of the biofilms grown on test panels was evaluated through pressure drop measurements as well as conventional and microscale PIV. High-resolution, 3D rigid replicas of select cases were generated via additive manufacturing using surface profiles obtained from a laser scanning system. Drag and flow measurements will be presented along with details of the growth process and the surface profile characterization method.
Directory of Open Access Journals (Sweden)
Staffan Johansson
2017-01-01
Full Text Available An important parameter in the reduction of fuel consumption of heavy-duty diesel engines is the Power Cylinder Unit (PCU; the PCU is the single largest contributor to engine frictional losses. Much attention, from both academia and industry, has been paid to reducing the frictional losses of the PCU in the boundary and mixed lubrication regime. However, previous studies have shown that a large portion of frictional losses in the PCU occur in the hydrodynamic lubrication regime. A novel texturing design with large types of surface features was experimentally analyzed using a tribometer setup. The experimental result shows a significant reduction of friction loss for the textured surfaces. Additionally, the textured surface did not exhibit wear. On the contrary, it was shown that the textured surfaces exhibited a smaller amount of abrasive scratches on the plateaus (compared to the reference plateau honed surface due to entrapment of wear particles within the textures. The decrease in hydrodynamic friction for the textured surfaces relates to the relative increase of oil film thickness within the textures. A tentative example is given which describes a method of decreasing hydrodynamic frictional losses in the full-scale application.
That's a Drag: The Effects of Drag Forces
Directory of Open Access Journals (Sweden)
Shane Maxemow
2009-01-01
Full Text Available Drag is a force that opposes motion due to an object's shape, material, and speed. This project defined what drag force is, derived the governing equation for drag and listed some applications of drag forces. Derivation of the drag equation was achieved using the Buckingham π theorem, a dimensional analysis tool. Lastly, this project explored the problem of how long and how far a dragster takes to stop once its parachute is deployed.
Hydrodynamic forces on inundated bridge decks
2009-05-01
The hydrodynamic forces experienced by an inundated bridge deck have great importance in the design of bridges. Specifically, the drag force, lift force, and the moment acting on the bridge deck under various levels of inundation and a range of flow ...
Murayama, M
1984-03-01
Decompression of human platelet-rich plasma (PRP) in siliconized glass or plastic to 380 mm Hg for 3 hours at 38 degrees C produced platelet aggregation independent of pO2. Aggregation also took place when PRP was compressed to 8,000 PSI and then decompressed slowly to one atmosphere (14.7 PSI) without gas bubble formation. Platelets also aggregated when plasma was decompressed hydrodynamically (Bernoulli effect) at room temperature. It was also found that the drugs piracetam (2-oxypyrolidine acetamide) and pentoxifylline (1-(5-oxohexyl)-theobromine) at 0.5 and 1.0 mM prevent thrombocyte aggregation. Implications for mountain sickness are discussed.
Active aerodynamic drag reduction on morphable cylinders
Guttag, M.; Reis, P. M.
2017-12-01
We study a mechanism for active aerodynamic drag reduction on morphable grooved cylinders, whose topography can be modified pneumatically. Our design is inspired by the morphology of the Saguaro cactus (Carnegiea gigantea), which possesses an array of axial grooves, thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. Our analog experimental samples comprise a spoked rigid skeleton with axial cavities, covered by a stretched elastomeric film. Decreasing the inner pressure of the sample produces axial grooves, whose depth can be accurately varied, on demand. First, we characterize the relation between groove depth and pneumatic loading through a combination of precision mechanical experiments and finite element simulations. Second, wind tunnel tests are used to measure the aerodynamic drag coefficient (as a function of Reynolds number) of the grooved samples, with different levels of periodicity and groove depths. We focus specifically on the drag crisis and systematically measure the associated minimum drag coefficient and the critical Reynolds number at which it occurs. The results are in agreement with the classic literature of rough cylinders, albeit with an unprecedented level of precision and resolution in varying topography using a single sample. Finally, we leverage the morphable nature of our system to dynamically reduce drag for varying aerodynamic loading conditions. We demonstrate that actively controlling the groove depth yields a drag coefficient that decreases monotonically with Reynolds number and is significantly lower than the fixed sample counterparts. These findings open the possibility for the drag reduction of grooved cylinders to be operated over a wide range of flow conditions.
Hydrodynamics of ocean pipelines
Energy Technology Data Exchange (ETDEWEB)
Yoshihara, S.; Toyoda, S.; Venkataramana, K.; Aiko, Y. (Kagoshima University, Kagoshima (Japan). Faculty of Engineering)
1993-09-30
This paper describes the current forces acting on cylindrical models in a steady flow, corresponding to the cases of rigid and large diameter pipelines in real seas. The models were placed in a circulating water channel normal to the direction of flow. The strains in the models were recorded using strain gauges, from which fluid forces in the horizontal and vertical directions were obtained. The drag coefficient, lift coefficient, and Straul number were calculated, and were illustrated against the Reynolds number. Consequently, the drag force was found to increase with flow velocity. In addition, it was shown that the variation of lift force was more complex and was affected by the eddies and other forms of turbulence around the models. For the model which consists of two pipes held together, it was found that the fluid forces were greater on the upstream side. It was provided that the fluid forces were also affected by the orientation of the pipelines. Furthermore, it was clarified that the values of hydrodynamic coefficients and Straul number were similar to the results for vertical cylinders in uniform flows. 5 refs., 16 figs.
Bionic Research on Bird Feather for Drag Reduction
Beibei Feng; Darong Chen; Jiadao Wang; Xingtuan Yang
2015-01-01
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 d...
GRAVITATIONAL DRAG ON A POINT MASS IN HYPERSONIC MOTION WITHIN A GAUSSIAN DISK
Energy Technology Data Exchange (ETDEWEB)
Canto, J.; Sanchez-Salcedo, F. J. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ap. 70-468, 04510 D.F. (Mexico); Esquivel, A.; Raga, A. C., E-mail: jsanchez@astro.unam.mx, E-mail: esquivel@nucleares.una.mx, E-mail: raga@nucleares.unam.mx [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510 Mexico D.F. (Mexico)
2013-01-01
We develop an analytical model for the accretion and gravitational drag on a point mass that moves hypersonically in the midplane of a gaseous disk with a Gaussian vertical density stratification. Such a model is of interest for studying the interaction between a planet and a protoplanetary disk, as well as the dynamical decay of massive black holes in galactic nuclei. The model assumes that the flow is ballistic, and gives fully analytical expressions for both the accretion rate onto the point mass and the gravitational drag it suffers. The expressions are further simplified by taking the limits of a thick and of a thin disk. The results for the thick disk reduce correctly to those for a uniform density environment. We find that for a thin disk (small vertical scaleheight compared to the gravitational radius), the accretion rate is proportional to the mass of the moving object and to the surface density of the disk, while the drag force is independent of the velocity of the object. The gravitational deceleration of the hypersonic perturber in a thin disk was found to be independent of its parameters (i.e., mass or velocity) and depends only on the surface mass density of the disk. The predictions of the model are compared to the results of three-dimensional hydrodynamical simulations, with reasonable agreement.
Drag Reduction Using Polysaccharides in a Taylor–Couette Flow
Directory of Open Access Journals (Sweden)
Pallavi Bhambri
2017-12-01
Full Text Available Three different polysaccharides, aloe vera, Tamarind powder and pineapple fibers, are utilized as drag reducing agents in a turbulent flow. Using a Taylor–Couette setup, consisting of a rotating inner cylinder, for measuring the drag reduction, a range of Reynolds numbers from 4 × 104 to 3 × 105 has been explored in this study. The results are in good agreement with previous studies on polysaccharides conducted in a pipe/channel flow and a maximum drag reduction of 35% has been observed. Further, novel additives such as cellulose nanocrystals (CNC, surfactants and CNC grafted with surfactants are also examined in this study for drag reduction. CNC due to its rigid rod structure reduced the drag by 30%. Surfactant, due to its unique micelle formation showed maximum drag reduction of 80% at low Re. Further, surfactant was grafted on CNC and was examined for drag reduction. However, drag reduction property of surfactant was observed to be significantly reduced after grafting on CNC. The effect of Reynolds number on drag reduction is studied for all the additives investigated in this study.
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.
Milne-Thomson, L M
2011-01-01
This classic exposition of the mathematical theory of fluid motion is applicable to both hydrodynamics and aerodynamics. Based on vector methods and notation with their natural consequence in two dimensions - the complex variable - it offers more than 600 exercises and nearly 400 diagrams. Prerequisites include a knowledge of elementary calculus. 1968 edition.
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 1; Issue 9. Hydrodynamic Lubrication Experiment with 'Floating' Drops. Jaywant H Arakeri K R Sreenivas. General Article Volume 1 Issue 9 September 1996 pp 51-58. Fulltext. Click here to view fulltext PDF. Permanent link:
Bonneau, Dominique; Souchet, Dominique
2014-01-01
This Series provides the necessary elements to the development and validation of numerical prediction models for hydrodynamic bearings. This book describes the rheological models and the equations of lubrication. It also presents the numerical approaches used to solve the above equations by finite differences, finite volumes and finite elements methods.
Directory of Open Access Journals (Sweden)
Muhammad Yasar Javaid
2017-07-01
Full Text Available We are developing a prototype underwater glider for subsea payload delivery. The idea is to use a glider to deliver payloads for subsea installations. In this type of application, the hydrodynamic forces and dynamic stability of the glider is of particular importance, as it has implications on the glider's endurance and operation. In this work, the effect of two different wing forms, rectangular and tapered, on the hydrodynamic characteristics and dynamic stability of the glider were investigated, to determine the optimal wing form. To determine the hydrodynamic characteristics, tow tank resistance tests were carried out using a model fitted alternately with a rectangular wing and tapered wing. Steady-state CFD analysis was conducted using the hydrodynamic coefficients obtained from the tests, to obtain the lift, drag and hydrodynamic derivatives at different angular velocities. The results show that the rectangular wing provides larger lift forces but with a reduced stability envelope. Conversely, the tapered wing exhibits lower lift force but improved dynamic stability.
Drag Reduction by Laminar Flow Control
Directory of Open Access Journals (Sweden)
Nils Beck
2018-01-01
Full Text Available The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag reduction is seen in laminar flow control by boundary layer suction. While most of the research so far has been on partial laminarization by application of Natural Laminar Flow (NLF and Hybrid Laminar Flow Control (HLFC to wings, complete laminarization of wings, tails and fuselages promises much higher gains. The potential drag reduction and suction requirements, including the necessary compressor power, are calculated on component level using a flow solver with viscid/inviscid coupling and a 3D Reynolds-Averaged Navier-Stokes (RANS solver. The effect on total aircraft drag is estimated for a state-of-the-art mid-range aircraft configuration using preliminary aircraft design methods, showing that total cruise drag can be halved compared to today’s turbulent aircraft.
Ciufolini, Ignazio
2007-09-06
The origin of inertia has intrigued scientists and philosophers for centuries. Inertial frames of reference permeate our daily life. The inertial and centrifugal forces, such as the pull and push that we feel when our vehicle accelerates, brakes and turns, arise because of changes in velocity relative to uniformly moving inertial frames. A classical interpretation ascribed these forces to acceleration relative to some absolute frame independent of the cosmological matter, whereas an opposite view related them to acceleration relative to all the masses and 'fixed stars' in the Universe. An echo and partial realization of the latter idea can be found in Einstein's general theory of relativity, which predicts that a spinning mass will 'drag' inertial frames along with it. Here I review the recent measurements of frame dragging using satellites orbiting Earth.
A Comparison of Experimental and Analytical Procedures to Measure Passive Drag in Human Swimming.
Directory of Open Access Journals (Sweden)
Tiago M Barbosa
Full Text Available The aim of this study was to compare the swimming hydrodynamics assessed with experimental and analytical procedures, as well as, to learn about the relative contributions of the friction drag and pressure drag to total passive drag. Sixty young talented swimmers (30 boys and 30 girls with 13.59±0.77 and 12.61±0.07 years-old, respectively were assessed. Passive drag was assessed with inverse dynamics of the gliding decay speed. The theoretical modeling included a set of analytical procedures based on naval architecture adapted to human swimming. Linear regression models between experimental and analytical procedures showed a high correlation for both passive drag (Dp = 0.777*Df+pr; R2 = 0.90; R2a = 0.90; SEE = 8.528; P<0.001 and passive drag coefficient (CDp = 1.918*CDf+pr; R2 = 0.96; R2a = 0.96; SEE = 0.029; P<0.001. On average the difference between methods was -7.002N (95%CI: -40.480; 26.475 for the passive drag and 0.127 (95%CI: 0.007; 0.247 for the passive drag coefficient. The partial contribution of friction drag and pressure drag to total passive drag was 14.12±9.33% and 85.88±9.33%, respectively. As a conclusion, there is a strong relationship between the passive drag and passive drag coefficient assessed with experimental and analytical procedures. The analytical method is a novel, feasible and valid way to gather insight about one's passive drag during training and competition. Analytical methods can be selected not only to perform race analysis during official competitions but also to monitor the swimmer's status on regular basis during training sessions without disrupting or time-consuming procedures.
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. Copyright © 2015 Elsevier Ltd
Energy Technology Data Exchange (ETDEWEB)
Castor, J I
2003-10-16
The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correct description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it is no more necessary to distinguish photons from atoms, nuclei and electrons, than it is
Drag and Torque on Clusters of N Arbitrary Spheres at Low Reynolds Number.
Filippov
2000-09-01
Hydrodynamics of particle clusters suspended in viscous fluids is a subject of considerable theoretical and practical importance. Using a multipole expansion of the flow velocity in a series of spherical harmonics, Lamb's fundamental solution of the Stokes flow outside a single sphere is generalized in this work to the case of N nonoverlapping spheres of arbitrary size with slip boundary conditions. The expansion coefficients are found by transforming the boundary conditions to the Lamb form and by transforming the spherical coordinates and solid spherical harmonics centered at different spheres. The problem is reduced to the solution of the linear system of equations for the expansion coefficients, which is carried out numerically. Based on the developed theory, the relation between the hydrodynamic and gyration radius of fractal-like aggregates with different structure is established. In another application, an asymptotic slip-regime dependence of the aggregate hydrodynamic radius on the Knudsen number and the number of particles is found by performing calculations of drag forces acting on the gas-borne fractal-like and straight chain aggregates. A good agreement is shown in comparing predictions of the described theory with available experimental and theoretical results on motion of various small sphere clusters in viscous fluid. Copyright 2000 Academic Press.
DEFF Research Database (Denmark)
Hansen, Jesper Schmidt; Dyre, Jeppe C.; Daivis, Peter J.
2011-01-01
We show by nonequilibrium molecular dynamics simulations that the Navier-Stokes equation does not correctly describe water flow in a nanoscale geometry. It is argued that this failure reflects the fact that the coupling between the intrinsic rotational and translational degrees of freedom becomes...... important for nanoflows. The coupling is correctly accounted for by the extended Navier-Stokes equations that include the intrinsic angular momentum as an independent hydrodynamic degree of freedom. © 2011 American Physical Society....
Drag reduction of a miniature boat with superhydrophobic grille bottom
Directory of Open Access Journals (Sweden)
C. G. Jiang
2011-09-01
Full Text Available Water strider can slide on water surface with a very small drag force using its long superhydrophobic legs. Inspired by the water strider legs, we report here a novel design of superhydrophobic grille structure for drag reduction. A miniature boat covered with a superhydrophobic grille at the bottom is fabricated and compared with a normal boat with flat bottom in the same size, and a significant drag reduction is obtained by the former. Experiments also reveal that the grille structure exhibits a remarkable loading capacity supplied by the water surface tension. It is found that the optimal design of such a miniature boat with a considerable loading capacity and a small drag can be realized through controlling the length and the spacing of the grilles. This study shows a new idea to reduce the fluid drag in microfluidics, micro electromechanical system and other engineering areas.
The Reduction in Drag of a Forward-sloping Windshield
Jacobs, Eastman N
1933-01-01
This paper gives results of a short investigation of the drag of a forward-sloping closed-cabin windshield. The drag of the windshield in both the original and a final modified form was determined from tests in the variable-density wind tunnel. The final form of the windshield was arrived at by modifying the original as the result of flow observations in the N.A.C.A. smoke tunnel. The investigation studied the utility of the N.A.C.A. smoke tunnel as applied to reducing the drag of objects for which the full dynamic scale could not be approached in the smoke tunnel, but designers should find the results of the flow observations and drag measurements of value. They show that most of the large drag added by the original windshield is eliminated by the modification of the windshield to the final form.
Remarks about the apparent increasing of the drag coefficient on flexible submarine cables
Energy Technology Data Exchange (ETDEWEB)
Marichal, D. [Ecole Centrale de Nantes, 44 (France)
2004-07-01
A lot of elongated flexible underwater structures (towing and mooring cables, trawl lines, oil risers...) are used in exploitation of sea resources. All theoretical calculations require to know the hydrodynamic forces acting on these structures (especially the drag coefficient). It was usually assumed that the drag coefficient of a cylindrical element is a constant and takes the value of 1.2 as a rigid cylinder at the typical Reynolds numbers. But, if the cylindrical structure has transverse vibrations - as it is usual for submarine cables -, an important increase of the drag coefficient seems to appear Our purpose is to show that the first explanation of the drag coefficient increase comes partly from the problem formulation. It is usual to think that the towing speed is very important compared with the transverse motion velocity. But, in fact, the drag results in the combination of the normal component of the flow and this transverse motion velocity. (author)
Experiment Evaluation of Skin Friction Drag by Surface Tailoring
Manigandan, S.; Gopal krishna, K.; Gagan Kumar, K.; Gunasekar, P.; Nithya, S.
2017-08-01
Reduction of drag is an important role of aerodynamic specialist in real time world. The performance of forward moving object improved when the drag is reduced. Skin friction drag caused when the fluid tending to shear along the surface of the body and it is dependent on energy expenditure. Initial research concluded that nearly 20 to 40% of total drag is skin friction drag, based on flight forward velocity. This means a lot of fuel burned. In this paper we investigate a methodology to reduce the skin friction drag by implementing different kinds of exterior treatments. The ideology inspired from the world fastest moving oceanic creature. Structures are fabricated based on the replica of scales of the oceanic creature. The outer skin of the aerofoil NACA0012 is modified like shark scales. Then it is tested using open type sub sonic wind tunnel. In addition to that, the leading edge thickness effect also studied. The turbulent flow phenomenon is validated at different velocities and compared with numerical results using STAR CCM+. From the plots and graphical results, it is found that the skin friction drag is generated less due to reduction of transverse shear stress present in turbulent flow and skin friction drag depends on boundary layer thickness and on the percentage of chord of flow separation. In addition to this, the result delivers that the ordinary polished surface produces more drag than the modified scales. The outlook of this technology is excrescence for different applications. This open section wind tunnel testing produces 10-15% reduction in drag and can be turn to high values when the experiment is conducted in closed section wind tunnel with real time atmospheric conditions, which can be done as a future work.
Kerr, James R; Manes, Costantino; Kemp, Paul S
2016-11-01
It is commonly assumed that stream-dwelling fish should select positions where they can reduce energetic costs relative to benefits gained and enhance fitness. However, the selection of appropriate hydrodynamic metrics that predict space use is the subject of recent debate and a cause of controversy. This is for three reasons: (1) flow characteristics are often oversimplified, (2) confounding variables are not always controlled and (3) there is limited understanding of the explanatory mechanisms that underpin the biophysical interactions between fish and their hydrodynamic environment. This study investigated the space use of brown trout, Salmo trutta, in a complex hydrodynamic flow field created using an array of different sized vertically oriented cylinders in a large open-channel flume in which confounding variables were controlled. A hydrodynamic drag function (D) based on single-point time-averaged velocity statistics that incorporates the influence of turbulent fluctuations was used to infer the energetic cost of steady swimming. Novel hydrodynamic preference curves were developed and used to assess the appropriateness of D as a descriptor of space use compared with other commonly used metrics. Zones in which performance-enhancing swimming behaviours (e.g. Kármán gaiting, entraining and bow riding) that enable fish to hold position while reducing energetic costs (termed 'specialised behaviours') were identified and occupancy was recorded. We demonstrate that energy conservation strategies play a key role in space use in an energetically taxing environment with the majority of trout groups choosing to frequently occupy areas in which specialised behaviours may be adopted or by selecting low-drag regions. © 2016. Published by The Company of Biologists Ltd.
Murray, Mark; Shorter, Alex; Howle, Laurens; Johnson, Mark; Moore, Michael
2012-11-01
The improvement and miniaturization of sensing technologies has made bio-logging tags, utilized for the study of marine mammal behavior, more practical. These sophisticated sensing packages require a housing which protects the electronics from the environment and provides a means of attachment to the animal. The hydrodynamic forces on these housings can inadvertently remove the tag or adversely affect the behavior or energetics of the animal. A modification to the original design of a suction cup bio-logging tag housing was desired to minimize the adverse forces. In this work, hydrodynamic loading of two suction cup tag designs, original and modified designs, were analyzed using computational fluid dynamics (CFD) models and validated experimentally. Overall, the simulation and experimental results demonstrated that a tag housing that minimized geometric disruptions to the flow reduced drag forces, and that a tag housing with a small frontal cross-sectional area close to the attachment surface reduced lift forces. Preliminary results from experimental work with a common dolphin cadaver indicates that the suction cups used to attach the tags to the animal provide sufficient attachment force to resist failure at predicted drag and lift forces in 10 m/s flow.
Guyon, Etienne; Petit, Luc; Mitescu, Catalin D
2015-01-01
This new edition is an enriched version of the textbook of fluid dynamics published more than 10 years ago. It retains the same physically oriented pedagogical perspective. This book emphasizes, as in the first edition, experimental inductive approaches and relies on the study of the mechanisms at play and on dimensional analysis rather than more formal approaches found in many classical textbooks in the field. The need for a completely new version also originated from the increase, over the last few decades, of the cross-overs between the mechanical and physical approaches, as is visible in international meetings and joint projects. Hydrodynamics is more widely linked today to other fields of experimental sciences: materials, environment, life sciences and earth sciences, as well as engineering sciences.
Renilson, Martin
2015-01-01
This book adopts a practical approach and presents recent research together with applications in real submarine design and operation. Topics covered include hydrostatics, manoeuvring, resistance and propulsion of submarines. The author briefly reviews basic concepts in ship hydrodynamics and goes on to show how they are applied to submarines, including a look at the use of physical model experiments. The issues associated with manoeuvring in both the horizontal and vertical planes are explained, and readers will discover suggested criteria for stability, along with rudder and hydroplane effectiveness. The book includes a section on appendage design which includes information on sail design, different arrangements of bow planes and alternative stern configurations. Other themes explored in this book include hydro-acoustic performance, the components of resistance and the effect of hull shape. Readers will value the author’s applied experience as well as the empirical expressions that are presented for use a...
Energy Technology Data Exchange (ETDEWEB)
Pomraning, G.C.
1982-12-31
This course was intended to provide the participant with an introduction to the theory of radiative transfer, and an understanding of the coupling of radiative processes to the equations describing compressible flow. At moderate temperatures (thousands of degrees), the role of the radiation is primarily one of transporting energy by radiative processes. At higher temperatures (millions of degrees), the energy and momentum densities of the radiation field may become comparable to or even dominate the corresponding fluid quantities. In this case, the radiation field significantly affects the dynamics of the fluid, and it is the description of this regime which is generally the charter of radiation hydrodynamics. The course provided a discussion of the relevant physics and a derivation of the corresponding equations, as well as an examination of several simplified models. Practical applications include astrophysics and nuclear weapons effects phenomena.
Hydrodynamic manoeuvrability data of a flatfish type AUV
DEFF Research Database (Denmark)
Aage, Christian; Wagner Smitt, Leif
1994-01-01
by two propellers and four thrusters. The data comprise added mass and inertia coefficients, damping, lift and drag coefficients of the vehicle and its control surfaces, as well as resistance and propulsion characteristics. The hydrodynamic data have been determined by full scale tests, using a towing...
Switchable and Tunable Aerodynamic Drag on Cylinders
Guttag, Mark; Lopéz Jiménez, Francisco; Upadhyaya, Priyank; Kumar, Shanmugam; Reis, Pedro
We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.
Thermo-hydrodynamic lubrication in hydrodynamic bearings
Bonneau, Dominique; Souchet, Dominique
2014-01-01
This Series provides the necessary elements to the development and validation of numerical prediction models for hydrodynamic bearings. This book describes the thermo-hydrodynamic and the thermo-elasto-hydrodynamic lubrication. The algorithms are methodically detailed and each section is thoroughly illustrated.
National Research Council Canada - National Science Library
Zhihua Wang; Xueying Yu; Jiaxu Li; Jigang Wang; Lei Zhang
2016-01-01
.... 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...
DRAG REDUCTION WITH SUPERHYDROPHOBIC RIBLETS
Energy Technology Data Exchange (ETDEWEB)
Barbier, Charlotte N [ORNL; D' Urso, Brian R [ORNL; Jenner, Elliot [University of Pittsburgh
2012-01-01
Samples combining riblets and superhydrophobic surfaces are fabricated at University of Pittsburgh and their drag reduction properties are studied at the Center for Nanophase Materials Sciences (CNMS) in Oak Ridge National Laboratory with a commercial cone-and-plate rheometer. In parallel to the experiments, numerical simulations are performed in order to estimate the slip length at high rotational speed. For each sample, a drag reduction of at least 5% is observed in both laminar and turbulent regime. At low rotational speed, drag reduction up to 30% is observed with a 1 mm deep grooved sample. As the rotational speed increases, a secondary flow develops causing a slight decrease in drag reductions. However, drag reduction above 15% is still observed for the large grooved samples. In the turbulent regime, the 100 microns grooved sample becomes more efficient than the other samples in drag reduction and manages to sustain a drag reduction above 15%. Using the simulations, the slip length of the 100 micron grooved sample is estimated to be slightly above 100 micron in the turbulent regime.
A framework for understanding drag parameterizations for coral reefs
Rosman, Johanna H.; Hench, James L.
2011-08-01
In a hydrodynamic sense, a coral reef is a complex array of obstacles that exerts a net drag force on water moving over the reef. This drag is typically parameterized in ocean circulation models using drag coefficients (CD) or roughness length scales (z0); however, published CD for coral reefs span two orders of magnitude, posing a challenge to predictive modeling. Here we examine the reasons for the large range in reported CD and assess the limitations of using CD and z0 to parameterize drag on reefs. Using a formal framework based on the 3-D spatially averaged momentum equations, we show that CD and z0 are functions of canopy geometry and velocity profile shape. Using an idealized two-layer model, we illustrate that CD can vary by more than an order of magnitude for the same geometry and flow depending on the reference velocity selected and that differences in definition account for much of the range in reported CD values. Roughness length scales z0 are typically used in 3-D circulation models to adjust CD for reference height, but this relies on spatially averaged near-bottom velocity profiles being logarithmic. Measurements from a shallow backreef indicate that z0 determined from fits to point measurements of velocity profiles can be very different from z0 required to parameterize spatially averaged drag. More sophisticated parameterizations for drag and shear stresses are required to simulate 3-D velocity fields over shallow reefs; in the meantime, we urge caution when using published CD and z0 values for coral reefs.
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.
Coulomb drag in quantum circuits.
Levchenko, Alex; Kamenev, Alex
2008-11-21
We study the drag effect in a system of two electrically isolated quantum point contacts, coupled by Coulomb interactions. Drag current exhibits maxima as a function of quantum point contacts 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 nonlinear regime the drag current is proportional to the shot noise of the driving circuit, suggesting that the Coulomb drag experiments may be a convenient way to measure the quantum shot noise. Remarkably, the transition to the nonlinear regime may occur at driving voltages substantially smaller than the temperature.
Experimental study of drag reduction in flumes and spillway tunnels
Directory of Open Access Journals (Sweden)
Ying-kui Wang
2010-06-01
Full Text Available 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.
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.
Indian Academy of Sciences (India)
When we grip an object and stop it from falling we again use friction. In many engineering systems, however, when two surfaces slide against one another friction is a nuisance. In this case friction has two undesirable effects: (1) it increases wear and (2) work that is not useful, needs to be done to overcome it. Thus, reducing.
Effects of Polymer Parameters on Drag Reduction.
Safieddine, Abbas Mohammad
by the recent "yo-yo" model of Ryskin. This work provides strong experimental evidence in support of the theories suggesting that drag reduction is a result of polymer extension in a turbulent flow field. This macromolecular extension leads to a local fluid viscosity increase, effectively altering the turbulent energy balance. This in turn leads to a reduction in the intensity of the smallest eddies, thereby reducing friction and enhancing flow.
Hydrodynamics challenge problem
Energy Technology Data Exchange (ETDEWEB)
Hornung, R. D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Keasler, J. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Gokhale, M. B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2011-06-09
The hydrodynamics challenge problem represents a classical HPC physics problem, namely high deformation event modeling via Lagrangian shock hydrodynamics. This challenge problem solves the Sedov blast wave problem for one material in three dimensions. The problem has an analytic solution, and can be scaled to arbitrarily large problem sizes. The reference code is drawn from a production LLNL hydrodynamics code.
Aerodynamic Drag Reduction Apparatus For Wheeled Vehicles In Ground Effect
Ortega, Jason M.; Salari, Kambiz
2005-12-13
An apparatus for reducing the aerodynamic drag of a wheeled vehicle in a flowstream, the vehicle having a vehicle body and a wheel assembly supporting the vehicle body. The apparatus includes a baffle assembly adapted to be positioned upstream of the wheel assembly for deflecting airflow away from the wheel assembly so as to reduce the incident pressure on the wheel assembly.
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.
HYDRODYNAMICS OF OSCILLATING WING ON THE PITCH ANGLE
Directory of Open Access Journals (Sweden)
Vitalii Korobov
2017-07-01
Full Text Available Purpose: research of the hydrodynamic characteristics of a wing in a nonstationary stream. Methods: The experimental studies of the hydrodynamic load acting on the wing of 1.5 elongation, wich harmonically oscillated respect to the transversal axis in the frequency range of 0.2-2.5 Hz. The flow speed in the hydrodynamic tunnel ranged of 0.2-1.5 m/s. Results: The instantaneous values of the coefficients of lift and drag / thrust on the pitch angle at unsteady flow depends on the Strouhal number.Discussion: with increasing oscillation frequency coefficients of hydrodynamic force components significantly higher than the data for the stationary blowing out of the wing.
Aerodynamic Drag and Gyroscopic Stability
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...
Viscous drag reduction in boundary layers
Bushnell, Dennis M. (Editor); Hefner, Jerry N. (Editor)
1990-01-01
The present volume discusses the development status of stability theory for laminar flow control design, applied aspects of laminar-flow technology, transition delays using compliant walls, the application of CFD to skin friction drag-reduction, active-wave control of boundary-layer transitions, and such passive turbulent-drag reduction methods as outer-layer manipulators and complex-curvature concepts. Also treated are such active turbulent drag-reduction technique applications as those pertinent to MHD flow drag reduction, as well as drag reduction in liquid boundary layers by gas injection, drag reduction by means of polymers and surfactants, drag reduction by particle addition, viscous drag reduction via surface mass injection, and interactive wall-turbulence control.
The Overall Drag Losses For A Combination of Bodies
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Sabah Al-Janabi
2013-05-01
Full Text Available The objective of this work is to obtain better understanding of the flow over a combination of bluff bodies in close enough proximity to strongly interact with each other. This interaction is often beneficial in that the drag of the overall system is reduced. Proto-types for this problem come from tractor- trailer and missiles, and from various add-on devices designed to reduce their drag. Thus, an experimental investigation was carried out by placing conical frontal bodies having a base diameter of 0.65 cylinder diameter with different vertex angles (30°, 50°, 70°, and 90°. It was found that, the bluffer cone with 90° vertex angle gives the best minimum drag, which is 31% lower than the drag of the isolated cylinder. Also an interesting phenomenon was observed in that, the minimum drags for all combinations are obtained at the same gap ratio (i.e.at g/d2= 0.365.
Behavior of passive admixture in a vortical hydrodynamic field
Directory of Open Access Journals (Sweden)
R.O.Bobrov
2006-01-01
Full Text Available The motion of passive admixture of spherical particles in the stationary hydrodynamic field of a swirling flow is studied. A spherical particle of a given mass in the hydrodynamic field of a swirling flow is located on a certain circular orbit, where the centrifugal force is compensated by the radial drag force due to the sink. This leads to the separation of the host fluid and admixture. A theory of Brownian motion of admixture in dilute solutions with a non-uniform flow is constructed.
Drag Reduction of Bacterial Cellulose Suspensions
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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.
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...
Hydrodynamic flow control in marine mammals.
Fish, Frank E; Howle, Laurens E; Murray, Mark M
2008-12-01
The ability to control the flow of water around the body dictates the performance of marine mammals in the aquatic environment. Morphological specializations of marine mammals afford mechanisms for passive flow control. Aside from the design of the body, which minimizes drag, the morphology of the appendages provides hydrodynamic advantages with respect to drag, lift, thrust, and stall. The flukes of cetaceans and sirenians and flippers of pinnipeds possess geometries with flexibility, which enhance thrust production for high efficiency swimming. The pectoral flippers provide hydrodynamic lift for maneuvering. The design of the flippers is constrained by performance associated with stall. Delay of stall can be accomplished passively by modification of the flipper leading edge. Such a design is exhibited by the leading edge tubercles on the flippers of humpback whales (Megaptera novaeangliae). These novel morphological structures induce a spanwise flow field of separated vortices alternating with regions of accelerated flow. The coupled flow regions maintain areas of attached flow and delay stall to high angles of attack. The delay of stall permits enhanced turning performance with respect to both agility and maneuverability. The morphological features of marine mammals for flow control can be utilized in the biomimetic design of engineered structures for increased power production and increased efficiency.
Stamhuis, Eize; Videler, Johannes
1998-01-01
The process of flow generation with metachronally beating pleopods in a tubiform burrow was studied by designing a hydrodynamic model based on a thrust-drag force balance. The drag of the tube (including the shrimp) comprises components for accelerating the water into the tube entrance, for
A Conventional Liner Acoustic/Drag Interaction Benchmark Database
Howerton, Brian M.; Jones, Michael G.
2017-01-01
The aerodynamic drag of acoustic liners has become a significant topic in the design of such for aircraft noise applications. In order to evaluate the benefits of concepts designed to reduce liner drag, it is necessary to establish the baseline performance of liners employing the typical design features of conventional configurations. This paper details a set of experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of a number of perforate-over-honeycomb liner configurations at flow speeds of M=0.3 and 0.5. These conventional liners are investigated to determine their resistance factors using a static pressure drop approach. Comparison of the resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 Hz at source sound pressure levels of 140 and 150 dB. Educed impedance and attenuation spectra are used to determine the interaction between acoustic performance and drag.
Numerical analysis of drag and lift reduction of square cylinder
Directory of Open Access Journals (Sweden)
Prasenjit Dey
2015-12-01
Full Text Available Flow around an extended triangular solid (thorn attached to a square cylinder is investigated numerically. The numerical analysis is carried out at low Reynolds number, Re = 100 & 180 for different non-dimensional thorn lengths (l΄ = 0. 2, 0.4 & 0.6, different inclination angles (θ = 5°, 10°, 15° and 20° and two different thorn positions. It is found that drag and lift reduction can be achieved by attaching the thorn on a square cylinder. It is observed that the fluctuation of the drag force as well as the lift force is reduced and there is a comparatively large variation of drag and lift when the thorn is placed at the front stagnation point instead of placing at rear stagnation point. The reduction of drag and lift coefficient are directly proportional to thorn length and thorn inclination angle. It is found that the drag and lift are minimized by 16% & 46% for Re = 100 respectively, and 22% & 60% for Re = 180 compared to a square model (without thorn.
Borazjani, Iman; Sotiropoulos, Fotis
2008-05-01
We employ numerical simulation to investigate the hydrodynamics of carangiform locomotion as the relative magnitude of viscous and inertial forces, i.e. the Reynolds number (Re), and the tail-beat frequency, i.e. the Strouhal number (St), are systematically varied. The model fish is a three-dimensional (3D) mackerel-like flexible body undulating with prescribed experimental kinematics of carangiform type. Simulations are carried out for three Re spanning the transitional and inertial flow regimes, Re=300 and 4000 (viscous flow), and infinity (inviscid flow). For each Re there is a critical Strouhal number, St*, at which the net mean force becomes zero, making constant-speed self-propulsion possible. St* is a decreasing function of Re and approaches the range of St at which most carangiform swimmers swim in nature (St approximately 0.25) only as Re approaches infinity. The propulsive efficiency at St* is an increasing function of Re while the power required for swimming is decreasing with Re. For all Re, however, the swimming power is shown to be significantly greater than that required to tow the rigid body at the same speed. We also show that the variation of the total drag and its viscous and form components with St depend on the Re. For Re=300, body undulations increase the drag over the rigid body level, while significant drag reduction is observed for Re=4000. This difference is shown to be due to the fact that at sufficiently high Re the drag force variation with St is dominated by its form component variation, which is reduced by undulatory swimming for St>0.2. Finally, our simulations clarify the 3D structure of various wake patterns observed in experiments--single and double row vortices--and suggest that the wake structure depends primarily on the St. Our numerical findings help elucidate the results of previous experiments with live fish, underscore the importance of scale (Re) effects on the hydrodynamic performance of carangiform swimming, and help
Great hammerhead sharks swim on their side to reduce transport costs.
Payne, Nicholas L; Iosilevskii, Gil; Barnett, Adam; Fischer, Chris; Graham, Rachel T; Gleiss, Adrian C; Watanabe, Yuuki Y
2016-07-26
Animals exhibit various physiological and behavioural strategies for minimizing travel costs. Fins of aquatic animals play key roles in efficient travel and, for sharks, the functions of dorsal and pectoral fins are considered well divided: the former assists propulsion and generates lateral hydrodynamic forces during turns and the latter generates vertical forces that offset sharks' negative buoyancy. Here we show that great hammerhead sharks drastically reconfigure the function of these structures, using an exaggerated dorsal fin to generate lift by swimming rolled on their side. Tagged wild sharks spend up to 90% of time swimming at roll angles between 50° and 75°, and hydrodynamic modelling shows that doing so reduces drag-and in turn, the cost of transport-by around 10% compared with traditional upright swimming. Employment of such a strongly selected feature for such a unique purpose raises interesting questions about evolutionary pathways to hydrodynamic adaptations, and our perception of form and function.
The effect of finger spreading on drag of the hand in human swimming
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.
Atmospheric and oceanic drag on sea ice
Tsamados, M.; Feltham, D. L.
2012-12-01
Pressure ridges, keels, floe edges and melt pond edges all introduce discrete obstructions to the flow of the air or ocean over the ice, and are a source of form drag. For typical ice covers the form drag contribution to the total drag is of comparable or greater magnitude to the surface or skin drag. In current climate models form drag is only accounted for by tuning of the air-ice and air-ocean drag coefficients, i.e. by altering the roughness length in a surface drag parameterization. The existing approach of skin drag parameter tuning, while numerically convenient, is poorly constrained by observations and fails to describe correctly the physics associated with the air-ice and ocean-ice drag. Here we combine recent theoretical developments to deduce the total neutral form drag coefficients from the key parameters of the ice cover such as ice concentration, size and area of the ridges and keels, freeboard and floe draft and size of melt ponds. We validate the assumptions of this parameterisation against remote sensing observations from airborne missions (IceBridge) and high resolution satellites. We incorporate the drag coefficients into the sea ice component of a climate model (the CICE model). This stage necessitates that the sea ice characteristics obtained locally from observations are mapped to the averaged sea ice quantities provided by the sea ice model at the larger grid cell length scale. We present results over the Arctic of a stand-alone version of the model and show the influence of the new drag parameterisation on the motion and mass of the ice cover. The new parameterisation allows the drag coefficients to be coupled to the sea ice state and therefore to evolve spatially and temporally. We test the predictions of the model against measured drag coefficients in several regions of the Arctic and find good agreement between model and observations.
Elementary classical hydrodynamics
Chirgwin, B H; Langford, W J; Maxwell, E A; Plumpton, C
1967-01-01
Elementary Classical Hydrodynamics deals with the fundamental principles of elementary classical hydrodynamics, with emphasis on the mechanics of inviscid fluids. Topics covered by this book include direct use of the equations of hydrodynamics, potential flows, two-dimensional fluid motion, waves in liquids, and compressible flows. Some general theorems such as Bernoulli's equation are also considered. This book is comprised of six chapters and begins by introducing the reader to the fundamental principles of fluid hydrodynamics, with emphasis on ways of studying the motion of a fluid. Basic c
Elasto-hydrodynamic lubrication
Dowson, D; Hopkins, D W
1977-01-01
Elasto-Hydrodynamic Lubrication deals with the mechanism of elasto-hydrodynamic lubrication, that is, the lubrication regime in operation over the small areas where machine components are in nominal point or line contact. The lubrication of rigid contacts is discussed, along with the effects of high pressure on the lubricant and bounding solids. The governing equations for the solution of elasto-hydrodynamic problems are presented.Comprised of 13 chapters, this volume begins with an overview of elasto-hydrodynamic lubrication and representation of contacts by cylinders, followed by a discussio
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.
