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.
Variability of Bed Drag on Cohesive Beds under Wave Action
Directory of Open Access Journals (Sweden)
Ilgar Safak
2016-04-01
Full Text Available Drag force at the bed acting on water flow is a major control on water circulation and sediment transport. Bed drag has been thoroughly studied in sandy waters, but less so in muddy coastal waters. The variation of bed drag on a muddy shelf is investigated here using field observations of currents, waves, and sediment concentration collected during moderate wind and wave events. To estimate bottom shear stress and the bed drag coefficient, an indirect empirical method of logarithmic fitting to current velocity profiles (log-law, a bottom boundary layer model for combined wave-current flow, and a direct method that uses turbulent fluctuations of velocity are used. The overestimation by the log-law is significantly reduced by taking turbulence suppression due to sediment-induced stratification into account. The best agreement between the model and the direct estimates is obtained by using a hydraulic roughness of 10 - 4 m in the model. Direct estimate of bed drag on the muddy bed is found to have a decreasing trend with increasing current speed, and is estimated to be around 0.0025 in conditions where wave-induced flow is relatively weak. Bed drag shows an increase (up to fourfold with increasing wave energy. These findings can be used to test the bed drag parameterizations in hydrodynamic and sediment transport models and the skills of these models in predicting flows in muddy environments.
Variability of bed drag on cohesive beds under wave action
Safak, Ilgar
2016-01-01
Drag force at the bed acting on water flow is a major control on water circulation and sediment transport. Bed drag has been thoroughly studied in sandy waters, but less so in muddy coastal waters. The variation of bed drag on a muddy shelf is investigated here using field observations of currents, waves, and sediment concentration collected during moderate wind and wave events. To estimate bottom shear stress and the bed drag coefficient, an indirect empirical method of logarithmic fitting to current velocity profiles (log-law), a bottom boundary layer model for combined wave-current flow, and a direct method that uses turbulent fluctuations of velocity are used. The overestimation by the log-law is significantly reduced by taking turbulence suppression due to sediment-induced stratification into account. The best agreement between the model and the direct estimates is obtained by using a hydraulic roughness of 10 m in the model. Direct estimate of bed drag on the muddy bed is found to have a decreasing trend with increasing current speed, and is estimated to be around 0.0025 in conditions where wave-induced flow is relatively weak. Bed drag shows an increase (up to fourfold) with increasing wave energy. These findings can be used to test the bed drag parameterizations in hydrodynamic and sediment transport models and the skills of these models in predicting flows in muddy environments.
Drag kings in the new wave: gender performance and participation.
Surkan, Kim
2002-01-01
In an examination of Midwestern drag king performers and communities that have emerged since the study by Volcano and Halberstam of king cultures in London, New York, and San Francisco, this article considers traditional and alternative ways of "doing drag," both performative and participatory, as a means of interrogating the proximity of a "new wave" of king culture to academic theory. Tracing the evolution of drag king performance in the Twin Cities from the 1996 workshop by Diane Torr to the formation of two distinct king troupes in the late 1990s demonstrates a particular trajectory in kinging that reflects a new consciousness and enactment of gender theory through artistic praxis. Participation plays a key role in breaking down the distance between spectator and performer in venues such as the First International Drag King Extravaganza in Columbus, Ohio, and Melinda Hubman's art installation "Performing Masculinities: Take a Chance on Gender" in Minneapolis. By engaging the "audience" in drag, the Extravaganza "Science Fair" successfully referenced drag kings' shared history with early American freak shows in a clever and critical way. Moving beyond the contest framework of early king shows, new drag king troupes like Minneapolis' Dykes Do Drag are "mixing it up" in an attempt to complicate notions of butch/femme gender roles, sexuality, and drag stereotypes.
On the parameterization scheme of gravity wave drag effect on the mean zonal flow of mesosphere
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Based on McFarlane's parameterization scheme of gravity wave drag, a refined gravity-wave-drag scheme is presented. Both the drag effect of the momentum flux and the dissipation effect of gravity wave breaking on the mean zonal flow are included in the refined parameterization scheme. The dissipation effect can be formulated with the gravity wave numbers and the mean quantities. The refined parameterization scheme may represent a complete drag effect of stationary gravity wave breaking on the mean zonal flow.
A Two-Wave Scheme for Orographic Gravity Wave Drag Parameterization
Institute of Scientific and Technical Information of China (English)
WANG Yuan; CAI Ninghao; TANG Jinyun
2008-01-01
When the magnitude of sub-scale ographic forcing is comparable with explicitly ordinary dynamic forcing, the drag effect reduced by ographic gravity wave is to be significant for maintaining dynamic balance of atmo-spheric circulation, as well as the momentum and energy transport. Such sub-scale ographic forcing should be introduced into numerically atmospheric model by means of drag being parameterized. Furthermore, the currently mature ographic gravity wave drag (OGWD) parameterization, i.e., the so-called first-generation(based on lineal single-wave theoretical framework) or the second-generation drag parameterization (includ-ing an important extra forcing by the contribution of critical level absorption), cannot correctly and effectly describe the vertical profile of wave stress under the influence of ambient wind shearing. Based on aforemen-tioned consideration, a new two-wave scheme was proposed to parameterize the ographic gravity wave drag by means of freely propagating gravity waves. It starts with a second order WKB approximation, and treats the wave stress attenuations caused by either the selective critical level absorption or the classical critical level absorption explicitly; while in the regions where critical levels are absent, it transports the wave stress vertically by two sinusoidal waves and deposits them and then damps them according to the wave saturation criteria. This scheme is thus used to conduct some sample computations over the Dabie Mountain region of East China, as an example. The results showed that the new two-wave scheme is able to model the vertical distribution of the wave stress more realistically.
