Absolute measurement of the total ion-drag force on a single plasma-confined microparticle at the void edge under microgravity conditions

NARCIS (Netherlands)

Beckers, J.; Trienekens, D.J.M.; Kroesen, G.M.W.

2013-01-01

We present an absolute measurement of the total ion-drag force on one single microparticle at the edge of the dust free region in low pressure complex plasmas: the void. In order to do so, the particle confinement position was monitored as a function of the gas pressure for two particle sizes under

CFD Prediction of Airfoil Drag in Viscous Flow Using the Entropy Generation Method

Directory of Open Access Journals (Sweden)

Wei Wang

2018-01-01

Full Text Available A new aerodynamic force of drag prediction approach was developed to compute the airfoil drag via entropy generation rate in the flow field. According to the momentum balance, entropy generation and its relationship to drag were derived for viscous flow. Model equations for the calculation of the local entropy generation in turbulent flows were presented by extending the RANS procedure to the entropy balance equation. The accuracy of algorithm and programs was assessed by simulating the pressure coefficient distribution and dragging coefficient of different airfoils under different Reynolds number at different attack angle. Numerical data shows that the total entropy generation rate in the flow field and the drag coefficient of the airfoil can be related by linear equation, which indicates that the total drag could be resolved into entropy generation based on its physical mechanism of energy loss.

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.

Racializing white drag.

Science.gov (United States)

Rhyne, Ragan

2004-01-01

While drag is primarily understood as a performance of gender, other performative categories such as race, class, and sexuality create drag meaning as well. Though other categories of identification are increasingly understood as essential elements of drag by performers of color, whiteness remains an unmarked category in the scholarship on drag performances by white queens. In this paper, I argue that drag by white queens must be understood as a performance of race as well as gender and that codes of gender excess are specifically constructed through the framework of these other axes of identity. This essay asks whether white performance by white queens necessarily reinscribes white supremacy through the performance of an unmarked white femininity, or might drag performance complicate (though not necessarily subvert) categories of race as well as gender? In this essay, I will suggest that camp drag performances, through the deployment of class as a crucial category of performative femininity, might indeed be a key site through which whiteness is denaturalized and its power challenged. Specifically, I will read on camp as a politicized mode of race, class and gender performance, focusing on the intersections of these categories of identity in the drag performance of Divine.

Pipeline Drag Reducers

International Nuclear Information System (INIS)

Marawan, H.

2004-01-01

Pipeline drag reducers have proven to be an extremely powerful tool in fluid transportation. High molecular weight polymers are used to reduce the frictional pressure loss ratio in crude oil pipelines, refined fuel and aqueous pipelines. Chemical structure of the main used pipeline drag reducers is one of the following polymers and copolymers classified according to the type of fluid to ; low density polyethylene, copolymer of I-hexane cross linked with divinyl benzene, polyacrylamide, polyalkylene oxide polymers and their copolymers, fluorocarbons, polyalkyl methacrylates and terpolymer of styrene, alkyl acrylate and acrylic acid. Drag reduction is the increase in pump ability of a fluid caused by the addition of small amounts of an additive to the fluid. The effectiveness of a drag reducer is normally expressed in terms of percent drag reduction. Frictional pressure loss in a pipeline system is a waste of energy and it costly. The drag reducing additive minimizes the flow turbulence, increases throughput and reduces the energy costs. The Flow can be increased by more than 80 % with existing assets. The effectiveness of the injected drag reducer in Mostorod to Tanta crude oil pipeline achieved 35.4 % drag reduction and 23.2 % flow increase of the actual performance The experimental application of DRA on Arab Petroleum Pipeline Company (Summed) achieved a flow increase ranging from 9-32 %

Thermal design of AOTV heatshields for a conical drag brake

Science.gov (United States)

Pitts, W. C.; Murbach, M. S.

1985-01-01

Results are presented from an on-going study of the thermal performance of thermal protection systems for a conical drag brake type AOTV. Three types of heatshield are considered: rigid ceramic insulation, flexible ceramic blankets, and ceramic cloths. The results for the rigid insulation apply to other types of AOTV as well. Charts are presented in parametric form so that they may be applied to a variety of missions and vehicle configurations. The parameters considered include: braking maneuver heat flux and total heat load, heatshield material and thickness, heatshield thermal mass and conductivity, absorptivity and emissivity of surfaces, thermal mass of support structure, and radiation transmission through thin heatshields. Results of temperature calculations presented show trends with and sensitivities to these parameters. The emphasis is on providing information that will be useful in estimating the minimum required mass of these heatshield materials.

Fuel Savings and Aerodynamic Drag Reduction from Rail Car Covers

Science.gov (United States)

Storms, Bruce; Salari, Kambiz; Babb, Alex

2008-01-01

The potential for energy savings by reducing the aerodynamic drag of rail cars is significant. A previous study of aerodynamic drag of coal cars suggests that a 25% reduction in drag of empty cars would correspond to a 5% fuel savings for a round trip [1]. Rail statistics for the United States [2] report that approximately 5.7 billion liters of diesel fuel were consumed for coal transportation in 2002, so a 5% fuel savings would total 284 million liters. This corresponds to 2% of Class I railroad fuel consumption nationwide. As part of a DOE-sponsored study, the aerodynamic drag of scale rail cars was measured in a wind tunnel. The goal of the study was to measure the drag reduction of various rail-car cover designs. The cover designs tested yielded an average drag reduction of 43% relative to empty cars corresponding to an estimated round-trip fuel savings of 9%.

Use of a pitot probe for determining wing section drag in flight

Science.gov (United States)

Saltzman, E. J.

1975-01-01

A wake traversing probe was used to obtain section drag and wake profile data from the wing of a sailplane. The transducer sensed total pressure defect in the wake as well as freestream total pressure on both sides of the sensing element when the probe moved beyond the wake. Profiles of wake total pressure defects plotted as a function of distance above and below the trailing edge plane were averaged for calculating section drag coefficients for flights at low dynamic pressures.

Perturbed Partial Cavity Drag Reduction at High Reynolds Numbers

Science.gov (United States)

Makiharju, Simo; Elbing, Brian; Wiggins, Andrew; Dowling, David; Perlin, Marc; Ceccio, Steven

2010-11-01

Ventilated partial cavities were investigated at Reynolds numbers to 80 million. These cavities could be suitable for friction drag reduction on ocean going vessels and thereby lead to environmental and economical benefits. The test model was a 3.05 m wide by 12.9 m long flat plate, with a 0.18 m backward-facing step and a cavity-terminating beach, which had an adjustable slope, tilt and height. The step and beach trapped a ventilated partial cavity over the longitudinal mid-section of the model. Large-scale flow perturbations, mimicking the effect of ambient ocean waves were investigated. For the conditions tested a cavity could be maintained under perturbed flow conditions when the gas flux supplied was greater than the minimum required to maintain a cavity under steady conditions, with larger perturbations requiring more excess gas flux to maintain the cavity. High-speed video was used to observe the unsteady three dimensional cavity closure, the overall cavity shape, and the cavity oscillations. Cavities with friction drag reduction exceeding 95% were attained at optimal conditions. A simplified energy cost-benefit analysis of partial cavity drag reduction was also performed. The results suggest that PCDR could potentially lead to energy savings.

Drag Reduction trough Special paints Coated on the hull

OpenAIRE

Izaguirre Alza, Patricia; Pérez Rojas, Luis; Núñez Basáñez, José Fernando

2010-01-01

The economic recession, the environmental impact as well as the continuous fossil fuel consumption encourage actions that focus on saving energy. In the vessels sector, one of the main objectives has always been to reach a hydro-dynamically optimum hull which gave the desired speed with minimum power. Hydrodynamic drag is basically divided into two parts: a) the friction between the water and the hull, and b) the wave generation due to the free-surface air-water. Presented in this paper...

Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows

Science.gov (United States)

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.

Correaltion of full-scale drag predictions with flight measurements on the C-141A aircraft. Phase 2: Wind tunnel test, analysis, and prediction techniques. Volume 1: Drag predictions, wind tunnel data analysis and correlation

Science.gov (United States)

Macwilkinson, D. G.; Blackerby, W. T.; Paterson, J. H.

1974-01-01

The degree of cruise drag correlation on the C-141A aircraft is determined between predictions based on wind tunnel test data, and flight test results. An analysis of wind tunnel tests on a 0.0275 scale model at Reynolds number up to 3.05 x 1 million/MAC is reported. Model support interference corrections are evaluated through a series of tests, and fully corrected model data are analyzed to provide details on model component interference factors. It is shown that predicted minimum profile drag for the complete configuration agrees within 0.75% of flight test data, using a wind tunnel extrapolation method based on flat plate skin friction and component shape factors. An alternative method of extrapolation, based on computed profile drag from a subsonic viscous theory, results in a prediction four percent lower than flight test data.

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.

Studies of Aerodynamic Drag.

Science.gov (United States)

1982-12-01

31. Strouhal number vs Reynolds number - Effect of Wind tunnel Blockage. 150- P ecrit 100- 50k- o present d Qta o Mitry (1977) --Shair et ati (1963) 0...forces measured by the balance. 4.12 Final Tests A comprehensive set of drag measurements was taken with the new drag plates, the drag plates being

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

Directory of Open Access Journals (Sweden)

C. López de Subijana

2010-09-01

Full Text Available

El penalty córner es una de las jugadas más importantes en el hockey hierba. El drag-flick es la técnica de golpeo más eficaz en las jugadas de penalty córner (McLaughin, 1997. Los objetivos del presente estudio fueron el describir los parámetros cinemáticos del drag-flick en jugadores de nivel internacional y analizar las diferencias intergénero. La muestra fueron trece sujetos, un modelo, seis hombres y seis mujeres. El sistema de captura automático VICON registró 20 lanzamientos de cada jugador con una frecuencia de muestreo de 250 Hz. Las velocidades máximas angulares de las caderas, hombros y stick  fueron superiores  (p<0.01 en el modelo que en ambos grupos de género. Mediante la comparación estadística del modelo con ambos grupos de género se han podido determinar las claves de este gesto técnico, siendo necesario un movimiento hacia atrás del stick (efecto látigo antes de la aceleración de caderas y hombros, para terminar el gesto con la máxima aceleración del stick.
Palabras Clave: Biomecánica, drag-flick, hockey hierba, cinemática

The penalty corner is one of the most important goal plays in field hockey. The drag-flick is more efficient than other techniques when playing a penalty corner. The aims of this study were to describe the kinematics of international field hockey players during the drag-flick and to analyse gender differences. Thirteen participants, one male drag-flicker, six males and six females participated in the study. VICON optoelectronic system measured the kinematic parameters from the drag-flick with six cameras sampling at 250 Hz. Twenty trials were captured from each subject. Ball velocity at release, hips maximum angular velocity, stick minimum and maximum angular velocities were higher (p<0.01 in the drag-flicker than in both gender groups. Comparing with the drag-flicker we have found the cues of the skill, being necessary a

Drag Reduction by Riblets & Sharkskin Denticles: A Numerical Study

Science.gov (United States)

Boomsma, Aaron

. For comparison, turbulent flow over drag-reducing scalloped riblets is also simulated with similar flow conditions and with the same numerical method. Although the denticles resemble riblets, both sharkskin arrangements increase total drag by 44-50%, while the riblets reduce drag by 5%. Analysis of the simulated flow fields shows that the turbulent flow around denticles is highly three-dimensional and separated, with 25% of the total drag being form drag. The complex three-dimensional shape of the denticles gives rise to a mean flow dominated by strong secondary flows in sharp contrast with the mean flow generated by riblets, which is largely two-dimensional. The so resulting three-dimensionality of sharkskin flows leads to an increase in the magnitude of the turbulence statistics near the denticles, which further contributes to increasing the total drag. The simulations also show that, at least for the simulated arrangements, sharkskin, in sharp contrast with drag-reducing riblets, is unable to isolate high shear stress near denticle ridges causing a significant portion of the denticle surface to be exposed to high mean shear. Lastly, it has been theorized that sharkskin might act similarly to vortex generators and prevent separation. In order to test this theory, we have conducted simulations with and without sharkskin upstream of a steady separation bubble. Using large eddy simulation, our study shows that sharkskin worsened the weak separation region and enlarged the separation bubble's boundaries. The cause was shown to originate due to the denticles acting as blockages, rather than vortex generators. In fact, our results showed that separation occurred just after the second row of denticles and that the turbulent flow was unable to recover its lost momentum. Streamwise turbulence intensities were decreased compared to the baseline case. Finally, in the present case, the sharkskin induced reversed flow within the denticles---something that was not observed with

5th Drag Reduction in Engineering Flows Meeting

CERN Document Server

1991-01-01

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

Air Layer Drag Reduction

Science.gov (United States)

Ceccio, Steven; Elbing, Brian; Winkel, Eric; Dowling, David; Perlin, Marc

2008-11-01

A set of experiments have been conducted at the US Navy's Large Cavitation Channel to investigate skin-friction drag reduction with the injection of air into a high Reynolds number turbulent boundary layer. Testing was performed on a 12.9 m long flat-plate test model with the surface hydraulically smooth and fully rough at downstream-distance-based Reynolds numbers to 220 million and at speeds to 20 m/s. Local skin-friction, near-wall bulk void fraction, and near-wall bubble imaging were monitored along the length of the model. The instrument suite was used to access the requirements necessary to achieve air layer drag reduction (ALDR). Injection of air over a wide range of air fluxes showed that three drag reduction regimes exist when injecting air; (1) bubble drag reduction that has poor downstream persistence, (2) a transitional regime with a steep rise in drag reduction, and (3) ALDR regime where the drag reduction plateaus at 90% ± 10% over the entire model length with large void fractions in the near-wall region. These investigations revealed several requirements for ALDR including; sufficient volumetric air fluxes that increase approximately with the square of the free-stream speed, slightly higher air fluxes are needed when the surface tension is reduced, higher air fluxes are required for rough surfaces, and the formation of ALDR is sensitive to the inlet condition.

Aerodynamic drag on intermodal railcars

Science.gov (United States)

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.

Coulomb drag in coherent mesoscopic systems

DEFF Research Database (Denmark)

Mortensen, Asger; Flensberg, Karsten; Jauho, Antti-Pekka

2001-01-01

We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both ballistic and disordered systems. The consequences can be worked out either by analytic means, such as th......We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both ballistic and disordered systems. The consequences can be worked out either by analytic means......, 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...

Bubble-induced skin-friction drag reduction and the abrupt transition to air-layer drag reduction

Science.gov (United States)

Elbing, Brian R.; Winkel, Eric S.; Lay, Keary A.; Ceccio, Steven L.; Dowling, David R.; Perlin, Marc

To investigate the phenomena of skin-friction drag reduction in a turbulent boundary layer (TBL) at large scales and high Reynolds numbers, a set of experiments has been conducted at the US Navy's William B. Morgan Large Cavitation Channel (LCC). Drag reduction was achieved by injecting gas (air) from a line source through the wall of a nearly zero-pressure-gradient TBL that formed on a flat-plate test model that was either hydraulically smooth or fully rough. Two distinct drag-reduction phenomena were investigated; bubble drag reduction (BDR) and air-layer drag reduction (ALDR).The streamwise distribution of skin-friction drag reduction was monitored with six skin-friction balances at downstream-distance-based Reynolds numbers to 220 million and at test speeds to 20.0msinitial zone1. These results indicated that there are three distinct regions associated with drag reduction with air injection: Region I, BDR; Region II, transition between BDR and ALDR; and Region III, ALDR. In addition, once ALDR was established: friction drag reduction in excess of 80% was observed over the entire smooth model for speeds to 15.3ms1 with the surface fully roughened (though approximately 50% greater volumetric air flux was required); and ALDR was sensitive to the inflow conditions. The sensitivity to the inflow conditions can be mitigated by employing a small faired step (10mm height in the experiment) that helps to create a fixed separation line.

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...... means such as perturbation theory or random matrix theory. The physics of Coulomb drag in the mesoscopic regime is very different from Coulomb drag between extended electron systems. In the mesoscopic regime we in general find fluctuations of the drag comparable to the mean value. Examples are vanishing...

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.

Drag Coefficient Estimation in Orbit Determination

Science.gov (United States)

McLaughlin, Craig A.; Manee, Steve; Lichtenberg, Travis

2011-07-01

Drag modeling is the greatest uncertainty in the dynamics of low Earth satellite orbits where ballistic coefficient and density errors dominate drag errors. This paper examines fitted drag coefficients found as part of a precision orbit determination process for Stella, Starlette, and the GEOSAT Follow-On satellites from 2000 to 2005. The drag coefficients for the spherical Stella and Starlette satellites are assumed to be highly correlated with density model error. The results using MSIS-86, NRLMSISE-00, and NRLMSISE-00 with dynamic calibration of the atmosphere (DCA) density corrections are compared. The DCA corrections were formulated for altitudes of 200-600 km and are found to be inappropriate when applied at 800 km. The yearly mean fitted drag coefficients are calculated for each satellite for each year studied. The yearly mean drag coefficients are higher for Starlette than Stella, where Starlette is at a higher altitude. The yearly mean fitted drag coefficients for all three satellites decrease as solar activity decreases after solar maximum.

Magnon-drag thermopile.

Science.gov (United States)

Costache, Marius V; Bridoux, German; Neumann, Ingmar; Valenzuela, Sergio O

2011-12-18

Thermoelectric effects in spintronics are gathering increasing attention as a means of managing heat in nanoscale structures and of controlling spin information by using heat flow. Thermal magnons (spin-wave quanta) are expected to play a major role; however, little is known about the underlying physical mechanisms involved. The reason is the lack of information about magnon interactions and of reliable methods to obtain it, in particular for electrical conductors because of the intricate influence of electrons. Here, we demonstrate a conceptually new device that enables us to gather information on magnon-electron scattering and magnon-drag effects. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon-drag thermoelectric effects. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. This information is crucial to understand the physics of electron-magnon interactions, magnon dynamics and thermal spin transport.

The Effect of Volumetric Porosity on Roughness Element Drag

Science.gov (United States)

Gillies, John; Nickling, William; Nikolich, George; Etyemezian, Vicken

2016-04-01

Much attention has been given to understanding how the porosity of two dimensional structures affects the drag force exerted by boundary-layer flow on these flow obstructions. Porous structures such as wind breaks and fences are typically used to control the sedimentation of sand and snow particles or create micro-habitats in their lee. Vegetation in drylands also exerts control on sediment transport by wind due to aerodynamic effects and interaction with particles in transport. Recent research has also demonstrated that large spatial arrays of solid three dimensional roughness elements can be used to reduce sand transport to specified targets for control of wind erosion through the effect of drag partitioning and interaction of the moving sand with the large (>0.3 m high) roughness elements, but porous elements may improve the effectiveness of this approach. A thorough understanding of the role porosity plays in affecting the drag force on three-dimensional forms is lacking. To provide basic understanding of the relationship between the porosity of roughness elements and the force of drag exerted on them by fluid flow, we undertook a wind tunnel study that systematically altered the porosity of roughness elements of defined geometry (cubes, rectangular cylinders, and round cylinders) and measured the associated change in the drag force on the elements under similar Reynolds number conditions. The elements tested were of four basic forms: 1) same sized cubes with tubes of known diameter milled through them creating three volumetric porosity values and increasing connectivity between the tubes, 2) cubes and rectangular cylinders constructed of brass screen that nested within each other, and 3) round cylinders constructed of brass screen that nested within each other. The two-dimensional porosity, defined as the ratio of total surface area of the empty space to the solid surface area of the side of the element presented to the fluid flow was conserved at 0.519 for

The effect of sodium hydroxide on drag reduction using banana peel as a drag reduction agent

Science.gov (United States)

Kaur, H.; Jaafar, A.

2018-02-01

Drag reduction is observed as reduced frictional pressure losses under turbulent flow conditions. Drag reduction agent such as polymers can be introduced to increase the flowrate of water flowing and reduce the water accumulation in the system. Currently used polymers are synthetic polymers, which will 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 was explored and assessed in this study using a rheometer, where a reduced a torque produced was perceived as a reduction of drag. This method proposed is less time consuming and is more practical which is producing carboxymethylcellulose from the banana peel. The cellulose powder was converted to carboxymethylcellulose (CMC) by etherification process. The carboxymethylation reaction during the synthesizing process was then optimized against the reaction temperature, reaction time and solubility. The biopolymers were then rheologically characterized, where the viscoelastic effects and the normal stresses produced by these biopolymers were utilized to further relate and explain the drag reduction phenomena. The research was structured to focus on producing the biopolymer and to assess the drag reduction ability of the biopolymer produced. The rheological behavior of the biopolymers was then analyzed based on the ability of reducing drag. The results are intended to expand the currently extremely limited experimental database. Based on the results, the biopolymer works as a good DRA.

Vorticity confinement technique for drag prediction

Science.gov (United States)

Povitsky, Alex; Snyder, Troy

2011-11-01

This work couples wake-integral drag prediction and vorticity confinement technique (VC) for the improved prediction of drag from CFD simulations. Induced drag computations of a thin wing are shown to be more accurate than the more widespread method of surface pressure integration when compared to theoretical lifting-line value. Furthermore, the VC method improves trailing vortex preservation and counteracts the shift from induced drag to numerical entropy drag with increasing distance of Trefftz plane downstream of the wing. Accurate induced drag prediction via the surface integration of pressure barring a sufficiently refined surface grid and increased computation time. Furthermore, the alternative wake-integral technique for drag prediction suffers from numerical dissipation. VC is shown to control the numerical dissipation with very modest computational overhead. The 2-D research code is used to test specific formulations of the VC body force terms and illustrate the computational efficiency of the method compared to a ``brute force'' reduction in spatial step size. For the 3-D wing simulation, ANSYS FLUENT is employed with the VC body force terms added to the solver with user-defined functions (UDFs). VC is successfully implemented to highly unsteady flows typical for Micro Air Vehicles (MAV) producing oscillative drag force either by natural vortex shedding at high angles of attack or by flapping wing motion.

CFD-DEM Simulation of Minimum Fluidisation Velocity in Two Phase Medium

Directory of Open Access Journals (Sweden)

H Khawaja

2016-09-01

Full Text Available In this work, CFD-DEM (computational fluid dynamics - discrete element method has been used to model the 2 phase flow composed of solid particle and gas in the fluidised bed. This technique uses the Eulerian and the Langrangian methods to solve fluid and particles respectively. Each particle is treated as a discrete entity whose motion is governed by Newton's laws of motion. The particle-particle and particle-wall interaction is modelled using the classical contact mechanics. The particles motion is coupled with the volume averaged equations of the fluid dynamics using drag law. In fluidised bed, particles start experiencing drag once the fluid is passing through. The solid particles response to it once drag experienced is just equal to the weight of the particles. At this moment pressure drop across the bed is just equal to the weight of particles divide by the cross-section area. This is the first regime of fluidization, also referred as ‘the regime of minimum fluidization’. In this study, phenomenon of minimum fluidization is studied using CFD-DEM simulation with 4 different sizes of particles 0.15 mm, 0.3 mm, 0.6 mm, and 1.2 mm diameters. The results are presented in the form of pressure drop across the bed with the fluid superficial velocity. The achieved results are found in good agreement with the experimental and theoretical data available in literature.

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...... means such as perturbation theory or random matrix theory. The physics of Coulomb drag in the mesoscopic regime is very different from Coulomb drag between extended electron systems. In the mesoscopic regime we in general find fluctuations of the drag comparable to the mean value. Examples are vanishing...

Engineering drag currents in Coulomb coupled quantum dots

Science.gov (United States)

Lim, Jong Soo; Sánchez, David; López, Rosa

2018-02-01

The Coulomb drag phenomenon in a Coulomb-coupled double quantum dot system is revisited with a simple model that highlights the importance of simultaneous tunneling of electrons. Previously, cotunneling effects on the drag current in mesoscopic setups have been reported both theoretically and experimentally. However, in both cases the sequential tunneling contribution to the drag current was always present unless the drag level position were too far away from resonance. Here, we consider the case of very large Coulomb interaction between the dots, whereby the drag current needs to be assisted by cotunneling events. As a consequence, a quantum coherent drag effect takes place. Further, we demonstrate that by properly engineering the tunneling probabilities using band tailoring it is possible to control the sign of the drag and drive currents, allowing them to flow in parallel or antiparallel directions. We also show that the drag current can be manipulated by varying the drag gate potential and is thus governed by electron- or hole-like transport.

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...... conditions, the drag coefficient does not depend systematically on z/L but decreases with wind speed for fixed intervals of z/L, where L is the Obukhov length. Even though the drag coefficient for weak wind conditions is sensitive to the exact method of calculation and choice of averaging time, the decrease...... of the drag coefficient with wind speed occurs for all of the calculation methods. A classification of flux calculation methods is constructed, which unifies the most common previous approaches. The roughness length corresponding to the usual Monin-Obukhov stability functions decreases with increasing wind...

Turbulent skin-friction drag on a slender body of revolution and Gray's Paradox

International Nuclear Information System (INIS)

Nesteruk, Igor; Cartwright, Julyan H E

2011-01-01

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.

No Winglets: What a Drag...Argument for Adding Winglets to Large Air Force Aircraft

Science.gov (United States)

2008-01-01

prices have once again brought improving aircraft aerodynamic efficiencies to the forefront of the energy conservation debate. Displaying how winglets ... winglet . Winglets are small, nearly vertical aerodynamic surfaces mounted on aircraft wingtips. Engineers design them with the same careful attention to...total drag.6 Since winglets , designed as small airfoils, reduce the aerodynamic drag associated with vortices by minimizing the amount of energy used

Estimation of the drag coefficient from the upper ocean response to a hurricane: A variational data assimilation approach

KAUST Repository

Zedler, Sarah

2013-08-01

We seek to determine whether a small number of measurements of upper ocean temperature and currents can be used to make estimates of the drag coefficient that have a smaller range of uncertainty than previously found. We adopt a numerical approach in an inverse problem setup using an ocean model and its adjoint, to assimilate data and to adjust the drag coefficient parameterization (here the free parameter) with wind speed that corresponds to the minimum of a model minus data misfit or cost function. Pseudo data are generated from a reference forward simulation, and are perturbed with different levels of Gaussian distributed noise. It is found that it is necessary to assimilate both surface current speed and temperature data to obtain improvement over previous estimates of the drag coefficient. When data is assimilated without any smoothing or constraints on the solution, the drag coefficient is overestimated at low wind speeds and there are unrealistic, high frequency oscillations in the adjusted drag coefficient curve. When second derivatives of the drag coefficient curve are penalized and the solution is constrained to experimental values at low wind speeds, the adjusted drag coefficient is within 10% of its target value. This result is robust to the addition of realistic random noise meant to represent turbulence due to the presence of mesoscale background features in the assimilated data, or to the wind speed time series to model its unsteady and gusty character. When an eddy is added to the background flow field in both the initial condition and the assimilated data time series, the target and adjusted drag coefficient are within 10% of one another, regardless of whether random noise is added to the assimilated data. However, when the eddy is present in the assimilated data but is not in the initial conditions, the drag coefficient is overestimated by as much as 30%. This carries the implication that when real data is assimilated, care needs to be taken in

Aerodynamic Drag Scoping Work.

Energy Technology Data Exchange (ETDEWEB)

Voskuilen, Tyler [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Erickson, Lindsay Crowl [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Knaus, Robert C. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2018-02-01

This memo summarizes the aerodynamic drag scoping work done for Goodyear in early FY18. The work is to evaluate the feasibility of using Sierra/Low-Mach (Fuego) for drag predictions of rolling tires, particularly focused on the effects of tire features such as lettering, sidewall geometry, rim geometry, and interaction with the vehicle body. The work is broken into two parts. Part 1 consisted of investigation of a canonical validation problem (turbulent flow over a cylinder) using existing tools with different meshes and turbulence models. Part 2 involved calculating drag differences over plate geometries with simple features (ridges and grooves) defined by Goodyear of approximately the size of interest for a tire. The results of part 1 show the level of noise to be expected in a drag calculation and highlight the sensitivity of absolute predictions to model parameters such as mesh size and turbulence model. There is 20-30% noise in the experimental measurements on the canonical cylinder problem, and a similar level of variation between different meshes and turbulence models. Part 2 shows that there is a notable difference in the predicted drag on the sample plate geometries, however, the computational cost of extending the LES model to a full tire would be significant. This cost could be reduced by implementation of more sophisticated wall and turbulence models (e.g. detached eddy simulations - DES) and by focusing the mesh refinement on feature subsets with the goal of comparing configurations rather than absolute predictivity for the whole tire.

Bioinspired surfaces for turbulent drag reduction.

Science.gov (United States)

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

2016-08-06

In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'. © 2016 The Author(s).

Measurement of drag and its cancellation

Energy Technology Data Exchange (ETDEWEB)

DeBra, D B; Conklin, J W, E-mail: johnwc@stanford.edu [Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305-4035 (United States)

2011-05-07

The design of drag cancellation missions of the future will take advantage of the technology experience of the past. The importance of data for modeling of the atmosphere led to at least six types of measurement: (a) balloon flights, (b) missile-launched falling spheres, (c) the 'cannonball' satellites of Ken Champion with accelerometers for low-altitude drag measurement (late 1960s and early 1970s), (d) the Agena flight of LOGACS (1967), a Bell MESA accelerometer mounted on a rotating platform to spectrally shift low-frequency errors in the accelerometer, (e) a series of French low-level accelerometers (e.g. CACTUS, 1975), and (f) correction of differential accelerations for drag errors in measuring gravity gradient on a pair of satellites (GRACE, 2002). The independent invention of the drag-free satellite concept by Pugh and Lange (1964) to cancel external disturbance added implementation opportunities. Its first flight application was for ephemeris prediction improvement with the DISCOS flight (1972)-still the only extended free test mass flight. Then successful flights for reduced disturbance environment for science measurement with gyros on GP-B (2004) and for improved accuracy in geodesy and ocean studies (GOCE, 2009) each using accelerometer measurements to control the drag-canceling thrust. LISA, DECIGO, BBO and other gravity wave-measuring satellite systems will push the cancellation of drag to new levels.

Measurement of drag and its cancellation

International Nuclear Information System (INIS)

DeBra, D B; Conklin, J W

2011-01-01

The design of drag cancellation missions of the future will take advantage of the technology experience of the past. The importance of data for modeling of the atmosphere led to at least six types of measurement: (a) balloon flights, (b) missile-launched falling spheres, (c) the 'cannonball' satellites of Ken Champion with accelerometers for low-altitude drag measurement (late 1960s and early 1970s), (d) the Agena flight of LOGACS (1967), a Bell MESA accelerometer mounted on a rotating platform to spectrally shift low-frequency errors in the accelerometer, (e) a series of French low-level accelerometers (e.g. CACTUS, 1975), and (f) correction of differential accelerations for drag errors in measuring gravity gradient on a pair of satellites (GRACE, 2002). The independent invention of the drag-free satellite concept by Pugh and Lange (1964) to cancel external disturbance added implementation opportunities. Its first flight application was for ephemeris prediction improvement with the DISCOS flight (1972)-still the only extended free test mass flight. Then successful flights for reduced disturbance environment for science measurement with gyros on GP-B (2004) and for improved accuracy in geodesy and ocean studies (GOCE, 2009) each using accelerometer measurements to control the drag-canceling thrust. LISA, DECIGO, BBO and other gravity wave-measuring satellite systems will push the cancellation of drag to new levels.

Correlated Coulomb Drag in Capacitively Coupled Quantum-Dot Structures.

Science.gov (United States)

Kaasbjerg, Kristen; Jauho, Antti-Pekka

2016-05-13

We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs)-a bias-driven 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 that accounts for higher-order tunneling (cotunneling) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multielectron 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. Interestingly, the direction of the drag current is not determined by the drive current, but by an interplay between the energy-dependent lead couplings. Studying the drag mechanism in a graphene-based CQD heterostructure, we show that the predictions of our theory are consistent with recent experiments on Coulomb drag in CQD systems.

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....

Drag De-Orbit Device: A New Standard Re-Entry Actuator for CubeSats

Science.gov (United States)

Guglielmo, David; Omar, Sanny R.; Bevilacqua, Riccardo

2017-01-01

With the advent of CubeSats, research in Low Earth Orbit (LEO) becomes possible for universities and small research groups. Only a handful of launch sites can be used, due to geographical and political restrictions. As a result, common orbits in LEO are becoming crowded due to the additional launches made possible by low-cost access to space. CubeSat design principles require a maximum of a 25-year orbital lifetime in an effort to reduce the total number of spacecraft in orbit at any time. Additionally, since debris may survive re-entry, it is ideal to de-orbit spacecraft over unpopulated areas to prevent casualties. The Drag Deorbit Device (D3) is a self-contained targeted re-entry subsystem intended for CubeSats. By varying the cross-wind area, the atmospheric drag can be varied in such a way as to produce desired maneuvers. The D3 is intended to be used to remove spacecraft from orbit to reach a desired target interface point. Additionally, attitude stabilization is performed by the D3 prior to deployment and can replace a traditional ADACS on many missions.This paper presents the hardware used in the D3 and operation details. Four stepper-driven, repeatedly retractable booms are used to modify the cross-wind area of the D3 and attached spacecraft. Five magnetorquers (solenoids) over three axes are used to damp rotational velocity. This system is expected to be used to improve mission flexibility and allow additional launches by reducing the orbital lifetime of spacecraft.The D3 can be used to effect a re-entry to any target interface point, with the orbital inclination limiting the maximum latitude. In the chance that the main spacecraft fails, a timer will automatically deploy the booms fully, ensuring the spacecraft will at the minimum reenter the atmosphere in the minimum possible time, although not necessarily at the desired target interface point. Although this does not reduce the risk of casualties, the 25-year lifetime limit is still respected, allowing

Drag Reduction by Leidenfrost Vapor Layers

KAUST Repository

Vakarelski, Ivan Uriev

2011-05-23

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

Drag reduction through self-texturing compliant bionic materials

Science.gov (United States)

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

2017-01-01

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

Drag of ballistic electrons by an ion beam

Energy Technology Data Exchange (ETDEWEB)

Gurevich, V. L.; Muradov, M. I., E-mail: mag.muradov@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2015-12-15

Drag of electrons of a one-dimensional ballistic nanowire by a nearby one-dimensional beam of ions is considered. We assume that the ion beam is represented by an ensemble of heavy ions of the same velocity V. The ratio of the drag current to the primary current carried by the ion beam is calculated. The drag current turns out to be a nonmonotonic function of velocity V. It has a sharp maximum for V near v{sub nF}/2, where n is the number of the uppermost electron miniband (channel) taking part in conduction and v{sub nF} is the corresponding Fermi velocity. This means that the phenomenon of ion beam drag can be used for investigation of the electron spectra of ballistic nanostructures. We note that whereas observation of the Coulomb drag between two parallel quantum wires may in general be complicated by phenomena such as tunneling and phonon drag, the Coulomb drag of electrons of a one-dimensional ballistic nanowire by an ion beam is free of such spurious effects.

Atomistically informed solute drag in Al–Mg

International Nuclear Information System (INIS)

Zhang, F; Curtin, W A

2008-01-01

Solute drag in solute-strengthened alloys, caused by diffusion of solute atoms around moving dislocations, controls the stress at deformation rates and temperatures useful for plastic forming processes. In the technologically important Al–Mg alloys, the solute drag stresses predicted by classical theories are much larger than experiments, which is resolved in general by eliminating the singularity of the dislocation core via Peierls–Nabarro-type models. Here, the drag stress versus dislocation velocity is computed numerically using a realistic dislocation core structure obtained from an atomistic model to investigate the role of the core and obtain quantitative stresses for comparison with experiment. The model solves a discrete diffusion equation in a reference frame moving with the dislocation, with input solute enthalpies and diffusion activation barriers in the core computed by or estimated from atomistic studies. At low dislocation velocities, the solute drag stress is controlled by bulk solute diffusion because the core diffusion occurs too quickly. In this regime, the drag stress can be obtained using a Peierls–Nabarro model with a core spreading parameter tuned to best match the atomistic models. At intermediate velocities, both bulk and core diffusion can contribute to the drag, leading to a complex stress–velocity relationship showing two peaks in stress. At high velocities, the drag stress is controlled solely by diffusion within and across the core. Like the continuum models, the drag stress is nearly linear in solute concentration. The Orowan relationship is used to connect dislocation velocity to deformation strain rate. Accounting for the dependence of mobile dislocation density on stress, the simulations are in good agreement with experiments on Al–Mg alloys over a range of concentrations and temperatures

Drag Reduction by Leidenfrost Vapor Layers

KAUST Repository

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

2011-01-01

, 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

Drag force, drag torque, and Magnus force coefficients of rotating spherical particle moving in fluid

Czech Academy of Sciences Publication Activity Database

Lukerchenko, Nikolay; Kvurt, Y.; Keita, Ibrahima; Chára, Zdeněk; Vlasák, Pavel

2012-01-01

Roč. 30, č. 1 (2012), s. 55-67 ISSN 0272-6351 R&D Projects: GA AV ČR IAA200600603; GA ČR GA103/09/1718 Institutional research plan: CEZ:AV0Z20600510 Keywords : drag force * drag torque * Magnus force * Reynolds number * rotational Reynolds number Subject RIV: BK - Fluid Dynamics Impact factor: 0.435, year: 2012

On the Drag Effect of a Refuelling Pellet

DEFF Research Database (Denmark)

Chang, Tinghong; Michelsen, Poul

1981-01-01

A refueling pellet is subjected mainly to two kinds of drags: (1) inertial drag caused by the motion of the pellet relative to the surrounding plasma, and (2) ablation drag caused by an uneven ablation rate of the front and the rear surface of the pellet in an inhomogeneous plasma. Computational ...... results showed that for reasonable combinations of pellet size and injection speed, the drag effect is hardly detectable for plasma conditions prevailing in current large tokamaks....

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.

Drag reduction through self-texturing compliant bionic materials

OpenAIRE

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

2017-01-01

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, sem...

Progress towards a Drag-free SmallSat

Science.gov (United States)

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.

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.

Frictional Magneto-Coulomb Drag in Graphene Double-Layer Heterostructures.

Science.gov (United States)

Liu, Xiaomeng; Wang, Lei; Fong, Kin Chung; Gao, Yuanda; Maher, Patrick; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Dean, Cory; Kim, Philip

2017-08-04

Coulomb interaction between two closely spaced parallel layers of conductors can generate the frictional drag effect by interlayer Coulomb scattering. Employing graphene double layers separated by few-layer hexagonal boron nitride, we investigate density tunable magneto- and Hall drag under strong magnetic fields. The observed large magnetodrag and Hall-drag signals can be related with Laudau level filling status of the drive and drag layers. We find that the sign and magnitude of the drag resistivity tensor can be quantitatively correlated to the variation of magnetoresistivity tensors in the drive and drag layers, confirming a theoretical formula for magnetodrag in the quantum Hall regime. The observed weak temperature dependence and ∼B^{2} dependence of the magnetodrag are qualitatively explained by Coulomb scattering phase-space argument.

Gravitational waves and dragging effects

Science.gov (United States)

Bičák, Jiří; Katz, Joseph; Lynden-Bell, Donald

2008-08-01

Linear and rotational dragging effects of gravitational waves on local inertial frames are studied in purely vacuum spacetimes. First, the linear dragging caused by a simple cylindrical pulse is investigated. Surprisingly strong transverse effects of the pulse are exhibited. The angular momentum in cylindrically symmetric spacetimes is then defined and confronted with some results in the literature. In the main part, a general procedure is developed for studying weak gravitational waves with translational but not axial symmetry which can carry angular momentum. After a suitable averaging the rotation of local inertial frames due to such rotating waves can be calculated explicitly and illustrated graphically. This is done in detail in the accompanying paper. Finally, the rotational dragging is given for strong cylindrical waves interacting with a rotating cosmic string with a small angular momentum.

Drag coefficient Variability and Thermospheric models

Science.gov (United States)

Moe, Kenneth

Satellite drag coefficients depend upon a variety of factors: The shape of the satellite, its altitude, the eccentricity of its orbit, the temperature and mean molecular mass of the ambient atmosphere, and the time in the sunspot cycle. At altitudes where the mean free path of the atmospheric molecules is large compared to the dimensions of the satellite, the drag coefficients can be determined from the theory of free-molecule flow. The dependence on altitude is caused by the concentration of atomic oxygen which plays an important role by its ability to adsorb on the satellite surface and thereby affect the energy loss of molecules striking the surface. The eccentricity of the orbit determines the satellite velocity at perigee, and therefore the energy of the incident molecules relative to the energy of adsorption of atomic oxygen atoms on the surface. The temperature of the ambient atmosphere determines the extent to which the random thermal motion of the molecules influences the momentum transfer to the satellite. The time in the sunspot cycle affects the ambient temperature as well as the concentration of atomic oxygen at a particular altitude. Tables and graphs will be used to illustrate the variability of drag coefficients. Before there were any measurements of gas-surface interactions in orbit, Izakov and Cook independently made an excellent estimate that the drag coefficient of satellites of compact shape would be 2.2. That numerical value, independent of altitude, was used by Jacchia to construct his model from the early measurements of satellite drag. Consequently, there is an altitude dependent bias in the model. From the sparce orbital experiments that have been done, we know that the molecules which strike satellite surfaces rebound in a diffuse angular distribution with an energy loss given by the energy accommodation coefficient. As more evidence accumulates on the energy loss, more realistic drag coefficients are being calculated. These improved drag

Evaluation of Skin Friction Drag for Liner Applications in Aircraft

Science.gov (United States)

Gerhold, Carl H.; Brown, Martha C.; Jasinski, Christopher M.

2016-01-01

A parameter that is gaining significance in the evaluation of acoustic liner performance is the skin friction drag induced by air flow over the liner surface. Estimates vary widely regarding the amount of drag the liner induces relative to a smooth wall, from less than a 20% increase to nearly 100%, and parameters such as face sheet perforate hole diameter, percent open area, and sheet thickness are expected to figure prominently in the skin friction drag. Even a small increase in liner drag can impose an economic penalty, and current research is focused on developing 'low drag' liner concepts, with the goal being to approach the skin friction drag of a smooth wall. The issue of skin friction drag takes on greater significance as airframe designers investigate the feasibility of putting sound absorbing liners on the non-lifting surfaces of the wings and fuselage, for the purpose of reducing engine noise reflected and scattered toward observers on the ground. Researchers at the NASA Langley Research Center have embarked on investigations of liner skin friction drag with the aims of: developing a systematic drag measurement capability, establishing the drag of current liners, and developing liners that produce reduced drag without compromising acoustic performance. This paper discusses the experimental procedures that have been developed to calculate the drag coefficient based on the change in momentum thickness and the companion research program being carried out to measure the drag directly using a force balance. Liner samples that are evaluated include a solid wall with known roughness and conventional liners with perforated facesheets of varying hole diameter and percent open area.

Design of a High Viscosity Couette Flow Facility for Patterned Surface Drag Measurements

Science.gov (United States)

Johnson, Tyler; Lang, Amy

2009-11-01

Direct drag measurements can be difficult to obtain with low viscosity fluids such as air or water. In this facility, mineral oil is used as the working fluid to increase the shear stress across the surface of experimental models. A mounted conveyor creates a flow within a plexiglass tank. The experimental model of a flat or patterned surface is suspended above a moving belt. Within the gap between the model and moving belt a Couette flow with a linear velocity profile is created. PIV measurements are used to determine the exact velocities and the Reynolds numbers for each experiment. The model is suspended by bars that connect to the pillow block housing of each bearing. Drag is measured by a force gauge connected to linear roller bearings that slide along steel rods. The patterned surfaces, initially consisting of 2-D cavities, are embedded in a plexiglass plate so as to keep the total surface area constant for each experiment. First, the drag across a flat plate is measured and compared to theoretical values for laminar Couette flow. The drag for patterned surfaces is then measured and compared to a flat plate.

Disturbance of eelgrass Zostera marina by commercial mussel Mytilus edulis harvesting in Maine: Dragging impacts and habitat recovery

Science.gov (United States)

Neckles, Hilary A.; Short, Frederick T.; Barker, Seth; Kopp, Blaine S.

2005-01-01

We studied the effects of commercial harvest of blue mussels Mytilus edulis on eelgrass Zostera marina L. in Maquoit Bay, Maine, USA, at a hierarchy of scales. We used aerial photography, underwater video, and eelgrass population- and shoot-based measurements to quantify dragging impacts within 4 sites that had been disturbed at different times over an approximate 7 yr interval, and to project eelgrass meadow recovery rates. Dragging had disturbed 10% of the eelgrass cover in Maquoit Bay, with dragged sites ranging from 3.4 to 31.8 ha in size. Dragging removed above- and belowground plant material from the majority of the bottom in the disturbed sites. One year following dragging, eelgrass shoot density, shoot height and total biomass of disturbed sites averaged respectively 2 to 3%, 46 to 61% and model based on measured rates of lateral patch-expansion (mean 12.5 cm yr-1) and new-patch recruitment (mean 0.19 patches m-2 yr-1) yielded a mean bed recovery time of 9 to 11 yr following dragging, depending on initial degree of plant removal. Model simulations suggested that with favorable environmental conditions, eelgrass beds might recover from dragging disturbance in 6 yr; conversely, recovery under conditions less conducive to eelgrass growth could require 20 yr or longer. This study shows that mussel dragging poses a severe threat to eelgrass in this region and that regulations to protect eelgrass from dragging impacts would maintain the integrity of a substantial amount of habitat.

LOFT drag-disc turbine tansducer shroud and cover weld analysis and evaluation

International Nuclear Information System (INIS)

Martinell, J.S.

1978-01-01

The results are presented of stress analysis and evaluation of the drag-disc turbine transducer (DTT) shroud and cover welds used in the Loss-of-Fluid Test (LOFT) facility. The analysis concerns LOFT DTTs currently installed and/or planned for use in future experiments by LOFT Experimental Measurements Branch personnel. Thermal/hydraulic conditions for Experiments L1-5 and L2-4 (for all nuclear tests) were used to predict the loads experienced by the various shroud and cover welds. The results of this analysis include minimum fatigue life for all subject welds, and Applied Mechanics Branch recommendations for improving the structural integrity of critically stressed welds

On Wings of the Minimum Induced Drag: Spanload Implications for Aircraft and Birds

Science.gov (United States)

Bowers, Albion H.; Murillo, Oscar J.; Jensen, Robert (Red); Eslinger, Brian; Gelzer, Christian

2016-01-01

For nearly a century Ludwig Prandtl's lifting-line theory remains a standard tool for understanding and analyzing aircraft wings. The tool, said Prandtl, initially points to the elliptical spanload as the most efficient wing choice, and it, too, has become the standard in aviation. Having no other model, avian researchers have used the elliptical spanload virtually since its introduction. Yet over the last half-century, research in bird flight has generated increasing data incongruous with the elliptical spanload. In 1933 Prandtl published a little-known paper presenting a superior spanload: any other solution produces greater drag. We argue that this second spanload is the correct model for bird flight data. Based on research we present a unifying theory for superior efficiency and coordinated control in a single solution. Specifically, Prandtl's second spanload offers the only solution to three aspects of bird flight: how birds are able to turn and maneuver without a vertical tail; why birds fly in formation with their wingtips overlapped; and why narrow wingtips do not result in wingtip stall. We performed research using two experimental aircraft designed in accordance with the fundamentals of Prandtl's second paper, but applying recent developments, to validate the various potentials of the new spanload, to wit: as an alternative for avian researchers, to demonstrate the concept of proverse yaw, and to offer a new method of aircraft control and efficiency.