On the backreaction of frame dragging
Herdeiro, Carlos A R; Warnick, Claude M
2009-01-01
The backreaction on black holes due to dragging heavy, rather than test, objects is discussed. As a case study, a regular black Saturn system where the central black hole has vanishing intrinsic angular momentum, J^{BH}=0, is considered. It is shown that there is a correlation between the sign of two response functions. One is interpreted as a moment of inertia of the black ring in the black Saturn system. The other measures the variation of the black ring horizon angular velocity with the central black hole mass, for fixed ring mass and angular momentum. The two different phases defined by these response functions collapse, for small central black hole mass, to the thin and fat ring phases. In the fat phase, the zero area limit of the black Saturn ring has reduced spin j^2>1, which is related to the behaviour of the ring angular velocity. Using the `gravitomagnetic clock effect', for which a universality property is exhibited, it is shown that frame dragging measured by an asymptotic observer decreases, in b...
Benschop, H.O.G.; Westerweel, J.; Breugem, W.P.
2015-01-01
The use of drag reducing surface textures is a promising passive method to reduce fuel consumption. Probably most wellknown is the utilisation of shark-skin inspired ridges or riblets parallel to the mean flow. They can reduce drag up to 10%. Recently another bio-inspired texture based on bird
Dielectric barrier discharge actuator for vehicle drag reduction at highway speeds
Directory of Open Access Journals (Sweden)
Subrata Roy
2016-02-01
Full Text Available We propose and demonstrate reduction of aerodynamic drag for a realistic geometry at highway speeds using serpentine dielectric barrier discharge actuators. A comparable linear plasma actuator fails to reduce the drag at these speeds. Experimental data collected for linear and serpentine plasma actuators under quiescent operating conditions show that the serpentine design has profound effect on near wall flow structure and resulting drag. For certain actuator arrangement, the measured drag reduced by over 14% at 26.8 m/s (60 mph and over 10% at 31.3 m/s (70 mph opening up realistic possibility of reasonable energy savings for full scale ground vehicles. In addition, the power consumption data and drag reduction effectiveness for different input signals are also presented.
Transformations of integrable hydrodynamic chains and their hydrodynamic reductions
Pavlov, Maxim V.
2006-01-01
Hydrodynamic reductions of the hydrodynamic chain associated with dispersionless limit of 2+1 Harry Dym equation are found by the Miura type and reciprocal transformations applied to the Benney hydrodynamic chain.
Turbulent skin-friction drag on a slender body of revolution and Gray's Paradox
Energy Technology Data Exchange (ETDEWEB)
Nesteruk, Igor [Institute of Hydromechanics, National Academy of Sciences of Ukraine, Kyiv (Ukraine); Cartwright, Julyan H E [Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada (Spain)
2011-12-22
The boundary layer on a slender body of revolution differs considerably from that on a flat plate, but these two cases can be connected by the Mangler-Stepanov transformations. The presented analysis shows that turbulent frictional drag on a slender rotationally symmetric body is much smaller than the flat-plate concept gives and the flow can remain laminar at larger Reynolds numbers. Both facts are valid for an unseparated flow pattern and enable us to revise the turbulent drag estimation of a dolphin, presented by Gray 74 years ago, and to resolve his paradox, since experimental data testify that dolphins can achieve flow without separation. The small values of turbulent skin-friction drag on slender bodies of revolution have additional interest for further experimental investigations and for applications of shapes without boundary-layer separation to diminish the total drag and noise of air- and hydrodynamic hulls.
Whose drag is it anyway? Drag kings and monarchy in the UK.
Willox, Annabelle
2002-01-01
This chapter will show that the term "drag" in drag queen has a different meaning, history and value to the term "drag" in drag king. By exposing this basic, yet fundamental, difference this paper will expose the problems inherent in the assumption of parity between the two forms of drag. An exposition of how camp has been used to comprehend and theorise drag queens will facilitating an understanding of the parasitic interrelationship between camp and drag queen performances, while a critique of "Towards a Butch-Femme Aesthetic," by Sue Ellen Case, will point out the problematic assumptions made about camp when attributed to a cultural location different to the drag queen. By interrogating the historical, cultural and theoretical similarities and differences between drag kings, butches, drag queens and femmes this paper will expose the flawed assumption that camp can be attributed to all of the above without proviso, and hence expose why drag has a fundamentally different contextual meaning for kings and queens. This chapter will conclude by examining the work of both Judith Halberstam and Biddy Martin and the practical examples of drag king and queen performances provided at the UK drag contest held at The Fridge in Brixton, London on 23 June 1999.
Drag and drop display & builder
Energy Technology Data Exchange (ETDEWEB)
Bolshakov, Timofei B.; Petrov, Andrey D.; /Fermilab
2007-12-01
The Drag and Drop (DnD) Display & Builder is a component-oriented system that allows users to create visual representations of data received from data acquisition systems. It is an upgrade of a Synoptic Display mechanism used at Fermilab since 2002. Components can be graphically arranged and logically interconnected in the web-startable Project Builder. Projects can be either lightweight AJAX- and SVG-based web pages, or they can be started as Java applications. The new version was initiated as a response to discussions between the LHC Controls Group and Fermilab.
Surface pressure drag for hydrostatic two-layer flow over axisymmetric mountains
Energy Technology Data Exchange (ETDEWEB)
Leutbecher, M.
2000-07-01
The effect of partial reflections on surface pressure drag is investigated for hydrostatic gravity waves in two-layer flow with piecewise constant buoyancy frequency. The variation of normalized surface pressure drag with interface height is analyzed for axisymmetric mountains. The results are compared with the familiar solution for infinitely long ridges. The drag for the two-layer flow is normalized with the drag of one-layer flow, which has the buoyancy frequency of the lower layer. An analytical expression for the normalized drag of axisymmetric mountains is derived from linear theory of steady flow. Additionally, two-layer flow over finite-height axisymmetric mountains is simulated numerically for flow with higher stability in the upper layer. The temporal evolution of the surface pressure drag is examined in a series of experiments with different interface and mountain heights. The focus is on the linear regime and the nonlinear regime of nonbreaking gravity waves. The dispersion of gravity waves in flow over isolated mountains prevents that the entire wave spectrum is in resonance at the same interface height, which is the case in hydrostatic flow over infinitely long ridges. In consequence, the oscillation of the normalized drag with interface height is smaller for axisymmetric mountains than for infinitely long ridges. However, even for a reflection coefficient as low as 1/3 the drag of an axisymmetric mountain can be amplified by 50% and reduced by 40%. The nonlinear drag becomes steady in the numerical experiments in which no wave breaking occurs. The steady state nonlinear drag agrees quite well with the prediction of linear theory if the linear drag is computed for a slightly lowered interface. (orig.)
Effects of drafting on hydrodynamic and metabolic responses in front crawl swimming
Janssen, M.; Wilson, B.D.; Toussaint, H.M.
2009-01-01
Purpose: Effects of drafting on the hydrodynamic and metabolic responses of the drafter behind and at the side of a passive and an active lead swimmer were related to the influence of a lead swimmer on the flow field of the draftee. Methods: Passive drag of the draft swimmer was compared for the
Development of a remotely controlled testing platform with low-drag air-ventilated hull
Matveev, Konstantin I.; Perry, Nicholaus I.; Mattson, Alexander W.; Chaney, Christopher S.
2015-03-01
This paper addresses the development and testing of a remotely controlled boat platform with an innovative air-ventilated hull. The application of air cavities on the underside of ship hulls is a promising means for reducing hydrodynamic drag and pollutant emissions and increasing marine transportation efficiency. Despite this concept's potential, design optimization and high-performance operation of novel air-cavity ships remain a challenging problem. Hull construction and sensor instrumentation of the model-scale air-cavity boat is described in the paper. The modular structure of the hull allows for easy modifications, and an electric propulsion unit enables self-propelled operation. The boat is controlled remotely via a radio transmission system. Results of initial tests are reported, including thrust, speed, and airflow rate in several loading conditions. The constructed platform can be used for optimizing air-cavity systems and testing other innovative hull designs. This system can be also developed into a high-performance unmanned boat.
Dragging cylinders in slow viscous flows
Luca, Elena; Crowdy, Darren
2015-11-01
The so-called ``dragging problem'' in slow viscous fluids is an important basic flow with many applications. In two dimensions, the Stokes paradox means there is no solution to the dragging problem for a cylinder in free space. The presence of walls changes this; the solutions exist, but are not easy to find without purely numerical methods. This talk describes new ``transform methods'' that produce convenient, semi-analytical solutions to dragging problems for cylinders in various geometries. We apply the techniques to low-Reynolds-number swimming where dragging problem solutions can be combined with the reciprocal theorem to compute swimmer dynamics in confined domains.
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.
Effect of structure height on the drag reduction performance using rotating disk apparatus
Rashed, Musaab K.; Abdulbari, Hayder A.; Amran Mohd Salleh, Mohamad; Halim Shah Ismail, M.
2017-02-01
The drag reduction characteristics in a rotating disk apparatus were investigated by using structured disks with different riblet types and dimensions. Two disk types were fabricated with right angle triangular (RAT) grooves and space v-shape (SV) grooves, with six dimensions for each type. A high-accuracy rotating disk apparatus was fabricated and then used to investigate the turbulent drag reduction characterization of the disk in diesel fuel. In this work, the effects of several parameters are investigated; riblet types, riblet dimensions, and rotational disk speed (rpm) on the drag reduction performance. It was found that the surface structure of the disk reduced the drag, this was clearly seen from the comparison of torque values of smooth and structured disks. Drag reduction for structured disks was higher than that for smooth disks, and SV-grooves showed better drag reduction performance than RAT-grooves. In addition, it was observed that the drag reduction performance increased with decreasing groove height for both groove types. The maximum drag reduction achieved in this study was 37.368% for SV-groove at 1000 rpm, compared with 30% for RAT-groove, at the same rotational speed.
Drag Reduction of a Pipe Flow Using Nata de Coco Suspensions
Directory of Open Access Journals (Sweden)
Satoshi Ogata
2014-08-01
Full Text Available The addition of drag-reducing agents to reduce pipe friction loss has attracted attention as a method to conserve energy. In addition to reducing drag, these agents are required to have a low environmental load and conserve natural resources. Therefore, naturally occurring biopolymer additives, which are considered to have a low environmental load, have recently received much attention. Here we focused on nata de coco, a type of biopolymer that exhibits low mechanical degradation, and found that it reduced drag by up to 25% at a concentration of 50 ppm. With respect to the drag reduction (DR mechanism, we investigated the relation between DR phenomena and the fiber structure of nata de coco by visualization. As a result, we found that the DR effect appeared only when a network of nata de coco fibers was formed in the suspension. In addition, DR increased as the size of the network of nata de coco fibers increased.
Disruptive Innovation in Numerical Hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Waltz, Jacob I. [Los Alamos National Laboratory
2012-09-06
We propose the research and development of a high-fidelity hydrodynamic algorithm for tetrahedral meshes that will lead to a disruptive innovation in the numerical modeling of Laboratory problems. Our proposed innovation has the potential to reduce turnaround time by orders of magnitude relative to Advanced Simulation and Computing (ASC) codes; reduce simulation setup costs by millions of dollars per year; and effectively leverage Graphics Processing Unit (GPU) and future Exascale computing hardware. If successful, this work will lead to a dramatic leap forward in the Laboratory's quest for a predictive simulation capability.
Angulo, A. A.; Kuranz, C. C.; Drake, R. P.; Huntington, C. M.; Park, H.-S.; Remington, B. A.; Kalantar, D.; MacLaren, S.; Raman, K.; Miles, A.; Trantham, Matthew; Kline, J. L.; Flippo, K.; Doss, F. W.; Shvarts, D.
2016-10-01
This poster will describe simulations based on results from ongoing laboratory astrophysics experiments at the National Ignition Facility (NIF) relevant to the effects of radiative shock on hydrodynamically unstable surfaces. The experiments performed on NIF uniquely provide the necessary conditions required to emulate radiative shock that occurs in astrophysical systems. The core-collapse explosions of red supergiant stars is such an example wherein the interaction between the supernova ejecta and the circumstellar medium creates a region susceptible to Rayleigh-Taylor (R-T) instabilities. Radiative and nonradiative experiments were performed to show that R-T growth should be reduced by the effects of the radiative shocks that occur during this core-collapse. Simulations were performed using the radiation hydrodynamics code Hyades using the experimental conditions to find the mean interface acceleration of the instability and then further analyzed in the buoyancy drag model to observe how the material expansion contributes to the mix-layer growth. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas under Grant Number DE-FG52-09NA29548.
Hirano, Tetsufumi; van der Kolk, Naomi; Bilandzic, Ante
The main purpose of the lecture was to lead students and young postdocs to the frontier of the hydrodynamic description of relativistic heavy-ion collisions (H.I.C.) in order for them to understand talks and posters presented in the Quark Matter 2008 (QM08) conference in Jaipur, India [1]. So the most recent studies were not addressed in this lecture as they would be presented during the QM08 conference itself. Also, we try to give a very pedagogical lecture here. For the readers who may want to study relativistic hydrodynamics and its application to H.I.C. as an advanced course, we strongly recommend them to consult the references. This lecture note is divided into three parts. In the first part we give a brief introduction to relativistic hydrodynamics in the context of H.I.C. In the second part we present the formalism and some fundamental aspects of relativistic ideal and viscous hydrodynamics.
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...
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 ...
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...
Hydrodynamic advantages of swimming by salp chains.
Sutherland, Kelly R; Weihs, Daniel
2017-08-01
Salps are marine invertebrates comprising multiple jet-propelled swimming units during a colonial life-cycle stage. Using theory, we show that asynchronous swimming with multiple pulsed jets yields substantial hydrodynamic benefit due to the production of steady swimming velocities, which limit drag. Laboratory comparisons of swimming kinematics of aggregate salps (Salpa fusiformis and Weelia cylindrica) using high-speed video supported that asynchronous swimming by aggregates results in a smoother velocity profile and showed that this smoother velocity profile is the result of uncoordinated, asynchronous swimming by individual zooids. In situ flow visualizations of W. cylindrica swimming wakes revealed that another consequence of asynchronous swimming is that fluid interactions between jet wakes are minimized. Although the advantages of multi-jet propulsion have been mentioned elsewhere, this is the first time that the theory has been quantified and the role of asynchronous swimming verified using experimental data from the laboratory and the field. © 2017 The Author(s).
Hydrodynamic performance of the minke whale (Balaenoptera acutorostrata) flipper.
Cooper, Lisa Noelle; Sedano, Nils; Johansson, Stig; May, Bryan; Brown, Joey D; Holliday, Casey M; Kot, Brian W; Fish, Frank E
2008-06-01
Minke whales (Balaenoptera acutorostrata) are the smallest member of balaenopterid whales and little is known of their kinematics during feeding maneuvers. These whales have narrow and elongated flippers that are small relative to body size compared to related species such as right and gray whales. No experimental studies have addressed the hydrodynamic properties of minke whale flippers and their functional role during feeding maneuvers. This study integrated wind tunnel, locomotion and anatomical range of motion data to identify functional parameters of the cambered minke whale flipper. A full-sized cast of a minke whale flipper was used in wind tunnel testing of lift, drag and stall behavior at six speeds, corresponding to swimming speeds of 0.7-8.9 m s(-1). Flow over the model surface stalled between 10 degrees and 14 degrees angle of attack (alpha) depending on testing speed. When the leading edge was rotated ventrally, loss in lift occurred around -18 degrees alpha regardless of speed. Range of mobility in the fresh limb was approximately 40% greater than the range of positive lift-generating angles of attack predicted by wind tunnel data (+14 degrees alpha). Video footage, photographs and observations of swimming, engulfment feeding and gulping minke whales showed limb positions corresponding to low drag in wind tunnel tests, and were therefore hydrodynamically efficient. Flippers play an important role in orienting the body during feeding maneuvers as they maintain trim of the body, an action that counters drag-induced torque of the body during water and prey intake.
Investigation of drag reduction through a flapping mechanism on circular cylinder
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.
Granular drag and the kinetics of jamming
Brzinski, Theodore A., III
The first part of this thesis focuses on the study of the force exerted by a granular packing on an intruder. During impact, this force can be described by the linear combination of an inertial drag and a rate-independent frictional force that is proportional to depth. We measure the torque acting on a rod rotated perpendicular to its axis in a granular bed at steady state, and demonstrate that the resisting force is of the same form, though smaller. We then alter the hydrostatic loading on the bed by generating a homogenized airflow through the bed, and show that for horizontal motion the frictional force is due to friction acting at gravity-loaded contacts. Next we directly measure the force acting on quasistatically, vertically lowered intruders under two sets of varied conditions. First we vary the shape of the projectile in order to alter the fraction of the projectile surface that moves parallel vs perpendicular to the medium, and find that the frictional force acts primarily normal to the intruder surface. Second, we alter the hydrostatic loading as above, and confirm that gravity-loading of the grains sets the magnitude of the resisting force for quasi-static vertical motion as well. Finally, we consider the case of impact onto wet grains. We conduct conventional impact experiments wherein a spherical projectile impacts onto a granular packing with a known impact speed. We vary the liquid, impact speed, and degree of saturation, and find that the penetration depth is decreased for all wetting fractions, and that the penetration depth has a non-monotonic dependence on liquid saturation. In the fully saturated case, we recover the same scaling of penetration depth with geometry, impact speed and packing density as in the dry case, though the penetrations are shallower, suggesting a hydrodynamic contribution to the net stopping force. The second part of this thesis focuses on the kinetics of the jamming transition. In particular, we observe a dispersion of
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%.
Numerical study on aerodynamic drag reduction of passenger cars
Sanchez Martinez, Javier
2015-01-01
The scope of this work is to identify potential improvements on Passenger cars Aerodynimcs (Drag reduction and Downforce increase) to help to minimize fuel consumption and hence reduce exhaust emisions. The Ahmed body (Bluff body) is representative of a passenger car under aerodynamical point of view. A lot of studies and literature exists as far as test reports of the Ahmed body on wind tunel tests. This work can be divided onto 2 steps. First step is to perform qualitative numerical simulat...
Directory of Open Access Journals (Sweden)
Chitra Arora
2010-06-01
Full Text Available A well defined relationship connecting settling velocity with sediment geometry and ambient properties is an essential pre-requisite for coastal and hydraulic engineering studies. An established relationship for settling velocity of sandy particles assuming spherical shape geometry is available in the literature. In reality, the sediment particles need not be spherical at all times, which influences settling velocity that is strongly biased to the drag coefficient. Based on quantitative comparison with measured data collected at Oahu Islands located in the Hawaiian archipelago, USA this work provides a relationship between drag coefficient and particle shape factor for sand grains viz; sand, sandy loam and fine sandy loam typically found in coastal environment (typical size ranges from 0.05 to 2.0 mm. The particle Reynolds number and shape factor are evaluated for each grain. The drag coefficient evaluated as function of nominal diameter and Reynolds number show a positive correlation over a wide range of shape factors used in this study. A comprehensive correlation has been developed of the drag coefficient for non-spherical particles as a function of Reynolds number and particle shape. Further a regression analysis was performed on the functional dependence of drag coefficient on particle shape. Based on this study, it could be advocated the validity of Krumbien shape factor holds well for the above characterized grain size and various particle shapes considered. Hence, the settling velocity of particles has a functional dependence on estimated drag coefficient with important implications for modeling sediment transport and swash zone hydrodynamics.
Directory of Open Access Journals (Sweden)
Sezar Gülbaz
2015-01-01
Full Text Available The land development and increase in urbanization in a watershed affect water quantityand water quality. On one hand, urbanization provokes the adjustment of geomorphicstructure of the streams, ultimately raises peak flow rate which causes flood; on theother hand, it diminishes water quality which results in an increase in Total SuspendedSolid (TSS. Consequently, sediment accumulation in downstream of urban areas isobserved which is not preferred for longer life of dams. In order to overcome thesediment accumulation problem in dams, the amount of TSS in streams and inwatersheds should be taken under control. Low Impact Development (LID is a BestManagement Practice (BMP which may be used for this purpose. It is a land planningand engineering design method which is applied in managing storm water runoff inorder to reduce flooding as well as simultaneously improve water quality. LID includestechniques to predict suspended solid loads in surface runoff generated over imperviousurban surfaces. In this study, the impact of LID-BMPs on surface runoff and TSS isinvestigated by employing a calibrated hydrodynamic model for Sazlidere Watershedwhich is located in Istanbul, Turkey. For this purpose, a calibrated hydrodynamicmodel was developed by using Environmental Protection Agency Storm WaterManagement Model (EPA SWMM. For model calibration and validation, we set up arain gauge and a flow meter into the field and obtain rainfall and flow rate data. Andthen, we select several LID types such as retention basins, vegetative swales andpermeable pavement and we obtain their influence on peak flow rate and pollutantbuildup and washoff for TSS. Consequently, we observe the possible effects ofLID on surface runoff and TSS in Sazlidere Watershed.
Air Drag Effects on the Missile Trajectories
Directory of Open Access Journals (Sweden)
F. A. Abd El-Salam
2011-01-01
Full Text Available The equations of motion of a missile under the air drag effects are constructed. The modified TD88 is surveyed. Using Lagrange's planetary equations in Gauss form, the perturbations, due to the air drag in the orbital elements, are computed between the eccentric anomalies of the burn out and the reentry points [Ebo,2π−Ebo], respectively. The range equation is expressed as an infinite series in terms of the eccentricity e and the eccentric anomaly E. The different errors in the missile-free range due to the drag perturbations in the missile trajectory are obtained.
Skin friction drag reduction in turbulent flow using spanwise traveling surface waves
Musgrave, Patrick F.; Tarazaga, Pablo A.
2017-04-01
A major technological driver in current aircraft and other vehicles is the improvement of fuel efficiency. One way to increase the efficiency is to reduce the skin friction drag on these vehicles. This experimental study presents an active drag reduction technique which decreases the skin friction using spanwise traveling waves. A novel method is introduced for generating traveling waves which is low-profile, non-intrusive, and operates under various flow conditions. This wave generation method is discussed and the resulting traveling waves are presented. These waves are then tested in a low-speed wind tunnel to determine their drag reduction potential. To calculate the drag reduction, the momentum integral method is applied to turbulent boundary layer data collected using a pitot tube and traversing system. The skin friction coefficients are then calculated and the drag reduction determined. Preliminary results yielded a drag reduction of ≍ 5% for 244Hz traveling waves. Thus, this novel wave generation method possesses the potential to yield an easily implementable, non-invasive drag reduction technology.
Hydrodynamic analysis of human swimming based on VOF method.
Zhan, Jie-Min; Li, Tian-Zeng; Chen, Xue-Bin; Li, Y S
2017-05-01
A 3-D numerical model, based on the Navier-Strokes equations and the RNG k-ε turbulence closure, for studying hydrodynamic drag on a swimmer with wave-making resistance taken into account is established. The volume of fluid method is employed to capture the undulation of the free surface. The simulation strategy is evaluated by comparison of the computed results with experimental data. The computed results are in good agreement with data from mannequin towing experiments. The effects of the swimmer's head position and gliding depth on the drag force at different velocities are then investigated. It is found that keeping the head aligned with the body is the optimal posture in streamlined gliding. Also wave-making resistance is significant within 0.3 m depth from the free surface.
Hydrodynamic Vortex on Surfaces
Ragazzo, Clodoaldo Grotta; de Barros Viglioni, Humberto Henrique
2017-10-01
The equations of motion for a system of point vortices on an oriented Riemannian surface of finite topological type are presented. The equations are obtained from a Green's function on the surface. The uniqueness of the Green's function is established under hydrodynamic conditions at the surface's boundaries and ends. The hydrodynamic force on a point vortex is computed using a new weak formulation of Euler's equation adapted to the point vortex context. An analogy between the hydrodynamic force on a massive point vortex and the electromagnetic force on a massive electric charge is presented as well as the equations of motion for massive vortices. Any noncompact Riemann surface admits a unique Riemannian metric such that a single vortex in the surface does not move ("Steady Vortex Metric"). Some examples of surfaces with steady vortex metric isometrically embedded in R^3 are presented.
Drag and heat flux reduction mechanism of blunted cone with aerodisks
Huang, Wei; Li, Lang-quan; Yan, Li; Zhang, Tian-tian
2017-09-01
The major challenge among a number of design requirements for hypersonic vehicles is the reduction of drag and aerodynamic heating. Of all these techniques of drag and heat flux reduction, application of forward facing aerospike conceived in 1950s is an effective and simpler technique to reduce the drag as well as the heat transfer rate for blunt nosed bodies at hypersonic Mach numbers. In this paper, the flow fields around a blunt cone with and without aerodisk flying at hypersonic Mach numbers are computed numerically, and the numerical simulations are conducted by specifying the freestream velocity, static pressure and static temperatures at the inlet of the computational domain with a three-dimensional, steady, Reynolds-averaged Navier-Stokes equation. An aerodisk is attached to the tip of the rod to reduce the drag and heat flux further. The influences of the length of rod and the diameter of aerodisk on the drag and heat flux reduction mechanism are analyzed comprehensively, and eight configurations are taken into consideration in the current study. The obtained results show that for all aerodisks, the reduction in drag of the blunt body is proportional to the extent of the recirculation dead air region. For long rods, the aerodisk is found not that beneficial in reducing the drag, and an aerodisk is more effective than an aerospike. The spike produces a region of recirculation separated flow that shields the blunt-nosed body from the incoming flow, and the recirculation region is formed around the root of the spike up to the reattachment point of the flow at the shoulder of the blunt body. The dynamic pressure in the recirculation area is highly reduced and thus leads to the decrease in drag and heat load on the surface of the blunt body. Because of the reattachment of the shear layer on the shoulder of the blunt body, the pressure near that point becomes large.
Discovery of riblets in a bird beak (Rynchops) for low fluid drag
Martin, Samuel; Bhushan, Bharat
2016-01-01
Riblet structures found on fast-swimming shark scales, such as those found on a mako shark, have been shown to reduce fluid drag. In previous experimental and modelling studies, riblets have been shown to provide drag reduction by lifting vortices formed in turbulent flow, decreasing overall shear stresses. Skimmer birds (Rynchops) are the only birds to catch fish in flight by flying just above the water surface with a submerged beak to fish for food. Because they need to quickly catch prey, ...
Forced wetting and hydrodynamic assist
Blake, Terence D.; Fernandez-Toledano, Juan-Carlos; Doyen, Guillaume; De Coninck, Joël
2015-11-01
Wetting is a prerequisite for coating a uniform layer of liquid onto a solid. Wetting failure and air entrainment set the ultimate limit to coating speed. It is well known in the coating art that this limit can be postponed by manipulating the coating flow to generate what has been termed "hydrodynamic assist," but the underlying mechanism is unclear. Experiments have shown that the conditions that postpone air entrainment also reduce the apparent dynamic contact angle, suggesting a direct link, but how the flow might affect the contact angle remains to be established. Here, we use molecular dynamics to compare the outcome of steady forced wetting with previous results for the spontaneous spreading of liquid drops and apply the molecular-kinetic theory of dynamic wetting to rationalize our findings and place them on a quantitative footing. The forced wetting simulations reveal significant slip at the solid-liquid interface and details of the flow immediately adjacent to the moving contact line. Our results confirm that the local, microscopic contact angle is dependent not simply only on the velocity of wetting but also on the nature of the flow that drives it. In particular, they support an earlier suggestion that during forced wetting, an intense shear stress in the vicinity of the contact line can assist surface tension forces in promoting dynamic wetting, thus reducing the velocity-dependence of the contact angle. Hydrodynamic assist then appears as a natural consequence of wetting that emerges when the contact line is driven by a strong and highly confined flow. Our theoretical approach also provides a self-consistent model of molecular slip at the solid-liquid interface that enables its magnitude to be estimated from dynamic contact angle measurements. In addition, the model predicts how hydrodynamic assist and slip may be influenced by liquid viscosity and solid-liquid interactions.
Marinho, Daniel A; Barbosa, Tiago M; Rouboa, Abel I; Silva, António J
2011-09-01
Nowadays the underwater gliding after the starts and the turns plays a major role in the overall swimming performance. Hence, minimizing hydrodynamic drag during the underwater phases should be a main aim during swimming. Indeed, there are several postures that swimmers can assume during the underwater gliding, although experimental results were not conclusive concerning the best body position to accomplish this aim. Therefore, the purpose of this study was to analyse the effect in hydrodynamic drag forces of using different body positions during gliding through computational fluid dynamics (CFD) methodology. For this purpose, two-dimensional models of the human body in steady flow conditions were studied. Two-dimensional virtual models had been created: (i) a prone position with the arms extended at the front of the body; (ii) a prone position with the arms placed alongside the trunk; (iii) a lateral position with the arms extended at the front and; (iv) a dorsal position with the arms extended at the front. The drag forces were computed between speeds of 1.6 m/s and 2 m/s in a two-dimensional Fluent(®) analysis. The positions with the arms extended at the front presented lower drag values than the position with the arms aside the trunk. The lateral position was the one in which the drag was lower and seems to be the one that should be adopted during the gliding after starts and turns.
Biological implications of the hydrodynamics of swimming at or near the surface and in shallow water
Energy Technology Data Exchange (ETDEWEB)
Blake, R W [Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4 (Canada)], E-mail: blake@zoology.ubc.ca
2009-03-01
The origins and effects of wave drag at and near the surface and in shallow water are discussed in terms of the dispersive waves generated by streamlined technical bodies of revolution and by semi-aquatic and aquatic animals with a view to bearing on issues regarding the design and function of autonomous surface and underwater vehicles. A simple two-dimensional model based on energy flux, allowing assessment of drag and its associated wave amplitude, is applied to surface swimming in Lesser Scaup ducks and is in good agreement with measured values. It is argued that hydrodynamic limitations to swimming at speeds associated with the critical Froude number ({approx}0.5) and hull speed do not necessarily set biological limitations as most behaviours occur well below the hull speed. From a comparative standpoint, the need for studies on the hull displacement of different forms is emphasized. For forms in surface proximity, drag is a function of both Froude and Reynolds numbers. Whilst the depth dependence of wave drag is not particularly sensitive to Reynolds number, its magnitude is, with smaller and slower forms subject to relatively less drag augmentation than larger, faster forms that generate additional resistance due to ventilation and spray. A quasi-steady approach to the hydrodynamics of swimming in shallow water identifies substantial drag increases relative to the deeply submerged case at Froude numbers of about 0.9 that could limit the performance of semi-aquatic and aquatic animals and autonomous vehicles. A comparative assessment of fast-starting trout and upside down catfish shows that the energy losses of fast-starting fish are likely to be less for fish in surface proximity in deep water than for those in shallow water. Further work on unsteady swimming in both circumstances is encouraged. Finally, perspectives are offered as to how autonomous surface and underwater vehicles in surface proximity and shallow water could function to avoid prohibitive
Analytical Ballistic Trajectories with Approximately Linear Drag
National Research Council Canada - National Science Library
Giliam J. P. de Carpentier
2014-01-01
This paper introduces a practical analytical approximation of projectile trajectories in 2D and 3D roughly based on a linear drag model and explores a variety of different planning algorithms for these trajectories...
Satellite Formation Control Using Atmospheric Drag
National Research Council Canada - National Science Library
Hajovsky, Blake B
2007-01-01
This study investigates the use of a linear quadratic terminal controller to reconfigure satellite formations using atmospheric drag actuated control while minimizing the loss of energy of the formation...
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.
Drag Performance of Twist Morphing MAV Wing
Ismail N.I.; Zulkifli A.H.; Talib R.J.; Zaini H.; Yusoff H.
2016-01-01
Morphing wing is one of latest evolution found on MAV wing. However, due to few design problems such as limited MAV wing size and complicated morphing mechanism, the understanding of its aerodynamic behaviour was not fully explored. In fact, the basic drag distribution induced by a morphing MAV wing is still remained unknown. Thus, present work is carried out to compare the drag performance between a twist morphing wing with membrane and rigid MAV wing design. A quasi-static aeroelastic analy...
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.
Thermal lift generation and drag reduction in rarefied aerodynamics
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.
Hydrodynamic separator sediment retention testing.
2010-03-01
Hydrodynamic separators are widely used in urban areas for removal of suspended sediments and floatables from : stormwater due to limited land availability for the installation of above ground stormwater best management : practices (BMPs). Hydrodynam...
Drag Performance of Twist Morphing MAV Wing
Directory of Open Access Journals (Sweden)
Ismail N.I.
2016-01-01
Full Text Available Morphing wing is one of latest evolution found on MAV wing. However, due to few design problems such as limited MAV wing size and complicated morphing mechanism, the understanding of its aerodynamic behaviour was not fully explored. In fact, the basic drag distribution induced by a morphing MAV wing is still remained unknown. Thus, present work is carried out to compare the drag performance between a twist morphing wing with membrane and rigid MAV wing design. A quasi-static aeroelastic analysis by using the Ansys-Fluid Structure Interaction (FSI method is utilized in current works to predict the drag performance a twist morphing MAV wing design. Based on the drag pattern study, the results exhibits that the morphing wing has a partial similarities in overall drag pattern with the baseline (membrane and rigid wing. However, based CD analysis, it shows that TM wing induced higher CD magnitude (between 25% to 82% higher than to the baseline wing. In fact, TM wing also induced the largest CD increment (about 20% to 27% among the wings. The visualization on vortex structure revealed that TM wing also produce larger tip vortex structure (compared to baseline wings which presume to promote higher induce drag component and subsequently induce its higher CD performance.
The application of single particle hydrodynamics in continuum models of multiphase flow
Decker, Rand
1988-01-01
A review of the application of single particle hydrodynamics in models for the exchange of interphase momentum in continuum models of multiphase flow is presented. Considered are the equations of motion for a laminar, mechanical two phase flow. Inherent to this theory is a model for the interphase exchange of momentum due to drag between the dispersed particulate and continuous fluid phases. In addition, applications of two phase flow theory to de-mixing flows require the modeling of interphase momentum exchange due to lift forces. The applications of single particle analysis in deriving models for drag and lift are examined.
Bosonization and quantum hydrodynamics
Indian Academy of Sciences (India)
Bosonization and quantum hydrodynamics. GIRISH S SETLUR. Department of Physics, Indian Institute of Technology, Guwahati, North Guwahati .... and Haldane [3] breaks up the Fermi surface into patches where the separation between the patches ∆kF ≫ Λ ∼ ∆q. Not only is this contrived, it involves the introduction of one ...
Skew resisting hydrodynamic seal
Conroy, William T.; Dietle, Lannie L.; Gobeli, Jeffrey D.; Kalsi, Manmohan S.
2001-01-01
A novel hydrodynamically lubricated compression type rotary seal that is suitable for lubricant retention and environmental exclusion. Particularly, the seal geometry ensures constraint of a hydrodynamic seal in a manner preventing skew-induced wear and provides adequate room within the seal gland to accommodate thermal expansion. The seal accommodates large as-manufactured variations in the coefficient of thermal expansion of the sealing material, provides a relatively stiff integral spring effect to minimize pressure-induced shuttling of the seal within the gland, and also maintains interfacial contact pressure within the dynamic sealing interface in an optimum range for efficient hydrodynamic lubrication and environment exclusion. The seal geometry also provides for complete support about the circumference of the seal to receive environmental pressure, as compared the interrupted character of seal support set forth in U.S. Pat. Nos. 5,873,576 and 6,036,192 and provides a hydrodynamic seal which is suitable for use with non-Newtonian lubricants.
Smoothed Particle Hydrodynamic Simulator
Energy Technology Data Exchange (ETDEWEB)
2016-10-05
This code is a highly modular framework for developing smoothed particle hydrodynamic (SPH) simulations running on parallel platforms. The compartmentalization of the code allows for rapid development of new SPH applications and modifications of existing algorithms. The compartmentalization also allows changes in one part of the code used by many applications to instantly be made available to all applications.
Directory of Open Access Journals (Sweden)
Chonghai Huang
Full Text Available Abstract Turbulence with a relatively larger vortex is obtained in drag-reducing surfactant solution, which provides an excellent condition for the application of small scale grooves. In this work, the coupling drag reduction performance of surfactant solution and grooves was experimentally investigated to explore the complementary possibility between their drag reduction mechanisms. The cationic surfactant cetyltrimethyl ammonium chloride (CTAC mixed with the counterion salt sodium salicylate (NaSal was experimented in smooth or grooved channel, respectively, at the mass concentrations of 50-150 ppm. It was found that the surfactant solutions gave more effective drag reduction in the grooved channel by the interaction between the "restriction effect" and "peak effect" of grooves. Moreover, the critical temperature and critical Reynolds number of the surfactant solution were smaller in the grooved channel, and the friction factor in the grooved channel increased much more rapidly than that in the smooth channel when Re is larger than a critical value.
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.
Drag reduction by natural polymeric additives in PMDS microchannel: Effect of types of additives
Directory of Open Access Journals (Sweden)
Ling Fiona W.M.
2017-01-01
Full Text Available Drag reduction technology was used in medical applications to enhance the blood flow in semiclogged blood streams which can be an alternative treatment for atherosclerosis. In this present study, natural polymeric drag reducing additives (DRA was introduced to replace synthetic polymer which has the possibility of bringing side effects to human health. Three different sources, namely okra, aloe vera and hibiscus were utilized to extract the natural polymeric additives which were then tested in custom made microchannel simulating human heart blood vessels. The performance of different types of additives was evaluated using pressure measurements. The maximum drag reduction up to 63.48% is achieved using 300 ppm of hibiscus mucilage at operating pressure of 50 mbar. In this present work, hibiscus showed the best drag reduction performance, giving the highest %FI in most of the cases. This experimental results proved that these natural polymeric additives could be utilized as DRA in enhancing the blood flow in semiclogged blood streams.
DEFF Research Database (Denmark)
Aage, Christian
1998-01-01
these properties and to program the control systemm comprise added mass and inertia coefficients, damping, lift and drag coefficients of the vehicle and its control surfaces, as well as resistance and propulsion characteristics. Only few hydrodynamic data for AUVs have yet been published, so dedicated tests...
Hydrodynamic modulation of pluripotent stem cells
2012-01-01
Controlled expansion and differentiation of pluripotent stem cells (PSCs) using reproducible, high-throughput methods could accelerate stem cell research for clinical therapies. Hydrodynamic culture systems for PSCs are increasingly being used for high-throughput studies and scale-up purposes; however, hydrodynamic cultures expose PSCs to complex physical and chemical environments that include spatially and temporally modulated fluid shear stresses and heterogeneous mass transport. Furthermore, the effects of fluid flow on PSCs cannot easily be attributed to any single environmental parameter since the cellular processes regulating self-renewal and differentiation are interconnected and the complex physical and chemical parameters associated with fluid flow are thus difficult to independently isolate. Regardless of the challenges posed by characterizing fluid dynamic properties, hydrodynamic culture systems offer several advantages over traditional static culture, including increased mass transfer and reduced cell handling. This article discusses the challenges and opportunities of hydrodynamic culture environments for the expansion and differentiation of PSCs in microfluidic systems and larger-volume suspension bioreactors. Ultimately, an improved understanding of the effects of hydrodynamics on the self-renewal and differentiation of PSCs could yield improved bioprocessing technologies to attain scalable PSC culture strategies that will probably be requisite for the development of therapeutic and diagnostic applications. PMID:23168068
Anisotropic hydrodynamics for conformal Gubser flow
Energy Technology Data Exchange (ETDEWEB)
Strickland, Michael; Nopoush, Mohammad [Kent State University, Kent OH 44242 (United States); Ryblewski, Radoslaw [The H. Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland)
2016-12-15
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3){sub q} symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
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.
Geometry Mediated Drag Reduction in Taylor-Couette Flows
Raayai, Shabnam; McKinley, Gareth
2015-11-01
Micro-scale ribbed surfaces have been shown to be able to modify surface properties such as skin friction on both natural and fabricated surfaces. Previous experiments have shown that ribbed surfaces can reduce skin friction in turbulent flow by up to 4-8% in the presence of zero or mild pressure gradients. Our previous computations have shown a substantial reduction in skin friction using micro-scaled ribs of sinusoidal form in high Reynolds number laminar boundary layer flow. The mechanism of this reduction is purely viscous, through a geometrically-controlled retardation of the flow in the grooves of the surface. The drag reduction achieved depends on the ratio of the amplitude to the wavelength of the surface features and can be presented as a function of the wavelength expressed in dimensionless wall units. Here we extend this work, both experimentally and numerically, to consider the effect of similar ribs on steady viscous flow between concentric cylinders (Taylor-Couette flow). For the experimental work, the inner rotating cylinder (rotor) is machined with stream-wise V-groove structures and experiments are performed with fluids of different viscosity to compare the measured frictional torques to the corresponding values on a smooth flat rotor as a measure of drag reduction. The numerical work is performed using the OpenFOAM®open source software to compare the results and understand the physical mechanisms underlying this drag reduction phenomenon.