Hypersonic wave drag reduction performance of cylinders with repetitive laser energy depositions
Energy Technology Data Exchange (ETDEWEB)
Fang, J; Hong, Y J; Li, Q; Huang, H, E-mail: fangjuan314@163.com [Academy of Equipment Command and Technology, Post Box 3380-86, Huairou Dis. Beijing 101416 (China)
2011-02-01
It has been widely research that wave drag reduction on hypersonic vehicle by laser energy depositions. Using laser energy to reduce wave drag can improve vehicle performance. A second order accurate scheme based on finite-difference method and domain decomposition of structural grid is used to compute the drag performance of cylinders in a hypersonic flow of Mach number 2 at altitude of 15km with repetitive energy depositions. The effects of frequency on drag reduction are studied. The calculated results show: the recirculation zone is generated due to the interaction between bow shock over the cylinder and blast wave produced by energy deposition, and a virtual spike which is supported by an axis-symmetric recirculation, is formed in front of the cylinder. By increasing the repetitive frequency, the drag is reduced and the oscillation of the drag is decreased; however, the energy efficiency decreases by increasing the frequency.
Modeling Jupiter's Quasi Quadrennial Oscillation (QQO) with Wave Drag Parameterizations
Cosentino, Rick; Morales-Juberias, Raul; Greathouse, Thomas K.; Orton, Glenn S.
2016-10-01
The QQO in Jupiter's atmosphere was first discovered after 7.8 micron infrared observations spanning the 1980's and 1990's detected a temperature oscillation near 10 hPa (Orton et al. 1991, Science 252, 537, Leovy et. al. 1991, Nature 354, 380, Friedson 1999, Icarus 137, 34). New observations using the Texas Echelon cross-dispersed Echelle Spectrograph (TEXES), mounted on the NASA Infrared Telescope facility (IRTF), have been used to characterize a complete cycle of the QQO between January 2012 and January 2016 (Greathouse et al. 2016, DPS) . These new observations not only show the thermal oscillation at 10 hPa, but they also show that the QQO extends upwards in Jupiter's atmosphere to pressures as high as 0.4 hPa. We incorporated three different wave-drag parameterizations into the EPIC General Circulation Model (Dowling et al. 1998, Icarus 132, 221) to simulate the observed Jovian QQO temperature signatures as a function of latitude, pressure and time using results from the TEXES datasets as new constraints. Each parameterization produces unique results and offers insight into the spectra of waves that likely exist in Jupiter's atmosphere to force the QQO. High-frequency gravity waves produced from convection are extremely difficult to directly observe but likely contribute a significant portion to the QQO momentum budget. We use different models to simulate the effects of waves such as these, to indirectly explore their spectrum in Jupiter's atmosphere by varying their properties. The model temperature outputs show strong correlations to equatorial and mid-latitude temperature fields retrieved from the TEXES datasets at different epochs. Our results suggest the QQO phenomenon could be more than one alternating zonal jet that descends over time in response to Jovian atmospheric forcing (e.g. gravity waves from convection).Research funding provided by the NRAO Grote Reber Pre-Doctoral Fellowship. Computing resources include the NMT PELICAN cluster and the CISL
Effects of surface drag on low-level frontogenesis within baroclinic waves
Institute of Scientific and Technical Information of China (English)
ZHANG Yi; TAN ZheMin
2007-01-01
Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope especially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection dominates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are reduced.
Effects of surface drag on low-level frontogenesis within baroclinic waves
Institute of Scientific and Technical Information of China (English)
2007-01-01
Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope espe- cially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection domi- nates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are re- duced.
Drag reduction through wave-current interactions with a marine hydrofoil
Tully, Susan; Viola, Ignazio Maria; Ingram, David
2015-11-01
A hydrofoil exposed to oscillating flow experiences a reduction in drag due to the Knoller-Betz effect. This is experimentally identifiable by an increasingly inverted von Kármán wake and a corresponding thrust force on the foil. The rate of drag reduction, dependent on plunge amplitude and frequency, reduces with unsteady flow phenomena at higher reduced frequencies. For experimental ease, investigations of this effect have relied on actively plunging/pitching a foil within a steady current. However, one potential application is to drag reduction in high-speed ships adopting submerged foils. In this case the foil is travelling through wave-current induced oscillatory flow, resulting in an additional dynamic variation of hydrostatic pressure across the chord; a phenomena not fully addressed in previous experiments. Here we investigate the effects of this pressure gradient on drag reduction for a stationary foil in combined waves and current, through a combination of force measurements and particle image velocimetry.