Hydrodynamic Drag on Streamlined Projectiles and Cavities

KAUST Repository

Jetly, Aditya

2016-04-19

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

Superfluid drag in the two-component Bose-Hubbard model

Science.gov (United States)

Sellin, Karl; Babaev, Egor

2018-03-01

In multicomponent superfluids and superconductors, co- and counterflows of components have, in general, different properties. A. F. Andreev and E. P. Bashkin [Sov. Phys. JETP 42, 164 (1975)] discussed, in the context of He3/He4 superfluid mixtures, that interparticle interactions produce a dissipationless drag. The drag can be understood as a superflow of one component induced by phase gradients of the other component. Importantly, the drag can be both positive (entrainment) and negative (counterflow). The effect is known to have crucial importance for many properties of diverse physical systems ranging from the dynamics of neutron stars and rotational responses of Bose mixtures of ultracold atoms to magnetic responses of multicomponent superconductors. Although substantial literature exists that includes the drag interaction phenomenologically, only a few regimes are covered by quantitative studies of the microscopic origin of the drag and its dependence on microscopic parameters. Here we study the microscopic origin and strength of the drag interaction in a quantum system of two-component bosons on a lattice with short-range interaction. By performing quantum Monte Carlo simulations of a two-component Bose-Hubbard model we obtain dependencies of the drag strength on the boson-boson interactions and properties of the optical lattice. Of particular interest are the strongly correlated regimes where the ratio of coflow and counterflow superfluid stiffnesses can diverge, corresponding to the case of saturated drag.

Modelling of Aerodynamic Drag in Alpine Skiing

OpenAIRE

Elfmark, Ola

2017-01-01

Most of the breaking force in the speed disciplines in alpine skiing is caused by the aerodynamic drag, and a better knowledge of the drag force is therefore desirable to gain time in races. In this study a complete database of how the drag area (CDA) changes, with respect to the different body segments, was made and used to explain a complete body motion in alpine skiing. Three experiments were performed in the wind tunnel at NTNU, Trondheim. The database from a full body measurement on an a...

Search for a solute-drag effect in dendritic solidification

International Nuclear Information System (INIS)

Eckler, K.; Herlach, D.M.; Aziz, M.J.

1994-01-01

The authors report the results of an indirect experimental test for the solute-drag effect in alloy solidification by fitting the data of Eckler et.al. for Ni-B dendrite tip velocities vs undercooling to models in several ways. The unknown equilibrium partition coefficient, k e , was varied as a fitting parameter. When they combine the dendrite growth model of Boettinger et al. with the Continuous Growth Model (CGM) of Aziz and Kaplan with solute drag, they cannot fit the data for any value of k e . When they combine dendrite growth theory with the CGM without solute drag, they obtain a reasonable fit to the data for k e = 4 x 10 -6 . When they combine dendrite growth theory with a new partial-solute-drag interpolation between the with-solute-drag and the without-solute-drag versions of the CGM, they obtain a still better fit to the data for k e = 2.8 x 10 - 4. This result points out the possibility of partial solute-drag during solidification and the importance of an independent determination of k e in order to distinguish between models

On the origin of the drag force on golf balls

Science.gov (United States)

Balaras, Elias; Beratlis, Nikolaos; Squires, Kyle

2017-11-01

It is well establised that dimples accelerate the drag-crisis on a sphere. The result of the early drag-crisis is a reduction of the drag coefficient by more than a factor of two when compared to a smooth sphere at the same Reynolds number. However, when the drag coefficients for smooth and dimpled spheres in the supercritical regime are compared, the latter is higher by a factor of two to three. To understand the origin of this behavior we conducted direct numerical simulations of the flow around a dimpled sphere, which is similar to commercially available golf balls, in the supercritical regime. By comparing the results to those for a smooth sphere it is found that dimples, although effective in accelerating the drag crisis, impose a local drag-penalty, which contributes significantly to the overall drag force. This finding challenges the broadly accepted view, that the dimples only indirectly affect the drag force on a golf ball by manipulating the structure of the turbulent boundary layer near the wall and consequently affect global separation. Within this view, typically the penalty on the drag force imposed by the dimples is assumed to be small and coming primarily from skin friction. The direct numerical simulations we will report reveal a very different picture.

Experimental evaluation of the drag force and drag torque acting on a rotating spherical particle moving in fluid

Czech Academy of Sciences Publication Activity Database

Lukerchenko, Nikolay; Kvurt, Y.; Kharlamov, Alexander; Chára, Zdeněk; Vlasák, Pavel

2008-01-01

Roč. 56, č. 2 (2008), s. 88-94 ISSN 0042-790X R&D Projects: GA AV ČR IAA200600603 Institutional research plan: CEZ:AV0Z20600510 Keywords : drag force * drag torque * spherical particle * rotational movement * translational movement Subject RIV: DA - Hydrology ; Limnology

A Conventional Liner Acoustic/Drag Interaction Benchmark Database

Science.gov (United States)

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.

Relativistic Gas Drag on Dust Grains and Implications

Energy Technology Data Exchange (ETDEWEB)

Hoang, Thiem, E-mail: thiemhoang@kasi.re.kr [Korea Astronomy and Space Science Institute, Daejeon 34055 (Korea, Republic of); Korea University of Science and Technology, Daejeon, 34113 (Korea, Republic of)

2017-09-20

We study the drag force on grains moving at relativistic velocities through interstellar gas and explore its application. First, we derive a new analytical formula of the drag force at high energies and find that it is significantly reduced compared to the classical model. Second, we apply the obtained drag force to calculate the terminal velocities of interstellar grains by strong radiation sources such as supernovae and active galactic nuclei (AGNs). We find that grains can be accelerated to relativistic velocities by very luminous AGNs. We then quantify the deceleration of relativistic spacecraft proposed by the Breakthrough Starshot initiative due to gas drag on a relativistic lightsail. We find that the spacecraft’s decrease in speed is negligible because of the suppression of gas drag at relativistic velocities, suggesting that the lightsail may be open for communication during its journey to α Centauri without causing a considerable delay. Finally, we show that the damage to relativistic thin lightsails by interstellar dust is a minor effect.

London 2012 Paralympic swimming: passive drag and the classification system.

Science.gov (United States)

Oh, Yim-Taek; Burkett, Brendan; Osborough, Conor; Formosa, Danielle; Payton, Carl

2013-09-01

The key difference between the Olympic and Paralympic Games is the use of classification systems within Paralympic sports to provide a fair competition for athletes with a range of physical disabilities. In 2009, the International Paralympic Committee mandated the development of new, evidence-based classification systems. This study aims to assess objectively the swimming classification system by determining the relationship between passive drag and level of swimming-specific impairment, as defined by the current swimming class. Data were collected on participants at the London 2012 Paralympic Games. The passive drag force of 113 swimmers (classes 3-14) was measured using an electro-mechanical towing device and load cell. Swimmers were towed on the surface of a swimming pool at 1.5 m/s while holding their most streamlined position. Passive drag ranged from 24.9 to 82.8 N; the normalised drag (drag/mass) ranged from 0.45 to 1.86 N/kg. Significant negative associations were found between drag and the swimming class (τ = -0.41, p < 0.01) and normalised drag and the swimming class (τ = -0.60, p < 0.01). The mean difference in drag between adjacent classes was inconsistent, ranging from 0 N (6 vs 7) to 11.9 N (5 vs 6). Reciprocal Ponderal Index (a measure of slenderness) correlated moderately with normalised drag (r(P) = -0.40, p < 0.01). Although swimmers with the lowest swimming class experienced the highest passive drag and vice versa, the inconsistent difference in mean passive drag between adjacent classes indicates that the current classification system does not always differentiate clearly between swimming groups.

The elaborate plumage in peacocks is not such a drag.

Science.gov (United States)

Askew, Graham N

2014-09-15

One of the classic examples of an exaggerated sexually selected trait is the elaborate plumage that forms the train in male peafowl Pavo cristatus (peacock). Such ornaments are thought to reduce locomotor performance as a result of their weight and aerodynamic drag, but this cost is unknown. Here, the effect that the train has on take-off flight in peacocks was quantified as the sum of the rates of change of the potential and kinetic energies of the body (P(CoM)) in birds with trains and following the train's removal. There was no significant difference between P(CoM) in birds with and without a train. The train incurs drag during take-off; however, while this produces a twofold increase in parasite drag, parasite power only accounts for 0.1% of the total aerodynamic power. The train represented 6.9% of body weight and is expected to increase induced power. The absence of a detectable effect on take-off performance does not necessarily mean that there is no cost associated with possessing such ornate plumage; rather, it suggests that given the variation in take-off performance per se, the magnitude of any effect of the train has little meaningful functional relevance. © 2014. Published by The Company of Biologists Ltd.

Drag reduction of nata de coco suspensions in circular pipe flow

Science.gov (United States)

Warashina, J.; Ogata, S.

2015-04-01

Reducing pipe friction by adding a drag-reducing agent has attracted interest as a means to reduce energy consumption. In addition to reducing drag, these agents are required to have a low environmental load and conserve natural resources. However, no drag-reducing agent currently satisfies both these conditions. We focused on nata de coco and found that the nata de coco fiber reduced drag by up to 25%. With respect to the mechanism of drag reduction by nata de coco fiber, the relationship between drag-reduction phenomena and the fiber form of nata de coco was investigated by visualization. We also found that the drag-reduction effect appeared to be due to the formation of networks of tangled fibers of nata de coco. However, drag reduction did not occur in the case in which fibers of nata de coco did not form networks.

High accuracy satellite drag model (HASDM)

Science.gov (United States)

Storz, Mark F.; Bowman, Bruce R.; Branson, Major James I.; Casali, Stephen J.; Tobiska, W. Kent

The dominant error source in force models used to predict low-perigee satellite trajectories is atmospheric drag. Errors in operational thermospheric density models cause significant errors in predicted satellite positions, since these models do not account for dynamic changes in atmospheric drag for orbit predictions. The Air Force Space Battlelab's High Accuracy Satellite Drag Model (HASDM) estimates and predicts (out three days) a dynamically varying global density field. HASDM includes the Dynamic Calibration Atmosphere (DCA) algorithm that solves for the phases and amplitudes of the diurnal and semidiurnal variations of thermospheric density near real-time from the observed drag effects on a set of Low Earth Orbit (LEO) calibration satellites. The density correction is expressed as a function of latitude, local solar time and altitude. In HASDM, a time series prediction filter relates the extreme ultraviolet (EUV) energy index E10.7 and the geomagnetic storm index ap, to the DCA density correction parameters. The E10.7 index is generated by the SOLAR2000 model, the first full spectrum model of solar irradiance. The estimated and predicted density fields will be used operationally to significantly improve the accuracy of predicted trajectories for all low-perigee satellites.

Drag Reducing and Cavitation Resistant Coatings

Energy Technology Data Exchange (ETDEWEB)

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).

Assessment of passive drag in swimming by numerical simulation and analytical procedure.

Science.gov (United States)

Barbosa, Tiago M; Ramos, Rui; Silva, António J; Marinho, Daniel A

2018-03-01

The aim was to compare the passive drag-gliding underwater by a numerical simulation and an analytical procedure. An Olympic swimmer was scanned by computer tomography and modelled gliding at a 0.75-m depth in the streamlined position. Steady-state computer fluid dynamics (CFD) analyses were performed on Fluent. A set of analytical procedures was selected concurrently. Friction drag (D f ), pressure drag (D pr ), total passive drag force (D f +pr ) and drag coefficient (C D ) were computed between 1.3 and 2.5 m · s -1 by both techniques. D f +pr ranged from 45.44 to 144.06 N with CFD, from 46.03 to 167.06 N with the analytical procedure (differences: from 1.28% to 13.77%). C D ranged between 0.698 and 0.622 by CFD, 0.657 and 0.644 by analytical procedures (differences: 0.40-6.30%). Linear regression models showed a very high association for D f +pr plotted in absolute values (R 2  = 0.98) and after log-log transformation (R 2  = 0.99). The C D also obtained a very high adjustment for both absolute (R 2  = 0.97) and log-log plots (R 2  = 0.97). The bias for the D f +pr was 8.37 N and 0.076 N after logarithmic transformation. D f represented between 15.97% and 18.82% of the D f +pr by the CFD, 14.66% and 16.21% by the analytical procedures. Therefore, despite the bias, analytical procedures offer a feasible way of gathering insight on one's hydrodynamics characteristics.

Intelligent Control for Drag Reduction on the X-48B Vehicle

Science.gov (United States)

Griffin, Brian Joseph; Brown, Nelson Andrew; Yoo, Seung Yeun

2011-01-01

This paper focuses on the development of an intelligent control technology for in-flight drag reduction. The system is integrated with and demonstrated on the full X-48B nonlinear simulation. The intelligent control system utilizes a peak-seeking control method implemented with a time-varying Kalman filter. Performance functional coordinate and magnitude measurements, or independent and dependent parameters respectively, are used by the Kalman filter to provide the system with gradient estimates of the designed performance function which is used to drive the system toward a local minimum in a steepestdescent approach. To ensure ease of integration and algorithm performance, a single-input single-output approach was chosen. The framework, specific implementation considerations, simulation results, and flight feasibility issues related to this platform are discussed.

Drag reduction in channel flow using nonlinear control

Science.gov (United States)

Keefe, Laurence R.

1993-01-01

Two nonlinear control schemes have been applied to the problem of drag reduction in channel flow. Both schemes have been tested using numerical simulations at a mass flux Reynolds numbers of 4408, utilizing 2D nonlinear neutral modes for goal dynamics. The OGY-method, which requires feedback, reduces drag to 60-80 percent of the turbulent value at the same Reynolds number, and employs forcing only within a thin region near the wall. The H-method, or model-based control, fails to achieve any drag reduction when starting from a fully turbulent initial condition, but shows potential for suppressing or retarding laminar-to-turbulent transition by imposing instead a transition to a low drag, nonlinear traveling wave solution to the Navier-Stokes equation. The drag in this state corresponds to that achieved by the OGY-method. Model-based control requires no feedback, but in experiments to date has required the forcing be imposed within a thicker layer than the OGY-method. Control energy expenditures in both methods are small, representing less than 0.1 percent of the uncontrolled flow's energy.

Spin-transfer mechanism for magnon-drag thermopower

NARCIS (Netherlands)

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

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.

Resolvent-based feedback control for turbulent friction drag reduction

Science.gov (United States)

Kawagoe, Aika; Nakashima, Satoshi; Luhar, Mitul; Fukagata, Koji

2017-11-01

Suboptimal control for turbulent friction drag reduction has been studied extensively. Nakashima et al. (accepted) extended resolvent analysis to suboptimal control, and for the control where the streamwise wall shear stress is used as an input (Case ST), they revealed the control effect across spectral space is mixed: there are regions of drag increase as well as reduction. This suggests that control performance may be improved if the control is applied for selective wavelengths, or if a new law is designed to suppress the spectral region leading to drag increase. In the present study, we first assess the effect of suboptimal control for selective wavelengths via DNS. The friction Reynolds number is set at 180. For Case ST, resolvent analysis predicts drag reduction at long streamwise wavelengths. DNS with control applied only for this spectral region, however, did not result in drag reduction. Then, we seek an effective control law using resolvent analysis and propose a new law. DNS results for this law are consistent with predictions from resolvent analysis, and about 10% drag reduction is attained. Further, we discuss how this law reduces the drag from a dynamical and theoretical point of view. This work was supported through Grant-in-Aid for Scientic Research (C) (No. 25420129) by Japan Society for the Promotion of Science (JSPS).

Electron drag in ferromagnetic structures separated by an insulating interface

Science.gov (United States)

Kozub, V. I.; Muradov, M. I.; Galperin, Y. M.

2018-06-01

We consider electron drag in a system of two ferromagnetic layers separated by an insulating interface. The source of it is expected to be magnon-electron interactions. Namely, we assume that the external voltage is applied to the "active" layer stimulating electric current through this layer. In its turn, the scattering of the current-carrying electrons by magnons leads to a magnon drag current within this layer. The 3-magnons interactions between magnons in the two layers (being of non-local nature) lead to magnon drag within the "passive" layer which, correspondingly, produce electron drag current via processes of magnon-electron scattering. We estimate the drag current and compare it to the phonon-induced one.

Airflow in Gravity Sewers - Determination of Wastewater Drag Coefficient.

Science.gov (United States)

Bentzen, Thomas Ruby; Østertoft, Kristian Kilsgaard; Vollertsen, Jes; Fuglsang, Emil Dietz; Nielsen, Asbjørn Haaning

2016-03-01

Several experiments have been conducted in order to improve the understanding of the wastewater drag and the wall frictional force acting on the headspace air in gravity sewers. The aim of the study is to improve the data basis for a numerical model of natural sewer ventilation. The results 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 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 was found.

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.)

Measurements of drag and flow over biofilm

Science.gov (United States)

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.

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.

Creating drag and lift curves from soccer trajectories

Science.gov (United States)

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.

First ever in situ observations of Venus' polar upper atmosphere density using the tracking data of the Venus Express Atmospheric Drag Experiment (VExADE)

Science.gov (United States)

Rosenblatt, P.; Bruinsma, S. L.; Müller-Wodarg, I. C. F.; Häusler, B.; Svedhem, H.; Marty, J. C.

2012-02-01

On its highly elliptical 24 h orbit around Venus, the Venus Express (VEX) spacecraft briefly reaches a periapsis altitude of nominally 250 km. Recently, however, dedicated and intense radio tracking campaigns have taken place in August 2008, October 2009, February and April 2010, for which the periapsis altitude was lowered to the 186-176 km altitude range in order to be able to probe the upper atmosphere of Venus above the North Pole for the first time ever in situ. As the spacecraft experiences atmospheric drag, its trajectory is measurably perturbed during the periapsis pass, allowing us to infer total atmospheric mass density at the periapsis altitude. A Precise Orbit Determination (POD) of the VEX motion is performed through an iterative least-squares fitting process to the Doppler tracking data, acquired by the VEX radioscience experiment (VeRa). The drag acceleration is modelled using an initial atmospheric density model (VTS3 model, Hedin, A.E., Niemann, H.B., Kasprzak, W.T., Seiff, A. [1983]. J. Geophys. Res. 88, 73-83). A scale factor of the drag acceleration is estimated for each periapsis pass, which scales Hedin's density model in order to best fit the radio tracking data. Reliable density scale factors have been obtained for 10 passes mainly from the second (October 2009) and third (April 2010) VExADE campaigns, which indicate a lower density by a factor of about 1.8 than Hedin's model predicts. These first ever in situ polar density measurements at solar minimum have allowed us to construct a diffusive equilibrium density model for Venus' thermosphere, constrained in the lower thermosphere primarily by SPICAV-SOIR measurements and above 175 km by the VExADE drag measurements (Müller-Wodarg et al., in preparation). The preliminary results of the VExADE campaigns show that it is possible to obtain with the POD technique reliable estimates of Venus' upper atmosphere densities at an altitude of around 175 km. Future VExADE campaigns will benefit from

Nonuniform charging effects on ion drag force in drifting dusty plasmas

International Nuclear Information System (INIS)

Chang, Dong-Man; Chang, Won-Seok; Jung, Young-Dae

2006-01-01

The nonuniform polarization charging effects on the ion drag force are investigated in drifting dusty plasmas. The ion drag force due to the ion-dust grain interaction is obtained as a function of the dust charge, ion charge, plasma temperature, Mach number, Debye length, and collision energy. The result shows that the nonuniform charging effects enhance the momentum transfer cross section as well as the ion drag force. It is found that the momentum transfer cross section and the ion drag force including nonuniform polarization charging effects increase with increasing the Mach number and also the ion drag force increases with increasing the temperature. In addition, it is found that the ion drag force is slightly decreasing with an increase of the Debye length

Microsputterer with integrated ion-drag focusing for additive manufacturing of thin, narrow conductive lines

Science.gov (United States)

Kornbluth, Y. S.; Mathews, R. H.; Parameswaran, L.; Racz, L. M.; Velásquez-García, L. F.

2018-04-01

We report the design, modelling, and proof-of-concept demonstration of a continuously fed, atmospheric-pressure microplasma metal sputterer that is capable of printing conductive lines narrower than the width of the target without the need for post-processing or lithographic patterning. Ion drag-induced focusing is harnessed to print narrow lines; the focusing mechanism is modelled via COMSOL Multiphysics simulations and validated with experiments. A microplasma sputter head with gold target is constructed and used to deposit imprints with minimum feature sizes as narrow as 9 µm, roughness as small as 55 nm, and electrical resistivity as low as 1.1 µΩ · m.

Dragging of inertial frames.

Science.gov (United States)

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.

Friction and drag forces on spheres propagating down inclined planes

Science.gov (United States)

Tee, Yi Hui; Longmire, Ellen

2017-11-01

When a submerged sphere propagates along an inclined wall at terminal velocity, it experiences gravity, drag, lift, and friction forces. In the related equations of motion, the drag, lift and friction coefficients are unknown. Experiments are conducted to determine the friction and drag coefficients of the sphere over a range of Reynolds numbers. Through high speed imaging, translational and rotational velocities of spheres propagating along a glass plate are determined in liquids with several viscosities. The onset of sliding motion is identified by computing the dimensionless rotation rate of the sphere. Using drag and lift coefficients for Re friction coefficients are calculated for several materials. The friction coefficients are then employed to estimate the drag coefficient for 350 frictional force over this Re range. Supported by NSF (CBET-1510154).

Bilateral macular colobomata: Temporal dragging of optic disc

Directory of Open Access Journals (Sweden)

David J Mathew

2015-01-01

Full Text Available A 13-year-old male presented with decreased vision and squint from childhood. He had bilateral large colobomata at the macula in each eye, the one on the right being larger than the left. The disc was dragged temporally with straightening of the temporal retinal vessels. This is a case report of bilateral large macular coloboma and serves to report its association with a temporally dragged disc and straightened temporal retinal vessels. A dragged disc if present with a colobomatous defect at the macula may strengthen the case for diagnosis of macular coloboma and help exclude other differentials.

Oscillating Sign of Drag in High Landau Levels

International Nuclear Information System (INIS)

von Oppen, Felix; Simon, Steven H.; Stern, Ady

2001-01-01

Motivated by experiments, we study the sign of the Coulomb drag voltage in a double layer system in a strong magnetic field. We show that the commonly used Fermi golden rule approach implicitly assumes a linear dependence of intralayer conductivity on density, and is thus inadequate in strong magnetic fields. Going beyond this approach, we show that the drag voltage commonly changes sign with density difference between the layers. We find that, in the quantum Hall regime, the Hall and longitudinal drag resistivities may be comparable. Our results are also relevant for pumping and acoustoelectric experiments

Experimental and numerical investigation of low-drag intervals in turbulent boundary layer

Science.gov (United States)

Park, Jae Sung; Ryu, Sangjin; Lee, Jin

2017-11-01

It has been widely investigated that there is a substantial intermittency between high and low drag states in wall-bounded shear flows. Recent experimental and computational studies in a turbulent channel flow have identified low-drag time intervals based on wall shear stress measurements. These intervals are a weak turbulence state characterized by low-speed streaks and weak streamwise vortices. In this study, the spatiotemporal dynamics of low-drag intervals in a turbulent boundary layer is investigated using experiments and simulations. The low-drag intervals are monitored based on the wall shear stress measurement. We show that near the wall conditionally-sampled mean velocity profiles during low-drag intervals closely approach that of a low-drag nonlinear traveling wave solution as well as that of the so-called maximum drag reduction asymptote. This observation is consistent with the channel flow studies. Interestingly, the large spatial stretching of the streak is very evident in the wall-normal direction during low-drag intervals. Lastly, a possible connection between the mean velocity profile during the low-drag intervals and the Blasius profile will be discussed. This work was supported by startup funds from the University of Nebraska-Lincoln.

On the Effect of Rigid Swept Surface Waves on Turbulent Drag

Science.gov (United States)

Denison, M.; Wilkinson, S. P.; Balakumar, P.

2015-01-01

Passive turbulent drag reduction techniques are of interest as a cost effective means to improve air vehicle fuel consumption. In the past, rigid surface waves slanted at an angle from the streamwise direction were deemed ineffective to reduce skin friction drag due to the pressure drag that they generate. A recent analysis seeking similarities to the spanwise shear stress generated by spatial Stokes layers suggested that there may be a range of wavelength, amplitude, and orientation in which the wavy surface would reduce turbulent drag. The present work explores, by experiments and Direct Numerical Simulations (DNS), the effect of swept wavy surfaces on skin friction and pressure drag. Plates with shallow and deep wave patterns were rapid-prototyped and tested using a drag balance in the 7x11 inch Low-Speed Wind Tunnel at the NASA LaRC Research Center. The measured drag o set between the wavy plates and the reference at plate is found to be within the experimental repeatability limit. Oil vapor flow measurements indicate a mean spanwise flow over the deep waves. The turbulent flow in channels with at walls, swept wavy walls and spatial Stokes spanwise velocity forcing was simulated at a friction Reynolds number of two hundred. The time-averaged and dynamic turbulent flow characteristics of the three channel types are compared. The drag obtained for the channel with shallow waves is slightly larger than for the at channel, within the range of the experiments. In the case of the large waves, the simulation over predicts the drag. The shortcomings of the Stokes layer analogy model for the estimation of the spanwise shear stress and drag are discussed.

Superhydrophobic and polymer drag reduction in turbulent Taylor-Couette flow

Science.gov (United States)

Rajappan, Anoop; McKinley, Gareth H.

2017-11-01

We use a custom-built Taylor-Couette apparatus (radius ratio η = 0.75) to study frictional drag reduction by dilute polymer solutions and superhydrophobic (SH) surfaces in turbulent flows for 15000 analysis. We also investigate drag reduction by dilute polymer solutions, and show that natural biopolymers from plant mucilage can be an inexpensive and effective alternative to synthetic polymers in drag reduction applications, approaching the same maximum drag reduction asymptote. Finally we explore combinations of the two methods - one arising from wall slip and the other due to changes in turbulence dynamics in the bulk flow - and find that the two effects are not additive; interestingly, the effectiveness of polymer drag reduction is drastically reduced in the presence of an SH coating on the wall. This study was financially supported by the Office of Naval Research (ONR) through Contract No. 3002453814.

Geodetic precession or dragging of inertial frames?

International Nuclear Information System (INIS)

Ashby, N.; Shahid-Saless, B.

1990-01-01

In metric theories of gravity the principle of general covariance allows one to describe phenomena by means of any convenient choice of coordinate system. In this paper it is shown that in an appropriately chosen coordinate system, geodetic precession of a gyroscope orbiting a spherically symmetric, spinning mass can be recast as a Lense-Thirring frame-dragging effect without invoking spatial curvature. The origin of this reference frame moves around the source but the frame axes point in fixed directions. The drag can be interpreted to arise from the orbital angular momentum of the source around the origin of the reference frame. In this reference frame the effects of geodetic precession and Lense-Thirring drag due to intrinsic angular momentum of the source have the same origin, namely, gravitomagnetism

Drag prediction for blades at high angle of attack using CFD

DEFF Research Database (Denmark)

Sørensen, Niels N.; Michelsen, J.A.

2004-01-01

In the present paper it is first demonstrated that state of the art 3D CFD codes are. capable of predicting the correct dependency of the integrated drag of a flat plate placed perpendicular to the flow. This is in strong contrast to previous 2D investigations of infinite plates, where computations...... are known to severely overpredict drag. We then demonstrate that the computed drag distribution along the plate span deviate from the general expectation of 2D behavior at the central part of the plate, an important finding in connection with the theoretical estimation of drag behavior on wind turbine...... blades. The computations additionally indicate that a tip effect is present that produces increased drag near the end of the plate, which is opposite of the assumptions generally used in drag estimation for blades. Following this several wind turbine blades are analyzed, ranging from older blades...

Wave drag as the objective function in transonic fighter wing optimization

Science.gov (United States)

Phillips, P. S.

1984-01-01

The original computational method for determining wave drag in a three dimensional transonic analysis method was replaced by a wave drag formula based on the loss in momentum across an isentropic shock. This formula was used as the objective function in a numerical optimization procedure to reduce the wave drag of a fighter wing at transonic maneuver conditions. The optimization procedure minimized wave drag through modifications to the wing section contours defined by a wing profile shape function. A significant reduction in wave drag was achieved while maintaining a high lift coefficient. Comparisons of the pressure distributions for the initial and optimized wing geometries showed significant reductions in the leading-edge peaks and shock strength across the span.

Navier slip model of drag reduction by Leidenfrost vapor layers

KAUST Repository

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

KAUST Repository

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

2017-01-01

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 (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.

Theory of Coulomb drag for massless Dirac fermions

International Nuclear Information System (INIS)

Carrega, M; Principi, A; Polini, M; Tudorovskiy, T; Katsnelson, M I

2012-01-01

Coulomb drag between two unhybridized graphene sheets separated by a dielectric spacer has recently attracted considerable theoretical interest. We first review, for the sake of completeness, the main analytical results which have been obtained by other authors. We then illustrate pedagogically the minimal theory of Coulomb drag between two spatially separated two-dimensional systems of massless Dirac fermions which are both away from the charge-neutrality point. This relies on second-order perturbation theory in the screened interlayer interaction and on Boltzmann-transport theory. In this theoretical framework and in the low-temperature limit, we demonstrate that, to leading (i.e. quadratic) order in temperature, the drag transresistivity is completely insensitive to the precise intralayer momentum-relaxation mechanism (i.e. to the functional dependence of the transport scattering time on energy). We also provide analytical results for the low-temperature drag transresistivity for both cases of ‘thick’ and ‘thin’ spacers and for arbitrary values of the dielectric constants of the media surrounding the two Dirac-fermion layers. Finally, we present numerical results for the low-temperature drag transresistivity for the case when one of the media surrounding the Dirac-fermion layers has a frequency-dependent dielectric constant. We conclude by suggesting an experiment that can potentially allow for the observation of departures from the canonical quadratic-in-temperature behavior of the transresistivity. (paper)

The 3D CFD study of gliding swimmer on passive hydrodynamics drag

Directory of Open Access Journals (Sweden)

Vishveshwar Rajendra Mantha

2014-04-01

Full Text Available The aim of this study was to analyze the effect of depth on the hydrodynamic drag coefficient during the passive underwater gliding after the starts and turns. The swimmer hydrodynamics performance was studied by the application of computational fluid dynamics (CFD method. The steady-state CFD simulations were performed by the application of k - omega turbulent model and volume of fluid method to obtain two-phase flow around a three-dimensional swimmer model when gliding near water surface and at different depths from the water surface. The simulations were conducted for four different swimming pool size, each with different depth, i.e., 1.0, 1.5, 2.0 and 3.0 m for three different velocities, i.e., 1.5, 2.0 and 2.5 m/s, with swimmer gliding at different depths with intervals of 0.25 m, each starting from the water surface, respectively. The numerical results of pressure drag and total coefficients at individual average race velocities were obtained. The results showed that the drag coefficient decreased as depth increased, with a trend toward reduced fluctuation after 0.5m depth from the water surface. The selection of the appropriate depth during the gliding phase should be a main concern of swimmers and coaches.

Investigation of Drag Coefficient for Rigid Ballute-like Shapes

Science.gov (United States)

Carnasciali, Maria-Isabel; Mastromarino, Anthony

2014-11-01

One common method of decelerating an object during atmospheric entry, descent, and landing is the use of parachutes. Another deceleration technology is the ballute - a combination of balloon and parachute. A CFD study was conducted using commercially available software to investigate the flow-field and the coefficient of drag for various rigid ballute-like shapes at varying Reynolds numbers. The impact of size and placement of the burble-fence as well as number, size, and shape of inlets was considered. Recent experimental measurements conducted during NASA's Low-Density Supersonic Decelerator program revealed a much higher coefficient of drag (Cd) for ballutes than previously encountered. Using atmospheric drag to slow down and land reduces the need for heavy fuel and rocket engines and thus, high values of drag are desired. Funding for this work, in part, provided by the CT Space Grant Consortium.

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.

Ad/dressing the nation: drag and authenticity in post-apartheid South Africa.

Science.gov (United States)

Spruill, Jennifer

2004-01-01

This paper examines a style of drag in South Africa that features "traditional African" clothing. In a region in which homosexuality is denigrated as a colonial, European import and "unAfrican," the meaning of "traditional drag" is deeply inflected by the question of cultural authenticity. This dragging practice fits within a distinctly post-colonial production of tradition and its self-conscious display--in the form of attire--of a decidedly "gay" one. Traditional drag also responds to ongoing politics within and between lesbian and gay communities about racial "representivity" and "transformation." The paper focuses on displays of traditional drag at Johannesburg's Gay and Lesbian Pride Parade but also explores the complex politics of publicity and address suggested by varying contexts in which traditional dress and drag are mobilized.

Understanding the Minimum Wage: Issues and Answers.

Science.gov (United States)

Employment Policies Inst. Foundation, Washington, DC.

This booklet, which is designed to clarify facts regarding the minimum wage's impact on marketplace economics, contains a total of 31 questions and answers pertaining to the following topics: relationship between minimum wages and poverty; impacts of changes in the minimum wage on welfare reform; and possible effects of changes in the minimum wage…

Drag force in a D-instanton background

Science.gov (United States)

Zhang, Zi-qiang; Luo, Zhong-jie; Hou, De-fu

2018-06-01

We study the drag force and diffusion coefficient with respect to a moving heavy quark in a D-instanton background, which corresponds to the Yang-Mills theory in the deconfining, high-temperature phase. It is shown that the presence of the D-instanton density tends to increase the drag force and decrease the diffusion coefficient, reverse to the effects of the velocity and the temperature. Moreover, the inclusion of the D-instanton density makes the medium less viscous.

The contact drag of towed demersal fishing gear components

Science.gov (United States)

O'Neill, F. G.; Summerbell, K.; Ivanović, A.

2018-01-01

The contact demersal towed fishing gears make with the seabed can lead to penetration of the substrate, lateral displacement of the sediment and a pressure field transmitted through the sediment. It will also contribute to the overall drag of the fishing gear. Consequently, there can be environmental effects such as habitat alteration and benthic mortality, and impacts to the fuel efficiency of the fishing operation which will affect emissions of nitrogen oxides, sulphur oxides and greenhouse gases such as CO2. Here we present the results of experimental trials that measure the contact drag of a range of elements that represent some of the components of towed demersal gears that are in contact with the seabed. We show that the contact drag of the gear components depends on their weight, geometry, the type of sediment on which they are towed and whether they are rolling or not. As expected, the contact drag of each gear component increases as its weight increases and the drag of fixed elements is greater than that of the rolling ones. The dependence on aspect ratio is more complex and the drag (per unit area) of narrow cylinders is less than that of wider ones when they roll on the finer sediment or are fixed (not permitted to roll) on the coarser sediment. When they roll on the coarse sediment there is no dependence on aspect ratio. Our results also suggest that fixed components may penetrate the seabed to a lesser depth when they are towed at higher speeds but when they roll there is no such relationship.

Identification of integrated airframe: Propulsion effects on an F-15 aircraft for application to drag minimization

Science.gov (United States)

Schkolnik, Gerard S.

1993-01-01

The application of an adaptive real-time measurement-based performance optimization technique is being explored for a future flight research program. The key technical challenge of the approach is parameter identification, which uses a perturbation-search technique to identify changes in performance caused by forced oscillations of the controls. The controls on the NASA F-15 highly integrated digital electronic control (HIDEC) aircraft were perturbed using inlet cowl rotation steps at various subsonic and supersonic flight conditions to determine the effect on aircraft performance. The feasibility of the perturbation-search technique for identifying integrated airframe-propulsion system performance effects was successfully shown through flight experiments and postflight data analysis. Aircraft response and control data were analyzed postflight to identify gradients and to determine the minimum drag point. Changes in longitudinal acceleration as small as 0.004 g were measured, and absolute resolution was estimated to be 0.002 g or approximately 50 lbf of drag. Two techniques for identifying performance gradients were compared: a least-squares estimation algorithm and a modified maximum likelihood estimator algorithm. A complementary filter algorithm was used with the least squares estimator.

Identification of integrated airframe-propulsion effects on an F-15 aircraft for application to drag minimization

Science.gov (United States)

Schkolnik, Gerald S.

1993-01-01

The application of an adaptive real-time measurement-based performance optimization technique is being explored for a future flight research program. The key technical challenge of the approach is parameter identification, which uses a perturbation-search technique to identify changes in performance caused by forced oscillations of the controls. The controls on the NASA F-15 highly integrated digital electronic control (HIDEC) aircraft were perturbed using inlet cowl rotation steps at various subsonic and supersonic flight conditions to determine the effect on aircraft performance. The feasibility of the perturbation-search technique for identifying integrated airframe-propulsion system performance effects was successfully shown through flight experiments and postflight data analysis. Aircraft response and control data were analyzed postflight to identify gradients and to determine the minimum drag point. Changes in longitudinal acceleration as small as 0.004 g were measured, and absolute resolution was estimated to be 0.002 g or approximately 50 lbf of drag. Two techniques for identifying performance gradients were compared: a least-squares estimation algorithm and a modified maximum likelihood estimator algorithm. A complementary filter algorithm was used with the least squares estimator.

Experimental Investigation of the Fresnel Drag Effect in RF Coaxial Cables

Directory of Open Access Journals (Sweden)

Cahill R. T.

2011-01-01

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

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

International Nuclear Information System (INIS)

Ramirez-Munoz, J.; Salinas-Rodriguez, E.; Soria, A.; Gama-Goicochea, A.

2011-01-01

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.

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.

Grafted natural polymer as new drag reducing agent: An experimental approach

Directory of Open Access Journals (Sweden)

Abdulbari Hayder A.

2012-01-01

Full Text Available The present investigation introduces a new natural drag reducing agent which has the ability to improve the flow in pipelines carrying aqueous or hydrocarbon liquids in turbulent flow. Okra (Abelmoschus esculentus mucilage drag reduction performance was tested in water and hydrocarbon (gas-oil media after grafting. The drag reduction test was conducted in a buildup closed loop liquid circulation system consists of two pipes 0.0127 and 0.0381 m Inside Diameter (ID, four testing sections in each pipe (0.5 to 2.0 m, tank, pump and pressure transmitters. Reynolds number (Re, additive concentration and the transported media type (water and gas-oil, were the major drag reduction variables investigated. The experimental results show that, new additive drag reduction ability is high with maximum percentage of drag reduction (%Dr up to 60% was achieved. The experimental results showed that the drag reduction ability increased by increasing the additive concentration. The %Dr was found to increase by increasing the Re by using the water-soluble additive while it was found to decrease by increasing the Re when using the oil-soluble additive. The %Dr was higher in the 0.0381 m ID pipe. Finally, the grafted and natural mucilage showed high resistance to shear forces when circulated continuously for 200 seconds in the closed-loop system.

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

International Nuclear Information System (INIS)

Fang, J; Hong, Y J; Li, Q; Huang, H

2011-01-01

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.

Reynolds number dependence of drag reduction by rodlike polymers

NARCIS (Netherlands)

Amarouchene, Y.; Bonn, D.; Kellay, H.; Lo, T.-S.; L'vov, V.S.; Procaccia, I.

2008-01-01

We present experimental and theoretical results addressing the Reynolds number (Re) dependence of drag reduction by sufficiently large concentrations of rodlike polymers in turbulent wall-bounded flows. It is shown that when Re is small the drag is enhanced. On the other hand, when Re increases, the

Frictional Coulomb drag in strong magnetic fields

DEFF Research Database (Denmark)

Bønsager, Martin Christian; Flensberg, Karsten; Hu, Ben Yu-Kuang

1997-01-01

A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21) is eval......A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21...

Aerodynamic drag reduction tests on a box-shaped vehicle

Science.gov (United States)

Peterson, R. L.; Sandlin, D. R.

1981-01-01

The intent of the present experiment is to define a near optimum value of drag coefficient for a high volume type of vehicle through the use of a boattail, on a vehicle already having rounded front corners and an underbody seal, or fairing. The results of these tests will constitute a baseline for later follow-on studies to evaluate candidate methods of obtaining afterbody drag coefficients approaching the boattail values, but without resorting to such impractical afterbody extensions. The current modifications to the box-shaped vehicle consisted of a full and truncated boattail in conjunction with the faired and sealed underbody. Drag results from these configurations are compared with corresponding wind tunnel results of a 1/10 scale model. Test velocities ranged up to 96.6 km/h (60 mph) and the corresponding Reynolds numbers ranged up to 1.3 x 10 to the 7th power based on the vehicles length which includes the boattail. A simple coast-down technique was used to define drag.

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

KAUST Repository

Vakarelski, Ivan Uriev

2016-09-08

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

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

KAUST Repository

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

2016-01-01

The drag coefficient CD of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re∼3×105. 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.

A Numerical Method for Calculating the Wave Drag of a Configuration from the Second Derivative of the Area Distribution of a Series of Equivalent Bodies of Revolution

Science.gov (United States)

Levy, Lionel L., Jr.; Yoshikawa, Kenneth K.

1959-01-01

A method based on linearized and slender-body theories, which is easily adapted to electronic-machine computing equipment, is developed for calculating the zero-lift wave drag of single- and multiple-component configurations from a knowledge of the second derivative of the area distribution of a series of equivalent bodies of revolution. The accuracy and computational time required of the method to calculate zero-lift wave drag is evaluated relative to another numerical method which employs the Tchebichef form of harmonic analysis of the area distribution of a series of equivalent bodies of revolution. The results of the evaluation indicate that the total zero-lift wave drag of a multiple-component configuration can generally be calculated most accurately as the sum of the zero-lift wave drag of each component alone plus the zero-lift interference wave drag between all pairs of components. The accuracy and computational time required of both methods to calculate total zero-lift wave drag at supersonic Mach numbers is comparable for airplane-type configurations. For systems of bodies of revolution both methods yield similar results with comparable accuracy; however, the present method only requires up to 60 percent of the computing time required of the harmonic-analysis method for two bodies of revolution and less time for a larger number of bodies.

EFFECTIVENESS OF NYLON DRAG STRAPS FOR BRAKING MONORAIL SLEDS.

Science.gov (United States)

Velocity versus coast distance measurements on two monorail rocket sleds were conducted on the Holloman track to obtain numerical information on the...sleds and the drag straps. The straps as described are shown to increase the effective drag area of the monorail sleds used by approximately one square

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

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...

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

Directory of Open Access Journals (Sweden)

Huawei Chen

2014-06-01

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

Computational investigations of blunt body drag-reduction spikes in hypersonic flows

International Nuclear Information System (INIS)

Kamran, N.; Zahir, S.; Khan, M.A.

2003-01-01

Drag is an important parameter in the designing of high-speed vehicles. Such vehicles include hypervelocity projectiles, reentry modules, and hypersonic aircrafts. Therefore, there exists an active or passive technique to reduce drag due to the high pressures at nosetip region of the vehicle. Drag can be reduced by attaching a forward facing spike on the nose of the vehicle. The present study reviews and deals with the CFD analysis made on a standard blunt body to reduce aerodynamic drag due to the attachment of forward facing spikes for High-Speed vehicles. Different spike lengths have been examined to study the forebody flowfield. The investigation concludes that spikes are an effective way to reduce the aerodynamic drag due to reduced dynamic pressure on the nose caused by the separated flow on the spikes. With the accomplishment of confidence on computational data, study was extended in hypersonic Mach range with a drag prediction accuracy of ± 10%. In the present work, viscous fluid dynamics studies were performed for a complete freestream Mach number range of 5.0, 6.0, 7.0 and 8.0 for different spike lengths and zero degree angle of attack. (author)

On the Fetch Dependent Drag Coefficient over Coastal and Inland Seas

DEFF Research Database (Denmark)

Geernaert, G. L.; Smith, J. A.

a maximum when the phase speed of the dominant wind wave has a value near 7 u*, where u* is the friction velocity. This corresponds to a maximum near 2 km fetch during moderate windspeed, and the maximum value of the drag coefficient corresponds to an increased fetch of 13 km for windspeeds of 20 m/sec. We......The drag coefficient has been postulated by many investigators to depend on fetch. For constant windspeed and stability, laboratory data generally show an increasing drag coefficient with fetch while field observations show a decreasing dependence. In this study, we show that if one combines...... the spectral form of the roughness length proposed by Kitaigorodskii with the JONSWAP wave spectrum and extrapolate to very short fetch, then the predicted drag coefficient exhibits a behaviour which coarsely reproduces field and laboratory observations. The results indicate that the drag coefficient exhibits...

Modelling of Structural Loads in Drag Augmented Space Debris Removal Concepts

DEFF Research Database (Denmark)

Kristensen, Anders Schmidt; Nikolajsen, Jan Ánike; Lauridsen, Peter Riddersholm

2017-01-01

A Self-deployable Deorbiting Space Structure (SDSS) is used for drag augmented space debris removal. A highly flexible frame allows for a folding of the structure by bifurcation. This research models the structural loads during the deployment and unfolding of the drag sail in Low Earth Orbit (LEO......). The Spacecraft travels with 7.8 km/s at deployment. As the drag sail unfolds instantaneously the structure must withstand the loads from the unfolding and the drag. Thermal loads are included in the FEA as the temperature varies from -80°C to +80°C during deorbit. The results are used to verify the structural...

Effect of structure height on the drag reduction performance using rotating disk apparatus

Energy Technology Data Exchange (ETDEWEB)

Rashed, Musaab K; Salleh, Mohamad Amran Mohd; Ismail, M Halim Shah [Department of Chemical and Environmental Engineering, Faculty of Engineering, University Putra Malaysia (Malaysia); Abdulbari, Hayder A, E-mail: hayder.bari@gmail.com [Center of Excellence for Advanced Research in Fluid Flow, Universiti Malaysia Pahang (Malaysia)

2017-02-15

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. (paper)

Effect of guideway discontinuities on magnetic levitation and drag forces

International Nuclear Information System (INIS)

Rossing, T.D.; Korte, R.; Hull, J.R.

1991-01-01

Transients in the lift and drag forces on a NdFeB permanent magnet were observed as the magnet passed over various discontinuities in a rotating aluminum disk at velocities of 4 to 25 m/s. For full cuts in the disk, the amplitude of the lift and drag transients and the wave form of the drag transient depend on the width, and the amplitudes are much larger than for partial cuts. The use of a backing plate to join two cut segments is ineffective

Wake-Model Effects on Induced Drag Prediction of Staggered Boxwings

Directory of Open Access Journals (Sweden)

Julian Schirra

2018-01-01

Full Text Available For staggered boxwings the predictions of induced drag that rely on common potential-flow methods can be of limited accuracy. For example, linear, freestream-fixed wake models cannot resolve effects related to wake deflection and roll-up, which can have significant affects on the induced drag projection of these systems. The present work investigates the principle impact of wake modelling on the accuracy of induced drag prediction of boxwings with stagger. The study compares induced drag predictions of a higher-order potential-flow method that uses fixed and relaxed-wake models, and of an Euler-flow method. Positive-staggered systems at positive angles of attack are found to be particularly prone to higher-order wake effects due to vertical contraction of wakes trajectories, which results in smaller effective height-to-span ratios than compared with negative stagger and thus closer interactions between trailing wakes and lifting surfaces. Therefore, when trying to predict induced drag of positive staggered boxwings, only a potential-flow method with a fully relaxed-wake model will provide the high-degree of accuracy that rivals that of an Euler method while being computationally significantly more efficient.