Frictional Drag Reduction by Bubbles in Taylor-Couette Flow
Murai, Yuichi; Oiwa, Hiroshi; Takeda, Yasushi
2006-11-01
Frictional drag reduction provided with small bubbles is investigated experimentally using a Couette-Taylor flow system, i.e. shear flow between concentric cylinders. Torque and bubble behavior are measured up to Re=4500 when air bubbles are injected constantly and rise through the cells. Silicone oil is used for avoiding uncertain interfacial property of bubbles as well as for keeping nearly mono-sized bubbles. We assess the effect of drag reduction with two types of evaluation factors, i.e. sensitivity and power gain. The sensitivity exceeds unity at Redrag is reduced more than the drop of mixture density. This originates from accumulation of bubbles into the rotating inner cylinder, which is little affected by turbulence. The power gain, which is defined by drag reduction power per bubble injection power, takes the highest value of O(10) at higher Re numbers around 2500. The image processing measurement finds this reason to be disappearance of azimuthal waves when the organized bubbles distribution transits from toroidal to spiral modes. Moreover, the axial spacing of bubble clouds expands during the transition, enforcing the reduction of momentum exchange.
The effect of shape on drag: a physics exercise inspired by biology
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.
Doyon, Benjamin; Dubail, Jérôme; Konik, Robert; Yoshimura, Takato
2017-11-01
The theory of generalized hydrodynamics (GHD) was recently developed as a new tool for the study of inhomogeneous time evolution in many-body interacting systems with infinitely many conserved charges. In this Letter, we show that it supersedes the widely used conventional hydrodynamics (CHD) of one-dimensional Bose gases. We illustrate this by studying "nonlinear sound waves" emanating from initial density accumulations in the Lieb-Liniger model. We show that, at zero temperature and in the absence of shocks, GHD reduces to CHD, thus for the first time justifying its use from purely hydrodynamic principles. We show that sharp profiles, which appear in finite times in CHD, immediately dissolve into a higher hierarchy of reductions of GHD, with no sustained shock. CHD thereon fails to capture the correct hydrodynamics. We establish the correct hydrodynamic equations, which are finite-dimensional reductions of GHD characterized by multiple, disjoint Fermi seas. We further verify that at nonzero temperature, CHD fails at all nonzero times. Finally, we numerically confirm the emergence of hydrodynamics at zero temperature by comparing its predictions with a full quantum simulation performed using the NRG-TSA-abacus algorithm. The analysis is performed in the full interaction range, and is not restricted to either weak- or strong-repulsion regimes.
Young swimmers' classification based on kinematics, hydrodynamics, and anthropometrics.
Barbosa, Tiago M; Morais, Jorge E; Costa, Mário J; Goncalves, José; Marinho, Daniel A; Silva, António J
2014-04-01
The aim of this article has been to classify swimmers based on kinematics, hydrodynamics, and anthropometrics. Sixty-seven young swimmers made a maximal 25 m front-crawl to measure with a speedometer the swimming velocity (v), speed-fluctuation (dv) and dv normalized to v (dv/v). Another two 25 m bouts with and without carrying a perturbation device were made to estimate active drag coefficient (CDa). Trunk transverse surface area (S) was measured with photogrammetric technique on land and in the hydrodynamic position. Cluster 1 was related to swimmers with a high speed fluctuation (ie, dv and dv/v), cluster 2 with anthropometrics (ie, S) and cluster 3 with a high hydrodynamic profile (ie, CDa). The variable that seems to discriminate better the clusters was the dv/v (F=53.680; PPPPv (F=5.375; P=.01). Stepwise discriminant analysis extracted 2 functions: Function 1 was mainly defined by dv/v and S (74.3% of variance), whereas function 2 was mainly defined by CDa (25.7% of variance). It can be concluded that kinematics, hydrodynamics and anthropometrics are determinant domains in which to classify and characterize young swimmers' profiles.
Directory of Open Access Journals (Sweden)
Milda Bilinauskaite
2013-01-01
Full Text Available The aim of this paper is to determine the hydrodynamic characteristics of swimmer’s scanned hand models for various combinations of both the angle of attack and the sweepback angle and shape and velocity of swimmer's hand, simulating separate underwater arm stroke phases of freestyle (front crawl swimming. Four realistic 3D models of swimmer's hand corresponding to different combinations of separated/closed fingers positions were used to simulate different underwater front crawl phases. The fluid flow was simulated using FLUENT (ANSYS, PA, USA. Drag force and drag coefficient were calculated using (computational fluid dynamics CFD in steady state. Results showed that the drag force and coefficient varied at the different flow velocities on all shapes of the hand and variation was observed for different hand positions corresponding to different stroke phases. The models of the hand with thumb adducted and abducted generated the highest drag forces and drag coefficients. The current study suggests that the realistic variation of both the orientation angles influenced higher values of drag, lift, and resultant coefficients and forces. To augment resultant force, which affects swimmer's propulsion, the swimmer should concentrate in effectively optimising achievable hand areas during crucial propulsive phases.
Hydrodynamics of Turning Flocks.
Yang, Xingbo; Marchetti, M Cristina
2015-12-18
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks.
Superluminous Supernovae hydrodynamic models
Orellana, M.
2017-07-01
We use our radiation hydrodynamic code in order to simulate magnetar powered Superluminous Supernovae (SLSNe). It is assumed that a central rapidly rotating magnetar deposits all its rotational energy into the ejecta where is added to the usual power. The magnetar luminosity and spin-down timescale are adopted as the free parameters of the model. For the case of ASASSN-15lh, which has been claimed as the most luminous supernova ever discovered, we have found physically plausible magnetar parameters can reproduce the overall shape of the bolometric light curve (LC) provided the progenitor mass is ≍ 8M⊙. The ejecta dynamics of this event shows signs of the magnetar energy input which deviates the expansion from the usually assumed homologous behaviour. Our numerical experiments lead us to conclude that the hydrodynamical modeling is necessary in order to derive the properties of powerful magnetars driving SLSNe.
Frictional drag reduction by bubble injection
Murai, Yuichi
2014-07-01
The injection of gas bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. This explains why a number of different void-drag reduction relationships have been reported to date, while early works pursued a simple universal mechanism. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. Each regime has inherent physics of bubbly liquid, highlighted by keywords such as bubbly mixture rheology, the spectral response of bubbles in turbulence, buoyancy-dominated bubble behavior, and gas cavity breakup. Among the regimes, bubbles in some selected situations lose the drag reduction effect owing to extra momentum transfer promoted by their active motions. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. This article reviews the roles of bubbles in drag reduction, which have been revealed from fundamental studies of simplified flow geometries and from development of measurement techniques that resolve the inner layer structure of bubble-mixed turbulent boundary layers.
Blaedel, Kenneth L.; Davis, Pete J.; Landram, Charles S.
2000-01-01
A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.
Hydrodynamics of insect spermatozoa
Pak, On Shun; Lauga, Eric
2010-11-01
Microorganism motility plays important roles in many biological processes including reproduction. Many microorganisms propel themselves by propagating traveling waves along their flagella. Depending on the species, propagation of planar waves (e.g. Ceratium) and helical waves (e.g. Trichomonas) were observed in eukaryotic flagellar motion, and hydrodynamic models for both were proposed in the past. However, the motility of insect spermatozoa remains largely unexplored. An interesting morphological feature of such cells, first observed in Tenebrio molitor and Bacillus rossius, is the double helical deformation pattern along the flagella, which is characterized by the presence of two superimposed helical flagellar waves (one with a large amplitude and low frequency, and the other with a small amplitude and high frequency). Here we present the first hydrodynamic investigation of the locomotion of insect spermatozoa. The swimming kinematics, trajectories and hydrodynamic efficiency of the swimmer are computed based on the prescribed double helical deformation pattern. We then compare our theoretical predictions with experimental measurements, and explore the dependence of the swimming performance on the geometric and dynamical parameters.
High yield DNA fragmentation using cyclical hydrodynamic shearing
Shui, Lingling; Sparreboom, Wouter; Spang, Peter; Roeser, Tina; Nieto, Benjamin; Guasch, Francesc; Corbera, Antoni Homs; van den Berg, Albert; Carlen, Edwin
2013-01-01
We report a new DNA fragmentation technique that significantly simplifies conventional hydrodynamic shearing fragmentation by eliminating the need for sample recirculation while maintaining high fragmentation yield and low fragment length variation, and therefore, reduces instrument complexity and
A Novel Method to Determine the Hydrodynamic Coefficients of an Eyeball ROV
Yh, Eng; Ws, Lau; Low, E.; Ggl, Seet; Cs, Chin
2009-01-01
A good dynamics model is essential and critical for the successful design of navigation and control system of an underwater vehicle. However, it is difficult to determine from the hydrodynamic forces, the inertial added mass terms and the drag coefficients. In this paper, a new experimental method has been used to find the hydrodynamic forces for the ROV II, a remotely operated underwater vehicle. The proposed method is based on the classical free decay test, but with the spring oscillation replaced by a pendulum motion. The experiment results determined from the free decay test of a scaled model compared well with the simulation results obtained from well-established computational fluid dynamics (CFD) program. Thus, the proposed approach can be used to find the added mass and drag coefficients for other underwater vehicles.
A Novel Method to Determine the Hydrodynamic Coefficients of an Eyeball ROV
Energy Technology Data Exchange (ETDEWEB)
Yh, Eng; Ws, Lau; Low, E.; Ggl, Seet; Cs, Chin [Robotic Research Center, School of Mechanical & Aerospace Engineering (MAE), Nanyang Technological University, 50 Nanyang Ave, 639798 Singapore (Singapore)
2009-01-12
A good dynamics model is essential and critical for the successful design of navigation and control system of an underwater vehicle. However, it is difficult to determine from the hydrodynamic forces, the inertial added mass terms and the drag coefficients. In this paper, a new experimental method has been used to find the hydrodynamic forces for the ROV II, a remotely operated underwater vehicle. The proposed method is based on the classical free decay test, but with the spring oscillation replaced by a pendulum motion. The experiment results determined from the free decay test of a scaled model compared well with the simulation results obtained from well‐established computational fluid dynamics (CFD) program. Thus, the proposed approach can be used to find the added mass and drag coefficients for other underwater vehicles.
Validation of Hydrodynamic Load Models Using CFD for the OC4-DeepCwind Semisubmersible: Preprint
Energy Technology Data Exchange (ETDEWEB)
Benitz, M. A.; Schmidt, D. P.; Lackner, M. A.; Stewart, G. M.; Jonkman, J.; Robertson, A.
2015-03-01
Computational fluid dynamics (CFD) simulations were carried out on the OC4-DeepCwind semi-submersible to obtain a better understanding of how to set hydrodynamic coefficients for the structure when using an engineering tool such as FAST to model the system. The focus here was on the drag behavior and the effects of the free-surface, free-ends and multi-member arrangement of the semi-submersible structure. These effects are investigated through code-to-code comparisons and flow visualizations. The implications on mean load predictions from engineering tools are addressed. The work presented here suggests that selection of drag coefficients should take into consideration a variety of geometric factors. Furthermore, CFD simulations demonstrate large time-varying loads due to vortex shedding, which FAST's hydrodynamic module, HydroDyn, does not model. The implications of these oscillatory loads on the fatigue life needs to be addressed.
Midea, Anthony C.; Austin, Thomas; Pao, S. Paul; DeBonis, James R.; Mani, Mori
2005-01-01
Nozzle boattail drag is significant for the High Speed Civil Transport (HSCT) and can be as high as 25 percent of the overall propulsion system thrust at transonic conditions. Thus, nozzle boattail drag has the potential to create a thrust drag pinch and can reduce HSCT aircraft aerodynamic efficiencies at transonic operating conditions. In order to accurately predict HSCT performance, it is imperative that nozzle boattail drag be accurately predicted. Previous methods to predict HSCT nozzle boattail drag were suspect in the transonic regime. In addition, previous prediction methods were unable to account for complex nozzle geometry and were not flexible enough for engine cycle trade studies. A computational fluid dynamics (CFD) effort was conducted by NASA and McDonnell Douglas to evaluate the magnitude and characteristics of HSCT nozzle boattail drag at transonic conditions. A team of engineers used various CFD codes and provided consistent, accurate boattail drag coefficient predictions for a family of HSCT nozzle configurations. The CFD results were incorporated into a nozzle drag database that encompassed the entire HSCT flight regime and provided the basis for an accurate and flexible prediction methodology.
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°.
Bolzon, Michael; Kelso, Richard; Arjomandi, Maziar
2016-03-01
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°.
Special vortex in relativistic hydrodynamics
Chupakhin, A. P.; Yanchenko, A. A.
2017-10-01
An exact solution of the Euler equations governing the flow of a compressible fluid in relativistic hydrodynamics is found and studied. It is a relativistic analogue of the Ovsyannikov vortex (special vortex) investigated earlier for classical gas dynamics. Solutions are partially invariant of Defect 1 and Rank 2 with respect to the rotation group. A theorem on the representation of the factor-system in the form of a union of a non-invariant subsystem for the function determining the deviation of the velocity vector from the meridian, and invariant subsystem for determination of thermodynamic parameters, the Lorentz factor and the radial velocity component is proved. Compatibility conditions for the overdetermined non-invariant subsystem are obtained. A stationary solution of this type is studied in detail. It is proved that its invariant subsystem reduces to an implicit differential equation. For this equation, the manifold of branching of solutions is investigated, and a set of singular points is found.
Plasmon drag effect in metal nanostructures
Noginova, N.; Rono, V.; Bezares, F. J.; Caldwell, J. D.
2013-11-01
In order to better understand the mechanism of the photon drag effect in plasmonic nanostructures, photo-induced electric signals have been studied in gold and silver films and various plasmonic nanostructures. The spectral dependence of the effect points to the primary role of individual localized plasmon resonances in the photo-induced electromotive force (emf) generation responsible for the photon drag effect. We demonstrate the potential to engineer both the magnitude and polarity of the emf with nanoscale geometry and provide a simple model based on the intrinsic nonlinearity of metal in defining this effect.
ASTROPHYSICS: Neutron Stars Imply Relativity's a Drag.
Schilling, G
2000-09-01
A new finding, based on x-rays from distant neutron stars, could be the first clear evidence of a weird relativistic effect called frame dragging, in which a heavy chunk of spinning matter wrenches the space-time around it like an eggbeater. Using data from NASA's Rossi X-ray Timing Explorer, three astronomers in Amsterdam found circumstantial evidence for frame dragging in the flickering of three neutron stars in binary systems. They announced their results in the 1 September issue of The Astrophysical Journal.
New drag laws for flapping flight
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.
Correlated Coulomb drag in capacitively coupled quantum-dot structures
DEFF Research Database (Denmark)
Kaasbjerg, Kristen; Jauho, Antti-Pekka
2016-01-01
We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs) -- a biasdriven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach which accounts for higher-order tunneling (cotunneling......) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multi-electron cotunneling processes. Our theory establishes the conditions for a nonzero drag as well as the direction of the drag current in terms of microscopic system parameters...... on Coulomb drag in CQD systems....
Kalra, Tarandeep S.; Aretxabaleta, Alfredo; Seshadri, Pranay; Ganju, Neil K.; Beudin, Alexis
2017-01-01
Coastal hydrodynamics can be greatly affected by the presence of submerged aquatic vegetation. The effect of vegetation has been incorporated into the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System. The vegetation implementation includes the plant-induced three-dimensional drag, in-canopy wave-induced streaming, and the production of turbulent kinetic energy by the presence of vegetation. In this study, we evaluate the sensitivity of the flow and wave dynamics to vegetation parameters using Sobol' indices and a least squares polynomial approach referred to as Effective Quadratures method. This method reduces the number of simulations needed for evaluating Sobol' indices and provides a robust, practical, and efficient approach for the parameter sensitivity analysis. The evaluation of Sobol' indices shows that kinetic energy, turbulent kinetic energy, and water level changes are affected by plant density, height, and to a certain degree, diameter. Wave dissipation is mostly dependent on the variation in plant density. Performing sensitivity analyses for the vegetation module in COAWST provides guidance for future observational and modeling work to optimize efforts and reduce exploration of parameter space.
Hydrodynamics experiments with soap films and soap bubbles: A short review of recent experiments
Kellay, H.
2017-11-01
In this short review, I focus on recent experiments that benefit from the advantages offered by the two-dimensionality of the flow in suspended thin liquid films to reconsider hydrodynamics problems which have resisted a full understanding. The first problem discussed here concerns friction drag in channel flows. The use of turbulent channel flows, using thin liquid films, allows measurements of friction drag as well as mean velocity profiles for flows with different spectral exponents. Is there a link between the spectral properties of the turbulence and the mean velocity profiles or the frictional drag? This is the first question considered. The second issue examined considers the long time dynamics of large scale vortices. These are obtained in half bubbles rendered "turbulent" through thermal convection. These vortices, which live in a quasi two-dimensional environment, have a long time dynamics where their vorticity goes through what seems to be a well-defined cycle with generic features.
HYDRODYNAMIC ANALYSIS OF DIFFERENT THUMB POSITIONS IN SWIMMING
Directory of Open Access Journals (Sweden)
António J. Silva
2009-03-01
Full Text Available The aim of the present study was to analyze the hydrodynamic characteristics of a true model of a swimmer hand with the thumb in different positions using numerical simulation techniques. A three-dimensional domain was created to simulate the fluid flow around three models of a swimmer hand, with the thumb in different positions: thumb fully abducted, partially abducted, and adducted. These three hand models were obtained through computerized tomography scans of an Olympic swimmer hand. Steady-state computational fluid dynamics analyses were performed using the Fluent® code. The forces estimated in each of the three hand models were decomposed into drag and lift coefficients. Angles of attack of hand models of 0º, 45º and 90º, with a sweep back angle of 0º were used for the calculations. The results showed that the position with the thumb adducted presented slightly higher values of drag coefficient compared with thumb abducted positions. Moreover, the position with the thumb fully abducted allowed increasing the lift coefficient of the hand at angles of attack of 0º and 45º. These results suggested that, for hand models in which the lift force can play an important role, the abduction of the thumb may be better, whereas at higher angles of attack, in which the drag force is dominant, the adduction of the thumb may be preferable
Superhydrophobic copper tubes with possible flow enhancement and drag reduction
Shirtcliffe, NJ; McHale, G; Newton, MI; Zhang, Y.
2009-01-01
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...
Directory of Open Access Journals (Sweden)
Hongru Zhao
2016-11-01
Full Text Available The vertical migration and accumulation of Microcystis is an important process in water blooms, and colony migration is influenced by colony size and wind-wave disturbance. The vertical migration of Microcystis colonies in turbulence can be simulated in a numerical model. In this study, we model such migration by coupling the colony size and hydrodynamics, including the gravity, colony buoyancy, and the viscous drag force of turbulence. The turbulence intensity was represented by the turbulent kinetic energy (KZ; the larger the KZ, the stronger the wind-wave disturbance. The simulated vertical distribution of Microcystis well agreed with the measured values in a laboratory experiment indicating that our model can simulate the vertical distribution of Microcystis under different hydrodynamic conditions. We also found a size-dependent critical turbulent kinetic energy (TKZ, such that if the turbulent kinetic energy of water exceeds the critical value (i.e., KZ > TKZ, the colonies sink under the drag forces of turbulence; conversely, if KZ < TKZ, the colonies can overcome the turbulent mixing and float. The TKZ of each colony was linearly related to colony diameter. The model is crucial for prediction and prevention of water blooms. The simulated threshold turbulent kinetic energy, at which water blooms disappear in Lake Taihu (a large freshwater lake in the Yangtze Delta, Jiangsu Province, China, was 55.5 cm2 s−2.
Investigation of Tractor Base Bleeding for Heavy Vehicle Aerodynamic Drag Reduction
Energy Technology Data Exchange (ETDEWEB)
Ortega, J; Salari, K; Storms, B
2007-10-25
One of the main contributors to the aerodynamic drag of a heavy vehicle is tractor-trailer gap drag, which arises when the vehicle operates within a crosswind. Under this operating condition, freestream flow is entrained into the tractor-trailer gap, imparting a momentum exchange to the vehicle and subsequently increasing the aerodynamic drag. While a number of add-on devices, including side extenders, splitter plates, vortex stabilizers, and gap sealers, have been previously tested to alleviate this source of drag, side extenders remain the primary add-on device of choice for reducing tractor-trailer gap drag. However, side extenders are not without maintenance and operational issues. When a heavy vehicle pivots sharply with respect to the trailer, as can occur during loading or unloading operations, the side extenders can become crushed against the trailer. Consequently, fleet operators are forced to incur additional costs to cover the repair or replacement of the damaged side extenders. This issue can be overcome by either shortening the side extenders or by devising an alternative drag reduction concept that can perform just as effectively as side extenders. To explore such a concept, we investigate tractor base bleeding as a means of reducing gap drag. Wind tunnel measurements are made on a 1:20 scale heavy vehicle model at a vehicle width-based Reynolds number of 420,000. The tractor bleeding flow, which is delivered through a porous material embedded within the tractor base, is introduced into the tractor-trailer gap at bleeding coefficients ranging from 0.0-0.018. To determine the performance of tractor base bleeding under more realistic operating conditions, computational fluid dynamics simulations are performed on a full-scale heavy vehicle within a crosswind for bleeding coefficients ranging from 0.0-0.13.
How to fake hydrodynamic signals
Energy Technology Data Exchange (ETDEWEB)
Romatschke, Paul [Department of Physics, 390 UCB, University of Colorado at Boulder, Boulder, CO (United States); Center for Theory of Quantum Matter, University of Colorado, Boulder, CO 80309 (United States)
2016-12-15
Flow signatures in experimental data from relativistic ion collisions, are usually interpreted as a fingerprint of the presence of a hydrodynamic phase during the evolution of these systems. I review some theoretical ideas to ‘fake’ this hydrodynamic behavior in p+A and A+A collisions. I find that transverse flow and femtoscopic measurements can easily be forged through non-hydrodynamic evolution, while large elliptic flow requires some non-vanishing interactions in the hot phase.
Foundations of radiation hydrodynamics
Mihalas, Dimitri
1999-01-01
Radiation hydrodynamics is a broad subject that cuts across many disciplines in physics and astronomy: fluid dynamics, thermodynamics, statistical mechanics, kinetic theory, and radiative transfer, among others. The theory developed in this book by two specialists in the field can be applied to the study of such diverse astrophysical phenomena as stellar winds, supernova explosions, and the initial phases of cosmic expansion, as well as the physics of laser fusion and reentry vehicles. As such, it provides students with the basic tools for research on radiating flows.Largely self-contained,
Design of Low Drag Bluff Road Vehicles
Van Raemdonck, G.M.R.
2012-01-01
Low drag bluff road vehicle design can be obtained effectively and efficiently with a three phase approach that uses numerical simulations, scaled wind tunnel experiments and full-scale road testing. By applying this generalised method, SideWings were developed for an improved trailer underbody flow
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.
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...
Drag reduction capability of uniform blowing in supersonic wall-bounded turbulent flows
Kametani, Yukinori; Kotake, Ayane; Fukagata, Koji; Tokugawa, Naoko
2017-12-01
Drag reduction capability of uniform blowing in supersonic turbulent boundary layers is investigated by means of direct numerical simulation of channel flows with uniform blowing on one side and suction on the other. The bulk Reynolds number based on the bulk density, the bulk mean velocity, the channel half-width, and the viscosity on the wall is set to Reb=3000 . The bulk Mach number is set at 0.8 and 1.5 to investigate a subsonic and a supersonic condition, respectively. The amplitude of the blowing or suction is set to be 0.1%, 0.3%, or 0.5% of the bulk mass flow rate. At both Mach numbers, modifications of the mean streamwise velocity profiles with blowing and suction are found to be similar to those in an incompressible turbulent channel flow: The skin friction is reduced on the blowing side, while it is increased on the suction side. As for the drag reducing effect of blowing, the drag reduction rate and net-energy saving rate are hardly affected by the Mach number, while the control gain is increased with the increase of Mach number due to the increased density near the wall. The compressibility effect of drag reduction and enhancement is also examined using the physical decomposition of the skin friction drag. A noticeable Mach number effect is found only for the contribution terms containing the viscosity, which is increased by the increased temperature.
Kinetic theory of hydrodynamic flows. II. The drag on a sphere and on a cylinder
Beijeren, H. van; Dorfman, J.R.
1980-01-01
In this paper we continue the study of solutions of the extended Boltzmann equation started previously. In particular, we study an iterated solution of the equation that can be used to describe the flow of a rarefied gas around a macroscopic object. We discuss the rarefied flow and then show how the
Load responsive hydrodynamic bearing
Kalsi, Manmohan S.; Somogyi, Dezso; Dietle, Lannie L.
2002-01-01
A load responsive hydrodynamic bearing is provided in the form of a thrust bearing or journal bearing for supporting, guiding and lubricating a relatively rotatable member to minimize wear thereof responsive to relative rotation under severe load. In the space between spaced relatively rotatable members and in the presence of a liquid or grease lubricant, one or more continuous ring shaped integral generally circular bearing bodies each define at least one dynamic surface and a plurality of support regions. Each of the support regions defines a static surface which is oriented in generally opposed relation with the dynamic surface for contact with one of the relatively rotatable members. A plurality of flexing regions are defined by the generally circular body of the bearing and are integral with and located between adjacent support regions. Each of the flexing regions has a first beam-like element being connected by an integral flexible hinge with one of the support regions and a second beam-like element having an integral flexible hinge connection with an adjacent support region. A least one local weakening geometry of the flexing region is located intermediate the first and second beam-like elements. In response to application of load from one of the relatively rotatable elements to the bearing, the beam-like elements and the local weakening geometry become flexed, causing the dynamic surface to deform and establish a hydrodynamic geometry for wedging lubricant into the dynamic interface.
14 CFR 25.697 - Lift and drag devices, controls.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Lift and drag devices, controls. 25.697....697 Lift and drag devices, controls. (a) Each lift device control must be designed so that the pilots....101(d). Lift and drag devices must maintain the selected positions, except for movement produced by an...
Drag Analysis from PIV Data in Speed Sports
Terra, W.; Sciacchitano, A.; Scarano, F.
2016-01-01
Aerodynamic drag is computed from velocity measurements obtained with particle image velocimetry (PIV). This allows determining the drag force in combination with the visualization of the flow structures responsible for drag generation. Two experiments are conducted to illustrate the working
Hydrodynamic effects on a predator approaching a group of preys
De Rosis, Alessandro
2014-11-01
A numerical approach to predict the hydrodynamics involving a predator approaching a group of 100 preys is presented. A collective behavioural model is adopted to predict the two-dimensional space-time evolution of the predator-preys system that is supposed to be immersed in a fluid. The preys manifest mutual repulsion, attraction and orientation, while the predator is idealized as an individual to be strongly repulsed. During the motion, the predator experiences a resistance induced by the encompassing fluid. Such effect is accounted for by computing the hydrodynamic force and by modifying the predator’s velocity given by the behavioural equations. A numerical campaign is carried out by varying the predator’s drag coefficient. Moreover, analyses characterized by progressively wider predator’s perception areas are performed, thus highlighting the role of the hydrodynamics over the behavioural interactions. In order to estimate the predator’s performance, an ad-hoc parameter is proposed. Moreover, findings in terms of trajectories and angular momentum of the group of preys are discussed. Present findings show that the sole collective behavioural equations are insufficient to predict the performance of a predator that is immersed in a fluid, since its motion is drastically affected by the resistance of the surrounding fluid.
Collisions and drag in debris discs with eccentric parent belts
Löhne, T.; Krivov, A. V.; Kirchschlager, F.; Sende, J. A.; Wolf, S.
2017-08-01
Context. High-resolution images of circumstellar debris discs reveal off-centred rings that indicate past or ongoing perturbation, possibly caused by secular gravitational interaction with unseen stellar or substellar companions. The purely dynamical aspects of this departure from radial symmetry are well understood. However, the observed dust is subject to additional forces and effects, most notably collisions and drag. Aims: To complement the studies of dynamics, we therefore aim to understand how the addition of collisional evolution and drag forces creates new asymmetries and strengthens or overrides existing ones. Methods: We augmented our existing numerical code Analysis of Collisional Evolution (ACE) by an azimuthal dimension, the longitude of periapse. A set of fiducial discs with global eccentricities ranging from 0 to 0.4 was evolved over gigayear timescales. Size distribution and spatial variation of dust were analysed and interpreted. We discuss the basic impact of belt eccentricity on spectral energy distributions and images. Results: We find features imposed on characteristic timescales. First, radiation pressure defines size cut-offs that differ between periapse and apoapse, resulting in an asymmetric halo. The differences in size distribution make the observable asymmetry of the halo depend on wavelength. Second, collisional equilibrium prefers smaller grains on the apastron side of the parent belt, reducing the effect of pericentre glow and the overall asymmetry. Third, Poynting-Robertson drag fills the region interior to an eccentric belt such that the apastron side is more tenuous. Interpretation and prediction of the appearance in scattered light is problematic when spatial and size distribution are coupled.
Innovative Flow Control Concepts for Drag Reduction
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
Features of Dolphin Skin with Potential Hydrodynamic Importance
1993-09-01
various theories [51. Conicerning the itdea that dolphins might activehý change their skin surface to reduce hydrodynamnic drag. he stated. "An...for histology (mnounting Iin paraffin. sectioning on a mnicrotoinic. and mounting on microscope slidest. ste took care that the sections were
Hydrodynamic trail following in a California sea lion (Zalophus californianus).
Gläser, Nele; Wieskotten, Sven; Otter, Christian; Dehnhardt, Guido; Hanke, Wolf
2011-02-01
The mystacial vibrissae of pinnipeds constitute a sensory system for active touch and detection of hydrodynamic events. Harbour seals (Phoca vitulina) and California sea lions (Zalophus californianus) can both detect hydrodynamic stimuli caused by a small sphere vibrating in the water (hydrodynamic dipole stimuli). Hydrodynamic trail following has only been shown in harbour seals. Hydrodynamical and biomechanical studies of single vibrissae of the two species showed that the specialized undulated structure of harbour seal vibrissae, as opposed to the smooth structure of sea lion vibrissae, suppresses self-generated noise in the actively moving animal. Here we tested whether also sea lions were able to perform hydrodynamic trail following in spite of their non-specialized hair structure. Hydrodynamic trails were generated by a remote-controlled miniature submarine. Linear trails could be followed with high accuracy, comparable to the performance of harbour seals, but in contrast, increasing delay resulted in a reduced performance as compared to harbour seals. The results of this study are consistent with the hypothesis that structural differences in the vibrissal hair types of otariid compared to phocid pinnipeds lead to different sensitivity of the vibrissae during forward swimming, but still reveal a good performance even in the species with non-specialized hair type.
Hydrodynamics of Ship Propellers
DEFF Research Database (Denmark)
Breslin, John P.; Andersen, Poul
This book deals with flows over propellers operating behind ships, and the hydrodynamic forces and moments which the propeller generates on the shaft and on the ship hull.The first part of the text is devoted to fundamentals of the flow about hydrofoil sections (with and without cavitation......) and about wings. It then treats propellers in uniform flow, first via advanced actuator disc modelling, and then using lifting-line theory. Pragmatic guidance is given for design and evaluation of performance, including the use of computer modelling.The second part covers the development of unsteady forces...... arising from operation in non-uniform hull wakes. First, by a number of simplifications, various aspects of the problem are dealt with separately until the full problem of a non-cavitating, wide-bladed propeller in a wake is treated by a new and completely developed theory. Next, the complicated problem...
Foundations of radiation hydrodynamics
Mihalas, D.; Mihalas, B. W.
This book is the result of an attempt, over the past few years, to gather the basic tools required to do research on radiating flows in astrophysics. The microphysics of gases is discussed, taking into account the equation of state of a perfect gas, the first and second law of thermodynamics, the thermal properties of a perfect gas, the distribution function and Boltzmann's equation, the collision integral, the Maxwellian velocity distribution, Boltzmann's H-theorem, the time of relaxation, and aspects of classical statistical mechanics. Other subjects explored are related to the dynamics of ideal fluids, the dynamics of viscous and heat-conducting fluids, relativistic fluid flow, waves, shocks, winds, radiation and radiative transfer, the equations of radiation hydrodynamics, and radiating flows. Attention is given to small-amplitude disturbances, nonlinear flows, the interaction of radiation and matter, the solution of the transfer equation, acoustic waves, acoustic-gravity waves, basic concepts of special relativity, and equations of motion and energy.
Hydrodynamics of Peristaltic Propulsion
Athanassiadis, Athanasios; Hart, Douglas
2014-11-01
A curious class of animals called salps live in marine environments and self-propel by ejecting vortex rings much like jellyfish and squid. However, unlike other jetting creatures that siphon and eject water from one side of their body, salps produce vortex rings by pumping water through siphons on opposite ends of their hollow cylindrical bodies. In the simplest cases, it seems like some species of salp can successfully move by contracting just two siphons connected by an elastic body. When thought of as a chain of timed contractions, salp propulsion is reminiscent of peristaltic pumping applied to marine locomotion. Inspired by salps, we investigate the hydrodynamics of peristaltic propulsion, focusing on the scaling relationships that determine flow rate, thrust production, and energy usage in a model system. We discuss possible actuation methods for a model peristaltic vehicle, considering both the material and geometrical requirements for such a system.
Karakashev, Stoyan I.
2017-08-01
This brief review article is devoted to all the aspects related to hydrodynamics of foams. For this reason, we focused at first on the methods for studying the basic structural units of the foams—the foam films (FF) and the Plateau borders (PB), thus reviewing the literature about their drainage. After this, we scrutinized in detail the Derjaguin's works on the electrostatic disjoining pressure along with its Langmuir's interpretation, the microscopic and macroscopic approaches in the theory of the van der Waals disjoining pressure, the DLVO theory, the steric disjoining pressure of de Gennes, and the more recent works on non-DLVO forces. The basic methods for studying of foam drainage are presented as well. Engineering and other applications of foam are reviewed as well. All these aspects are presented from retrospective and perspective viewpoints.
Hydrodynamic effects on coalescence.
Energy Technology Data Exchange (ETDEWEB)
Dimiduk, Thomas G.; Bourdon, Christopher Jay; Grillet, Anne Mary; Baer, Thomas A.; de Boer, Maarten Pieter; Loewenberg, Michael (Yale University, New Haven, CT); Gorby, Allen D.; Brooks, Carlton, F.
2006-10-01
The goal of this project was to design, build and test novel diagnostics to probe the effect of hydrodynamic forces on coalescence dynamics. Our investigation focused on how a drop coalesces onto a flat surface which is analogous to two drops coalescing, but more amenable to precise experimental measurements. We designed and built a flow cell to create an axisymmetric compression flow which brings a drop onto a flat surface. A computer-controlled system manipulates the flow to steer the drop and maintain a symmetric flow. Particle image velocimetry was performed to confirm that the control system was delivering a well conditioned flow. To examine the dynamics of the coalescence, we implemented an interferometry capability to measure the drainage of the thin film between the drop and the surface during the coalescence process. A semi-automated analysis routine was developed which converts the dynamic interferogram series into drop shape evolution data.
Drag and diffusion of heavy quarks in a hot and anisotropic QCD medium
Energy Technology Data Exchange (ETDEWEB)
Srivastava, P.K.; Patra, Binoy Krishna [Indian Institute of Technology Roorkee, Department of Physics, Roorkee (India)
2017-06-15
The propagation of heavy quarks (HQs) in a medium was quite often modeled by the Fokker-Planck (FP) equation. Since the transport coefficients, related to drag and diffusion processes, are the main ingredients in the FP equation, the evolution of HQs is thus effectively controlled by them. At the initial stage of the relativistic heavy-ion collisions, asymptotic weak-coupling causes the free-streaming motions of partons in the beam direction and the expansions in transverse directions are almost frozen, hence an anisotropy in the momentum space sets in. Since HQs are too produced in the same time, the study of the effect of momentum anisotropy on the drag and diffusion coefficients becomes highly desirable. In this article we have thus studied the drag and diffusion of HQs in the anisotropic medium and found that the presence of the anisotropy reduces both drag and diffusion coefficients. In addition, the anisotropy introduces an angular dependence to both the drag and diffusion coefficients, as a result both coefficients get more inflated when the partons are moving transversely to the direction of anisotropy than when moving parallel to the direction of anisotropy. (orig.)
Drag crisis moderation by thin air layers sustained on superhydrophobic spheres falling in water
Jetly, Aditya
2018-01-22
We investigate the effect of thin air layers naturally sustained on superhydrophobic surfaces on the terminal velocity and drag force of metallic spheres free falling in water. The surface of 20 mm to 60 mm steel or tungsten-carbide spheres is rendered superhydrophobic by a simple coating process that uses commercially available hydrophobic agent. By comparing the free fall of unmodified spheres and superhydrophobic spheres in a 2.5 meters tall water tank, It is demonstrated that even a very thin air layer (~ 1 – 2 μm) that covers the freshly dipped superhydrophobic sphere, can reduce the drag force on the spheres by up to 80 %, at Reynolds numbers 105 - 3×105 , owing to an early drag crisis transition. This study complements prior investigations on the drag reduction efficiency of model gas layers sustained on heated metal spheres falling in liquid by the Leidenfrost effect. The drag reduction effects are expected to have significant implication for the development of sustainable air-layer-based energy saving technologies.
Velocity and Drag Evolution From the Leading Edge of a Model Mangrove Forest
Maza, Maria; Adler, Katherine; Ramos, Diogo; Garcia, Adrian Mikhail; Nepf, Heidi
2017-11-01
An experimental study of unidirectional flow through a model mangrove forest measured both velocity and forces on individual trees. The individual trees were 1/12th scale models of mature Rhizophora, including 24 prop roots distributed in a three-dimensional layout. Thirty-two model trees were distributed in a staggered array producing a 2.5 m long forest. The velocity evolved from a boundary layer profile at the forest leading edge to a vertical profile determined by the vertical distribution of frontal area, with significantly higher velocity above the prop roots. Fully developed conditions were reached at the fifth tree row from the leading edge. Within the root zone the velocity was reduced by up to 50% and the TKE was increased by as much as fivefold, relative to the upstream conditions. TKE in the root zone was mainly produced by root and trunk wakes, and it agreed in magnitude with the estimation obtained using the Tanino and Nepf (2008) formulation. Maximum TKE occurred at the top of the roots, where a strong shear region was associated with the change in frontal area. The drag measured on individual trees decreased from the leading edge and reached a constant value at the fifth row and beyond, i.e., in the fully developed region. The drag exhibited a quadratic dependence on velocity, which justified the definition of a quadratic drag coefficient. Once the correct drag length-scale was defined, the measured drag coefficients collapsed to a single function of Reynolds number.
Delta method, an empirical drag buildup technique
Feagin, R. C.; Morrison, W. D.
1978-01-01
An empirical drag correlation technique was developed from analysis of 19 subsonic and supersonic military aircraft and 15 advanced or supercritical airfoil configurations which can be applied in conceptual and advanced aircraft design activities. The Delta Method may be used for estimating the clean wing drag polar for cruise and maneuver conditions up to buffet onset, and to approximately Mach 2.0. This technique incorporates a unique capability of predicting the off-design performance of advanced or supercritical airfoil sections. The buffet onset limit may also be estimated. The method is applicable to wind tunnel models as well as to full scale configurations. This technique has been converted into a computer code for use on the IBM 360 and CDC 7600 computer facilities at NASA AMES. Results obtained using this method to predict known aircraft characteristics are good and agreement can be obtained within a degree of accuracy judged to be sufficient for the initial processes of preliminary design.
Stokes’ and Lamb's viscous drag laws
Eames, I.; Klettner, C. A.
2017-03-01
Since Galileo used his pulse to measure the time period of a swinging chandelier in the 17th century, pendulums have fascinated scientists. It was not until Stokes' (1851 Camb. Phil. Soc. 9 8-106) (whose interest was spurred by the pendulur time pieces of the mid 19th century) treatise on viscous flow that a theoretical framework for the drag on a sphere at low Reynolds number was laid down. Stokes' famous drag law has been used to determine two fundamental physical constants—the charge on an electron and Avogadro's constant—and has been used in theories which have won three Nobel prizes. Considering its illustrious history it is then not surprising that the flow past a sphere and its two-dimensional analog, the flow past a cylinder, form the starting point of teaching flow past a rigid body in undergraduate level fluid mechanics courses. Usually starting with the two-dimensional potential flow past a cylinder, students progress to the three-dimensional potential flow past a sphere. However, when the viscous flow past rigid bodies is taught, the three-dimensional example of a sphere is first introduced, and followed by (but not often), the two-dimensional viscous flow past a cylinder. The reason why viscous flow past a cylinder is generally not taught is because it is usually explained from an asymptotic analysis perspective. In fact, this added mathematical complexity is why the drag on a cylinder was only solved in 1911, 60 years after the drag on a sphere. In this note, we show that the viscous flow past a cylinder can be explained without the need to introduce any asymptotic analysis while still capturing all the physical insight of this classic fluid mechanics problem.