Response spectrum method for extreme wave loading with higher order components of drag force
Reza, Tabeshpour Mohammad; Mani, Fatemi Dezfouli; Mohammad Ali, Dastan Diznab; Saied, Mohajernasab; Saied, Seif Mohammad
2017-01-01
Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea surface levels. When the fundamental period of the offshore structure is about one third of the main period of wave loading, the results indicate the linearized drag term is not capable of achieving a reliable deformation response spectrum.
The Influence of wave state and sea spray on drag coefficient from low to high wind speeds
Shi, Jian; Zhong, Zhong; Li, Xunqiang; Jiang, Guorong; Zeng, Wenhua; Li, Yan
2016-02-01
Ocean waves alter the roughness of sea surface, and sea spray droplets redistribute the momentum flux at the air-sea interface. Hence, both wave state and sea spray influence sea surface drag coefficient. Based on the new sea spray generation function which depends on sea surface wave, a wave-dependent sea spray stress is obtained. According to the relationship between sea spray stress and the total wind stress on the sea surface, a new formula of drag coefficient at high wind speed is acquired. With the analysis of the new drag coefficient, it is shown that the drag coefficient reduces at high wind speed, indicating that the sea spray droplets can limit the increase of drag coefficient. However, the value of high wind speed corresponding to the initial reduced drag coefficient is not fixed, and it depends on the wave state, which means the influence of wave cannot be ignored. Comparisons between the theoretical and measured sea surface drag coefficients in field and laboratory show that under different wave ages, the theoretical result of drag coefficient could include the measured data, and it means that the new drag coefficient can be used properly from low to high wind speeds under any wave state condition.
Variation of the drag coefficient with wind and wave state
Byars, Beverly J.
1985-01-01
Approved for public release; distribution unlimited The dissipation method is used to obtain estimates for the friction velocity, U>t, as well as values for the neutral drag coefficient, C-^jj, for data collected from a coastal tower off San Diego, California. C-q-^ is found to be independent of the ten-meter height windspeed, U-j^q, for velocities between 4-9 m/sec. Its value is estimated to be (0.94+0.4)10 which compares well with values by Smith (1980) and Large and...
A non-axisymmetric linearized supersonic wave drag analysis: Mathematical theory
Barnhart, Paul J.
1996-01-01
A Mathematical theory is developed to perform the calculations necessary to determine the wave drag for slender bodies of non-circular cross section. The derivations presented in this report are based on extensions to supersonic linearized small perturbation theory. A numerical scheme is presented utilizing Fourier decomposition to compute the pressure coefficient on and about a slender body of arbitrary cross section.
Institute of Scientific and Technical Information of China (English)
DENG Zengan; ZHAO Dongliang; WU Kejian; YU Ting; SHI Jian
2008-01-01
By taking into consideration the effects of ocean surface wave-induced Stokes drift velocity U,w and current velocityU,c on the drag coefficient,the spatial distributions of drag coefficient and wind stress in 2004 are computed over the tropical andnorthern Pacific using an empirical drag coefficient parameterization formula based on wave steepness and wind speed.The globalocean current field is generated from the Hybrid Coordinate Ocean Model (HYCOM) and the wave data are generated from Wave-watch Ⅲ (WW3).The spatial variability of the drag coefficient and wind stress is analyzed.Preliminary results indicate that theocean surface Stokes drift velocity and current velocity exert an important influence on the wind stress.The results also show thatconsideration of the effects of the ocean surface Stokes drift velocity and current velocity on the wind stress can significantly im-prove the modeling of ocean circulation and air-sea interaction processes.
Nosaeva, T. A.; Syrodoev, G. A.
2016-12-01
We study the effect of electron drag in a semiconductor superlattice during intraband absorption of a biharmonic electromagnetic wave in a process accompanied by the emission (absorption) of a phonon. The problem has been solved in the second order of perturbation theory. The effective interaction Hamiltonian method makes it possible to take into account the multiphoton nature of the electromagnetic wave absorption. With increasing field, the current increases and attains a peak value, after which it decreases in an oscillatory manner due to the ionization stabilization effect.