Modification of near-wall coherent structures in polymer drag reduced flow: simulation

Science.gov (United States)

Dubief, Yves; White, Christopher; Shaqfeh, Eric; Moin, Parviz; Lele, Sanjiva

2002-11-01

Polymer drag reduced flows are investigated through direct numerical simulations of viscoelastic flows. The solver for the viscoelastic model (FENE-P) is based on higher-order finite difference schemes and a novel implicit time integration method. Its robustness allows the simulation of all drag reduction (DR) regimes from the onset to the maximum drag reduction (MDR). It also permits the use of realistic polymer length and concentration. The maximum polymer extension in our simulation matches that of a polystyrene molecule of 10^6 molecular weight. Two distinct regimes of polymer drag reduced flows are observed: at low drag reduction (LDR, DR< 40-50%), the near-wall structure is essentially similar to Newtonian wall turbulence whereas the high drag reduction regime (HDR, DR from 40-50% to MDR) shows significant differences in the organization of the coherent structures. The 3D information provided by numerical simulations allows the determination of the interaction of polymers and near-wall coherent structures. To isolate the contribution of polymers in the viscous sublayer, the buffer and the outer region of the flow, numerical experiments are performed where the polymer concentration is varied in the wall-normal direction. Finally a mechanism of polymer drag reduction derived from our results and PIV measurements is discussed.

Discovery of riblets in a bird beak (Rynchops) for low fluid drag.

Science.gov (United States)

Martin, Samuel; Bhushan, Bharat

2016-08-06

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, reducing drag on their beak is advantageous. For the first time, riblet structures found on the beak of the skimmer bird have been studied experimentally and computationally for low fluid drag properties. In this study, skimmer replicas were studied for drag reduction through pressure drop in closed-channel, turbulent water flow. Pressure drop measurements are compared for black and yellow skimmer beaks in two configurations, and mako shark skin. In addition, two configurations of skimmer beak were modelled to compare drag properties and vortex structures. Results are discussed, and a conceptual model is presented to explain a possible drag reduction mechanism in skimmers.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'. © 2016 The Author(s).

Pengaruh Variasi Jarak Penghalang Segitiga di depan Silinder Arah Vertikal terhadap Drag

Directory of Open Access Journals (Sweden)

I Putu Gede Gunawan Tista

2018-04-01

Full Text Available Salah satu cara untuk menghemat energi pada pesawat terbang dan bluff body lainnya adalah dengan mengurangi drag. Drag erat hubungannya dengan separasi aliran. Semakin awal terjadi separasi maka drag semakin meningkat. Oleh karena itu upaya yang dilakukan untuk mengurangi drag adalah dengan memanipulasi medan aliran fluida. Manipulasi aliran bisa dilakukan secara pasif antara lain menempelkan sebuah sirip pada bluff body, melubangi bluff body, menambahkan spiral pada bluff body dan menempatkan penghalang yang lebih kecil didepan bluff body. Penelitian ini yaitu dengan cara  menempatkan penghalang berbentuk segitiga didepan silinder. Dalam penelitian ini pengujian dilakukan pada wind tunnel, yang terdiri dari blower, pipa pitot, manometer, pipa silinder, dan segitiga penghalang. Penempatan penghalang divariasikan pada arah vertikal posisi y = 0, y = 5 mm, y = 10 mm, y = 15 mm, sedangkan posisi penghalang pada arah horisontal pada jarak  60 mm terhadap silinder dengan panjang sisi segitiga adalah 8 mm. Distribusi tekanan diperoleh dengan mengukur tekanan permukaan silinder pada 36 titik dengan interval 10o. Data yang diukur adalah tekanan permukaan silinder, tekanan statis, dan kecepatan aliran fluida. Hasil penelitian menunjukkan bahwa terjadi penurunan drag pada saat diberi penghalang segitiga dibandingkan dengan tanpa diberi penghalang segitiga. Nilai koefisien drag untuk silinder tanpa diberi penghalang yaitu 0.1276. Sedangkan dari variasi jarak penghalang pada arah vertikal diperoleh penurunan koefisien drag tertinggi adalah pada posisi  y = 0 yaitu sebesar 0,0186. Besarnya penurunan drag pada posisi ini adalah 85,45% dibandingkan dengan tanpa penghalang. One of the ways to reduce energy consumption an airplane and the other bluff body is by decreasing the drag.  The drag is closely related to the flow of separation. The early separation, then the drag will increase. Based on the fact the effort to decrease drag is conducted by

Determination of the Drag Resistance Coefficients of Different Vehicles

Science.gov (United States)

Fahsl, Christoph; Vogt, Patrik

2018-01-01

While it has been demonstrated how air resistance could be analyzed by using mobile devices, this paper demonstrates a method of how to determine the drag resistance coefficient "c" of a commercial automobile by using the acceleration sensor of a smartphone or tablet. In an academic context, the drag resistance is often mentioned, but…

Thermospheric density and satellite drag modeling

Science.gov (United States)

Mehta, Piyush Mukesh

The United States depends heavily on its space infrastructure for a vast number of commercial and military applications. Space Situational Awareness (SSA) and Threat Assessment require maintaining accurate knowledge of the orbits of resident space objects (RSOs) and the associated uncertainties. Atmospheric drag is the largest source of uncertainty for low-perigee RSOs. The uncertainty stems from inaccurate modeling of neutral atmospheric mass density and inaccurate modeling of the interaction between the atmosphere and the RSO. In order to reduce the uncertainty in drag modeling, both atmospheric density and drag coefficient (CD) models need to be improved. Early atmospheric density models were developed from orbital drag data or observations of a few early compact satellites. To simplify calculations, densities derived from orbit data used a fixed CD value of 2.2 measured in a laboratory using clean surfaces. Measurements from pressure gauges obtained in the early 1990s have confirmed the adsorption of atomic oxygen on satellite surfaces. The varying levels of adsorbed oxygen along with the constantly changing atmospheric conditions cause large variations in CD with altitude and along the orbit of the satellite. Therefore, the use of a fixed CD in early development has resulted in large biases in atmospheric density models. A technique for generating corrections to empirical density models using precision orbit ephemerides (POE) as measurements in an optimal orbit determination process was recently developed. The process generates simultaneous corrections to the atmospheric density and ballistic coefficient (BC) by modeling the corrections as statistical exponentially decaying Gauss-Markov processes. The technique has been successfully implemented in generating density corrections using the CHAMP and GRACE satellites. This work examines the effectiveness, specifically the transfer of density models errors into BC estimates, of the technique using the CHAMP and

Investigation of drag effect using the field signature method

International Nuclear Information System (INIS)

Wan, Zhengjun; Liao, Junbi; Tian, Gui Yun; Cheng, Liang

2011-01-01

The potential drop (PD) method is an established non-destructive evaluation (NDE) technique. The monitoring of internal corrosion, erosion and cracks in piping systems, based on electrical field mapping or direct current potential drop array, is also known as the field signature method (FSM). The FSM has been applied in the field of submarine pipe monitoring and land-based oil and gas transmission pipes and containers. In the experimental studies, to detect and calculate the degree of pipe corrosion, the FSM analyses the relationships between the electrical resistance and pipe thickness using an electrode matrix. The relevant drag effect or trans-resistance will cause a large margin of error in the application of resistance arrays. It is the first time that the drag effect in the paper is investigated and analysed in resistance networks with the help of the FSM. Subsequently, a method to calculate the drag factors and eliminate its errors is proposed and presented. Theoretical analysis, simulation and experimental results show that the measurement accuracy can be improved by eliminating the errors caused by the drag effect

Spanwise drag variation on low Re wings -- revisited

Science.gov (United States)

Yang, Shanling; Spedding, Geoffrey

2011-11-01

Aerodynamic performance measurement and prediction of airfoils and wings at chord Reynolds numbers below 105 is both difficult and increasingly important in application to small-scale aircraft. Not only are the aerodynamics strongly affected by the dynamics of the unstable laminar boundary layer but the flow is decreasingly likely to be two-dimensional as Re decreases. The spanwise variation of the flow along a two-dimensional geometry is often held to be responsible for the large variations in measured profile drag coefficient. Here we measure local two-dimensional drag coefficients along a finite wing using non-intrusive PIV methods. Variations in Cd (y) can be related to local flow variations on the wing itself. Integrated values can be compared with force balance data, and the proper description of drag components at low Re will be discussed.

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.

Significance of relative velocity in drag force or drag power estimation for a tethered float

Digital Repository Service at National Institute of Oceanography (India)

Vethamony, P.; Sastry, J.S.

There is difference in opinion regarding the use of relative velocity instead of particle velocity alone in the estimation of drag force or power. In the present study, a tethered spherical float which undergoes oscillatory motion in regular waves...

Variational and symplectic integrators for satellite relative orbit propagation including drag

Science.gov (United States)

Palacios, Leonel; Gurfil, Pini

2018-04-01

Orbit propagation algorithms for satellite relative motion relying on Runge-Kutta integrators are non-symplectic—a situation that leads to incorrect global behavior and degraded accuracy. Thus, attempts have been made to apply symplectic methods to integrate satellite relative motion. However, so far all these symplectic propagation schemes have not taken into account the effect of atmospheric drag. In this paper, drag-generalized symplectic and variational algorithms for satellite relative orbit propagation are developed in different reference frames, and numerical simulations with and without the effect of atmospheric drag are presented. It is also shown that high-order versions of the newly-developed variational and symplectic propagators are more accurate and are significantly faster than Runge-Kutta-based integrators, even in the presence of atmospheric drag.

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.

Preliminary Theoretical Interpretation of the Tajmar Frame Dragging Effect Through the GEM Theory

International Nuclear Information System (INIS)

Brandenburg, John

2009-01-01

A preliminary theoretical explanation for the large amplitude frame dragging effect seen by Tajmar et al.(2007) is proposed. A simple theory of quantum photon fields mediating electrodynamics is derived based on concepts from QED. These are then expressed as quantum wave functions for rotating EM systems. Based on the GEM theory, it is proposed that gravitational frame dragging relies on similar photon wave functions. The constructive interference of the frame dragging fields with co-rotating EM photon fields coupled to Bose-Einstein components in matter at low temperatures results in a large frame dragging term due to a mixed gravity-EM term that is larger by a factor of approximately 10 20 than ordinary frame dragging.

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...

Flexural phonon limited phonon drag thermopower in bilayer graphene

Science.gov (United States)

Ansari, Mohd Meenhaz; Ashraf, SSZ

2018-05-01

We investigate the phonon drag thermopower from flexural phonons as a function of electron temperature and carrier concentration in the Bloch-Gruneisen regime in non-strained bilayer graphene using Boltzmann transport equation approach. The flexural phonons are expected to be the major source of intrinsic scattering mechanism in unstrained bilayer graphene due to their large density. The flexural phonon modes dispersion relation is quadratic so these low energy flexural phonons abound at room temperature and as a result deform the bilayer graphene sheet in the out of plane direction and affects the transport properties. We also produce analytical result for phonon-drag thermopower from flexural phonons and find that phonon-drag thermopower depicts T2 dependence on temperature and n-1 on carrier concentration.

Aerodynamic Efficiency Analysis on Modified Drag Generator of Tanker-Ship Using Symmetrical Airfoil

Science.gov (United States)

Moranova, Starida; Rahmat Hadiyatul A., S. T.; Indra Permana S., S. T.

2018-04-01

Time reduction of tanker ship spent in the sea should be applied for solving problems occured in oil and gas distribution, such as the unpunctuality of the distribution and oil spilling. The aerodynamic design for some parts that considered as drag generators is presumed to be one of the solution, utilizing our demand of the increasing speed. This paper suggests two examples of the more-aerodynamic design of a part in the tanker that is considered a drag generator, and reports the value of drag generated from the basic and the suggested aerodynamic designs. The new designs are made by adding the NACA airfoil to the cross section of the drag generator. The scenario is assumed with a 39 km/hour speed of tanker, neglecting the hydrodynamic effects occured in the tanker by cutting it at the waterline which separated the drag between air and water. The results of produced drag in each design are calculated by Computational Fluid Dynamic method.

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

Science.gov (United States)

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

2016-10-03

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

Average Skin-Friction Drag Coefficients from Tank Tests of a Parabolic Body of Revolution (NACA RM-10)

Science.gov (United States)

Mottard, Elmo J; Loposer, J Dan

1954-01-01

Average skin-friction drag coefficients were obtained from boundary-layer total-pressure measurements on a parabolic body of revolution (NACA rm-10, basic fineness ratio 15) in water at Reynolds numbers from 4.4 x 10(6) to 70 x 10(6). The tests were made in the Langley tank no. 1 with the body sting-mounted at a depth of two maximum body diameters. The arithmetic mean of three drag measurements taken around the body was in good agreement with flat-plate results, but, apparently because of the slight surface wave caused by the body, the distribution of the boundary layer around the body was not uniform over part of the Reynolds number range.

Moffies, artists, and queens: race and the production of South African gay male drag.

Science.gov (United States)

Swarr, Amanda Lock

2004-01-01

This article draws on seventeen months of ethnographic fieldwork in South Africa to explore the experiences of urban and township drag performers. I show that two distinct sex-gender-sexuality systems have emerged based in the sociopolitical history of South Africa, and I argue that urban drag produces race oppositionally and examine how township femininity creates raced forms of gender, sex, and sexuality. Contemporary South African drag foregrounds the performativity and constitution of race and gender. My analysis attempts to challenge definitions of "drag" and "audience," suggesting the necessity for an integrated reconceptualization of drag studies.

Monte Carlo calculations of the free-molecule drag on chains of uniform spheres

International Nuclear Information System (INIS)

Dahneke, B.; Chan, P.

1980-01-01

Monte Carlo calculations of the free-molecule drag on straight chains of uniform spheres are presented. The drag on a long chain is expressed in terms of the drag on a basic chain unit (two hemispheres touching at their poles) multiplied by the number of spheres in the chain. Since there is no interaction between the basic chain units, it is argued that the results also apply as a good approximation to the drag on kinked and branched chains covering a broad range of geometries. Experimental data are cited which support this claim

Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries

Science.gov (United States)

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.

Numerical simulation of drag-reducing channel flow by using bead-spring chain model

International Nuclear Information System (INIS)

Fujimura, M.; Atsumi, T.; Mamori, H.; Iwamoto, K.; Murata, A.; Masuda, M.; Ando, H.

2017-01-01

Highlights: • Numerical simulations of drag-reduced turbulent flow by polymer additives were performed by using a discrete element model. • A decreasing pressure-strain correlation mainly contributes to drag reduction by polymer addition. • Energy transport by the polymer attenuates the turbulence. • The viscoelastic effects on the drag-reducing flow are intensified with increasing relaxation time of polymer. • The polymer energy transport is related to the orientation of the polymer. - Abstract: Numerical simulations of the drag-reducing turbulent channel flow caused by polymer addition are performed. A bead-spring chain model is employed as a model of polymer aggregation. The model consists of beads and springs to represent the polymer dynamics. Three drag-reduction cases are studied with different spring constants that correspond to the relaxation time of the polymer. The energy budget is mainly focused upon to discuss the drag-reduction mechanism. Our results show that a decreasing pressure-strain correlation mainly contributes to strengthening the anisotropy of the turbulence. Furthermore, energy transport by the polymer models attenuates the turbulence. These viscoelastic effects on the drag-reducing flow are intensified with decreasing spring constant. By visualizing the flow field, it is found that this polymer energy transport is related to the orientation of the polymer.

Pengaruh variasi lebar alur berbentuk segi empat pada permukaan silinder terhadap koefisien drag

Directory of Open Access Journals (Sweden)

Si Putu Gede Gunawan Tista

2018-01-01

Full Text Available Abstrak Kemajuan ilmu pengetahuan dan teknologi khususnya tentang ilmu mekanika fluida telah berkembang pesat.Ilmu mekanika fluida telah banyak memberikan kontribusi terhadap aspek kehidupan manusia, sebagai contoh adalah aliran fluida melintasi suatu silinder. Dalam aplikasi engineering banyak ditemukan peralatan menggunakan silinder seperti cerobong asap, tiang penyangga jembatan dan sebagainya. Peralatan-peralatan ini mengalami hembusan udara setiap saat sehingga kekuatan konstruksinya mengalami penurunan, hal ini disebabkan adanya drag yang arahnya searah aliran. Upaya yang dilakukan untuk mengurangi drag adalah dengan memanipulasi medan aliran. Manipulasi medan aliran dilakukan dengan membuat alur berbentuk segi empat pada permukaan silinder. Tujuan dari penelitian ini adalah menganalisa pengaruh variasi lebar alur berbentuk segi empat pada permukaan silinder terhadap koefisien drag. Penelitian ini dilakukan pada wind tunnel yang terdiri dari blower, pipa pitot, inclined manometer, U manometer, timbangan digital, dan silinder. Benda uji berupa silinder berdiameter 60 mm dan panjang 420 mm diletakkan vertikal di dalam wind tunnel. Lebar alur pada permukaan silinder divariasikan yaitu 3 mm, 4 mm, dan 5 mm. Pengujian distribusi tekanan diperoleh dengan mengukur tekanan permukaan silinder pada 36 titik dengan interval 10o. Pengujian gaya drag dilakukan dengan menggunakan timbangan digital yang mencatat besarnya massa, untuk mendapatkan gaya drag dikalikan dengan gravitasi. Hasil penelitian menunjukkan terjadi penurunan koefisien drag pada silinder beralur dibandingkan tanpa alur. Nilai koefisien terendah terjadi pada lebar alur 4 mm besarnya CD = 0,3734. Besarnya penurunan drag adalah 22,3 % dibandingkan tanpa alur. Kata kunci: pengurangan drag, lebar alur, alur segi empat, silinder Abstract Advances in science and technology, especially on the science of fluid mechanics has been growing. Science of fluid mechanics has contributed a lot of

Riblet drag reduction in mild adverse pressure gradients: A numerical investigation

International Nuclear Information System (INIS)

Boomsma, Aaron; Sotiropoulos, Fotis

2015-01-01

Highlights: • We model several differently sized scalloped riblets using LES. • Riblets were modeled in both ZPG and mild APG and compared to each other and to a baseline (flat plate) case. • Scalloped riblets in the mild APG reduce drag only slightly more than those in ZPG. • Maximum values of streamwise turbulence intensities, streamwise vorticity, and TKE are proportional to riblet width. • Primary Reynolds shear stresses and turbulence energy production scale with riblet drag reduction. - Abstract: Riblet films are a passive method of turbulent boundary layer control that can reduce viscous drag. They have been studied with great detail for over 30 years. Although common riblet applications include flows with Adverse Pressure Gradients (APG), nearly all research thus far has been performed in channel flows. Recent research has provided motivation to study riblets in more complicated turbulent flows with claims that riblet drag reduction can double in mild APG common to airfoils at moderate angles of attack. Therefore, in this study, we compare drag reduction by scalloped riblet films between riblets in a zero pressure gradient and those in a mild APG using high-resolution large eddy simulations. In order to gain a fundamental understanding of the relationship between drag reduction and pressure gradient, we simulated several different riblet sizes that encompassed a broad range of s"+ (riblet width in wall units), similarly to many previously published experimental studies. We found that there was only a slight improvement in drag reduction for riblets in the mild APG. We also observed that peak values of streamwise turbulence intensity, turbulent kinetic energy, and streamwise vorticity scale with riblet width. Primary Reynolds shear stresses and turbulence kinetic energy production however scale with the ability of the riblet to reduce skin-friction.

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.

Simulating Electrophoresis with Discrete Charge and Drag

Science.gov (United States)

Mowitz, Aaron J.; Witten, Thomas A.

A charged asymmetric rigid cluster of colloidal particles in saline solution can respond in exotic ways to an electric field: it may spin or move transversely. These distinctive motions arise from the drag force of the neutralizing countercharge surrounding the cluster. Because of this drag, calculating the motion of arbitrary asymmetric objects with nonuniform charge is impractical by conventional methods. Here we present a new method of simulating electrophoresis, in which we replace the continuous object and the surrounding countercharge with discrete point-draggers, called Stokeslets. The balance of forces imposes a linear, self-consistent relation among the drag and Coulomb forces on the Stokeslets, which allows us to easily determine the object's motion via matrix inversion. By explicitly enforcing charge+countercharge neutrality, the simulation recovers the distinctive features of electrophoretic motion to few-percent accuracy using as few as 1000 Stokeslets. In particular, for uniformly charged objects, we observe the characteristic Smoluchowski independence of mobility on object size and shape. We then discuss electrophoretic motion of asymmetric objects, where our simulation method is particularly advantageous. This work is supported by a Grant from the US-Israel Binational Science Foundation.

Drag reduction by a polymeric aluminium soap

Energy Technology Data Exchange (ETDEWEB)

Rodriquez, F.

1971-04-12

The pressure drop per unit length of pipe during the turbulent flow of liquids is reduced by certain additives. Most such drag reducing or friction-reducing agents are polymers of very high molecular weight. Some time ago, aluminum soaps were described as reducing drag in organic solvents, but the viscosity in laminar flow of such solutions was much higher than that of the solvents. More recently, it was found that aluminum dioleate and aluminum palmitate did not reduce turbulent friction until the solute concentration reached 0.75%. The viscosity at this concentration was 2 or 3 times that of the solvent, benzene. Exploratory work with aluminum di-2-ethylhexanoate indicates that it is an effective drag-reducing agent at concentrations which increase the viscosity of toluene by less than 10%. The dependence of the effectiveness on concentration is similar to that of most polymers. Taking into account the normal change in friction factor with Reynolds number together with end effects in the apparatus, the maximum effectiveness (x = 54 cm) corresponds to a a decrease in friction factor to less than a quarter of the original value for toluene alone. (13 refs.)

Drag of evaporating or condensing droplets in low Reynolds number flow

International Nuclear Information System (INIS)

Dukowicz, J.K.

1984-01-01

The steady-state drag of evaporating or condensing droplets in low Reynolds number flow is computed. Droplet drag in air is obtained for five representative liquids (water, methanol, benzene, heptane, octane) for a range of ambient temperatures, pressures, and vapor concentrations. The drag is in general increased for a condensing droplet, and decreased for an evaporating droplet. The changes in drag can be quite large and depend in detail on the degree of evaporation or condensation, and on the individual liquid and vapor properties. The present results are used to test the existing experimentally derived correlations of Eisenklam and Yuen and Chen in the low Reynolds number regime. The Yuen and Chen correlation is found to be quite successful, but only in the case of condensation or mild evaporation. An improved correlation is suggested for evaporating droplets

Departure of microscopic friction from macroscopic drag in molecular fluid dynamics

Energy Technology Data Exchange (ETDEWEB)

Hanasaki, Itsuo [Institute of Engineering, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo 184-8588 (Japan); Fujiwara, Daiki; Kawano, Satoyuki, E-mail: kawano@me.es.osaka-u.ac.jp [Graduate School of Engineering Science, Osaka University, Machikaneyama-cho 1-3, Toyonaka, Osaka 560-8531 (Japan)

2016-03-07

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

Determining the drag coefficient of rotational symmetric objects falling through liquids

International Nuclear Information System (INIS)

Houari, Ahmed

2012-01-01

I will propose here a kinematic approach for measuring the drag coefficient of rotational symmetric objects falling through liquids. For this, I will show that one can obtain a measurement of the drag coefficient of a rotational symmetric object by numerically solving the equation of motion describing its fall through a known liquid contained in a vertical tube. The experimental value of the drag coefficient of an object with a particular shape is obtained by measuring the fall distance of the object at any recorded time along its entire falling path. (paper)

Further development of drag bodies for the measurement of mass flow rates during blowdown experiments

International Nuclear Information System (INIS)

Brockmann, E.; John, H.; Reimann, J.

1983-01-01

Drag bodies have already been used for sometime for the measurement of mass flow rates in blowdown experiments. Former research concerning the drag body behaviour in non-homogeneous two-phase flows frequently dealt with special effects by means of theoretical models only. For pipe flows most investigations were conducted for ratios of drag plate area to pipe cross section smaller 0.02. The present paper gives the results of experiments with drag bodies in a horizontal, non-homogeneous two-phase pipe flow with slip, which were carried through under the sponsorship of the German Ministry for Research and Technology (BMFT). Special interest was layed on the behaviour of the drag coefficient in stationary flows and at various cross sectional ratios. Both design and response of various drag bodies, which were developed at the Battelle-Institut, were tested in stationary and instationary two-phase flows. The influences of density and velocity profiles as well as the drag body position were studied. The results demonstrate, that the drag body is capable of measuring mass flow rates in connection with a gamma densitometer also in non-homogeneous two-phase flows. Satisfying results could be obtained, using simply the drag coefficient which was determined from single-phase flow calibrations

Measurements of the Drag Coefficient of Simulated Micrometeoroids

Science.gov (United States)

DeLuca, M.; Munsat, T.; Sternovsky, Z.

2017-12-01

The dust accelerator facility operated at the University of Colorado is used to simulate meteoric ablation, including measuring the ionization efficiency over a wide range of velocities (e.g., DeLuca et al., Planet. Space Sci., submitted, 2017). This presentation reports on the most recent experimental measurements of the drag coefficient that determines the particles' slowdown from their frictional interaction with the atmosphere. The measurements indicate that meteors experience considerably more slowdown than usually assumed. The simulated meteors consisted of submicron sized aluminum particles shot into an air chamber held at 200 mTorr pressure at velocities between 1 - 10 km/s using the dust accelerator and meteor ablation facility. The slowdown is calculated from precise timing measurements made using pickup tube detectors placed upstream and near the entrance to the air chamber, and an impact detector inside the air chamber at the downstream end of the chamber. Supporting modeling calculations show that the particles have little or no mass loss during their interaction with air and thus constant radius can be assumed. Preliminary results for the drag coefficient calculated from these timing measurements reveal that the aluminum particles have a drag coefficient of 1.51 ± 0.24 in air, which is higher than typically assumed in meteoric ablation models (usually 0.5 to 1), indicating that meteors may experience more air drag than previously assumed. More detailed measurements over a wider parameter range are underway.

Numerical Study of Natural Supercavitation Influenced by Rheological Properties of Turbulent Drag-Reducing Additives

Directory of Open Access Journals (Sweden)

Chen-Xing Jiang

2014-08-01

Full Text Available Natural supercavitations in water and turbulent drag-reducing solution were numerically simulated using unsteady Reynolds averaged Navier-Stokes (RANS scheme with mixture-multiphase model. The Cross viscosity equation was adopted to represent the fluid property of aqueous solution of drag-reducing additives. The characteristics of natural supercavity configuration and overall resistance of the navigating body were presented, respectively. The numerical simulation results indicated that, at the same cavitation number, the length and diameter of supercavity in drag-reducing solution are larger than those in water, and the drag coefficient of navigating body in solution is smaller than that in water; the surface tension plays an important role in incepting and maintaining the cavity. Turbulent drag-reducing additives have the potential in enhancement of supercavitation, drag reduction, and decrease of turbulent vortex structures. Numerical simulation results are consistent with the available experimental data.

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

KAUST Repository

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

2015-01-01

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

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

KAUST Repository

Vakarelski, Ivan Uriev

2015-07-24

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

Toy Model of Frame-Dragging Magnetosphere for the M87 Jet

Indian Academy of Sciences (India)

2016-01-27

Jan 27, 2016 ... Toy Model of Frame-Dragging Magnetosphere for the M87 Jet ... The outermost layer of jet is driven by the frame-dragging effect in the Kerr ... All these have helped shorten the publication time and have improved the visibility ...

Lift, drag, and guidance forces on alternating polarity magnets, using loop guideways

International Nuclear Information System (INIS)

Lindenbaum, S.D.; Lee, M.S.

1975-01-01

Exact solutions of track current, lift force, and drag force, together with their velocity dependence, have been computed for a vehicle carrying a finite number of fixed current alternating polarity superconducting magnets, suspended at various heights over structured track guideways of the single- and double-loop (''null'') types. Results for the double-loop case are compared with those of a previously reported approximate analysis. The analytical method is then applied to a study of a low-drag guidance loop guideway which is integrable with lift loop guideways utilizing a common set of vehicle magnets. Solutions are obtained for guidance track restoring forces, lateral destabilization forces, and lift force degradation as functions of lateral displacement from symmetry. The dependence of lift, drag, and lift-to-drag on track loop parameters is studied and the linear dependence of lift-to-drag on loop time constant confirmed. The contribution to the forces made by successive addition of alternating polarity magnets is calculated and the marked reduction in lift force pulsation noted

Optical-phonon-induced frictional drag in coupled two-dimensional electron gases

DEFF Research Database (Denmark)

Hu, Ben Yu-Kuang

1998-01-01

The role of optical phonons in frictional drag between two adjacent but electrically isolated two-dimensional electron gases is investigated. Since the optical phonons in III-V materials have a considerably larger coupling to electrons than acoustic phonons (which are the dominant drag mechanism ...

The Role of Rough Topography in Mediating Impacts of Bottom Drag in Eddying Ocean Circulation Models.

Science.gov (United States)

Trossman, David S; Arbic, Brian K; Straub, David N; Richman, James G; Chassignet, Eric P; Wallcraft, Alan J; Xu, Xiaobiao

2017-08-01

Motivated by the substantial sensitivity of eddies in two-layer quasi-geostrophic (QG) turbulence models to the strength of bottom drag, this study explores the sensitivity of eddies in more realistic ocean general circulation model (OGCM) simulations to bottom drag strength. The OGCM results are interpreted using previous results from horizontally homogeneous, two-layer, flat-bottom, f-plane, doubly periodic QG turbulence simulations and new results from two-layer β -plane QG turbulence simulations run in a basin geometry with both flat and rough bottoms. Baroclinicity in all of the simulations varies greatly with drag strength, with weak drag corresponding to more barotropic flow and strong drag corresponding to more baroclinic flow. The sensitivity of the baroclinicity in the QG basin simulations to bottom drag is considerably reduced, however, when rough topography is used in lieu of a flat bottom. Rough topography reduces the sensitivity of the eddy kinetic energy amplitude and horizontal length scales in the QG basin simulations to bottom drag to an even greater degree. The OGCM simulation behavior is qualitatively similar to that in the QG rough bottom basin simulations in that baroclinicity is more sensitive to bottom drag strength than are eddy amplitudes or horizontal length scales. Rough topography therefore appears to mediate the sensitivity of eddies in models to the strength of bottom drag. The sensitivity of eddies to parameterized topographic internal lee wave drag, which has recently been introduced into some OGCMs, is also briefly discussed. Wave drag acts like a strong bottom drag in that it increases the baroclinicity of the flow, without strongly affecting eddy horizontal length scales.

Analysis of Zero Reynolds Shear Stress Appearing in Dilute Surfactant Drag-Reducing Flow

Directory of Open Access Journals (Sweden)

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.

An experimental determination of the drag coefficient of a Mens 8+ racing shell.

Science.gov (United States)

Buckmann, James G; Harris, Samuel D

2014-01-01

This study centered around an experimental analysis of a Mens Lightweight Eight racing shell and, specifically, determining an approximation for the drag coefficient. A testing procedure was employed that used a Global Positioning System (GPS) unit in order to determine the acceleration and drag force on the shell, and through calculations yield a drag coefficient. The testing was run over several days in numerous conditions, and a 95% confidence interval was established to capture the results. The results obtained, over these varying trials, maintained a successful level of consistency. The significance of this study transcends the determination an approximation for the drag coefficient of the racing shell; it defined a successful means of quantifying performance of the shell itself. The testing procedures outlined in the study represent a uniform means of evaluating the factors that influence drag on the shell, and thus influence speed.

Coordination of multiple appendages in drag-based swimming.

Science.gov (United States)

Alben, Silas; Spears, Kevin; Garth, Stephen; Murphy, David; Yen, Jeannette

2010-11-06

Krill are aquatic crustaceans that engage in long distance migrations, either vertically in the water column or horizontally for 10 km (over 200,000 body lengths) per day. Hence efficient locomotory performance is crucial for their survival. We study the swimming kinematics of krill using a combination of experiment and analysis. We quantify the propulsor kinematics for tethered and freely swimming krill in experiments, and find kinematics that are very nearly metachronal. We then formulate a drag coefficient model which compares metachronal, synchronous and intermediate motions for a freely swimming body with two legs. With fixed leg velocity amplitude, metachronal kinematics give the highest average body speed for both linear and quadratic drag laws. The same result holds for five legs with the quadratic drag law. When metachronal kinematics is perturbed towards synchronous kinematics, an analysis shows that the velocity increase on the power stroke is outweighed by the velocity decrease on the recovery stroke. With fixed time-averaged work done by the legs, metachronal kinematics again gives the highest average body speed, although the advantage over synchronous kinematics is reduced.

Research on the aerodynamic characteristics of a lift drag hybrid vertical axis wind turbine

Directory of Open Access Journals (Sweden)

Xiaojing Sun

2016-01-01

Full Text Available Compared with a drag-type vertical axis wind turbines, one of the greatest advantages for a lift-type vertical axis wind turbines is its higher power coefficient (Cp. However, the lift-type vertical axis wind turbines is not a self-starting turbine as its starting torque is very low. In order to combine the advantage of both the drag-type and the lift-type vertical axis wind turbines, a lift drag hybrid vertical axis wind turbines was designed in this article and its aerodynamics and starting performance was studied in detail with the aid of computational fluid dynamics simulations. Numerical results indicate that the power coefficient of this lift drag hybrid vertical axis wind turbines declines when the distance between its drag-type blades and the center of rotation of the turbine rotor increases, whereas its starting torque can be significantly improved. Studies also show that unlike the lift-type vertical axis wind turbines, this lift drag hybrid-type vertical axis wind turbines could be able to solve the problem of low start-up torque. However, the installation position of the drag blade is very important. If the drag blade is mounted very close to the spindle, the starting torque of the lift drag hybrid-type vertical axis wind turbines may not be improved at all. In addition, it has been found that the power coefficient of the studied vertical axis wind turbines is not as good as expected and possible reasons have been provided in this article after the pressure distribution along the surfaces of the airfoil-shaped blades of the hybrid turbine was analyzed.

Drag reduction of a reverse-engineered vehicle

Energy Technology Data Exchange (ETDEWEB)

Lecrivain, G.; Slaouti, A.; Kennedy, I. [Manchester Metropolitan Univ., Manchester (United Kingdom). Dept. of Engineering and Technology

2007-08-09

The aerodynamic performance of a hand-made sports car was numerically assessed using computational fluid dynamics (CFD) analysis of various shape modifications. The purpose was to achieve a lower drag design. Reverse-engineering was used to create a virtual model of complex 3D shapes for which no computer-aided drawings (CAD) data existed. From the predicted flow, the body could be redesigned for better performance prior to its remanufacturing. This paper described the multidisciplinary procedure involving reverse-engineering and CAD that was used to recreate a suitable watertight model of the sports car. The different errors embedded in the successive stages leading to the final model were accurately assessed and minimized. The whole vehicle was remodelled for drag reduction. Surface reconstruction was carried out, an an accurate set of high quality Non-Uniform Rational B-Spline (NURBS) surfaces was produced over the polygonal mesh resulting in a fine visual surface finish with smooth lines and contours, as required in the automotive industry. Further modifications were implemented for the purpose of drag reduction and to improve its aerodynamic performance. The application described in this paper can be extended to any other similarly intricate vehicle or industrial component. 12 refs., 1 tab., 11 figs.

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.

Total Sulfur Amino Acid Requirements Are Not Altered in Children with Chronic Renal Insufficiency, but Minimum Methionine Needs Are Increased.

Science.gov (United States)

Elango, Rajavel; Humayun, Mohammad A; Turner, Justine M; Rafii, Mahroukh; Langos, Veronika; Ball, Ronald O; Pencharz, Paul B

2017-10-01

Background: The total sulfur amino acid (TSAA) and minimum Met requirements have been previously determined in healthy children. TSAA metabolism is altered in kidney disease. Whether TSAA requirements are altered in children with chronic renal insufficiency (CRI) is unknown. Objective: We sought to determine the TSAA (Met in the absence of Cys) requirements and minimum Met (in the presence of excess Cys) requirements in children with CRI. Methods: Five children (4 boys, 1 girl) aged 10 ± 2.6 y with CRI were randomly assigned to receive graded intakes of Met (0, 5, 10, 15, 25, and 35 mg · kg -1 · d -1 ) with no Cys in the diet. Four of the children (3 boys, 1 girl) were then randomly assigned to receive graded dietary intakes of Met (0, 2.5, 5, 7.5, 10, and 15 mg · kg -1 · d -1 ) with 21 mg · kg -1 · d -1 Cys. The mean TSAA and minimum Met requirements were determined by measuring the oxidation of l-[1- 13 C]Phe to 13 CO 2 (F 13 CO 2 ). A 2-phase linear-regression crossover analysis of the F 13 CO 2 data identified a breakpoint at minimal F 13 CO 2 Urine samples collected from all study days and from previous studies of healthy children were measured for sulfur metabolites. Results: The mean and population-safe (upper 95% CI) intakes of TSAA and minimum Met in children with CRI were determined to be 12.6 and 15.9 mg · kg -1 · d -1 and 7.3 and 10.9 mg · kg -1 · d -1 , respectively. In healthy school-aged children the mean and upper 95% CI intakes of TSAA and minimum Met were determined to be 12.9 and 17.2 mg · kg -1 · d -1 and 5.8 and 7.3 mg · kg -1 · d -1 , respectively. A comparison of the minimum Met requirements between healthy children and children with CRI indicated significant ( P < 0.05) differences. Conclusion: These results suggest that children with CRI have a similar mean and population-safe TSAA to that of healthy children, suggesting adequate Cys synthesis via transsulfuration, but higher minimum Met requirement, suggesting reduced

An Aerodynamic Database for the Mk 82 General Purpose Low Drag Bomb

National Research Council Canada - National Science Library

Krishnamoorthy, L

1997-01-01

The drag database of the Mk 82 General Purpose Low Drag bomb, the primary gravity weapon in the RAAF inventory, has some shortcomings in the quality and traceability of data, and in the variations due...

Improvements of evaporation drag model

International Nuclear Information System (INIS)

Li Xiaoyan; Yang Yanhua; Xu Jijun

2004-01-01

A special observable experiment facility has been established, and a series of experiments have been carried out on this facility by pouring one or several high-temperature particles into a water pool. The experiment has verified the evaporation drag model, which believe the non-symmetric profile of the local evaporation rate and the local density of the vapor would bring about a resultant force on the hot particle so as to resist its motion. However, in Yang's evaporation drag model, radiation heat transfer is taken as the only way to transfer heat from hot particle to the vapor-liquid interface and all of the radiation energy is deposited on the vapor-liquid interface, thus contributing to the vaporization rate and mass balance of the vapor film. So, the heat conduction and the heat convection are taken into account in improved model. At the same time, the improved model given by this paper presented calculations of the effect of hot particles temperature on the radiation absorption behavior of water

On the variability of sea drag in finite water depth

Science.gov (United States)

Toffoli, A.; Loffredo, L.; Le Roy, P.; LefèVre, J.-M.; Babanin, A. V.

2012-11-01

The coupling between the atmospheric boundary layer and the ocean surface in large-scale models is usually parameterized in terms of the sea drag coefficient, which is routinely estimated as a function of mean wind speed. The scatter of data around such parametric dependencies, however, is very significant and imposes a serious limitation on the forecasts and predictions that make use of sea surface drag parameterizations. The analysis of an atmospheric and wave data set collected in finite water depth at the Lake George measurement site (Australia) suggests that this variability relates to a number of parameters at the air-sea interface other than wind speed alone. In particular, results indicate that the sea drag depends on water depth and wave steepness, which make the wave profile more vertically asymmetric, and the concentration of water vapor in the air, which modifies air density and friction velocity. These dependencies are used to derive parametric functions based on the combined contribution of wind, waves and relative humidity. A standard statistical analysis confirms a substantial improvement in the prediction of the drag coefficient and sea surface roughness when additional parameters are taken into account.

Ser e estar drag queen: um estudo sobre a configuração da identidade queer Being a drag queen: a study on the characterization of the queer identity

Directory of Open Access Journals (Sweden)

Maria Teresa Vargas Chidiac

2004-12-01

Full Text Available O principal objetivo deste estudo foi identificar o processo de formação da identidade queer das drag queens do circuito Balneário Camboriú e Florianópolis. Para atingir este propósito, foi investigado como se processa a relação de identificação das drag queens com o gênero feminino e masculino. Abordou-se também de que modo configura-se a relação entre o sujeito e a personagem drag queen, descrevendo a sua visão sobre a própria sexualidade. Estes dados foram obtidos através de pesquisa exploratória com três sujeitos através de entrevistas, sendo o roteiro semidirigido, além de terem sido realizadas visitas em suas moradias e em casas noturnas onde faziam apresentações artísticas. Os entrevistados relataram que a identidade das drags se diferencia de suas identidades pessoais em diversos aspectos. A drag possui características físicas e psicológicas, além de posturas e atitudes, que são próprias da personagem e que a distinguem do sujeito que a compõe. Mas houve relatos com freqüência que existem situações em que personagem e sujeito que a compõe se confundem. Através dos resultados, pode-se identificar como a configuração da identidade está relacionada com a socialização e com as transformações do corpo. Os sujeitos que interpretam as drag queens manifestam esse jogo de identidades, de ambos os gêneros, configurando o que pode se identificar com uma identidade queer.The main objective of this study was to identify the formation process of queer identity of some drag queens in the cities of Balneário Camboriú and Florianópolis, in the state of Santa Catarina, south of Brazil. In order to achieve this objective, we investigated how the drag queens identify themselves with the female and male genders. In addition, we investigated how the relation between the interviewed subjects and their drag queen character gets established through their description of their own sexuality. The data was collected

Microblowing Technique for Drag Reduction, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — NASA seeks to develop technologies for aircraft drag reduction which contribute to improved aerodynamic efficiency in support of national goals for reducing fuel...

Thermal Transport and Drag Force in Improved Holographic QCD

CERN Document Server

Gürsoy, Umut; Michalogiorgakis, Georgios; Nitti, Francesco; 10.1088

2009-01-01

We calculate the bulk viscosity, drag force and jet quenching parameter in Improved Holographic QCD. We find that the bulk viscosity rises near the phase transition but does not exceed the shear viscosity. The drag force shows the effects of asymptotic freedom both as a function of velocity and temperature. It indicates diffusion times of heavy quarks in rough agreement with data. The jet quenching parameter values computed via the light-like Wilson loop are in the lower range suggested by data.

Observation and Numerical Experiments for Drag Coefficient Under Typhoon Wind Forcing

Institute of Scientific and Technical Information of China (English)

CAO Huiqiu; ZHOU Liangming; LI Shuiqing; WANG Zhifeng

2017-01-01

This paper presents a study on drag coefficients under typhoon wind forcing based on observations and numerical experiments.The friction velocity and wind speed are measured at a marine observation platform in the South China Sea.Three typhoons:SOULIK (2013),TRAMI (2013) and FITOW (2013) are observed at a buoy station in the northeast sea area of Pingtan Island.A new parameterization is formulated for the wind drag coefficient as a function of wind speed.It is found that the drag coefficient (Ca) increases linearly with the slope of 0.083× 10-3 for wind speed less than 24 m s-1.To investigate the drag coefficient under higher wind conditions,three numerical experiments are implemented for these three typhoons using SWAN wave model.The wind input data are objective reanalysis datasets,which are assimilated with many sources and provided every six hours with the resolution of 0.125° ×0.125°.The numerical simulation results show a good agreement with wave observation data under typhoon wind forcing.The results indicate that the drag coefficient levels off with the linear slope of 0.012× 10-3 for higher wind speeds (less than 34 m s-1) and the new parameterization improvese the simulation accuracy compared with the Wu (1982) default used in SWAN.

A grid-independent EMMS/bubbling drag model for bubbling and turbulent fluidization

DEFF Research Database (Denmark)

Luo, Hao; Lu, Bona; Zhang, Jingyuan

2017-01-01

The EMMS/bubbling drag model takes the effects of meso-scale structures (i.e. bubbles) into modeling of drag coefficient and thus improves coarse-grid simulation of bubbling and turbulent fluidized beds. However, its dependence on grid size has not been fully investigated. In this article, we adopt...... a two-step scheme to extend the EMMS/bubbling model to the sub-grid level. Thus the heterogeneity index, HD, which accounts for the hydrodynamic disparity between homogeneous and heterogeneous fluidization, can be correlated as a function of both local voidage and slip velocity. Simulations over...... a periodic domain show the new drag model is less sensitive to grid size because of the additional dependence on local slip velocity. When applying the new drag model to simulations of realistic bubbling and turbulent fluidized beds, we find grid-independent results are easier to obtain for high...

Hydrodynamic flows of non-Fermi liquids: Magnetotransport and bilayer drag

Science.gov (United States)

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.

Effects of stern-foil submerged elevation on the lift and drag of a hydrofoil craft

Science.gov (United States)

Suastika, K.; Apriansyah

2018-03-01

Effects of the stern-foil submerged elevation on the lift and drag of a hydrofoil craft are studied by using computational fluid dynamics (CFD) and by considering three alternative stern-foil submerged elevations. The submerged elevation of the front foil is kept constant in all the alternatives. From among the alternatives, the deepest stern-foil placement results in the highest stern-foil lift with the highest foil’s lift-to-drag ratio. However, considering the lift-to-drag ratio of the whole foil-strut-hull system, the shallowest stern-foil placement results in the highest lift-to-drag ratio. The struts and the foil’s submerged elevation significantly affects the drag of the whole foil-strut-hull system.

Drag force in a strongly coupled anisotropic plasma

Science.gov (United States)

Chernicoff, Mariano; Fernández, Daniel; Mateos, David; Trancanelli, Diego

2012-08-01

We calculate the drag force experienced by an infinitely massive quark propagating at constant velocity through an anisotropic, strongly coupled {N} = 4 plasma by means of its gravity dual. We find that the gluon cloud trailing behind the quark is generally misaligned with the quark velocity, and that the latter is also misaligned with the force. The drag coefficient μ can be larger or smaller than the corresponding isotropic value depending on the velocity and the direction of motion. In the ultra-relativistic limit we find that generically μ ∝ p. We discuss the conditions under which this behaviour may extend to more general situations.

Reducing drag of a commuter train, using engine exhaust momentum

Science.gov (United States)

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%.

Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni

NARCIS (Netherlands)

Watzman, Sarah J.; Duine, Rembert A.|info:eu-repo/dai/nl/304830127; Tserkovnyak, Yaroslav; Boona, Stephen R.; Jin, Hyungyu; Prakash, Arati; Zheng, Yuanhua; Heremans, Joseph P.

2016-01-01

Magnon-drag is shown to dominate the thermopower of elemental Fe from 2 to 80 K and of elemental Co from 150 to 600 K; it is also shown to contribute to the thermopower of elemental Ni from 50 to 500 K. Two theoretical models are presented for magnon-drag thermopower. One is a hydrodynamic theory

Magnon-drag thermopower and Nernst coefficient in Fe, Co and Ni

NARCIS (Netherlands)

Watzman, S.J.; Duine, R.A.; Tserkovnyak, Y.; Jin, H.; Prakash, A.; Zheng, Y.; Heremans, J.P.

2016-01-01

Magnon drag is shown to dominate the thermopower of elemental Fe from 2 to 80 K and of elemental Co from 150 to 600 K; it is also shown to contribute to the thermopower of elemental Ni from 50 to 500 K. Two theoretical models are presented for magnon-drag thermopower. One is a hydrodynamic theory

Separability of drag and thrust in undulatory animals and machines

Science.gov (United States)

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.