BARABÁŠ, Vít
2013-01-01
The work (the bachelor´s thesis) deals with a new way of web application management via the "drag and drop" technique in the HTML5 programming language. The work is divided into two parts. The first part consists of DND API description in HTML5. The support analysis within common web browsers is included as a part of this description. The second, practical part of the thesis focuses on a concept and the following realisation of a photogallery using DND API.
MEASUREMENT OF WIND DRAG FORCES ON TREES
Hiroyoshi, SHI-IGAI; Toru, Maruyama; Professor, Institute of Engineering Mechanics, University of Tsukuba; Engineer, Nissei Jushi Kogyo
1988-01-01
Trees have a lot of effects on soil conservation at mountainous regions. However, they often trigger land slides or mud avalanches if they cannot resist against strong winds, since the fallen trees may dam up mud and water and that natural dam eventually collapses, which triggers landslides. We developed a technique to estimate the total mass of trees in vivo and evaluated the wind force which acts on trees under natural conditions. The evaluated wind drag coefficients of trees whose height i...
Optimal Projectile Shapes for Minimum Total Drag
1977-05-01
distribltion UnlciI. I?, DIST RIBUION STATEMENT (0I the 4betrAVI M.4f*4 #A Dilo &O 1C It it*,ent~ Ifea He1.lot) ill SUPPLEMENTARY 40166 It. KtY WORDS...Exterior Ballistics Division. Released by: It. A. NIFMANN. Head Warf are Analysis Department Ui TABLE OF CONTENTS ACKNOWLED.IGUEMENT...I ANALYSIS ........................................... 2 DRAG..........................................- OP’TIMIZATION MI’TH
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.
Drag of a Cottrell atmosphere by an edge dislocation in a smectic-A liquid crystal.
Oswald, P; Lejček, L
2017-10-01
In a recent letter (P. Oswald et al., EPL 103, 46004 (2013)), we have shown that a smectic-A phase hardens in compression normal to the layers when the liquid crystal is doped with gold nanoparticles. This is due to the formation of Cottrell clouds nearby the core of the edge dislocations and the appearance of an additional drag force that reduces their mobility. We theoretically calculate the shape of the Cottrell cloud and the associated drag force as a function of the climb velocity of the dislocations. The main result is that the drag force depends on velocity and vanishes when the temperature tends to the smectic-A-to-nematic transition temperature. The role of the diffusion anisotropy is also evaluated.
Drag reduction by surface treatment in turbulent Taylor-Couette flow
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.
A Bubble-Based Drag Model at the Local-Grid Level for Eulerian Simulation of Bubbling Fluidized Beds
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Kun Hong
2016-01-01
Full Text Available A bubble-based drag model at the local-grid level is proposed to simulate gas-solid flows in bubbling fluidized beds of Geldart A particles. In this model, five balance equations are derived from the mass and the momentum conservation. This set of equations along with necessary correlations for bubble diameter and voidage of emulsion phase is solved to obtain seven local structural parameters (uge, upe, εe, δb, ub, db, and ab which describe heterogeneous flows of bubbling fluidized beds. The modified drag coefficient obtained from the above-mentioned structural parameters is then incorporated into the two-fluid model to simulate the hydrodynamics of Geldart A particles in a lab-scale bubbling fluidized bed. The comparison between experimental and simulation results for the axial and radial solids concentration profiles is promising.
Drag-Free Control and Drag Force Recovery of Small Satellites
Nguyen, Anh N.; Conklin, John W.
2017-01-01
Drag-free satellites provide autonomous precision orbit determination, accurately map the static and time varying components of Earth's mass distribution, aid in our understanding of the fundamental force of gravity, and will ultimately open up a new window to our universe through the detection and observation of gravitational waves. At the heart of this technology is a gravitational reference sensor, which (a) contains and shields a free-floating proof mass from all non-gravitational forces, and (b) precisely measures the position of the test mass inside the sensor. Thus, both test mass and spacecraft follow a pure geodesic in spacetime. By tracking the position of a low Earth orbiting drag-free satellite we can directly determine the detailed shape of geodesics and through analysis, the higher order harmonics of the Earths geopotential. This paper explores two different drag-free control systems on small satellites. The first drag-free control system is a continuously compensated single thruster 3-unit CubeSat with a suspension-free spherical proof-mass. A feedback control system commands the thruster and Attitude and Determination Control System to fly the tender spacecraft with respect to the test mass. The spheres position is sensed with a LED-based differential optical shadow sensor, its electric charge controlled by photoemission using UV LEDs, and the spacecraft position is maintained with respect to the sphere using an ion electrospray propulsion system. This configuration is the most fuel-efficient drag-free system possible today. The second drag-free control system is an electro-statically suspended cubical proof-mass that is operated with a low duty cycle, limiting suspension force noise over brief, known time intervals on a small GRACE-II -like satellite. The readout is performed using a laser interferometer, which is immune to the dynamic range limitations of voltage references. This system eliminates the need for a thruster, enabling drag
REVIEW OF PASSIVE DRAG REDUCTION TECHNIQUES FOR BLUFF ROAD VEHICLES
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Alaman Altaf
2014-05-01
Full Text Available ABSTRACT:This paper presents a review of the techniques used to reduce aerodynamic drag over bluff bodies such as cylinders, spheres, 2D bodies with blunt backs and their application to commercial road vehicles. The recent research carried out on the drag reduction is presented and categorised. A new classification of the techniques is introduced and major contributions under them are shown. It can be concluded that there is not much work done with realistic 3D bluff bodies, especially using passive methods.ABSTRAK: Kertas kerja ini membentangkan kaji selidik semula teknik yang digunakan untuk mengurangkan seret aerodinamik ke atas jasad tubir seperti silinder, sfera, jasad 2D dengan belakang tumpul dan aplikasinya terhadap kenderaan jalan raya komersial. Pengurangan seretan dibentangkan dan dikategorikan dengan kajian terkini. Klasifikasi teknik terkini diperkenalkan dan sumbangan utamanya diperbentangkan. Secara kesimpulannya terdapat banyak tugasan yang tidak yang dapat dijalankan dengan menggunakan jasad tubir 3D sebenar, terutamanya dengan penggunaan kaedah pasif.
Drag reduction of a rapid vehicle in supercavitating flow
Directory of Open Access Journals (Sweden)
D. Yang
2017-01-01
Full Text Available Supercavitation is one of the most attractive technologies to achieve high speed for underwater vehicles. However, the multiphase flow with high-speed around the supercavitating vehicle (SCV is difficult to simulate accurately. In this paper, we use modified the turbulent viscosity formula in the Standard K-Epsilon (SKE turbulent model to simulate the supercavitating flow. The numerical results of flow over several typical cavitators are in agreement with the experimental data and theoretical prediction. In the last part, a flying SCV was studied by unsteady numerical simulation. The selected computation setup corresponds to an outdoor supercavitating experiment. Only very limited experimental data was recorded due to the difficulties under the circumstance of high-speed underwater condition. However, the numerical simulation recovers the whole scenario, the results are qualitatively reasonable by comparing to the experimental observations. The drag reduction capacity of supercavitation is evaluated by comparing with a moving vehicle launching at the same speed but without supercavitation. The results show that the supercavitation reduces the drag of the vehicle dramatically.
Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows
Raayai-Ardakani, Shabnam; McKinley, Gareth H.
2017-09-01
Inspired by the design of the ribbed structure of shark skin, passive drag reduction methods using stream-wise riblet surfaces have previously been developed and tested over a wide range of flow conditions. Such textures aligned in the flow direction have been shown to be able to reduce skin friction drag by 4%-8%. Here, we explore the effects of periodic sinusoidal riblet surfaces aligned in the flow direction (also known as a "wrinkled" texture) on the evolution of a laminar boundary layer flow. Using numerical analysis with the open source Computational Fluid Dynamics solver OpenFOAM, boundary layer flow over sinusoidal wrinkled plates with a range of wavelength to plate length ratios ( λ / L ), aspect ratios ( 2 A / λ ), and inlet velocities are examined. It is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the high-speed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Additionally, we explore how the boundary layer thickness, local average shear stress distribution, and total drag force on the wrinkled plate vary with the aspect ratio of the riblets as well as the length of the plate. We show that riblets with an aspect ratio of close to unity lead to the highest reduction in the total drag, and that because of the interplay between the local stress distribution on the plate and stream-wise evolution of the boundary layer the plate has to exceed a critical length to give a net decrease in the total drag force.
Parameterization of wind turbine impacts on hydrodynamics and sediment transport
Rivier, Aurélie; Bennis, Anne-Claire; Pinon, Grégory; Magar, Vanesa; Gross, Markus
2016-10-01
Monopile foundations of offshore wind turbines modify the hydrodynamics and sediment transport at local and regional scales. The aim of this work is to assess these modifications and to parameterize them in a regional model. In the present study, this is achieved through a regional circulation model, coupled with a sediment transport module, using two approaches. One approach is to explicitly model the monopiles in the mesh as dry cells, and the other is to parameterize them by adding a drag force term to the momentum and turbulence equations. Idealised cases are run using hydrodynamical conditions and sediment grain sizes typical from the area located off Courseulles-sur-Mer (Normandy, France), where an offshore windfarm is under planning, to assess the capacity of the model to reproduce the effect of the monopile on the environment. Then, the model is applied to a real configuration on an area including the future offshore windfarm of Courseulles-sur-Mer. Four monopiles are represented in the model using both approaches, and modifications of the hydrodynamics and sediment transport are assessed over a tidal cycle. In relation to local hydrodynamic effects, it is observed that currents increase at the side of the monopile and decrease in front of and downstream of the monopile. In relation to sediment transport effect, the results show that resuspension and erosion occur around the monopile in locations where the current speed increases due to the monopile presence, and sediments deposit downstream where the bed shear stress is lower. During the tidal cycle, wakes downstream of the monopile reach the following monopile and modify the velocity magnitude and suspended sediment concentration patterns around the second monopile.
Low Drag Porous Ship with Superhydrophobic and Superoleophilic Surface for Oil Spills Cleanup.
Wang, Gang; Zeng, Zhixiang; Wang, He; Zhang, Lin; Sun, Xiaodong; He, Yi; Li, Longyang; Wu, Xuedong; Ren, Tianhui; Xue, Qunji
2015-12-02
To efficiently remove and recycle oil spills, we construct aligned ZnO nanorod arrays on the surface of the porous stainless steel wire mesh to fabricate a porous unmanned ship (PUS) with properties of superhydrophobicity, superoleophilicity, and low drag by imitating the structure of nonwetting leg of water strider. The superhydrophobicity of the PUS is stable, which can support 16.5 cm water column with pore size of 100 μm. Water droplet can rebound without adhesion. In the process of oil/water separation, when the PUS contacts with oil, the oil is quickly pulled toward and penetrates into the PUS automatically. The superhydrophobicity and low water adhesion force of the PUS surface endow the PUS with high oil recovery capacity (above 94%) and drag-reducing property (31% at flowing velocity of 0.38m/s). In addition, the PUS has good corrosion resistance and reusability. We further investigate the wetting behavior of water and oil, oil recovery capacity, drag-reducing property, and corrosion resistance of the PUS after oil absorbed. The PUS surface changes significantly from superhydrophobic to hydrophobic after absorbing oil. However, the oil absorbed PUS possesses better drag-reducing property and corrosion resistance due to the changes of the motion state of the water droplets.
Engineering Hydrodynamic AUV Hulls
Allen, J.
2016-12-01
AUV stands for autonomous underwater vehicle. AUVs are used in oceanography and are similar to gliders. MBARIs AUVs as well as other AUVs map the ocean floor which is very important. They also measure physical characteristics of the water, such as temperature and salinity. My science fair project for 4th grade was a STEM activity in which I built and tested 3 different AUV bodies. I wanted to find out which design was the most hydrodynamic. I tested three different lengths of AUV hulls to see which AUV would glide the farthest. The first was 6 inches. The second was 12 inches and the third was 18 inches. I used clay for the nosecone and cut a ruler into two and made it the fin. Each AUV used the same nosecone and fin. I tested all three designs in a pool. I used biomimicry to create my hypothesis. When I was researching I found that long slim animals swim fastest. So, my hypothesis is the longer AUV will glide farthest. In the end I was right. The longer AUV did glide the farthest.
Lotic Water Hydrodynamic Model
Energy Technology Data Exchange (ETDEWEB)
Judi, David Ryan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tasseff, Byron Alexander [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-01-23
Water-related natural disasters, for example, floods and droughts, are among the most frequent and costly natural hazards, both socially and economically. Many of these floods are a result of excess rainfall collecting in streams and rivers, and subsequently overtopping banks and flowing overland into urban environments. Floods can cause physical damage to critical infrastructure and present health risks through the spread of waterborne diseases. Los Alamos National Laboratory (LANL) has developed Lotic, a state-of-the-art surface water hydrodynamic model, to simulate propagation of flood waves originating from a variety of events. Lotic is a two-dimensional (2D) flood model that has been used primarily for simulations in which overland water flows are characterized by movement in two dimensions, such as flood waves expected from rainfall-runoff events, storm surge, and tsunamis. In 2013, LANL developers enhanced Lotic through several development efforts. These developments included enhancements to the 2D simulation engine, including numerical formulation, computational efficiency developments, and visualization. Stakeholders can use simulation results to estimate infrastructure damage and cascading consequences within other sets of infrastructure, as well as to inform the development of flood mitigation strategies.
Reconfiguration parameters for drag of flexible cylindrical elements
John, Chapman; Wilson, Bruce; Gulliver, John
2015-11-01
This presentation compares parameters that characterize reconfiguration effects on flow resistance and drag. The drag forces occurring on flexible bluff bodies are different from the drag occurring on rigid bluff bodies due to reconfiguration. Drag force data, collected using a torque sensor in a flume, for simple cylindrical obstructions of the same shape and size but with different flexibility is used to fit drag parameters. The key parameter evaluated is a reference velocity factor u to account for drag reduction due to reconfiguration, similar to a Vogel exponent. Our equations preserves the traditional exponent of the drag relationship, but places a factor onto the drag coefficient for flexible elements, rather than a Vogel exponent arrangement applied to the flow velocity. Additionally we relate the reference velocity factor u to the modulus of elasticity of the material through the Cauchy Number. The use of a reference velocity factor u in place of a Vogel exponent appears viable to account for how the drag forces are altered by reconfiguration. The proposed formulation for drag reduction is more consistently estimated for the range of flexibilities in this study. Unfortunately, the mechanical properties of vegetation are not often readily available for reconfiguration relationships to the elastic modulus of vegetation to be of immediate practical use.
Hydrodynamics of electrons in graphene
Lucas, Andrew; Chung Fong, Kin
2018-02-01
Generic interacting many-body quantum systems are believed to behave as classical fluids on long time and length scales. Due to rapid progress in growing exceptionally pure crystals, we are now able to experimentally observe this collective motion of electrons in solid-state systems, including graphene. We present a review of recent progress in understanding the hydrodynamic limit of electronic motion in graphene, written for physicists from diverse communities. We begin by discussing the ‘phase diagram’ of graphene, and the inevitable presence of impurities and phonons in experimental systems. We derive hydrodynamics, both from a phenomenological perspective and using kinetic theory. We then describe how hydrodynamic electron flow is visible in electronic transport measurements. Although we focus on graphene in this review, the broader framework naturally generalizes to other materials. We assume only basic knowledge of condensed matter physics, and no prior knowledge of hydrodynamics.
Anomalous hydrodynamics in two dimensions
Indian Academy of Sciences (India)
s12043-015-1167-5; ePublication: 14 January 2016. Abstract. A new approach is presented to discuss two-dimensional hydrodynamics with gauge and gravitational anomalies. Exact constitutive relations for the stress tensor and charge current are.
An introduction to astrophysical hydrodynamics
Shore, Steven N
1992-01-01
This book is an introduction to astrophysical hydrodynamics for both astronomy and physics students. It provides a comprehensive and unified view of the general problems associated with fluids in a cosmic context, with a discussion of fluid dynamics and plasma physics. It is the only book on hydrodynamics that addresses the astrophysical context. Researchers and students will find this work to be an exceptional reference. Contents include chapters on irrotational and rotational flows, turbulence, magnetohydrodynamics, and instabilities.
Hemodynamics of a hydrodynamic injection
Directory of Open Access Journals (Sweden)
Tsutomu Kanefuji
2014-01-01
Full Text Available The hemodynamics during a hydrodynamic injection were evaluated using cone beam computed tomography (CBCT and fluoroscopic imaging. The impacts of hydrodynamic (5 seconds and slow (60 seconds injections into the tail veins of mice were compared using 9% body weight of a phase-contrast medium. Hydrodynamically injected solution traveled to the heart and drew back to the hepatic veins (HV, which led to liver expansion and a trace amount of spillover into the portal vein (PV. The liver volumes peaked at 165.6 ± 13.3% and 165.5 ± 11.9% of the original liver volumes in the hydrodynamic and slow injections, respectively. Judging by the intensity of the CBCT images at the PV, HV, right atrium, liver parenchyma (LP, and the inferior vena cava (IVC distal to the HV conjunction, the slow injection resulted in the higher intensity at PV than at LP. In contrast, a significantly higher intensity was observed in LP after hydrodynamic injection in comparison with that of PV, suggesting that the liver took up the iodine from the blood flow. These results suggest that the enlargement speed of the liver, rather than the expanded volume, primarily determines the efficiency of hydrodynamic delivery to the liver.
Seasonal Variations in Drag Coefficient over a Sastrugi-Covered Snowfield in Coastal East Antarctica
Amory, Charles; Gallée, Hubert; Naaim-Bouvet, Florence; Favier, Vincent; Vignon, Etienne; Picard, Ghislain; Trouvilliez, Alexandre; Piard, Luc; Genthon, Christophe; Bellot, Hervé
2017-02-01
The surface of windy Antarctic snowfields is subject to drifting snow, which leads to the formation of sastrugi. In turn, sastrugi contribute to the drag exerted by the snow surface on the atmosphere and hence influence drifting snow. Although the surface drag over rough sastrugi fields has been estimated for individual locations in Antarctica, its variation over time and with respect to drifting snow has received little attention. Using year-round data from a meteorological mast, seasonal variations in the neutral drag coefficient at a height of 10 m (C_{{ DN}10}) in coastal Adelie Land are presented and discussed in light of the formation and behaviour of sastrugi based on observed aeolian erosion patterns. The measurements revealed high C_{{ DN}10} values (≥ 2 × 10^{-3}) and limited drifting snow (35% of the time) in summer (December-February) versus lower C_{{ DN}10} values (≈ 1.5 × 10^{-3}) associated with more frequent drifting snow (70% of the time) in winter (March-November). Without the seasonal distinction, there was no clear dependence of C_{{ DN}10} on friction velocity or wind direction, but observations revealed a general increase in C_{{ DN}10} with rising air temperature. The main hypothesis defended here is that higher temperatures increase snow cohesion and the development of sastrugi just after snow deposition while inhibiting the sastrugi streamlining process by raising the erosion threshold. This increases the contribution of the sastrugi form drag to the total surface drag in summer when winds are lighter and more variable. The analysis also showed that, in the absence of erosion, single snowfall events can reduce C_{{ DN}10} to 1 × 10^{-3} due to the burying of pre-existing microrelief under newly deposited snow. The results suggest that polar atmospheric models should account for spatial and temporal variations in snow surface roughness through a dynamic representation of the sastrugi form drag.
Directory of Open Access Journals (Sweden)
Aswar Rustam
2017-09-01
Full Text Available Mangrove is the only ecosistem that grows and develops in the coastal area. This study was conducted to analyze the mangrove forest vegetation to create a simulation of the root sistem of Rhizophora apiculata Bl. related to its ability in the process of hydrodynamic fluid of seawater in the Lompo village, District Awangpone, Bone Regency, South Sulawesi. Criteria that used as a model reference had minimum age approximately five years and minimum height of about 2 m. The variables that measure were height, diameter, and length of the roots. The parameters of the simulation are the average speed of sea level, the dynamic pressure of seawater, as well as drag coefficient of Gulf of Bone. Based on this research, vegetation area with highest density located at second kilometer, medium density located at first kilometer, and the lowest density located at third kilometer. The average velocity of seawater, the lowest is in the natural cropping pattern of highest density, meanwhile the highest is in the parallel cropping pattern of lowest density. Dynamic pressure, the lowest is in the natural cropping pattern of highest density, meanwhile the highest is in the parallel cropping pattern of lowest density. The drag coefficient, the highest is in the natural cropping pattern of highest density, meanwhile the lowest is in the parallel cropping pattern of lowest density. Keywords: drag coefficient, hydrodynamics, mangrove, Rhizophora apiculata Bl., simulation
Boundary layer thickness effect on boattail drag
Blaha, B. J.; Chamberlain, R.; Bober, L. J.
1976-01-01
A combined experimental and analytical program was conducted to investigate the effects of boundary layer changes on the flow over high angle boattail nozzles. The tests were run on an isolated axisymmetric sting mounted model. Various boattail geometries were investigated at high subsonic speeds over a range of boundary layer thicknesses. In general, boundary layer effects were small at speeds up to Mach 0.8. However, at higher speeds significant regions of separated flow were present on the boattail. When separation was present large reductions in boattail drag resulted with increasing boundary layer thickness. The analysis predicts both of these trends.
Zedler, S. E.
2009-04-25
The drag coefficient parameterization of wind stress is investigated for tropical storm conditions using model sensitivity studies. The Massachusetts Institute of Technology (MIT) Ocean General Circulation Model was run in a regional setting with realistic stratification and forcing fields representing Hurricane Frances, which in early September 2004 passed east of the Caribbean Leeward Island chain. The model was forced with a NOAA-HWIND wind speed product after converting it to wind stress using four different drag coefficient parameterizations. Respective model results were tested against in situ measurements of temperature profiles and velocity, available from an array of 22 surface drifters and 12 subsurface floats. Changing the drag coefficient parameterization from one that saturated at a value of 2.3 × 10 -3 to a constant drag coefficient of 1.2 × 10-3 reduced the standard deviation difference between the simulated minus the measured sea surface temperature change from 0.8°C to 0.3°C. Additionally, the standard deviation in the difference between simulated minus measured high pass filtered 15-m current speed reduced from 15 cm/s to 5 cm/s. The maximum difference in sea surface temperature response when two different turbulent mixing parameterizations were implemented was 0.3°C, i.e., only 11% of the maximum change of sea surface temperature caused by the storm. Copyright 2009 by the American Geophysical Union.
Zedler, S. E.; Niiler, P. P.; Stammer, D.; Terrill, E.; Morzel, J.
2009-04-01
The drag coefficient parameterization of wind stress is investigated for tropical storm conditions using model sensitivity studies. The Massachusetts Institute of Technology (MIT) Ocean General Circulation Model was run in a regional setting with realistic stratification and forcing fields representing Hurricane Frances, which in early September 2004 passed east of the Caribbean Leeward Island chain. The model was forced with a NOAA-HWIND wind speed product after converting it to wind stress using four different drag coefficient parameterizations. Respective model results were tested against in situ measurements of temperature profiles and velocity, available from an array of 22 surface drifters and 12 subsurface floats. Changing the drag coefficient parameterization from one that saturated at a value of 2.3 × 10-3 to a constant drag coefficient of 1.2 × 10-3 reduced the standard deviation difference between the simulated minus the measured sea surface temperature change from 0.8°C to 0.3°C. Additionally, the standard deviation in the difference between simulated minus measured high pass filtered 15-m current speed reduced from 15 cm/s to 5 cm/s. The maximum difference in sea surface temperature response when two different turbulent mixing parameterizations were implemented was 0.3°C, i.e., only 11% of the maximum change of sea surface temperature caused by the storm.
Drag Reduction of an Airfoil Using Deep Learning
Jiang, Chiyu; Sun, Anzhu; Marcus, Philip
2017-11-01
We reduced the drag of a 2D airfoil by starting with a NACA-0012 airfoil and used deep learning methods. We created a database which consists of simulations of 2D external flow over randomly generated shapes. We then developed a machine learning framework for external flow field inference given input shapes. Past work which utilized machine learning in Computational Fluid Dynamics focused on estimations of specific flow parameters, but this work is novel in the inference of entire flow fields. We further showed that learned flow patterns are transferable to cases that share certain similarities. This study illustrates the prospects of deeper integration of data-based modeling into current CFD simulation frameworks for faster flow inference and more accurate flow modeling.
Kalra, Tarandeep S.; Aretxabaleta, Alfredo; Seshadri, Pranay; Ganju, Neil K.; Beudin, Alexis
2017-12-01
Coastal hydrodynamics can be greatly affected by the presence of submerged aquatic vegetation. The effect of vegetation has been incorporated into the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system. The vegetation implementation includes the plant-induced three-dimensional drag, in-canopy wave-induced streaming, and the production of turbulent kinetic energy by the presence of vegetation. In this study, we evaluate the sensitivity of the flow and wave dynamics to vegetation parameters using Sobol' indices and a least squares polynomial approach referred to as the Effective Quadratures method. This method reduces the number of simulations needed for evaluating Sobol' indices and provides a robust, practical, and efficient approach for the parameter sensitivity analysis. The evaluation of Sobol' indices shows that kinetic energy, turbulent kinetic energy, and water level changes are affected by plant stem density, height, and, to a lesser degree, diameter. Wave dissipation is mostly dependent on the variation in plant stem density. Performing sensitivity analyses for the vegetation module in COAWST provides guidance to optimize efforts and reduce exploration of parameter space for future observational and modeling work.
Hydrodynamics of a Digitized Adult Humpback Whale Flipper
Fassmann, Wesley N.; McDonald, Samuel J.; Thomson, Scott L.; Fish, Frank E.
2013-11-01
During feeding, humpback whales turn with a turn radius of up to 1 /6th of their length towards schools of fish enclosed by bubble nets. This high maneuverability requirement is facilitated by high aspect ratio flippers with leading edge tubercles that delay stall. Previous experimental and computational studies have used idealized models, such as airfoils with scalloped leading edges, to explore the influence of leading edge tubercles on boundary layer separation, vortex generation, and airfoil lift and drag characteristics. Owing to the substantial size of the flipper, no studies have been performed on a digitized adult humpback flipper with real geometry. In this study the hydrodynamics of a realistic humpback flipper model were explored. The model was developed by digitizing a sequence of 18 images circumscribing the suspended flipper of a beached humpback whale. A physical prototype was constructed based on the resulting 3D model, along with a complementary model with the tubercles removed. Experimentally-obtained measurements of lift and drag were used to study the influence of the tubercles. In the presentation, digitization and flow measurement methods are described, and the flow data and results are presented and discussed.
Research of tare hydrodynamic behaviour at sterilization of canned fish
Directory of Open Access Journals (Sweden)
Alexeev G. V.
2016-09-01
Full Text Available The paper is devoted to research on improving the equipment that ensures the absolute safety of mineral nutrients in the production of sterilized canned fish. The results of experimental study of hydrodynamic characteristics moving sterilized jars of canned fish of different sizes under the influence of circulating gas-liquid heat-carrying medium in the capacity have been presented. Some experimental setup with organized top-down and bottom-up flows in it modeling a sterilizer (autoclave has been proposed for the research. The experiments have been performed in the superficial gas velocity ranging from 0.03 m/s to 0.15 m/s corresponding to stable operation of the apparatus. Cans drag coefficient in the flow of heat-carrying medium has been determined by two methods for two heat-carrying media – pure glycerol and water solutions in experiments on precipitation and air – cans when blowing in the wind tunnel. The significant difference in the rates of cans upstream and downstream is reliably established, and therefore it has been proposed to use for the cans' motion characterization the indicator averaged over the two specified rates and called cans circulation speed. An empirical equation describing the dependence of the cans circulation rate from the superficial gas velocity has been obtained. Based on the analysis of studies some empirical dependencies on calculation of the drag coefficients of various types of packaging in the range of Reynolds criterion values from 1 to 4 000 have been offered. The necessity of using the qualifying factor for calculating the real drag on the results of the experiment has been determined.
Air Flows in Gravity Sewers - Determination of Wastewater Drag Coefficient
DEFF Research Database (Denmark)
Bentzen, Thomas Ruby; Østertoft, Kristian; Vollertsen, Jes
2016-01-01
surface drags were found by log-law models of the velocity distribution in turbulent flows to fit velocity profiles measured from the water surface and by integrating the water surface drags along the wetted perimeter, mean water surface drags were found and a measure of the water surface drag coefficient...... of the study shows that by integrating the top/side wall shear stresses the log-law models for the air velocity distribution along the unwetted perimeter resulted in a good agreement with the friction forces calculated by use of the Colebrook-White formula for hydraulic smooth pipes. Secondly, the water...
Drag reduction properties of superhydrophobic mesh pipes
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 pipe of the same diameter. This demonstrates that a 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.
Aquatic prey capture in snakes: the link between morphology, behavior and hydrodynamics
Segall, Marion; Herrel, Anthony; Godoy-Diana, Ramiro; Funevol Team; Pmmh Team
2017-11-01
Natural selection favors animals that are the most successful in their fitness-related behaviors, such as foraging. Secondary adaptations pose the problem of re-adapting an already 'hypothetically optimized' phenotype to new constraints. When animals forage underwater, they face strong physical constraints, particularly when capturing a prey. The capture requires the predator to be fast and to generate a high acceleration to catch the prey. This involves two main constraints due to the surrounding fluid: drag and added mass. Both of these constraints are related to the shape of the animal. We experimentally explore the relationship between shape and performance in the context of an aquatic strike. As a model, we use 3D-printed snake heads of different shapes and frontal strike kinematics based on in vivo observations. By using direct force measurements, we compare the drag and added mass generated by aquatic and non-aquatic snake models during a strike. Our results show that drag is optimized in aquatic snakes. Added mass appears less important than drag for snakes during an aquatic strike. The flow features associated to the hydrodynamic forces measured allows us to propose a mechanism rendering the shape of the head of aquatic snakes well adapted to catch prey underwater. Region Ile de France and the doctoral school Frontieres du Vivant (FdV) - Programme Bettencourt.
Computational modeling and analysis of the hydrodynamics of human swimming
von Loebbecke, Alfred
Computational modeling and simulations are used to investigate the hydrodynamics of competitive human swimming. The simulations employ an immersed boundary (IB) solver that allows us to simulate viscous, incompressible, unsteady flow past complex, moving/deforming three-dimensional bodies on stationary Cartesian grids. This study focuses on the hydrodynamics of the "dolphin kick". Three female and two male Olympic level swimmers are used to develop kinematically accurate models of this stroke for the simulations. A simulation of a dolphin undergoing its natural swimming motion is also presented for comparison. CFD enables the calculation of flow variables throughout the domain and over the swimmer's body surface during the entire kick cycle. The feet are responsible for all thrust generation in the dolphin kick. Moreover, it is found that the down-kick (ventral position) produces more thrust than the up-kick. A quantity of interest to the swimming community is the drag of a swimmer in motion (active drag). Accurate estimates of this quantity have been difficult to obtain in experiments but are easily calculated with CFD simulations. Propulsive efficiencies of the human swimmers are found to be in the range of 11% to 30%. The dolphin simulation case has a much higher efficiency of 55%. Investigation of vortex structures in the wake indicate that the down-kick can produce a vortex ring with a jet of accelerated fluid flowing through its center. This vortex ring and the accompanying jet are the primary thrust generating mechanisms in the human dolphin kick. In an attempt to understand the propulsive mechanisms of surface strokes, we have also conducted a computational analysis of two different styles of arm-pulls in the backstroke and the front crawl. These simulations involve only the arm and no air-water interface is included. Two of the four strokes are specifically designed to take advantage of lift-based propulsion by undergoing lateral motions of the hand
Hydrodynamic interactions in metachronal paddling: effects of varying stroke kinematics
Samaee, Milad; Kasoju, Vishwa; Lai, Hong Kuan; Santhanakrishnan, Arvind
2017-11-01
Crustaceans such as shrimp and krill use a drag-based technique for propulsion, in which multiple pairs of limbs are paddled rhythmically from the tail to the head. Each limb is phase-shifted in time relative to its neighbor. Most studies of this type of metachronal swimming have focused on the jet formed in the animal's wake. However, synergistic hydrodynamic interactions between adjacent limbs in metachrony have received minimal attention. We used a dynamically scaled robotic model to experimentally investigate how variations in stroke kinematics impact inter-paddle hydrodynamic interactions and thrust generation. Physical models of limbs were fitted to the robot and paddled with two different motion profiles (MPs)-1) MP1: metachronal power stroke (PS) and metachronal recovery stroke (RS); and 2) MP2: metachronal PS and synchronous RS. Stroke frequency and amplitude were maintained constant across both MPs. Our results show that MP2 produced faster jets in the thrust-generating direction as compared to MP1. The necessity for a pause in MP2 after completion of PS by the paddles leading the motion, prior to executing the synchronous RS, aided in further downstream flow propagation. The effect of using asymmetric stroke kinematics on thrust generated will be discussed.
In situ hydrodynamic lateral force calibration of AFM colloidal probes.
Ryu, Sangjin; Franck, Christian
2011-11-01
Lateral force microscopy (LFM) is an application of atomic force microscopy (AFM) to sense lateral forces applied to the AFM probe tip. Recent advances in tissue engineering and functional biomaterials have shown a need for the surface characterization of their material and biochemical properties under the application of lateral forces. LFM equipped with colloidal probes of well-defined tip geometries has been a natural fit to address these needs but has remained limited to provide primarily qualitative results. For quantitative measurements, LFM requires the successful determination of the lateral force or torque conversion factor of the probe. Usually, force calibration results obtained in air are used for force measurements in liquids, but refractive index differences between air and liquids induce changes in the conversion factor. Furthermore, in the case of biochemically functionalized tips, damage can occur during calibration because tip-surface contact is inevitable in most calibration methods. Therefore, a nondestructive in situ lateral force calibration is desirable for LFM applications in liquids. Here we present an in situ hydrodynamic lateral force calibration method for AFM colloidal probes. In this method, the laterally scanned substrate surface generated a creeping Couette flow, which deformed the probe under torsion. The spherical geometry of the tip enabled the calculation of tip drag forces, and the lateral torque conversion factor was calibrated from the lateral voltage change and estimated torque. Comparisons with lateral force calibrations performed in air show that the hydrodynamic lateral force calibration method enables quantitative lateral force measurements in liquid using colloidal probes.
Parameterization of a surface drag coefficient in conventionally neutral planetary boundary layer
Energy Technology Data Exchange (ETDEWEB)
Esau, I.N. [Nansen Environmental and Remote Sensing Center, Bergen (Norway)
2004-07-01
Modern large-scale models (LSMs) rely on surface drag coefficients to parameterize turbulent exchange between surface and the first computational level in the atmosphere. A classical parameterization in an Ekman boundary layer is rather simple. It is based on a robust concept of a layer of constant fluxes. In such a layer (log-layer), the mean velocity profile is logarithmic. It results in an universal dependence of the surface drag coefficient on a single internal non-dimensional parameter, namely the ratio of a height within this layer to a surface roughness length scale. A realistic near-neutral planetary boundary layer (PBL) is usually much more shallow than the idealized Ekman layer. The reason is that the PBL is developing against a stably stratified free atmosphere. The ambient atmospheric stratification reduces the PBL depth and simultaneously the depth of the log-layer. Therefore, the first computational level in the LSMs may be placed above the log-layer. In such a case, the classical parameterization is unjustified and inaccurate. The paper proposes several ways to improve the classical parameterization of the surface drag coefficient for momentum. The discussion is focused on a conventionally neutral PBL, i.e. on the neutrally stratified PBL under the stably stratified free atmosphere. The analysis is based on large eddy simulation (LES) data. This data reveals that discrepancy between drag coefficients predicted by the classical parameterization and the actual drag coefficients can be very large in the shallow PBL. The improved parameterizations provide a more accurate prediction. The inaccuracy is reduced to one-tenth of the actual values of the coefficients. (orig.)
Parameterization of a surface drag coefficient in conventionally neutral planetary boundary layer
Directory of Open Access Journals (Sweden)
I. N. Esau
2004-11-01
Full Text Available Modern large-scale models (LSMs rely on surface drag coefficients to parameterize turbulent exchange between surface and the first computational level in the atmosphere. A classical parameterization in an Ekman boundary layer is rather simple. It is based on a robust concept of a layer of constant fluxes. In such a layer (log-layer, the mean velocity profile is logarithmic. It results in an universal dependence of the surface drag coefficient on a single internal non-dimensional parameter, namely the ratio of a height within this layer to a surface roughness length scale. A realistic near-neutral planetary boundary layer (PBL is usually much more shallow than the idealized Ekman layer. The reason is that the PBL is developing against a stably stratified free atmosphere. The ambient atmospheric stratification reduces the PBL depth and simultaneously the depth of the log-layer. Therefore, the first computational level in the LSMs may be placed above the log-layer. In such a case, the classical parameterization is unjustified and inaccurate.
The paper proposes several ways to improve the classical parameterization of the surface drag coefficient for momentum. The discussion is focused on a conventionally neutral PBL, i.e. on the neutrally stratified PBL under the stably stratified free atmosphere. The analysis is based on large eddy simulation (LES data. This data reveals that discrepancy between drag coefficients predicted by the classical parameterization and the actual drag coefficients can be very large in the shallow PBL. The improved parameterizations provide a more accurate prediction. The inaccuracy is reduced to one-tenth of the actual values of the coefficients.
Directory of Open Access Journals (Sweden)
Xiao-xu Du
2014-03-01
Full Text Available The accurate research on the hydrodynamics of unmanned underwater vehicle (UUV, which moves close to the sea bottom, has a great significance for its maneuverability. The structured grid of the computational models with different distances to the sea bottom and attack angles is generated by Ansys ICEM, and the flow field near the sea bottom is simulated using CFX. The characteristics of the drag, lift, pitching moment influenced by the distance to sea bottom and the attack angle are studied. The result shows that the drag coefficient increases with the decrease of distance, while it increases with the increase of attack angle. There exists attraction force when UUV moves close to the sea bottom, and the attraction force increases with the decrease in distance. The lift coefficient increases with the increase in attack angle. The absolute value of the pitching moment coefficient increases with the decrease in distance and the increase in attack angle.
A bullet fired in dry water: an investigative activity to learn hydrodynamics concepts
Azevedo Leitão, Ulisses; dos Anjos Pinheiro da Silva, Antonio; Trindade do Nascimento, Natália Cristina; Mara Benedita da Cruz Gervásio, Lilian
2017-01-01
In this paper we report an investigative activity on hydrodynamics, in the context of an inquiry-based learning project. The aim is to analyse the experiment of a bullet shot underwater. Using Tracker, a video analysing and modelling software, the displacement of the bullet was measured as function of time, processing a slow motion video from YouTube. It was found that the displacement of the bullet is well described in the first 20 ms by the inviscid flow regime, where the Newtonian drag force overcomes the viscous drag. This behaviour is discussed in the context of what Richard Feynman’s famous Lectures on Physics describes as ‘The Flow of Dry Water’.
Can we reduce debris flow to an equivalent one-phase flow?
Chareyre, B.; Marzougui, D.; Chauchat, J.
2015-09-01
A recent extension of the discrete element method is reported for the simulation of dense mixtures of non-colloidal particles and viscous fluids in the non-inertial regime. As an application, we examine the interplay between rate dependent dilatancy and hydro-mechanical coupling which can be expected in debris flow. The numerical model includes sphere-sphere contacts using a soft contact approach [2], short range hydrodynamic interactions defined by frame-invariant expressions of forces and torques in the lubrication approximation, and drag forces resulting from the poromechanical coupling computed with the DEM-PFV technique [3]. The bulk shear stress is decomposed into contact stress and hydrodynamic stress. Both contributions are shown to be increasing functions of a dimensionless shear rate Iv, in agreement with experimental results [4]. Statistics of microstructural variables highlight a complex interplay between solid contacts and hydrodynamic interactions. In contrast with a popular idea, the results suggest that lubrication may not necessarily reduce the contribution of contact forces to the bulk shear stress. The proposed model is general and applies directly to sheared satured granular media in which pore pressure feedback plays a key role. We argue that it can be the case for debris fow, especially during the triggering phase, when run-out include transitional phases, and when the flow is stopped. It is then concluded that debris cannot be computed by assuming solely the rheological properties of an equivalent mixture.
Boundary effects on the drag of a cylinder in axial motion at low Reynolds number
Energy Technology Data Exchange (ETDEWEB)
Wehbeh, E.G.