Differences in gravity wave drag between realistic oblique and assumed vertical propagation
Kalisch, Silvio; Preusse, Peter; Ern, Manfred; Eckermann, Stephen D.; Riese, Martin
2014-09-01
Gravity wave (GW) parametrizations for general circulation models (GCMs) restrict the propagation of GWs to the vertical direction. The influence of this vertical-only propagation assumption on the distribution of GW drag (GWD) has not yet been investigated. Thus, we present results of two global GW ray tracing simulations, one with full three-dimensional propagation (GWO) and a second one with vertical-only propagation (GWV) of GWs for January and July 2008. The Gravity wave Regional Or Global RAy Tracer (GROGRAT) was used to perform these simulations with a global homogeneous and isotropic launch distribution. Both simulations, GWO and GWV, are analyzed with respect to GWD in the zonal and meridional direction. The location of zonal GWD maxima changes. GWO shows in comparison to GWV a poleward shift of zonal GWD in both seasons with increased GWD at the summer stratopause. The meridional GWD is much stronger in the GWO case, spatially correlated with the zonal drag, and is generally poleward directed. These features in zonal and meridional drag are consistent with a general prevalence of poleward propagation of GWs. Additional simulations suggest that this is due to the Coriolis effect as well as wind filtering around the tropopause, allowing more GWs to propagate into the middle atmosphere. We infer how GWs of different horizontal wavelengths and phase speeds cause the main differences in GWD in the middle atmosphere. A simple test for GCMs is proposed to assess the effects of the altered meridional drag on the general circulation and the interaction with planetary waves.
Teixeira, Miguel A. C.; Paci, Alexandre; Belleudy, Anne
2017-04-01
The drag associated with 3D trapped lee waves generated at a density interface by an axisymmetric obstacle is evaluated using a linear non-hydrostatic model. These waves propagate at temperature inversions capping the boundary layer in the atmosphere, or at the oceanic thermocline, generated by, for example, drifting ice keels. They are responsible for near-surface drag that may be misrepresented as turbulent form drag in numerical models. This drag receives contributions from a continuous wavenumber range forced by the obstacle, in contrast with 2D flow (where only discrete wave modes exist), as the waves are able to vary their angle of incidence with respect to the incoming flow to satisfy their dispersion relationship. Hence (and again in contrast with 2D linear flow), the drag is non-zero both for subcritical and supercritical flow, and attains a maximum for a value of the Froude number slightly smaller than 1. This drag maximum has lower magnitude than in the hydrostatic limit, due to the effect of wave dispersion. The drag calculated from the model is in good agreement with that obtained from experiments carried out in a laboratory water flume that use axisymmetric obstacles of different heights, especially for the lowest obstacle (as would be expected). The best agreement is achieved when the effects of both a rigid lid bounding the fluid layer further away from the obstacle, and friction (represented as a Rayleigh damping), are taken into account. The model is not as quantitatively accurate when the highest obstacle used in the experiments is considered, as this corresponds to stronger flow nonlinearity. But, even in that case, the model has a qualitatively correct behaviour, which is much more accurate than the 3D hydrostatic or 2D non-hydrostatic limits. This suggests that 3D and non-hydrostatic effects to a large extent determine the drag behaviour observed in the experiments. The wave signatures associated with this behaviour are dominated by transverse
Sound power spectrum and wave drag of a propeller in flight
Hanson, D. B.
1989-01-01
Theory is presented for the sound power and sound power spectrum of a single rotation propeller in forward flight. Calculations are based on the linear wave equation with sources distributed over helicoidal surfaces to represent effects of blade thickness and steady loading. Sound power is distributed continuously over frequecy, as would be expected from Doppler effects, rather than in discrete harmonics. The theory is applied to study effects of sweep and Mach number in propfans. An acoustic efficiency is defined as the ratio of radiated sound power to shaft input power. This value is the linear estimate of the effect of wave drag due to the supersonic blade section speeds. It is shown that the acoustic efficiency is somewhat less than 1 percent for a well designed propfan.
Rind, D.; Suozzo, R.; Balachandran, N. K.
1988-01-01
The variability which arises in the GISS Global Climate-Middle Atmosphere Model on two time scales is reviewed: interannual standard deviations, derived from the five-year control run, and intraseasonal variability as exemplified by statospheric warnings. The model's extratropical variability for both mean fields and eddy statistics appears reasonable when compared with observations, while the tropical wind variability near the stratopause may be excessive possibly, due to inertial oscillations. Both wave 1 and wave 2 warmings develop, with connections to tropospheric forcing. Variability on both time scales results from a complex set of interactions among planetary waves, the mean circulation, and gravity wave drag. Specific examples of these interactions are presented, which imply that variability in gravity wave forcing and drag may be an important component of the variability of the middle atmosphere.
A Novel Drag-Free Design for a Geostationary Gravitational Wave Project
National Aeronautics and Space Administration — Given the large volume and additional mass available for scientific use on planned commercial geostationary platforms, we have conceived an alternative drag-free...
Effects of surface drag on upper-level frontogenesis within a developing baroclinic wave
Zhang, Yi; Tan, Zhemin; Chu, Kekuan
2016-08-01
This paper investigates the effects of surface drag on upper-level front with a three-dimensional nonhydrostatic mesoscale numerical model (MM5). To this end, a new and simple potential vorticity intrusion (PVI) index is proposed to quantitatively describe the extent and path that surface drag affects upper-level front. From a PV perspective, the formation of the upper-level front is illustrated as the tropopause folding happens from the stratosphere. The PVI index shows a good correlation with the minimum surface pressure, and tends to increase with the deepening of the surface cyclone and upper-level front. The surface drag acts to damp and delay the development of upper-level front, which could reduce the growth rate of the PVI index. However, the damping presents different effects in different development stages. It is the most significant during the rapid development stage of the surface cyclone. Compared with no surface drag cases, the tropopause is less inclined to intrude into the troposphere due to the surface drag. Positive feedback between the surface cyclone and upper-level front could accelerate the development of the frontal system.