Elaboration and evaluation of maqui juice (Aristotelia chilensis (Mol. Stuntz by steam drag

Directory of Open Access Journals (Sweden)

Ximena Araneda

2014-09-01

Full Text Available The aim of this study was develop and evaluate maqui juice (Aristotelia chilensis (Mol. Stuntz, to be potentially considered as a functional beverage of natural origin, without chemical additives and minimally processed, using the technique of steam drag of type artisanal. Fruit harvested manually was used in the Region of The Araucanía (Chile. Two juice concentrates with sugar and without sugar were produced. Analyzes such as were conducted: content of soluble solids, pH, acidity, moisture content, dry matter (DM, total ash, total sugars (AT, crude protein (PC, total polyphenols (PFT and total carbohydrates (CHT, the polyphenol content highlighting for unsweetened juice with 993.2 mg 100 mL-1 EAG and juice with sugar 829.208 mg 100 mL-1 EAG. Therefore, the technique allows to extract juice with minimal processing machin, presenting this high concentration of polyphenols.

Experimental Study of Drag Resistance using a Laboratory Scale Rotary Set-Up

DEFF Research Database (Denmark)

Erik Weinell, Claus; Olsen, Kenneth N.; Christoffersen, Martin W.

2003-01-01

This work covers an experimental study of the drag resistance of different painted surfaces and simulated large-scale irregularities, viz. dry spraying, weld seams, barnacle fouling and paint remains. A laboratory scale rotary set-up was used to determine the drag resistance, and the surface...

Drag on a slip spherical particle moving in a couple stress fluid

Directory of Open Access Journals (Sweden)

E.A. Ashmawy

2016-06-01

Full Text Available The creeping motion of a rigid slip sphere in an unbounded couple stress fluid is investigated. The linear slip boundary condition and the vanishing couple stress condition are applied on the surface of the sphere. A simple formula for the drag force acting on a slip sphere translating in an unbounded couple stress fluid is obtained. Special cases of the deduced drag formula are concluded and compared with analogous results in the literature. The normalized drag force experienced by the fluid on the slip sphere is represented graphically and the effects of slip parameter and viscosity coefficients are discussed.

Kevlar/PMR-15 reduced drag DC-9 reverser stang fairing

Science.gov (United States)

Kawai, R. T.

1982-01-01

A reduced drag fairing for the afterbody enclosing the thrust reverser actuators on the DC-9 has been developed with Kevlar-49/PMR-15 advanced composite material. The improved fairing reduces airplane drag 1% compared to the production baseline. Use of composites reduces weight 40% compared to an equivalent metal fairing. The Kevlar-49/PMR-15 advanced composite is an organic matrix material system that can be used at temperatures up to 500 F.

Quantifying drag on wellbore casings in moving salt sheets

Science.gov (United States)

Weijermars, R.; Jackson, M. P. A.; Dooley, T. P.

2014-08-01

Frontier hydrocarbon development projects in the deepwater slopes of the Gulf of Mexico Basin, Santos Basin and Lower Congo Basin all require wells to cross ductile layers of autochthonous or allochthonous salt moving at peak rates of 100 mm yr-1. The Couette-Poiseuille number is introduced here to help pinpoint the depth of shear stress reversal in such salt layers. For any well-planned through salt, the probable range of creep forces of moving salt needs to be taken into account when designing safety margins and load-factor tolerance of the well casing. Drag forces increase with wellbore diameter, but more significantly with effective viscosity and speed of the creeping salt layer. The potential drag forces on cased wellbores in moving salt sheets are estimated analytically using a range of salt viscosities (1015-1019 Pa s) and creep rates (0-10 mm yr-1). Drag on perfectly rigid casing of infinite strength may reach up to 13 Giga Newton per meter wellbore length in salt having a viscosity of 1019 Pa s. Well designers may delay stress accumulations due to salt drag when flexible casing accommodates some of the early displacement and strain. However, all creeping salt could displace, fracture and disconnect well casing, eventually. The shear strength of typical heavy duty well casing (about 1000 MPa) can be reached due to drag by moving salt. Internal flow of salt will then fracture the casing near salt entry and exit points, but the structural damage is likely to remain unnoticed early in the well-life when the horizontal shift of the wellbore is still negligibly small (at less than 1 cm yr-1). Disruption of casing and production flow lines within the anticipated service lifetime of a well remains a significant risk factor within distinct zones of low-viscosity salt which may reach ultrafast creep rates of 100 mm yr-1.

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

DEFF Research Database (Denmark)

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

2015-01-01

This review presents a systematic overview of the literature and describes the experimental methods used to quantify the drag of hull coatings. It also summarizes the findings of hull coating's drag performance and identifies the main parameters impacting it. The advantages and disadvantages...... of the reported methods listed in this review provide an assessment of the most efficient methods to quantify the drag performance of hull coatings. This review determines that drag performance of hull coating technology varies depending on whether the coating condition is newly applied, after dynamic or static...... seawater exposure. The summarized data reveal that, while several methods have attempted to quantify drag performance of hull coatings, other methods must be explored in order to accurately measure the long-term drag performance of hull coatings in conditions mimicking those that ship hulls encounter...

Parameterizing Subgrid-Scale Orographic Drag in the High-Resolution Rapid Refresh (HRRR) Atmospheric Model

Science.gov (United States)

Toy, M. D.; Olson, J.; Kenyon, J.; Smirnova, T. G.; Brown, J. M.

2017-12-01

The accuracy of wind forecasts in numerical weather prediction (NWP) models is improved when the drag forces imparted on atmospheric flow by subgrid-scale orography are included. Without such parameterizations, only the terrain resolved by the model grid, along with the small-scale obstacles parameterized by the roughness lengths can have an effect on the flow. This neglects the impacts of subgrid-scale terrain variations, which typically leads to wind speeds that are too strong. Using statistical information about the subgrid-scale orography, such as the mean and variance of the topographic height within a grid cell, the drag forces due to flow blocking, gravity wave drag, and turbulent form drag are estimated and distributed vertically throughout the grid cell column. We recently implemented the small-scale gravity wave drag paramterization of Steeneveld et al. (2008) and Tsiringakis et al. (2017) for stable planetary boundary layers, and the turbulent form drag parameterization of Beljaars et al. (2004) in the High-Resolution Rapid Refresh (HRRR) NWP model developed at the National Oceanic and Atmospheric Administration (NOAA). As a result, a high surface wind speed bias in the model has been reduced and small improvement to the maintenance of stable layers has also been found. We present the results of experiments with the subgrid-scale orographic drag parameterization for the regional HRRR model, as well as for a global model in development at NOAA, showing the direct and indirect impacts.

Pengaruh variasi jarak antar ring berbentuk segi empat pada permukaan silinder terhadap koefisien drag

Directory of Open Access Journals (Sweden)

Si Putu Gede Gunawan Tista

2016-12-01

Full Text Available Abstrak: Dalam aplikasi engineering banyak ditemukan peralatan yang menggunakan silinder seperti tiang penyangga jembatan,cerobong asap, tiang pancang pengeboran minyak lepas pantai dan sebagainya. Peralatan-peralatan tersebutmengalami hembusan udara setiap saat, yang menyebabkan kekuatan konstruksinya berkurang, akibat adanya drag.Tujuan dari penelitian ini adalah untuk mengetahui pengaruh variasi jarak antar ring berbentuk segi empat padapermukaan silinder terhadap koefisien drag. Penelitian ini dilakukan pada wind tunnel (lorong udara yang terdiri dariblower (untuk menghembuskan udara, pipa pitot, U tube manometer, inclined manometer, neraca digital, silinderdengan ring segi empat. Pada penelitian ini, dilakukan dengan memvariasikan Jarak antar ring yaitu 30 mm, 40 mm, 50mm, 60 mm dan 70 mm. Silinder diletakkan vertikal dalam wind tunnel dengan diameter D = 60 mm. Gaya dragdiperoleh dengan menggunakan neraca digital yang mencatat besarnya massa, kemudian dikalikan dengan percepatangravitasi. Distribusi tekanan diperoleh dengan mengukur tekanan pada permukaan silinder menggunakan inclinedmanometer pada 36 titik dengan interval 10o. Hasil penelitian menunjukkan semakin besar jarak antar ring koefisiendrag semakin besar. Koefisien Drag terendah terjadi pada jarak antar ring L = 30 mm atau L/D = 0.50, besarnya CD =0,606352. Besarnya penurunan drag dibandingkan tanpa ring adalah 29,3 %.Kata kunci: Silinder, ring segi empat, jarak antar ring, koefisien drag Abstract: In many engineering applications there are many types of equipment that use cylinders, such as smoke chimney, bridgesupport column, etc. The equipment is undergoing drag due to the airflow that flows through it. The existence of the dragwill reduce its lifetime. One of the efforts to reduce drag is to create a rectangular ring on the surface of the cylinder. Thepurpose of this study was to determine the effect of variations in the distance between the ring of a rectangular ring onthe

Measurements of long-range enhanced collisional velocity drag through plasma wave damping

Science.gov (United States)

Affolter, M.; Anderegg, F.; Dubin, D. H. E.; Driscoll, C. F.

2018-05-01

We present damping measurements of axial plasma waves in magnetized, multispecies ion plasmas. At high temperatures T ≳ 10-2 eV, collisionless Landau damping dominates, whereas, at lower temperatures T ≲ 10-2 eV, the damping arises from interspecies collisional drag, which is dependent on the plasma composition and scales roughly as T-3 /2 . This drag damping is proportional to the rate of parallel collisional slowing, and is found to exceed classical predictions of collisional drag damping by as much as an order of magnitude, but agrees with a new collision theory that includes long-range collisions. Centrifugal mass separation and collisional locking of the species occur at ultra-low temperatures T ≲ 10-3 eV, which reduce the drag damping from the T-3 /2 collisional scaling. These mechanisms are investigated by measuring the damping of higher frequency axial modes, and by measuring the damping in plasmas with a non-equilibrium species profile.

Stokes’ and Lamb's viscous drag laws

International Nuclear Information System (INIS)

Eames, I; Klettner, C A

2017-01-01

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. (paper)

Determination of balloon gas mass and revised estimates of drag and virtual mass coefficients

Science.gov (United States)

Robbins, E.; Martone, M.

1993-01-01

In support of the NASA Balloon Program, small-scale balloons were flown with varying lifting gas and total system mass. Instrument packages were developed to measure and record acceleration and temperature data during these tests. Top fitting and instrument payload accelerations were measured from launch to steady state ascent and through ballast drop transients. The development of the small lightweight self-powered Stowaway Special instrument packages is discussed along with mathematical models developed to determine gas mass, drag and virtual mass coefficients.

Nature of the Venus thermosphere derived from satellite drag measurements (solicited paper)

Science.gov (United States)

Keating, G.; Theriot, M.; Bougher, S.

2008-09-01

From drag measurements obtained by Pioneer Venus and Magellan, the Venus upper atmosphere was discovered to be much colder than Earth's, even though Venus is much closer to the Sun than the Earth. On the dayside, exospheric temperatures are near 300K compared to Earth's of near 1200K [1]. This is thought to result principally from 15 micron excitation of carbon dioxide by atomic oxygen resulting in very strong 15 micron emission to space, cooling off the upper atmosphere [2]. On the nightside the Venus upper atmosphere is near 100K [3], compared to Earth where temperatures are near 900K. The nightside Venus temperatures drop with altitude contrary to a thermosphere where temperatures rise with altitude. As a result, the very cold nightside is called a "cryosphere" rather than a thermosphere. This is the first cryosphere discovered in the solar system [1]. Temperatures sharply drop near the terminator. Apparently, heat is somehow blocked near the terminator from being significantly transported to the nightside [4]. Recently, drag studies were performed on a number of Earth satellites to establish whether the rise of carbon dioxide on Earth was cooling the Earth's thermosphere similar to the dayside of Venus. Keating et al. [5] discovered that a 10 percent drop in density near 350km at solar minimum occurred globally over a period of 20 years with a 10 per cent rise in carbon dioxide. This should result in about a factor of 2 decline in density from 1976 values, by the end of the 21st century brought on by thermospheric cooling. Subsequent studies have confirmed these results. Thus we are beginning to see the cooling of Earth's upper atmosphere apparently from the same process cooling the Venus thermosphere. Fig. 1 VIRA Exospheric Temperatures Atmospheric drag data from the Pioneer Venus Orbiter and Magellan were combined to generate an improved version of the Venus International Reference Atmosphere (VIRA) [6], [7]. A "fountain effect" was discovered where the

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

Science.gov (United States)

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

2017-06-08

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

Bioinspired superhydrophobic, self-cleaning and low drag surfaces

Science.gov (United States)

Bhushan, Bharat

2013-09-01

Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. This article provides an overview of four topics: (1) Lotus Effect used to develop superhydrophobic and self-cleaning/antifouling surfaces with low adhesion, (2) Shark Skin Effect to develop surfaces with low fluid drag and anti-fouling characteristics, and (3-4) Rice Leaf and Butterfly Wing Effect to develop superhydrophobic and self-cleaning surfaces with low drag. Rice Leaf and Butterfly Wings combine the Shark Skin and Lotus Effects.

Minimum Q Electrically Small Antennas

DEFF Research Database (Denmark)

Kim, O. S.

2012-01-01

Theoretically, the minimum radiation quality factor Q of an isolated resonance can be achieved in a spherical electrically small antenna by combining TM1m and TE1m spherical modes, provided that the stored energy in the antenna spherical volume is totally suppressed. Using closed-form expressions...... for a multiarm spherical helix antenna confirm the theoretical predictions. For example, a 4-arm spherical helix antenna with a magnetic-coated perfectly electrically conducting core (ka=0.254) exhibits the Q of 0.66 times the Chu lower bound, or 1.25 times the minimum Q....

Drag and Lift Estimation from 3-D Velocity Field Data Measured by Multi-Plane Stereo PIV

OpenAIRE

加藤, 裕之; 松島, 紀佐; 上野, 真; 小池, 俊輔; 渡辺, 重哉; Kato, Hiroyuki; Matsushima, Kisa; Ueno, Makoto; Koike, Shunsuke; Watanabe, Shigeya

2013-01-01

For airplane design, it is crucial to have tools that can accurately predict airplane drag and lift. Usually drag and lift prediction methods are force measurement using wind tunnel balance. Unfortunately, balance data do not provide information contribution of airplane to components to drag and lift for more precise and competitive airplane design. To obtain such information, a wake integration method for use drag and lift estimation was developed for use in wake survey data analysis. Wake s...

Wigs, laughter, and subversion: Charles Busch and strategies of drag performance.

Science.gov (United States)

Niles, Richard

2004-01-01

This paper examines the strategies of drag performer/ playwright Charles Busch. His performance aesthetic is explored and shown to be subversive even though its initial impulse is to entertain. Basing my arguments on the work of Judith Butler, Elin Diamond, and others, I argue that drag queens like Busch can not only entertain but also make audiences question and criticize through drag's power to create a Brechtian alienation effect and historicize the subject. After showing how he can be viewed as a drag queen, I give a brief biography and discuss such contested terms as "camp" and "gay sensibility." I then focus on Busch's staged reading of Ibsen's Hedda Gahler andA Doll's House, both done in one afternoon at Theatre for The New City (6 May 2000). By examining the performance of Busch and his fellow actors, I demonstrate how a contemporary relevancy is achieved by having the roles played by a female impersonator whose acting choices are filtered through a gay sensibility. The ongoing dialectic between spectator and performer creates a historicized moment in performance that underscores the gender dynamics in unexpected and stimulating ways.

Drag and diffusion of heavy quarks in a hot and anisotropic QCD medium

International Nuclear Information System (INIS)

Srivastava, P.K.; Patra, Binoy Krishna

2017-01-01

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 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.)

Thermal lift generation and drag reduction in rarefied aerodynamics

Science.gov (United States)

Pekardan, Cem; Alexeenko, Alina

2016-11-01

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

Airfoil Drag Reduction using Controlled Trapped Vorticity Concentrations

Science.gov (United States)

Desalvo, Michael; Glezer, Ari

2017-11-01

The aerodynamic performance of a lifting surface at low angles of attack (when the base flow is fully attached) is improved through fluidic modification of its ``apparent'' shape by superposition of near-surface trapped vorticity concentrations. In the present wind tunnel investigations, a controlled trapped vorticity concentration is formed on the pressure surface of an airfoil (NACA 4415) using a hybrid actuator comprising a passive obstruction of scale O(0.01c) and an integral synthetic jet actuator. The jet actuation frequency [Stact O(10)] is selected to be at least an order of magnitude higher than the characteristic unstable frequency of the airfoil wake, thereby decoupling the actuation from the global instabilities of the base flow. Regulation of vorticity accumulation in the vicinity of the actuator by the jet effects changes in the local pressure, leading in turn to changes in the airfoil's drag and lift. Trapped vorticity can lead to a significant reduction in drag and reduced lift (owing to the sense of the vorticity), e.g. at α =4° and Re = 6.7 .105 the drag and lift reductions are 14% and 2%, respectively. PIV measurements show the spatial variation in the distribution of vorticity concentrations and yield estimates of the corresponding changes in circulation.

Aerodynamic drag reduction by vertical splitter plates

Science.gov (United States)

Gilliéron, Patrick; Kourta, Azeddine

2010-01-01

The capacity of vertical splitter plates placed at the front or the rear of a simplified car geometry to reduce drag, with and without skew angle, is investigated for Reynolds numbers between 1.0 × 106 and 1.6 × 106. The geometry used is a simplified geometry to represent estate-type vehicles, for the rear section, and MPV-type vehicle. Drag reductions of nearly 28% were obtained for a zero skew angle with splitter plates placed at the front of models of MPV or utility vehicles. The results demonstrate the advantage of adapting the position and orientation of the splitter plates in the presence of a lateral wind. All these results confirm the advantage of this type of solution, and suggest that this expertise should be used in the automotive field to reduce consumption and improve dynamic stability of road vehicles.

Switchable and Tunable Aerodynamic Drag on Cylinders

Science.gov (United States)

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.

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

Directory of Open Access Journals (Sweden)

Salam Hadi Hussein

2017-05-01

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

The effects of Poynting–Robertson drag on solar sails

Directory of Open Access Journals (Sweden)

F.A. Abd El-Salam

2018-06-01

Full Text Available In the present work, the concept of solar sailing and its developing spacecraft are presented. The effects of Poynting–Robertson drag on solar sails are considered. Some analytical control laws with some mentioned input constraints for optimizing solar sails dynamics in heliocentric orbit using Lagrange’s planetary equations are obtained. Optimum force vector in a required direction is maximized by deriving optimal sail cone angle. New control laws that maximize thrust to obtain certain required maximization in some particular orbital element are obtained. Keywords: Poynting–Robertson drag, Solar sail, Control laws, Optimal sail, Cone angle

Development of drag disk and turbines at the INEL

International Nuclear Information System (INIS)

Goodrich, L.D.; Edson, J.L.; Averill, R.H.

1984-01-01

One of the parameters that must be measured in nuclear safety research is mass flow rate. The reactor environment associated with two-phase flow makes this measurement difficult. To accomplish this at the Idaho National Engineering Laboratory, a drag disk and turbine transducer conbination was developed. These transducers can withstand >2000 h of continuous operation in the reactor environment. Mechanical problems have been solved with these transducers to the point where the electrical coils are now the limiting factor on lifetime. This paper presents the results of the development of the drag disk and turbine with problems and solutions pointed out

Optimal control of lift/drag ratios on a rotating cylinder

Science.gov (United States)

Ou, Yuh-Roung; Burns, John A.

1992-01-01

We present the numerical solution to a problem of maximizing the lift to drag ratio by rotating a circular cylinder in a two-dimensional viscous incompressible flow. This problem is viewed as a test case for the newly developing theoretical and computational methods for control of fluid dynamic systems. We show that the time averaged lift to drag ratio for a fixed finite-time interval achieves its maximum value at an optimal rotation rate that depends on the time interval.

Microscopic Theory of Magnon-Drag Thermoelectric Transport in Ferromagnetic Metals

OpenAIRE

Miura, Daisuke; Sakuma, Akimasa

2012-01-01

A theoretical study of the magnon-drag Peltier and Seebeck effects in ferromagnetic metals is presented. A magnon heat current is described perturbatively from the microscopic viewpoint with respect to electron--magnon interactions and the electric field. Then, the magnon-drag Peltier coefficient $\\Pi_\\MAG$ is obtained as the ratio between the magnon heat current and the electric charge current. We show that $\\Pi_\\MAG=C_\\MAG T^{5/2}$ at a low temperature $T$; that the coefficient $C_\\MAG$ is ...

The influence of numerical models on determining the drag coefficient

Directory of Open Access Journals (Sweden)

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.

Evaluation of WRF Simulations With Different Selections of Subgrid Orographic Drag Over the Tibetan Plateau

Science.gov (United States)

Zhou, X.; Beljaars, A.; Wang, Y.; Huang, B.; Lin, C.; Chen, Y.; Wu, H.

2017-09-01

Weather Research and Forecasting (WRF) simulations with different selections of subgrid orographic drag over the Tibetan Plateau have been evaluated with observation and ERA-Interim reanalysis. Results show that the subgrid orographic drag schemes, especially the turbulent orographic form drag (TOFD) scheme, efficiently reduce the 10 m wind speed bias and RMS error with respect to station measurements. With the combination of gravity wave, flow blocking and TOFD schemes, wind speed is simulated more realistically than with the individual schemes only. Improvements are also seen in the 2 m air temperature and surface pressure. The gravity wave drag, flow blocking drag, and TOFD schemes combined have the smallest station mean bias (-2.05°C in 2 m air temperature and 1.27 hPa in surface pressure) and RMS error (3.59°C in 2 m air temperature and 2.37 hPa in surface pressure). Meanwhile, the TOFD scheme contributes more to the improvements than the gravity wave drag and flow blocking schemes. The improvements are more pronounced at low levels of the atmosphere than at high levels due to the stronger drag enhancement on the low-level flow. The reduced near-surface cold bias and high-pressure bias over the Tibetan Plateau are the result of changes in the low-level wind components associated with the geostrophic balance. The enhanced drag directly leads to weakened westerlies but also enhances the a-geostrophic flow in this case reducing (enhancing) the northerlies (southerlies), which bring more warm air across the Himalaya Mountain ranges from South Asia (bring less cold air from the north) to the interior Tibetan Plateau.

In-situ measurement of electroosmotic drag coefficient in Nafion membrane for the PEMFC.

Science.gov (United States)

Peng, Zhe; Morin, Arnaud; Huguet, Patrice; Schott, Pascal; Pauchet, Joël

2011-11-10

A new method based on hydrogen pump has been developed to measure the electroosmotic drag coefficient in representative PEMFC operating conditions. It allows eliminating the back-flow of water which leads to some errors in the calculation of this coefficient with previously reported electrochemical methods. Measurements have been performed on 50 μm thick Nafion membranes both extruded and recast. Contrary to what has been described in most of previous published works, the electroosmotic drag coefficient decreases as the membrane water content increases. The same trend is observed for temperatures between 25 and 80 °C. For the same membrane water content, the electroosmotic drag coefficient increases with temperature. In the same condition, there is no difference in drag coefficient for extruded Nafion N112 and recast Nafion NRE212. These results are discussed on the basis of the two commonly accepted proton transport mechanisms, namely, Grotthus and vehicular.

Drag crisis moderation by thin air layers sustained on superhydrophobic spheres falling in water

KAUST Repository

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.

Drag Measurements over Embedded Cavities in a Low Reynolds Number Couette Flow

Science.gov (United States)

Gilmer, Caleb; Lang, Amy; Jones, Robert

2010-11-01

Recent research has revealed that thin-walled, embedded cavities in low Reynolds number flow have the potential to reduce the net viscous drag force acting on the surface. This reduction is due to the formation of embedded vortices allowing the outer flow to pass over the surface via a roller bearing effect. It is also hypothesized that the scales found on butterfly wings may act in a similar manner to cause a net increase in flying efficiency. In this experimental study, rectangular embedded cavities were designed as a means of successfully reducing the net drag across surfaces in a low Reynolds number flow. A Couette flow was generated via a rotating conveyor belt immersed in a tank of high viscosity mineral oil above which the plates with embedded cavities were placed. Drag induced on the plate models was measured using a force gauge and compared directly to measurements acquired over a flat plate. Various cavity aspect ratios and gap heights were tested in order to determine the conditions under which the greatest drag reductions occurred.

Drag Reduction through Pulsed Plasma Actuators, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Drag reduction is a fundamental necessity in all aerodynamic designs, as it directly affects aircraft fuel efficiency which in turn affects endurance, range, and...

Drag Reduction Through Distributed Electric Propulsion

Science.gov (United States)

Stoll, Alex M.; Bevirt, JoeBen; Moore, Mark D.; Fredericks, William J.; Borer, Nicholas K.

2014-01-01

One promising application of recent advances in electric aircraft propulsion technologies is a blown wing realized through the placement of a number of electric motors driving individual tractor propellers spaced along each wing. This configuration increases the maximum lift coefficient by providing substantially increased dynamic pressure across the wing at low speeds. This allows for a wing sized near the ideal area for maximum range at cruise conditions, imparting the cruise drag and ride quality benefits of this smaller wing size without decreasing takeoff and landing performance. A reference four-seat general aviation aircraft was chosen as an exemplary application case. Idealized momentum theory relations were derived to investigate tradeoffs in various design variables. Navier-Stokes aeropropulsive simulations were performed with various wing and propeller configurations at takeoff and landing conditions to provide insight into the effect of different wing and propeller designs on the realizable effective maximum lift coefficient. Similar analyses were performed at the cruise condition to ensure that drag targets are attainable. Results indicate that this configuration shows great promise to drastically improve the efficiency of small aircraft.

Controlling turbulent drag across electrolytes using electric fields.

Science.gov (United States)

Ostilla-Mónico, Rodolfo; Lee, Alpha A

2017-07-01

Reversible in operando control of friction is an unsolved challenge that is crucial to industrial tribology. Recent studies show that at low sliding velocities, this control can be achieved by applying an electric field across electrolyte lubricants. However, the phenomenology at high sliding velocities is yet unknown. In this paper, we investigate the hydrodynamic friction across electrolytes under shear beyond the transition to turbulence. We develop a novel, highly parallelised numerical method for solving the coupled Navier-Stokes Poisson-Nernst-Planck equation. Our results show that turbulent drag cannot be controlled across dilute electrolytes using static electric fields alone. The limitations of the Poisson-Nernst-Planck formalism hint at ways in which turbulent drag could be controlled using electric fields.

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...

Aerodynamic drag reduction by vertical splitter plates

Energy Technology Data Exchange (ETDEWEB)

Gillieron, Patrick [Renault Group, Research Division, Fluid Mechanics and Aerodynamics, Guyancourt (France); Kourta, Azeddine [Polytech' Orleans, Institut PRISME, ESA, Orleans (France)

2010-01-15

The capacity of vertical splitter plates placed at the front or the rear of a simplified car geometry to reduce drag, with and without skew angle, is investigated for Reynolds numbers between 1.0 x 10{sup 6} and 1.6 x 10{sup 6}. The geometry used is a simplified geometry to represent estate-type vehicles, for the rear section, and MPV-type vehicle. Drag reductions of nearly 28% were obtained for a zero skew angle with splitter plates placed at the front of models of MPV or utility vehicles. The results demonstrate the advantage of adapting the position and orientation of the splitter plates in the presence of a lateral wind. All these results confirm the advantage of this type of solution, and suggest that this expertise should be used in the automotive field to reduce consumption and improve dynamic stability of road vehicles. (orig.)

Oral cavity hydrodynamics and drag production in Balaenid whale suspension feeding.

Directory of Open Access Journals (Sweden)

Jean Potvin

Full Text Available 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.

Oral cavity hydrodynamics and drag production in Balaenid whale suspension feeding.

Science.gov (United States)

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.

Can large-scale oblique undulations on a solid wall reduce the turbulent drag?

Science.gov (United States)

Ghebali, Sacha; Chernyshenko, Sergei I.; Leschziner, Michael A.

2017-10-01

Direct numerical simulations of fully developed turbulent channel flows with wavy walls are undertaken. The wavy walls, skewed with respect to the mean flow direction, are introduced as a means of emulating a Spatial Stokes Layer (SSL) induced by in-plane wall motion. The transverse shear strain above the wavy wall is shown to be similar to that of a SSL, thereby affecting the turbulent flow and leading to a reduction in the turbulent skin-friction drag. However, some important differences with respect to the SSL case are brought to light too. In particular, the phase variations of the turbulent properties are accentuated and, unlike in the SSL case, there is a region of increased turbulence production over a portion of the wall, above the leeward side of the wave, thus giving rise to a local increase in dissipation. The pressure- and friction-drag levels are carefully quantified for various flow configurations, exhibiting a combined maximum overall-drag reduction of about 0.6%. The friction-drag reduction is shown to behave approximately quadratically for small wave slopes and then linearly for higher slopes, whilst the pressure-drag penalty increases quadratically. The transverse shear-strain layer is shown to be approximately Reynolds-number independent when the wave geometry is scaled in wall units.

Magnetic Viscous Drag for Friction Labs

Science.gov (United States)

Gaffney, Chris; Catching, Adam

2016-01-01

The typical friction lab performed in introductory mechanics courses is usually not the favorite of either the student or the instructor. The measurements are not all that easy to make, and reproducibility is usually a troublesome issue. This paper describes the augmentation of such a friction lab with a study of the viscous drag on a magnet…

The Effects of Propulsive Jetting on Drag of a Streamlined body

Science.gov (United States)

Krieg, Michael; Mohseni, Kamran

2017-11-01

Recently an abundance of bioinspired underwater vehicles have emerged to leverage eons of evolution. Our group has developed a propulsion technique inspired by jellyfish and squid. Propulsive jets are generated by ingesting and expelling water from a flexible internal cavity. We have demonstrated thruster capabilities for maneuvering on AUV platforms, where the internal thruster geometry minimized forward drag; however, such a setup cannot characterize propulsive efficiency. Therefore, we created a new streamlined vehicle platform that produces unsteady jets for forward propulsion rather than maneuvering. The streamlined jetting body is placed in a water tunnel and held stationary while jetting frequency and background flow velocity are varied. For each frequency/velocity pair the flow field is measured around the surface and in the wake using PIV. Using the zero jetting frequency as a baseline for each background velocity, the passive body drag is related to the velocity distribution. For cases with active jetting the drag and jetting forces are estimated from the velocity field and compared to the passive case. For this streamlined body, the entrainment of surrounding flow into the propulsive jet can reduce drag forces in addition to the momentum transfer of the jet itself. Office of Naval Research.

Determination of the drag resistance coefficients of different vehicles

Science.gov (United States)

Fahsl, Christoph; Vogt, Patrik

2018-05-01

While it has been demonstrated how air resistance could be analyzed by using mobile devices, this paper demonstrates a method of how to determine the drag resistance coefficient c of a commercial automobile by using the acceleration sensor of a smartphone or tablet. In an academic context, the drag resistance is often mentioned, but little attention is paid to quantitative measurements. This experiment was driven by the fact that this physical value is most certainly neglected because of its difficult measurability. In addition to that, this experiment gives insights on how the aerodynamic factor of an automobile affects the energy dissipation and thus how much power is required by automobile transportation.

Control of the electromagnetic drag using fluctuating light fields

Science.gov (United States)

Pastor, Víctor J. López; Marqués, Manuel I.

2018-05-01

An expression for the electromagnetic drag force experienced by an electric dipole in a light field consisting of a monochromatic plane wave with polarization and phase randomly fluctuating is obtained. The expression explicitly considers the transformations of the field and frequency due to the Doppler shift and the change of the polarizability response of the electric dipole. The conditions to be fulfilled by the polarizability of the dipole in order to obtain a positive, a null, and a negative drag coefficient are analytically determined and checked against numerical simulations for the dynamics of a silver nanoparticle. The theoretically predicted diffusive, superdiffusive, and exponentially accelerated dynamical regimes are numerically confirmed.

Fluid drag reduction and efficient self-cleaning with rice leaf and butterfly wing bioinspired surfaces

Science.gov (United States)

Bixler, Gregory D.; Bhushan, Bharat

2013-08-01

Researchers are continually inspired by living nature to solve complex challenges. For example, unique surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we present an overview of rice leaf and butterfly wing fluid drag and self-cleaning studies. In addition, we examine two other promising aquatic surfaces in nature known for such properties, including fish scales and shark skin. Morphology, drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of wettability, viscosity, and velocity. Liquid repellent coatings are utilized to recreate or combine various effects. Discussion is provided along with conceptual models describing the role of surface structures related to low drag, self-cleaning, and antifouling properties. Modeling provides design guidance when developing novel low drag and self-cleaning surfaces for applications in the medical, marine, and industrial fields.

On the influence of drag effect on acoustic modes in two-condensate relativistic superfluid systems

International Nuclear Information System (INIS)

Vil'chinskij, S.I.

1999-01-01

Equations of velocities of acoustic excitations in a relativistic two-condensate superfluid system are derived with due account of reciprocal drag of superfluid motion (drag effect). The influence of the drag effect on acoustic modes in the system is considered. It is shown that the effect does not influence the nature of acoustic excitation oscillations but produces changes in the velocities of the second, third and fourth sounds

Virtual Photon Contribution to Frictional Drag in Double-layer Devices

DEFF Research Database (Denmark)

Donarini, Andrea; Ferrari, R.; Jauho, Antti-Pekka

2003-01-01

Frictional drag between coupled two-dimensional charge systems is commonly viewed as a second order effect arising either from screened Coulomb interaction, or phonon exchange. We point out that for single-photon exchange the first order contribution does not have to vanish even at T = 0, and eva......Frictional drag between coupled two-dimensional charge systems is commonly viewed as a second order effect arising either from screened Coulomb interaction, or phonon exchange. We point out that for single-photon exchange the first order contribution does not have to vanish even at T = 0...

High Speed Civil Transport (HSCT) Isolated Nacelle Transonic Boattail Drag Study and Results Using Computational Fluid Dynamics (CFD)

Science.gov (United States)

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.

Wingtip Vortices and Free Shear Layer Interaction in the Vicinity of Maximum Lift to Drag Ratio Lift Condition

Science.gov (United States)

Memon, Muhammad Omar

Cost-effective air-travel is something everyone wishes for when it comes to booking flights. The continued and projected increase in commercial air travel advocates for energy efficient airplanes, reduced carbon footprint, and a strong need to accommodate more airplanes into airports. All of these needs are directly affected by the magnitudes of drag these aircraft experience and the nature of their wingtip vortex. A large portion of the aerodynamic drag results from the airflow rolling from the higher pressure side of the wing to the lower pressure side, causing the wingtip vortices. The generation of this particular drag is inevitable however, a more fundamental understanding of the phenomenon could result in applications whose benefits extend much beyond the relatively minuscule benefits of commonly-used winglets. Maximizing airport efficiency calls for shorter intervals between takeoffs and landings. Wingtip vortices can be hazardous for following aircraft that may fly directly through the high-velocity swirls causing upsets at vulnerably low speeds and altitudes. The vortex system in the near wake is typically more complex since strong vortices tend to continue developing throughout the near wake region. Several chord lengths distance downstream of a wing, the so-called fully rolled up wing wake evolves into a combination of a discrete wingtip vortex pair and a free shear layer. Lift induced drag is generated as a byproduct of downwash induced by the wingtip vortices. The parasite drag results from a combination of form/pressure drag and the upper and lower surface boundary layers. These parasite effects amalgamate to create the free shear layer in the wake. While the wingtip vortices embody a large portion of the total drag at lifting angles, flow properties in the free shear layer also reveal their contribution to the aerodynamic efficiency of the aircraft. Since aircraft rarely cruise at maximum aerodynamic efficiency, a better understanding of the balance

Influence of Blocker Distance Variations in form of Triangle in Front of Cylinder toward Drag Coefficien

Directory of Open Access Journals (Sweden)

Si Putu Gede Gunawan Tista

2012-11-01

Full Text Available One of the ways to reduce energy consumption on the air plane and the other bluff bodies are by decreasing the drag. Drag isclosely related to the flow separation. The earlier separation, then the drag will increase more. Based of the fact the effort todecrease drag is conducted by manipulating the field of fluid flow. Stream manipulation was be done by installing Triangleobstacle in front of cylinder. The purpose of this research is to analyze the effect of various distance triangle obstacle in front ofcylinder on drag. The present experiment was done by placing triangle rod in front of the cylinder. In the present research, theexperiment was conducted in the wind tunnel, which consisted of blower, pitot pipe, manometer, cylinder pipe, and triangle rod.The triangle was positioned at L/D = 1.19, L/D = 1.43, L/D = 1.67, L/D = 1.9, L/D = 2.14, L/D = 2.38, L/D = 2.62, and L/D =2.86 by upstream from the cylinder. The triangle was 8 mm uniform side. The Reynolds number based on the cylinder diameter (D= 42 mm was Re = 1.81 x 104. The research results showed that the triangle rod could decrease the drag of cylinder. Coefficientdrag for cylinder without triangle rod was 0.1276 while the biggest decrease of coefficient of drag with triangle rod washappened at L/D = 1.43 which was 0.0188. It means that the drag of cylinder with triangle rod was 85.25% lower than thecylinder alone.

Mechanism of drag reduction for circular cylinders with patterned surface

International Nuclear Information System (INIS)

Butt, U.; Jehring, L.; Egbers, C.

2014-01-01

Highlights: • Reduced drag of patterned cylinders over a wide range of Re numbers. • Hexagonal patterns cannot be characterized as roughness structures. • Hexagonal bumps affect the flow like spherical dimples of smaller k/d ratio do. • Main separation is delayed caused by a partial separation. • Angle of a separation line is not constant over the length of cylinder. -- Abstract: In this paper, the flow over cylinders with a patterned surface (k/d = 1.98 × 10 −2 ) is investigated in a subsonic wind tunnel over Reynolds numbers ranging from 3.14 × 10 4 to 2.77 × 10 5 by measuring drag, flow visualization and measuring velocity profiles above the surface of the cylinders, to observe the effect of hexagonal patterns on the flow of air. These patterns can also be referred as hexagonal dimples or bumps depending on their configuration. The investigations revealed that a patterned cylinder with patterns pressed outwards has a drag coefficient of about 0.65 times of a smooth one. Flow visualization techniques including surface oil-film technique and velocity profile measurement were employed to elucidate this effect, and hence present the mechanism of drag reduction. The measurement of velocity profiles using hot-wire anemometry above the surface reveal that a hexagonal bump cause local separation generating large turbulence intensity along the separating shear layer. Due to this increased turbulence, the flow reattaches to the surface with higher momentum and become able to withstand the pressure gradient delaying the main separation significantly. Besides that, the separation does not appear to occur in a straight line along the length of the cylinder as in case of most passive drag control methods, but follow exactly the hexagonal patterns forming a wave with its crest at 115° and trough at 110°, in contrast to the laminar separation line at 85° for a smooth cylinder

Mechanics of load-drag-unload contact cleaning of gecko-inspired fibrillar adhesives.

Science.gov (United States)

Abusomwan, Uyiosa A; Sitti, Metin

2014-10-14

Contact self-cleaning of gecko-inspired synthetic adhesives with mushroom-shaped tips has been demonstrated recently using load-drag-unload cleaning procedures similar to that of the natural animal. However, the underlying mechanics of contact cleaning has yet to be fully understood. In this work, we present a detailed experiment of contact self-cleaning that shows that rolling is the dominant mechanism of cleaning for spherical microparticle contaminants, during the load-drag-unload procedure. We also study the effect of dragging rate and normal load on the particle rolling friction. A model of spherical particle rolling on an elastomer fibrillar adhesive interface is developed and agrees well with the experimental results. This study takes us closer to determining design parameters for achieving self-cleaning fibrillar adhesives.

Effect of Phonon Drag on the Thermopower in a Parabolic Quantum Well

Energy Technology Data Exchange (ETDEWEB)

Hasanov, Kh. A., E-mail: xanlarhasanli@rambler.ru; Huseynov, J. I. [Azerbaijan State Pedagogical University (Azerbaijan); Dadashova, V. V. [Baku State University (Azerbaijan); Aliyev, F. F. [National Academy of Sciences of Azerbaijan, Abdullaev Institute of Physics (Azerbaijan)

2016-03-15

The theory of phonon-drag thermopower resulting from a temperature gradient in the plane of a two-dimensional electron gas layer in a parabolic quantum well is developed. The interaction mechanisms between electrons and acoustic phonons are considered, taking into account potential screening of the interaction. It is found that the effect of electron drag by phonons makes a significant contribution to the thermopower of the two-dimensional electron gas. It is shown that the consideration of screening has a significant effect on the drag thermopower. For the temperature dependence of the thermopower in a parabolic GaAs/AlGaAs quantum well in the temperature range of 1–10 K, good agreement between the obtained theoretical results and experiments is shown.

Experimental and Numerical Study of Water Entry Supercavity Influenced by Turbulent Drag-Reducing Additives

Directory of Open Access Journals (Sweden)

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.

Bluff-body drag reduction using a deflector

Science.gov (United States)

Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi; Gilliéron, Patrick

2011-02-01

A passive flow control on a generic car model was experimentally studied. This control consists of a deflector placed on the upper edge of the model rear window. The study was carried out in a wind tunnel at Reynolds numbers based on the model height of 3.1 × 105 and 7.7 × 105. The flow was investigated via standard and stereoscopic particle image velocimetry, Kiel pressure probes and surface flow visualization. The aerodynamic drag was measured using an external balance and calculated using a wake survey method. Drag reductions up to 9% were obtained depending on the deflector angle. The deflector increases the separated region on the rear window. The results show that when this separated region is wide enough, it disrupts the development of the counter-rotating longitudinal vortices appearing on the lateral edges of the rear window. The current study suggests that flow control on such geometries should consider all the flow structures that contribute to the model wake flow.

Effects of Increasing Drag on Conjunction Assessment

Science.gov (United States)

Frigm, Ryan Clayton; McKinley, David P.

2010-01-01

Conjunction Assessment Risk Analysis relies heavily on the computation of the Probability of Collision (Pc) and the understanding of the sensitivity of this calculation to the position errors as defined by the covariance. In Low Earth Orbit (LEO), covariance is predominantly driven by perturbations due to atmospheric drag. This paper describes the effects of increasing atmospheric drag through Solar Cycle 24 on Pc calculations. The process of determining these effects is found through analyzing solar flux predictions on Energy Dissipation Rate (EDR), historical relationship between EDR and covariance, and the sensitivity of Pc to covariance. It is discovered that while all LEO satellites will be affected by the increase in solar activity, the relative effect is more significant in the LEO regime around 700 kilometers in altitude compared to 400 kilometers. Furthermore, it is shown that higher Pc values can be expected at larger close approach miss distances. Understanding these counter-intuitive results is important to setting Owner/Operator expectations concerning conjunctions as solar maximum approaches.

The Locus of the apices of projectile trajectories under constant drag

OpenAIRE

Hernández-Saldaña, H.

2017-01-01

We present an analytical solution for the projectile coplanar motion under constant drag parametrised by the velocity angle. We found the locus formed by the apices of the projectile trajectories. The range and time of flight are obtained numerically and we find that the optimal launching angle is smaller than in the free drag case. This is a good example of problems with constant dissipation of energy that includes curvature, and it is proper for intermediate courses of mechanics.

Aerodynamic drag control by pulsed jets on simplified car geometry

Science.gov (United States)

Gilliéron, Patrick; Kourta, Azeddine

2013-02-01

Aerodynamic drag control by pulsed jets is tested in a wind tunnel around a simplified car geometry named Ahmed body with a rear slant angle of 35°. Pulsed jet actuators are located 5 × 10-3 m from the top of the rear window. These actuators are produced by a pressure difference ranging from 1.5 to 6.5 × 105 Pa. Their excitation frequency can vary between 10 and 550 Hz. The analysis of the control effects is based on wall visualizations, aerodynamic drag coefficient measurements, and the velocity fields obtained by 2D PIV measurements. The maximum drag reduction is 20 % and is obtained for the excitation frequency F j = 500 Hz and for the pressure difference ∆ P = 1.5 × 105 Pa. This result is linked with a substantial reduction in the transverse development of the longitudinal vortex structures coming from the left and right lateral sides of the rear window, with a displacement of the vortex centers downstream and with a decrease in the transverse rotational absolute values of these structures.

A biomechanical comparison in the lower limb and lumbar spine between a hit and drag flick in field hockey.

Science.gov (United States)

Ng, Leo; Rosalie, Simon M; Sherry, Dorianne; Loh, Wei Bing; Sjurseth, Andreas M; Iyengar, Shrikant; Wild, Catherine Y

2018-03-01

Research has revealed that field hockey drag flickers have greater odds of hip and lumbar injuries compared to non-drag flickers (DF). This study aimed to compare the biomechanics of a field hockey hit and a specialised field hockey drag flick. Eighteen male and seven female specialised hockey DF performed a hit and a drag flick in a motion analysis laboratory with an 18-camera three-dimensional motion analysis system and a calibrated multichannel force platform to examine differences in lower limb and lumbar kinematics and kinetics. Results revealed that drag flicks were performed with more of a forward lunge on the left lower limb resulting in significantly greater left ankle dorsiflexion, knee, hip and lumbar flexion (Pshit. Drag flicks were also performed with significantly greater lateral flexion (P hit. Differences in kinematics lead to greater shear, compression and tensile forces in multiple left lower limb and lumbar joints in the drag flick compared to the hit (P hit may have ramifications with respect to injury in field hockey drag flickers.

Venus thermosphere and exosphere - First satellite drag measurements of an extraterrestrial atmosphere

Science.gov (United States)

Keating, G. M.; Tolson, R. H.; Hinson, E. W.

1979-01-01

Atmospheric drag measurements obtained from the study of the orbital decay of Pioneer Venus I indicate that atomic oxygen predominates in the Venus atmosphere above 160 kilometers. Drag measurements give evidence that conditions characteristic of a planetary thermosphere disappear near sundown, with inferred exospheric temperatures sharply dropping from approximately 300 K to less than 150 K. Observed densities are generally lower than given by theoretical models.

Coulomb Drag as a Probe of Coupled Plasmon Modes in Parallel Quantum Wells

DEFF Research Database (Denmark)

Flensberg, Karsten; Hu, Ben Yu-Kuang

1994-01-01

parameters. The acoustic mode causes a sharp upturn in the scaled drag rate with increasing temperature at T≈0.2TF. Other experimental signatures of the plasmon-dominated drag rate are a d-3 dependence on the well separation d and a peak as a function of relative densities at matched Fermi velocities....

Wave drag reduction due to a self-aligning aerodisk

Science.gov (United States)

Schnepf, Ch.; Wysocki, O.; Schülein, E.

2015-06-01

The effect of a self-aligning aerodisk on the wave drag of a blunt slender body in a pitching maneuver has been numerically investigated. The self-alignment was realized by a coupling of the flow solver and a flight mechanics tool. The slender body was pitched with high repetition rate between α = 0° and 20° at M = 1.41. Even at high α, the concept could align the aerodisk to the oncoming flow. In comparison to the reference body without a self-aligning aerodisk, a distinct drag reduction is achieved. A comparison with existing experimental data shows a qualitatively good agreement considering the shock and separation structure and the kinematics of the aerodisk.

Development of a Kevlar/PMR-15 reduced drag DC-9 nacelle fairing

Science.gov (United States)

Kawai, R. T.; Hrach, F. J.