1987-01-01
This work is an experimental study of the Stokes drag on a right circular cylinder moving with constant velocity through a Newtonian viscous fluid. The cylinder velocity is parallel to its longitudinal axis, and the fluid is bounded on the outside by a fixed coaxial cylindrical tube of circular cross section. The length-to-diameter ratio of the moving cylinder ranges from 1.0 to 390, the ratio of the width of the annular gap to the cylinder length ranges from 0.0077 to 0.86, and the ratio ..cap alpha.. of the cylinder diameter to the tube diameter ranges from 0.022 to 0.91. Experimental values of the drag are compared with a theoretical expression which assumes a flow entirely axial in the annular region and a drag that is due entirely to the viscous stress on the cylinder side plus the effect of the dynamic pressure difference on the ends of the cylinder. A second problem is considered in which a thin circular disk moves broadside through a viscous fluid toward a plane wall that is parallel to the disk. An expression obtained for the Stokes drag agrees with the experiment and reduces to known theoretical results at extremes of large and small distances form the disk to the plane.
Lift and Drag on Cylinder of Octagonal Cross-Section in a Turbulent Stream
Directory of Open Access Journals (Sweden)
Md. Jomir Hossain
2013-12-01
Full Text Available An experimental investigation of surface static pressure distributions on octagonal cylinder in uniform and turbulent flows was carried out. The study was performed on both the single cylinder and the group of two cylinders, two cylinders were used, one was at the upstream side, and the other was at the downstream side of the flow. They were placed centrally along the flow direction. The inter-spacing space between the two cylinders was varied at 1D, 2D, 3D, 4D, 5D, 6D, 7D and 8D, where D is the width of the cylinder across the flow direction. The pressure coefficients were calculated from the measured values of the surface static pressure distribution on the cylinder. Then the drag and lift coefficients were obtained from the pressure coefficients by the numerical integration method. It was observed that at various angles of attack, the values of the lift coefficients and drag coefficients were insignificant compared to those for a sharp-edged square cylinder. The strength of the vortex shedding was shown to be reduced as the intensity of the incident turbulence was increased. Measurements of drag at various angles of attack (0° to 40° showed that with increase in turbulence level the minimum drag occurred at smaller values of angle of attack.
Hydrodynamics of oceans and atmospheres
Eckart, Carl
1960-01-01
Hydrodynamics of Oceans and Atmospheres is a systematic account of the hydrodynamics of oceans and atmospheres. Topics covered range from the thermodynamic functions of an ideal gas and the thermodynamic coefficients for water to steady motions, the isothermal atmosphere, the thermocline, and the thermosphere. Perturbation equations, field equations, residual equations, and a general theory of rays are also presented. This book is comprised of 17 chapters and begins with an introduction to the basic equations and their solutions, with the aim of illustrating the laws of dynamics. The nonlinear
Anisotropic hydrodynamics: Motivation and methodology
Energy Technology Data Exchange (ETDEWEB)
Strickland, Michael
2014-06-15
In this proceedings contribution I review recent progress in our understanding of the bulk dynamics of relativistic systems that possess potentially large local rest frame momentum-space anisotropies. In order to deal with these momentum-space anisotropies, a reorganization of relativistic viscous hydrodynamics can be made around an anisotropic background, and the resulting dynamical framework has been dubbed “anisotropic hydrodynamics”. I also discuss expectations for the degree of momentum-space anisotropy of the quark–gluon plasma generated in relativistic heavy ion collisions at RHIC and LHC from second-order viscous hydrodynamics, strong-coupling approaches, and weak-coupling approaches.
Drag reduction via micro bubble injection in boundary layer of channel flows
Energy Technology Data Exchange (ETDEWEB)
Hassan, Y.A. [Texas A and M Univ., Dept. of Nuclear Engineering, College Station, Texas (United States)
2004-07-01
Full text of publication follows:Methods to reduce the drag in turbulent flows have been carried out for the past several decades. Reducing skin friction has obvious advantages through improvements in fuel economy, range (as in case of commercial ships and aircraft) or in peak speed (desirable in military or racing applications) and for less impact on the environment due to less fuel consumption. Recently, the reduction of turbulent friction between a solid surface and fluid by adding drag reducing additives has received increasing attention for saving power and reducing the pollution. Polymers and surfactants injections, wall oscillations, traveling waves, blowing and suction, and micro-bubble injection are examples among active additives. Riblets are an example of passive techniques to achieve drag reduction. However, a consensus about understanding the mechanism that governs this phenomenon has not been reached. In this paper, an investigation of turbulent structure modification of fully developed channel flow by micro-bubble injection close to the upper wall was studied. Two-dimensional velocity components at Reynolds number of 5128 based on the half height of the channel and bulk velocity were measured. The particle image velocimetry technique was utilized to obtain the two-dimensional velocity fields of the fluid and the micro-bubbles. Micro-bubbles with an average diameter of 30 {mu}m were injected into the buffer layer. Various values of void fractions were used to evaluate the effects of micro-bubbles concentration on the drag reduction. Modifications in the length and time scales were detected by calculating two-point correlation coefficients. Streamline length and time scales were increased. On the contrary, the normal length and time scales were decreased with the increase of the drag reduction. The presence of the micro-bubbles with low local concentration of 4% achieved 40% drag reduction. A decrease in the Reynolds stresses were achieved as the void
Analysis of Drag Reduction Methods and Mechanisms of Turbulent
Tao, Liu; Jiegang, Mu; Zhengzan, Shi; Peijian, Zhou
2017-01-01
Turbulent flow is a difficult issue in fluid dynamics, the rules of which have not been totally revealed up to now. Fluid in turbulent state will result in a greater frictional force, which must consume great energy. Therefore, it is not only an important influence in saving energy and improving energy utilization rate but also an extensive application prospect in many fields, such as ship domain and aerospace. Firstly, bionic drag reduction technology is reviewed and is a hot research issue now, the drag reduction mechanism of body surface structure is analyzed, such as sharks, earthworms, and dolphins. Besides, we make a thorough study of drag reduction characteristics and mechanisms of microgrooved surface and compliant wall. Then, the relevant drag reduction technologies and mechanisms are discussed, focusing on the microbubbles, the vibrant flexible wall, the coating, the polymer drag reduction additives, superhydrophobic surface, jet surface, traveling wave surface drag reduction, and the composite drag reduction methods. Finally, applications and advancements of the drag reduction technology in turbulence are prospected. PMID:29104425
Spin-transfer mechanism for magnon-drag thermopower
Lucassen, M.E.|info:eu-repo/dai/nl/314406913; Wong, C.H.; Duine, R.A.|info:eu-repo/dai/nl/304830127; Tserkovnyak, Y.
2011-01-01
We point out a relation between the dissipative spin-transfer-torque parameter β and the contribution of magnon drag to the thermoelectric power in conducting ferromagnets. Using this result, we estimate β in iron at low temperatures, where magnon drag is believed to be the dominant contribution to
Analysis of Drag Reduction Methods and Mechanisms of Turbulent
Directory of Open Access Journals (Sweden)
Gu Yunqing
2017-01-01
Full Text Available Turbulent flow is a difficult issue in fluid dynamics, the rules of which have not been totally revealed up to now. Fluid in turbulent state will result in a greater frictional force, which must consume great energy. Therefore, it is not only an important influence in saving energy and improving energy utilization rate but also an extensive application prospect in many fields, such as ship domain and aerospace. Firstly, bionic drag reduction technology is reviewed and is a hot research issue now, the drag reduction mechanism of body surface structure is analyzed, such as sharks, earthworms, and dolphins. Besides, we make a thorough study of drag reduction characteristics and mechanisms of microgrooved surface and compliant wall. Then, the relevant drag reduction technologies and mechanisms are discussed, focusing on the microbubbles, the vibrant flexible wall, the coating, the polymer drag reduction additives, superhydrophobic surface, jet surface, traveling wave surface drag reduction, and the composite drag reduction methods. Finally, applications and advancements of the drag reduction technology in turbulence are prospected.
14 CFR 25.699 - Lift and drag device indicator.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Lift and drag device indicator. 25.699 Section 25.699 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION....699 Lift and drag device indicator. (a) There must be means to indicate to the pilots the position of...
Liu, J.; Huang, H. L.; Li, L. Z.; Qu, T. C.; Wu, Y.; Chen, S.; Yang, J. L.; Rao, X.
2017-07-01
The otter board is one of the main components of single boat trawl fisheries. An oval cambered double slotted otter board was developed for improving the expansion performance of trawl net in bottom trawl fisheries. A flume model experiment was conducted to measure the lift coefficient (C L), drag coefficient (C D), and lift to drag ratio (K) in different angles of attack (α). The experimental results are as follows : (1) The C L and K value show a trend of increasing at the beginning and then decreasing with the increase of angle of attack, the C D value reflects an upward trend as the angle of attack increases; (2) The D3 otter board (front flow deflector angle at 29°) showed a better hydrodynamic performance. When α=30°, the max lift coefficient (C Lmax) was 1.464, in this case C D = 0.554 and K=2.643. When α=15°, the max lift to drag ratio (K max) was 4.165, C L =0.633, and C D = 0.152. This suggests that the best working scope for the angle of attack is between 15°~30°, in which case, C L>0.633 and K>2.643. The mean value of the lift coefficient was 1.071 and the mean of the lift to drag ratio was 3.482. Comparative analysis of the hydrodynamic performance of different types of otter boards showed that the D3 otter board both had good expansion performance and efficiency, which can provide a reference basis for further optimization of the bottom trawl otter board.
Dancing droplets: Contact angle, drag, and confinement
Benusiglio, Adrien; Cira, Nate; Prakash, Manu
2015-11-01
When deposited on a clean glass slide, a mixture of water and propylene glycol forms a droplet of given contact angle, when both pure liquids spread. (Cira, Benusiglio, Prakash: Nature, 2015). The droplet is stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow from the border to the apex of the droplets. The apparent contact angle of the droplets depends on both their composition and the external humidity as captured by simple models. These droplets present remarkable properties such as lack of a large pinning force. We discuss the drag on these droplets as a function of various parameters. We show theoretical and experimental results of how various confinement geometries change the vapor gradient and the dynamics of droplet attraction.
A Study of Drag Force in Isothermal Bubbly Flow
Directory of Open Access Journals (Sweden)
C. Li
2009-12-01
Full Text Available Driven by the extensive demands of simulating highly concentrated gas bubbly flows in many engineering fields, numerical studies have been performed to investigate the neighbouring effect of a swarm of bubbles on the interfacial drag forces. In this study, a novel drag coefficient correlation (Simonnet et al., 2007 in terms of local void fraction coupled with the population balance model based on average bubble number density (ABND has been implemented and compared with Ishii-Zuber densely distributed fluid particles drag model. The predicted local radial distributions of three primitive variables: gas void fraction, Sauter mean bubble diameter, and gas velocity, are validated against the experimental data of Hibiki et al. (2001. In general, satisfactory agreements between predicted and measured results are achieved by both drag force models. With additional consideration for closely packed bubbles, the latest coefficient model by Simonnet et al. (2007 shows considerably better performance in capturing the reduction of drag forces incurred by neighbouring bubbles.
Mars entry guidance based on an adaptive reference drag profile
Liang, Zixuan; Duan, Guangfei; Ren, Zhang
2017-08-01
The conventional Mars entry tracks a fixed reference drag profile (FRDP). To improve the landing precision, a novel guidance approach that utilizes an adaptive reference drag profile (ARDP) is presented. The entry flight is divided into two phases. For each phase, a family of drag profiles corresponding to various trajectory lengths is planned. Two update windows are investigated for the reference drag profile. At each window, the ARDP is selected online from the profile database according to the actual range-to-go. The tracking law for the selected drag profile is designed based on the feedback linearization. Guidance approaches using the ARDP and the FRDP are then tested and compared. Simulation results demonstrate that the proposed ARDP approach achieves much higher guidance precision than the conventional FRDP approach.
Directory of Open Access Journals (Sweden)
Amjad Asad
2017-01-01
Full Text Available In this paper, the hydrodynamics of a bubble column is investigated numerically using the discrete bubble model, which tracks the dispersed bubbles individually in a liquid column. The discrete bubble model is combined with the volume of fluid approach to account for a proper free surface boundary condition at the liquid–gas interface. This improves describing the backflow region, which takes place close to the wall region. The numerical simulation is conducted by means of the open source computational fluid dynamics library OpenFOAM®. In order to validate the numerical model, experimental results of a bubble column are used. The numerical prediction shows an overall good agreement compared to the experimental data. The effect of injection conditions and the influence of the drag closures on bubble dynamics are investigated in the current paper. Here, the significant effect of injection boundary conditions on bubble dynamics and flow velocity in the studied cavity is revealed. Moreover, the impact of the choice of the drag closure on the liquid velocity field and on bubble behavior is indicated by comparing three drag closures derived from former studies.
Aerodynamic drag modeling of alpine skiers performing giant slalom turns.
Meyer, Frédéric; Le Pelley, David; Borrani, Fabio
2012-06-01
Aerodynamic drag plays an important role in performance for athletes practicing sports that involve high-velocity motions. In giant slalom, the skier is continuously changing his/her body posture, and this affects the energy dissipated in aerodynamic drag. It is therefore important to quantify this energy to understand the dynamic behavior of the skier. The aims of this study were to model the aerodynamic drag of alpine skiers in giant slalom simulated conditions and to apply these models in a field experiment to estimate energy dissipated through aerodynamic drag. The aerodynamic characteristics of 15 recreational male and female skiers were measured in a wind tunnel while holding nine different skiing-specific postures. The drag and the frontal area were recorded simultaneously for each posture. Four generalized and two individualized models of the drag coefficient were built, using different sets of parameters. These models were subsequently applied in a field study designed to compare the aerodynamic energy losses between a dynamic and a compact skiing technique. The generalized models estimated aerodynamic drag with an accuracy of between 11.00% and 14.28%, and the individualized models estimated aerodynamic drag with an accuracy between 4.52% and 5.30%. The individualized model used for the field study showed that using a dynamic technique led to 10% more aerodynamic drag energy loss than using a compact technique. The individualized models were capable of discriminating different techniques performed by advanced skiers and seemed more accurate than the generalized models. The models presented here offer a simple yet accurate method to estimate the aerodynamic drag acting upon alpine skiers while rapidly moving through the range of positions typical to turning technique.
Non-Newtonian effects on the coastdown phenomenon of hydrodynamic journal bearings
Energy Technology Data Exchange (ETDEWEB)
Sheeja, D.; Prabhu, B.S. (Indian Inst. of Technology, Madras (India))
1993-07-01
The behavior of a rotating system after its power supply is cut off is called the coastdown phenomenon. An experimental investigation of the coastdown characteristics was carried out on a rotor rig, with different types of lubricants including a Newtonian oil, a blend of ISOVG 32 and hydrogenated styrene isoprene, multigrade oils, and aqueous polymer solutions in a hydrodynamic journal bearing. The characteristics were plotted in terms of deceleration vs. speed, which resembled the Stribeck diagram of friction due to viscous drag. Thus, the apparent Stribeck diagrams of friction for the above oils were obtained by plotting the derived coefficient of friction against the reciprocal Sommerfeld number. 11 refs.
Non-Newtonian effects on the coastdown phenomenon of hydrodynamic journal bearings
Sheeja, D.; Prabhu, B. S.
1993-07-01
The behavior of a rotating system after its power supply is cut off is called the coastdown phenomenon. An experimental investigation of the coastdown characteristics was carried out on a rotor rig, with different types of lubricants including a Newtonian oil, a blend of ISOVG 32 and hydrogenated styrene isoprene, multigrade oils, and aqueous polymer solutions in a hydrodynamic journal bearing. The characteristics were plotted in terms of deceleration vs. speed, which resembled the Stribeck diagram of friction due to viscous drag. Thus, the apparent Stribeck diagrams of friction for the above oils were obtained by plotting the derived coefficient of friction against the reciprocal Sommerfeld number.
Numerical Hydrodynamics in General Relativity
Directory of Open Access Journals (Sweden)
Font José A.
2003-01-01
Full Text Available The current status of numerical solutions for the equations of ideal general relativistic hydrodynamics is reviewed. With respect to an earlier version of the article, the present update provides additional information on numerical schemes, and extends the discussion of astrophysical simulations in general relativistic hydrodynamics. Different formulations of the equations are presented, with special mention of conservative and hyperbolic formulations well-adapted to advanced numerical methods. A large sample of available numerical schemes is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. A comprehensive summary of astrophysical simulations in strong gravitational fields is presented. These include gravitational collapse, accretion onto black holes, and hydrodynamical evolutions of neutron stars. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances on the formulation of the gravitational field and hydrodynamic equations and the numerical methodology designed to solve them.
Hydrodynamics of a quark droplet
DEFF Research Database (Denmark)
Bjerrum-Bohr, Johan J.; Mishustin, Igor N.; Døssing, Thomas
2012-01-01
We present a simple model of a multi-quark droplet evolution based on the hydrodynamical description. This model includes collective expansion of the droplet, effects of the vacuum pressure and surface tension. The hadron emission from the droplet is described following Weisskopf's statistical...
Boundary Effects on the Drag of a Cylinder in Axial Motion at Low Reynolds Number.
Wehbeh, Elias George
1987-09-01
This work is an experimental study of the Stokes drag on a right circular cylinder moving with constant velocity through a Newtonian viscous fluid. The cylinder velocity is parallel to its longitudinal axis, and the fluid is bounded on the outside by a fixed coaxial cylindrical tube of circular cross section. The length to diameter ratio of the moving cylinder ranges from 1.0 to 390, the ratio of the width of the annular gap to the cylinder length ranges from 0.0077 to 0.86, and the ratio alpha of the cylinder diameter to the tube diameter ranges from 0.022 to 0.91. Experimental values of the drag are compared with a theoretical expression which assumes a flow that is entirely axial in the annular region and a drag that is due entirely to the viscous stress on the cylinder side plus the effect of the dynamic pressure difference on the ends of the cylinder. An end correction term is obtained which is found to be proportional to the annular gap width and to the square root of alpha . This term is found to be consistent with previous numerical studies of the narrow gap case and with experimental studies of the wide gap case. Drag values are also presented for the situation in which the bottom of the tube is open to a larger fluid reservoir. A second problem is considered in which a thin circular disk moves broadside through a viscous fluid toward a plane wall that is parallel to the disk. An expression for the Stokes drag is obtained which agrees with the experiment and reduces to known theoretical results at extremes of large and small distances from the disk to the plane.
Symposium on Naval Hydrodynamics (10th), Hydrodynamics for Safety Fundamental Hydrodynamics
1974-01-01
the retention of the air cushion. The momentum drag (a pcl) will all therefore be less. sustention of the vehicle above the water However, the power... sustention of the ISACV above the may be different and a compromise may therefore water surface, (1- a) denotes the proportimn of have to be reached in...equipment. Compressed air can also be pair of submeiged hulls, the latter contributing produced and stored in the hulls during" slack to the sustention of the
Hydrodynamic Expansion of Pellicles Caused by e-Beam Heating
Ho, D
2000-01-01
Placing a pellicle in front of a x-ray converter target for radiographic applications can confine the backstreaming ions and target plasma to a shorter channel so that the cumulative effect on e-beam focusing is reduced. The pellicle is subject to heating by e-beam since the pellicle is placed upstream of the target. The calculation of the hydrodynamic expansion, caused by the heating, using the radiation hydrodynamics code LASNEX is presented in this report. Calculations show that mylar pellicles disintegrate at the end of a multi-pulse intense e-beam while beryllium and carbon pellicles remain intact. The expansions for the kapton-carbon multi-layered targets are also examined. Hydrodynamic expansions for pellicles with various e-beam spot radii are calculated for DARHT-II beam parameters. All the simulation results indicate that the backstreaming ions can be stopped.
Moving least-squares corrections for smoothed particle hydrodynamics
Directory of Open Access Journals (Sweden)
Ciro Del Negro
2011-12-01
Full Text Available First-order moving least-squares are typically used in conjunction with smoothed particle hydrodynamics in the form of post-processing filters for density fields, to smooth out noise that develops in most applications of smoothed particle hydrodynamics. We show how an approach based on higher-order moving least-squares can be used to correct some of the main limitations in gradient and second-order derivative computation in classic smoothed particle hydrodynamics formulations. With a small increase in computational cost, we manage to achieve smooth density distributions without the need for post-processing and with higher accuracy in the computation of the viscous term of the Navier–Stokes equations, thereby reducing the formation of spurious shockwaves or other streaming effects in the evolution of fluid flow. Numerical tests on a classic two-dimensional dam-break problem confirm the improvement of the new approach.
FUSELAGE SHAPE OPTIMIZATION AIMED AT WING-FUSELAGE CONFIGURATION DRAG REDUCTION AT SUPERSONIC SPEEDS
Directory of Open Access Journals (Sweden)
2016-01-01
Full Text Available The problem of fuselage shape optimization of the wing-body configuration is considered in the following three formulations. In the first one, the angle of attack is fixed and equal to zero, the wing has a symmetric airfoil, and the fuse- lage is based on circular cross sections. In the second one, the fuselage cross sections are elliptical. In the third one, the angle of attack is varied, the lifting force coefficient is fixed, the wing is preliminary optimized, the fuselage is designed by the cross sections that consist of upper and lower half-ellipses with a possibility of a shift along vertical axis. The configu- ration volume, fuselage length, shape and position of the wing are fixed. The drag coefficient is the objective function. The optimization is carried out by the Indirect Optimization based on Self-Organization (IOSO technology. Aerodynamic coef- ficients are obtained from the solution of the RANS equations with SST turbulence model by the ANSYS CFX software on the structured multiblock meshes. The results obtained by the optimization are compared with the configuration that is de- signed by traditional means. The fuselage of this configuration has a cylindrical part in the area of the wing-fuselage con- nection and nose part of the von Karman’s ogive shape. The solution of the optimization problem in the first formulation reduces drag coefficient at zero angle of attack by approximately 3 %. The use of the fuselage with elliptical cross sections makes it possible to reduce drag coefficient at zero angle of attack by 9 %. The solution of the optimization problem in first two formulations reduces drag coefficient at the wide range of angles of attack. When the lifting coefficient is selected for the third problem formulation as constraint the drag reduction is about 7 %. Additional drag reduction of about 2,5 % is obtained by the use of the fuselage asymmetric relative to the horizontal plane. The optimal fuselage design has a
Characterization of aerodynamic drag force on single particles: Final report
Energy Technology Data Exchange (ETDEWEB)
Kale, S.R.
1987-10-01
An electrodynamic balance was used to measure the drag coefficient and also to record the size and shape of spheres, and coal and oil shale particles (100 ..mu..m to 200 ..mu..m in size). The electrodynamic balance consisted of a central, and two end electrodes. The resulting electric field stably suspended a charged particle. A suspended particle, back illuminated by a light emitting diode, was viewed by a video camera. The image was analyzed for particle position control and was calibrated to give the diameter of spheres, or the area equivalent diameter of nonspherical particles. The drag coefficient was calculated from the air velocity and the dc voltage required to keep the particle at the balance center. The particle Reynolds number varied from 0.2 to 13. Three particles each of coal and oil shale were captured and photographed by a scanning electron microscope and the motion of all the particles was recorded on video tape. Drag coefficient vs Reynolds number data for spheres agreed well with correlations. Data for thirteen particles each of coal and oil shale indicated a power law relationship between drag coefficient and Reynolds number. All these particles exhibited higher drag than spheres and were also observed to rotate. The rotation, however, did not affect the drag coefficient. The choice of characteristic dimension affects the drag characteristics of oil shale more strongly than for coal, owing to the flake-like shape of oil shale. 38 figs., 5 tabs.
Gas Drag on a Rotating Body with Gravity
Hidenori, TAKEDA; Yoshitsugu, NAKAGAWA; Department of Aeronautics and Astronautics, Faculty of Engineering Kyoto University; Department of Earth and Planetary Sciences, Faculty of Science Kobe University
2000-01-01
In growth processes of planetesimals and protoplanets, the gas drag on them plays important roles. It is interesting to study the gas flows around rotating celestial bodies with gravity, and it is important to evaluate the gas drag on those bodies from the viewpoint of planetary cosmogony. In order to understand the effects of the rotation and the gravity of such bodies on the gas drag and also to observe lift and torque, we performed three-dimensional numerical simulations for the flows arou...
Frictional drag between quantum wells mediated by phonon exchange
DEFF Research Database (Denmark)
Bønsager, M.C.; Flensberg, Karsten; Hu, Ben Yu-Kuang
1998-01-01
lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation......We use the Kubo formalism to evaluate the contribution of acoustic-phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate (tau(D)(-l)). However, tau(D)(-l) becomes finite when phonon scattering from either...
Drag force scaling for penetration into granular media.
Katsuragi, Hiroaki; Durian, Douglas J
2013-05-01
Impact dynamics is measured for spherical and cylindrical projectiles of many different densities dropped onto a variety non-cohesive granular media. The results are analyzed in terms of the material-dependent scaling of the inertial and frictional drag contributions to the total stopping force. The inertial drag force scales similar to that in fluids, except that it depends on the internal friction coefficient. The frictional drag force scales as the square-root of the density of granular medium and projectile, and hence cannot be explained by the combination of granular hydrostatic pressure and Coulomb friction law. The combined results provide an explanation for the previously observed penetration depth scaling.
Drag Reduction Properties of Nanofluids in Microchannels
Directory of Open Access Journals (Sweden)
H.A. Abdulbari
2015-12-01
Full Text Available An experimental investigation of the drag reduction (DR individualities in different sized micro channels was carried out with nanopowder additives (NAs (bismuth(III oxide, iron(II/III oxide, silica, and titanium(IV oxide water suspensions/fluids. The primary objective was to evaluate the effects of various concentrations of NAs with different microchannel sizes (50, 100, and 200 µm on the pressure drop of a system in a single phase. A critical concentration was observed with all the NAs, above which increasing the concentration was not effective. Based on the experimental results, the optimum DR percentages were calculated. The optimum percentages were found to be as follows: bismuth III oxides: ~65% DR, 200 ppm and a microchannel size of 100 µm; iron II/III oxides: ~57% DR, 300 ppm, and a microchannel size of 50 µm; titanium IV oxides: ~57% DR, 200 ppm, and a microchannel size of 50 µm, and silica: 55% DR, 200 ppm, and a microchannel size of 50 µm.
Turbulent drag reduction through oscillating discs
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...
Drag reduction and the dynamics of turbulence in simple and complex fluidsa)
Graham, Michael D.
2014-10-01
Addition of a small amount of very large polymer molecules or micelle-forming surfactants to a liquid can dramatically reduce the energy dissipation it exhibits in the turbulent flow regime. This rheological drag reduction phenomenon is widely used, for example, in the Alaska pipeline, but it is not well-understood, and no comparable technology exists to reduce turbulent energy consumption in flows of gases, in which polymers or surfactants cannot be dissolved. The most striking feature of this phenomenon is the existence of a so-called maximum drag reduction (MDR) asymptote: for a given geometry and driving force, there is a maximum level of drag reduction that can be achieved through addition of polymers. Changing the concentration, molecular weight or even the chemical structure of the additives has little to no effect on this asymptotic value. This universality is the major puzzle of drag reduction. We describe direct numerical simulations of turbulent minimal channel flow of Newtonian fluids and viscoelastic polymer solutions. Even in the absence of polymers, we show that there are intervals of "hibernating" turbulence that display very low drag as well as many other features of the MDR asymptote observed in polymer solutions. As Weissenberg number increases to moderate values the frequency of these intervals also increases, and a simple theory captures key features of the intermittent dynamics observed in the simulations. At higher Weissenberg number, these intervals are altered - for example, their duration becomes substantially longer and the instantaneous Reynolds shear stress during them becomes very small. Additionally, simulations of "edge states," dynamical trajectories that lie on the boundary between turbulent and laminar flow, display characteristics that are similar to those of hibernating turbulence and thus to the MDR asymptote, again even in the absence of polymer additives. Based on these observations, we propose a tentative unified description
Hydrodynamics from Landau initial conditions
Energy Technology Data Exchange (ETDEWEB)
Sen, Abhisek [University of Tennessee, Knoxville (UTK); Gerhard, Jochen [Frankfurt Institute for Advanced Studies (FIAS), Germany; Torrieri, Giorgio [Universidade Estadual de Campinas, Instituto de Física " Gleb Wataghin" (IFGW), Sao Paulo, Brazil; Read jr, Kenneth F. [University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL); Wong, Cheuk-Yin [ORNL
2015-01-01
We investigate ideal hydrodynamic evolution, with Landau initial conditions, both in a semi-analytical 1+1D approach and in a numerical code incorporating event-by-event variation with many events and transverse density inhomogeneities. The object of the calculation is to test how fast would a Landau initial condition transition to a commonly used boost-invariant expansion. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of O (20 - 30%) expected at freezeout for most scenarios. Moreover, the deviation from boost-invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, 2+1 dimensional hydrodynamics is inadequate to extract transport coefficients of the quark-gluon plasma. Based on [1, 2
Boundary layer thickness effect on boattail drag. [wind tunnel tests for drag reduction
Blaha, B. J.; Chamberlin, R.; Bober, L. J.
1976-01-01
A combined experimental and analytical program has been conducted at the NASA Lewis Research Center, to investigate the effects of boundary layer changes on the flow over high angle boattail nozzles. The tests were run on an isolated axisymmetric sting mounted model. Various boattail geometries were investigated at high subsonic speeds over a range of boundary layer thicknesses. In general, boundary layer effects were small at speeds up to Mach 0.8. However, at higher speeds significant regions of separated flow were present on the boattail. When separation was present large reductions in boattail drag resulted with increasing boundary layer thickness. The analysis predicts both of these trends.
Hydrodynamic model in isospin channels
Energy Technology Data Exchange (ETDEWEB)
Lipparini, E.; Stringari, S.
1987-08-31
The Steinwedel-Jensen hydrodynamic model is generalized to study isovector collective modes excited in charge-exchange reactions. Results are given for the energy splittings between the different isospin components of the giant dipole and monopole resonances recently observed in (p,n) and (..pi../sup +- /,..pi../sup 0/) reactions. The quenching of the ..delta..T/sub z/ = +1 excitation strength in Nnot =Z nuclei with respect to the N = Z case is also discussed.
Student Conceptual Difficulties in Hydrodynamics
Suarez, Alvaro; Kahan, Sandra; Zavala, Genaro; Marti, Arturo C.
2017-01-01
We describe a study on the conceptual difficulties faced by college students in understanding hydrodynamics of ideal fluids. This study was based on responses obtained in hundreds of written exams complemented with several oral interviews, which were held with first-year engineering and science university students. Their responses allowed us to identify a series of misconceptions unreported in the literature so far. The study findings demonstrate that the most critical difficulties arise from...
Numerical Hydrodynamics in Special Relativity.
Martí, José Maria; Müller, Ewald
2003-01-01
This review is concerned with a discussion of numerical methods for the solution of the equations of special relativistic hydrodynamics (SRHD). Particular emphasis is put on a comprehensive review of the application of high-resolution shock-capturing methods in SRHD. Results of a set of demanding test bench simulations obtained with different numerical SRHD methods are compared. Three applications (astrophysical jets, gamma-ray bursts and heavy ion collisions) of relativistic flows are discussed. An evaluation of various SRHD methods is presented, and future developments in SRHD are analyzed involving extension to general relativistic hydrodynamics and relativistic magneto-hydrodynamics. The review further provides FORTRAN programs to compute the exact solution of a 1D relativistic Riemann problem with zero and nonzero tangential velocities, and to simulate 1D relativistic flows in Cartesian Eulerian coordinates using the exact SRHD Riemann solver and PPM reconstruction. Supplementary material is available for this article at 10.12942/lrr-2003-7 and is accessible for authorized users.
Hydrodynamic instabilities in miscible fluids
Truzzolillo, Domenico; Cipelletti, Luca
2018-01-01
Hydrodynamic instabilities in miscible fluids are ubiquitous, from natural phenomena up to geological scales, to industrial and technological applications, where they represent the only way to control and promote mixing at low Reynolds numbers, well below the transition from laminar to turbulent flow. As for immiscible fluids, the onset of hydrodynamic instabilities in miscible fluids is directly related to the physics of their interfaces. The focus of this review is therefore on the general mechanisms driving the growth of disturbances at the boundary between miscible fluids, under a variety of forcing conditions. In the absence of a regularizing mechanism, these disturbances would grow indefinitely. For immiscible fluids, interfacial tension provides such a regularizing mechanism, because of the energy cost associated to the creation of new interface by a growing disturbance. For miscible fluids, however, the very existence of interfacial stresses that mimic an effective surface tension is debated. Other mechanisms, however, may also be relevant, such as viscous dissipation. We shall review the stabilizing mechanisms that control the most common hydrodynamic instabilities, highlighting those cases for which the lack of an effective interfacial tension poses deep conceptual problems in the mathematical formulation of a linear stability analysis. Finally, we provide a short overview on the ongoing research on the effective, out of equilibrium interfacial tension between miscible fluids.
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
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.
Chunbao, Liu; Li, Li; Yulong, Lei; 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.
Turbulent and Transitional Modeling of Drag on Oceanographic Measurement Devices
Directory of Open Access Journals (Sweden)
J. P. Abraham
2012-01-01
Full Text Available Computational fluid dynamic techniques have been applied to the determination of drag on oceanographic devices (expendable bathythermographs. Such devices, which are used to monitor changes in ocean heat content, provide information that is dependent on their drag coefficient. Inaccuracies in drag calculations can impact the estimation of ocean heating associated with global warming. Traditionally, ocean-heating information was based on experimental correlations which related the depth of the device to the fall time. The relation of time-depth is provided by a fall-rate equation (FRE. It is known that FRE depths are reasonably accurate for ocean environments that match the experiments from which the correlations were developed. For other situations, use of the FRE may lead to depth errors that preclude XBTs as accurate oceanographic devices. Here, a CFD approach has been taken which provides drag coefficients that are used to predict depths independent of an FRE.
Dizziness Can Be a Drag: Coping with Balance Disorders
... Issues Subscribe August 2012 Print this issue Dizziness Can Be a Drag Coping with Balance Disorders Send ... enough to send them to a doctor. Dizziness can range from feeling lightheaded to woozy to disoriented. ...
Drag force and jet propulsion investigation of a swimming squid
Directory of Open Access Journals (Sweden)
Tabatabaei Mahdi
2015-01-01
Full Text Available In this study, CAD model of a squid was obtained by taking computer tomography images of a real squid. The model later placed into a computational domain to calculate drag force and performance of jet propulsion. The drag study was performed on the CAD model so that drag force subjected to real squid was revealed at squid’s different swimming speeds and comparison has been made with other underwater creatures (e.g., a dolphin, sea lion and penguin. The drag coefficient (referenced to total wetted surface area of squid is 0.0042 at Reynolds number 1.6x106 that is a %4.5 difference from Gentoo penguin. Besides, jet flow of squid was simulated to observe the flow region generated in the 2D domain utilizing dynamic mesh method to mimic the movement of squid’s mantle cavity.
Drag Force in a Gas Fluidized Granular Bed
Brzinski, T. A.; Durian, D. J.
2008-03-01
We use a rheometer to measure the torque acting on a rotating bar in a bed of gas-fluidized glass beads. We vary rotation rate from .001-10rps, vary depth from 1-10 cm, and increase the fluidizing gas flow from no flow well into the fluidized regime. We observe that at high rotation rates the drag is roughly proportional to velocity squared. At low rates we can rescale the measured torque by depth, and observe a collapse of the data. These results agree with the predictions of a granular drag force model which has proven effective in predicting granular impact dynamics. The model consists of an inertial drag term, which is depth-independent and scales as velocity squared, and a frictional drag term, which is independent of rate and varies linearly with depth. We find, as expected, that while the frictional term is airflow-dependent the inertial term is uncoupled from the fluidization.
Rotating cylinder drag balance with application to riblets
Energy Technology Data Exchange (ETDEWEB)
Hall, T.; Joseph, D. [Minnesota Univ., Minneapolis, MN (United States). Dept. of Aerospace Engineering and Mechanics
2000-09-01
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
Shell selection of hermit crabs is influenced by fluid drag
Casillas, Barbara; Ledesma, Rene; Alcaraz, Guillermina; Zenit, Roberto
2010-11-01
The flow around gastropod shells used by hermit crabs (Calcinus californiensis) was visualized experimentally. These crabs choose their shells according to many factors; we found that the choice of shell (shape and weight) is directly related to the drag caused over them by the exposure to wave action. Tests were conducted in a wind tunnel to investigate flow differences for shells of various shapes. A particle image velocimetry (PIV) system was used to visualize the flow field. The images above show the flow field around two types of shells (Thais speciosa and Nerita scabircosta) for Reynolds numbers of O(10^5). Using a control volume analysis, the drag coefficient was inferred. Several shell geometries, orientations and mean flow velocities were tested. In this talk, the flow and drag force will be shown for the different arrangements. A discussion of the relation between drag and shape will be presented.
Zhu, Liang; Chen, Xiong; Li, Yingkun; Musa, Omer; Zhou, Changsheng
2018-01-01
When flying at supersonic or hypersonic speeds through the air, the drag and severe heating have a great impact on the vehicles, thus the drag reduction and thermal protection studies have attracted worldwide attention. In the current study, the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k - ω turbulence model have been employed to investigate the flow behavior induced by a novel combinational lateral jet and spike concept in supersonic flows. A coupling conjugate heat transfer (CHT) approach has been applied to investigate the thermal protection, which takes the heat transfer of structure into consideration. After the code was validated by the available experimental results and the gird independency analysis was carried out, the influences of the spike length ratio, lateral jet pressure ratio and lateral jet location on the drag and heat reduction performance are analyzed comprehensively. The obtained results show that a remarkable reduction in the drag and heat flux is achieved when a lateral jet is added to the spike. This implies that the combinational lateral jet and spike concept in supersonic flows have a great benefit to the drag and heat reduction. Both the drag and heat reduction decrease with the increase of the lateral jet pressure ratio, and the heat flux is more sensitive to the lateral jet pressure ratio. The lateral jet should not be located in the bottom of the spike in order to realize better drag and heat reduction performance. The drag and heat flux could be reduced by about 45% by reasonable lateral jet location. The drag decreases with the increase of the spike length ratio whereas the heat flux is affected by the spike length ratio just in a certain range.
Frame dragging in black hole-pulsar binaries
Wex, N.
1999-01-01
The discovery of frame-dragging effects in binary pulsar timing experiments requires a compact companion with sufficiently large spin. A pulsar orbiting a fast rotating black hole could provide an appropriate test system. In this paper we address questions concerning the identification of a black hole companion in such a system, the measurability of the frame dragging caused by the rotation of the black hole, and the measurability of the quadrupole moment, which would prove the presence of a ...
Sensitivity analysis of factors affecting torque and drag modelling
Hashmi, Muhammad Jahanzeb
2014-01-01
Master's thesis in Petroleum engineering *KAR OK KONF 2016* As the modern day extended reached wells are getting longer and more complex, the torque and drag is one of the restraining aspects for achieving the target depth. Torque and drag becomes a precarious issue, for example it can be difficult to land the long completion string. Therefore, understanding the friction in the wellbore and how it affects hook load and torque is essential for well path design in planning phase as well ...
Drag force in a charged N = 4 SYM plasma
Energy Technology Data Exchange (ETDEWEB)
Caceres, Elena [Facultad de Ciencias, Universidad de Colima, Bernal Diaz del Castillo 340, Colima (Mexico); Gueijosa, Alberto [Departamento de Fisica de Altas Energias, Instituto de Ciencias Nucleares, Universidad Autonoma de Mexico, Apdo. Postal 70-543, D.F. 04510 (Mexico)
2006-11-15
Following recent developments, we employ the AdS/CFT correspondence to determine the drag force exerted on an external quark that moves through an N = 4 super-Yang-Mills plasma with a non-zero R-charge density (or, equivalently, a non-zero chemical potential). We find that the drag force is larger than in the case where the plasma is neutral, but the dependence on the charge is non-monotonic.
Progress towards a Drag-free SmallSat
Saraf, Shailendhar
The net force acting on a drag-free satellite is purely gravitational as all other forces, mainly atmospheric drag and solar radiation pressure, are canceled out. In order to achieve this, a free floating reference (test mass) inside the satellite is shielded against all forces but gravity and a system of thrusters is commanded by a control algorithm such that the relative displacement between the reference and the satellite stays constant. The main input to that control algorithm is the output of a sensor which measures the relative displacement between the satellite and the test mass. Internal disturbance forces such as electrostatic or magnetic forces cannot be canceled out his way and have to be minimized by a careful design of the satellite. A drag-free technology package is under development at Stanford since 2004. It includes an optical displacement sensor to measure the relative position of the test mass inside the satellite, a caging mechanism to lock the test mass during launch, a UV LED based charge management system to minimize the effect of electrostatic forces, a thermal enclosure, and the drag-free control algorithms. Possible applications of drag-free satellites in fundamental physics (Gravity Probe B, LISA), geodesy (GOCE), and navigation (TRIAD I). In this presentation we will highlight the progress of the technology development towards a drag-free mission. The planned mission on a SaudiSat bus will demonstrate drag-free technology on a small spacecraft at a fraction of the cost of previous drag-free missions. The target acceleration noise is 10-12 m/sec2. With multiple such satellites a GRACE-like mission with improved sensitivity and potentially improved spatial and temporal resolution can be achieved.