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
Directory of Open Access Journals (Sweden)
Nohr Christian
2009-12-01
Full Text Available The pathways of energy supply for mixing the deep waters of the Baltic Sea is largely unknown. In this paper, a parameterization of the internal wave drag forces on barotropic motion is developed and implemented into a two-dimensional shallow water model of the Baltic Sea. The model is validated against observed sea levels. The dissipation of barotropic motion by internal wave drag that is quantified from the model results show that breaking internal waves generated by wind forced barotropic motions can contribute significantly to diapycnal mixing in the deep water of the Baltic Sea.
2016-04-19
and Ginis , 20 0 0 ). To do so, we need to ave accurate estimate of the drag coefficient. The results in this tudy indicate that WAVEWATCH III with...storm relative flight tracks during the SRA measurements. The gray, magenta, and cyan boxes indicate the model domain used for the September 9, 12 and 14...spectra set A-DT match with that calculated from odel spectra set A very well, indicating again that the diagnostic ail of f −4.5 gives good estimate
Role of on-board discharge in shock wave drag reduction and plasma cloaking
Institute of Scientific and Technical Information of China (English)
Qiu Xiao-Ming; Tang De-Li; Sun Ai-Ping; Liu Wan-Dong; Zeng Xue-Jun
2007-01-01
In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance between the magnetic pressure and gas pressure of plane shock of a partially ionized gas consisting of the environmental gas around the nose of the vehicle and the on-board discharge-produced plasma. The relation between the shock strength and the discharge-induced magnetic pressure is studied by means of a set of one-fluid, hydromagnetic equations reformed for the present purpose, where the discharge-induced magnetic field consists of the electron current (produced by the discharge)-induced magnetic field and the partially ionized gas flow-induced one. A formula for the relation between the above parameters is derived. It shows that the discharge-induced magnetic pressure can minimize the shock strength,successfully explaining the two recent experimental observations on attached bow shock mitigation and elimination in a supersonic flow during on-board discharge [Phys. Plasmas 9 (2002) 721 and Phys. Plasmas 7 (2000) 1345]. In addition,the formula implies that the shock elimination leaves room for a layer of higher-density plasma rampart moving around the nose of the vehicle, being favourable to the plasma radar cloaking of the vehicle. The reason for it is expounded.
Institute of Scientific and Technical Information of China (English)
TANG Jin-yun; TANG Jie; WANG Yuan
2007-01-01
A new analytical model was developed to predict the gravity wave drag (GWD) induced by an isolated 3-dimensional mountain, over which a stratified, nonrotating non-Boussinesq sheared flow is impinged. The model is confined to small amplitude motion and assumes the ambient velocity varying slowly with height. The modified Taylor-Goldstein equation with variable coefficients is solved with a Wentzel-KramersBrillouin (WKB) approximation, formally valid at high Richardson numbers. With this WKB solution, generic formulae of second order accuracy, for the GWD and surface pressure perturbation (both for hydrostatic and non-hydrostatic flow) are presented, enabling a rigorous treatment on the effects by vertical variations in wind profiles. In an ideal test to the circular bell-shaped mountain, it was found that when the wind is linearly sheared,that the GWD decreases as the Richardson number decreases. However, the GWD for a forward sheared wind (wind increases with height) decreases always faster than that for the backward sheared wind (wind deceases with height). This difference is evident whenever the model is hydrostatic or not.
Impact of Parameterized Lee Wave Drag on the Energy Budget of an Eddying Global Ocean Model
2013-08-26
ten- sor can be calculated from Tðx;yÞ¼ qN ð2pÞ2 R dkdljPðk; lÞj k2 j~kj qN ð2pÞ2 R dkdljPðk; lÞj kl j~kj qN ð2pÞ2 R dkdljPðk; lÞj kl j~kj qN ð2pÞ2...linear regres- sion using functions of the velocity potential for linear mountain waves) described in the Appendix of G05 but applied to the syn- thetic
Wiese, Michael R.
1987-01-01
Documented is an aeronautical geometry conversion package which translates wave-drag geometry into the Langley Wireframe Geometry Standard (LaWGS) format and then into a format which is used by the Supersonic Implicit Marching Potential (SIMP) program. The programs described were developed by Computer Sciences Corporation for the Advanced Vehicles Division/Advanced Concepts Branch at NASA Langley Research Center. Included also are the input and output from a benchmark test case.
Belan, Marco
2013-01-01
The background of this work is the problem of reducing the aerodynamic turbulent friction drag, which is an important source of energy waste in innumerable technological fields. We develop a theoretical framework aimed at predicting the behaviour of existing drag reduction techniques when used at the large values of Re which are typical of applications. We focus on one recently proposed and very promising technique, which consists in creating at the wall streamwise-travelling waves of spanwise velocity. A perturbation analysis of the Navier-Stokes equations that govern the fluid motion is carried out, for the simplest wall-bounded flow geometry, i.e. the plane channel flow. The streamwise base flow is perturbed by the spanwise time-varying base flow induced by the travelling waves. An asymptotic expansion is then carried out with respect to the velocity amplitude of the travelling wave. The analysis, although based on several assumptions, leads to predictions of drag reduction that agree well with the measure...