1980-01-01

The paper describes an advanced composite fairing designed to reduce drag on DC-9 nacelles as a part of the NASA Engine Component Improvement Program. This fairing is the aft enclosure for the thrust reverser actuator system on JT8D engine nacelles and is subjected to a 500 F exhaust flow during the reverse thrust. A reduced-drag configuration was developed by using in-flight tuft surveys for flow visualization in order to identify areas with low-quality flow, and then modifying the aerodynamic lines to improve the flow. A fabrication method for molding the part in an autoclave was developed; this material system is suitable for 500 F. The resultant composite fairing reduces the overall aircraft drag 1% with a weight reduction of 40% when compared with a metal component.

Role of Elasto-Inertial Turbulence in Polymer Drag Reduction

Science.gov (United States)

Dubief, Yves; Sid, Samir; Terrapon, Vincent

2017-11-01

Elasto-Inertial Turbulence (EIT) is a peculiar state of turbulence found in dilute polymer solutions flowing in parallel wall flows over a wide range of Reynolds numbers. At subcritical Reynolds numbers, appropriate boundary conditions trigger EIT, a self-sustaining cycle of energy transfers between thin sheets of stretched polymers and velocity perturbations, which translates into an increase of friction drag. For critical and supercritical Reynolds numbers, polymer additives may lead to significant drag reduction, bounded by the asymptotic state known as Maximum Drag Reduction (MDR). The present research investigates the role of EIT in the dynamics of critical and supercritical Reynolds number wall flows. Using high-fidelity direct numerical simulations of channel flows and the FENE-P model, we establish that (i) EIT is two-dimensional, (ii) the scales essential to the existence of EIT are sub-Kolmogorov, and (iii) EIT drives MDR at low and possibly moderate Reynolds number turbulent flows. These findings were validated in two different codes and using unprecedented resolutions for polymer flows. YD is grateful for the support of Binational Science Foundation. SS and VT acknowledges Fonds de la Recherche Scientifique (FNRS), MarieCurie Career Integration Grant and computing allocation from University of Liege and PRACE.

Locus of the apices of projectile trajectories under constant drag

Science.gov (United States)

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.

A hypersonic lift mechanism with decoupled lift and drag surfaces

Science.gov (United States)

Xu, YiZhe; Xu, ZhiQi; Li, ShaoGuang; Li, Juan; Bai, ChenYuan; Wu, ZiNiu

2013-05-01

In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The shock-shock interaction theory in conjunction with a three dimensional correction and checked with computational fluid dynamics (CFD) is used to analyze the lift and drag forces as function of the geometrical parameters and inflow Mach number. Through this study, though limited to only inviscid flow, we conclude that it is possible to obtain a high lift to drag ratio by suitably arranging the shock interaction generator.

Low-Lift Drag of the Grumman F9F-9 Airplane as Obtained by a 1/7.5-Scale Rocket-Boosted Model and by Three 1/45.85-Scale Equivalent-Body Models between Mach Numbers of 0.8 and 1.3, TED No. NACA DE 391

Science.gov (United States)

Stevens, Joseph E.

1955-01-01

Low-lift drag data are presented herein for one 1/7.5-scale rocket-boosted model and three 1/45.85-scale equivalent-body models of the Grumman F9F-9 airplane, The data were obtained over a Reynolds number range of about 5 x 10(exp 6) to 10 x 10(exp 6) based on wing mean aerodynamic chord for the rocket model and total body length for the equivalent-body models. The rocket-boosted model showed a drag rise of about 0,037 (based on included wing area) between the subsonic level and the peak supersonic drag coefficient at the maximum Mach number of this test. The base drag coefficient measured on this model varied from a value of -0,0015 in the subsonic range to a maximum of about 0.0020 at a Mach number of 1.28, Drag coefficients for the equivalent-body models varied from about 0.125 (based on body maximum area) in the subsonic range to about 0.300 at a Mach number of 1.25. Increasing the total fineness ratio by a small amount raised the drag-rise Mach number slightly.

Drag reduction: enticing turbulence, and then an industry.

Science.gov (United States)

Spalart, Philippe R; McLean, J Douglas

2011-04-13

We examine drag-reduction proposals, as presented in this volume and in general, first with concrete examples of how to bridge the distance from pure science through engineering to what makes inventions go into service; namely, the value to the public. We point out that the true drag reduction can be markedly different from an estimate based simply on the difference between turbulent and laminar skin friction over the laminarized region, or between the respective skin frictions of the baseline and the riblet-treated flow. In some situations, this difference is favourable, and is due to secondary differences in pressure drag. We reiterate that the benefit of riblets, if it is expressed as a percentage in skin-friction reduction, is unfortunately lower at full-size Reynolds numbers than in a small-scale experiment or simulation. The Reynolds number-independent measure of such benefits is a shift of the logarithmic law, or 'ΔU(+)'. Anticipating the design of a flight test and then a product, we note the relative ease in representing riblets or laminarization in computational fluid dynamics, in contrast with the huge numerical and turbulence-modelling challenge of resolving active flow control systems in a calculation of the full flow field. We discuss in general terms the practical factors that have limited applications of concepts that would appear more than ready after all these years, particularly riblets and laminar-flow control.

Applicability of the minimum entropy generation method for optimizing thermodynamic cycles

Institute of Scientific and Technical Information of China (English)

Cheng Xue-Tao; Liang Xin-Gang

2013-01-01

Entropy generation is often used as a figure of merit in thermodynamic cycle optimizations.In this paper,it is shown that the applicability of the minimum entropy generation method to optimizing output power is conditional.The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power when the total heat into the system of interest is not prescribed.For the cycles whose working medium is heated or cooled by streams with prescribed inlet temperatures and prescribed heat capacity flow rates,it is theoretically proved that both the minimum entropy generation rate and the minimum entropy generation number correspond to the maximum output power when the virtual entropy generation induced by dumping the used streams into the environment is considered.However,the minimum principle of entropy generation is not tenable in the case that the virtual entropy generation is not included,because the total heat into the system of interest is not fixed.An irreversible Carnot cycle and an irreversible Brayton cycle are analysed.The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power if the heat into the system of interest is not prescribed.

Applicability of the minimum entropy generation method for optimizing thermodynamic cycles

International Nuclear Information System (INIS)

Cheng Xue-Tao; Liang Xin-Gang

2013-01-01

Entropy generation is often used as a figure of merit in thermodynamic cycle optimizations. In this paper, it is shown that the applicability of the minimum entropy generation method to optimizing output power is conditional. The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power when the total heat into the system of interest is not prescribed. For the cycles whose working medium is heated or cooled by streams with prescribed inlet temperatures and prescribed heat capacity flow rates, it is theoretically proved that both the minimum entropy generation rate and the minimum entropy generation number correspond to the maximum output power when the virtual entropy generation induced by dumping the used streams into the environment is considered. However, the minimum principle of entropy generation is not tenable in the case that the virtual entropy generation is not included, because the total heat into the system of interest is not fixed. An irreversible Carnot cycle and an irreversible Brayton cycle are analysed. The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power if the heat into the system of interest is not prescribed. (general)

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%.

Predicting lethal entanglements as a consequence of drag from fishing gear.

Science.gov (United States)

van der Hoop, Julie M; Corkeron, Peter; Henry, Allison G; Knowlton, Amy R; Moore, Michael J

2017-02-15

Large whales are frequently entangled in fishing gear and sometimes swim while carrying gear for days to years. Entangled whales are subject to additional drag forces requiring increased thrust power and energy expenditure over time. To classify entanglement cases and aid potential disentanglement efforts, it is useful to know how long an entangled whale might survive, given the unique configurations of the gear they are towing. This study establishes an approach to predict drag forces on fishing gear that entangles whales, and applies this method to ten North Atlantic right whale cases to estimate the resulting increase in energy expenditure and the critical entanglement duration that could lead to death. Estimated gear drag ranged 11-275N. Most entanglements were resolved before critical entanglement durations (mean±SD 216±260days) were reached. These estimates can assist real-time development of disentanglement action plans and U.S. Federal Serious Injury assessments required for protected species. Copyright © 2016 Elsevier Ltd. All rights reserved.

Lift vs. drag based mechanisms for vertical force production in the smallest flying insects.

Science.gov (United States)

Jones, S K; Laurenza, R; Hedrick, T L; Griffith, B E; Miller, L A

2015-11-07

We used computational fluid dynamics to determine whether lift- or drag-based mechanisms generate the most vertical force in the flight of the smallest insects. These insects fly at Re on the order of 4-60 where viscous effects are significant. Detailed quantitative data on the wing kinematics of the smallest insects is not available, and as a result both drag- and lift-based strategies have been suggested as the mechanisms by which these insects stay aloft. We used the immersed boundary method to solve the fully-coupled fluid-structure interaction problem of a flexible wing immersed in a two-dimensional viscous fluid to compare three idealized hovering kinematics: a drag-based stroke in the vertical plane, a lift-based stroke in the horizontal plane, and a hybrid stroke on a tilted plane. Our results suggest that at higher Re, a lift-based strategy produces more vertical force than a drag-based strategy. At the Re pertinent to small insect hovering, however, there is little difference in performance between the two strategies. A drag-based mechanism of flight could produce more vertical force than a lift-based mechanism for insects at Re<5; however, we are unaware of active fliers at this scale. Copyright © 2015 Elsevier Ltd. All rights reserved.

Influence of Surface Roughness on Polymer Drag Reduction

National Research Council Canada - National Science Library

Ceccio, Steven L; Dowling, David R; Perlin, Marc; Solomon, Michael

2007-01-01

.... The details of that effort can be found in the final technical report for that project. The purpose of the additional investigation was to examine the physics and engineering of friction drag reduction methods for turbulent boundary layers (TBL...

Vehicle wheel drag coefficient in relation to travelling velocity - CFD analysis

Science.gov (United States)

Leśniewicz, P.; Kulak, M.; Karczewski, M.

2016-10-01

In order to understand the aerodynamic losses associated with a rotating automobile wheel, a detailed characteristics of the drag coefficient in relation to the applied velocity are necessary. Single drag coefficient value is most often reported for the commercially available vehicles, much less is revealed about the influence of particular car components on the energy consumption in various driving cycles. However, detailed flow potential losses determination is desired for performance estimation. To address these needs, the numerical investigation of an isolated wheel is proposed herein.

Drag reduction of dense fine-grained slurries

Czech Academy of Sciences Publication Activity Database

Vlasák, Pavel; Chára, Zdeněk; Štern, Petr

2010-01-01

Roč. 58, č. 4 (2010), s. 261-270 ISSN 0042-790X R&D Projects: GA ČR(CZ) GAP105/10/1574 Institutional research plan: CEZ:AV0Z20600510 Keywords : kaolin slurry * drag reduction * experimental investigation * peptization * slurry rheology Subject RIV: BK - Fluid Dynamics Impact factor: 0.553, year: 2010

Can Hall drag be observed in Coulomb coupled quantum wells in a magnetic field?

DEFF Research Database (Denmark)

Hu, Ben Yu-Kuang

1997-01-01

We study the transresistivity rho(21) (or equivalently, the drag rate) of two Coulomb-coupled quantum wells in the presence of a perpendicular magnetic field, using semi-classical transport theory. Elementary arguments seem to preclude any possibility of observation of ''Hall drag'' (i.e., a non...

Numerical study of water entry supercavitating flow around a vertical circular cylinder influenced by turbulent drag-reducing additives

International Nuclear Information System (INIS)

Jiang, C X; Cheng, J P; Li, F C

2015-01-01

This paper attempts to introduce a numerical simulation procedure to simulate water-entry problems influenced by turbulent drag-reducing additives in a viscous incompressible medium. Firstly we performed a numerical investigation on water-entry supercavities in water and turbulent drag-reducing solution at the impact velocity of 28.4 m/s to confirm the accuracy of the numerical method. Based on the verification, projectile entering water and turbulent drag-reducing solution at relatively high velocity of 142.7 m/s (phase transition is considered) is simulated. The cross viscosity equation was adopted to represent the shear-thinning characteristic of aqueous solution of drag-reducing additives. The configuration and dynamic characteristics of water entry supercavity, flow resistance were discussed respectively. It was obtained that the numerical simulation results are in consistence with experimental data. Numerical results show that the supercavity length in drag-reducing solution is larger than one in water and the velocity attenuates faster at high velocity than at low velocity; the influence of drag-reducing solution is more obvious at high impact velocity. Turbulent drag-reducing additives have the great potential for enhancement of supercavity

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.

The strong thermoelectric effect in nanocarbon generated by the ballistic phonon drag of electrons

International Nuclear Information System (INIS)

Eidelman, E D; Vul', A Ya

2007-01-01

The thermoelectric power and thermoelectric figure of merit for carbon nanostructure consisting of graphite-like (sp 2 ) and diamond-like (sp 3 ) regions have been investigated. The probability of electron collisions with quasi-ballistic phonons in sp 2 regions has been analysed for the first time. We have shown that the probability is not small. We have analysed the influence of various factors on the process of the electron-ballistic phonon drag (the phonon drag effect). The thermoelectric power and thermoelectric figure of merit under conditions of ballistic transport were found to be substantially higher than those in the cases of drag by thermalized phonons and of electron diffusion. The thermoelectric figure of merit (ZT) in the case of a ballistic phonon contribution to the phonon drag of electrons should be 50 times that for chaotic phonons and 500 times that in the case of the diffusion process. In that case ZT should be a record (ZT≥2-3)

Coulomb drag in electron-hole bilayer: Mass-asymmetry and exchange correlation effects

Science.gov (United States)

Arora, Priya; Singh, Gurvinder; Moudgil, R. K.

2018-04-01

Motivated by a recent experiment by Zheng et al. [App. Phys. Lett. 108, 062102 (2016)] on coulomb drag in electron-hole and hole-hole bilayers based on GaAs/AlGaAs semiconductor heterostructure, we investigate theoretically the influence of mass-asymmetry and temperature-dependence of correlations on the drag rate. The correlation effects are dealt with using the Vignale-Singwi effective inter-layer interaction model which includes correlations through local-field corrections to the bare coulomb interactions. However, in this work, we have incorporated only the intra-layer correlations using the temperature-dependent Hubbard approximation. Our results display a reasonably good agreement with the experimental data. However, it is crucial to include both the electron-hole mass-asymmetry and temperature-dependence of correlations. Mass-asymmetry and correlations are found to result in a substantial enhancement of drag resistivity.

Drag reduction by dimples? - A complementary experimental/numerical investigation

International Nuclear Information System (INIS)

Lienhart, Hermann; Breuer, Michael; Koeksoy, Cagatay

2008-01-01

The paper is concerned with an experimental and numerical investigation of the turbulent flow over dimpled surfaces. Shallow dimples distributed regularly over the wall of a plane channel with large aspect ratio are used to study their effect on the friction drag. The resulting pressure drop in the channel was measured for smooth and dimpled walls. In addition to these investigations on internal flows, an external flow study was performed and boundary-layer profiles were measured using a Pitot-tube rake. Complementary to the measurements, direct numerical simulations for the internal flow configuration with and without dimples were carried out for two different grid resolutions and analyzed in detail. The objective was to clarify whether or not dimples cause reduction of the skin-friction drag

Physics and control of wall turbulence for drag reduction.

Science.gov (United States)

Kim, John

2011-04-13

Turbulence physics responsible for high skin-friction drag in turbulent boundary layers is first reviewed. A self-sustaining process of near-wall turbulence structures is then discussed from the perspective of controlling this process for the purpose of skin-friction drag reduction. After recognizing that key parts of this self-sustaining process are linear, a linear systems approach to boundary-layer control is discussed. It is shown that singular-value decomposition analysis of the linear system allows us to examine different approaches to boundary-layer control without carrying out the expensive nonlinear simulations. Results from the linear analysis are consistent with those observed in full nonlinear simulations, thus demonstrating the validity of the linear analysis. Finally, fundamental performance limit expected of optimal control input is discussed.

Sunspots and the physics of magnetic flux tubes. II. Aerodynamic drag

International Nuclear Information System (INIS)

Parker, E.N.

1979-01-01

The aerodynamic drag on a slender flux tube stretched vertically across a convective cell may push the flux tube into the updrafts or into the downdrafts, depending on the density stratification of the convecting fluid and the asymmetry of the fluid motions. The drag is approximately proportional to the local kinetic energy density, so the density stratification weights the drag in favor of the upper layers where the density is low, tending to push the vertical tube into the downdrafts. If, however, the horizontal motions in the convective cell are concentrated toward the bottom of the cell, they may dominate over the upper layers, pushing the tube into the updrafts. In the simple, idealized circumstance of a vertical tube extending across a fluid of uniform density in a convective cell that is symmetric about its midplane, the net aerodynamic drag vanishes in lowest order. The higher order contributions, including the deflection of the tube, then provide a nonvanishing force pushing the tube into a stable equilibrium midway between the updraft and the downdraft.It is pointed out that in the strongly stratified convective zone of the Sun, a downdraft herds flux tubes together into a cluster, while an updraft disperses them. To account for the observed strong cohesion of the cluster of flux tubes that make up a sunspot, we propose a downdraft of the order 2 km s - 1 through the cluster of seprate tubes beneath the sunspot

A diagnostic model to estimate winds and small-scale drag from Mars Observer PMIRR data

Science.gov (United States)

Barnes, J. R.

1993-01-01

Theoretical and modeling studies indicate that small-scale drag due to breaking gravity waves is likely to be of considerable importance for the circulation in the middle atmospheric region (approximately 40-100 km altitude) on Mars. Recent earth-based spectroscopic observations have provided evidence for the existence of circulation features, in particular, a warm winter polar region, associated with gravity wave drag. Since the Mars Observer PMIRR experiment will obtain temperature profiles extending from the surface up to about 80 km altitude, it will be extensively sampling middle atmospheric regions in which gravity wave drag may play a dominant role. Estimating the drag then becomes crucial to the estimation of the atmospheric winds from the PMIRR-observed temperatures. An interative diagnostic model based upon one previously developed and tested with earth satellite temperature data will be applied to the PMIRR measurements to produce estimates of the small-scale zonal drag and three-dimensional wind fields in the Mars middle atmosphere. This model is based on the primitive equations, and can allow for time dependence (the time tendencies used may be based upon those computed in a Fast Fourier Mapping procedure). The small-scale zonal drag is estimated as the residual in the zonal momentum equation; the horizontal winds having first been estimated from the meridional momentum equation and the continuity equation. The scheme estimates the vertical motions from the thermodynamic equation, and thus needs estimates of the diabatic heating based upon the observed temperatures. The latter will be generated using a radiative model. It is hoped that the diagnostic scheme will be able to produce good estimates of the zonal gravity wave drag in the Mars middle atmosphere, estimates that can then be used in other diagnostic or assimilation efforts, as well as more theoretical studies.

Experimental measurement of unsteady drag on shock accelerated micro-particles

Science.gov (United States)

Bordoloi, Ankur; Martinez, Adam; Prestridge, Katherine

2016-11-01

The unsteady drag history of shock accelerated micro-particles in air is investigated in the Horizontal Shock Tube (HST) facility at Los Alamos National laboratory. Drag forces are estimated based on particle size, particle density, and instantaneous velocity and acceleration measured on hundreds of post-shock particle tracks. We use previously implemented 8-frame Particle Tracking Velocimetry/Anemometry (PTVA) diagnostics to analyze particles in high spatiotemporal resolution from individual particle trajectories. We use a simultaneous LED based shadowgraph to register shock location with respect to a moving particle in each frame. To measure particle size accurately, we implement a Phase Doppler Particle Analyzer (PDPA) in synchronization with the PTVA. In this presentation, we will corroborate with more accuracy our earlier observation that post-shock unsteady drag coefficients (CD(t)) are manifold times higher than those predicted by theoretical models. Our results will also show that all CD(t) measurements collapse on a master-curve for a range of particle size, density, Mach number and Reynolds number when time is normalized by a shear velocity based time scale, t* = d/(uf-up) , where d is particle diameter, and uf and up are post-shock fluid and particle velocities.

An investigation of drag reduction on box-shaped ground vehicles

Science.gov (United States)

Muirhead, V. U.

1976-01-01

A wind tunnel investigation was conducted to determine the reduction in drag which could be obtained by making various configuration changes to a box-shaped ground vehicle. Tests were conducted at yaw (relative wind) angles of 0, 5, 10, 20, and 30 degrees and Reynolds numbers of 300,000 to 850,000. The power required to overcome the aerodynamic drag was reduced by a maximum of 73% for a head wind for the best configuration relative to the smooth bottom box-shape, or 75% relative to the rough bottom box-shape. The reduction for a 20 MPH wind at 30 deg to the vehicle path was, respectively, 77% and 79%.

Bluff-body drag reduction using a deflector

Energy Technology Data Exchange (ETDEWEB)

Fourrie, Gregoire; Keirsbulck, Laurent; Labraga, Larbi [Univ Lille Nord de France, Lille (France); UVHC, TEMPO, Valenciennes (France); Gillieron, Patrick [Fluid Mechanics and Aerodynamics, Renault Group, Research Division, Guyancourt (France)

2011-02-15

A passive flow control on a generic car model was experimentally studied. This control consists of a deflector placed on the upper edge of the model rear window. The study was carried out in a wind tunnel at Reynolds numbers based on the model height of 3.1 x 10{sup 5} and 7.7 x 10{sup 5}. The flow was investigated via standard and stereoscopic particle image velocimetry, Kiel pressure probes and surface flow visualization. The aerodynamic drag was measured using an external balance and calculated using a wake survey method. Drag reductions up to 9% were obtained depending on the deflector angle. The deflector increases the separated region on the rear window. The results show that when this separated region is wide enough, it disrupts the development of the counter-rotating longitudinal vortices appearing on the lateral edges of the rear window. The current study suggests that flow control on such geometries should consider all the flow structures that contribute to the model wake flow. (orig.)

ISM-induced erosion and gas-dynamical drag in the Oort Cloud

Science.gov (United States)

Stern, S. Alan

1990-01-01

The model presently used to examine the physical interactions between the ISM and the Oort Cloud can account for sputtering, sticking, and grain-impact erosion, as well as gas drag, by envisioning the ISM as a multiphase medium with distinct atomic and molecular cloud-phase regimes and coronal and warm/ambient gas-phase regimes. Erosion, which reduces the effectiveness of the thermal and radiation-damage processes acting on cometary surfaces in the Oort cloud, is found to be the dominant ISM interaction; ISM drag effects were found to efficiently remove submicron particles from the Cloud.

Micro-fibers shape effects on gas exchange in Total Artificial Lung

KAUST Repository

Qamar, Adnan; Guglani, Aditya; Samtaney, Ravi

2014-01-01

Flow and oxygen transport dynamics of a pulsatile flow past an array of square and circular cross section micro-fiber is numerically investigated in the present work. The study is motivated to optimize the design of an Total Artificial Lung (TAL) under clinical trials. Effects of three non-dimensional parameters: Reynolds number, non-dimensional amplitude of free stream velocity and Keulegan Carpenter number on oxygen transport and total drag (resistance) of both the fibers are studied. Range of parameters investigated corresponds to operating range of TAL. For most of the cases investigated, results show enhanced oxygen transport for square fiber but higher resistance when compare with the circular fiber case under almost all flow conditions. For both fibers, oxygen transfer rate are enhanced at higher Reynolds number, higher velocity amplitude and lower KC values. Overall drag is found to decrease with increasing Reynolds number and decreasing amplitude and is not significantly effected by Keulegan Carpenter number. © 2014 IEEE.

Micro-fibers shape effects on gas exchange in Total Artificial Lung

KAUST Repository

Qamar, Adnan

2014-02-01

Flow and oxygen transport dynamics of a pulsatile flow past an array of square and circular cross section micro-fiber is numerically investigated in the present work. The study is motivated to optimize the design of an Total Artificial Lung (TAL) under clinical trials. Effects of three non-dimensional parameters: Reynolds number, non-dimensional amplitude of free stream velocity and Keulegan Carpenter number on oxygen transport and total drag (resistance) of both the fibers are studied. Range of parameters investigated corresponds to operating range of TAL. For most of the cases investigated, results show enhanced oxygen transport for square fiber but higher resistance when compare with the circular fiber case under almost all flow conditions. For both fibers, oxygen transfer rate are enhanced at higher Reynolds number, higher velocity amplitude and lower KC values. Overall drag is found to decrease with increasing Reynolds number and decreasing amplitude and is not significantly effected by Keulegan Carpenter number. © 2014 IEEE.

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 drag and lift of different non-spherical particles from low to high Re

Science.gov (United States)

Sanjeevi, Sathish K. P.; Padding, Johan

2017-11-01

The present work investigates a simplified drag and lift model that can be used for different non-spherical particles. The flow around different non-spherical particles is studied using a multi-relaxation-time lattice Boltzmann method. We compute the mean drag coefficient CD , ϕ at different incident angles ϕ for a wide range of Reynolds numbers (Re). We show that the sine-squared drag law CD , ϕ =CD , ϕ =0° +(CD , ϕ =90° -CD , ϕ =0°) sin2 ϕ holds up to large Reynolds numbers Re = 2000 . The sine-squared dependence of CD occurs at Stokes flow (very low Re) due to linearity of the flow fields. We explore the physical origin behind the sine-squared law at high Re , and reveal that surprisingly, this does not occur due to linearity of flow fields. Instead, it occurs due to an interesting pattern of pressure distribution contributing to the drag, at higher Re , for different incident angles. Similarly, we find that the equivalent theoretical equation of lift coefficient CL can provide a decent approximation, even at high Re , for elongated particles. Such a drag and lift law valid at high Re is very much useful for Euler-Lagrangian fluidization simulations of the non-spherical particles. European Research Council (ERC) consolidator Grant scheme, Contract No. 615096 (NonSphereFlow).

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

Energy Technology Data Exchange (ETDEWEB)

Watanabe, Sho; Fukagata, Koji [Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522 (Japan); Mamori, Hiroya, E-mail: fukagata@mech.keio.ac.jp [Department of Mechanical Engineering, Tokyo University of Science, Niijuku 6-3-1, Katsushika-ku, Tokyo 125-8585 (Japan)

2017-04-15

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

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.

Drag of Clean and Fouled Net Panels--Measurements and Parameterization of Fouling.

Directory of Open Access Journals (Sweden)

Lars Christian Gansel

Full Text Available Biofouling is a serious problem in marine aquaculture and it has a number of negative impacts including increased forces on aquaculture structures and reduced water exchange across nets. This in turn affects the behavior of fish cages in waves and currents and has an impact on the water volume and quality inside net pens. Even though these negative effects are acknowledged by the research community and governmental institutions, there is limited knowledge about fouling related effects on the flow past nets, and more detailed investigations distinguishing between different fouling types have been called for. This study evaluates the effect of hydroids, an important fouling organism in Norwegian aquaculture, on the forces acting on net panels. Drag forces on clean and fouled nets were measured in a flume tank, and net solidity including effect of fouling were determined using image analysis. The relationship between net solidity and drag was assessed, and it was found that a solidity increase due to hydroids caused less additional drag than a similar increase caused by change in clean net parameters. For solidities tested in this study, the difference in drag force increase could be as high as 43% between fouled and clean nets with same solidity. The relationship between solidity and drag force is well described by exponential functions for clean as well as for fouled nets. A method is proposed to parameterize the effect of fouling in terms of an increase in net solidity. This allows existing numerical methods developed for clean nets to be used to model the effects of biofouling on nets. Measurements with other types of fouling can be added to build a database on effects of the accumulation of different fouling organisms on aquaculture nets.

Application of the FUN3D Unstructured-Grid Navier-Stokes Solver to the 4th AIAA Drag Prediction Workshop Cases

Science.gov (United States)

Lee-Rausch, Elizabeth M.; Hammond, Dana P.; Nielsen, Eric J.; Pirzadeh, S. Z.; Rumsey, Christopher L.

2010-01-01

FUN3D Navier-Stokes solutions were computed for the 4th AIAA Drag Prediction Workshop grid convergence study, downwash study, and Reynolds number study on a set of node-based mixed-element grids. All of the baseline tetrahedral grids were generated with the VGRID (developmental) advancing-layer and advancing-front grid generation software package following the gridding guidelines developed for the workshop. With maximum grid sizes exceeding 100 million nodes, the grid convergence study was particularly challenging for the node-based unstructured grid generators and flow solvers. At the time of the workshop, the super-fine grid with 105 million nodes and 600 million elements was the largest grid known to have been generated using VGRID. FUN3D Version 11.0 has a completely new pre- and post-processing paradigm that has been incorporated directly into the solver and functions entirely in a parallel, distributed memory environment. This feature allowed for practical pre-processing and solution times on the largest unstructured-grid size requested for the workshop. For the constant-lift grid convergence case, the convergence of total drag is approximately second-order on the finest three grids. The variation in total drag between the finest two grids is only 2 counts. At the finest grid levels, only small variations in wing and tail pressure distributions are seen with grid refinement. Similarly, a small wing side-of-body separation also shows little variation at the finest grid levels. Overall, the FUN3D results compare well with the structured-grid code CFL3D. The FUN3D downwash study and Reynolds number study results compare well with the range of results shown in the workshop presentations.

Drag reduction in reservoir rock surface: Hydrophobic modification by SiO_2 nanofluids

International Nuclear Information System (INIS)

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

2017-01-01

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

Self-determined shapes and velocities of giant near-zero drag gas cavities

KAUST Repository

Vakarelski, Ivan Uriev

2017-09-09

Minimizing the retarding force on a solid moving in liquid is the canonical problem in the quest for energy saving by friction and drag reduction. For an ideal object that cannot sustain any shear stress on its surface, theory predicts that drag force will fall to zero as its speed becomes large. However, experimental verification of this prediction has been challenging. We report the construction of a class of self-determined streamlined structures with this free-slip surface, made up of a teardrop-shaped giant gas cavity that completely encloses a metal sphere. This stable gas cavity is formed around the sphere as it plunges at a sufficiently high speed into the liquid in a deep tank, provided that the sphere is either heated initially to above the Leidenfrost temperature of the liquid or rendered superhydrophobic in water at room temperature. These sphere-in-cavity structures have residual drag coefficients that are typically less than Embedded Image those of solid objects of the same dimensions, which indicates that they experienced very small drag forces. The self-determined shapes of the gas cavities are shown to be consistent with the Bernoulli equation of potential flow applied on the cavity surface. The cavity fall velocity is not arbitrary but is uniquely predicted by the sphere density and cavity volume, so larger cavities have higher characteristic velocities.

A Low Cost Inflatable CubeSat Drag Brake Utilizing Sublimation

Science.gov (United States)

Horn, Adam Charles

The United Nations Inter-Agency Debris Coordination Committee has adopted a 25-year post-mission lifetime requirement for any satellite orbiting below 2000 km in order to mitigate the growing orbital debris threat. Low-cost CubeSats have become important satellite platforms with startling capabilities, but this guideline restricts them to altitudes below 600 km because they remain in orbit too long. In order to enable CubeSat deployments at higher release altitudes, a low-cost, ultra-reliable deorbit device is needed. This thesis reports on efforts to develop a deployable and passively inflatable drag brake that can deorbit from higher orbital altitudes, thereby complying with the 25-year orbital lifetime guideline. On the basis of concepts first implemented during the NASA Echo Satellite Project, this study investigated the design of an inflatable CubeSat drag device that utilizes sublimating benzoic acid powder as the inflation propellant. Testing has focused on demonstrating the functionality of charging a Mylar drag brake bladder with appropriate quantities of benzoic acid powder, and the exposure to a controlled-temperature vacuum chamber causing the bladder to inflate. Although results show a measureable increase in internal pressure when introduced to anticipated orbital temperatures, a significant air-derived expansion prior to sublimation was encountered due to the undetectable volume of ambient residual air in the fabricated membrane bladders. These tests have demonstrated the feasibility of this approach, thereby demonstrating that this concept can create a potentially smaller and less expensive drag device, eliminating inflation gas tanks and valves. In that way, this system can provide a low-cost, miniaturized system that reduces a CubeSat's orbital lifetime to less than 25 years, when placed at higher orbital altitude.

The Effect of Air Drag in Optimal Power-Limited Rendezvous Between Coplanar Low-Earth Orbits

Directory of Open Access Journals (Sweden)

Gil-Young Maeng

1998-06-01

Full Text Available The effect of air drag was researched when a low-earth orbit spacecraft using power-limited thruster rendezvoused another low-earth orbit spacecraft. The air density was assumed to decrease exponentially. The radius of parking orbit was 6655.935 km and that of target orbit was 7321.529 km. From the trajectories of active vehicles, the fuel consumption and the magnitude of thrust acceleration, we could conclude that the effect of air drag had to be considered in fuel optimal rendezvous problem between low-earth orbit spacecrafts. In multiple-revolution rendezvous case, the air drag was more effective.

AERODYNAMICS ASSESSMENT USING CFD FOR A LOW DRAG SHELL ECO-MARATHON CAR

OpenAIRE

Abo-Serie, E.

2017-01-01

Having a small car running with low power can be achieved byreducing the aerodynamics drag, rolling resistance and mechanical frictionsbetween the moving parts. The Shell Eco-Marathon competition held around theworld with events in Europe, USA and Asia shows every year new techniques andideas to reduce the power needed to drive the car. The record of over 3400 kmon the equivalent of a single litre of fuel is an indication of how car can runefficiently. The problem with these low drag cars is ...

Collisionless ion drag force on a spherical grain

International Nuclear Information System (INIS)

Hutchinson, I H

2006-01-01

The ion drag force on a spherical grain situated in a flowing collisionless plasma is obtained from the specialized coordinate electrostatic particle and thermals in cell simulation code (SCEPTIC) (Hutchinson 2002 Plasma Phys. Control. Fusion 44 1953, Hutchinson 2003 Plasma Phys. Control. Fusion 45 1477, Hutchinson 2005 Plasma Phys. Control. Fusion 47 71) and compared with recent analytic approximate treatments in the interesting and relevant case when the Debye length is only moderately larger than the sphere radius. There is a substantial complex structure in the results for transonic flows, which is explained in terms of the details of ion orbits. Naturally the prior analytic approximations miss this structure, and as a result they seriously underestimate the drag for speeds near the sound speed. An easy-to-evaluate expression for force is provided that fits the comprehensive results of the code. This expression, with minor modification, also fits the results even for Debye length much smaller than the sphere radius

Design and development of drag-disc flowmeter for measurement of transient two-phase flow

International Nuclear Information System (INIS)

Sreenivas Rao, G.; Kukreja, V.; Dolas, P.K.; Venkat Raj, V.

1990-01-01

Experiments have been carried out to test the suitability of drag-disc flowmeter for measuring two-phase flow. Calibration tests carried out under single-phase and two-phase flow conditions have confirmed the suitability of the drag-disc flowmeter. The experimental work and the results obtained are presented and discussed in the paper. (author). 3 refs., 6 figs

ISM-induced erosion and gas-dynamical drag in the Oort Cloud

International Nuclear Information System (INIS)

Stern, S.A.

1990-01-01

The model presently used to examine the physical interactions between the ISM and the Oort Cloud can account for sputtering, sticking, and grain-impact erosion, as well as gas drag, by envisioning the ISM as a multiphase medium with distinct atomic and molecular cloud-phase regimes and coronal and warm/ambient gas-phase regimes. Erosion, which reduces the effectiveness of the thermal and radiation-damage processes acting on cometary surfaces in the Oort cloud, is found to be the dominant ISM interaction; ISM drag effects were found to efficiently remove submicron particles from the Cloud. 67 refs

Satellite drag effects due to uplifted oxygen neutrals during super magnetic storms

Science.gov (United States)

Lakhina, Gurbax S.; Tsurutani, Bruce T.

2017-12-01

During intense magnetic storms, prompt penetration electric fields (PPEFs) through E × B forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the dayside super-fountain effect. Ion-neutral drag forces between the upward moving O+ (oxygen ions) and oxygen neutrals will elevate the oxygen atoms to higher altitudes. This paper gives a linear calculation indicating how serious the effect may be during an 1859-type (Carrington) superstorm. It is concluded that the oxygen neutral densities produced at low-Earth-orbiting (LEO) satellite altitudes may be sufficiently high to present severe satellite drag. It is estimated that with a prompt penetrating electric field of ˜ 20 mV m-1 turned on for 20 min, the O atoms and O+ ions are uplifted to 850 km where they produce about 40-times-greater satellite drag per unit mass than normal. Stronger electric fields will presumably lead to greater uplifted mass.

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

Science.gov (United States)

De Gregorio, F.

2017-08-01

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

Drag reduction by streamwise traveling wave-like Lorenz Force in channel flow

International Nuclear Information System (INIS)

Mamori, Hiroya; Fukagata, Koji

2011-01-01

Skin-friction drag reduction effect of traveling wave-like wall-normal Lorenz force in a fully developed turbulent channel flow is investigated by means of direct numerical simulation. A sinusoidal profile of the wall-normal body force is assumed as the Lorenz force. While upstream traveling waves reduce the drag in the case of blowing/suction, standing waves reduce it in the case of present forcing. Visualization of vortical structure under the standing wave-like wall-normal Lorenz force reveals that the near-wall streamwise vortices, which increase the skin-friction drag, disappear and spanwise roller-like vortices are generated instead. Three component decomposition of the Reynolds shear stress indicates that the spanwise roller-like vortices contribute to the negative Reynolds shear stress in the region near the wall, similarly to the case of laminar flows. While the analogy between the wall-normal and streamwise forcings can be expected, the statistics are found to exhibit different behaviors due to the difference in the energy flow.

Flow Patterns and Thermal Drag in a One-Dimensional Inviscid Channel with Heating or Cooling

Institute of Scientific and Technical Information of China (English)

无

1993-01-01

In this paper investigations on the flow patterns and the thermal drag phenomenon in one -dimensional inviscid channel flow with heating or cooling are described and discussed:expressions of flow rate ratio and thermal drag coefficient for different flow patterns and its physical mechanism are presented.

Experimental evaluation of the drag coefficient of water rockets by a simple free-fall test

Energy Technology Data Exchange (ETDEWEB)

Barrio-Perotti, R; Blanco-Marigorta, E; Argueelles-Diaz, K; Fernandez-Oro, J [Departamento de Energia, Universidad de Oviedo, Campus de Viesques, 33271 Gijon, Asturias (Spain)], E-mail: barrioraul@uniovi.es

2009-09-15

The flight trajectory of a water rocket can be reasonably calculated if the magnitude of the drag coefficient is known. The experimental determination of this coefficient with enough precision is usually quite difficult, but in this paper we propose a simple free-fall experiment for undergraduate students to reasonably estimate the drag coefficient of water rockets made from plastic soft drink bottles. The experiment is performed using relatively small fall distances (only about 14 m) in addition with a simple digital-sound-recording device. The fall time is inferred from the recorded signal with quite good precision, and it is subsequently introduced as an input of a Matlab (registered) program that estimates the magnitude of the drag coefficient. This procedure was tested first with a toy ball, obtaining a result with a deviation from the typical sphere value of only about 3%. For the particular water rocket used in the present investigation, a drag coefficient of 0.345 was estimated.

Wavelet Analysis on Turbulent Structure in Drag-Reducing Channel Flow Based on Direct Numerical Simulation

Directory of Open Access Journals (Sweden)

Xuan Wu

2013-01-01

Full Text Available Direct numerical simulation has been performed to study a polymer drag-reducing channel flow by using a discrete-element model. And then, wavelet analyses are employed to investigate the multiresolution characteristics of velocity components based on DNS data. Wavelet decomposition is applied to decompose velocity fluctuation time series into ten different frequency components including approximate component and detailed components, which show more regular intermittency and burst events in drag-reducing flow. The energy contribution, intermittent factor, and intermittent energy are calculated to investigate characteristics of different frequency components. The results indicate that energy contributions of different frequency components are redistributed by polymer additives. The energy contribution of streamwise approximate component in drag-reducing flow is up to 82%, much more than 25% in the Newtonian flow. Feature of turbulent multiscale structures is shown intuitively by continuous wavelet transform, verifying that turbulent structures become much more regular in drag-reducing flow.

Drag power kite with very high lift coefficient

NARCIS (Netherlands)

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

On the development of lift and drag in a rotating and translating cylinder

Science.gov (United States)

Martin-Alcantara, Antonio; Sanmiguel-Rojas, Enrique; Fernandez-Feria, Ramon

2014-11-01

The two-dimensional flow around a rotating cylinder is investigated numerically using a vorticity forces formulation with the aim of analyzing the flow structures, and their evolutions, that contribute to the lift and drag forces on the cylinder. The Reynolds number, based on the cylinder diameter and steady free-stream speed, considered is Re = 200 , while the non-dimensional rotation rate (ratio of the surface speed and free-stream speed) selected were α = 1 and 3. For α = 1 the wake behind the cylinder for the fully developed flow is oscillatory due to vortex shedding, and so are the lift and drag forces. For α = 3 the fully developed flow is steady with constant (high) lift and (low) drag. Each of these cases is considered in two different transient problems, one with angular acceleration of the cylinder and constant speed, and the other one with translating acceleration of the cylinder and constant rotation. Special attention is paid to explaining the mechanisms of vortex shedding suppression for high rotation (when α = 3) and its relation to the mechanisms by which the lift is enhanced and the drag is almost suppressed when the fully developed flow is reached. Supported by the Ministerio de Economia y Competitividad of Spain Grant No. DPI2013-40479-P.

Gain-assisted superluminal propagation and rotary drag of photon and surface plasmon polaritons

Science.gov (United States)

Khan, Naveed; Amin Bacha, Bakht; Iqbal, Azmat; Ur Rahman, Amin; Afaq, A.

2017-07-01

Superluminal propagation of light is a well-established phenomenon and has motivated immense research interest that has led to state-of-the-art knowledge and potential applications in the emerging technology of quantum optics and photonics. This study presents a theoretical analysis of the gain-assisted superluminal light propagation in a four-level N -type atomic system by exploiting the scheme of electromagnetically induced gain and superluminal propagation of surface plasmon polaritons (SPPs) along the gain-assisted atomic-metal interface simultaneously. In addition, a theoretical demonstration is presented on the comparison between Fresnel's rotary photon drag and SPP drag in view of light polarization state rotation by rotating the coherent atomic medium and the atomic-metal interface, respectively. Analogous to photon drag in the superluminal anomalous dispersion region where light polarization rotation occurs opposite the rotation of the gain-assisted atomic medium, the rotation of the atomic-metal interface also rotates the polarization state of SPPs opposite the rotation of the interface. This further confirms the superluminal nature of SPPs propagating along the interface with negative group velocity. Rabi frequencies of the control and pump fields considerably modify both photon and SPP drag coefficients. Metal conductivity also controls SPP propagation.

Effects of cusped field thruster on the performance of drag-free control system

Science.gov (United States)

Cui, K.; Liu, H.; Jiang, W. J.; Sun, Q. Q.; Hu, P.; Yu, D. R.

2018-03-01

With increased measurement tasks of space science, more requirements for the spacecraft environment have been put forward. Those tasks (e.g. the measurement of Earth's steady state gravity field anomalies) lead to the desire for developing drag-free control. Higher requirements for the thruster performance are made due to the demand for the drag-free control system and real-time compensation for non-conservative forces. Those requirements for the propulsion system include wide continuous throttling ability, high resolution, rapid response, low noise and so on. As a promising candidate, the cusped field thruster has features such as the high working stability, the low erosion rate, a long lifetime and the simple structure, so that it is chosen as the thruster to be discussed in this paper. Firstly, the performance of a new cusped field thruster is tested and analyzed. Then a drag-free control scheme based on the cusped field thruster is designed to evaluate the performance of this thruster. Subsequently, the effects of the thrust resolution, transient response time and thrust uncertainty on the controller are calculated respectively. Finally, the performance of closed-loop system is analyzed, and the simulation results verify the feasibility of applying cusped field thruster to drag-free flight in the space science measurement tasks.

Predicting Minimum Control Speed on the Ground (VMCG) and Minimum Control Airspeed (VMCA) of Engine Inoperative Flight Using Aerodynamic Database and Propulsion Database Generators

Science.gov (United States)

Hadder, Eric Michael

There are many computer aided engineering tools and software used by aerospace engineers to design and predict specific parameters of an airplane. These tools help a design engineer predict and calculate such parameters such as lift, drag, pitching moment, takeoff range, maximum takeoff weight, maximum flight range and much more. However, there are very limited ways to predict and calculate the minimum control speeds of an airplane in engine inoperative flight. There are simple solutions, as well as complicated solutions, yet there is neither standard technique nor consistency throughout the aerospace industry. To further complicate this subject, airplane designers have the option of using an Automatic Thrust Control System (ATCS), which directly alters the minimum control speeds of an airplane. This work addresses this issue with a tool used to predict and calculate the Minimum Control Speed on the Ground (VMCG) as well as the Minimum Control Airspeed (VMCA) of any existing or design-stage airplane. With simple line art of an airplane, a program called VORLAX is used to generate an aerodynamic database used to calculate the stability derivatives of an airplane. Using another program called Numerical Propulsion System Simulation (NPSS), a propulsion database is generated to use with the aerodynamic database to calculate both VMCG and VMCA. This tool was tested using two airplanes, the Airbus A320 and the Lockheed Martin C130J-30 Super Hercules. The A320 does not use an Automatic Thrust Control System (ATCS), whereas the C130J-30 does use an ATCS. The tool was able to properly calculate and match known values of VMCG and VMCA for both of the airplanes. The fact that this tool was able to calculate the known values of VMCG and VMCA for both airplanes means that this tool would be able to predict the VMCG and VMCA of an airplane in the preliminary stages of design. This would allow design engineers the ability to use an Automatic Thrust Control System (ATCS) as part

Simultaneous drag and flow measurements of Olympic skeleton athletes

Science.gov (United States)

Moon, Yae Eun; Digiulio, David; Peters, Steve; Wei, Timothy

2009-11-01

The Olympic sport of skeleton involves an athlete riding a small sled face first down a bobsled track at speeds up to 130 km/hr. In these races, the difference between gold and missing the medal stand altogether can be hundredths of a second per run. As such, reducing aerodynamic drag through proper body positioning is of first order importance. To better study the flow behavior and to improve the performance of the athletes, we constructed a static force balance system on a mock section of a bobsled track. Athlete and the sled are placed on the force balance system which is positioned at the exit of an open loop wind tunnel. Simultaneous drag force and DPIV velocity field measurements were made along with video recordings of body position to aid the athletes in determining their optimal aerodynamic body position.

Suboptimal control for drag reduction in turbulent pipe flow

International Nuclear Information System (INIS)

Choi, Jung Il; Sung, Hyung Jin; Xu, Chun Xiao

2001-01-01

A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables ∂ρ/∂θ / w and ∂ν θ /∂r / w are applied with two actuations φ θ and φ γ . To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at Re τ =150 are performed. When the control law is applied, a 13∼23% drag reduction is achieved. The most effective drag reduction is made at the pair of ∂υ θ /∂r / w and φ γ . An impenetrable virtual wall concept is useful for analyzing the near-wall suction and blowing. The virtual wall concept is useful for analyzing the near-wall behavior of the controlled flow. Comparison of the present suboptimal control with that of turbulent channel flow reveals that the curvature effect is insignificant

Control of Nonlinear Coupled Electromagnetic Actuators for Active Drag Reduction in Turbulent Flow

OpenAIRE

Seidler, Florian; Trabert, Julius; Dück, Marcel; van Waasen, Stefan; Schiek, Michael; Abel, Dirk; Castelan, E. B.