Hickey, Owen A; Holm, Christian; Smiatek, Jens
2014-04-28
In this article we examine the electrophoretic stretching of polyelectrolytes between parallel uncharged plates using molecular dynamics simulations. We compare simulations where the fluid is modeled implicitly using a Langevin thermostat, which ignore hydrodynamic interactions, to simulations with an explicit lattice-Boltzmann fluid that take hydrodynamic interactions into account. The difference between simulations with and without hydrodynamic interactions is larger for longer polyelectrolytes, as one would expect. Furthermore, we present simulation results which show that the effects of hydrodynamic interactions are reduced as the distance between the confining plates is diminished. The main result of our study is that hydrodynamic interactions play a larger role in systems with a shorter Debye length, in contrast to conventional wisdom.
Navier slip model of drag reduction by Leidenfrost vapor layers
Berry, Joseph D.
2017-10-17
Recent experiments found that a hot solid sphere that is able to sustain a stable Leidenfrost vapor layer in a liquid exhibits significant drag reduction during free fall. The variation of the drag coefficient with Reynolds number deviates substantially from the characteristic drag crisis behavior at high Reynolds numbers. Measurements based on liquids of different viscosities show that the onset of the drag crisis depends on the viscosity ratio of the vapor to the liquid. Here we attempt to characterize the complexity of the Leidenfrost vapor layer with respect to its variable thickness and possible vapor circulation within, in terms of the Navier slip model that is defined by a slip length. Such a model can facilitate tangential flow and thereby alter the behavior of the boundary layer. Direct numerical and large eddy simulations of flow past a sphere at moderate to high Reynolds numbers (102≤Re≤4×104) are employed to quantify comparisons with experimental results, including the drag coefficient and the form of the downstream wake on the sphere. This provides a simple one parameter characterization of the drag reduction phenomenon due to a stable vapor layer that envelops a solid body.
Navier slip model of drag reduction by Leidenfrost vapor layers
Berry, Joseph D.; Vakarelski, Ivan U.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.
2017-10-01
Recent experiments found that a hot solid sphere that is able to sustain a stable Leidenfrost vapor layer in a liquid exhibits significant drag reduction during free fall. The variation of the drag coefficient with Reynolds number deviates substantially from the characteristic drag crisis behavior at high Reynolds numbers. Measurements based on liquids of different viscosities show that the onset of the drag crisis depends on the viscosity ratio of the vapor to the liquid. Here we attempt to characterize the complexity of the Leidenfrost vapor layer with respect to its variable thickness and possible vapor circulation within, in terms of the Navier slip model that is defined by a slip length. Such a model can facilitate tangential flow and thereby alter the behavior of the boundary layer. Direct numerical and large eddy simulations of flow past a sphere at moderate to high Reynolds numbers (1 02≤Re≤4 ×1 04) are employed to quantify comparisons with experimental results, including the drag coefficient and the form of the downstream wake on the sphere. This provides a simple one parameter characterization of the drag reduction phenomenon due to a stable vapor layer that envelops a solid body.
Directory of Open Access Journals (Sweden)
S Dutz
Full Text Available Magnetic forces and curvature-induced hydrodynamic drag have both been studied and employed in continuous microfluidic particle separation and enrichment schemes. Here we combine the two. We investigate consequences of applying an outwardly directed magnetic force to a dilute suspension of magnetic microspheres circulating in a spiral microfluidic channel. This force is realized with an array of permanent magnets arranged to produce a magnetic field with octupolar symmetry about the spiral axis. At low flow rates particles cluster around an apparent streamline of the flow near the outer wall of the turn. At high flow rates this equilibrium is disrupted by the induced secondary (Dean flow and a new equilibrium is established near the inner wall of the turn. A model incorporating key forces involved in establishing these equilibria is described, and is used to extract quantitative information about the magnitude of local Dean drag forces from experimental data. Steady-state fractionation of suspensions by particle size under the combined influence of magnetic and hydrodynamic forces is demonstrated. Extensions of this work could lead to new continuous microscale particle sorting and enrichment processes with improved fidelity and specificity.
Dutz, S; Hayden, M E; Häfeli, U O
2017-01-01
Magnetic forces and curvature-induced hydrodynamic drag have both been studied and employed in continuous microfluidic particle separation and enrichment schemes. Here we combine the two. We investigate consequences of applying an outwardly directed magnetic force to a dilute suspension of magnetic microspheres circulating in a spiral microfluidic channel. This force is realized with an array of permanent magnets arranged to produce a magnetic field with octupolar symmetry about the spiral axis. At low flow rates particles cluster around an apparent streamline of the flow near the outer wall of the turn. At high flow rates this equilibrium is disrupted by the induced secondary (Dean) flow and a new equilibrium is established near the inner wall of the turn. A model incorporating key forces involved in establishing these equilibria is described, and is used to extract quantitative information about the magnitude of local Dean drag forces from experimental data. Steady-state fractionation of suspensions by particle size under the combined influence of magnetic and hydrodynamic forces is demonstrated. Extensions of this work could lead to new continuous microscale particle sorting and enrichment processes with improved fidelity and specificity.
The Berlin oil channel for drag reduction research
Bechert, D. W.; Hoppe, G.; van der Hoeven, J. G. Th.; Makris, R.
1992-03-01
For drag reduction research an oil channel has been designed and built. It is also well suited for investigations on turbulent flow and in particular on the dynamics of the viscous sublayer near the wall. The thickness of the viscous sublayer ( y += 5) can be varied between 1 and 4 mm. Surfaces with longitudinal ribs (“riblets”), which are known to reduce drag, can have fairly large dimensions. The lateral spacing of the ribs can lie between 3 and 10 mm, as compared to about 0.5 mm spacing for conventional wind tunnels. It has been proved by appropriate tests that the oil channel data are completely equivalent to data from other facilities and with other mean flow geometries. However, the shear stress data from the new oil channel are much more accurate than previous data due to a novel differential shear force balance with an accuracy of ±0.2%. In addition to shear stress measurements, velocity fluctuation measurements can be carried out with hot wire or hot film probes. In order to calibrate these probes, a moving sled permits to emulate the flow velocities with the fluid in the channel at rest. A number of additional innovations contribute to the improvement of the measurements, such as, e.g., (i) novel adjustable turbulators to maintain equilibrium turbulence in the channel, (ii) a “bubble trap” to avoid bubbles in the channel at high flow velocities, (iii) a simple method for the precision calibration of manometers, and (iv) the elimination of (Coulomb) friction in ball bearings. This latter fairly general invention is used for the wheels of the calibration unit of the balance. The channel has a cross section of 25 × 85 cm and is 11 m long. It is filled with about 4.5 metric tons of baby oil (white paraffine oil), which is transparent and odorless like water. The kinematic viscosity of the oil is v = 1.2×10-5 m2/s, and the highest (average) velocity is 1.29 m/s. Thus, the Reynolds number range (calculated with the channel width, 0.25 m) lies between
Aerodynamic drag of modern soccer balls.
Asai, Takeshi; Seo, Kazuya
2013-12-01
Soccer balls such as the Adidas Roteiro that have been used in soccer tournaments thus far had 32 pentagonal and hexagonal panels. Recently, the Adidas Teamgeist II and Adidas Jabulani, respectively having 14 and 8 panels, have been used at tournaments; the aerodynamic characteristics of these balls have not yet been verified. Now, the Adidas Tango 12, having 32 panels, has been developed for use at tournaments; therefore, it is necessary to understand its aerodynamic characteristics. Through a wind tunnel test and ball trajectory simulations, this study shows that the aerodynamic resistance of the new 32-panel soccer ball is larger in the high-speed region and lower in the middle-speed region than that of the previous 14- and 8-panel balls. The critical Reynolds number of the Roteiro, Teamgeist II, Jabulani, and Tango 12 was ~2.2 × 10(5) (drag coefficient, C d ≈ 0.12), ~2.8 × 10(5) (C d ≈ 0.13), ~3.3 × 10(5) (C d ≈ 0.13), and ~2.4 × 10(5) (C d ≈ 0.15), respectively. The flight trajectory simulation suggested that the Tango 12, one of the newest soccer balls, has less air resistance in the medium-speed region than the Jabulani and can thus easily acquire large initial velocity in this region. It is considered that the critical Reynolds number of a soccer ball, as considered within the scope of this experiment, depends on the extended total distance of the panel bonds rather than the small designs on the panel surfaces.
Bag-breakup control of surface drag in hurricanes
Troitskaya, Yuliya; Zilitinkevich, Sergej; Kandaurov, Alexander; Ermakova, Olga; Kozlov, Dmitry; Sergeev, Daniil
2016-04-01
consequent breaking of short-lived, sail-like pieces of the water-surface film - "bags". On the base of general principles of statistical physics (model of a canonical ensemble) we developed statistics of the "bag-breakup" events: their number and statistical distribution of geometrical parameters depending on wind speed. Basing on the developed statistics, we estimated the surface stress caused by bags as the average sum of stresses caused by individual bags depending on their eometrical parameters. The resulting stress is subjected to counteracting impacts of the increasing wind speed: the increasing number of bags, and their decreasing sizes and life times and the balance yields a peaking dependence of the bag resistance on the wind speed: the share of bag-stress peaks at U10 35 m/s and then reduces. Peaking of surface stress associated with the "bag-breakup" explains seemingly paradoxical non-monotonous wind-dependence of surface drag coefficient peaking at winds about 35 m/s. This work was supported by the Russian Foundation of Basic Research (14-05-91767, 13-05-12093, 16-05-00839, 14-05-91767, 16-55-52025, 15-35-20953) and experiment and equipment was supported by Russian Science Foundation (Agreements 14-17-00667 and 15-17-20009 respectively), Yu.Troitskaya, A.Kandaurov and D.Sergeev were partially supported by FP7 Collaborative Project No. 612610.
Drag reduction in reservoir rock surface: Hydrophobic modification by SiO{sub 2} nanofluids
Energy Technology Data Exchange (ETDEWEB)
Yan, Yong-Li, E-mail: yylhill@163.com [College of Chemistry & Chemical Engineering, Xi’an Shiyou University, Xi’an 710065 (China); Cui, Ming-Yue; Jiang, Wei-Dong; He, An-Le; Liang, Chong [Langfang Branch of Research Institute of Petroleum Exploration & Development, Langfang 065007 (China)
2017-02-28
Graphical abstract: The micro-nanoscale hierarchical structures at the sandstone core surface are constructed by adsorption of the modified silica nanoparticles, which leads to the effect of drag reduction to improve the low injection rate in ultra-low permeability reservoirs. - Highlights: • A micro-nanoscale hierarchical structure is formed at the reservoir rock surface. • An inversion has happened from hydrophilic into hydrophobic modified by nanofluids. • The effect of drag reduction to improve the low injection rate is realized. • The mechanism of drag reduction induced from the modified core surface was unclosed. - Abstract: 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
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.)
Entropy-limited hydrodynamics: a novel approach to relativistic hydrodynamics
Guercilena, Federico; Radice, David; Rezzolla, Luciano
2017-07-01
We present entropy-limited hydrodynamics (ELH): a new approach for the computation of numerical fluxes arising in the discretization of hyperbolic equations in conservation form. ELH is based on the hybridisation of an unfiltered high-order scheme with the first-order Lax-Friedrichs method. The activation of the low-order part of the scheme is driven by a measure of the locally generated entropy inspired by the artificial-viscosity method proposed by Guermond et al. (J. Comput. Phys. 230(11):4248-4267, 2011, doi: 10.1016/j.jcp.2010.11.043). Here, we present ELH in the context of high-order finite-differencing methods and of the equations of general-relativistic hydrodynamics. We study the performance of ELH in a series of classical astrophysical tests in general relativity involving isolated, rotating and nonrotating neutron stars, and including a case of gravitational collapse to black hole. We present a detailed comparison of ELH with the fifth-order monotonicity preserving method MP5 (Suresh and Huynh in J. Comput. Phys. 136(1):83-99, 1997, doi: 10.1006/jcph.1997.5745), one of the most common high-order schemes currently employed in numerical-relativity simulations. We find that ELH achieves comparable and, in many of the cases studied here, better accuracy than more traditional methods at a fraction of the computational cost (up to {˜}50% speedup). Given its accuracy and its simplicity of implementation, ELH is a promising framework for the development of new special- and general-relativistic hydrodynamics codes well adapted for massively parallel supercomputers.
Anthony Papadopoulos
2009-01-01
The first-degree power-law polynomial function is frequently used to describe activity metabolism for steady swimming animals. This function has been used in hydrodynamics-based metabolic studies to evaluate important parameters of energetic costs, such as the standard metabolic rate and the drag power indices. In theory, however, the power-law polynomial function of any degree greater than one can be used to describe activity metabolism for steady swimming animals. In fact, activity metaboli...
Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics.
Strozzi, D J; Bailey, D S; Michel, P; Divol, L; Sepke, S M; Kerbel, G D; Thomas, C A; Ralph, J E; Moody, J D; Schneider, M B
2017-01-13
The effects of laser-plasma interactions (LPI) on the dynamics of inertial confinement fusion hohlraums are investigated via a new approach that self-consistently couples reduced LPI models into radiation-hydrodynamics numerical codes. The interplay between hydrodynamics and LPI-specifically stimulated Raman scatter and crossed-beam energy transfer (CBET)-mostly occurs via momentum and energy deposition into Langmuir and ion acoustic waves. This spatially redistributes energy coupling to the target, which affects the background plasma conditions and thus, modifies laser propagation. This model shows reduced CBET and significant laser energy depletion by Langmuir waves, which reduce the discrepancy between modeling and data from hohlraum experiments on wall x-ray emission and capsule implosion shape.
Lukerchenko, Nikolay
2010-01-01
The drag torque, drag force and Magnus force acting on a spheroid rotating around its axis of symmetry and moving perpendicularly to this axis in initially quiescent water were studied using experimental data and numerical simulation. The prolate spheroid with ratio of the axes 4/3 was speeded up in special device, which ensured the required rotational and translational velocity in the given plane. A video system was used to record the spheroid motion in water. Using the video records the sph...
Lukerchenko, Nikolay
2010-01-01
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The dimensionless drag force, Magnus force, and drag torque coefficients were determined from the comparison of the calculated translational and angular velocities and trajectory with experimental ones for the rough particle. The proper value of the correction coefficients were established from condition of the best fittin...
Experimental measurement and CFD simulation on the hydrodynamics of an internal-loop airlift reactor
Directory of Open Access Journals (Sweden)
Liew Shi Yan
2017-01-01
Full Text Available This paper concerns with the experimental measurement and computational fluid dynamics simulation on local hydrodynamics of a gas-liquid internal-loop airlift reactor. The aim of this work is to study the sensitivity of the drag models and the significance of considering the lift force on the predictive accuracy of the simulation. The experimental analysis was carried out using laser Doppler anemometry at three different heights (i.e. Y = 0.20 m, 0.30 m and 0.38 m across the riser and downcomerat volumetric flow rate of 0.30 m3/h to provide validation for the simulation results. A transient three-dimensional gasliquid internal-loop airlift reactor was carried out using FLUENT 16.2 by implementing the two-fluid model approach. The Eulerian-Eulerian multiphase and standard κ-ε dispersed turbulence model wereemployed in this study. Results suggest that the spherical drag model performed poorly and that the drag model governed by Rayleigh-Taylor shows promising accuracy in the prediction of overall mean axial liquid velocity. On the other hand, the consideration of lift model shows slightly improvement in accuracy. These findings may serve as a guidance for future scale-up and design of airlift reactor studies
Sagong, Woong; Jeon, Woo-Pyung; Choi, Haecheon
2013-01-01
The sailfish and swordfish are known as the fastest sea animals, reaching their maximum speeds of around 100 km/h. In the present study, we investigate the hydrodynamic characteristics of these fishes in their cruise speeds of about 1 body length per second. We install a taxidermy specimen of each fish in a wind tunnel, and measure the drag on its body and boundary-layer velocity above its body surface at the Reynolds number corresponding to its cruising condition. The drag coefficients of the sailfish and swordfish based on the free-stream velocity and their wetted areas are measured to be 0.0075 and 0.0091, respectively, at their cruising conditions. These drag coefficients are very low and comparable to those of tuna and pike and smaller than those of dogfish and small-size trout. On the other hand, the long bill is one of the most distinguished features of these fishes from other fishes, and we study its role on the ability of drag modification. The drag on the fish without the bill or with an artificially-made shorter one is slightly smaller than that with the original bill, indicating that the bill itself does not contribute to any drag reduction at its cruise speed. From the velocity measurement near the body surface, we find that at the cruise speed flow separation does not occur over the whole body even without the bill, and the boundary layer flow is affected only at the anterior part of the body by the bill.
Directory of Open Access Journals (Sweden)
Woong Sagong
Full Text Available The sailfish and swordfish are known as the fastest sea animals, reaching their maximum speeds of around 100 km/h. In the present study, we investigate the hydrodynamic characteristics of these fishes in their cruise speeds of about 1 body length per second. We install a taxidermy specimen of each fish in a wind tunnel, and measure the drag on its body and boundary-layer velocity above its body surface at the Reynolds number corresponding to its cruising condition. The drag coefficients of the sailfish and swordfish based on the free-stream velocity and their wetted areas are measured to be 0.0075 and 0.0091, respectively, at their cruising conditions. These drag coefficients are very low and comparable to those of tuna and pike and smaller than those of dogfish and small-size trout. On the other hand, the long bill is one of the most distinguished features of these fishes from other fishes, and we study its role on the ability of drag modification. The drag on the fish without the bill or with an artificially-made shorter one is slightly smaller than that with the original bill, indicating that the bill itself does not contribute to any drag reduction at its cruise speed. From the velocity measurement near the body surface, we find that at the cruise speed flow separation does not occur over the whole body even without the bill, and the boundary layer flow is affected only at the anterior part of the body by the bill.
Annual Report: Hydrodynamics and Radiative Hydrodynamics with Astrophysical Applications
Energy Technology Data Exchange (ETDEWEB)
R. Paul Drake
2005-12-01
We report the ongoing work of our group in hydrodynamics and radiative hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining high-quality scaling data using a backlit pinhole and obtaining the first (ever, anywhere) Thomson-scattering data from a radiative shock. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, obtaining the first (ever, anywhere) dual-axis radiographic data using backlit pinholes and ungated detectors. All these experiments have applications to astrophysics, discussed in the corresponding papers either in print or in preparation. We also have obtained preliminary radiographs of experimental targets using our x-ray source. The targets for the experiments have been assembled at Michigan, where we also prepare many of the simple components. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.
Air-Induced Drag Reduction at High Reynolds Numbers: Velocity and Void Fraction Profiles
Elbing, Brian; Mäkiharju, Simo; Wiggins, Andrew; Dowling, David; Perlin, Marc; Ceccio, Steven
2010-11-01
The injection of air into a turbulent boundary layer forming over a flat plate can reduce the skin friction. With sufficient volumetric fluxes an air layer can separate the solid surface from the flowing liquid, which can produce drag reduction in excess of 80%. Several large scale experiments have been conducted at the US Navy's Large Cavitation Channel on a 12.9 m long flat plate model investigating bubble drag reduction (BDR), air layer drag reduction (ALDR) and the transition between BDR and ALDR. The most recent experiment acquired phase velocities and void fraction profiles at three downstream locations (3.6, 5.9 and 10.6 m downstream from the model leading edge) for a single flow speed (˜6.4 m/s). The profiles were acquired with a combination of electrode point probes, time-of-flight sensors, Pitot tubes and an LDV system. Additional diagnostics included skin-friction sensors and flow-field image visualization. During this experiment the inlet flow was perturbed with vortex generators immediately upstream of the injection location to assess the robustness of the air layer. From these, and prior measurements, computational models can be refined to help assess the viability of ALDR for full-scale ship applications.
On the Application of Contour Bumps for Transonic Drag Reduction(Invited)
Milholen, William E., II; Owens, Lewis R.
2005-01-01
The effect of discrete contour bumps on reducing the transonic drag at off-design conditions on an airfoil have been examined. The research focused on fully-turbulent flow conditions, at a realistic flight chord Reynolds number of 30 million. State-of-the-art computational fluid dynamics methods were used to design a new baseline airfoil, and a family of fixed contour bumps. The new configurations were experimentally evaluated in the 0.3-m Transonic Cryogenic Tunnel at the NASA Langley Research center, which utilizes an adaptive wall test section to minimize wall interference. The computational study showed that transonic drag reduction, on the order of 12% - 15%, was possible using a surface contour bump to spread a normal shock wave. The computational study also indicated that the divergence drag Mach number was increased for the contour bump applications. Preliminary analysis of the experimental data showed a similar contour bump effect, but this data needed to be further analyzed for residual wall interference corrections.
Nation Drag: Uses of the Exotic
Directory of Open Access Journals (Sweden)
Micol Seigel
2009-02-01
Full Text Available In Uneven Encounters, the forthcoming book from which this article is excerpted, Micol Seigel chronicles the exchange of popular culture between Brazil and the United States in the years between the World Wars, and she demonstrates how that exchange affected ideas of race and nation in both countries. From Americans interpreting advertisements for Brazilian coffee or dancing the Brazilian maxixe, to Rio musicians embracing the “foreign” qualities of jazz, Seigel traces a lively, cultural back-and-forth. Along the way, she shows how race and nation are constructed together, by both non-elites and elites, and gleaned from global cultural and intellectual currents as well as local, regional, and national ones. Seigel explores the circulation of images of Brazilian coffee and of maxixe in the United States during the period just after the imperial expansions of the early twentieth century. Exoticist interpretations structured North Americans’ paradoxical sense of self as productive “consumer citizens.” Some people, however, could not simply assume the privileges of citizenship. In their struggles against racism, Afro-descended citizens living in the cities of Rio de Janeiro, São Paulo, New York, and Chicago encountered images and notions of each other, and found them useful. Seigel introduces readers to cosmopolitan Afro-Brazilians and African Americans who rarely traveled far but who absorbed ideas from abroad nonetheless. African American vaudeville artists saw the utility of pretending to “be” Brazilian to cross the color line on stage. Putting on “nation drag,” they passed not from one race to another but out of familiar racial categories entirely. Afro-Brazilian journalists reported intensively on foreign, particularly North American, news and eventually entered into conversation with the U.S. black press in a collaborative but still conflictual dialogue. Seigel suggests that projects comparing U.S. and Brazilian racial
Progress in smooth particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Wingate, C.A.; Dilts, G.A.; Mandell, D.A.; Crotzer, L.A.; Knapp, C.E.
1998-07-01
Smooth Particle Hydrodynamics (SPH) is a meshless, Lagrangian numerical method for hydrodynamics calculations where calculational elements are fuzzy particles which move according to the hydrodynamic equations of motion. Each particle carries local values of density, temperature, pressure and other hydrodynamic parameters. A major advantage of SPH is that it is meshless, thus large deformation calculations can be easily done with no connectivity complications. Interface positions are known and there are no problems with advecting quantities through a mesh that typical Eulerian codes have. These underlying SPH features make fracture physics easy and natural and in fact, much of the applications work revolves around simulating fracture. Debris particles from impacts can be easily transported across large voids with SPH. While SPH has considerable promise, there are some problems inherent in the technique that have so far limited its usefulness. The most serious problem is the well known instability in tension leading to particle clumping and numerical fracture. Another problem is that the SPH interpolation is only correct when particles are uniformly spaced a half particle apart leading to incorrect strain rates, accelerations and other quantities for general particle distributions. SPH calculations are also sensitive to particle locations. The standard artificial viscosity treatment in SPH leads to spurious viscosity in shear flows. This paper will demonstrate solutions for these problems that they and others have been developing. The most promising is to replace the SPH interpolant with the moving least squares (MLS) interpolant invented by Lancaster and Salkauskas in 1981. SPH and MLS are closely related with MLS being essentially SPH with corrected particle volumes. When formulated correctly, JLS is conservative, stable in both compression and tension, does not have the SPH boundary problems and is not sensitive to particle placement. The other approach to
Students’ conceptual difficulties in hydrodynamics
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Alvaro Suarez
2017-11-01
Full Text Available We describe a study on the conceptual difficulties faced by college students in understanding hydrodynamics of ideal fluids. This study was based on responses obtained in hundreds of written exams complemented with several oral interviews, which were held with first-year engineering and science university students. Their responses allowed us to identify a series of misconceptions unreported in the literature so far. The study findings demonstrate that the most critical difficulties arise from the students’ inability to establish a link between the kinematics and dynamics of moving fluids, and from a lack of understanding regarding how different regions of a system interact.
Students' conceptual difficulties in hydrodynamics
Suarez, Alvaro; Kahan, Sandra; Zavala, Genaro; Marti, Arturo C.
2017-12-01
We describe a study on the conceptual difficulties faced by college students in understanding hydrodynamics of ideal fluids. This study was based on responses obtained in hundreds of written exams complemented with several oral interviews, which were held with first-year engineering and science university students. Their responses allowed us to identify a series of misconceptions unreported in the literature so far. The study findings demonstrate that the most critical difficulties arise from the students' inability to establish a link between the kinematics and dynamics of moving fluids, and from a lack of understanding regarding how different regions of a system interact.
Hydrodynamic characteristics of UASB bioreactors.
John, Siby; Tare, Vinod
2011-10-01
The hydrodynamic characteristics of UASB bioreactors operated under different organic loading and hydraulic loading rates were studied, using three laboratory scale models treating concocted sucrose wastewater. Residence time distribution (RTD) analysis using dispersion model and tanks-in-series model was directed towards the characterization of the fluid flow pattern in the reactors and correlation of the hydraulic regime with the biomass content and biogas production. Empty bed reactors followed a plug flow pattern and the flow pattern changed to a large dispersion mixing with biomass and gas production. Effect of increase in gas production on the overall hydraulics was insignificant.
Hydrodynamic loading of tensegrity structures
Wroldsen, Anders S.; Johansen, Vegar; Skelton, Robert E.; Sørensen, Asgeir J.
2006-03-01
This paper introduces hydrodynamic loads for tensegrity structures, to examine their behavior in marine environments. Wave compliant structures are of general interest when considering large marine structures, and we are motivated by the aquaculture industry where new concepts are investigated in order to make offshore installations for seafood production. This paper adds to the existing models and software simulations of tensegrity structures exposed to environmental loading from waves and current. A number of simulations are run to show behavior of the structure as a function of pretension level and string stiffness for a given loading condition.
Numerical Hydrodynamics in General Relativity
Directory of Open Access Journals (Sweden)
Font José A.
2000-05-01
Full Text Available The current status of numerical solutions for the equations of ideal general relativistic hydrodynamics is reviewed. Different formulations of the equations are presented, with special mention of conservative and hyperbolic formulations well-adapted to advanced numerical methods. A representative sample of available numerical schemes is discussed and particular emphasis is paid to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. A comprehensive summary of relevant astrophysical simulations in strong gravitational fields, including gravitational collapse, accretion onto black holes and evolution of neutron stars, is also presented.
Hydrodynamics and stellar winds an introduction
Maciel, Walter J
2014-01-01
Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.
Hydrodynamic Properties of Planing Surfaces and Flying Boats
Sokolov, N. A.
1950-01-01
The study of the hydrodynamic properties of planing bottom of flying boats and seaplane floats is at the present time based exclusively on the curves of towing tests conducted in tanks. In order to provide a rational basis for the test procedure in tanks and practical design data, a theoretical study must be made of the flow at the step and relations derived that show not only qualitatively but quantitatively the inter-relations of the various factors involved. The general solution of the problem of the development of hydrodynamic forces during the motion of the seaplane float or flying boat is very difficult for it is necessary to give a three-dimensional solution, which does not always permit reducing the analysis to the form of workable computation formulas. On the other had, the problem is complicated by the fact that the object of the analysis is concerned with two fluid mediums, namely, air and water, which have a surface of density discontinuity between them. The theoretical and experimental investigations on the hydrodynamics of a ship cannot be completely carried over to the design of floats and flying-boat hulls, because of the difference in the shape of the contour lines of the bodies, and, because of the entirely different flow conditions from the hydrodynamic viewpoint.
Microscale Electro-Hydrodynamic Cell Printing with High Viability.
He, Jiankang; Zhao, Xiang; Chang, Jinke; Li, Dichen
2017-12-01
Cell printing has gained extensive attentions for the controlled fabrication of living cellular constructs in vitro. Various cell printing techniques are now being explored and developed for improved cell viability and printing resolution. Here an electro-hydrodynamic cell printing strategy is developed with microscale resolution (95%). Unlike the existing electro-hydrodynamic cell jetting or printing explorations, insulating substrate is used to replace conventional semiconductive substrate as the collecting surface which significantly reduces the electrical current in the electro-hydrodynamic printing process from milliamperes (>0.5 mA) to microamperes (printed cells. The smallest width of the electro-hydrodynamically printed hydrogel filament is 82.4 ± 14.3 µm by optimizing process parameters. Multiple hydrogels or multilayer cell-laden constructs can be flexibly printed under cell-friendly conditions. The printed cells in multilayer hydrogels kept alive and gradually spread during 7-days culture in vitro. This exploration offers a novel and promising cell printing strategy which might benefit future biomedical innovations such as microscale tissue engineering, organ-on-a-chip systems, and nanomedicine. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Effect of Drag-Reducing Polymer Injection on the Lift and Drag of a Two- Dimensional Hydrofoil
1974-09-01
Engineering Analysis of Cargo Handling-UX, Allocation of Containers in a Trade Route," F. Cesar Toecano, Report 60-110, December 1960, 35 p. 17. "An... Vallejo September 12, 1973 "Project Risk anagsemnt II," Management Seminar, Mare Island Naval Shipyard, Vallejo , California November 15, 1973...Management I1," Management Sednar, Mare Island Naval Shipyard, Vallejo , California December 27, 1973 34 Other Presentations A. H. Feller "Computer
Tang, Hao; Hu, Fuxiang; Xu, Liuxiong; Dong, Shuchuang; Zhou, Cheng; Wang, Xuefang
2017-10-01
Knotless polyethylene (PE) netting has been widely used in aquaculture cages and fishing gears, especially in Japan. In this study, the hydrodynamic coefficient of six knotless PE netting panels with different solidity ratios were assessed in a flume tank under various attack angles of netting from 0° (parallel to flow) to 90° (perpendicular to flow) and current speeds from 40 cm s-1 to 130 cm s-1. It was found that the drag coefficient was related to Reynolds number, solidity ratio and attack angle of netting. The solidity ratio was positively related with drag coefficient for netting panel perpendicular to flow, whereas when setting the netting panel parallel to the flow the opposite result was obtained. For netting panels placed at an angle to the flow, the lift coefficient reached the maximum at an attack angle of 50° and then decreased as the attack angle further increased. The solidity ratio had a dual influence on drag coefficient of inclined netting panels. Compared to result in the literature, the normal drag coefficient of knotless PE netting measured in this study is larger than that of nylon netting or Dyneema netting.
Drag phenomena within a torque converter driven automotive transmission - laminar flow approach
Alexa, O.; Marinescu, M.; Olaru, Gh; Costache, D.; Ilie, C. O.; Vinturis, V.
2015-11-01
When discussing a torque converter driven, automotive transmission with respect to the vehicle's coasting mode, automotive engineers have to take into account the slip between the converter's propeller and turbine. If the turbine isn't locked to the propellers during coasting process, drag phenomena within the converter's fluid occur and they have to be properly assessed when computing the coasting process dynamics. The best way to make the needed evaluation is to have a separate torque converter and test it on a test bench, if the data provided by the manufacturer, in this respect, weren't available. But there are several issues that could baffle this action. Among them, one could find the lack of information from the manufacturer, missing (bankrupted) manufacturer, classified information, old (out of date) products and so on. An even more challenging situation consists in dealing with a military special vehicle. Actually, the vehicle that would be subjected to the following topic is a military tracked, heavy vehicle (MBT) with a planetary driveline, driven by its engine via a hydraulic torque converter. In the attempt to assess its’ coasting dynamic performances, we faced the problem of the reverse rotation of the torque converter that strongly influences the general drag of the vehicle's motion. Hence, this paper tries to provide a method to determine the transmission overall drag considering the torque converter as being its main contributor. The method is based on the experimental research our team has performed in the last several months. Using high-quality software and adjacent mathematics while assuming a certain sort of flow type within the torque converter, we aimed at determining the parameter of interest of the flow. The method can be successfully used for all type of hydrodynamic components of the transmission under the condition of developing the necessary experimental research. As far as the test were concerned, they were the typical ones designed
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.
Energy Technology Data Exchange (ETDEWEB)
Myong, H.K. [Kookmin University, Seoul (Korea, Republic of)
1998-10-01
A low-Reynolds-number k-{epsilon} turbulence model is applied to predict drag reduction performance for actual L-shaped (blade-type) riblets with finite-thickness in fully-developed flows between infinite parallel planes. The present turbulence model is a modified version of the Launder & Sharma`s k-{epsilon} model (LS model), in which the gradient production term in {epsilon}-equation is modeled to have only the normal derivative terms. The present predictions for drag reduction behavior such as the maximum drag reduction and effects of riblets on turbulence quantities are in good agreement with both the experiments and the recent DNS results: differences in the mean velocity profile and turbulent quantities are found to be limited to the riblet cavity region. Turbulence quantities are also reduced in drag-reducing configurations. Possible shortcomings in the present model using an isotropic turbulent viscosity are also discussed particularly with reference to the absence of any turbulence-driven secondary motions. (author). 14 refs., 9 figs.
Ferapontov, E. V.
2001-01-01
Hydrodynamic surfaces are solutions of hydrodynamic type systems viewed as non-parametrized submanifolds of the hodograph space. We propose an invariant differential-geometric characterization of hydrodynamic surfaces by expressing the curvature form of the characteristic web in terms of the reciprocal invariants.
Fluctuating hydrodynamics for ionic liquids
Energy Technology Data Exchange (ETDEWEB)
Lazaridis, Konstantinos [Department of Mathematics and Statistics, Washington State University, Pullman, 99163 (United States); Wickham, Logan [Department of Computer Science, Washington State University, Richland, 99354 (United States); Voulgarakis, Nikolaos, E-mail: n.voulgarakis@wsu.edu [Department of Mathematics and Statistics, Washington State University, Pullman, 99163 (United States)
2017-04-25
We present a mean-field fluctuating hydrodynamics (FHD) method for studying the structural and transport properties of ionic liquids in bulk and near electrified surfaces. The free energy of the system consists of two competing terms: (1) a Landau–Lifshitz functional that models the spontaneous separation of the ionic groups, and (2) the standard mean-field electrostatic interaction between the ions in the liquid. The numerical approach used to solve the resulting FHD-Poisson equations is very efficient and models thermal fluctuations with remarkable accuracy. Such density fluctuations are sufficiently strong to excite the experimentally observed spontaneous formation of liquid nano-domains. Statistical analysis of our simulations provides quantitative information about the properties of ionic liquids, such as the mixing quality, stability, and the size of the nano-domains. Our model, thus, can be adequately parameterized by directly comparing our prediction with experimental measurements and all-atom simulations. Conclusively, this work can serve as a practical mathematical tool for testing various theories and designing more efficient mixtures of ionic liquids. - Highlights: • A new fluctuating hydrodynamics method for ionic liquids. • Description of ionic liquid morphology in bulk and near electrified surfaces. • Direct comparison with experimental measurements.
Hydromechanical transmission with hydrodynamic drive
Orshansky, Jr., deceased, Elias; Weseloh, William E.
1979-01-01
This transmission has a first planetary gear assembly having first input means connected to an input shaft, first output means, and first reaction means, and a second planetary gear assembly having second input means connected to the first input means, second output means, and second reaction means connected directly to the first reaction means by a reaction shaft. First clutch means, when engaged, connect the first output means to an output shaft in a high driving range. A hydrodynamic drive is used; for example, a torque converter, which may or may not have a stationary case, has a pump connected to the second output means, a stator grounded by an overrunning clutch to the case, and a turbine connected to an output member, and may be used in a starting phase. Alternatively, a fluid coupling or other type of hydrodynamic drive may be used. Second clutch means, when engaged, for connecting the output member to the output shaft in a low driving range. A variable-displacement hydraulic unit is mechanically connected to the input shaft, and a fixed-displacement hydraulic unit is mechanically connected to the reaction shaft. The hydraulic units are hydraulically connected together so that when one operates as a pump the other acts as a motor, and vice versa. Both clutch means are connected to the output shaft through a forward-reverse shift arrangement. It is possible to lock out the torque converter after the starting phase is over.
Inducer Hydrodynamic Load Measurement Devices
Skelley, Stephen E.; Zoladz, Thomas F.
2002-01-01
Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This "rotating balance" was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining both the amplitude and frequency content associated with operating in various cavitation modes. The second device - a high frequency response pressure transducer surface mounted on a rotating component - was merely an extension of existing technology for application in water. MSFC has recently completed experimental evaluations of both the rotating balance and surface-mount transducers in a water test loop. The measurement bandwidth of the rotating balance was severely limited by the relative flexibility of the device itself, resulting in an unexpectedly low structural bending mode and invalidating the higher frequency response data. Despite these limitations, measurements confirmed that the integrated loads on the four-bladed inducer respond to both cavitation intensity and cavitation phenomena. Likewise, the surface-mount pressure transducers were subjected to a range of temperatures and flow conditions in a non-rotating environment to record bias shifts and transfer functions between the transducers and a reference device. The pressure transducer static performance was within manufacturer's specifications and dynamic response accurately followed that of the reference.
Physical phantom of craniospinal hydrodynamics.
Bouzerar, R; Czosnyka, M; Czosnyka, Z; Balédent, Olivier
2012-01-01
Inside the craniospinal system, blood, and cerebrospinal fluid (CSF) interactions occurring through volume exchanges are still not well understood. We built a physical model of this global hydrodynamic system. The main objective was to study, in controlled conditions, CSF-blood interactions to better understand the phenomenon underlying pathogenesis of hydrocephalus. A structure representing the cranium is connected to the spinal channel. The cranium is divided into compartments mimicking anatomical regions such as ventricles or aqueduct cerebri. Resistive and compliant characteristics of blood and CSF compartments can be assessed or measured using pressure and flow sensors incorporated in the model. An arterial blood flow input is generated by a programmable pump. Flows and pressures inside the system are simultaneously recorded. Preliminary results show that the model can mimic venous and CSF flows in response to arterial pressure input. Pulse waveforms and volume flows were measured and confirmed that they partially replicated the data previously obtained with phase-contrast magnetic resonance imaging. The phantom shows that CSF oscillations directly result from arteriovenous flow, and intracranial pressure measurements show that the model obeys an exponential relationship between pressure and intracranial volume expansion. The phantom will be useful to investigate the hydrodynamic hypotheses underlying development of hydrocephalus.
The hydrodynamics of lamprey locomotion
Leftwich, Megan C.
The lamprey, an anguilliform swimmer, propels itself by undulating most of its body. This type of swimming produces flow patterns that are highly three-dimensional in nature and not very well understood. However, substantial previous work has been done to understand two-dimensional unsteady propulsion, the possible wake structures and thrust performance. Limited studies of three-dimensional propulsors with simple geometries have displayed the importance of the third dimension in designing unsteady swimmers. Some of the results of those studies, primarily the ways in which vorticity is organized in the wake region, are seen in lamprey swimming as well. In the current work, the third dimension is not the only important factor, but complex geometry and body undulations also contribute to the hydrodynamics. Through dye flow visualization, particle induced velocimetry and pressure measurements, the hydrodynamics of anguilliform swimming are studied using a custom built robotic lamprey. These studies all indicate that the undulations of the body are not producing thrust. Instead, it is the tail which acts to propel the animal. This conclusion led to further investigation of the tail, specifically the role of varying tail flexibility on hydrodymnamics. It is found that by making the tail more flexible, one decreases the coherence of the vorticity in the lamprey's wake. Additional flexibility also yields less thrust.