Energy Technology Data Exchange (ETDEWEB)
Destarac, D. [Office National d' Etudes et de Recherches Aerospatiales (ONERA), 92 - Chatillon (France); Van der Vooren, J. [Senior research scientist, retired, Hoekse Waard (Netherlands)
2004-09-01
Drag/thrust analysis of jet-propelled transonic transport aircraft on the basis of calculated viscous flow is discussed. Unique definitions for viscous drag plus wave drag and for induced drag are established. The concept of additive through flow drag is introduced. Drag/thrust bookkeeping is given attention. All drag components can be calculated in the flow region adjacent to the aircraft, where numerical accuracy is expectingly highest. Uniform handling of complex aircraft configurations is brought within reach. Near-field/far-field drag balances are exact. Computational aspects are discussed, in particular the elimination of spurious drag sources. Numerical examples are given for a wing-body and for a wing-body-pylon-nacelle configuration. In either case, the spurious drag sources are eliminated. Acceptable agreement is obtained for the total drag in the first case, and for the installation drag in the second case. Extension of the analysis presented to propeller-driven transport aircraft is straightforward. (author)
Coulomb drag in the mesoscopic regime
DEFF Research Database (Denmark)
Mortensen, N.A.; Flensberg, Karsten; Jauho, Antti-Pekka
2002-01-01
We present a theory for Coulomb drag between two mesoscopic systems which expresses the drag in terms of scattering matrices and wave functions. The formalism can be applied to both ballistic and disordered systems and the consequences can be studied either by numerical simulations or analytic...... average drag for chaotic 2D-systems and dominating fluctuations of drag between quasi-ballistic wires with almost ideal transmission....
Tinetti, Ana F.; Maglieri, Domenic J.; Driver, Cornelius; Bobbitt, Percy J.
2011-01-01
A detailed geometric description, in wave drag format, has been developed for the Convair B-58 and North American XB-70-1 delta wing airplanes. These descriptions have been placed on electronic files, the contents of which are described in this paper They are intended for use in wave drag and sonic boom calculations. Included in the electronic file and in the present paper are photographs and 3-view drawings of the two airplanes, tabulated geometric descriptions of each vehicle and its components, and comparisons of the electronic file outputs with existing data. The comparisons include a pictorial of the two airplanes based on the present geometric descriptions, and cross-sectional area distributions for both the normal Mach cuts and oblique Mach cuts above and below the vehicles. Good correlation exists between the area distributions generated in the late 1950s and 1960s and the present files. The availability of these electronic files facilitates further validation of sonic boom prediction codes through the use of two existing data bases on these airplanes, which were acquired in the 1960s and have not been fully exploited.
Lift and Drag Control on a Lambda Wing Using Leading-Edge Slot Pulsation of Various Wave Forms
Bouras, Constantinos; Nagib, Hassan; Durst, Franz; Heim, Ulrich
2000-11-01
Direct force measurements of lift and drag for a three-dimensional wing with a lambda-shaped planform are made in the Fejer Wind Tunnel at IIT using high angles of attack with and without various unsteady forcing conditions through a leading-edge slot. In addition to changing the pulsation frequency in the range of 2--200 Hz, the waveform was varied between sinusoidal, triangular and square shapes. This was made possible by a novel device called Luftikus, designed and manufactured by Dragerwerke GmbH, Lubeck, Germany, and originally tested at the Fluid Mechanics Institute (LSTM), Erlangen University, Germany. Substantial enhancements in the lift and the lift-to-drag ratio are achieved over a wide range of forcing frequencies with an optimum improvement at a particular dimensionless frequency scaling with the freestream speed and a representative chord length. However, the variation of the shape of the waveform does not lead to significant changes.
Huang, Y.; Weisberg, R.H.; Zheng, L.; Zijlema, M.
2013-01-01
The effects of wind input parameterizations on wave estimations under hurricane conditions are examined using the unstructured grid, third-generation wave model, Simulating WAves Nearshore (SWAN). Experiments using Hurricane Ike wind forcing, which impacted the Gulf of Mexico in 2008, illustrate tha
Huang, Y.; Weisberg, R.H.; Zheng, L.; Zijlema, M.
2013-01-01
The effects of wind input parameterizations on wave estimations under hurricane conditions are examined using the unstructured grid, third-generation wave model, Simulating WAves Nearshore (SWAN). Experiments using Hurricane Ike wind forcing, which impacted the Gulf of Mexico in 2008, illustrate tha
Huang, Y.; Weisberg, R.H.; Zheng, L.; Zijlema, M.