2016-01-01

The research group FOR1779 “active drag reduction via wavy surface oscillations” develops robust methods for reduction of turbulent friction drag by flow control. The planned concentration on unsteady flow conditions requires a control of the electromagnetic actuator system for generation of transversal surface waves. The bars are positioned in parallel and coupled with an aluminum surface to generate a travelling wave perpendicular to the flow field. The actuator system can be approximately ...

Numerical investigation of drag and heat flux reduction mechanism of the pulsed counterflowing jet on a blunt body in supersonic flows

Science.gov (United States)

Zhang, Rui-rui; Huang, Wei; Yan, Li; Li, Lang-quan; Li, Shi-bin; Moradi, R.

2018-05-01

To design a kind of aerospace vehicle, the drag and heat flux reduction are the most important factors. In the current study, the counterflowing jet, one of the effective drag and heat flux reduction concepts, is investigated numerically by the two-dimensional axisymmetric Reynolds-averaged Navier-Stokes equations coupled with the SST k-ω turbulence model. An axisymmetric numerical simulation mode of the counterflowing jet on the supersonic vehicle nose-tip is established, and the numerical method employed is validated by the experimental schlieren images and experimental data in the open literature. A pulsed counterflowing jet scheme is proposed, and it uses a sinusoidal function to control the total and static pressures of the counterflowing jet. The obtained results show that the long penetration mode does not exist in the whole turnaround, even in a relatively small range of the jet total and static pressures, and this is different from the phenomenon obtained under the steady condition in the open literature. At the same time, it is observed that the variation of the physical parameters, such as the Stanton number induced by the pulsed jet, has an obvious periodicity and hysteresis phenomenon.

Simple interphase drag model for numerical two-fluid modeling of two-phase flow systems

International Nuclear Information System (INIS)

Chow, H.; Ransom, V.H.

1984-01-01

The interphase drag model that has been developed for RELAP5/MOD2 is based on a simple formulation having flow regime maps for both horizontal and vertical flows. The model is based on a conventional semi-empirical formulation that includes the product of drag coefficient, interfacial area, and relative dynamic pressure. The interphase drag model is implemented in the RELAP5/MOD2 light water reactor transient analysis code and has been used to simulate a variety of separate effects experiments to assess the model accuracy. The results from three of these simulations, the General Electric Company small vessel blowdown experiment, Dukler and Smith's counter-current flow experiment, and a Westinghouse Electric Company FLECHT-SEASET forced reflood experiment, are presented and discussed

"It Has No Color, It Has No Gender, It's Gender Bending": Gender and Sexuality Fluidity and Subversiveness in Drag Performance.

Science.gov (United States)

Egner, Justine; Maloney, Patricia

2016-07-01

Gender identity is a key question for drag performers. Previous research has shown a lack of consensus about the subversiveness and gender fluidity of drag performers. This article examines the question: How does the relationship between performers and their audience affect the subversive nature and gender representation of drag performers in this study? Furthermore, is this relationship complicated by sexuality? This study uses ethnographic and interview methods, examining experiences of 10 drag performers. Findings indicate mutuality in the relationship between performers and audience. The recursiveness of this relationship provides a constant feedback to the performers in their effort to displace the audience's previously held notions. The performers have fluid understandings of gender and sexuality, often presenting multiple genders in and out of drag. Interactions between performers and their audience indicate their belief in gender fluidity; moreover, the drag performers themselves desire to be subversive and gender and sexually fluid.

Comparison of the characteristics of granular propellant movement in interior ballistics based on the interphase drag model

International Nuclear Information System (INIS)

Jang, Jin Sung; Oh, Seok Hawn; Roh, Tae Seong

2014-01-01

Interior ballistics are completed in tens of milliseconds, as are all gun-firing phenomena. Thus, some data cannot be measured directly through experimentation. Therefore, such complex gun-firing phenomena are traditionally clarified by numerical analysis. In the two phase flow of interior ballistics, interphase drag has a strong effect on propellant particle movement. This drag is a momentum sink in the gas phase and a corresponding source of momentum for the solid phase. Previous studies have calculated the drag force on the propellant particles using Ergun's empirical equation, which was developed for a dense bed and relates the drag to the pressure drop through porous media. However, the particulate bed is fluidized in the course of the cycle of interior ballistics, thus indicating that the flow field is ransient with regions of high Reynolds number beyond the range of experimental data. The Ergun equation is examined through a compensation study and calibrated based on the Reynolds number using the numerical method. Moreover, the influence of different drag models on flow behavior and propellant movement in interior ballistics is analyzed.

Clock transport synchronisation and the dragging of inertial frames

International Nuclear Information System (INIS)

Rosenblum, Arnold

1987-01-01

It is shown that it is possible, by using the lack of synchronisation of clocks by clock transport synchronisation in circular orbits, to test for the dragging of inertial frames in Einstein's theory of general relativity. Possible experiments are discussed. (author)

Determination of the hypersonic-continuum/rarefied-flow drag coefficient of the Viking lander capsule 1 aeroshell from flight data

Science.gov (United States)

Blanchard, R. C.; Walberg, G. D.

1980-01-01

Results of an investigation to determine the full scale drag coefficient in the high speed, low density regime of the Viking lander capsule 1 entry vehicle are presented. The principal flight data used in the study were from onboard pressure, mass spectrometer, and accelerometer instrumentation. The hypersonic continuum flow drag coefficient was unambiguously obtained from pressure and accelerometer data; the free molecule flow drag coefficient was indirectly estimated from accelerometer and mass spectrometer data; the slip flow drag coefficient variation was obtained from an appropriate scaling of existing experimental sphere data. Comparison of the flight derived drag hypersonic continuum flow regime except for Reynolds numbers from 1000 to 100,000, for which an unaccountable difference between flight and ground test data of about 8% existed. The flight derived drag coefficients in the free molecule flow regime were considerably larger than those previously calculated with classical theory. The general character of the previously determined temperature profile was not changed appreciably by the results of this investigation; however, a slightly more symmetrical temperature variation at the highest altitudes was obtained.

Small-scale orographic gravity wave drag in stable boundary layers and its impact on synoptic systems and near surface meteorology

NARCIS (Netherlands)

Tsiringakis, Aristofanis; Steeneveld, G.J.; Holtslag, A.A.M.

2017-01-01

At present atmospheric models for weather and climate use enhanced turbulent drag under stable conditions, because these empirically provide the necessary momentum drag for accurate forecast of synoptic systems. The enhanced mixing (also known as the "long-tail"), introduces drag that can not be

Using wind setdown and storm surge on Lake Erie to calibrate the air-sea drag coefficient.

Science.gov (United States)

Drews, Carl

2013-01-01

The air-sea drag coefficient controls the transfer of momentum from wind to water. In modeling storm surge, this coefficient is a crucial parameter for estimating the surge height. This study uses two strong wind events on Lake Erie to calibrate the drag coefficient using the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) modeling system and the the Regional Ocean Modeling System (ROMS). Simulated waves are generated on the lake with Simulating WAves Nearshore (SWAN). Wind setdown provides the opportunity to eliminate wave setup as a contributing factor, since waves are minimal at the upwind shore. The study finds that model results significantly underestimate wind setdown and storm surge when a typical open-ocean formulation without waves is used for the drag coefficient. The contribution of waves to wind setdown and storm surge is 34.7%. Scattered lake ice also increases the effective drag coefficient by a factor of 1.1.

Drag reduction and thrust generation by tangential surface motion in flow past a cylinder

Science.gov (United States)

Mao, Xuerui; Pearson, Emily

2018-03-01

Sensitivity of drag to tangential surface motion is calculated in flow past a circular cylinder in both two- and three-dimensional conditions at Reynolds number Re ≤ 1000 . The magnitude of the sensitivity maximises in the region slightly upstream of the separation points where the contour lines of spanwise vorticity are normal to the cylinder surface. A control to reduce drag can be obtained by (negatively) scaling the sensitivity. The high correlation of sensitivities of controlled and uncontrolled flow indicates that the scaled sensitivity is a good approximation of the nonlinear optimal control. It is validated through direct numerical simulations that the linear range of the steady control is much higher than the unsteady control, which synchronises the vortex shedding and induces lock-in effects. The steady control injects angular momentum into the separating boundary layer, stabilises the flow and increases the base pressure significantly. At Re=100 , when the maximum tangential motion reaches 50% of the free-stream velocity, the vortex shedding, boundary-layer separation and recirculation bubbles are eliminated and 32% of the drag is reduced. When the maximum tangential motion reaches 2.5 times of the free-stream velocity, thrust is generated and the power savings ratio, defined as the ratio of the reduced drag power to the control input power, reaches 19.6. The mechanism of drag reduction is attributed to the change of the radial gradient of spanwise vorticity (partial r \\hat{ζ } ) and the subsequent accelerated pressure recovery from the uncontrolled separation points to the rear stagnation point.

Pengaruh Penempatan Penghalang Berbentuk Silinder Pada Posisi Vertikal Dengan Variasi Jarak Horisontal Di Depan Silinder Utama Terhadap Koefisien Drag

Directory of Open Access Journals (Sweden)

Si Putu Gede Gunawan Tista

2012-11-01

Full Text Available One of the ways to reduce energy consumption on the air plane and the other bluff bodies are by decreasing the drag. Dragis closely related to the flow separation. The earlier separation, then the drag will increase more. Based of the fact the effortto decrease drag is conducted by manipulating the field of fluid flow. Stream manipulation was be done by installingcylindrical obstacle in front of main cylinder. The purpose of this research is to analyze the effect of placement cylindricalobstacle at vertical position in the various horizontal distance in front of main cylinder on drag coefficient . In thisresearch, the experiment was conducted in the wind tunnel, which consisted of blower, pitot pipe, manometer, cylinder pipe,and cylinder rod. The cylindrical obstacle was positioned at vertical (y=14 mm in the various horizontal distanceL/D = 1.41, L/D = 1.56, L/D = 1.72, L/D = 1.88, L/D = 2.03, L/D = 2.19, and L/D = 2.81 by upstream from the maincylinder. Diameter cylinder obstacle was 8 mm.. The Reynolds number based on the main cylinder diameter (D = 42 mmwas Re = 3.42 x 104. The research results showed that the cylinder rod could decrease the drag coefficient of main cylinder.Drag coefficient for cylinder without cylinder rod was 0.167 while the biggest decrease of coefficient of drag with cylindricalobstacle was happened at L/D = 1.72 which was 0,0593. It means that the drag coefficient of main cylinder with cylindricalobstacle was 64.5% lower than the cylinder alone.

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

KAUST Repository

Vakarelski, Ivan Uriev; Chan, Derek Y C; Thoroddsen, Sigurdur T

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.

Computing nonsimple polygons of minimum perimeter

NARCIS (Netherlands)

Fekete, S.P.; Haas, A.; Hemmer, M.; Hoffmann, M.; Kostitsyna, I.; Krupke, D.; Maurer, F.; Mitchell, J.S.B.; Schmidt, A.; Schmidt, C.; Troegel, J.

2018-01-01

We consider the Minimum Perimeter Polygon Problem (MP3): for a given set V of points in the plane, find a polygon P with holes that has vertex set V , such that the total boundary length is smallest possible. The MP3 can be considered a natural geometric generalization of the Traveling Salesman

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 Obtained by the Addition of a Boattail to a Box Shaped Vehicle. M.S. Thesis

Science.gov (United States)

Peterson, R. L.

1981-01-01

Coast down tests were performed on a box shaped ground vehicle used to simulate the aerodynamic drag of high volume transports such as delivery vans, motor homes and trucks. The results of these tests define the reduction in aerodynamic drag that can be obtained by the addition of either a boattail or a truncated boattail to an otherwise blunt based vehicle. Test velocities ranged up to 96.6 km/h (60 mph) with Reynolds numbers to 1.3 x 10 the 7th power. The full boattail provided an average 32 percent reduction in drag at highway speeds whereas the truncated boattail provided an average 31 percent reduction in drag as compared to the configuration having the blunt base. These results are compared with one tenth scale wind tunnel model data.

Numerical Characterisation of Active Drag and Lift Control for a Circular Cylinder in Cross-Flow

Directory of Open Access Journals (Sweden)

Philip McDonald

2017-11-01

Full Text Available Synthetic jet actuators have shown promise to control drag and lift for a bluff body in cross-flow. Using unsteady RANS CFD modelling, a significant modification of the drag coefficient for a circular cylinder in cross-flow at R e = 3900 is achieved by varying the actuation frequency. The variation in actuation frequency corresponds to a range in Stokes number of 2.4 < S t o < 6.4. The trends in drag coefficient modification largely agree with the findings of past publications, achieving a maximum drag reduction at S t o = 4.9 for a fixed jet Reynolds number of the synthetic jet of R e U ¯ o = 12. A decrease in the adverse pressure gradient near the jet orifice correlated with a momentum increase in the viscous sublayer and stronger vortical structures at the rear of the cylinder. In these same conditions, a decrease in turbulence intensity was observed in the far field wake, which is a relevant finding in the context of wind and tidal turbine arrays.

Nano-particle drag prediction at low Reynolds number using a direct Boltzmann-BGK solution approach

Science.gov (United States)

Evans, B.

2018-01-01

This paper outlines a novel approach for solution of the Boltzmann-BGK equation describing molecular gas dynamics applied to the challenging problem of drag prediction of a 2D circular nano-particle at transitional Knudsen number (0.0214) and low Reynolds number (0.25-2.0). The numerical scheme utilises a discontinuous-Galerkin finite element discretisation for the physical space representing the problem particle geometry and a high order discretisation for molecular velocity space describing the molecular distribution function. The paper shows that this method produces drag predictions that are aligned well with the range of drag predictions for this problem generated from the alternative numerical approaches of molecular dynamics codes and a modified continuum scheme. It also demonstrates the sensitivity of flow-field solutions and therefore drag predictions to the wall absorption parameter used to construct the solid wall boundary condition used in the solver algorithm. The results from this work has applications in fields ranging from diagnostics and therapeutics in medicine to the fields of semiconductors and xerographics.

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

Energy Technology Data Exchange (ETDEWEB)

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

2011-06-15

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

Satellite drag effects due to uplifted oxygen neutrals during super magnetic storms

Directory of Open Access Journals (Sweden)

G. S. Lakhina

2017-12-01

Full Text Available During intense magnetic storms, prompt penetration electric fields (PPEFs through E  ×  B forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the dayside super-fountain effect. Ion-neutral drag forces between the upward moving O+ (oxygen ions and oxygen neutrals will elevate the oxygen atoms to higher altitudes. This paper gives a linear calculation indicating how serious the effect may be during an 1859-type (Carrington superstorm. It is concluded that the oxygen neutral densities produced at low-Earth-orbiting (LEO satellite altitudes may be sufficiently high to present severe satellite drag. It is estimated that with a prompt penetrating electric field of ∼ 20 mV m−1 turned on for 20 min, the O atoms and O+ ions are uplifted to 850 km where they produce about 40-times-greater satellite drag per unit mass than normal. Stronger electric fields will presumably lead to greater uplifted mass.

Linear drag law for high-Reynolds-number flow past an oscillating body

Science.gov (United States)

Agre, Natalie; Childress, Stephen; Zhang, Jun; Ristroph, Leif

2016-07-01

An object immersed in a fast flow typically experiences fluid forces that increase with the square of speed. Here we explore how this high-Reynolds-number force-speed relationship is affected by unsteady motions of a body. Experiments on disks that are driven to oscillate while progressing through air reveal two distinct regimes: a conventional quadratic relationship for slow oscillations and an anomalous scaling for fast flapping in which the time-averaged drag increases linearly with flow speed. In the linear regime, flow visualization shows that a pair of counterrotating vortices is shed with each oscillation and a model that views a train of such dipoles as a momentum jet reproduces the linearity. We also show that appropriate scaling variables collapse the experimental data from both regimes and for different oscillatory motions into a single drag-speed relationship. These results could provide insight into the aerodynamic resistance incurred by oscillating wings in flight and they suggest that vibrations can be an effective means to actively control the drag on an object.

Analysis of Satellite Drag Coefficient Based on Wavelet Transform

Science.gov (United States)

Liu, Wei; Wang, Ronglan; Liu, Siqing

Abstract: Drag coefficient sequence was obtained by solving Tiangong1 continuous 55days GPS orbit data with different arc length. The same period solar flux f10.7 and geomagnetic index Ap ap series were high and low frequency multi-wavelet decomposition. Statistical analysis results of the layers sliding correlation between space environmental parameters and decomposition of Cd, showed that the satellite drag coefficient sequence after wavelet decomposition and the corresponding level of f10.7 Ap sequence with good lag correlation. It also verified that the Cd prediction is feasible. Prediction residuals of Cd with different regression models and different sample length were analysed. The results showed that the case was best when setting sample length 20 days and f10.7 regression model were used. It also showed that NRLMSIS-00 model's response in the region of 350km (Tiangong's altitude) and low-middle latitude (Tiangong's inclination) is excessive in ascent stage of geomagnetic activity Ap and is inadequate during fall off segment. Additionally, the low-frequency decomposition components NRLMSIS-00 model's response is appropriate in f10.7 rising segment. High frequency decomposition section, Showed NRLMSIS-00 model's response is small-scale inadequate during f10.7 ascent segment and is reverse in decline of f10.7. Finally, the potential use of a summary and outlook were listed; This method has an important reference value to improve the spacecraft orbit prediction accuracy. Key words: wavelet transform; drag coefficient; lag correlation; Tiangong1;space environment

Effects of Focal vs Total Cryotherapy and Minimum Tumor Temperature on Patient-reported Quality of Life Compared With Active Surveillance in Patients With Prostate Cancer.

Science.gov (United States)

Werneburg, Glenn T; Kongnyuy, Michael; Halpern, Daniel M; Salcedo, Jose M; Chen, Connie; LeSueur, Amanda; Kosinski, Kaitlin E; Schiff, Jeffrey T; Corcoran, Anthony T; Katz, Aaron E

2018-03-01

To investigate the effects of focal (hemiablation) or total cryotherapy and minimum tumor temperature on patient-reported quality of life (QoL) in patients with prostate cancer. An Institutional Review Board-approved database was reviewed for patients who underwent cryotherapy or active surveillance (AS). QoL questionnaire responses were collected and scores were analyzed for differences between focal and total cryotherapy and between very cold (total of 197 patients responded to a total of 547 questionnaires. Focal and total cryotherapy patients had initially lower sexual function scores relative to AS (year 1 mean difference focal: -31.7, P total: -48.1, P total cryotherapy sexual function scores were not statistically significantly different from the AS cohort by postprocedural year 4. Very cold and moderate-cold temperatures led to initially lower sexual function scores relative to AS (year 1 very cold: -38.1, P total cryotherapy and between very cold and moderate-cold temperature groups. Focal cryotherapy and moderate-cold (≥-76°C) temperature were associated with favorable sexual function relative to total cryotherapy and very cold temperature, respectively. No significant differences in urinary function or bowel habits were observed between groups. Copyright © 2017 Elsevier Inc. All rights reserved.

Design and development of drag-disc flow meter for measurement of transient two-phase flow

International Nuclear Information System (INIS)

Sreenivas Rao, G.; Kukreja, V.; Dolas, P.K.; Venkat Raj, V.

1989-01-01

Experiments have been carried out to test the suitability of drag-disc flowmeter for measuring two-phase flow. Calibration tests carried out under single-phase and two-phase flow conditions have confirmed the suitability of the drag-disc flowmeter. The experimental work and the results obtained are presented and discussed in the paper. (author). 6 figs

Method and apparatus for reducing the drag of flows over surfaces

Science.gov (United States)

Keefe, Laurence R. (Inventor)

1998-01-01

An apparatus, and its accompanying method, for reducing the drag of flows over a surface includes arrays of small disks and sensors. The arrays are embedded in the surface and may extend above, or be depressed below, the surface, provided they remain hydraulically smooth either when operating or when inactive. The disks are arranged in arrays of various shapes, and spaced according to the cruising speed of the vehicle on which the arrays are installed. For drag reduction at speeds of the order of 30 meters/second, preferred embodiments include disks that are 0.2 millimeter in diameter and spaced 0.4 millimeter apart. For drag reduction at speeds of the order of 300 meters/second, preferred embodiments include disks that are 0.045 millimeter in diameter and spaced 0.09 millimeter apart. Smaller and larger dimensions for diameter and spacing are also possible. The disks rotate in the plane of the surface, with their rotation axis substantially perpendicular to the surface. The rotating disks produce velocity perturbations parallel to the surface in the overlying boundary layer. The sensors sense the flow at the surface and connect to control circuitry that adjusts the rotation rates and duty cycles of the disks accordingly. Suction and blowing holes can be interspersed among, or made coaxial with, the disks for creating general three-component velocity perturbations in the near-surface region. The surface can be a flat, planar surface or a nonplanar surface, such as a triangular riblet surface. The present apparatus and method have potential applications in the field of aeronautics for improving performance and efficiency of commercial and military aircraft, and in other industries where drag is an obstacle, including gas and oil delivery through long-haul pipelines.

Electro—magnetic control of shear flow over a cylinder for drag reduction and lift enhancement

International Nuclear Information System (INIS)

Zhang Hui; Fan Bao-Chun; Chen Zhi-Hua; Chen Shuai; Li Hong-Zhi

2013-01-01

In this paper, the electro—magnetic control of a cylinder wake in shear flow is investigated numerically. The effects of the shear rate and Lorentz force on the cylinder wake, the distribution of hydrodynamic force, and the drag/lift phase diagram are discussed in detail. It is revealed that Lorentz force can be classified into the field Lorentz force and the wall Lorentz force and they affect the drag and lift forces independently. The drag/lift phase diagram with a shape of ''8'' consists of two closed curves, which correspond to the halves of the shedding cycle dominated by the upper and lower vortices respectively. The free stream shear (K > 0) induces the diagram to move downward and leftward, so that the average lift force directs toward the downside. With the upper Lorentz force, the diagram moves downwards and to the right by the field Lorentz force, thus resulting in the drag increase and the lift reduction, whereas it moves upward and to the left by the wall Lorentz force, leading to the drag reduction and the lift increase. Finally the diagram is dominated by the wall Lorentz force, thus moving upward and leftward. Therefore the upper Lorentz force, which enhances the lift force, can be used to overcome the lift loss due to the free stream shear, which is also obtained in the experiment. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Solar and Drag Sail Propulsion: From Theory to Mission Implementation

Science.gov (United States)

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

Direct numerical simulations of drag reduction in turbulent channel flow over bio-inspired herringbone riblet-texture

NARCIS (Netherlands)

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

Influence of drag force upon the shortest time trajectory of an aircraft

Directory of Open Access Journals (Sweden)

Andrei CRAIFALEANU

2015-06-01

Full Text Available The shortest time trajectory of an aircraft between two given locations is determined using a simple mathematical model. By taking into account the drag force (viscous friction force with the air, a problem of variational calculus is obtained which consists in determining two functions that minimize a functional, subject to a non-holonomic constraint. The trajectory is determined directly, by numerical integration of Euler equations with multipliers. Three types of drag forces were considered: constant, linear and quadratic. The results are verified through comparison to the values obtained from numerical minimization of the involved functional approximate forms.

Accounting for Laminar Run & Trip Drag in Supersonic Cruise Performance Testing

Science.gov (United States)

Goodsell, Aga M.; Kennelly, Robert A.

1999-01-01

An improved laminar run and trip drag correction methodology for supersonic cruise performance testing was derived. This method required more careful analysis of the flow visualization images which revealed delayed transition particularly on the inboard upper surface, even for the largest trip disks. In addition, a new code was developed to estimate the laminar run correction. Once the data were corrected for laminar run, the correct approach to the analysis of the trip drag became evident. Although the data originally appeared confusing, the corrected data are consistent with previous results. Furthermore, the modified approach, which was described in this presentation, extends prior historical work by taking into account the delayed transition caused by the blunt leading edges.

Electron drag by solitons in superlattices in an external magnetic field

International Nuclear Information System (INIS)

Vyazovskii, M.V.; Syrodoev, G.A.

1996-01-01

The soliton-electric effect accompanying the propagation of an electromagnetic soliton along an axis of a superlattice in an external magnetic field directed along the magnetic field of the soliton is studied. It is assumed that the duration γ-1 of the soliton pulse is much shorter than the free flight time of an electron. It is shown that in the absence of a constant magnetic field the drag current varies as sin(αsech2γt) (α is a constant determined by the parameters of the superlattice). In the presence of a constant magnetic field of intensity H0>>Hs, where Hs is the amplitude of the soliton field, the drag current oscillates

Dusty plasmas in a constant electric field: Role of the electron drag force

International Nuclear Information System (INIS)

Khrapak, S.A.; Morfill, G.E.

2004-01-01

We investigate the forces experienced by a microparticle immersed in a weakly ionized plasma with constant electric field. These are electric force and the forces associated with the momentum transfer from electrons and ions drifting in the field (electron and ion drag forces). It is shown that the effect of the electron drag, which is often neglected, can be substantial in a certain parameter range. Numerical calculation of the forces for a reasonable set of plasma parameters is performed to illustrate the importance of this effect

Do spinors give rise to a frame-dragging effect?

International Nuclear Information System (INIS)

Randono, Andrew

2010-01-01

We investigate the effect of the intrinsic spin of a fundamental spinor field on the surrounding spacetime geometry. We show that despite the lack of a rotating stress-energy source (and despite claims to the contrary) the intrinsic spin of a spin-half fermion gives rise to a frame-dragging effect analogous to that of orbital angular momentum, even in Einstein-Hilbert gravity where torsion is constrained to be zero. This resolves a paradox regarding the counter-force needed to restore Newton's third law in the well-known spin-orbit interaction. In addition, the frame-dragging effect gives rise to a long-range gravitationally mediated spin-spin dipole interaction coupling the internal spins of two sources. We argue that despite the weakness of the interaction, the spin-spin interaction will dominate over the ordinary inverse square Newtonian interaction in any process of sufficiently high energy for quantum field theoretical effects to be non-negligible.

Drag reduction by natural polymeric additives in PMDS microchannel: Effect of types of additives

OpenAIRE

Ling Fiona W.M.; Abdulbari Hayder A.

2017-01-01

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 ...

Bioinspired Surface for Low Drag, Self-Cleaning, and Antifouling: Shark Skin, Butterfly and Rice Leaf Effects

Science.gov (United States)

Bixler, Gregroy D.

In this thesis, first presented is an overview of inorganic-fouling and biofouling which is generally undesirable for many medical, marine, and industrial applications. A survey of nature's flora and fauna are studied in order to discover new antifouling methods that could be mimicked for engineering applications. New antifouling methods will presumably incorporate a combination of physical and chemical controls. Presented are mechanisms and experimental results focusing on laminar and turbulent drag reducing shark skin inspired riblet surfaces. This includes new laser etched and riblet film samples for closed channel drag using water, oil, and air as well as in wind tunnel. Also presented are mechanisms and experimental results focusing on the newly discovered rice and butterfly wing effect surfaces. Morphology, drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of sample geometrical dimensions, wettability, viscosity, and velocity. Hierarchical liquid repellent coatings combining nano- and micro-sized features and particles are utilized to recreate or combine various effects. Such surfaces have been fabricated with photolithography, soft lithography, hot embossing, and coating techniques. Discussion is provided along with new conceptual models describing the role of surface structures related to low drag, self-cleaning, and antifouling properties. Modeling provides design guidance when developing novel low drag and self-cleaning surfaces for medical, marine, and industrial applications.

Future Drag Measurements from Venus Express

Science.gov (United States)

Keating, Gerald; Mueller-Wodarg, Ingo; Forbes, Jeffrey M.; Yelle, Roger; Bruinsma, Sean; Withers, Paul; Lopez-Valverde, Miguel Angel; Theriot, Res. Assoc. Michael; Bougher, Stephen

Beginning in July 2008 during the Venus Express Extended Mission, the European Space Agency will dramatically drop orbital periapsis from near 250km to near 180km above the Venus North Polar Region. This will allow orbital decay measurements of atmospheric densities to be made near the Venus North Pole by the VExADE (Venus Express Atmospheric Drag Experiment) whose team leader is Ingo Mueller-Wodarg. VExADE consists of two parts VExADE-ODA (Orbital Drag Analysis from radio tracking data) and VExADE-ACC (Accelerometer in situ atmospheric density measurements). Previous orbital decay measurements of the Venus thermosphere were obtained by Pioneer Venus from the 1970's into the 1990's and from Magellan in the 1990's. The major difference is that the Venus Express will provide measurements in the North Polar Region on the day and night sides, while the earlier measurements were obtained primarily near the equator. The periapsis will drift upwards in altitude similar to the earlier spacecraft and then be commanded down to its lower original values. This cycle in altitude will allow estimates of vertical structure and thus thermospheric temperatures in addition to atmospheric densities. The periapsis may eventually be lowered even further so that accelerometers can more accurately obtain density measurements of the polar atmosphere as a function of altitude, latitude, longitude, local solar time, pressure, Ls, solar activity, and solar wind on each pass. Bias in accelerometer measurements will be determined and corrected for by accelerometer measurements obtained above the discernable atmosphere on each pass. The second experiment, VExADE-ACC, is similar to the accelerometer experiments aboard Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter that carried similar accelerometers in orbit around Mars. The risk involved in the orbital decay and accelerometer measurements is minimal. We have not lost any spacecraft orbiting Venus or Mars due to unexpected

Experimental investigation of drag reduction by forward facing high ...

Indian Academy of Sciences (India)

Substantial aerodynamic drag, while flying at hypersonic Mach number, due to the presence of strong ... atmospheric flight of hypersonic vehicles, large-angle blunt-cone configurations are preferred at the cost of .... This paper is dedicated to Dr P R Viswanath for his contributions to experimental research in aerodynamics.

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures.

Science.gov (United States)

Gamucci, A; Spirito, D; Carrega, M; Karmakar, B; Lombardo, A; Bruna, M; Pfeiffer, L N; West, K W; Ferrari, A C; Polini, M; Pellegrini, V

2014-12-19

Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

On the determination of the neutral drag coefficient in the convective boundary layer

DEFF Research Database (Denmark)

Grachev, A.A.; Fairall, C.W.; Larsen, Søren Ejling

1998-01-01

Based on the idea that free convection can be considered as a particular case of forced convection, where the gusts driven by the large-scale eddies are scaled with the Deardorff convective velocity scale, a new formulation for the neutral drag coefficient, C-Dn, in the convective boundary layer...... for mean wind speed less than about 2 m s(-1). The new approach also clarifies several contradictory results from earlier works. Some aspects related to an alternate definition of the neutral drag coefficient and the wind speed and the stress averaging procedure are considered....

Trade-off between drag reduction and light interception of macrophytes: comparing five aquatic plants with contrasting morphology

NARCIS (Netherlands)

Bal, K.D.; Bouma, T.J.; Buis, K.; Struyf, E.; Jonas, S.; Backx, H.; Meire, P.

2011-01-01

1. Macrophytes in running waters experience an often dynamic and harsh environment. To avoid breakage, plants have to reduce the experienced drag force. However, by reducing leaf area, photosynthetic production is less. Aquatic plants therefore have to find a balance between reducing drag and

An Experimental Investigation of the Effect of a Canard Control on the Lift, Drag, and Pitching Moment of an Aspect-Ratio 2.0 Triangular Wing Incorporating a Form of Conical Camber

Science.gov (United States)

Menees, Gene P.; Boyd, John W.

1959-01-01

The results of an experimental investigation to determine the effect of a canard control on the lift, drag, and pitching-moment characteristics of an aspect-ratio-2.0 triangular wing incorporating a form of conical camber are presented. The canard had a triangular plan form of aspect ratio 2.0 and was mounted in the extended chord plane of the wing. The ratio of the area of the exposed canard panels to the total wing area was 6.9 percent, and the ratio of the total areas was 12.9 percent. Data were obtained at Mach numbers from 0.70 to 2.22 through an angle-of-attack range from -6 deg to +18 deg with the canard on, and with the canard off. To provide a basis for comparison, the canard was also tested with a symmetrical wing having the same plan form, aspect ratio, and thickness distribution as the cambered wing. The results of the investigation showed that at the high subsonic speeds the gain in maximum lift-drag ratio achieved by camber was considerably reduced by the addition of a canard. At the supersonic speeds, the addition of the canard did not change the effect of camber on the maximum lift-drag ratios.

Improved theoretical approximation for the ion drag force in collisionless plasma with strong ion-grain coupling

International Nuclear Information System (INIS)

Khrapak, S. A.; Nosenko, V.; Morfill, G. E.; Merlino, R.

2009-01-01

We point out a deficiency in our previous analytic calculation of the ion drag force for conditions of the experiment by Nosenko et al. [Phys. Plasmas 14, 103702 (2007)]. An inaccurate approximation is corrected and the ion drag force is recalculated. The improved model yields better overall agreement with the experimental results as compared to the original calculation.

Electric Motorboat Drag Racing: A Hands-On Physics Project that Motivates Students from Start to Finish

Science.gov (United States)

Barry, Reno

2008-01-01

Electric Motorboat Drag Racing is a culminating high school physics project designed to apply and bring to life many content standards for physics. Students need to be given several weeks at home to design and build their model-sized electric motorboats for the 5-meter drag racing competition down rain gutters. In the process, they are discussing…

Improved Orbit Determination and Forecasts with an Assimilative Tool for Atmospheric Density and Satellite Drag Specification

Science.gov (United States)

Crowley, G.; Pilinski, M.; Sutton, E. K.; Codrescu, M.; Fuller-Rowell, T. J.; Matsuo, T.; Fedrizzi, M.; Solomon, S. C.; Qian, L.; Thayer, J. P.

2016-12-01

Much as aircraft are affected by the prevailing winds and weather conditions in which they fly, satellites are affected by the variability in density and motion of the near earth space environment. Drastic changes in the neutral density of the thermosphere, caused by geomagnetic storms or other phenomena, result in perturbations of LEO satellite motions through drag on the satellite surfaces. This can lead to difficulties in locating important satellites, temporarily losing track of satellites, and errors when predicting collisions in space. We describe ongoing work to build a comprehensive nowcast and forecast system for specifying the neutral atmospheric state related to orbital drag conditions. The system outputs include neutral density, winds, temperature, composition, and the satellite drag derived from these parameters. This modeling tool is based on several state-of-the-art coupled models of the thermosphere-ionosphere as well as several empirical models running in real-time and uses assimilative techniques to produce a thermospheric nowcast. This software will also produce 72 hour predictions of the global thermosphere-ionosphere system using the nowcast as the initial condition and using near real-time and predicted space weather data and indices as the inputs. Features of this technique include: • Satellite drag specifications with errors lower than current models • Altitude coverage up to 1000km • Background state representation using both first principles and empirical models • Assimilation of satellite drag and other datatypes • Real time capability • Ability to produce 72-hour forecasts of the atmospheric state In this paper, we will summarize the model design and assimilative architecture, and present preliminary validation results. Validation results will be presented in the context of satellite orbit errors and compared with several leading atmospheric models including the High Accuracy Satellite Drag Model, which is currently used

Phonon Drag in Thin Films, Cases of Bi2Te3 and ZnTe

Science.gov (United States)

Chi, Hang; Uher, Ctirad

2014-03-01

At low temperatures, in (semi-)conductors subjected to a thermal gradient, charge carriers (electrons and holes) are swept (dragged) by out-of-equilibrium phonons due to strong electron-phonon interaction, giving rise to a large contribution to the Seebeck coefficient called the phonon-drag effect. Such phenomenon was surprisingly observed in our recent transport study of highly mismatched alloys as potential thermoelectric materials: a significant phonon-drag thermopower reaching 1.5-2.5 mV/K was recorded for the first time in nitrogen-doped ZnTe epitaxial layers on GaAs (100). In thin films of Bi2Te3, we demonstrate a spectacular influence of substrate phonons on charge carriers. We show that one can control and tune the position and magnitude of the phonon-drag peak over a wide range of temperatures by depositing thin films on substrates with vastly different Debye temperatures. Our experiments also provide a way to study the nature of the phonon spectrum in thin films, which is rarely probed but clearly important for a complete understanding of thin film properties and the interplay of the substrate and films. This work is supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0000957.

Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion

Science.gov (United States)

Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S.; Chen, Gang

2015-01-01

Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect—a coupling phenomenon between electrons and nonequilibrium phonons—in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons. PMID:26627231

Investigation into the Mechanism of Polymer Thread Drag Reduction

Science.gov (United States)

1990-01-01

They conducted experiments in a 3.75 cm diameter pipe, Re = 85,000, where they injected drag reducing solutions of guar gum and polyacrylamide, P-295 a...manufactured by Dow Chemical. Concentrations of 5000 ppm and 466 ppm based on weight were used in the experiments. The dry powder was suspended in 300

Drag reduction behavior of hydrolyzed polyacrylamide/xanthan gum mixed polymer solutions

Institute of Scientific and Technical Information of China (English)

Mehdi Habibpour; Peter E.Clark

2017-01-01

Partially hydrolyzed polyacrylamide (HPAM) as the main component of slickwater fracturing fluid is a shear-sensitive polymer,which suffers from mechanical degradation at turbulent flow rates.Five different concentrations of HPAM as well as mixtures of polyacrylamide/xanthan gum were prepared to investigate the possibility of improving shear stability of HPAM.Drag reduction (DR)measurements were performed in a closed flow loop.For HPAM solutions,the extent of DR increased from 30％ to 67％ with increasing HPAM concentration from 100 to 1000 wppm.All the HPAM solutions suffered from mechanical degradation and loss of DR efficiency over the shearing period.Results indicated that the resistance to shear degradation increased with increasing polymer concentration.DR efficiency of 600 wppm xanthan gum (XG)was 38％,indicating that XG was not as good a drag reducer as HPAM.But with only 6％ DR decline,XG solution exhibited a better shear stability compared to HPAM solutions.Mixed HPAM/XG solutions initially exhibited greater DR (40％ and 55％) compared to XG,but due to shear degradation,DR％ dropped for HPAM/XG solutions.Compared to 200 wppm HPAM solution,addition of XG did not improve the drag reduction efficiency of HPAM/XG mixed solutions though XG slightly improved the resistance against mechanical degradation in HPAM/XG mixed polymer solutions.

Studies of drag on the nanocomposite superhydrophobic surfaces

Energy Technology Data Exchange (ETDEWEB)

Brassard, Jean-Denis [Anti-icing Materials International Laboratory (AMIL), Université du Québec à Chicoutimi, 555 Boulevard de l‘Université, Chicoutimi, Québec, Canada G7H 2B1 (Canada); Centre Universitaire de Recherche sur l’Aluminium (CURAL), Université du Québec à Chicoutimi, 555 Boulevard de l‘Université, Chicoutimi, Québec, Canada G7H 2B1 (Canada); Sarkar, D.K., E-mail: dsarkar@uqac.ca [Centre Universitaire de Recherche sur l’Aluminium (CURAL), Université du Québec à Chicoutimi, 555 Boulevard de l‘Université, Chicoutimi, Québec, Canada G7H 2B1 (Canada); Perron, Jean [Anti-icing Materials International Laboratory (AMIL), Université du Québec à Chicoutimi, 555 Boulevard de l‘Université, Chicoutimi, Québec, Canada G7H 2B1 (Canada)

2015-01-01

Graphical abstract: - Highlights: • The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. • SA-functionalization of ZnO nanoparticles in the thin films was confirmed by XRD and FTIR. • The measured rms roughness of the thin film is found to be 12 ± 1 μm with the adhesion of 5B on glass. • The wetting property shows that the surface of the film is superhydrophobic with the CA of 156 ± 4° and CAH of 4 ± 2°. • The drag reduction on the surface of superhydrophobic glass sphere is 16% lower than as-received glass sphere. - Abstract: The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. The X-ray diffraction (XRD) studies show the formation of zinc stearate on ZnO nanoparticles as the confirmation of SA-functionalization of ZnO nanoparticles in the thin films. Morphological analyses reveal the presence of micro-holes with the presence of irregular nanoparticles. The measured root mean square (rms) roughness of the thin film is found to be 12 ± 1 μm with the adhesion of 5B on both glass and aluminum substrates. The wetting property shows that the surface of the film is superhydrophobic with the contact angle of water of 156 ± 4° having contact angle hysteresis (CAH) of 4 ± 2°. The average terminal velocity in the water of the as-received glass spheres and superhydrophobic spheres were found to be 0.66 ± 0.01 m/s and 0.72 ± 0.01 m/s respectively. Consequently, the calculated average coefficients of the surface drag of the as-received glass sphere and superhydrophobic glass sphere were 2.30 ± 0.01 and 1.93 ± 0.03, respectively. Hence, the drag reduction on the surface of superhydrophobic glass sphere is found to be approximately 16% lower than as-received glass sphere.

Studies of drag on the nanocomposite superhydrophobic surfaces

International Nuclear Information System (INIS)

Brassard, Jean-Denis; Sarkar, D.K.; Perron, Jean

2015-01-01

Graphical abstract: - Highlights: • The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. • SA-functionalization of ZnO nanoparticles in the thin films was confirmed by XRD and FTIR. • The measured rms roughness of the thin film is found to be 12 ± 1 μm with the adhesion of 5B on glass. • The wetting property shows that the surface of the film is superhydrophobic with the CA of 156 ± 4° and CAH of 4 ± 2°. • The drag reduction on the surface of superhydrophobic glass sphere is 16% lower than as-received glass sphere. - Abstract: The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. The X-ray diffraction (XRD) studies show the formation of zinc stearate on ZnO nanoparticles as the confirmation of SA-functionalization of ZnO nanoparticles in the thin films. Morphological analyses reveal the presence of micro-holes with the presence of irregular nanoparticles. The measured root mean square (rms) roughness of the thin film is found to be 12 ± 1 μm with the adhesion of 5B on both glass and aluminum substrates. The wetting property shows that the surface of the film is superhydrophobic with the contact angle of water of 156 ± 4° having contact angle hysteresis (CAH) of 4 ± 2°. The average terminal velocity in the water of the as-received glass spheres and superhydrophobic spheres were found to be 0.66 ± 0.01 m/s and 0.72 ± 0.01 m/s respectively. Consequently, the calculated average coefficients of the surface drag of the as-received glass sphere and superhydrophobic glass sphere were 2.30 ± 0.01 and 1.93 ± 0.03, respectively. Hence, the drag reduction on the surface of superhydrophobic glass sphere is found to be approximately 16% lower than as-received glass sphere

Resistive Heating and Ion Drag in Saturn's Thermosphere

Science.gov (United States)

Vriesema, Jess William; Koskinen, Tommi; Yelle, Roger V.

2017-10-01

One of the most puzzling observations of the jovian planets is that the thermospheres of Jupiter, Saturn, Uranus and Neptune are all several times hotter than solar heating can account for (Strobel and Smith 1973; Yelle and Miller 2004; Muller-Wodarg et al. 2006). On Saturn, resistive heating appears sufficient to explain these temperatures in auroral regions, but the particular mechanism(s) responsible for heating the lower latitudes remains unclear. The most commonly proposed heating mechanisms are breaking gravity waves and auroral heating at the poles followed by redistribution of energy to mid-and low latitudes. Both of these energy sources are potentially important but also come with significant problems. Wave heating would have to be continuous and global to produce consistently elevated temperatures and the strong Coriolis forces coupled with polar ion drag appear to hinder redistribution of auroral energy (see Strobel et al. 2016 for review). Here we explore an alternative: wind-driven electrodynamics that can alter circulation and produce substantial heating outside of the auroral region. Smith (2013) showed this in-situ mechanism to be potentially significant in Jupiter’s thermosphere. We present new results from an axisymmetric, steady-state model that calculates resistive (Joule) heating rates through rigorous solutions of the electrodynamic equations for the coupled neutral atmosphere and ionosphere of Saturn. At present, we assume a dipole magnetic field and neglect any contributions from the magnetosphere. We use ion mixing ratios from the model of Kim et al. (2014) and the observed temperature-pressure profile from Koskinen et al. (2015) to calculate the generalized conductivity tensor as described by Koskinen et al. (2014). We calculate the current density under the assumption that it has no divergence and use it to calculate the resistive heating rates and ion drag. Our results suggest that resistive heating and ion drag at low latitudes likely

Plasmon enhancement of Coulomb drag in double-quantum-well systems

DEFF Research Database (Denmark)

Flensberg, Karsten; Hu, Ben Yu-Kuang

1995-01-01

We derive an expression for the drag rate (i.e., interlayer momentum transfer rate) for carriers in two coupled two-dimensional gases to lowest nonvanishing order in the screened interlayer electron-electron interaction, valid for arbitrary intralayer scattering mechanisms, using the Boltzmann tr...

Effect of truncated cone roughness element density on hydrodynamic drag

Science.gov (United States)

Womack, Kristofer; Schultz, Michael; Meneveau, Charles

2017-11-01

An experimental study was conducted on rough-wall, turbulent boundary layer flow with roughness elements whose idealized shape model barnacles that cause hydrodynamic drag in many applications. Varying planform densities of truncated cone roughness elements were investigated. Element densities studied ranged from 10% to 79%. Detailed turbulent boundary layer velocity statistics were recorded with a two-component LDV system on a three-axis traverse. Hydrodynamic roughness length (z0) and skin-friction coefficient (Cf) were determined and compared with the estimates from existing roughness element drag prediction models including Macdonald et al. (1998) and other recent models. The roughness elements used in this work model idealized barnacles, so implications of this data set for ship powering are considered. This research was supported by the Office of Naval Research and by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

MICROSCOPE mission: drag-free and attitude control system expertise activities toward the scientific team

Science.gov (United States)

Delavault, Stéphanie; Prieur, Pascal; Liénart, Thomas; Robert, Alain; Guidotti, Pierre-Yves

2018-04-01

Microscope is a CNES-ESA-ONERA-CNRS-OCA-DLR-ZARM mission dedicated to the test of the Equivalence Principle with an improved accuracy of 10-15. The 300 kg drag-free microsatellite was launched on April 25th 2016 into a 710 km dawndusk sun-synchronous orbit for a 2-year mission. To comply with stringent requirements, the drag-free and attitude control system (DFACS) involves the scientific accelerometer as main sensor and a set of 8 cold gas proportional thrusters. Once in mission mode, within the CNES drag-free expertise center (CECT) the DFACS team provides several services to the system and to the scientific mission center: cold gas monitoring and management, `Attitude' ancillary data, DFACS expertise ancillary data. For this purpose, expertise tools have been implemented in the CECT, using the flexibility and efficiency of Matlab™ utilities. This paper presents the role of the CECT within the mission and details the expertise activities of the DFACS team illustrated with some typical in flight results.

CFD Study of Drag and Lift of Sepak Takraw Ball at Different Face Orientations

Directory of Open Access Journals (Sweden)

Abdul Syakir Abdul Mubin

2015-01-01

Full Text Available There have been a significant number of researches on computational fluid dynamic (CFD analysis of balls used in sports such as golf balls, tennis balls, and soccer balls. Sepak takraw is a high speed court game predominantly played in Southeast Asia using mainly the legs and head. The sepak takraw ball is unique because it is not enclosed and made of woven plastic. Hence a study of its aerodynamicswould give insight into its behaviour under different conditions of play. In this study the dynamics of the fluid around a static sepak takraw ball was investigated at different wind speeds for three different orientations using CFD. It was found that although the drag did not differ very much, increasing the wind velocity causes an increase in drag. The lift coefficientvaries as the velocity increases and does not show a regular pattern. The drag and lift coefficients are influenced by the orientation of the sepak takraw ball.