Hydrodynamic instability of meandering channels
Ali, Sk Zeeshan; Dey, Subhasish
2017-12-01
In this paper, we explore the hydrodynamic instability of meandering channels driven by the turbulent flow. The governing equations of channel dynamics with suitable boundary conditions are closed with the fluid and granular constitutive relationships. A regular expansion of the fundamental variables is employed to linearize the parent equations by superimposing the perturbations on the basic unperturbed flow. The channel dynamics reveal a resonance phenomenon which occurs when the key variables fall in the vicinity of the distinct critical values. The resonance phenomenon preserves its distinctive signature in different flow regimes which are guided by the characteristic values of the shear Reynolds number. The hydrodynamic analysis indicates that the fluid friction and the volumetric sediment flux play a decisive role to characterize the channel instability in different flow regimes. The growths of azimuthal velocity perturbation in phase with curvature, bed topography perturbation, bend amplification rate, and meander propagation speed in different flow regimes are investigated by varying the meander wavenumber, Shields number, channel aspect ratio, and relative roughness number. The analysis is capable to capture the effects of grain size on azimuthal velocity perturbation, bed topography perturbation, bend amplification rate, and meandering propagation speed over a wide range of shear Reynolds numbers. The variations of resonant wavenumbers in different flow regimes with the Shields number, channel aspect ratio, and relative roughness number are addressed. For a specific flow regime, the upstream and downstream migrations of meandering channels are typically governed by the Shields number, channel aspect ratio, and relative roughness number.
Nuclear Hydrodynamics with Viscosity and Heat Conduction.
Sedlak, Joseph Edmond
A one-dimensional, relativistic, hydrodynamic model is developed to study the effects of heat conduction in moderate energy heavy-ion collisions (1-30 MeV kinetic energy per particle in the center-of-mass frame). A simple argument is presented for the temperature and density dependences of the transport coefficients which enter the fluid equations. With a temperature dependent thermal conductivity, the heat equation is nonlinear. The solution to this equation is given and then is used to find expressions for the thermal relaxation time. The equation of state for infinite nuclear matter is discussed. A modification must be added to extend this to finite nuclei with diffuse surfaces: the inhomogeneity of the density affects the binding energy. This nonlocal correction is written as a volume integral of density differences weighted by the long range part of the nucleon-nucleon potential. It is demonstrated that an equation having the same form as the classical Euler equation can be derived from a quantum variational principle. By analogy, this equation indicates how the nonlocal binding energy correction leads to a nonlocal pressure. A review of the relativistic hydrodynamic equations is given. It is shown how the stress-energy tensor must be constructed to guarantee non-negative entropy production. The system of equations is solved numerically with various choices for the initial kinetic energy and the thermal conductivity. It is found that the conductivity has a strong influence on the evolution of the density distribution. When conductivity is included, the final kinetic energy is substantially reduced, and the critical initial kinetic energy, below which fusion occurs, changes from 1 MeV to 5 MeV per particle. These effects are interpreted by comparing the collision time to the thermal relaxation time.
Creating drag and lift curves from soccer trajectories
Goff, John Eric; Kelley, John; Hobson, Chad M.; Seo, Kazuya; Asai, Takeshi; Choppin, S. B.
2017-07-01
Trajectory analysis is an alternative to using wind tunnels to measure a soccer ball’s aerodynamic properties. It has advantages over wind tunnel testing such as being more representative of game play. However, previous work has not presented a method that produces complete, speed-dependent drag and lift coefficients. Four high-speed cameras in stereo-calibrated pairs were used to measure the spatial co-ordinates for 29 separate soccer trajectories. Those trajectories span a range of launch speeds from 9.3 to 29.9 m s-1. That range encompasses low-speed laminar flow of air over a soccer ball, through the drag crises where air flow is both laminar and turbulent, and up to high-speed turbulent air flow. Results from trajectory analysis were combined to give speed-dependent drag and lift coefficient curves for the entire range of speeds found in the 29 trajectories. The average root mean square error between the measured and modelled trajectory was 0.028 m horizontally and 0.034 m vertically. The drag and lift crises can be observed in the plots of drag and lift coefficients respectively.
Dusty gas with one fluid in smoothed particle hydrodynamics
Laibe, Guillaume; Price, Daniel J.
2014-05-01
In a companion paper we have shown how the equations describing gas and dust as two fluids coupled by a drag term can be re-formulated to describe the system as a single-fluid mixture. Here, we present a numerical implementation of the one-fluid dusty gas algorithm using smoothed particle hydrodynamics (SPH). The algorithm preserves the conservation properties of the SPH formalism. In particular, the total gas and dust mass, momentum, angular momentum and energy are all exactly conserved. Shock viscosity and conductivity terms are generalized to handle the two-phase mixture accordingly. The algorithm is benchmarked against a comprehensive suit of problems: DUSTYBOX, DUSTYWAVE, DUSTYSHOCK and DUSTYOSCILL, each of them addressing different properties of the method. We compare the performance of the one-fluid algorithm to the standard two-fluid approach. The one-fluid algorithm is found to solve both of the fundamental limitations of the two-fluid algorithm: it is no longer possible to concentrate dust below the resolution of the gas (they have the same resolution by definition), and the spatial resolution criterion h limitation is that it does not capture multi-streaming of dust in the limit of zero coupling, suggesting that in this case a hybrid approach may be required.
Directory of Open Access Journals (Sweden)
D. Vatvani
2012-07-01
Full Text Available To simulate winds and water levels, numerical weather prediction (NWP and storm surge models generally use the traditional bulk relation for wind stress, which is characterized by a wind drag coefficient. A still commonly used drag coefficient in those models, some of them were developed in the past, is based on a relation, according to which the magnitude of the coefficient is either constant or increases monotonically with increasing surface wind speed (Bender, 2007; Kim et al., 2008; Kohno and Higaki, 2006. The NWP and surge models are often tuned independently from each other in order to obtain good results. Observations have indicated that the magnitude of the drag coefficient levels off at a wind speed of about 30 m s^{−1}, and then decreases with further increase of the wind speed. Above a wind speed of approximately 30 m s^{−1}, the stress above the air-sea interface starts to saturate. To represent the reducing and levelling off of the drag coefficient, the original Charnock drag formulation has been extended with a correction term.
In line with the above, the Delft3D storm surge model is tested using both Charnock's and improved Makin's wind drag parameterization to evaluate the improvements on the storm surge model results, with and without inclusion of the wave effects. The effect of waves on storm surge is included by simultaneously simulating waves with the SWAN model on identical model grids in a coupled mode. However, the results presented here will focus on the storm surge results that include the wave effects.
The runs were carried out in the Gulf of Mexico for Katrina and Ivan hurricane events. The storm surge model was initially forced with H^{*}wind data (Powell et al., 2010 to test the effect of the Makin's wind drag parameterization on the storm surge model separately. The computed wind, water levels and waves are subsequently compared with observation data. Based on the good
On the energy economics of air lubrication drag reduction
Directory of Open Access Journals (Sweden)
Simo A. Mäkiharju
2012-12-01
Full Text Available Air lubrication techniques for frictional drag reduction on ships have been proposed by numerous researchers since the 19th century. However, these techniques have not been widely adopted as questions persist about their drag reduction performance beyond the laboratory, as well as energy and economic cost-benefit. This paper draws on data from the literature to consider the suitability of air lubrication for large ocean going and U.S. Great Lakes ships, by establishing the basic energy economic calculations and presenting results for a hypothetical air lubricated ship. All the assumptions made in the course of the analysis are clearly stated so that they can be refined when considering application of air lubrication to a specific ship. The analysis suggests that, if successfully implemented, both air layer and partial cavity drag reduction could lead to net energy savings of 10 to 20%, with corresponding reductions in emissions.
Separability of drag and thrust in undulatory animals and machines
Bale, Rahul; Neveln, Izaak D; Bhalla, Amneet Pal Singh; MacIver, Malcolm A; Patankar, Neelesh A
2014-01-01
For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal- istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation fram...
Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries
Howerton, Brian M.; Jones, Michael G.
2016-01-01
Interest in characterization of the aerodynamic drag of acoustic liners has increased in the past several years. This paper details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of centerline flow Mach number equals 0.3 and 0.5. Various perforate geometries and orientations are investigated to determine their resistance factors using a static pressure drop approach. Comparison of these resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 hertz at source sound pressure levels of 140 and 150 decibels. Educed impedance and attenuation spectra are used to determine the impact of variations in perforate geometry on acoustic performance.
Directory of Open Access Journals (Sweden)
Joung Tae-Hwan
2014-06-01
Full Text Available This paper examines the suitability of using the Computational Fluid Dynamics (CFD tools, ANSYSCFX, as an initial analysis tool for predicting the drag and propulsion performance (thrust and torque of a concept underwater vehicle design. In order to select an appropriate thruster that will achieve the required speed of the Underwater Disk Robot (UDR, the ANSYS-CFX tools were used to predict the drag force of the UDR. Vertical Planar Motion Mechanism (VPMM test simulations (i.e. pure heaving and pure pitching motion by CFD motion analysis were carried out with the CFD software. The CFD results reveal the distribution of hydrodynamic values (velocity, pressure, etc. of the UDR for these motion studies. Finally, CFD bollard pull test simulations were performed and compared with the experimental bollard pull test results conducted in a model basin. The experimental results confirm the suitability of using the ANSYS-CFX tools for predicting the behavior of concept vehicles early on in their design process.
Directory of Open Access Journals (Sweden)
Tae-Hwan Joung
2014-06-01
Full Text Available This paper examines the suitability of using the Computational Fluid Dynamics (CFD tools, ANSYS-CFX, as an initial analysis tool for predicting the drag and propulsion performance (thrust and torque of a concept underwater vehicle design. In order to select an appropriate thruster that will achieve the required speed of the Underwater Disk Robot (UDR, the ANSYS-CFX tools were used to predict the drag force of the UDR. Vertical Planar Motion Mechanism (VPMM test simulations (i.e. pure heaving and pure pitching motion by CFD motion analysis were carried out with the CFD software. The CFD results reveal the distribution of hydrodynamic values (velocity, pressure, etc. of the UDR for these motion studies. Finally, CFD bollard pull test simulations were performed and compared with the experimental bollard pull test results conducted in a model basin. The experimental results confirm the suitability of using the ANSYS-CFX tools for predicting the behavior of concept vehicles early on in their design process.
Johanning, L.; Bearman, P. W.; Graham, J. M. R.
2001-10-01
Measurements of the hydrodynamic damping acting on a vertical, 0.5 m diameter cylinder in planar oscillatory motion at Stokes parameter, β, up to 1.4×105are presented. The results are also shown as a variation of drag coefficient, Cd, with Keulegan-Carpenter number, KC, where the range of KC numbers studied is from 1×10-3to 1. The experiments were carried out in the Delta Flume at Delft Hydraulics Laboratories in Holland and the cylinder was mounted from a pendulum suspension system. The hydrodynamic damping is the sum of radiation damping, due to gravity waves generated by the cylinder piercing the water surface, and viscous damping. A frequency-domain solution from Dalrymple & Dean (1972) is used to predict the radiation damping. An estimate of the viscous damping is then obtained by subtracting the predicted radiation damping from the measured hydrodynamic damping. Results for the viscous damping derived in this way are found to be close to those expected from experimental studies carried out by Bearman & Russell (1996) and Chaplin & Subbiah (1996) to measure viscous damping on a submerged cylinder.
Unsteady hydrodynamic forces acting on a robotic hand and its flow field.
Takagi, Hideki; Nakashima, Motomu; Ozaki, Takashi; Matsuuchi, Kazuo
2013-07-26
This study aims to clarify the mechanism of generating unsteady hydrodynamic forces acting on a hand during swimming in order to directly measure the forces, pressure distribution, and flow field around the hand by using a robotic arm and particle image velocimetry (PIV). The robotic arm consisted of the trunk, shoulder, upper arm, forearm, and hand, and it was independently computer controllable in five degrees of freedom. The elbow-joint angle of the robotic arm was fixed at 90°, and the arm was moved in semicircles around the shoulder joint in a plane perpendicular to the water surface. Two-component PIV was used for flow visualization around the hand. The data of the forces and pressure acting on the hand were sampled at 200Hz and stored on a PC. When the maximum resultant force acting on the hand was observed, a pair of counter-rotating vortices appeared on the dorsal surface of the hand. A vortex attached to the hand increased the flow velocity, which led to decreased surface pressure, increasing the hydrodynamic forces. This phenomenon is known as the unsteady mechanism of force generation. We found that the drag force was 72% greater and the lift force was 4.8 times greater than the values estimated under steady flow conditions. Therefore, it is presumable that swimmers receive the benefits of this unsteady hydrodynamic force. Copyright © 2013 Elsevier Ltd. All rights reserved.
Aziz, A. M. Y.; Harun, M. N.; Syahrom, Ardiyansyah; Omar, A. H.
2017-04-01
This paper presents a study of the hydrodynamics of several rowing blade designs. The study was done using Computational Fluid Dynamics (CFD) which enabled the investigation to be done similar to the experimental study, but with additional hydrodynamic visualization for further analysis and understanding. The CFD method was validated using quasi-static experimental data from Caplan (2007). Besides that, the proposed CFD analyses have improved the precious CFD results with the percentage of error of 6.58 percent of lift and 0.69 percent of drag force compared to 33.65 and 18.75 percent obtained by Coppel (2010). Consequent to the successful validation, the study then proceeded with the real size of Macon, Big balde and Fat blade. It was found that the hydrodynamic performance of the Fat blade was the highest due to the area, aspect ratio and the shape of the blade. Besides that, distribution of pressure for all models were also investigated which deepened the understanding of the blade fluid mechanics of rowing.
Hydrodynamics, Fungal Physiology, and Morphology.
Serrano-Carreón, L; Galindo, E; Rocha-Valadéz, J A; Holguín-Salas, A; Corkidi, G
2015-01-01
Filamentous cultures, such as fungi and actinomycetes, contribute substantially to the pharmaceutical industry and to enzyme production, with an annual market of about 6 billion dollars. In mechanically stirred reactors, most frequently used in fermentation industry, microbial growth and metabolite productivity depend on complex interactions between hydrodynamics, oxygen transfer, and mycelial morphology. The dissipation of energy through mechanically stirring devices, either flasks or tanks, impacts both microbial growth through shearing forces on the cells and the transfer of mass and energy, improving the contact between phases (i.e., air bubbles and microorganisms) but also causing damage to the cells at high energy dissipation rates. Mechanical-induced signaling in the cells triggers the molecular responses to shear stress; however, the complete mechanism is not known. Volumetric power input and, more importantly, the energy dissipation/circulation function are the main parameters determining mycelial size, a phenomenon that can be explained by the interaction of mycelial aggregates and Kolmogorov eddies. The use of microparticles in fungal cultures is also a strategy to increase process productivity and reproducibility by controlling fungal morphology. In order to rigorously study the effects of hydrodynamics on the physiology of fungal microorganisms, it is necessary to rule out the possible associated effects of dissolved oxygen, something which has been reported scarcely. At the other hand, the processes of phase dispersion (including the suspended solid that is the filamentous biomass) are crucial in order to get an integral knowledge about biological and physicochemical interactions within the bioreactor. Digital image analysis is a powerful tool for getting relevant information in order to establish the mechanisms of mass transfer as well as to evaluate the viability of the mycelia. This review focuses on (a) the main characteristics of the two most
Aero-acoustics of Drag Generating Swirling Exhaust Flows
Shah, P. N.; Mobed, D.; Spakovszky, Z. S.; Brooks, T. F.; Humphreys, W. M. Jr.
2007-01-01
Aircraft on approach in high-drag and high-lift configuration create unsteady flow structures which inherently generate noise. For devices such as flaps, spoilers and the undercarriage there is a strong correlation between overall noise and drag such that, in the quest for quieter aircraft, one challenge is to generate drag at low noise levels. This paper presents a rigorous aero-acoustic assessment of a novel drag concept. The idea is that a swirling exhaust flow can yield a steady, and thus relatively quiet, streamwise vortex which is supported by a radial pressure gradient responsible for pressure drag. Flows with swirl are naturally limited by instabilities such as vortex breakdown. The paper presents a first aero-acoustic assessment of ram pressure driven swirling exhaust flows and their associated instabilities. The technical approach combines an in-depth aerodynamic analysis, plausibility arguments to qualitatively describe the nature of acoustic sources, and detailed, quantitative acoustic measurements using a medium aperture directional microphone array in combination with a previously established Deconvolution Approach for Mapping of Acoustic Sources (DAMAS). A model scale engine nacelle with stationary swirl vanes was designed and tested in the NASA Langley Quiet Flow Facility at a full-scale approach Mach number of 0.17. The analysis shows that the acoustic signature is comprised of quadrupole-type turbulent mixing noise of the swirling core flow and scattering noise from vane boundary layers and turbulent eddies of the burst vortex structure near sharp edges. The exposed edges are the nacelle and pylon trailing edge and the centerbody supporting the vanes. For the highest stable swirl angle setting a nacelle area based drag coefficient of 0.8 was achieved with a full-scale Overall Sound Pressure Level (OASPL) of about 40dBA at the ICAO approach certification point.
Hydrodynamics Versus Intracellular Coupling in the Synchronization of Eukaryotic Flagella
Quaranta, G.; Aubin, M.E.; Tam, D.S.W.
2015-01-01
The influence of hydrodynamic forces on eukaryotic flagella synchronization is investigated by triggering phase locking between a controlled external flow and the flagella of C. reinhardtii. Hydrodynamic forces required for synchronization are over an order of magnitude larger than hydrodynamic
Superhydrophobic copper tubes with possible flow enhancement and drag reduction.
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.
Nguyen, Nhan; James Urnes, Sr.
2012-01-01
Lightweight aircraft design has received a considerable attention in recent years as a means for improving cruise efficiency. Reducing aircraft weight results in lower lift requirements which directly translate into lower drag, hence reduced engine thrust requirements during cruise. The use of lightweight materials such as advanced composite materials has been adopted by airframe manufacturers in current and future aircraft. Modern lightweight materials can provide less structural rigidity while maintaining load-carrying capacity. As structural flexibility increases, aeroelastic interactions with aerodynamic forces and moments become an increasingly important consideration in aircraft design and aerodynamic performance. Furthermore, aeroelastic interactions with flight dynamics can result in issues with vehicle stability and control. Abstract This paper describes a recent aeroelastic modeling effort for an elastically shaped aircraft concept (ESAC). The aircraft model is based on the rigid-body generic transport model (GTM) originally developed at NASA Langley Research Center. The ESAC distinguishes itself from the GTM in that it is equipped with highly flexible wing structures as a weight reduction design feature. More significantly, the wings are outfitted with a novel control effector concept called variable camber continuous trailing edge (VCCTE) flap system for active control of wing aeroelastic deflections to optimize the local angle of attack of wing sections for improved aerodynamic efficiency through cruise drag reduction and lift enhancement during take-off and landing. The VCCTE flap is a multi-functional and aerodynamically efficient device capable of achieving high lift-to-drag ratios. The flap system is comprised of three chordwise segments that form the variable camber feature of the flap and multiple spanwise segments that form a piecewise continuous trailing edge. By configuring the flap camber and trailing edge shape, drag reduction could be
Locus of the apices of projectile trajectories under constant drag
Hernández-Saldaña, H.
2017-11-01
Using the hodograph method, we present an analytical solution for projectile coplanar motion under constant drag, parametrised by the velocity angle. We find the locus formed by the apices of the projectile trajectories, and discuss its implementation for the motion of a particle on an inclined plane in presence of Coulomb friction. The range and time of flight are obtained numerically, and we find that the optimal launching angle is smaller than in the drag-free case. This is a good example of a problem with constant dissipation of energy that includes curvature; it is appropriate for intermediate courses of mechanics.
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...
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)
Hydrodynamic enhanced dielectrophoretic particle trapping
Miles, Robin R.
2003-12-09
Hydrodynamic enhanced dielectrophoretic particle trapping carried out by introducing a side stream into the main stream to squeeze the fluid containing particles close to the electrodes producing the dielelectrophoretic forces. The region of most effective or the strongest forces in the manipulating fields of the electrodes producing the dielectrophoretic forces is close to the electrodes, within 100 .mu.m from the electrodes. The particle trapping arrangement uses a series of electrodes with an AC field placed between pairs of electrodes, which causes trapping of particles along the edges of the electrodes. By forcing an incoming flow stream containing cells and DNA, for example, close to the electrodes using another flow stream improves the efficiency of the DNA trapping.
Hydrodynamic Limit for Interacting Neurons
De Masi, A.; Galves, A.; Löcherbach, E.; Presutti, E.
2015-02-01
This paper studies the hydrodynamic limit of a stochastic process describing the time evolution of a system with N neurons with mean-field interactions produced both by chemical and by electrical synapses. This system can be informally described as follows. Each neuron spikes randomly following a point process with rate depending on its membrane potential. At its spiking time, the membrane potential of the spiking neuron is reset to the value 0 and, simultaneously, the membrane potentials of the other neurons are increased by an amount of potential . This mimics the effect of chemical synapses. Additionally, the effect of electrical synapses is represented by a deterministic drift of all the membrane potentials towards the average value of the system. We show that, as the system size N diverges, the distribution of membrane potentials becomes deterministic and is described by a limit density which obeys a non linear PDE which is a conservation law of hyperbolic type.
Staggered Schemes for Fluctuating Hydrodynamics
Balboa, F; Delgado-Buscalioni, R; Donev, A; Fai, T; Griffith, B; Peskin, C S
2011-01-01
We develop numerical schemes for solving the isothermal compressible and incompressible equations of fluctuating hydrodynamics on a grid with staggered momenta. We develop a second-order accurate spatial discretization of the diffusive, advective and stochastic fluxes that satisfies a discrete fluctuation-dissipation balance, and construct temporal discretizations that are at least second-order accurate in time deterministically and in a weak sense. Specifically, the methods reproduce the correct equilibrium covariances of the fluctuating fields to third (compressible) and second (incompressible) order in the time step, as we verify numerically. We apply our techniques to model recent experimental measurements of giant fluctuations in diffusively mixing fluids in a micro-gravity environment [A. Vailati et. al., Nature Communications 2:290, 2011]. Numerical results for the static spectrum of non-equilibrium concentration fluctuations are in excellent agreement between the compressible and incompressible simula...
Hydrodynamics of active permeating gels
Energy Technology Data Exchange (ETDEWEB)
Callan-Jones, A C [Laboratoire Charles Coulomb, UMR 5521 CNRS-UM2, Universite Montpellier II, 34095 Montpellier Cedex 5 (France); Juelicher, F, E-mail: andrew.callan-jones@univ-montp2.fr [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzerstrasse 38, 01187 Dresden (Germany)
2011-09-15
We develop a hydrodynamic theory of active permeating gels with viscoelasticity in which a polymer network is embedded in a background fluid. This situation is motivated by active processes in the cell cytoskeleton in which motor molecules generate elastic stresses in the network, which can drive permeation flows of the cytosol. Our approach differs from earlier ones by considering the elastic strain in the polymer network as a slowly relaxing dynamical variable. We first present the general ideas for the case of a passive, isotropic gel and then extend this description to a polar, active gel. We discuss two specific cases to illustrate the role of permeation in active gels: self-propulsion of a thin slab of gel relative to a substrate driven by filament polymerization and depolymerization; and non-equilibrium deswelling of a gel driven by molecular motors.
Anomalous hydrodynamics kicks neutron stars
Energy Technology Data Exchange (ETDEWEB)
Kaminski, Matthias, E-mail: mski@ua.edu [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487 (United States); Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 5C2 (Canada); Uhlemann, Christoph F. [Department of Physics, University of Washington, Seattle, WA 98195 (United States); Bleicher, Marcus [Frankfurt Institute for Advanced Studies, Goethe-Universität Frankfurt (Germany); Institut für Theoretische Physik, Goethe Universität Frankfurt (Germany); Schaffner-Bielich, Jürgen [Institut für Theoretische Physik, Goethe Universität Frankfurt (Germany)
2016-09-10
Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to a thousand kilometers per second. We argue that this remarkable effect can be explained as a manifestation of quantum anomalies on astrophysical scales. To theoretically describe the early stage in the life of neutron stars we use hydrodynamics as a systematic effective-field-theory framework. Within this framework, anomalies of the Standard Model of particle physics as underlying microscopic theory imply the presence of a particular set of transport terms, whose form is completely fixed by theoretical consistency. The resulting chiral transport effects in proto-neutron stars enhance neutrino emission along the internal magnetic field, and the recoil can explain the order of magnitude of the observed kick velocities.
Beijeren, H. van; Dorfman, J.R.
1980-01-01
We consider the flow of a dilute gas around a macroscopic heavy object. The state of the gas is described by an extended Boltzmann equation where the interactions between the gas molecules and the object are taken into account in computing the rate of change of the distribution function of the gas.
Hydrodynamic dispersion within porous biofilms
Davit, Y.
2013-01-23
Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher\\'s equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels\\' network; (2) the solute\\'s diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport. © 2013 American Physical Society.
The hydrodynamics of dolphin drafting
Directory of Open Access Journals (Sweden)
Weihs Daniel
2004-05-01
Full Text Available Abstract Background Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. Results Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers. Conclusions A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members.
Eghlima, Z.; Mansour, K.
2017-04-01
Drag reduction at high speed flows around blunt bodies is one of the major challenges in the field of aerodynamics. Using of spikes and counterflow jets each of them separately for reducing of drag force is well known. The present work is description of flow field around a hemispherical nose cylinder with a new combination of spike and counterflow jet at free stream of Mach number of 6.The air gas was injected through the nozzle at the nose of the hemispherical model at sonic speed. In this numerical analysis, axisymmetric Reynolds-averaged Navier-Stokes equations was solved by k-ω (SST) turbulence model. The results were validated with experimental results for spiked body without jet condition. Then the results presented for different lengths of spike and different pressures of counterflow jets. The results show a significant reduction in the drag coefficient about 86-90% compared to the spherical cylinder model without jet and spike for practical models (L/D=1.5 and 2). Furthermore also our results indicate that the drag reduction is increased even more with increasing of the length of the spike.
Colossal Seebeck effect enhanced by quasi-ballistic phonons dragging massive electrons in FeSb2.
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.
Directory of Open Access Journals (Sweden)
Gómez L. C.
2004-01-01
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.
Papadopoulos, Anthony
2009-01-01
The first-degree power-law polynomial function is frequently used to describe activity metabolism for steady swimming animals. This function has been used in hydrodynamics-based metabolic studies to evaluate important parameters of energetic costs, such as the standard metabolic rate and the drag power indices. In theory, however, the power-law polynomial function of any degree greater than one can be used to describe activity metabolism for steady swimming animals. In fact, activity metabolism has been described by the conventional exponential function and the cubic polynomial function, although only the power-law polynomial function models drag power since it conforms to hydrodynamic laws. Consequently, the first-degree power-law polynomial function yields incorrect parameter values of energetic costs if activity metabolism is governed by the power-law polynomial function of any degree greater than one. This issue is important in bioenergetics because correct comparisons of energetic costs among different steady swimming animals cannot be made unless the degree of the power-law polynomial function derives from activity metabolism. In other words, a hydrodynamics-based functional form of activity metabolism is a power-law polynomial function of any degree greater than or equal to one. Therefore, the degree of the power-law polynomial function should be treated as a parameter, not as a constant. This new treatment not only conforms to hydrodynamic laws, but also ensures correct comparisons of energetic costs among different steady swimming animals. Furthermore, the exponential power-law function, which is a new hydrodynamics-based functional form of activity metabolism, is a special case of the power-law polynomial function. Hence, the link between the hydrodynamics of steady swimming and the exponential-based metabolic model is defined.
Directory of Open Access Journals (Sweden)
Anthony Papadopoulos
Full Text Available The first-degree power-law polynomial function is frequently used to describe activity metabolism for steady swimming animals. This function has been used in hydrodynamics-based metabolic studies to evaluate important parameters of energetic costs, such as the standard metabolic rate and the drag power indices. In theory, however, the power-law polynomial function of any degree greater than one can be used to describe activity metabolism for steady swimming animals. In fact, activity metabolism has been described by the conventional exponential function and the cubic polynomial function, although only the power-law polynomial function models drag power since it conforms to hydrodynamic laws. Consequently, the first-degree power-law polynomial function yields incorrect parameter values of energetic costs if activity metabolism is governed by the power-law polynomial function of any degree greater than one. This issue is important in bioenergetics because correct comparisons of energetic costs among different steady swimming animals cannot be made unless the degree of the power-law polynomial function derives from activity metabolism. In other words, a hydrodynamics-based functional form of activity metabolism is a power-law polynomial function of any degree greater than or equal to one. Therefore, the degree of the power-law polynomial function should be treated as a parameter, not as a constant. This new treatment not only conforms to hydrodynamic laws, but also ensures correct comparisons of energetic costs among different steady swimming animals. Furthermore, the exponential power-law function, which is a new hydrodynamics-based functional form of activity metabolism, is a special case of the power-law polynomial function. Hence, the link between the hydrodynamics of steady swimming and the exponential-based metabolic model is defined.
Effect of Hydrodynamic Interactions on Reaction Rates in Membranes.
Oppenheimer, Naomi; Stone, Howard A
2017-07-25
The Brownian motion of two particles in three dimensions serves as a model for predicting the diffusion-limited reaction rate, as first discussed by von Smoluchowski. Deutch and Felderhof extended the calculation to account for hydrodynamic interactions between the particles and the target, which results in a reduction of the rate coefficient by about half. Many chemical reactions take place in quasi-two-dimensional systems, such as on the membrane or surface of a cell. We perform a Smoluchowski-like calculation in a quasi-two-dimensional geometry, i.e., a membrane surrounded by fluid, and account for hydrodynamic interactions between the particles. We show that rate coefficients are reduced relative to the case of no interactions. The reduction is more pronounced than the three-dimensional case due to the long-range nature of two-dimensional flows. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Drag and lift forces on particles in a rotating flow
Bluemink, J.J.; Lohse, Detlef; Prosperetti, Andrea; van Wijngaarden, L.; van Wijngaarden, L.
2010-01-01
A freely rotating sphere in a solid-body rotating flow is experimentally investigated. When the sphere is buoyant, it reaches an equilibrium position from which drag and lift coefficients are determined over a wide range of particle Reynolds numbers (2 ≤ Re ≤ 1060). The wake behind the sphere is
Drag power kite with very high lift coefficient
Bauer, F.; Kennel, R.M.; Hackl, C.M.; Campagnolo, F.; Patt, M.; Schmehl, R.
2018-01-01
As an alternative to conventional wind turbines, this study considered kites with onboard wind turbines driven by a high airspeed due to crosswind flight (“drag power”). The hypothesis of this study was, that if the kite's lift coefficient is maximized, then the power, energy yield, allowed costs
Experimental investigation of drag reduction by forward facing high ...
Indian Academy of Sciences (India)
Josyula et al. 2001; Hayashi & Asoy 2003; Balla Venukumar et al 2006). Drag reduction by counterflowing supersonic jet for a 60. ◦ apex angle blunt cone is investigated in the HST2 shock tunnel at a flow Mach number of 8. Some of the results ...
Drag force and surface roughness measurements on freshwater biofouled surfaces.
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.
Towards unified drag laws for inertial flow through fibrous materials
Yazdchi, K.; Luding, Stefan
2012-01-01
We give a comprehensive survey of published experimental, numerical and theoretical work on the drag law correlations for fluidized beds and flow through porous media, together with an attempt of systematization. Ranges of validity as well as limitations of commonly used relations (i.e. the Ergun
Drag reduction in bubbly Taylor-Couette turbulence
van den Berg, Th.H.; Luther, S.; Lathrop, Daniel P.; Lohse, Detlef
2005-01-01
In Taylor-Couette flow the total energy dissipation rate and therefore the drag can be determined by measuring the torque on the system. We do so for Reynolds numbers between Re=7×104 and Re=106 after having injected (i) small bubbles (R=1 mm) up to a volume concentration of α=5% and (ii) buoyant
Single Gradientless Light Beam Drags Particles as Tractor Beams
DEFF Research Database (Denmark)
Novitsky, Andrey; Qiu, Cheng-Wei; Wang, Haifeng
2011-01-01
is the strong nonparaxiality of the light beam, which contributes to the pulling force owing to momentum conservation. The nonparaxiality of the Bessel beam can be manipulated to possess a dragging force along both the radial longitudinal directions, i.e., a "tractor beam" with stable trajectories is achieved...
Separability of drag and thrust in undulatory animals and machines
Bale, Rahul; Shirgaonkar, Anup A.; Neveln, Izaak D.; Bhalla, Amneet Pal Singh; Maciver, Malcolm A.; Patankar, Neelesh A.
2014-12-01
For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal-istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation framework helps to predict the observed height of the ribbon fin of electric knifefish, a diverse group of neotropical fish which are an important model system in sensory neurobiology. We also show how drag-thrust separation leads to models that can predict the swimming velocity of an organism or a robotic vehicle.
The compressibility rule for drag of airfoil noses
Jones, R. T.; Vandyke, M. D.
1976-01-01
It is shown that the drag of any semi-infinite airfoil section in purely subsonic inviscid flow follows precisely the Prandtl-Glauert compressibility rule. The result for the parabola has application to leading edge corrections in thin airfoil theory.
Spacecraft Re-Entry Impact Point Targeting Using Aerodynamic Drag
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.
Plasmon-mediated Coulomb drag between graphene waveguides
DEFF Research Database (Denmark)
Shylau, Artsem A.; Jauho, Antti-Pekka
2014-01-01
We analyze theoretically charge transport in Coulomb coupled graphene waveguides (GWGs). The GWGs are defined using antidot lattices, and the lateral geometry bypasses many technological challenges of earlier designs. The drag resistivity ρD, which is a measure of the many-particle interactions...
Exploring the Aerodynamic Drag of a Moving Cyclist
Theilmann, Florian; Reinhard, Christopher
2016-01-01
Although the physics of cycling itself is a complex mixture of aerodynamics, physiology, mechanics, and heuristics, using cycling as a context for teaching physics has a tradition of certainly more than 30 years. Here, a possible feature is the discussion of the noticeable resistant forces such as aerodynamic drag and the associated power…
Drag force in a cold or hot granular medium
Seguin, A.; Gondret, P.
2017-09-01
We measure experimentally and analyze the resisting force exerted by a bidimensional packing of small disks on a larger intruder disk dragged horizontally at constant velocity V0. Depending on the vibration level of the packing that leads to a granular "cold" or "hot" packing, two force regimes are observed. At low vibration level ("cold" granular medium), the drag force F does not depend on V0, whereas for high vibrations ("hot" granular medium), the drag force increases linearly with V0. Both regimes can be understood by the balance of two "granular temperatures" that can be defined in the system: a bulk temperature Tb imposed by the external vibration to the overall packing and a local temperature T0 induced by the own motion of the intruder disk in its vicinity. All experimental data obtained for different sizes and velocities of the intruder disk are shown to be governed by the temperature ratio T0/Tb . A critical velocity V0 c, above which the system switches from "hot" to "cold," can be obtained in this frame. Finally, we discuss how these two "viscous" regimes should be followed by an inertial regime where the drag force F should increase as V0 2 at high enough velocity values, for V0 greater than a critical value V0 i corresponding to high enough Reynolds or Froude number.
Drag reduction by applying speedstrips on rowing oars
Kuyt, C. B.; Greidanus, A.J.; Westerweel, J.; Jansen, A.J.
2016-01-01
The objective of this study was to determine the advantage of the application of speedstrips to rowing oars for a lightweight single sculler. The research method comprehended three steps: (1) the analysis of the rowing oar movement, (2) the determination of the change in drag and (3) the
Experimental investigation of drag reduction by forward facing high ...
Indian Academy of Sciences (India)
... 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 ...
Biomimetic shark skin: design, fabrication and hydrodynamic function.
Wen, Li; Weaver, James C; Lauder, George V
2014-05-15
Although the functional properties of shark skin have been of considerable interest to both biologists and engineers because of the complex hydrodynamic effects of surface roughness, no study to date has successfully fabricated a flexible biomimetic shark skin that allows detailed study of hydrodynamic function. We present the first study of the design, fabrication and hydrodynamic testing of a synthetic, flexible, shark skin membrane. A three-dimensional (3D) model of shark skin denticles was constructed using micro-CT imaging of the skin of the shortfin mako (Isurus oxyrinchus). Using 3D printing, thousands of rigid synthetic shark denticles were placed on flexible membranes in a controlled, linear-arrayed pattern. This flexible 3D printed shark skin model was then tested in water using a robotic flapping device that allowed us to either hold the models in a stationary position or move them dynamically at their self-propelled swimming speed. Compared with a smooth control model without denticles, the 3D printed shark skin showed increased swimming speed with reduced energy consumption under certain motion programs. For example, at a heave frequency of 1.5 Hz and an amplitude of ± 1 cm, swimming speed increased by 6.6% and the energy cost-of-transport was reduced by 5.9%. In addition, a leading-edge vortex with greater vorticity than the smooth control was generated by the 3D printed shark skin, which may explain the increased swimming speeds. The ability to fabricate synthetic biomimetic shark skin opens up a wide array of possible manipulations of surface roughness parameters, and the ability to examine the hydrodynamic consequences of diverse skin denticle shapes present in different shark species. © 2014. Published by The Company of Biologists Ltd.
Low-Amplitude Ultrasound Enhances Hydrodynamic-Based Gene Delivery to Rat Kidney
Xing, Yifei; Pua, Eric C.; Lu, Xiaochun; Zhong, Pei
2009-01-01
The synergistic combination of hydrodynamics-based gene delivery and ultrasound was investigated to achieve improved gene transfer to the kidney. Plasmids encoding firefly luciferase and Erythropoietin (EPO) gene were delivered into the left kidney of rats by single or combinative application of renal vein hydrodynamic injection and ultrasound treatment with or without the addition of ultrasound contrast agents (UCA). Ultrasound exposure was found to enhance the efficiency of hydrodynamics-based gene delivery for both luciferase and EPO expression. An ultrasound exposure intensity of 2 W/cm2 at 10% duty cycle for 15 min., produced a maximal gene expression 4.5 times higher than hydrodynamic delivery alone. Duration, location, and tissue-specificity of gene expression were not changed by ultrasound exposure. Application of UCA reduced the intensity and exposure duration of ultrasound treatment needed for optimal expression. Appropriate application of ultrasound and UCA did not alter histological structure or impair physiological function of the treated kidney. PMID:19523454
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.
Tuning bacterial hydrodynamics with magnetic fields
Pierce, C. J.; Mumper, E.; Brown, E. E.; Brangham, J. T.; Lower, B. H.; Lower, S. K.; Yang, F. Y.; Sooryakumar, R.
2017-06-01
Magnetotactic bacteria are a group of motile prokaryotes that synthesize chains of lipid-bound, magnetic nanoparticles called magnetosomes. This study exploits their innate magnetism to investigate previously unexplored facets of bacterial hydrodynamics at surfaces. Through use of weak, uniform, external magnetic fields and local, micromagnetic surface patterns, the relative strength of hydrodynamic, magnetic, and flagellar force components is tuned through magnetic control of the bacteria's orientation. The resulting swimming behaviors provide a means to experimentally determine hydrodynamic parameters and offer a high degree of control over large numbers of living microscopic entities. The implications of this controlled motion for studies of bacterial motility near surfaces and for micro- and nanotechnology are discussed.
Boussinesq modeling of wave-induced hydrodynamics in coastal wetlands
Chakrabarti, Agnimitro; Brandt, Steven R.; Chen, Qin; Shi, Fengyan
2017-05-01
In this paper, an improved formulation of the vegetation drag force, applicable for the fully nonlinear Boussinesq equations and based on the use of the depth-varying, higher-order expansion of the horizontal velocity, in the quadratic vegetation drag law has been presented. The model uses the same numerical schemes as FUNWAVE TVD but is based on the CACTUS framework. The model is validated for wave height and setup, against laboratory experiments with and without vegetation cover. The wave attenuation results using the improved formulation were compared with those using the first-order reference velocity as well as with analytical solutions using linear wave theory. The analytical solution using the depth-varying velocity, predicted by the linear wave theory, was shown to match the model results with the fully expanded velocity approach very well for all wave cases, except under near-emergent and emergent conditions (when the ratio of stem height to water depth is greater than 0.75) and when the Ursell (Ur) number is less than 5. Simulations during peak storm waves, during Hurricane Isaac, showed that vegetation is very effective in reducing setup on platforms and in reducing the wave energy within the first few hundred meters.
Recent Progress in Polymer Drag Reduction
1974-10-01
polysaccharides as friction-reducing agents were reported [121; a linseed-gum extract gave approximately the rame friction-reduan« performance as the...polymers is the natural polysaccharide okra [37], which has the advantage of good compatibility with blood, having been used as a blood plasma...substitute. In pulsile flow, okra gives a good friction-reduction effect, extending to Reynolds numbers below the normal transition for Newtonian fluids
76 FR 34859 - Safety Zone; Augusta Southern Nationals Drag Boat Race, Savannah River, Augusta, GA
2011-06-15
... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; Augusta Southern Nationals Drag Boat Race... during the Augusta Southern Nationals Drag Boat Race. The Augusta Southern Nationals Drag Boat Race will consist of a series of high-speed boat races. The event is scheduled to take place from Thursday, July 14...