2013-01-01
The effects of wind input parameterizations on wave estimations under hurricane conditions are examined using the unstructured grid, third-generation wave model, Simulating WAves Nearshore (SWAN). Experiments using Hurricane Ike wind forcing, which impacted the Gulf of Mexico in 2008, illustrate
Coulomb drag in coherent mesoscopic systems
DEFF Research Database (Denmark)
Mortensen, Niels Asger; Flensberg, Karsten; Jauho, Antti-Pekka
2001-01-01
, such as the random matrix theory, or by numerical simulations. We show that Coulomb drag is sensitive to localized states, which usual transport measurements do not probe. For chaotic 2D systems we find a vanishing average drag, with a nonzero variance. Disordered 1D wires show a finite drag, with a large variance......We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both ballistic and disordered systems. The consequences can be worked out either by analytic means...
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...
DEFF Research Database (Denmark)
Leer, Jonatan
2013-01-01
with Jennifer Parson and Clarissa Dickson Wright (1996-1999). I will argue that the two self-declared fat women can be read as “gastronomic drags” by their transgression of a “recognizable” feminine way of “doing food”. The article is theoretically informed by the reflections on drag as subversive practice...... of appearing either too radical or not radical enough. The article concludes with some reflections on the development of the cooking show as a site for gendered negotiation from the 90’s and today....
Coulomb drag in the mesoscopic regime
DEFF Research Database (Denmark)
Mortensen, N. Asger; Flensberg, Karsten; Jauho, Antti-Pekka
2002-01-01
We present a theory for Coulomb drug between two mesoscopic systems which expresses the drag in terms of scattering matrices and wave functions. The formalism can be applied to both ballistic and disordered systems and the consequences can be studied either by numerical simulations or analytic...... average drag for chaotic 2D-systems and dominating fluctuations of drag between quasi-ballistic wires with almost ideal transmission....
2010-01-01
stratosphere. Moreover, given the improper thermodynamic environment conditions by the shortwave scheme, the role of the GWDO process is found to be limited...ity wave is an unresolved process in coarse resolution models, playing an important role in transporting momentum from source regions to regions where...polar night jet in the northern hemisphere and unrealistically strong extension of the tropospheric westerly jet into the strato - sphere in the
de Wit, R.; Hibbins, R. E.; Espy, P. J.
2014-12-01
Gravity waves (GWs) play an important role in the dynamics of the mesosphere/lower thermosphere (MLT) region, linking the lower to the upper atmosphere. GW filtering by the background zonal wind is furthermore believed to be the fundamental mechanism coupling the winter stratosphere to the summer polar mesopause, in which increased planetary wave (PW) activity in the former is related to enhanced temperatures in the latter through a chain of global MLT temperature anomalies. During major Sudden Stratospheric Warmings (SSWs) the interaction between PWs and the background flow leads to increased polar stratospheric temperatures and a reversal of the climatological winds from eastward to westward. As a result, large changes in GW filtering conditions occur, making SSWs an excellent tool to empirically test the inter-hemispheric coupling mechanism. In this study, mesopause GW forcing derived from meteor radar observations over Trondheim, Norway (63°N, 10°E) during the January 2013 major SSW is discussed in light of the polar vortex strength and selective filtering conditions over the same location to show the coupling between the polar winter stratosphere and MLT. Global temperature observations obtained with the Aura Microwave Limb Sounder (MLS) are subsequently used to study the temperature signature of the SSW in the MLT region over the winter pole in relation to the observed GW forcing. Furthermore, the temperature effect of the SSW throughout the middle atmosphere is tracked, away from the winter pole toward the summer pole, and compared to the temperature structure expected from the inter-hemispheric coupling mechanism.
Turbulent drag in a rotating frame
Campagne, Antoine; Gallet, Basile; Cortet, Pierre-Philippe; Moisy, Frédéric
2016-01-01
What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at constant angular velocity $\\omega$ in a water tank mounted on a platform rotating at a rate $\\Omega$. We report a dramatic reduction in drag as $\\Omega$ increases, down to values as low as $12$\\% of the non-rotating drag. At small Rossby number $Ro = \\omega/\\Omega$, the decrease in drag coefficient $K$ follows the approximate scaling law $K \\sim Ro$, which is predicted in the framework of nonlinear inertial wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction rather originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.
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...
Wind speed scaling and the drag coefficient
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Wind speed scaling in similarity law in wind-generated waves and the drag coefficient are studied. In analyzing the data in the wind wave channel, it is found that the u. scaling greatly reduces the scatter in the U10 scaling. The u. scaling has much less scatter than the scaling using other wind speeds. The friction velocity seems to play a distinctive role in wave growth. The result is important in the applications of the similarity law and in wave modeling. In theory it gives an insight into the mechanism of wind wave interaction. It is found that wave steepness is important in influencing the drag coefficient. The variability of the coefficients in the currently widely used drag form can be explained by the differences in wave steepness in the observations. A drag coefficient model with wind speed and wave steepness as parameters is proposed. An explanation for Kahma' s result that the u. scaling does not reduce the scatter in the U10 scaling is given.