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

Science.gov (United States)

Akbıyık, Hürrem; Erkan Akansu, Yahya; Yavuz, Hakan; Ertuğrul Bay, Ahmet

2016-03-01

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

Comments on the 'minimum flux corona' concept

International Nuclear Information System (INIS)

Antiochos, S.K.; Underwood, J.H.

1978-01-01

Hearn's (1975) models of the energy balance and mass loss of stellar coronae, based on a 'minimum flux corona' concept, are critically examined. First, it is shown that the neglect of the relevant length scales for coronal temperature variation leads to an inconsistent computation of the total energy flux F. The stability arguments upon which the minimum flux concept is based are shown to be fallacious. Errors in the computation of the stellar wind contribution to the energy budget are identified. Finally we criticize Hearn's (1977) suggestion that the model, with a value of the thermal conductivity modified by the magnetic field, can explain the difference between solar coronal holes and quiet coronal regions. (orig.) 891 WL [de

Effects of spinal cord injury-induced changes in muscle activation on foot drag in a computational rat ankle model.

Science.gov (United States)

Hillen, Brian K; Jindrich, Devin L; Abbas, James J; Yamaguchi, Gary T; Jung, Ranu

2015-04-01

Spinal cord injury (SCI) can lead to changes in muscle activation patterns and atrophy of affected muscles. Moderate levels of SCI are typically associated with foot drag during the swing phase of locomotion. Foot drag is often used to assess locomotor recovery, but the causes remain unclear. We hypothesized that foot drag results from inappropriate muscle coordination preventing flexion at the stance-to-swing transition. To test this hypothesis and to assess the relative contributions of neural and muscular changes on foot drag, we developed a two-dimensional, one degree of freedom ankle musculoskeletal model with gastrocnemius and tibialis anterior muscles. Anatomical data collected from sham-injured and incomplete SCI (iSCI) female Long-Evans rats as well as physiological data from the literature were used to implement an open-loop muscle dynamics model. Muscle insertion point motion was calculated with imposed ankle trajectories from kinematic analysis of treadmill walking in sham-injured and iSCI animals. Relative gastrocnemius deactivation and tibialis anterior activation onset times were varied within physiologically relevant ranges based on simplified locomotor electromyogram profiles. No-atrophy and moderate muscle atrophy as well as normal and injured muscle activation profiles were also simulated. Positive moments coinciding with the transition from stance to swing phase were defined as foot swing and negative moments as foot drag. Whereas decreases in activation delay caused by delayed gastrocnemius deactivation promote foot drag, all other changes associated with iSCI facilitate foot swing. Our results suggest that even small changes in the ability to precisely deactivate the gastrocnemius could result in foot drag after iSCI. Copyright © 2015 the American Physiological Society.

UO2 Grain Growth: Developing Phase Field Models for Pore Dragging, Solute Dragging and Anisotropic Grain Boundary Energies

International Nuclear Information System (INIS)

Ahmed, K.; Tonks, M.; Zhang, Y.; Biner, B.

2016-01-01

A detailed phase field model for the effect of pore drag on grain growth kinetics was implemented in MARMOT. The model takes into consideration both the curvature-driven grain boundary motion and pore migration by surface diffusion. As such, the model accounts for the interaction between pore and grain boundary kinetics, which tends to retard the grain growth process. Our 2D and 3D simulations demonstrate that the model capture all possible pore-grain boundary interactions proposed in theoretical models. For high enough surface mobility, the pores move along with the migrating boundary as a quasi-rigid-body, albeit hindering its migration rate compared to the pore-free case. For less mobile pores, the migrating boundary can separate from the pores. For the pore-controlled grain growth kinetics, the model predicts a strong dependence of the growth rate on the number of pores, pore size, and surface diffusivity in agreement with theroretical models. An evolution equation for the grain size that includes these parameters was derived and showed to agree well with numerical solution. It shows a smooth transition from boundary-controlled kinetics to pore-controlled kinetics as the surface diffusivity decreases or the number of pores or their size increases. This equation can be utilized in BISON to give accurate estimate for the grain size evolution. This will be accomplished in the near future. The effect of solute drag and anisotropy of grain boundary on grain growth will be investigated in future studies.

Microwave-Induced Magneto-Oscillations and Signatures of Zero-Resistance States in Phonon-Drag Voltage in Two-Dimensional Electron Systems.

Science.gov (United States)

Levin, A D; Momtaz, Z S; Gusev, G M; Raichev, O E; Bakarov, A K

2015-11-13

We observe the phonon-drag voltage oscillations correlating with the resistance oscillations under microwave irradiation in a two-dimensional electron gas in perpendicular magnetic field. This phenomenon is explained by the influence of dissipative resistivity modified by microwaves on the phonon-drag voltage perpendicular to the phonon flux. When the lowest-order resistance minima evolve into zero-resistance states, the phonon-drag voltage demonstrates sharp features suggesting that current domains associated with these states can exist in the absence of external dc driving.

Soil transference patterns on bras: Image processing and laboratory dragging experiments.

Science.gov (United States)

Murray, Kathleen R; Fitzpatrick, Robert W; Bottrill, Ralph S; Berry, Ron; Kobus, Hilton

2016-01-01

In a recent Australian homicide, trace soil on the victim's clothing suggested she was initially attacked in her front yard and not the park where her body was buried. However the important issue that emerged during the trial was how soil was transferred to her clothing. This became the catalyst for designing a range of soil transference experiments (STEs) to study, recognise and classify soil patterns transferred onto fabric when a body is dragged across a soil surface. Soil deposits of interest in this murder were on the victim's bra and this paper reports the results of anthropogenic soil transfer to bra-cups and straps caused by dragging. Transfer patterns were recorded by digital photography and photomicroscopy. Eight soil transfer patterns on fabric, specific to dragging as the transfer method, appeared consistently throughout the STEs. The distinctive soil patterns were largely dependent on a wide range of soil features that were measured and identified for each soil tested using X-ray Diffraction and Non-Dispersive Infra-Red analysis. Digital photographs of soil transfer patterns on fabric were analysed using image processing software to provide a soil object-oriented classification of all soil objects with a diameter of 2 pixels and above transferred. Although soil transfer patterns were easily identifiable by naked-eye alone, image processing software provided objective numerical data to support this traditional (but subjective) interpretation. Image software soil colour analysis assigned a range of Munsell colours to identify and compare trace soil on fabric to other trace soil evidence from the same location; without requiring a spectrophotometer. Trace soil from the same location was identified by linking soils with similar dominant and sub-dominant Munsell colour peaks. Image processing numerical data on the quantity of soil transferred to fabric, enabled a relationship to be discovered between soil type, clay mineralogy (smectite), particle size and

Incorporating modelled subglacial hydrology into inversions for basal drag

Directory of Open Access Journals (Sweden)

C. P. Koziol

2017-12-01

Full Text Available A key challenge in modelling coupled ice-flow–subglacial hydrology is initializing the state and parameters of the system. We address this problem by presenting a workflow for initializing these values at the start of a summer melt season. The workflow depends on running a subglacial hydrology model for the winter season, when the system is not forced by meltwater inputs, and ice velocities can be assumed constant. Key parameters of the winter run of the subglacial hydrology model are determined from an initial inversion for basal drag using a linear sliding law. The state of the subglacial hydrology model at the end of winter is incorporated into an inversion of basal drag using a non-linear sliding law which is a function of water pressure. We demonstrate this procedure in the Russell Glacier area and compare the output of the linear sliding law with two non-linear sliding laws. Additionally, we compare the modelled winter hydrological state to radar observations and find that it is in line with summer rather than winter observations.

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.

Comparison of gimbal approaches to decrease drag force and radar cross sectional area in missile application

Science.gov (United States)

Sakarya, Doǧan Uǧur

2017-05-01

Drag force effect is an important aspect of range performance in missile applications especially for long flight time. However, old fashioned gimbal approaches force to increase missile diameter. This increase has negative aspect of rising in both drag force and radar cross sectional area. A new gimbal approach was proposed recently. It uses a beam steering optical arrangement. Therefore, it needs less volume envelope for same field of regard and same optomechanical assembly than the old fashioned gimbal approaches. In addition to longer range performance achieved with same fuel in the new gimbal approach, this method provides smaller cross sectional area which can be more invisible in enemies' radar. In this paper, the two gimbal approaches - the old fashioned one and the new one- are compared in order to decrease drag force and radar cross sectional area in missile application. In this study; missile parameters are assumed to generate gimbal and optical design parameters. Optical design is performed according to these missile criteria. Two gimbal configurations are designed with respect to modeled missile parameters. Also analyzes are performed to show decreased drag force and radar cross sectional area in the new approach for comparison.

Drag Coefficient of Water Droplets Approaching the Leading Edge of an Airfoil

Science.gov (United States)

Vargas, Mario; Sor, Suthyvann; Magarino, Adelaida Garcia

2013-01-01

This work presents results of an experimental study on droplet deformation and breakup near the leading edge of an airfoil. The experiment was conducted in the rotating rig test cell at the Instituto Nacional de Tecnica Aeroespacial (INTA) in Madrid, Spain. An airfoil model was placed at the end of the rotating arm and a monosize droplet generator produced droplets that fell from above, perpendicular to the path of the airfoil. The interaction between the droplets and the airfoil was captured with high speed imaging and allowed observation of droplet deformation and breakup as the droplet approached the airfoil near the stagnation line. Image processing software was used to measure the position of the droplet centroid, equivalent diameter, perimeter, area, and the major and minor axes of an ellipse superimposed over the deforming droplet. The horizontal and vertical displacement of each droplet against time was also measured, and the velocity, acceleration, Weber number, Bond number, Reynolds number, and the drag coefficients were calculated along the path of the droplet to the beginning of breakup. Results are presented and discussed for drag coefficients of droplets with diameters in the range of 300 to 1800 micrometers, and airfoil velocities of 50, 70 and 90 meters/second. The effect of droplet oscillation on the drag coefficient is discussed.

Prospects for Measuring Planetary Spin and Frame-Dragging in Spacecraft Timing Signals

Energy Technology Data Exchange (ETDEWEB)

Schärer, Andreas; Bondarescu, Ruxandra [Department of Physics, University of Zurich, Zurich (Switzerland); Saha, Prasenjit [Department of Physics, University of Zurich, Zurich (Switzerland); Institute for Computational Science, University of Zurich, Zurich (Switzerland); Angélil, Raymond [Institute for Computational Science, University of Zurich, Zurich (Switzerland); Helled, Ravit [Institute for Computational Science, University of Zurich, Zurich (Switzerland); Department of Geosciences, Tel Aviv University, Tel Aviv (Israel); Jetzer, Philippe, E-mail: andreas.schaerer@physik.uzh.ch [Department of Physics, University of Zurich, Zurich (Switzerland)

2017-09-05

Satellite tracking involves sending electromagnetic signals to Earth. Both the orbit of the spacecraft and the electromagnetic signals themselves are affected by the curvature of spacetime. The arrival time of the pulses is compared to the ticks of local clocks to reconstruct the orbital path of the satellite to high accuracy, and implicitly measure general relativistic effects. In particular, Schwarzschild space curvature (static) and frame-dragging (stationary) due to the planet's spin affect the satellite's orbit. The dominant relativistic effect on the path of the signal photons is Shapiro delays due to static space curvature. We compute these effects for some current and proposed space missions, using a Hamiltonian formulation in four dimensions. For highly eccentric orbits, such as in the Juno mission and in the Cassini Grand Finale, the relativistic effects have a kick-like nature, which could be advantageous for detecting them if their signatures are properly modeled as functions of time. Frame-dragging appears, in principle, measurable by Juno and Cassini, though not by Galileo 5 and 6. Practical measurement would require disentangling frame-dragging from the Newtonian “foreground” such as the gravitational quadrupole which has an impact on both the spacecraft's orbit and the signal propagation. The foreground problem remains to be solved.

Force and flow at the onset of drag in plowed granular media.

Science.gov (United States)

Gravish, Nick; Umbanhowar, Paul B; Goldman, Daniel I

2014-04-01

We study the transient drag force FD on a localized intruder in a granular medium composed of spherical glass particles. A flat plate is translated horizontally from rest through the granular medium to observe how FD varies as a function of the medium's initial volume fraction, ϕ. The force response of the granular material differs above and below the granular critical state, ϕc, the volume fraction which corresponds to the onset of grain dilatancy. For ϕϕc, FD rapidly rises to a maximum and then decreases over further displacement. The maximum force for ϕ>ϕc increases with increasing drag velocity. In quasi-two-dimensional drag experiments, we use granular particle image velocimetry (PIV) to measure time resolved strain fields associated with the horizontal motion of a plate started from rest. PIV experiments show that the maxima in FD for ϕ>ϕc are associated with maxima in the spatially averaged shear strain field. For ϕ>ϕc the shear strain occurs in a narrow region in front of the plate, a shear band. For ϕϕc, surface particles move only during the formation of the shear band, coincident with the maxima in FD, after which the particles remain immobile until the sheared region reaches the measurement region.

Design and performance of the drag-disc turbine transducer

International Nuclear Information System (INIS)

Averill, R.H.; Goodrich, L.D.; Ford, R.E.

1979-01-01

Mass flow rates at the Loss-of-Fluid Test (LOFT) facility, EG and G Idaho, Inc., at the Idaho National Engineering Laboratory, are measured with the drag-disc turbine transducer (DTT). Operational description of the DTT and the developmental effort are discussed. Performance data and experiences with this transducer have been evaluated and are presented in this paper

Energy and IAQ Implications of Alternative Minimum Ventilation Rates in California Retail and School Buildings

Energy Technology Data Exchange (ETDEWEB)

Dutton, Spencer M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Fisk, William J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2015-01-01

For a stand-alone retail building, a primary school, and a secondary school in each of the 16 California climate zones, the EnergyPlus building energy simulation model was used to estimate how minimum mechanical ventilation rates (VRs) affect energy use and indoor air concentrations of an indoor-generated contaminant. The modeling indicates large changes in heating energy use, but only moderate changes in total building energy use, as minimum VRs in the retail building are changed. For example, predicted state-wide heating energy consumption in the retail building decreases by more than 50% and total building energy consumption decreases by approximately 10% as the minimum VR decreases from the Title 24 requirement to no mechanical ventilation. The primary and secondary schools have notably higher internal heat gains than in the retail building models, resulting in significantly reduced demand for heating. The school heating energy use was correspondingly less sensitive to changes in the minimum VR. The modeling indicates that minimum VRs influence HVAC energy and total energy use in schools by only a few percent. For both the retail building and the school buildings, minimum VRs substantially affected the predicted annual-average indoor concentrations of an indoor generated contaminant, with larger effects in schools. The shape of the curves relating contaminant concentrations with VRs illustrate the importance of avoiding particularly low VRs.

Equations for calculating interfacial drag and shear from void fraction correlations

International Nuclear Information System (INIS)

Putney, J.M.

1988-12-01

Equations are developed for calculating interfacial drag and shear coefficients for dispersed vapour flows from void fraction correlations. The equations have a sound physical basis and lead to physically correct coefficients in all flow situations. (author)

Droplet squeezing through a narrow constriction: Minimum impulse and critical velocity

Science.gov (United States)

Zhang, Zhifeng; Drapaca, Corina; Chen, Xiaolin; Xu, Jie

2017-07-01

Models of a droplet passing through narrow constrictions have wide applications in science and engineering. In this paper, we report our findings on the minimum impulse (momentum change) of pushing a droplet through a narrow circular constriction. The existence of this minimum impulse is mathematically derived and numerically verified. The minimum impulse happens at a critical velocity when the time-averaged Young-Laplace pressure balances the total minor pressure loss in the constriction. Finally, numerical simulations are conducted to verify these concepts. These results could be relevant to problems of energy optimization and studies of chemical and biomedical systems.

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.

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...... a voltage drop V-2 in another shell by the screened Coulomb interaction between the shells neglecting the intershell tunneling. We provide benchmark results for R-21 = V2/I-1 within the Fermi liquid theory using Boltzmann equations. The band structure gives rise to strongly chirality-dependent suppression...... 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...

development of a new drag coefficient model for oil and gas

African Journals Online (AJOL)

eobe

approximation of experimental data for e. R , from .... dynamic conditions in order to evaluate the drag and ... based on the experimental data for multiphase, water- oil-gas flow see ... Figure 6: Comparison of measured and model prediction.

Assessments of Bubble Dynamics Model and Influential Parameters in Microbubble Drag Reduction

National Research Council Canada - National Science Library

Skudarnov, P. V; Lin, C. X

2006-01-01

.... The effects of mixture density variation, free stream turbulence intensity, free stream velocity, and surface roughness on the microbubble drag reduction were studied using a single phase model based...

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

Directory of Open Access Journals (Sweden)

Liu Chunbao

2016-01-01

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

Experimental Studies on the Physics and Technology of Polymer Drag-Reduction

National Research Council Canada - National Science Library

Hanratty, Thomas

2004-01-01

.... Companion studies were carried out in the polymer laboratory of Anthony J. McHugh so that the performance of drag-reducing polymer solutions can be related to their rheological and rheo-optical properties in simple non-turbulent flows...

Minimum weight protection - Gradient method; Protection de poids minimum - Methode du gradient

Energy Technology Data Exchange (ETDEWEB)

Danon, R.

1958-12-15

After having recalled that, when considering a mobile installation, total weight has a crucial importance, and that, in the case of a nuclear reactor, a non neglectable part of weight is that of protection, this note presents an iterative method which results, for a given protection, to a configuration with a minimum weight. After a description of the problem, the author presents the theoretical formulation of the gradient method as it is applied to the concerned case. This application is then discussed, as well as its validity in terms of convergence and uniqueness. Its actual application is then reported, and possibilities of practical applications are evoked.

Biomimetic structures for fluid drag reduction in laminar and turbulent flows

International Nuclear Information System (INIS)

Jung, Yong Chae; Bhushan, Bharat

2010-01-01

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

Statistical Analysis of CFD Solutions From the Fifth AIAA Drag Prediction Workshop

Science.gov (United States)

Morrison, Joseph H.

2013-01-01

A graphical framework is used for statistical analysis of the results from an extensive N-version test of a collection of Reynolds-averaged Navier-Stokes computational fluid dynamics codes. The solutions were obtained by code developers and users from North America, Europe, Asia, and South America using a common grid sequence and multiple turbulence models for the June 2012 fifth Drag Prediction Workshop sponsored by the AIAA Applied Aerodynamics Technical Committee. The aerodynamic configuration for this workshop was the Common Research Model subsonic transport wing-body previously used for the 4th Drag Prediction Workshop. This work continues the statistical analysis begun in the earlier workshops and compares the results from the grid convergence study of the most recent workshop with previous workshops.

Angry Birds realized: water balloon launcher for teaching projectile motion with drag

International Nuclear Information System (INIS)

Edwards, Boyd F; Sam, David D; Christiansen, Michael A; Booth, William A; Jessup, Leslie O

2014-01-01

A simple, collapsible design for a large water balloon slingshot launcher features a fully adjustable initial velocity vector and a balanced launch platform. The design facilitates quantitative explorations of the dependence of the balloon range and time of flight on the initial speed, launch angle, and projectile mass, in an environment where quadratic air drag is important. Presented are theory and experiments that characterize this drag, and theory and experiments that characterize the nonlinear elastic energy and hysteresis of the latex tubing used in the slingshot. The experiments can be carried out with inexpensive and readily available tools and materials. The launcher provides an engaging way to teach projectile motion and elastic energy to students of a wide variety of ages. (paper)

The Unusual Minimum of Cycle 23: Observations and Interpretation

Science.gov (United States)

Martens, Petrus C.; Nandy, D.; Munoz-Jaramillo, A.

2009-05-01

The current minimum of cycle 23 is unusual in its long duration, the very low level to which Total Solar Irradiance (TSI) has fallen, and the small flux of the open polar fields. The deep minimum of TSI seems to be related to an unprecedented dearth of polar faculae, and hence to the small amount of open flux. Based upon surface flux transport models it has been suggested that the causes of these phenomena may be an unusually vigorous meridional flow, or even a deviation from Joy's law resulting in smaller Joy angles than usual for emerging flux in cycle 23. There is also the possibility of a connection with the recently inferred emergence in polar regions of bipoles that systematically defy Hale's law. Much speculation has been going on as to the consequences of this exceptional minimum: are we entering another global minimum, is this the end of the 80 year period of exceptionally high solar activity, or is this just a statistical hiccup? Dynamo simulations are underway that may help answer this question. As an aside it must be mentioned that the current minimum of TSI puts an upper limit in the TSI input for global climate simulations during the Maunder minimum, and that a possible decrease in future solar activity will result in a very small but not insignificant reduction in the pace of global warming.

Storm surge and wave simulations in the Gulf of Mexico using a consistent drag relation for atmospheric and storm surge models

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

Deconstructing Hub Drag. Part 2. Computational Development and Anaysis

Science.gov (United States)

2013-09-30

leveraged a Vertical Lift Consortium ( VLC )-funded hub drag scaling research effort. To confirm this objective, correlations are performed with the...Technology™ Demonstrator aircraft using an unstructured computational solver. These simpler faired elliptical geome- tries can prove to be challenging ...possible. However, additional funding was obtained from the Vertical Lift Consortium ( VLC ) to perform this study. This analysis is documented in

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

Science.gov (United States)

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.

Meu nome é “Híbrida”: Corpo, gênero e sexualidade na experiência drag queen

Directory of Open Access Journals (Sweden)

Joseylson Fagner Santos

2012-07-01

Full Text Available Homem e mulher, feminino e masculino: o comportamento social dos indivíduos é norteado por dicotomias que encontramos em corpos aprendidos e disciplinados. Nesse sentido, os papéis sociais de gênero vêm a ser fatores de diferenciação sexual, de forma a orientar a inteligibilidade dos corpos, através construções sociais de códigos estéticos, funcionais e comportamentais. A drag queen – representada como um corpo onde os papéis sociais de gênero encontram-se justapostos – apresenta, através da performance, a possibilidade de ressignificar as relações fixas entre gênero, corpo e sexo. Enquanto indivíduo que opera na transformação estética e comportamental de seus papéis de gênero, a drag permite pensar numa desnaturalização dos laços que envolvem esses conceitos. Diferente do travesti e do transexual, a drag queen questiona a fixidez de questões “hetero-normativas” através de um ato performativo, onde o corpo adquire signos específicos do sexo feminino e aplica a um corpo masculino, tornando-se “queer”. A experiência do corpo drag representa uma possibilidade de verificar o momento em que a normatividade da relação entre corpo, sexo e gênero entra em desconstrução, resultando num corpo híbrido. O artigo se propõe à reflexão sobre a formação da dicotomia masculino/feminino e a produção performativa de corpos drag.

New Analysis of Solute Drag in AA5754 by Precise Determination of Point Defect Generation and the Orowan Relation

Science.gov (United States)

Diak, Brad J.; Penlington, Alex; Saimoto, Shig

Serrated deformation in Al-Mg alloys creates problems that affect consumer product acceptability. This effect is usually attributed to the Portevin-LeChâtelier effect. In this study the inverse PLC effect due to solute drag on moving dislocations is examined in AA5754. The drag mechanism is dependent on the diffusivity of the solute which is in-turn dependent on the point defect evolution during deformation. Experimental determination of the parabolic James-Barnett drag profile by strain rate change experiments indicates the peak stress is centered at 1.5×10-9m/s, which requires a mechanical formation energy for vacancies of 0.4eV/at. A new slip-based constitutive relation was used to determine the evolution of vacancy volume fraction with deformation with strain, which is greater than the volume fraction of vacancies predicted by the solute drag profile.

An Examination of Drag Reduction Mechanisms in Marine Animals, with Potential Applications to Uninhabited Aerial Vehicles

Science.gov (United States)

Musick, John A.; Patterson, Mark R.; Dowd, Wesley W.

2002-01-01

Previous engineering research and development has documented the plausibility of applying biomimetic approaches to aerospace engineering. Past cooperation between the Virginia Institute of Marine Science (VIMS) and NASA focused on the drag reduction qualities of the microscale dermal denticles of shark skin. This technology has subsequently been applied to submarines and aircraft. The present study aims to identify and document the three-dimensional geometry of additional macroscale morphologies that potentially confer drag reducing hydrodynamic qualities upon marine animals and which could be applied to enhance the range and endurance of Uninhabited Aerial Vehicles (UAVs). Such morphologies have evolved over eons to maximize organismal energetic efficiency by reducing the energetic input required to maintain cruising speeds in the viscous marine environment. These drag reduction qualities are manifested in several groups of active marine animals commonly encountered by ongoing VIMS research programs: namely sharks, bony fishes such as tunas, and sea turtles. Through spatial data acquired by molding and digital imagery analysis of marine specimens provided by VIMS, NASA aims to construct scale models of these features and to test these potential drag reduction morphologies for application to aircraft design. This report addresses the efforts of VIMS and NASA personnel on this project between January and November 2001.

A novel drag force coefficient model for gas–water two-phase flows under different flow patterns

Energy Technology Data Exchange (ETDEWEB)

Shang, Zhi, E-mail: shangzhi@tsinghua.org.cn

2015-07-15

Graphical abstract: - Highlights: • A novel drag force coefficient model was established. • This model realized to cover different flow patterns for CFD. • Numerical simulations were performed under wide range flow regimes. • Validations were carried out through comparisons to experiments. - Abstract: A novel drag force coefficient model has been developed to study gas–water two-phase flows. In this drag force coefficient model, the terminal velocities were calculated through the revised drift flux model. The revised drift flux is different from the traditional drift flux model because the natural curve movement of the bubble was revised through considering the centrifugal force. Owing to the revisions, the revised drift flux model was to extend to 3D. Therefore it is suitable for CFD applications. In the revised drift flux model, the different flow patterns of the gas–water two-phase flows were able to be considered. This model innovatively realizes the drag force being able to cover different flow patterns of gas–water two-phase flows on bubbly flow, slug flow, churn flow, annular flow and mist flow. Through the comparisons of the numerical simulations to the experiments in vertical upward and downward pipe flows, this model was validated.

Statistical Investigation on Coherent Vortex Structure in Turbulent Drag Reducing Channel Flow with Blown Polymer Solution

International Nuclear Information System (INIS)

Ishitsuka, Shota; Motozawa, Masaaki; Kawaguchi, Yasuo; Iwamoto, Kaoru; Ando, Hirotomo; Senda, Tetsuya

2011-01-01

Coherent vortex structure in turbulent drag-reducing channel flow with blown polymer solution from the wall was investigated. As a statistical analysis, we carried out Galilean decomposition, swirling strength and linear stochastic estimation of the PIV data obtained by the PIV measurement in x – y plane. Reynolds number based on bulk velocity and channel height was set to 40000. As a result, the angle of shear layer that cleared up by using Galilean decomposition becomes small in the drag-reducing flow. Q3 events were observed near the shear layer. In addition, as a result of linear stochastic estimation (LSE) based on swirling strength, we confirmed that the velocity under the vortex core is strong in the water flow. This result shows Q2 (ejection) are dominant in the water flow. However, in the drag-reducing flow with blown polymer solution, the velocity above the vortex core become strong, that is, Q4 (sweep) events are relatively strong around the vortex core. This is the result of Q4 events to come from the channel center region because the polymer solution does not exist in this region. The typical structure like this was observed in the drag -reducing flow with blown polymer solution from the wall.

Low-Boom and Low-Drag Optimization of the Twin Engine Version of Silent Supersonic Business Jet

Science.gov (United States)

Sato, Koma; Kumano, Takayasu; Yonezawa, Masahito; Yamashita, Hiroshi; Jeong, Shinkyu; Obayashi, Shigeru

Multi-Objective Optimization has been applied to a design problem of the twin engine concept for Silent Supersonic Business Jet (SSBJ). This problem aims to find main wing, body, tail wing and engine nacelle configurations, which can minimize both sonic boom and drag in a supersonic cruising flight. The multi-objective genetic algorithm (MOGA) coupled with the Kriging model has been used to globally and effectively search for optimal design candidates in the multi-objective problem. The drag and the sonic boom have been evaluated by the computational fluid dynamics (CFD) simulation and the waveform parameter method. As a result, the present optimization has successfully obtained low-boom and low-drag design candidates, which are better than the baseline design by more than 40% regarding each performance. Moreover, the structure of design space has been visualized by the self-organizing map (SOM).

Binaries traveling through a gaseous medium: dynamical drag forces and internal torques

Energy Technology Data Exchange (ETDEWEB)

Sánchez-Salcedo, F. J. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Ciudad Universitaria, Apt. Postal 70 264, C.P. 04510, Mexico City (Mexico); Chametla, Raul O., E-mail: jsanchez@astro.unam.mx [Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, UP Adolfo López Mateos, Mexico City (Mexico)

2014-10-20

Using time-dependent linear theory, we investigate the morphology of the gravitational wake induced by a binary, whose center of mass moves at velocity V{sub cm} against a uniform background of gas. For simplicity, we assume that the components of the binary are on circular orbits about their common center of mass. The consequences of dynamical friction is twofold. First, gas dynamical friction may drag the center of mass of the binary and cause the binary to migrate. Second, drag forces also induce a braking torque, which causes the orbits of the components of the binary to shrink. We compute the drag forces acting on one component of the binary due to the gravitational interaction with its own wake. We show that the dynamical friction force responsible for decelerating the center of mass of the binary is smaller than it is in the point-mass case because of the loss of gravitational focusing. We show that the braking internal torque depends on the Mach numbers of each binary component about their center of mass, and also on the Mach number of the center of mass of the binary. In general, the internal torque decreases with increasing the velocity of the binary relative to the ambient gas cloud. However, this is not always the case. We also mention the relevance of our results to the period distribution of binaries.

Drag Reduction CFD Simulations and Flow Visualization of Light Vehicle-Trailer Systems

Science.gov (United States)

Sigurdson, Lorenz; Boyer, Henry; Lange, Carlos F.

2016-11-01

Experiments and CFD were performed to study the effect a deflector had on the flow and drag force associated with a 2010 F-150 truck and cargo trailer Light Vehicle-Trailer System (LVTS). Image Correlation Velocimetry (ICV) on smokewire streaklines measured the velocity field on the model mid-plane. CFD estimated the drag reduction as 13% at a Re of 14,900 with a moving ground-plane, and 17% without. Experiments suggested that the low Re does not diminish the full-scale relevance of the drag reduction results. One low Re effect was the presence of a separation bubble on the hood of the tow vehicle whose size reduced with an increase in Re. Three other characteristic flow patterns were identified: separation off the lead vehicle cab, stagnation of the free-stream on the trailer face for the no-deflector case, and subsequent separation at the trailer front corner. Comparisons of the ICV and CFD results with no deflector indicated good agreement in the direction of the velocity vectors, and the smoke streaklines and CFD streamlines also agreed well. However, for the deflector case, the CFD found an entirely different topological solution absent in the experiment. A pair of vertically-oriented mid-plane vortices were wrapped around the front of the trailer. Support from the Canadian Natural Sciences and Engineering Research Council Grant 41747 is gratefully acknowledged.

A Limited Evaluation of Full Scale Control Surface Deflection Drag (Have FUN)

National Research Council Canada - National Science Library

Reinhardt, R. B; Celi, Sean A; Geraghty, Jeffrey T; Stahl, James W; Glover, Victor J; Bowman, Geoffrey G

2007-01-01

The Have FUN (FUll Scale Numbers) Test Management Project was conducted at the request of the USAF TPS as an investigation into the drag caused by control surface deflection during dynamic soaring techniques...

Reducing Aerodynamic Drag on Empty Open Cargo Vehicles

Science.gov (United States)

Ross, James C.; Storms, Bruce L.; Dzoan, Dan

2009-01-01

Some simple structural modifications have been demonstrated to be effective in reducing aerodynamic drag on vehicles that have empty open cargo bays. The basic idea is to break up the airflow in a large open cargo bay by inserting panels to divide the bay into a series of smaller bays. In the case of a coal car, this involves inserting a small number (typically between two and four) of vertical full-depth or partial-depth panels.

Drag of a Supercritical Body of Revolution in Free Flight at Transonic Speeds and Comparison with Wind Tunnel Data

Science.gov (United States)

Usry, J. W.; Wallace, J. W.

1971-01-01

The forebody drag of a supercritical body of revolution was measured in free flight over a Mach number range of 0.85 to 1.05 and a Reynolds number range of 11.5 x 10 to the 6th power to 19.4 x 10 to the 6th power and was compared with wind-tunnel data. The forebody drag coefficient for a Mach number less than 0.96 was 0.111 compared with the wind-tunnel value of 0.103. A gradual increase in the drag occurred in the Langley 8-foot transonic pressure tunnel at a lower Mach number than in the Langley 16-foot transonic tunnel or in the free-flight test. The sharp drag rise occurred near Mach 0.98 in free flight whereas the rise occurred near Mach 0.99 in the Langley 16-foot transonic tunnel. The sharp rise was not as pronounced in the Langley 8-foot transonic pressure tunnel and was probably affected by tunnel-wall-interference effects. The increase occurred more slowly and at a higher Mach number. These results indicate that the drag measurements made in the wind tunnels near Mach 1 were significantly affected by the relative size of the model and the wind tunnel.

Drag resistance measurements for newly applied antifouling coatings and welding seams on ship hull surface

DEFF Research Database (Denmark)

Wang, Xueting; Olsen, S. M.; Andres, E.

Drag resistances of newly applied antifouling coatings and welding seams on ship hull surface have been investigated using a pilot-scale rotary setup. Both conventional biocide-based antifouling (AF) coatings and silicone-based fouling release (FR) coatings have been studied and compared in their......Drag resistances of newly applied antifouling coatings and welding seams on ship hull surface have been investigated using a pilot-scale rotary setup. Both conventional biocide-based antifouling (AF) coatings and silicone-based fouling release (FR) coatings have been studied and compared...

Development of a New Drag Coefficient Model for Oil and Gas ...

African Journals Online (AJOL)

Development of a New Drag Coefficient Model for Oil and Gas Multiphase Fluid Systems. ... PROMOTING ACCESS TO AFRICAN RESEARCH ... suspensions of solid particles are frequently encountered in many industrial processes including oil & gas production. ... EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT

Modeling drag reduction and meniscus stability of superhydrophobic surfaces comprised of random roughness

Science.gov (United States)

Samaha, Mohamed A.; Tafreshi, Hooman Vahedi; Gad-el-Hak, Mohamed

2011-01-01

Previous studies dedicated to modeling drag reduction and stability of the air-water interface on superhydrophobic surfaces were conducted for microfabricated coatings produced by placing hydrophobic microposts/microridges arranged on a flat surface in aligned or staggered configurations. In this paper, we model the performance of superhydrophobic surfaces comprised of randomly distributed roughness (e.g., particles or microposts) that resembles natural superhydrophobic surfaces, or those produced via random deposition of hydrophobic particles. Such fabrication method is far less expensive than microfabrication, making the technology more practical for large submerged bodies such as submarines and ships. The present numerical simulations are aimed at improving our understanding of the drag reduction effect and the stability of the air-water interface in terms of the microstructure parameters. For comparison and validation, we have also simulated the flow over superhydrophobic surfaces made up of aligned or staggered microposts for channel flows as well as streamwise or spanwise ridges configurations for pipe flows. The present results are compared with theoretical and experimental studies reported in the literature. In particular, our simulation results are compared with work of Sbragaglia and Prosperetti, and good agreement has been observed for gas fractions up to about 0.9. The numerical simulations indicate that the random distribution of surface roughness has a favorable effect on drag reduction, as long as the gas fraction is kept the same. This effect peaks at about 30% as the gas fraction increases to 0.98. The stability of the meniscus, however, is strongly influenced by the average spacing between the roughness peaks, which needs to be carefully examined before a surface can be recommended for fabrication. It was found that at a given maximum allowable pressure, surfaces with random post distribution produce less drag reduction than those made up of

Effect of local energy supply to a hypersonic flow on the drag of bodies with different nose bluntness

International Nuclear Information System (INIS)

Borzov, V.Yu.; Rybka, I.V.; Yur'ev, A.S.

1995-01-01

Parameters of the axisymmetric flow around bodies with different bluntness are compared in the case of constant energy supply to the main hypersonic flow. Flow structures, drag coefficients, and expenditure of energy on overcoming drag are analyzed with the effect of thermal energy on the flow taken into account for different bodies with equal volume

Reaching High Altitudes on Mars with an Inflatable Hypersonic Drag Balloon (Ballute)

CERN Document Server

Griebel, Hannes

2010-01-01

The concept of probing the atmosphere of planet Mars by means of a hypersonic drag balloon, a device known as a “ballute”, is a novel approach to planetary science. In this concept, the probe deploys an inflatable drag body out in space and may then enter the atmosphere either once or several times until it slowly descends towards the ground, taking continuous atmospheric and other readings across a large altitude and ground range. Hannes Griebel discusses the theory behind such a mission along with experience gained during its practical implementation, such as mission design, manufacturing, packing and deployment techniques as well as ground and flight tests. The author also studies other ballute applications, specifically emergency low Earth orbit recovery and delivering payloads to high altitude landing sites on Mars.

Studies of drag on the nanocomposite superhydrophobic surfaces

Science.gov (United States)

Brassard, Jean-Denis; Sarkar, D. K.; Perron, Jean

2015-01-01

The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. The X-ray diffraction (XRD) studies show the formation of zinc stearate on ZnO nanoparticles as the confirmation of SA-functionalization of ZnO nanoparticles in the thin films. Morphological analyses reveal the presence of micro-holes with the presence of irregular nanoparticles. The measured root mean square (rms) roughness of the thin film is found to be 12 ± 1 μm with the adhesion of 5B on both glass and aluminum substrates. The wetting property shows that the surface of the film is superhydrophobic with the contact angle of water of 156 ± 4° having contact angle hysteresis (CAH) of 4 ± 2°. The average terminal velocity in the water of the as-received glass spheres and superhydrophobic spheres were found to be 0.66 ± 0.01 m/s and 0.72 ± 0.01 m/s respectively. Consequently, the calculated average coefficients of the surface drag of the as-received glass sphere and superhydrophobic glass sphere were 2.30 ± 0.01 and 1.93 ± 0.03, respectively. Hence, the drag reduction on the surface of superhydrophobic glass sphere is found to be approximately 16% lower than as-received glass sphere.

Diffusion of drag-reducing polymer solutions within a rough-walled turbulent boundary layer

Science.gov (United States)

Elbing, Brian R.; Dowling, David R.; Perlin, Marc; Ceccio, Steven L.

2010-04-01

The influence of surface roughness on diffusion of wall-injected, drag-reducing polymer solutions within a turbulent boundary layer was studied with a 0.94 m long flat-plate test model at speeds of up to 10.6 m s-1 and Reynolds numbers of up to 9×106. The surface was hydraulically smooth, transitionally rough, or fully rough. Mean concentration profiles were acquired with planar laser induced fluorescence, which was the primary flow diagnostic. Polymer concentration profiles with high injection concentrations (≥1000 wppm) had the peak concentration shifted away from the wall, which was partially attributed to a lifting phenomenon. The diffusion process was divided into three zones—initial, intermediate, and final. Studies of polymer injection into a polymer ocean at concentrations sufficient for maximum drag reduction indicated that the maximum initial zone length is of the order of 100 boundary layer thicknesses. The intermediate zone results indicate that friction velocity and roughness height are important scaling parameters in addition to flow and injection conditions. Lastly, the current results were combined with those in Petrie et al. ["Polymer drag reduction with surface roughness in flat-plate turbulent boundary layer flow," Exp. Fluids 35, 8 (2003)] to demonstrate that the influence of polymer degradation increases with increased surface roughness.

Air-Induced Drag Reduction at High Reynolds Numbers: Velocity and Void Fraction Profiles

Science.gov (United States)

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.

Atmospheric Drag, Occultation ‘N’ Ionospheric Scintillation (ADONIS) mission proposal

Czech Academy of Sciences Publication Activity Database

Hettrich, S.; Kempf, Y.; Perakis, N.; Górski, J.; Edl, M.; Urbář, Jaroslav; Dósa, M.; Gini, F.; Roberts, O. W.; Schindler, S.; Schemmer, M.; Steenari, D.; Joldžić, N.; Ødegaard, L.-K. G.; Sarria, D.; Volwerk, M.; Praks, J.

2015-01-01

Roč. 5, Article Number: A2 (2015), s. 1-14 ISSN 2115-7251 Institutional support: RVO:68378289 Keywords : ionosphere (general) * thermosphere * space weather * drag * missions Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.846, year: 2015 http://www.swsc-journal.org/articles/swsc/abs/2015/01/swsc140006/swsc140006.html

Electron and phonon drag in thermoelectric transport through coherent molecular conductors

DEFF Research Database (Denmark)

Lü, Jing-Tao; Wang, Jian-Sheng; Hedegård, Per

2016-01-01

We study thermoelectric transport through a coherent molecular conductor connected to two electron and two phonon baths using the nonequilibrium Green's function method. We focus on the mutual drag between electron and phonon transport as a result of ‘momentum’ transfer, which happens only when...

Vertical, radial and drag force analysis of superconducting magnetic bearings

International Nuclear Information System (INIS)

Cansiz, Ahmet

2009-01-01

The behavior of the force between a permanent magnet (PM) and a high temperature superconductor (HTS) was tested with the frozen-image model based on flux pinning. It was found that the associated dipole moment assumptions of the method of the frozen image underestimate the force somewhat; thus a quadrupole moment analysis is proposed. The radial and drag forces associated with the rotation of the PM levitated above the HTS were measured by using a force transducer and by means of a cantilevered beam technique. The radial force was found not to be dependent on the radial direction, and the least radial force was found to be periodic with an angular displacement during the slow rotation of the PM relative to the HTS. The periodicity behavior of the force is attributed to the geometric eccentricity from the magnetization distribution of the PM and HTS. The drag force associated with the torsional stiffness of the levitated PM during the low and high rotational speeds was incorporated with the data from the literature.

Aeroelastic Modeling of Elastically Shaped Aircraft Concept via Wing Shaping Control for Drag Reduction

Science.gov (United States)

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

Centrality of collisions and total disintegration of nuclei

International Nuclear Information System (INIS)

Sulejmanov, M.K.; Abdinov, O.B.; Anoshin, A.I.; Bogdanowicz, J.; Kuznetsov, A.A.

1998-01-01

The interrelation of the processes of total disintegration of nuclei with the process, characterized by the 'centrality' of collisions and a minimum flow of energy of secondary particles emitted at a zero angle in pC, dC, 4 HeC and 12 CC interactions, is investigated at 4.2 A · GeV/c. The events with total disintegration of nuclei are characterized by a high degree 'centrality' of collisions and similar to the events having a minimum flow of energy of particles emitted at a zero angle

Aerodynamic drag of modern soccer balls.

Science.gov (United States)

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.

Ocean's response to Hurricane Frances and its implications for drag coefficient parameterization at high wind speeds

KAUST Repository

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.

Improvement in supply chain management for oil and gas sector using drag reduction theory

International Nuclear Information System (INIS)

Anjum, A.A.; Chughtai, A.; Shafeeq, A.; Muhammad, A.

2010-01-01

Supply chain management is an integrative philosophy about managing the flow of distribution channels from supplier to the consumer. PARCO, an oil and gas company in Pakistan has three existing pipelines. Out of three, two pipelines are running parallel from Karachi to Mehmood kot. One pipeline is of crude oil and meeting the demand of PARCO refinery while second pipeline is of High Speed Diesel (HSD) and third pipeline is of (HSD and Kerosene) running from Mehmood Kot to Machhike (Sheikhupura). PARCO supply petroleum products from Shikarpur, Mehmood Kot, Faisalabad and Machhike to oil marketing companies (OMCs) as per their share, standard and demand. The purpose of these pipelines is to meet the country demand for petroleum products at various locations all over Pakistan. In the peak season when OMCs have high demand and receipt of product from PARCO pipelines are less, there is a need to enhance the flow rate of oil inside the PARCO pipelines to fulfill the demand of OMCs. This could be done economically by the application of drag reduction theory. So by injecting drag reducer, dragging of the oil inside the pipeline could appreciably be reduced thereby improving the pumping of oil. (author)

An Investigation of the Drag and Pressure Recovery of a Submerged Inlet and a Nose Inlet in the Transonic Flight Range with Free-fall Models

Science.gov (United States)

Selna, James; Schlaff, Bernard A

1951-01-01

The drag and pressure recovery of an NACA submerged-inlet model and an NACA series I nose-inlet model were investigated in the transonic flight range. The tests were conducted over a mass-flow-ratio range of 0.4 to 0.8 and a Mach number range of about 0.8 to 1.10 employing large-scale recoverable free-fall models. The results indicate that the Mach number of drag divergence of the inlet models was about the same as that of a basic model without inlets. The external drag coefficients of the nose-inlet model were less than those of the submerged-inlet model throughout the test range. The difference in drag coefficient based on the maximum cross-sectional area of the models was about 0.02 at supersonic speeds and about 0.015 at subsonic speeds. For a hypothetical airplane with a ratio of maximum fuselage cross-sectional area to wing area of 0.06, the difference in airplane drag coefficient would be relatively small, about 0.0012 at supersonic speeds and about 0.0009 at subsonic speeds. Additional drag comparisons between the two inlet models are made considering inlet incremental and additive drag.

Drag &Drop, Mixed-Methodology-based Lab-on-Chip Design Optimization Software, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — The overall objective is to develop a ?mixed-methodology?, drag and drop, component library (fluidic-lego)-based, system design and optimization tool for complex...

Scaling crossover in thin-film drag dynamics of fluid drops in the Hele-Shaw cell

Science.gov (United States)

Okumura, Ko; Yahashi, Misato; Kimoto, Natsuki

2016-11-01

We study both experimentally and theoretically the descending motion due to gravity of a fluid drop surrounded by another immiscible fluid in a confined space between two parallel plates, i.e., in the Hele-Shaw cell. As a result, we show a new scaling regime of a nonlinear drag friction in viscous liquid that replaces the well-known Stokes' drag friction through a clear collapse of experimental data thanks to the scaling law. In the novel regime, the dissipation in the liquid thin film formed between the drop and cell walls governs the dynamics. The crossover of this scaling regime to another scaling regime in which the dissipation inside the droplet is dominant is clearly demonstrated and a phase diagram separating these scaling regimes is presented. To be published as, Y. Yahashi, N. Kimoto and K. Okumura, Scaling crossover in thin-film drag dynamics of fluid drops in the Hele-Shaw cell, Sci. Rep.(CC BY 4.0). This research was partly supported by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

Hydrodynamic Drag Force Measurement Of A Functionalized Surface Exhibiting Superhydrophobic Properties

Science.gov (United States)

2016-12-01

hydrodynamic skin friction is greatly reduced and the water is said to slip over the air layer [12]. A number of direct numerical simulations ( DNS ) [13...practical means of reducing drag. It is therefore important to investigate materials where in the passive state exhibit the desired qualities of

Experimental Studies on the Physics and Technology of Polymer Drag-Reduction

National Research Council Canada - National Science Library

Hanratty, Thomas

2004-01-01

.... Rheo-optical studies in a Couette device showed that effective polymer solutions develop turbidity over a range of shear rates characteristic of those used in the flow loop. This study shows that the drag reduction can be enhanced by using mixing and delivery procedures which enhance the formation aggregates.

Drag &Drop, Multiphysics & Neural Net-based Lab-on-Chip Optimization Software, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — The overall objective of this project is to develop a drag and drop, component library (fluidic lego) based, system simulation and optimization software for entire...

Do Minimum Wages Fight Poverty?