Hydrodynamic Instabilities Produced by Evaporation
Romo-Cruz, Julio Cesar Ruben; Hernandez-Zapata, Sergio; Ruiz-Chavarria, Gerardo
2012-11-01
When a liquid layer (alcohol in the present work) is in an environment where its relative humidity is less than 100 percent evaporation appears. When RH is above a certain threshold the liquid is at rest. If RH decreases below this threshold the flow becomes unstable, and hydrodynamic cells develop. The aim of this work is to understand the formation of those cells and its main features. Firstly, we investigate how the cell size depends on the layer width. We also study how temperature depends on the vertical coordinate when the cells are present. An inverse temperature gradient is found, that is, the bottom of liquid layer is colder than the free surface. This shows that the intuitive idea that the cells are due to a direct temperature gradient, following a Marangoni-like process, does not work. We propose the hypothesis that the evaporation produce a pressure gradient that is responsible of the cell development. On the other hand, using a Schlieren technique we study the topography of the free surface when cells are present. Finally the alcohol vapor layer adjacent to the liquid surface is explored using scattering experiments, giving some insight on the plausibility of the hypothesis described previously. Authors acknowledge support by DGAPA-UNAM under project IN116312 ``Vorticidad y ondas no lineales en fluidos.''
Hydrodynamics of unitary Fermi gases
Young, Ryan E.
Unitary fermi gases have been widely studied as they provide a tabletop archetype for re- search on strongly coupled many body systems and perfect fluids. Research into unitary fermi gases can provide insight into may other strongly interacting systems including high temperature superconductor, quark-gluon plasmas, and neutron stars. Within the unitary regime, the equilib- rium transport coefficients and thermodynamic properties are universal functions of density and temperature. Thus, unitary fermi gases provide a archetype to study nonperturbative many-body physics, which is of fundamental significance and crosses several fields. This thesis reports on two topics regarding unitary fermi gases. A recent string theory conjecture gives a lower bound for the dimensionless ratio of shear viscosity of entropy, η/s ≥ 4pi /kb . Unitary fermi gases are a candidate for prefect fluids, yet η/s is well above the string theory bound. Using a stochastic formulation of hydrodynamics, we calculate a lower bound for this ratio accounting for the momentum dissipation from fluctuations. This lower bound is in good agreement with both theoretical and experimental results. The second question addressed is the simulation of elliptic flow. Elliptic flow, first observed in 2002, is a characteristic of strongly coupled systems and has been studied in both quark-gluon plasmas and unitary fermi gases. As such, simulations of these systems are of interest. We test a variety of lattice Boltzmann models and compare the simulation results to the theoretical and experimental findings.
An implicit Smooth Particle Hydrodynamic code
Energy Technology Data Exchange (ETDEWEB)
Knapp, Charles E. [Univ. of New Mexico, Albuquerque, NM (United States)
2000-05-01
An implicit version of the Smooth Particle Hydrodynamic (SPH) code SPHINX has been written and is working. In conjunction with the SPHINX code the new implicit code models fluids and solids under a wide range of conditions. SPH codes are Lagrangian, meshless and use particles to model the fluids and solids. The implicit code makes use of the Krylov iterative techniques for solving large linear-systems and a Newton-Raphson method for non-linear corrections. It uses numerical derivatives to construct the Jacobian matrix. It uses sparse techniques to save on memory storage and to reduce the amount of computation. It is believed that this is the first implicit SPH code to use Newton-Krylov techniques, and is also the first implicit SPH code to model solids. A description of SPH and the techniques used in the implicit code are presented. Then, the results of a number of tests cases are discussed, which include a shock tube problem, a Rayleigh-Taylor problem, a breaking dam problem, and a single jet of gas problem. The results are shown to be in very good agreement with analytic solutions, experimental results, and the explicit SPHINX code. In the case of the single jet of gas case it has been demonstrated that the implicit code can do a problem in much shorter time than the explicit code. The problem was, however, very unphysical, but it does demonstrate the potential of the implicit code. It is a first step toward a useful implicit SPH code.
Hydrodynamic excitations in hot QCD plasma
Abbasi, Navid; Allahbakhshi, Davood; Davody, Ali; Taghavi, Seyed Farid
2017-12-01
We study the long wavelength excitations in rotating QCD fluid in the presence of an external magnetic field at finite vector and axial charge densities. We consider the fluctuations of vector and axial charge currents coupled to energy and momentum fluctuations and compute the S O (3 ) covariant dispersion relations of the six corresponding hydrodynamic modes. Among them, there are always two scalar chiral-magnetic-vortical-heat (CMVH) waves; in the absence of a magnetic field (vorticity) these waves reduce to chiral-vortical-heat (CVH) [chiral-magnetic-heat (CMH)] waves. While CMVH waves are a mixture of CMH and CVH waves, they have generally different velocities compared to the sum of velocities of the latter waves. The other four modes, which are made out of scalar-vector fluctuations, are mixed sound-Alfvén waves. We show that when the magnetic field is parallel with the vorticity, these four modes are the two ordinary sound modes together with two chiral Alfvén waves propagating along the common direction of the magnetic field and vorticity.
Anisotropic hydrodynamic function of dense confined colloids
Nygârd, Kim; Buitenhuis, Johan; Kagias, Matias; Jefimovs, Konstantins; Zontone, Federico; Chushkin, Yuriy
2017-06-01
Dense colloidal dispersions exhibit complex wave-vector-dependent diffusion, which is controlled by both direct particle interactions and indirect nonadditive hydrodynamic interactions mediated by the solvent. In bulk the hydrodynamic interactions are probed routinely, but in confined geometries their studies have been hitherto hindered by additional complications due to confining walls. Here we solve this issue by combining high-energy x-ray photon correlation spectroscopy and small-angle x-ray-scattering experiments on colloid-filled microfluidic channels to yield the confined fluid's hydrodynamic function in the short-time limit. Most importantly, we find the confined fluid to exhibit a strongly anisotropic hydrodynamic function, similar to its anisotropic structure factor. This observation is important in order to guide future theoretical research.
Polariton Superfluids Reveal Quantum Hydrodynamic Solitons
National Research Council Canada - National Science Library
A. Amo; S. Pigeon; D. Sanvitto; V. G. Sala; R. Hivet; I. Carusotto; F. Pisanello; G. Leménager; R. Houdré; E Giacobino; C. Ciuti; A. Bramati
2011-01-01
.... Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex...
Maldonado, S.; Suckale, J.; Ferreira, C.; Arkema, K.
2016-12-01
Increasing intensity and frequency of extreme meteorological events around the world highlight the need for resilient coastal defenses. For more than a century, it has been recognized that coastal ecosystems such as marshes and mangroves may mitigate the damage caused by natural hazards such as storms. Aquatic vegetation can potentially attenuate waves and currents through drag forces, with strong implications for sediment transport processes and hence morphological evolution. However, although observations exist that support such a theory, an accurate quantification of the protective role of coastal ecosystems remains a standing challenge for the scientific community, which manifests itself in the large, diverse set of available empirical expressions for parameterizing the fluid-vegetation interaction. We propose a comparison of different state-of-the-art parameterizations for the effect of vegetation on hydrodynamics (particularly, the drag coefficient), with varying degrees of complexity and number of required input variables. The inter-comparison of such alternatives, when validated against field data, can lead to a modeling framework that optimizes the trade-offs between complexity, input requirements and uncertainty in the results. We focus our numerical study on storm events in the marshes and wetlands of Chesapeake Bay. We simulate the hydrodynamics via the Non-Linear Shallow Water Equations, which are in turn solved numerically through a Finite Volume scheme. The simulations are complemented by an ongoing 2-years field campaign, where we continuously collect hydrodynamic measurements such as free surface elevation and vertical velocity profiles, biophysical characteristics of the vegetation and high-resolution topo-bathymetric data of the site. Field measurements are used for calibration and validation purposes. We also investigate some implications on sediment transport processes. We expect that results from our study can support policy makers and
Sogaro, Francesca; Poole, Robert; Dennis, David
2014-11-01
High-speed stereoscopic particle image velocimetry has been performed in fully developed turbulent pipe flow at moderate Reynolds numbers with and without a drag-reducing additive (an aqueous solution of high molecular weight polyacrylamide). Three-dimensional large and very large-scale motions (LSM and VLSM) are extracted from the flow fields by a detection algorithm and the characteristics for each case are statistically compared. The results show that the three-dimensional extent of VLSMs in drag reduced (DR) flow appears to increase significantly compared to their Newtonian counterparts. A statistical increase in azimuthal extent of DR VLSM is observed by means of two-point spatial autocorrelation of the streamwise velocity fluctuation in the radial-azimuthal plane. Furthermore, a remarkable increase in length of these structures is observed by three-dimensional two-point spatial autocorrelation. These results are accompanied by an analysis of the swirling strength in the flow field that shows a significant reduction in strength and number of the vortices for the DR flow. The findings suggest that the damping of the small scales due to polymer addition results in the undisturbed development of longer flow structures.
Drag reduction over dolphin skin via the pondermotive forcing of vortex filaments
Lisi, Antony Garrett
1999-11-01
The skin of Tursiops Truncatus is corrugated with small, quasi-periodic ridges running circumferentially about the torso. These ridges extend into the turbulent boundary layer and affect the evolution of coherent structures. The development and evolution of coherent structures over a surface is described by the formation and dynamics of vortex filaments. The dynamics of these filaments over a flat, non-ridged surface is determined analytically, as well as through numerical simulation, and found to agree with the observations of coherent structures in the turbulent boundary layer. The calculation of the linearized dynamics of the vortex filament, successful for the dynamics of a filament over a flat surface, is extended and applied to a vortex filament propagating over a periodically ridged surface. The surface ridges induce a rapid parametric forcing of the vortex filament, and alter the filament dynamics significantly. A consideration of the contribution of vortex filament induced flow to energy transport indicates that the behavior of the filament induced by the ridges can directly reduce surface drag by up to 8%. The size, shape, and distribution of cutaneous ridges for Tursiops Truncatus is found to be optimally configured to affect the filament dynamics and reduce surface drag for swimming velocities consistent with observation.
Inducer Hydrodynamic Forces in a Cavitating Environment
Skelley, Stephen E.
2004-01-01
Marshall Space Flight Center has developed and demonstrated a measurement device for sensing and resolving the hydrodynamic loads on fluid machinery. The device - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining the amplitude and frequency content associated with operating in various cavitation modes. The rotating balance was calibrated statically using a dead-weight load system in order to generate the 6 x 12 calibration matrix later used to convert measured voltages to engineering units. Structural modeling suggested that the rotating assembly first bending mode would be significantly reduced with the balance s inclusion. This reduction in structural stiffness was later confirmed experimentally with a hammer-impact test. This effect, coupled with the relatively large damping associated with the rotating balance waterproofing material, limited the device s bandwidth to approximately 50 Hertz Other pre-test validations included sensing the test article rotating assembly built-in imbalance for two configurations and directly measuring the assembly mass and buoyancy while submerged under water. Both tests matched predictions and confirmed the device s sensitivity while stationary and rotating. The rotating balance was then demonstrated in a water test of a full-scale Space Shuttle Main Engine high-pressure liquid oxygen pump inducer. Experimental data was collected a scaled operating conditions at three flow coefficients across a range of cavitation numbers for the single inducer geometry and radial clearance. Two distinct cavitation modes were observed symmetric tip vortex cavitation and alternate-blade cavitation. Although previous experimental tests on the same inducer demonstrated two additional
Hydrodynamic properties of whole arabic gum
Masuelli, Martin Alberto
2016-01-01
The most economically important of the hydrodynamic properties of a material are viscosity and density, which allow determining the intrinsic viscosity of raw materials used in the food industry. They serve as an indirect measure of molecular weight (M), hydrodynamic radius (RH), number of Simha, (ν(P)), Perrin parameter (P); hydration value (δ), Scheraga-Mandelkern parameter (β), and Flory parameters (0 and P0). Normally, these parameters are reported at a temperature of 25ºC, which limits t...
Relabeling symmetries in hydrodynamics and magnetohydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Padhye, N.; Morrison, P.J.
1996-04-01
Lagrangian symmetries and concomitant generalized Bianchi identities associated with the relabeling of fluid elements are found for hydrodynamics and magnetohydrodynamics (MHD). In hydrodynamics relabeling results in Ertel`s theorem of conservation of potential vorticity, while in MHD it yields the conservation of cross helicity. The symmetries of the reduction from Lagrangian (material) to Eulerian variables are used to construct the Casimir invariants of the Hamiltonian formalism.
[Numerical simulation on hydrodynamic character for algae growth].
Wang, Hua; Pang, Yong
2008-04-01
In order to quantificationally study the direct effects of hydrodynamic condition on the growth of algae, the Microcystis aeruginosa was chosen to carry through the disturbance-experiment. By keeping the same value of illumination, temperature and nutrition and changing the rotate speed of oscillator, the growing processes of algae under different disturbance intensities were researched. The hydraulic parameter was presented to amend the formula for the growth of algae. Take Neijiang as an example. A 2-D unsteady model for algae growth was established to forecast the scope of water blooms in Neijiang. It is found that the growth of algae is obviously influenced by hydrodynamic condition, and a condign low velocity is beneficial for its growth while both the quiescence condition and high velocity will restrain its growth rate. After the close of the water gate in Leading Channel, the velocity in Neijiang will be decreased, which accelerated the growth rate of algae, and the area of water blooms will be increased to 2.5 km2 which is about 36.8 percent of the total water surface area of Neijiang. Under the quiescent condition and the improved hydrodynamic condition, the growth rate of algae will be effectively controlled and the area of water blooms will be reduced to 0.78 km2 and 0.18 km2 respectively.
Entrainment in Superfluid Neutron-Star Crusts: Hydrodynamic Description and Microscopic Origin
Chamel, N.
2017-12-01
In spite of the absence of viscous drag, the neutron superfluid permeating the inner crust of a neutron star cannot flow freely and is entrained by the nuclear lattice similarly to laboratory superfluid atomic gases in optical lattices. The role of entrainment on the neutron superfluid dynamics is reviewed. For this purpose, a minimal hydrodynamical model of superfluidity in neutron-star crusts is presented. This model relies on a fully 4-dimensionally covariant action principle. The equivalence of this formulation with the more traditional approach is demonstrated. In addition, the different treatments of entrainment in terms of dynamical effective masses or superfluid density are clarified. The nuclear energy density functional theory employed for the calculations of all the necessary microscopic inputs is also reviewed, focusing on superfluid properties. In particular, the microscopic origin of entrainment and the different methods to estimate its importance are discussed.
Uchida, Nariya; Golestanian, Ramin; Bennett, Rachel R.
2017-10-01
Cooperative motion of flagella and cilia faciliates swimming of microorganisms and material transport in the body of multicellular organisms. Using minimal models, we address the roles of hydrodynamic interaction in synchronization and collective dynamics of flagella and cilia. Collective synchronization of bacterial flagella is studied with a model of bacterial carpets. Cilia and eukaryotic flagella are characterized by periodic modulation of their driving forces, which produces various patterns of two-body synchronization and metachronal waves. Long-range nature of the interaction introduces novel features in the dynamics of these model systems. The flagella of a swimmer synchronize also by a viscous drag force mediated through the swimmer's body. Recent advance in experimental studies of the collective dynamics of flagella, cilia and related artificial systems are summarized.
Motion of a nano-ellipsoid in a cylindrical vessel flow: Brownian and hydrodynamic interactions
Ramakrishnan, N; Eckmann, D M; Ayyaswamy, P S; Radhakrishnan, Ravi
2016-01-01
We present comprehensive numerical studies of the motion of a buoyant or a nearly neutrally buoyant nano-sized ellipsoidal particle in a fluid filled cylindrical tube without or with the presence of imposed pressure gradient (weak Poiseuille flow). The Fluctuating hydrodynamics approach and the Deterministic method are both employed. We ensure that the fluctuation-dissipation relation and the principle of thermal equipartition of energy are both satisfied. The major focus is on the effect of the confining boundary. Results for the velocity and angular velocity autocorrelations (VACF and AVACF), diffusivities, and drag and lift forces as functions of shape, aspect ratio, inclination angle, and proximity to the wall are presented. For the parameters considered, the boundary modifies the VACF and AVACF such that three distinct regimes are discernible --- an initial exponential decay, followed by an algebraic decay culminating in a second exponential decay. The first is due to thermal noise, the algebraic regime ...
Paardekooper, S.-J.; Papaloizou, J. C. B.
2009-04-01
We study the torque on low-mass protoplanets on fixed circular orbits, embedded in a protoplanetary disc in the isothermal limit. We consider a wide range of surface density distributions including cases where the surface density increases smoothly outwards. We perform both linear disc response calculations and non-linear numerical simulations. We consider a large range of viscosities, including the inviscid limit, as well as a range of protoplanet mass ratios, with special emphasis on the co-orbital region and the corotation torque acting between disc and protoplanet. For low-mass protoplanets and large viscosity, the corotation torque behaves as expected from linear theory. However, when the viscosity becomes small enough to enable horseshoe turns to occur, the linear corotation torque exists only temporarily after insertion of a planet into the disc, being replaced by the horseshoe drag first discussed by Ward. This happens after a time that is equal to the horseshoe libration period reduced by a factor amounting to about twice the disc aspect ratio. This torque scales with the radial gradient of specific vorticity, as does the linear torque, but we find it to be many times larger. If the viscosity is large enough for viscous diffusion across the co-orbital region to occur within a libration period, we find that the horseshoe drag may be sustained. If not, the corotation torque saturates leaving only the linear Lindblad torques. As the magnitude of the non-linear co-orbital torque (horseshoe drag) is always found to be larger than the linear torque, we find that the sign of the total torque may change even for mildly positive surface density gradients. In combination with a kinematic viscosity large enough to keep the torque from saturating, strong sustained deviations from linear theory and outward or stalled migration may occur in such cases.
Acceleration Noise Considerations for Drag-free Satellite Geodesy Missions
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
Pawar, Sanjay B
2018-01-01
The biomass productivity of microalgae cells mainly depends on the hydrodynamics of airlift bioreactor (ABR). Thus, the hydrodynamics of concentric tube ABR was initially studied using two-phase three-dimensional CFD simulations with the Eulerian-Lagrangian approach. The performance of ABR (17 L) was examined for different configurations of the draft tube using various drag models such as Grace, Ishii-Zuber, and Schiller-Naumann. The gas holdups in the riser and the downcomer were well predicted using E-L approach. This work was further extended to study the dispersion of microalgae cells in the ABR using three-phase CFD simulations. In this model (combined E-E and E-L), the solid phase (microalgae cells) was dispersed into the continuous liquid phase (water), while the gas phase (air bubbles) was modeled as a particle transport fluid. The effect of non-drag forces such as virtual mass and lift forces was also considered. Flow regimes were explained on the basis of the relative gas holdup distribution in the riser and the downcomer. The microalgae cells were found in suspension for the superficial gas velocities of 0.02-0.04 m s-1 experiencing an average shear of 23.52-44.56 s-1 which is far below the critical limit of cell damage.
Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis
Comiskey, P. M.; Yarin, A. L.; Attinger, D.
2017-07-01
A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the target (and perforated by the bullet) is predicted and compared with experimental data. The experimental data were acquired with a porous polyurethane foam sheet target impregnated with swine blood, and the blood drops were collected on a vertical cardstock sheet which was perforated by the blunt bullet. The highly porous target possesses a low hydraulic resistance and therefore resembles a pool of blood shot by a blunt bullet normally to its free surface. The back spatter pattern was predicted numerically and compared to the experimental data for the number of drops, their area, the total stain area, and the final impact angle as functions of radial location from the bullet hole in the cardstock sheet (the collection screen). Comparisons of the predicted results with the experimental data revealed satisfactory agreement. The predictions also allow one to find the impact Weber number on the collection screen, which is necessary to predict stain
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.
Directory of Open Access Journals (Sweden)
Shams-Ul. Islam
2017-04-01
Full Text Available This article presents a two-dimensional numerical study of the unsteady laminar flow from a square cylinder in presence of multiple small control cylinders. The cylinders are placed in an unconfined medium at low Reynolds numbers (Re = 100 and 160. Different flow phenomena are captured for the gap spacings (g = s/D, where s is the surface-to-surface distance between the main cylinder and small control cylinders and D is the size of the main cylinder between 0.25 – 3 and angle of attack (θ ranging from 300 to 1800. Numerical calculations are performed by using a lattice Boltzmann method. In this paper, the important flow physics of different observed flow patterns in terms of instantaneous vorticity contours visualization, time-trace analysis of drag and lift coefficients and power spectra analysis of lift coefficient are presented and discussed. Drag reduction and suppression of vortex shedding is also discussed in detail and compared with the available experimental and numerical results qualitatively as well as quantitatively. In addition, the mean drag coefficient, Strouhal number, root-mean-square values of the drag and lift coefficients are determined and compared with a single square cylinder without small control cylinders. We found that the drag is reduced 99.8% and 97.6% for (θ, g = (300, 3 at Re = 100 and 160, respectively.
Drag reduction in silica nanochannels induced by graphitic wall coatings
DEFF Research Database (Denmark)
Wagemann, Enrique; Walther, Jens Honore; Zambrano, Harvey
Transport of water in hydrophilic nanopores is of significant technological and scientific interest. Water flow through hydrophilic nanochannelsis known to experience enormous hydraulic resistance. Therefore, drag reduction is essential for the development of highly efficient nanofluidic devices....... In this work, we propose the use of graphitic materials as wall coatings in hydrophilic silica nanopores. Specifically, by conducting atomistic simulations, we investigate the flow inside slit and cylindrical silica channels with walls coated with graphene (GE) layers and carbonnanotubes (CNTs), respectively...... in the nanochannels. The influence of channel size is investigated by systematically varying channel heights and nanopore diameters. In particular, we present the computed water density and velocity profiles, volumetric flow rates, slip lengths and flow enhancements, to clearly demonstrate the drag reduction...
Drag of the cytosol as a transport mechanism in neurons.
Mussel, Matan; Zeevy, Keren; Diamant, Haim; Nevo, Uri
2014-06-17
Axonal transport is typically divided into two components, which can be distinguished by their mean velocity. The fast component includes steady trafficking of different organelles and vesicles actively transported by motor proteins. The slow component comprises nonmembranous materials that undergo infrequent bidirectional motion. The underlying mechanism of slow axonal transport has been under debate during the past three decades. We propose a simple displacement mechanism that may be central for the distribution of molecules not carried by vesicles. It relies on the cytoplasmic drag induced by organelle movement and readily accounts for key experimental observations pertaining to slow-component transport. The induced cytoplasmic drag is predicted to depend mainly on the distribution of microtubules in the axon and the organelle transport rate. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Ando, Tadashi; Chow, Edmond; Skolnick, Jeffrey
2013-09-28
Hydrodynamic interactions exert a critical effect on the dynamics of macromolecules. As the concentration of macromolecules increases, by analogy to the behavior of semidilute polymer solutions or the flow in porous media, one might expect hydrodynamic screening to occur. Hydrodynamic screening would have implications both for the understanding of macromolecular dynamics as well as practical implications for the simulation of concentrated macromolecular solutions, e.g., in cells. Stokesian dynamics (SD) is one of the most accurate methods for simulating the motions of N particles suspended in a viscous fluid at low Reynolds number, in that it considers both far-field and near-field hydrodynamic interactions. This algorithm traditionally involves an O(N(3)) operation to compute Brownian forces at each time step, although asymptotically faster but more complex SD methods are now available. Motivated by the idea of hydrodynamic screening, the far-field part of the hydrodynamic matrix in SD may be approximated by a diagonal matrix, which is equivalent to assuming that long range hydrodynamic interactions are completely screened. This approximation allows sparse matrix methods to be used, which can reduce the apparent computational scaling to O(N). Previously there were several simulation studies using this approximation for monodisperse suspensions. Here, we employ newly designed preconditioned iterative methods for both the computation of Brownian forces and the solution of linear systems, and consider the validity of this approximation in polydisperse suspensions. We evaluate the accuracy of the diagonal approximation method using an intracellular-like suspension. The diffusivities of particles obtained with this approximation are close to those with the original method. However, this approximation underestimates intermolecular correlated motions, which is a trade-off between accuracy and computing efficiency. The new method makes it possible to perform large
Effect of bevel angle of three-layer parallel plate on hydrodynamic performances of otter-board
Directory of Open Access Journals (Sweden)
Wang Lei
2017-01-01
Full Text Available The effect of bevel angle of three-layer parallel plate of otter-board on hydrodynamic performances is investigated by model wind tunnel test. Four otter-board models are designed with four different bevel angles (8°, 10°, 12° and 14° , and tested under the wind speed 28 m / s in wind tunnel. Model experiment is conducted to obtain the drag coefficients Cx, the lift coefficient Cy, the pitch moment coefficient Cm, the center of pressure coefficient Cp and calculated the lift-drag ratio Cy/Cx. The result shows that the maximum lift coefficient and the maximum lift-drag ratio of the otter-board model with a bevel angle 12 degree is higher, there is 2.598(a=65° and 2.607(a=37.5°; For comparison in stability of otter-board, the stability of the otter-board model with the bevel angle 8 degree is better by the comparative analysis of Cm and Cp, the absolute value of Cm is 0.174 and the minimum variation coefficient of Cp is 4.37%. The results can offer reference for the structural optimization design of trawl otter-board.
Clementi, Emanuela; Oddo, Paolo; Drudi, Massimiliano; Pinardi, Nadia; Korres, Gerasimos; Grandi, Alessandro
2017-10-01
This work describes the first step towards a fully coupled modelling system composed of an ocean circulation and a wind wave model. Sensitivity experiments are presented for the Mediterranean Sea where the hydrodynamic model NEMO is coupled with the third-generation wave model WaveWatchIII (WW3). Both models are implemented at 1/16° horizontal resolution and are forced by ECMWF 1/4° horizontal resolution atmospheric fields. The models are two-way coupled at hourly intervals exchanging the following fields: sea surface currents and temperature are transferred from NEMO to WW3 by modifying the mean momentum transfer of waves and the wind speed stability parameter, respectively. The neutral drag coefficient computed by WW3 is then passed to NEMO, which computes the surface stress. Five-year (2009-2013) numerical experiments were carried out in both uncoupled and coupled mode. In order to validate the modelling system, numerical results were compared with coastal and drifting buoys and remote sensing data. The results show that the coupling of currents with waves improves the representation of the wave spectrum. However, the wave-induced drag coefficient shows only minor improvements in NEMO circulation fields, such as temperature, salinity, and currents.
Measuring the Effects of Lift and Drag on Projectile Motion
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.…
Numerical simulation of flow hydrodynamics of struvite pellets in a liquid-solid fluidized bed.
Ye, Xin; Chu, Dongyuan; Lou, Yaoyin; Ye, Zhi-Long; Wang, Ming Kuang; Chen, Shaohua
2017-07-01
Phosphorus recovery in the form of struvite has been aroused in recent decades for its dual advantages in eutrophication control and resource protection. The usage of the struvite products is normally determined by the size which is largely depended on the hydrodynamics. In this study, flow behavior of struvite pellets was simulated by means of Eulerian-Eulerian two-fluid model combining with kinetic theory of granular flow in a liquid-solid fluidized bed reactor (FBR). A parametric study including the mesh size, time step, discretization strategy, turbulent model and drag model was first developed, followed by the evaluations of crucial operational conditions, particle characteristics and reactor shapes. The results showed that a cold model with the mesh resolution of 16×240, default time step of 0.001sec and first order discretization scheme was accurate enough to describe the fluidization. The struvite holdup profile using Syamlal-O'Brien drag model was best fitted to the experimental data as compared with other drag models and the empirical Richardson-Zaki equation. Regarding the model evaluation, it showed that liquid velocity and particle size played important roles on both solid holdups and velocities. The reactor diameter only influenced the solid velocity while the static bed height almost took no effect. These results are direct and can be applied to guide the operation and process control of the struvite fluidization. Moreover, the model parameters can also be used as the basic settings in further crystallization simulations. Copyright © 2016. Published by Elsevier B.V.
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.
Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity.
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.
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.
The influence of numerical models on determining the drag coefficient
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Dobeš Josef
2014-03-01
Full Text Available The paper deals with numerical modelling of body aerodynamic drag coefficient in the transition from laminar to turbulent flow regimes, where the selection of a suitable numerical model is problematic. On the basic problem of flow around a simple body – sphere selected computational models are tested. The values obtained by numerical simulations of drag coefficients of each model are compared with the graph of dependency of the drag coefficient vs. Reynolds number for a sphere. Next the dependency of Strouhal number vs. Reynolds number is evaluated, where the vortex shedding frequency values for given speed are obtained numerically and experimentally and then the values are compared for each numerical model and experiment. The aim is to specify trends for the selection of appropriate numerical model for flow around bodies problem in which the precise description of the flow field around the obstacle is used to define the acoustic noise source. Numerical modelling is performed by finite volume method using CFD code.
5th Drag Reduction in Engineering Flows Meeting
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...
Frame-dragging Effect in Strong Gravity Regime
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.
Impact of atmospheric and oceanic form drag parameterization on simulations of Arctic sea ice
Tsamados, Michel; Feltham, Daniel L.; Schroeder, David. F.; Farrell, Sinead L.; Kurtz, Nathan T.; Laxon, Seymour W.
2013-04-01
Pressure ridges, keels, floe edges and melt pond edges all introduce discrete obstructions to the flow of the air or ocean over the ice, and are a source of form drag. For typical ice covers the form drag contribution to the total drag is of comparable or greater magnitude to the surface or skin drag. In current climate models form drag is only accounted for by tuning of the air-ice and air-ocean drag coefficients, i.e. by altering the roughness length in a surface drag parameterization. The existing approach of skin drag parameter tuning, while numerically convenient, is poorly constrained by observations and fails to describe correctly the physics associated with the air-ice and ocean-ice drag. Here we combine recent theoretical developments to deduce the total neutral form drag coefficients from the key parameters of the ice cover such as ice concentration, size and area of the ridges and keels, freeboard and floe draft and size of melt ponds. We incorporate the drag coefficients into the sea ice component of a climate model (the CICE model). This stage necessitates that the sea ice characteristics obtained locally from observations are mapped to the averaged sea ice quantities provided by the sea ice model at the larger grid cell length scale. We present results over the Arctic of a stand-alone version of the model and show the influence of the new drag parameterization on the motion and mass of the ice cover. The new parameterization allows the drag coefficients to be coupled to the sea ice state and therefore to evolve spatially and temporally. We test the predictions of the model against measured drag coefficients in several regions of the Arctic and find good agreement between model and observations.
Modeling complex flow structures and drag around a submerged plant of varied posture
Boothroyd, Richard J.; Hardy, Richard J.; Warburton, Jeff; Marjoribanks, Timothy I.
2017-04-01
Although vegetation is present in many rivers, the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants. Here we report on a combined flume and numerical model experiment which incorporates time-averaged plant posture, collected through terrestrial laser scanning, into a computational fluid dynamics model to predict flow around a submerged riparian plant. For three depth-limited flow conditions (Reynolds number = 65,000-110,000), plant dynamics were recorded through high-definition video imagery, and the numerical model was validated against flow velocities collected with an acoustic Doppler velocimeter. The plant morphology shows an 18% reduction in plant height and a 14% increase in plant length, compressing and reducing the volumetric canopy morphology as the Reynolds number increases. Plant shear layer turbulence is dominated by Kelvin-Helmholtz type vortices generated through shear instability, the frequency of which is estimated to be between 0.20 and 0.30 Hz, increasing with Reynolds number. These results demonstrate the significant effect that the complex morphology of natural plants has on in-stream drag, and allow a physically determined, species-dependent drag coefficient to be calculated. Given the importance of vegetation in river corridor management, the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance.
Does skill specialisation influence individual differences in drag flicking speed and accuracy?
Rosalie, Simon M; McIntyre, Andrew S; Stockman, Stacey; King, Craig; Watkins, Cameron; Wild, Catherine Yvette; Ng, Leo
2017-03-01
Research has revealed that individual soccer goalkeepers respond differently to penalty shots, depending on their specific perceptual and motor capabilities. However, it remains unclear whether analogous differences exist between individual penalty takers, and if specialising in penalty taking affects the occurrence of differences between individuals. The present study examined individual differences in penalty shot speed and accuracy for specialists in penalty taking versus non-specialists. Expert specialist field hockey drag flickers and equivalently skilled non-specialists performed drag flicks towards predetermined targets placed in the face of a standard field hockey goal. Comparisons in shot speed and accuracy were made at a group level (specialists vs. non-specialists) as well as between individuals. Results revealed differences in both speed and accuracy between specialists, but only differences in speed between non-specialists. Specialists generated significantly greater shot speed than non-specialists (P < .001) and were more accurate to some, but not all, targets (top left, P < .006, bottom left P < .001). In addition, it was found that in specialists increasing practice correlated with decreasing accuracy. This may indicate that excessive practice could potentially reduce a specialist's accuracy in shooting towards specific targets.
A novel brewing process via controlled hydrodynamic cavitation
Albanese, Lorenzo; Meneguzzo, Francesco; Pagliaro, Mario
2016-01-01
This paper describes a completely new brewing equipment and process based upon controlled hydrodynamic cavitation, providing significant advantages in terms of lowered capital cost, reduced production time, enhanced energy and production efficiency, food safety, while preserving beer organoleptic qualities. Experiments carried out on real microbrewery volume scale using the new and conventional technology unquestionably confirm the relevance of the new findings. Impacts of these discoveries are potentially far reaching, as beer is the worldwide most widely consumed alcoholic beverage, therefore highly relevant to health, environment the economy and even to local identities.
Andreas, Edgar L.
1995-03-01
In part 1 (Andreas and Claffey, this issue) we observed some characteristics of the neutral stability air-ice drag coefficient at a reference height of 10 m (CDN10) that had not been documented before. Our main conclusion was that wind-driven snow continually alters the sea ice surface; the resulting snowdrifts determine how large CDN10 is. In particular, part 1 reported three observations that I would like to explain. (1) CDN10 is near 1.5×10-3 when the wind is well aligned with the drifted snow. (2) CDN10 is near 2.5×10-3 when the wind makes a large angle with the dominant orientation of the snowdrifts. (3) CDN10 can increase by 20% if, after being well aligned with the drift patterns, the mean wind direction shifts by as little as 20°. To investigate this behavior of CDN10 here I adapt a model developed by Raupach (1992) that partitions the total surface stress into contributions from form drag and skin friction. An essential part of this development was extending Raupach's model to the more complex geometry of sastrugi-like roughness elements. Assuming that 10-cm high sastrugi cover 15% of the surface, this physically based model reproduces the three main observations listed above. Thus the model seems to include the basic physics of air-ice momentum exchange. The main conclusion from this modeling is that 10-cm, sastrugilike snowdrifts, rather than pressure ridges, sustain most of the form drag over compact sea ice in the western Weddell Sea. Secondly, the modeling suggests that skin friction accounts for about 60% of the surface stress when the wind is well aligned with the sastrugi; but when the wind is not well aligned, form drag accounts for about 80% of the stress. The sastrugi are thus quite effective in streamlining the surface.
Drag reduction by polyethylene glycol in the tail arterial bed of normotensive and hypertensive rats
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K.L. Bessa
2011-08-01
Full Text Available This study was designed to evaluate the effect of drag reducer polymers (DRP on arteries from normotensive (Wistar and spontaneously hypertensive rats (SHR. Polyethylene glycol (PEG 4000 at 5000 ppm was perfused in the tail arterial bed with (E+ and without endothelium (E- from male, adult Wistar (N = 14 and SHR (N = 13 animals under basal conditions (constant flow at 2.5 mL/min. In these preparations, flow-pressure curves (1.5 to 10 mL/min were constructed before and 1 h after PEG 4000 perfusion. Afterwards, the tail arterial bed was fixed and the internal diameters of the arteries were then measured by microscopy and drag reduction was assessed based on the values of wall shear stress (WSS by computational simulation. In Wistar and SHR groups, perfusion of PEG 4000 significantly reduced pulsatile pressure (Wistar/E+: 17.5 ± 2.8; SHR/E+: 16.3 ± 2.7%, WSS (Wistar/E+: 36; SHR/E+: 40% and the flow-pressure response. The E- reduced the effects of PEG 4000 on arteries from both groups, suggesting that endothelial damage decreased the effect of PEG 4000 as a DRP. Moreover, the effects of PEG 4000 were more pronounced in the tail arterial bed from SHR compared to Wistar rats. In conclusion, these data demonstrated for the first time that PEG 4000 was more effective in reducing the pressure-flow response as well as WSS in the tail arterial bed of hypertensive than of normotensive rats and these effects were amplified by, but not dependent on, endothelial integrity. Thus, these results show an additional mechanism of action of this polymer besides its mechanical effect through the release and/or bioavailability of endothelial factors.
Hydrodynamic Modeling and Its Application in AUC.
Rocco, Mattia; Byron, Olwyn
2015-01-01
The hydrodynamic parameters measured in an AUC experiment, s(20,w) and D(t)(20,w)(0), can be used to gain information on the solution structure of (bio)macromolecules and their assemblies. This entails comparing the measured parameters with those that can be computed from usually "dry" structures by "hydrodynamic modeling." In this chapter, we will first briefly put hydrodynamic modeling in perspective and present the basic physics behind it as implemented in the most commonly used methods. The important "hydration" issue is also touched upon, and the distinction between rigid bodies versus those for which flexibility must be considered in the modeling process is then made. The available hydrodynamic modeling/computation programs, HYDROPRO, BEST, SoMo, AtoB, and Zeno, the latter four all implemented within the US-SOMO suite, are described and their performance evaluated. Finally, some literature examples are presented to illustrate the potential applications of hydrodynamics in the expanding field of multiresolution modeling. © 2015 Elsevier Inc. All rights reserved.
Solar and Drag Sail Propulsion: From Theory to Mission Implementation
Johnson, Les; Alhorn, Dean; Boudreaux, Mark; Casas, Joe; Stetson, Doug; Young, Roy
2014-01-01
Solar and drag sail technology is entering the mainstream for space propulsion applications within NASA and around the world. Solar sails derive propulsion by reflecting sunlight from a large, mirror- like sail made of a lightweight, reflective material. The continuous sunlight pressure provides efficient primary propulsion, without the expenditure of propellant or any other consumable, allowing for very high V maneuvers and long-duration deep space exploration. Drag sails increase the aerodynamic drag on Low Earth Orbit (LEO) spacecraft, providing a lightweight and relatively inexpensive approach for end-of-life deorbit and reentry. Since NASA began investing in the technology in the late 1990's, significant progress has been made toward their demonstration and implementation in space. NASA's Marshall Space Flight Center (MSFC) managed the development and testing of two different 20-m solar sail systems and rigorously tested them under simulated space conditions in the Glenn Research Center's Space Power Facility at Plum Brook Station, Ohio. One of these systems, developed by L'Garde, Inc., is planned for flight in 2015. Called Sunjammer, the 38m sailcraft will unfurl in deep space and demonstrate solar sail propulsion and navigation as it flies to Earth-Sun L1. In the Flight Center (MSFC) managed the development and testing of two different 20-m solar sail systems and rigorously tested them under simulated space conditions in the Glenn Research Center's Space Power Facility at Plum Brook Station, Ohio. One of these systems, developed by L'Garde, Inc., is planned for flight in 2015. Called Sunjammer, the 38m sailcraft will unfurl in deep space and demonstrate solar sail propulsion and navigation as it flies to Earth-Sun L1. In the interim, NASA MSFC funded the NanoSail-D, a subscale drag sail system designed for small spacecraft applications. The NanoSail-D flew aboard the Fast Affordable Science and Technology SATellite (FASTSAT) in 2010, also developed by MSFC
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
HYDRODYNAMIC PERFORMANCES OF SMALL SIZE SWATH CRAFT
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Ermina Begovic
2015-12-01
Full Text Available The good seakeeping characteristics of SWATH hull form are very interesting for small working craft and pleasure boats. Intrinsic limitations as the low values of weight per inch of immersion and transversal and longitudinal instability, can be acceptable and successfully managed when the mission profile does not ask for significant load variation and shift. The exploitation of SWATH concept is limited by the craft size, but if main dimensions allow enough static stability, this configuration appears very promising. SWATH behaviour in rough sea at zero and low speed have led to consider this hull form within the small craft design research program in progress at University of Naples Federico II. The design of small size SWATH working/pleasure craft has to begin from the consideration of strut waterplane areas that are the key factor to get acceptable static and dynamic stability. Displacement has to be reduced as most as possible to increase static stability, as shown by last design trends. The results of CFD analysis concerning SWATH resistance and propulsion, aspects are presented. A numerical evaluation of the hull-propeller interactions is performed, through simulations of self-propulsion tests with a simplified method (Actuator Disk model to discretize the propeller effect. The effective wake coefficient, the thrust deduction fraction and hull efficiency are provided. To validate CFD resistance results a comparison with experimental tests performed by Authors is reported. The presented work highlights different hydrodynamic aspects, comments advantages and critical issues of SWATH concept and reports detailed CFD modelling procedure with the aim to provide a reference for SWATH small craft design.