OpenAIRE

David Neumark; William Wascher

1997-01-01

The primary goal of a national minimum wage floor is to raise the incomes of poor or near-poor families with members in the work force. However, estimates of employment effects of minimum wages tell us little about whether minimum wages are can achieve this goal; even if the disemployment effects of minimum wages are modest, minimum wage increases could result in net income losses for poor families. We present evidence on the effects of minimum wages on family incomes from matched March CPS s...

The Drag-based Ensemble Model (DBEM) for Coronal Mass Ejection Propagation

Science.gov (United States)

Dumbović, Mateja; Čalogović, Jaša; Vršnak, Bojan; Temmer, Manuela; Mays, M. Leila; Veronig, Astrid; Piantschitsch, Isabell

2018-02-01

The drag-based model for heliospheric propagation of coronal mass ejections (CMEs) is a widely used analytical model that can predict CME arrival time and speed at a given heliospheric location. It is based on the assumption that the propagation of CMEs in interplanetary space is solely under the influence of magnetohydrodynamical drag, where CME propagation is determined based on CME initial properties as well as the properties of the ambient solar wind. We present an upgraded version, the drag-based ensemble model (DBEM), that covers ensemble modeling to produce a distribution of possible ICME arrival times and speeds. Multiple runs using uncertainty ranges for the input values can be performed in almost real-time, within a few minutes. This allows us to define the most likely ICME arrival times and speeds, quantify prediction uncertainties, and determine forecast confidence. The performance of the DBEM is evaluated and compared to that of ensemble WSA-ENLIL+Cone model (ENLIL) using the same sample of events. It is found that the mean error is ME = ‑9.7 hr, mean absolute error MAE = 14.3 hr, and root mean square error RMSE = 16.7 hr, which is somewhat higher than, but comparable to ENLIL errors (ME = ‑6.1 hr, MAE = 12.8 hr and RMSE = 14.4 hr). Overall, DBEM and ENLIL show a similar performance. Furthermore, we find that in both models fast CMEs are predicted to arrive earlier than observed, most likely owing to the physical limitations of models, but possibly also related to an overestimation of the CME initial speed for fast CMEs.

Magnetoquantum oscillations of the phonon-drag thermoelectric power in heterojunctions

International Nuclear Information System (INIS)

Lyo, S.K.

1989-01-01

A theory is presented for the low-temperature phonon-drag thermopower S xx in a semiconductor heterojunction in a strong magnetic field. Gigantic quantum oscillations (much larger than electron-diffusion contributions) are obtained. The temperature and field dependences of S xx agree well with recent data. Localized states yield flat valleys for the |S xx | minima in agreement with the data

Modification of the mean near-wall velocity profile of a high-Reynolds number turbulent boundary layer with the injection of drag-reducing polymer solutions

Science.gov (United States)

Elbing, Brian R.; Perlin, Marc; Dowling, David R.; Ceccio, Steven L.

2013-08-01

The current study explores the influence of polymer drag reduction on the near-wall velocity distribution in a turbulent boundary layer (TBL) and its dependence on Reynolds number. Recent moderate Reynolds number direct numerical simulation and experimental studies presented in White et al. [Phys. Fluids 24, 021701 (2012)], 10.1063/1.3681862 have challenged the classical representation of the logarithmic dependence of the velocity profile for drag-reduced flows, especially at drag reduction levels above 40%. In the present study, high Reynolds number data from a drag reduced TBL is presented and compared to the observations of White et al. [Phys. Fluids 24, 021701 (2012)], 10.1063/1.3681862. Data presented here were acquired in the TBL flow on a 12.9-m-long flat plate at speeds to 20.3 m s-1, achieving momentum thickness based Reynolds number to 1.5 × 105, which is an order of magnitude greater than that available in the literature. Polyethylene oxide solutions with an average molecular weight of 3.9 × 106 g mol-1 were injected into the flow at various concentrations and volumetric fluxes to achieve a particular level of drag reduction. The resulting mean near-wall velocity profiles show distinctly different behavior depending on whether they fall in the low drag reduction (LDR) or the high drag reduction (HDR) regimes, which are nominally divided at 40% drag reduction. In the LDR regime, the classical view that the logarithmic slope remains constant at the Newtonian value and the intercept constant increases with increasing drag reduction appears to be valid. However, in the HDR regime the behavior is no longer universal. The intercept constant continues to increase linearly in proportion to the drag reduction level until a Reynolds-number-dependent threshold is achieved, at which point the intercept constant rapidly decreases to that predicted by the ultimate profile. The rapid decrease in the intercept constant is due to the corresponding increase in the

Development of a New Drag Coefficient Model for Oil and Gas ...

African Journals Online (AJOL)

Development of a New Drag Coefficient Model for Oil and Gas Multiphase Fluid Systems. ... a helpful Frequently Asked Questions about PDFs. Alternatively, you can download the PDF file directly to your computer, from where it can be opened using a PDF reader. To download the PDF, click the Download link above.

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

Science.gov (United States)

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

2016-01-21

The mouthpart of a honeybee is a natural well-designed micropump that uses a reciprocating glossa through a temporary tube comprising a pair of galeae and labial palpi for loading nectar. The shapes and sizes of mouthparts differ among castes of honeybees, but the diversities of the functional microstructures inside the mouthparts of honeybee workers and drones remain poorly understood. Through scanning electron microscopy, we found the dimensional difference of uniformly distributed microridges on the inner galeae walls of Apis mellifera ligustica workers and drones. Subsequently, we recorded the feeding process of live honeybees by using a specially designed high-speed camera system. Considering the microridges and kinematics of the glossa, we constructed a hydrodynamic model to calculate the friction coefficient of the mouthpart. In addition, we test the drag reduction through the dimensional variations of the microridges on the inner walls of mouthparts. Theoretical estimations of the friction coefficient with respect to dipping frequency show that inner microridges can reduce friction during the feeding process of honeybees. The effects of drag reduction regulated by specific microridges were then compared. The friction coefficients of the workers and drones were found to be 0.011±0.007 (mean±s.d.) and 0.045±0.010, respectively. These results indicate that the mouthparts of workers are more capable of drag reduction compared with those of drones. The difference was analyzed by comparing the foraging behavior of the workers and drones. Workers are equipped with well-developed hypopharyngeal, and their dipping frequency is higher than that of drones. Our research establishes a critical link between microridge dimensions and drag reduction capability during the nectar feeding of honeybees. Our results reveal that microridges inside the mouthparts of honeybee workers and drones reflect the caste-related life cycles of honeybees. Copyright © 2015 Elsevier Ltd

Multi-Objective Flight Control for Drag Minimization and Load Alleviation of High-Aspect Ratio Flexible Wing Aircraft

Science.gov (United States)

Nguyen, Nhan; Ting, Eric; Chaparro, Daniel; Drew, Michael; Swei, Sean

2017-01-01

As aircraft wings become much more flexible due to the use of light-weight composites material, adverse aerodynamics at off-design performance can result from changes in wing shapes due to aeroelastic deflections. Increased drag, hence increased fuel burn, is a potential consequence. Without means for aeroelastic compensation, the benefit of weight reduction from the use of light-weight material could be offset by less optimal aerodynamic performance at off-design flight conditions. Performance Adaptive Aeroelastic Wing (PAAW) technology can potentially address these technical challenges for future flexible wing transports. PAAW technology leverages multi-disciplinary solutions to maximize the aerodynamic performance payoff of future adaptive wing design, while addressing simultaneously operational constraints that can prevent the optimal aerodynamic performance from being realized. These operational constraints include reduced flutter margins, increased airframe responses to gust and maneuver loads, pilot handling qualities, and ride qualities. All of these constraints while seeking the optimal aerodynamic performance present themselves as a multi-objective flight control problem. The paper presents a multi-objective flight control approach based on a drag-cognizant optimal control method. A concept of virtual control, which was previously introduced, is implemented to address the pair-wise flap motion constraints imposed by the elastomer material. This method is shown to be able to satisfy the constraints. Real-time drag minimization control is considered to be an important consideration for PAAW technology. Drag minimization control has many technical challenges such as sensing and control. An initial outline of a real-time drag minimization control has already been developed and will be further investigated in the future. A simulation study of a multi-objective flight control for a flight path angle command with aeroelastic mode suppression and drag

Thickened boundary layer theory for air film drag reduction on a van body surface

Science.gov (United States)

Xie, Xiaopeng; Cao, Lifeng; Huang, Heng

2018-05-01

To elucidate drag reduction mechanism on a van body surface under air film condition, a thickened boundary layer theory was proposed and a frictional resistance calculation model of the van body surface was established. The frictional resistance on the van body surface was calculated with different parameters of air film thickness. In addition, the frictional resistance of the van body surface under the air film condition was analyzed by computational fluid dynamics (CFD) simulation and different air film states that influenced the friction resistance on the van body surface were discussed. As supported by the CFD simulation results, the thickened boundary layer theory may provide reference for practical application of air film drag reduction on a van body surface.

Assessment of the Unstructured Grid Software TetrUSS for Drag Prediction of the DLR-F4 Configuration

Science.gov (United States)

Pirzadeh, Shahyar Z.; Frink, Neal T.

2002-01-01

An application of the NASA unstructured grid software system TetrUSS is presented for the prediction of aerodynamic drag on a transport configuration. The paper briefly describes the underlying methodology and summarizes the results obtained on the DLR-F4 transport configuration recently presented in the first AIAA computational fluid dynamics (CFD) Drag Prediction Workshop. TetrUSS is a suite of loosely coupled unstructured grid CFD codes developed at the NASA Langley Research Center. The meshing approach is based on the advancing-front and the advancing-layers procedures. The flow solver employs a cell-centered, finite volume scheme for solving the Reynolds Averaged Navier-Stokes equations on tetrahedral grids. For the present computations, flow in the viscous sublayer has been modeled with an analytical wall function. The emphasis of the paper is placed on the practicality of the methodology for accurately predicting aerodynamic drag data.

Implementations of non-drag interfacial forces into the CUPID code

International Nuclear Information System (INIS)

Park, I.K.; Cho, H.K.; Kim, J.; Yoon, H.Y.; Jeong, J.J.

2009-01-01

A component-scale thermal-hydraulics analysis module, the CUPID code has been being developed for a transient three-dimensional two-phase flow analysis of nuclear reactor components. The CUPID is based on a two-fluid, three-field model, which is solved by using an unstructured finite volume method. In the two-fluid momentum equation, the most important term to be modeled is the interfacial surface force. The simplest way to model this force is to formulate as the linear combination of various known interfacial forces such as the standard drag force, the virtual mass force, the Basset force, the lift force, the wall lift force, and the turbulent dispersion force. The standard drag force and the virtual mass force, which is essential for two-fluid computational models, are already considered in the CUPID code. In this paper, the wall lubrication force, the lift force, and the turbulent dispersion force including turbulence models, which play an important role on a radial distribution of the void in a two-phase flow, were implemented into the CUPID code, and the effect of these forces were verified qualitatively. (author)

Drag reduction in silica nanochannels induced by graphitic wall coatings

Science.gov (United States)

Wagemann, Enrique; Walther, J. H.; Zambrano, Harvey A.

2017-11-01

Transport of water in hydrophilic nanopores is of significant technological and scientific interest. Water flow through hydrophilic nanochannels is 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 carbon nanotubes (CNTs), respectively. We develop realistic force fields to simulate the systems of interest and systematically, compare flow rates in coated and uncoated nanochannels under different pressure gradients. Moreover, we assess the effect that GE and CNT translucencies to wettability have on water hydrodynamics 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 capabilities of graphitic wall coatings. We wish to thank partial funding from CRHIAM Conicyt/ Fondap Project 15130015 and computational support from DTU and NLHPC (Chile).

The hydrodynamic drag and the mobilisation of sediment into the water column of towed fishing gear components

Science.gov (United States)

O'Neill, F. G.; Summerbell, Keith David

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.

Ion conductivity and mass spectrometry of methanol diffusion and electroosmotic drag on proton-conducting membranes for the Direct Methanol Fuel Cell (DMFC); Ionische Leitfaehigkeit und massenspektrometrische Bestimmung der Methanol-Diffusion und des 'Electroosmotic Drag' an protonenleitenden Membranen fuer die Direkt-Methanol-Brennstoffzelle (DMFC)

Energy Technology Data Exchange (ETDEWEB)

Oeztuerk, N.

2001-07-01

The methanol permeability of the nafion membrane is one reason why the DMFC is not marketable as yet. As a result of diffusion, permeation and electroosmotic drag, methanol is transferred to the kation side where it will reduce the fuel cell performance. Research is going on world-wide to develop new materials that will prevent methanol crossover. The report describes the development of a measuring cell that will provide the necessary information on diffusion, permeation, electroosmotic drag and conductivity. [German] Ein wesentlicher Grund, der die Einfuehrung der DMFC noch verhindert, ist die Methanoldurchlaessigkeit der Nafion-Membran. Durch Diffusion und Permeation und durch den Electroosmotic Drag gelangt Methanol auf die Kathodenseite und fuehrt dann zu einem Leistungsabfall der Brennstoffzelle. Daher werden weltweit neue Materialien entwickelt, die bei guter lonenleitfaehigkeit den Methanol-crossover unterdruecken. Zur Beurteilung und Weiterentwicklung der neuen Materialien werden Informationen zur Diffusion, Permeation, zum Electroosmotic Drag und zur Leitfaehigkeit benoetigt. Um diese Parameter schnell und einfach zu bestimmen, wurde im Rahmen der vorliegenden Arbeit eine Messzelle weiter entwickelt. Diese Messzelle erlaubt die schnelle Bestimmung aller vier wichtigen Parameter. (orig.)

Mesoscopic fluctuations of Coulomb drag between quasiballistic one-dimensional wires

DEFF Research Database (Denmark)

Mortensen, Asger; Flensberg, Karsten; Jauho, Antti-Pekka

2002-01-01

that the fluctuations in G(12) differ dramatically from those of the diagonal conductance G(ii): the fluctuations are large and can even exceed the mean value, thus implying a possible reversal of the induced drag current. We report extensive numerical simulations elucidating the fluctuations for both correlated...... and uncorrelated disorder. We also present analytic arguments, which fully account for the trends observed numerically....

Drag reduction statistics in a channel flow

Energy Technology Data Exchange (ETDEWEB)

Jimenez-Bernal, Jose A. [Instituto Politecnico Nacional, LABINTHAP-SEPI-ESIME, Edif. 5, 3er piso Col. Lindavista, Mexico DF 07738 (Mexico); Hassan, Yassin A.; Gutierrez-Torres, Claudia del C. [Nuclear Engineering Department, Texas A and M University, College Station, TX 77843-3123 (United States)

2005-07-01

Full text of publication follows: Methods to reduce the drag have been studied for many years because of the promising payoffs that can be attained. In this investigation, the evaluation of statistics such as skewness, flatness, spectra of the stream-wise velocity fluctuations is performed for single phase flow and for two phase flow. Micro-bubbles with an average diameter of 30 {mu}m and a local void fraction of 4.8 % were produced by electrolysis and injected inside the boundary layer. This value of void fraction produced a 38.45 % decrease of the drag. The experiments were conducted in a channel flow at a Reynolds number Re 5128 (considering half height of the channel, the bulk velocity and the kinematics viscosity of the water). The channel was made of acrylic due to the optical properties of this material; its dimensions are 3.85 m long, 0.206 m wide and 0.056 m high. A pressure transducer that ranges from 0 to 35 Pa is located in the test station to measure the pressure drop in single phase flow; this pressure value is used to calculate the shear wall stress. The shear wall stress of two phase flow was measured from the velocity fields obtained from Particle Image Velocimetry (PIV) technique. PIV was utilized to measure instantaneous velocity fields in the stream-wise-normal (x-y) plane. The use of low-local values of void fraction caused a reduction of undesirable speckles effects and an absence of extreme brightness provoked by high bubble saturation. The measurements were carried out in the upper wall of the channel at 3.15 m downstream the inlet's channel. The PIV system is formed by a CCD camera with a resolution of 1008 x 1018 pixels and a double pulse laser with a maximum power 400 mJ and a wavelength of 532 nm (green light). The laser beam was transformed into a sheet of light by an array of cylindrical lenses. Two hundred frames with an area of 1.28 cm{sup 2} were recorded to obtain one hundred velocity fields. The time separation between

Drag reduction statistics in a channel flow

International Nuclear Information System (INIS)

Jimenez-Bernal, Jose A.; Hassan, Yassin A.; Gutierrez-Torres, Claudia del C.

2005-01-01

Full text of publication follows: Methods to reduce the drag have been studied for many years because of the promising payoffs that can be attained. In this investigation, the evaluation of statistics such as skewness, flatness, spectra of the stream-wise velocity fluctuations is performed for single phase flow and for two phase flow. Micro-bubbles with an average diameter of 30 μm and a local void fraction of 4.8 % were produced by electrolysis and injected inside the boundary layer. This value of void fraction produced a 38.45 % decrease of the drag. The experiments were conducted in a channel flow at a Reynolds number Re 5128 (considering half height of the channel, the bulk velocity and the kinematics viscosity of the water). The channel was made of acrylic due to the optical properties of this material; its dimensions are 3.85 m long, 0.206 m wide and 0.056 m high. A pressure transducer that ranges from 0 to 35 Pa is located in the test station to measure the pressure drop in single phase flow; this pressure value is used to calculate the shear wall stress. The shear wall stress of two phase flow was measured from the velocity fields obtained from Particle Image Velocimetry (PIV) technique. PIV was utilized to measure instantaneous velocity fields in the stream-wise-normal (x-y) plane. The use of low-local values of void fraction caused a reduction of undesirable speckles effects and an absence of extreme brightness provoked by high bubble saturation. The measurements were carried out in the upper wall of the channel at 3.15 m downstream the inlet's channel. The PIV system is formed by a CCD camera with a resolution of 1008 x 1018 pixels and a double pulse laser with a maximum power 400 mJ and a wavelength of 532 nm (green light). The laser beam was transformed into a sheet of light by an array of cylindrical lenses. Two hundred frames with an area of 1.28 cm 2 were recorded to obtain one hundred velocity fields. The time separation between consecutive pulses

Development of a Two-fluid Drag Law for Clustered Particles using Direct Numerical Simulation and Validation through Experiments

Energy Technology Data Exchange (ETDEWEB)

Gokaltun, Seckin [Florida International Univ., Miami, FL (United States); Munroe, Norman [Florida International Univ., Miami, FL (United States); Subramaniam, Shankar [Iowa State Univ., Ames, IA (United States)

2014-12-31

This study presents a new drag model, based on the cohesive inter-particle forces, implemented in the MFIX code. This new drag model combines an existing standard model in MFIX with a particle-based drag model based on a switching principle. Switches between the models in the computational domain occur where strong particle-to-particle cohesion potential is detected. Three versions of the new model were obtained by using one standard drag model in each version. Later, performance of each version was compared against available experimental data for a fluidized bed, published in the literature and used extensively by other researchers for validation purposes. In our analysis of the results, we first observed that standard models used in this research were incapable of producing closely matching results. Then, we showed for a simple case that a threshold is needed to be set on the solid volume fraction. This modification was applied to avoid non-physical results for the clustering predictions, when governing equation of the solid granular temperate was solved. Later, we used our hybrid technique and observed the capability of our approach in improving the numerical results significantly; however, improvement of the results depended on the threshold of the cohesive index, which was used in the switching procedure. Our results showed that small values of the threshold for the cohesive index could result in significant reduction of the computational error for all the versions of the proposed drag model. In addition, we redesigned an existing circulating fluidized bed (CFB) test facility in order to create validation cases for clustering regime of Geldart A type particles.

Minimum error discrimination for an ensemble of linearly independent pure states

International Nuclear Information System (INIS)

Singal, Tanmay; Ghosh, Sibasish

2016-01-01

Inspired by the work done by Belavkin (1975 Stochastics 1 315) and independently by Mochon, (2006 Phys. Rev. A 73 032328), we formulate the problem of minimum error discrimination (MED) of any ensemble of n linearly independent pure states by stripping the problem of its rotational covariance and retaining only the rotationally invariant aspect of the problem. This is done by embedding the optimal conditions in a matrix equality as well as matrix inequality. Employing the implicit function theorem in these conditions we get a set of first-order coupled ordinary nonlinear differential equations which can be used to drag the solution from an initial point (where solution is known) to another point (whose solution is sought). This way of obtaining the solution can be done through a simple Taylor series expansion and analytic continuation when required. Thus, we complete the work done by Belavkin and Mochon by ultimately leading their theory to a solution for the MED problem of linearly independent pure state ensembles. We also compare the computational complexity of our technique with the barrier-type interior point method of SDP and show that our technique is computationally as efficient as (actually, a bit more than) the SDP algorithm, with the added advantage of being much simpler to implement. (paper)

Toward understanding whether superhydrophobic surfaces can really decrease fluidic friction drag.

Science.gov (United States)

Su, Bin; Li, Mei; Lu, Qinghua

2010-04-20

Superhydrophobic surfaces in nature such as legs of water striders can get an extra supporting force from the deformed water surface they contact, leading to an anticipation of using water-repellent surfaces on ship and even submarine hulls to reduce friction drag. Here, we first fabricate superhydrophobic coatings with microstructures on glass balls by introducing hydrophobic silica nanoparticles into a polyethylene terephthalate (PET) film. Then, the movement of a superhydrophobic ball on and below water surface is investigated and compared with that of a highly hydrophilic normal glass ball. The results reveal that a superhydrophobic ball can fall more slowly under water compared with a normal glass ball, because the dense microbubbles trapped at the solid/water interface around the superhydrophobic ball act not as a reducer, but as an enhancer for the friction drag. In contrast, the faster movement of a superhydrophobic ball on the water surface can be mainly attributed to the great reduction of skin friction owing to the increased area of the solid/atmosphere interface.

Humanized HLA-DR4.RagKO.IL2RγcKO.NOD (DRAG) mice sustain the complex vertebrate life cycle of Plasmodium falciparum malaria.

Science.gov (United States)

Wijayalath, Wathsala; Majji, Sai; Villasante, Eileen F; Brumeanu, Teodor D; Richie, Thomas L; Casares, Sofia

2014-09-30

Malaria is a deadly infectious disease affecting millions of people in tropical and sub-tropical countries. Among the five species of Plasmodium parasites that infect humans, Plasmodium falciparum accounts for the highest morbidity and mortality associated with malaria. Since humans are the only natural hosts for P. falciparum, the lack of convenient animal models has hindered the understanding of disease pathogenesis and prompted the need of testing anti-malarial drugs and vaccines directly in human trials. Humanized mice hosting human cells represent new pre-clinical models for infectious diseases that affect only humans. In this study, the ability of human-immune-system humanized HLA-DR4.RagKO.IL2RγcKO.NOD (DRAG) mice to sustain infection with P. falciparum was explored. Four week-old DRAG mice were infused with HLA-matched human haematopoietic stem cells (HSC) and examined for reconstitution of human liver cells and erythrocytes. Upon challenge with infectious P. falciparum sporozoites (NF54 strain) humanized DRAG mice were examined for liver stage infection, blood stage infection, and transmission to Anopheles stephensi mosquitoes. Humanized DRAG mice reconstituted human hepatocytes, Kupffer cells, liver endothelial cells, and erythrocytes. Upon intravenous challenge with P. falciparum sporozoites, DRAG mice sustained liver to blood stage infection (average 3-5 parasites/microlitre blood) and allowed transmission to An. stephensi mosquitoes. Infected DRAG mice elicited antibody and cellular responses to the blood stage parasites and self-cured the infection by day 45 post-challenge. DRAG mice represent the first human-immune-system humanized mouse model that sustains the complex vertebrate life cycle of P. falciparum without the need of exogenous injection of human hepatocytes/erythrocytes or P. falciparum parasite adaptation. The ability of DRAG mice to elicit specific human immune responses to P. falciparum parasites may help deciphering immune correlates

Uniting ripple-formation theory under water and winds: A universal scaling relation for the wavelength of fluid-drag ripples across fluids and planetary bodies

Science.gov (United States)

Lapotre, M. G. A.; Lamb, M. P.; Ewing, R. C.; McElroy, B. J.

2016-12-01

Current ripples form on riverbeds and on the seafloor from viscous drag exerted by water flow over sand and are thought to be absent in subaerial systems, where ripple formation is dominated by a mechanism involving the impacting and splashing of sand grains. A fluid-drag mechanism, however, is not precluded in subaerial conditions and was originally hypothesized by R. A. Bagnold. Despite decades of observations in the field and in the laboratory, no universal scaling relation exists to predict the size of fluid-drag ripples. We combine dimensional analysis and a new extensive data compilation to develop a relationship and predict the equilibrium wavelength of current ripples. Our analysis shows that ripples are spaced farther apart when formed by more viscous fluids, smaller bed shear velocities, in coarser grains, or for smaller sediment specific gravity. Our scaling relation also highlights the abrupt transition between current ripples and subaqueous dunes, and thus allows for a process-based segregation of ripples from dunes. When adjusting for subaerial conditions, we predict the formation of decimeter-scale wind-drag ripples on Earth and meter-scale wind-drag ripples on Mars. The latter are ubiquitous on the Red Planet, and are found to co-exist with smaller decimeter-scale ripples, which we interpret as impact ripples. Because the predicted scale of terrestrial wind-drag ripples overlaps with that of impact ripples, it is possible that wind-drag ripples exist on Earth too, but are not recognized as such. When preserved in rocks, fluid-drag ripple stratification records flow directions and fluid properties that are crucial to constrain paleo-environments. Our new theory allows for predictions of ripple size, perhaps in both fluvial and eolian settings, and thus potentially represents a powerful tool for paleo-environmental reconstructions on different planetary bodies.

Impact of drag reducing polymers on the onset of instability in a pipe with reverse flow

Science.gov (United States)

Shashank, H. J.; Sreenivas, K. R.

2014-11-01

The objective of this study is to understand the mechanism by which drag reducing polymer (DRP) additives modify turbulent flow, so as to reduce turbulent drag. Reverse flow in a pipe occurs when the fluid close to the wall moves in an opposite direction to that of the core fluid. Reverse flow is established by using a piston-cylinder mechanism, the programmed motion of which imparts a known impulse to the fluid. When the piston is stopped at the end of the stroke, fluid inertia makes the core of the flow to continue in the same direction. In order to conserve mass, reverse flow is established close to the wall. An inflection point is thus formed, leading to flow instability above a critical Reynolds number. Dye and streak flow visualization experiments are performed to highlight the impact of DRP additives (polyethylene oxide, PEO, dissolved in water). The time of onset of the instability and the wavelength of the observed instability are studied in systems with and without DRP additives. This study will provide further insight into the phenomenon of turbulent polymer drag reduction.

Computation of drag and lift coefficients for simple two-dimensional objects with Reynolds number Re = 420 000

Directory of Open Access Journals (Sweden)

Matas Richard

2012-04-01

Full Text Available The article deals with comparison of drag and lift coefficients for simple two-dimensional objects, which are often discussed in fluid mechanics fundamentals books. The commercial CFD software ANSYS/FLUENT 13 was used for computation of flow fields around the objects and determination of the drag and lift coefficients. The flow fields of the two-dimensional objects were computed for velocity up to 160 km per hour and Reynolds number Re = 420 000. Main purpose was to verify the suggested computational domain and model settings for further more complex objects geometries. The more complex profiles are used to stabilize asymmetrical ('z'-shaped pantographs of high-speed trains. The trains are used in two-way traffic where the pantographs have to operate with the same characteristics in both directions. Results of the CFD computations show oscillation of the drag and lift coefficients over time. The results are compared with theoretical and experimental data and discussed. Some examples are presented in the paper.

Self-similar drag reduction in plug-flow of suspensions of macroscopic fibers

NARCIS (Netherlands)

Gillissen, J.J.J.; Hoving, J.P.

2012-01-01

Pipe flow experiments show that turbulent drag reduction in plug-flow of concentrated suspensions of macroscopic fibers is a self-similar function of the wall shear stress over the fiber network yield stress. We model the experimental observations, by assuming a central fiber network plug, whose

Statistical Analysis of CFD Solutions from the Fourth AIAA Drag Prediction Workshop

Science.gov (United States)

Morrison, Joseph H.

2010-01-01

A graphical framework is used for statistical analysis of the results from an extensive N-version test of a collection of Reynolds-averaged Navier-Stokes computational fluid dynamics codes. The solutions were obtained by code developers and users from the U.S., Europe, Asia, and Russia using a variety of grid systems and turbulence models for the June 2009 4th Drag Prediction Workshop sponsored by the AIAA Applied Aerodynamics Technical Committee. The aerodynamic configuration for this workshop was a new subsonic transport model, the Common Research Model, designed using a modern approach for the wing and included a horizontal tail. The fourth workshop focused on the prediction of both absolute and incremental drag levels for wing-body and wing-body-horizontal tail configurations. This work continues the statistical analysis begun in the earlier workshops and compares the results from the grid convergence study of the most recent workshop with earlier workshops using the statistical framework.

Effect of fastskin suits on performance, drag, and energy cost of swimming.

Science.gov (United States)

Chatard, Jean-Claude; Wilson, Barry

2008-06-01

To investigate the effect of fastskin suits on 25- to 800-m performances, drag, and energy cost of swimming. The performances, stroke rate and distance per stroke, were measured for 14 competitive swimmers in a 25-m pool, when wearing a normal suit (N) and when wearing a full-body suit (FB) or a waist-to-ankle suit (L). Passive drag, oxygen uptake, blood lactate, and the perceived exertion were measured in a flume. There was a 3.2% +/- 2.4% performance benefit for all subjects over the six distances covered at maximal speed wearing FB and L when compared with N. When wearing L, the gain was significantly lower (1.8% +/- 2.5%, P energy cost of swimming was significantly reduced when wearing FB and L by 4.5% +/- 5.4% and 5.5% +/- 3.1%, respectively (P energy cost of submaximal swimming and an increased distance per stroke, at the same stroke rates, and reduced freestyle performance time.

Evaluation of icing drag coefficient correlations applied to iced propeller performance prediction

Science.gov (United States)

Miller, Thomas L.; Shaw, R. J.; Korkan, K. D.

1987-01-01

Evaluation of three empirical icing drag coefficient correlations is accomplished through application to a set of propeller icing data. The various correlations represent the best means currently available for relating drag rise to various flight and atmospheric conditions for both fixed-wing and rotating airfoils, and the work presented here ilustrates and evaluates one such application of the latter case. The origins of each of the correlations are discussed, and their apparent capabilities and limitations are summarized. These correlations have been made to be an integral part of a computer code, ICEPERF, which has been designed to calculate iced propeller performance. Comparison with experimental propeller icing data shows generally good agreement, with the quality of the predicted results seen to be directly related to the radial icing extent of each case. The code's capability to properly predict thrust coefficient, power coefficient, and propeller efficiency is shown to be strongly dependent on the choice of correlation selected, as well as upon proper specificatioon of radial icing extent.

Rising above the Minimum Wage.

Science.gov (United States)

Even, William; Macpherson, David

An in-depth analysis was made of how quickly most people move up the wage scale from minimum wage, what factors influence their progress, and how minimum wage increases affect wage growth above the minimum. Very few workers remain at the minimum wage over the long run, according to this study of data drawn from the 1977-78 May Current Population…

Drag penalty due to the asperities in the substrate of super-hydrophobic and liquid infused surfaces

Science.gov (United States)

Garcia Cartagena, Edgardo J.; Arenas, Isnardo; Leonardi, Stefano

2017-11-01

Direct numerical simulations of two superposed fluids in a turbulent channel with a textured surface made of pinnacles of random height have been performed. The viscosity ratio between the two fluids are N =μo /μi = 50 (μo and μi are the viscosities of outer and inner fluid respectively) mimicking a super-hydrophobic surface (water over air) and N=2.5 (water over heptane) resembling a liquid infused surface. Two set of simulations have been performed varying the Reynolds number, Reτ = 180 and Reτ = 390 . The interface between the two fluids is flat simulating infinite surface tension. The position of the interface between the two fluids has been varied in the vertical direction from the base of the substrate (what would be a rough wall) to the highest point of the roughness. Drag reduction is very sensitive to the position of the interface between the two fluids. Asperities above the interface induce a large form drag and diminish considerably the drag reduction. When the mean height of the surface measured from the interface in the outer fluid is greater than one wall unit, k+ > 1 , the drag increases with respect to a smooth wall. Present results provide a guideline to the accuracy required in manufacturing super-hydrophobic and liquid infused surfaces. This work was supported under ONR MURI Grants N00014-12-0875 and N00014-12- 1-0962, Program Manager Dr. Ki-Han Kim. Numerical simulations were performed on the Texas Advanced Computer Center.

The effects of Poynting-Robertson drag on solar sails

Science.gov (United States)

Abd El-Salam, F. A.

2018-06-01

In the present work, the concept of solar sailing and its developing spacecraft are presented. The effects of Poynting-Robertson drag on solar sails are considered. Some analytical control laws with some mentioned input constraints for optimizing solar sails dynamics in heliocentric orbit using Lagrange's planetary equations are obtained. Optimum force vector in a required direction is maximized by deriving optimal sail cone angle. New control laws that maximize thrust to obtain certain required maximization in some particular orbital element are obtained.

Analytical Ballistic Trajectories with Approximately Linear Drag

Directory of Open Access Journals (Sweden)

Giliam J. P. de Carpentier

2014-01-01

Full Text Available 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. Although the trajectories are only approximate, they still capture many of the characteristics of a real projectile in free fall under the influence of an invariant wind, gravitational pull, and terminal velocity, while the required math for these trajectories and planners is still simple enough to efficiently run on almost all modern hardware devices. Together, these properties make the proposed approach particularly useful for real-time applications where accuracy and performance need to be carefully balanced, such as in computer games.

Early results of Latitude primary total elbow replacement with a minimum follow-up of 2 years.

Science.gov (United States)

Mehta, Saurabh S; Watts, Adam C; Talwalkar, Sumedh C; Birch, Ann; Nuttall, David; Trail, Ian A

2017-10-01

The aim of this study was to present outcomes of primary Latitude total elbow replacement (TER) with a minimum follow-up of 2 years. A retrospective cohort study was undertaken with prospective outcome data collection for the latest outcome. Included were 63 consecutive primary Latitude TERs in 58 patients performed during a period of 5 years at a specialist orthopedic hospital. The mean age of the patients was 62 years (33-85 years). Five primary TERs (4 patients) were lost to follow-up. The primary diagnosis was rheumatoid arthritis in 49, osteoarthritis in 8, and trauma in 6 elbows. The mean flexion-extension arc was 75° preoperatively and 97° postoperatively. Mean postoperative Elbex pain score was 19/100, and function score was 37/100. Mean postoperative scores were 42/100 for the Quick Disabilities of the Arm, Shoulder, and Hand and 38/50 for the elbow-specific American Shoulder and Elbow Surgeons assessment. Four patients died of unrelated causes, and 8 of 63 underwent further surgical intervention, including explantation and conversion from unlinked to linked implant. On radiographic review of 41 surviving TERs, aseptic radiologic loosening was observed of the humeral component in 4 elbows and of the ulnar component in 9. Seven elbows had no radial component, and of the remaining 34 elbows, 16 (47%) had signs of loosening of the radial implant. Complications included 1 heterotopic ossification, 1 olecranon fracture, and 3 further procedures for ulnar nerve entrapment. The results indicate that the early outcome of Latitude TER is comparable to that of other prostheses. There is concern about early radiologic loosening of the radial component. Crown Copyright © 2017. Published by Elsevier Inc. All rights reserved.

Structure design and experimental appraisal of the drag force type vertical axis wind turbine

International Nuclear Information System (INIS)

Kim, Dong Keon; Keum, Jong Yoon; Yoon, Soon Hyun

2006-01-01

Experiments were conducted to estimate the performance of drag force type vertical axis wind turbine with an opening-shutting rotor. It was operated by the difference in drag force generated on both sides of the blades. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was measured by using a pitot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller. Various design parameters, such as the number of blades(B), blade aspect ratio(W/R), angle of blades(α) and drag coefficient acting on a blade, were considered for optimal conditions. At the experiment of miniature model, maximum efficiency was found at N=15, α=60 .deg. and W/R=0.32. The measured test variables were power, torque, rotational speed, and wind speeds. The data presented are in the form of power and torque coefficients as a function of tip-speed ratio V/U. Maximum power was found in case of Ω=0.33, when the power and torque coefficient were 0.14 and 0.37 respectively. Comparing model test with prototype test, similarity law by advance ratio for vertical axis wind turbine was confirmed

A Minimum Fuel Based Estimator for Maneuver and Natrual Dynamics Reconstruction

Science.gov (United States)

Lubey, D.; Scheeres, D.

2013-09-01

The vast and growing population of objects in Earth orbit (active and defunct spacecraft, orbital debris, etc.) offers many unique challenges when it comes to tracking these objects and associating the resulting observations. Complicating these challenges are the inaccurate natural dynamical models of these objects, the active maneuvers of spacecraft that deviate them from their ballistic trajectories, and the fact that spacecraft are tracked and operated by separate agencies. Maneuver detection and reconstruction algorithms can help with each of these issues by estimating mismodeled and unmodeled dynamics through indirect observation of spacecraft. It also helps to verify the associations made by an object correlation algorithm or aid in making those associations, which is essential when tracking objects in orbit. The algorithm developed in this study applies an Optimal Control Problem (OCP) Distance Metric approach to the problems of Maneuver Reconstruction and Dynamics Estimation. This was first developed by Holzinger, Scheeres, and Alfriend (2011), with a subsequent study by Singh, Horwood, and Poore (2012). This method estimates the minimum fuel control policy rather than the state as a typical Kalman Filter would. This difference ensures that the states are connected through a given dynamical model and allows for automatic covariance manipulation, which can help to prevent filter saturation. Using a string of measurements (either verified or hypothesized to correlate with one another), the algorithm outputs a corresponding string of adjoint and state estimates with associated noise. Post-processing techniques are implemented, which when applied to the adjoint estimates can remove noise and expose unmodeled maneuvers and mismodeled natural dynamics. Specifically, the estimated controls are used to determine spacecraft dependent accelerations (atmospheric drag and solar radiation pressure) using an adapted form of the Optimal Control based natural dynamics

Employment effects of minimum wages

OpenAIRE

Neumark, David

2014-01-01

The potential benefits of higher minimum wages come from the higher wages for affected workers, some of whom are in low-income families. The potential downside is that a higher minimum wage may discourage employers from using the low-wage, low-skill workers that minimum wages are intended to help. Research findings are not unanimous, but evidence from many countries suggests that minimum wages reduce the jobs available to low-skill workers.

Fiscal Drag as an Automatic Stability Tool, in the Case of New Regulation with Price Criteria in Automotive Sectors Special Consumption Tax (SCT

Directory of Open Access Journals (Sweden)

Abdurrahman TARAKTAŞ

2017-12-01

Full Text Available Fiscal drag is a result of real or nominal expanding economy and progressive taxation. In general, individuals are forced to enter the upper tax bracket depending on their increased income or expenditure. More tax burden can result in less consumption. Fiscal drag, lack of spending or excessive taxation can cause the economy to slow down. Traditional view suggests that fiscal drag may serve as a natural automatic stabilizer to cool the economy. However, this view ignores the supply side and in particular the potential effects of the high tax burden on economy. This study examines the extent to which the expected automatic stabilization function can be performed and the possible side effects on economic balances and income distribution of fiscal drag in our country in the case of new regulation with price criteria in automotive sectors Special Consumption Tax (SCT.

EXPERIMENTAL INVESTIGATION OF THE IMPACT OF FLIGHT SPEED ON DRAG FORCE IN THE AUTOGYRO MODEL

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Zbigniew Czyż

2015-05-01

Full Text Available The paper presents the experimental investigation of the impact of velocity on drag force in the autogyro model. One of the methods which simulate motion of the flying object consists of using a wind tunnel. In this case, test object is stationary and the motion of air is forced by e.g. a special fan. The costs related with renting and the wind tunnel service are still very high. In this paper, the motion of the autogyro with respect to the air, was produced by fixing this model with scale to measure the drag force on the passenger car roof. The position of the object relative to the vehicle was checked on the basis of numerical analysis of the airflow around this vehicle. Based on the investigations, the field of velocity and pressure, and air flow formed around the contour of the vehicle which have been chosen, were determined. In addition, the drag force characteristic was determined as a function of velocity and it was compared with the values from the numerical analysis. This research is a form of verifying opportunities for this type of research on vehicles. The conclusions derived from the analysis of the results will be used in the future to carry out further research.

Anisotropic stokes drag and dynamic lift on cylindrical colloids in a nematic liquid crystal.

Science.gov (United States)

Rovner, Joel B; Lapointe, Clayton P; Reich, Daniel H; Leheny, Robert L

2010-11-26

We have measured the Stokes drag on magnetic nanowires suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB). The effective drag viscosity for wires moving perpendicular to the nematic director differs from that for motion parallel to the director by factors of 0.88 to 2.4, depending on the orientation of the wires and their surface anchoring. When the force on the wires is applied at an oblique angle to the director, the wires move at an angle to the force, demonstrating the existence of a lift force on particles moving in a nematic. This dynamic lift is significantly larger for wires with homeotropic anchoring than with longitudinal anchoring in the experiments, suggesting the lift force as a mechanism for sorting particles according to their surface properties.

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

Science.gov (United States)

Li, Jing; Tsubokura, Makoto; Tsunoda, Masaya

2015-11-01

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

Optimizing Internal Wave Drag in a Forward Barotropic Model with Semidiurnal Tides

Science.gov (United States)

2015-01-23

rates and patterns after tuning. This suggests that the directionality of the tensor scheme may not provide substantial additional benefit compared to...wave drag scheme Model (layers) Res [] Observations RMSE >1 km [cm] RMSE all depths [cm] Jayne and St. Laurent (2001) JSL JSL(1) 1=2 UT- CSR 6:7$ Egbert

Comparative study of total shoulder arthroplasty versus total shoulder surface replacement for glenohumeral osteoarthritis with minimum 2-year follow-up

NARCIS (Netherlands)

Kooistra, B.W.; Willems, W.J.H.; Lemmens, E.; Hartel, B.P.; Bekerom, M.P. van den; Deurzen, D.F.P. van

2017-01-01

BACKGROUND: Compared with total shoulder arthroplasty (TSA), total shoulder surface replacement (TSSR) may offer the advantage of preservation of bone stock and shorter surgical time, possibly at the expense of glenoid component positioning and increasing lateral glenohumeral offset. We hypothesized

TFH cells accumulate in mucosal tissues of humanized-DRAG mice and are highly permissive to HIV-1

Science.gov (United States)

Allam, Atef; Majji, Sai; Peachman, Kristina; Jagodzinski, Linda; Kim, Jiae; Ratto-Kim, Silvia; Wijayalath, Wathsala; Merbah, Melanie; Kim, Jerome H.; Michael, Nelson L.; Alving, Carl R.; Casares, Sofia; Rao, Mangala

2015-01-01

CD4+ T follicular helper cells (TFH) in germinal centers are required for maturation of B-cells. While the role of TFH-cells has been studied in blood and lymph nodes of HIV-1 infected individuals, its role in the mucosal tissues has not been investigated. We show that the gut and female reproductive tract (FRT) of humanized DRAG mice have a high level of human lymphocytes and a high frequency of TFH (CXCR5+PD-1++) and precursor-TFH (CXCR5+PD-1+) cells. The majority of TFH-cells expressed CCR5 and CXCR3 and are the most permissive to HIV-1 infection. A single low-dose intravaginal HIV-1 challenge of humanized DRAG mice results in 100% infectivity with accumulation of TFH-cells mainly in the Peyer’s patches and FRT. The novel finding of TFH-cells in the FRT may contribute to the high susceptibility of DRAG mice to HIV-1 infection. This mouse model thus provides new opportunities to study TFH-cells and to evaluate HIV-1 vaccines. PMID:26034905

Minimum Wages and Poverty

OpenAIRE

Fields, Gary S.; Kanbur, Ravi

2005-01-01

Textbook analysis tells us that in a competitive labor market, the introduction of a minimum wage above the competitive equilibrium wage will cause unemployment. This paper makes two contributions to the basic theory of the minimum wage. First, we analyze the effects of a higher minimum wage in terms of poverty rather than in terms of unemployment. Second, we extend the standard textbook model to allow for incomesharing between the employed and the unemployed. We find that there are situation...

Drag reduction mechanism by microbubble injection within a channel boundary layer

International Nuclear Information System (INIS)

Ling Zhen; Hassan, Y.

2005-01-01

In this study, the drag reduction due to microbubble injection in the boundary layer of a fully developed turbulent channel flow was investigated. Particle Image Velocimetry (PIV) techniques were taken. The effects of the presence of microbubbles in the boundary layer were assessed. A drag reduction of 38.4% was obtained with void fraction of 4.9%. The algorithms of wavelet auto-correlation maps were applied to the PIV velocity field measurement. Modifications in the wavelet auto-correlation maps due to the presence of microbubbles were studied and compared in three-dimensions. By using 3-D plotting routines and the wavelet auto-correlation maps, it can be deduced from this study that the microbubble injection within the boundary layer increases the turbulent energy of the streamwise velocity components of the large scale (large eddy size, low frequency) range and decreases the energy of the small scale (small eddy size, high frequency) range. The wavelet auto-correlation maps of the normal velocities indicate that the microbubble presence decrease the turbulent energy of normal velocity components for both the large scale (large eddy size, low frequency) and the small scale (small eddy size, high frequency) ranges. (authors)

Coulomb drag in anisotropic systems: a theoretical study on a double-layer phosphorene

NARCIS (Netherlands)

Saberi-Pouya, S.; Vazifehshenas, T.; Farmanbar Gelepordsari, M.; Salavati-Fard, T.

2016-01-01

We theoretically study the Coulomb drag resistivity in a double-layer electron system with highly anisotropic parabolic band structure using Boltzmann transport theory. As an example, we consider a double-layer phosphorene on which we apply our formalism. This approach, in principle, can be tuned

Dancing droplets: Contact angle, drag, and confinement

Science.gov (United States)

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.

Implementation of a turbulent orographic form drag scheme in WRF and its application to the Tibetan Plateau

Science.gov (United States)

Zhou, Xu; Yang, Kun; Wang, Yan

2018-04-01

Sub-grid-scale orographic variation (smaller than 5 km) exerts turbulent form drag on atmospheric flows and significantly retards the wind speed. The Weather Research and Forecasting model (WRF) includes a turbulent orographic form drag (TOFD) scheme that adds the drag to the surface layer. In this study, another TOFD scheme has been incorporated in WRF3.7, which exerts an exponentially decaying drag from the surface layer to upper layers. To investigate the effect of the new scheme, WRF with the old scheme and with the new one was used to simulate the climate over the complex terrain of the Tibetan Plateau from May to October 2010. The two schemes were evaluated in terms of the direct impact (on wind fields) and the indirect impact (on air temperature and precipitation). The new TOFD scheme alleviates the mean bias in the surface wind components, and clearly reduces the root mean square error (RMSEs) in seasonal mean wind speed (from 1.10 to 0.76 m s-1), when referring to the station observations. Furthermore, the new TOFD scheme also generally improves the simulation of wind profile, as characterized by smaller biases and RMSEs than the old one when referring to radio sounding data. Meanwhile, the simulated precipitation with the new scheme is improved, with reduced mean bias (from 1.34 to 1.12 mm day-1) and RMSEs, which is due to the weakening of water vapor flux at low-level atmosphere with the new scheme when crossing the Himalayan Mountains. However, the simulation of 2-m air temperature is little improved.