Evaluation of nacelle drag using Computational Fluid Dynamics
Directory of Open Access Journals (Sweden)
Luis Gustavo Trapp
2010-08-01
Full Text Available Thrust and drag components must be defined and properly accounted in order to estimate aircraft performance, and this hard task is particularty essential for propulsion system where drag components are functions of engine operating conditions. The present work describes a numerical method used to calculate the drag in different nacelles, long and short ducted. Two- and three-dimensional calculations were performed, solving the Reynolds Averaged Navier-Stokes (RANS equations with a commercial Computational Fluid Dynamics (CFD code. It is then possible to obtain four drag components: wave, induced, viscous and spurious drag using a far-field formulation. An expression in terms of entropy variations was shown and drag for different nacelle geometries was estimated.
Milne, Andrew J. B.; Fleck, Brian; Nobes, David; Sen, Debjyoti; Amirfazli, Alidad; University of Alberta Mechanical Engineering Collaboration
2013-11-01
We present the first ever direct measurements of the coefficient of drag on sessile drops at Reynolds numbers from the creeping flow regime up to the point of incipient motion, made using a newly developed floating element differential drag sensor. Surfaces of different wettabilities (PMMA, Teflon, and a superhydrophobic surface (SHS)), wet by water, hexadecane, and various silicone oils, are used to study the effects of drop shape, and fluid properties on drag. The relation between drag coefficient and Reynolds number (scaled by drop height) varies slightly with liquid-solid system and drop volume with results suggesting the drop experiences increased drag compared to similar shaped solid bodies due to drop oscillation influencing the otherwise laminar flow. Drops adopting more spherical shapes are seen to experience the greatest force at any given airspeed. This indicates that the relative exposed areas of drops is an important consideration in terms of force, with implications for the shedding of drops in applications such as airfoil icing and fuel cell flooding. The measurement technique used in this work can be adapted to measure drag force on other deformable, lightly adhered objects such as dust, sand, snow, vesicles, foams, and biofilms. The authours acknowledge NSERC, Alberta Innovates Technology Futures, and the Killam Trusts.
Drag Coefficient and Foam in Hurricane Conditions.
Golbraikh, E.; Shtemler, Y.
2016-12-01
he present study is motivated by recent findings of saturation and even decrease in the drag coefficient (capping) in hurricane conditions, which is accompanied by the production of a foam layer on the ocean surface. As it is difficult to expect at present a comprehensive numerical modeling of the drag coefficient saturation that is followed by wave breaking and foam production, there is no complete confidence and understanding of the saturation phenomenon. Our semi-empirical model is proposed for the estimation of the foam impact on the variation of the effective drag coefficient, Cd , with the reference wind speed U10 in stormy and hurricane conditions. The proposed model treats the efficient air-sea aerodynamic roughness length as a sum of two weighted aerodynamic roughness lengths for the foam-free and foam-covered conditions. On the available optical and radiometric measurements of the fractional foam coverage,αf, combined with direct wind speed measurements in hurricane conditions, which provide the minimum of the effective drag coefficient, Cd for the sea covered with foam. The present model yields Cd10 versus U10 in fair agreement with that evaluated from both open-ocean and laboratory measurements of the vertical variation of mean wind speed in the range of U10 from low to hurricane speeds. The present approach opens opportunities for drag coefficient modeling in hurricane conditions and hurricane intensity estimation by the foam-coverage value using optical and radiometric measurements.
Retrieval of ocean surface wind stress and drag coefficient from spaceborne SAR
Institute of Scientific and Technical Information of China (English)
杨劲松; 黄韦艮; 周长宝
2001-01-01
A model for retrieval of wind stress and drag coefficient on the sea surface with the data measured by spacebome synthetic aperture radar (SAR) has been developed based on the SAR imaging mechanisms of ocean surface capillary waves and short gravity waves. This model consists of radiometric calibration, wind speed retrieval and wind stress and drag coefficient calculation. A Radarsat SAR image has been used to calculate wind stress and drag coeffi cient. Good results have been achieved.
Low-drag events in transitional wall-bounded turbulence
Whalley, Richard D.; Park, Jae Sung; Kushwaha, Anubhav; Dennis, David J. C.; Graham, Michael D.; Poole, Robert J.
2017-03-01
Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 - 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.
Directory of Open Access Journals (Sweden)
C. Bossuet
Full Text Available Systematic westerly biases in the southern hemisphere wintertime flow and easterly equatorial biases are experienced in the Météo-France climate model. These biases are found to be much reduced when a simple parameterization is introduced to take into account the vertical momentum transfer through the gravity waves excited by deep convection. These waves are quasi-stationary in the frame of reference moving with convection and they propagate vertically to higher levels in the atmosphere, where they may exert a significant deceleration of the mean flow at levels where dissipation occurs. Sixty-day experiments have been performed from a multiyear simulation with the standard 31 levels for a summer and a winter month, and with a T42 horizontal resolution. The impact of this parameterization on the integration of the model is found to be generally positive, with a significant deceleration in the westerly stratospheric jet and with a reduction of the easterly equatorial bias. The sensitivity of the Météo-France climate model to vertical resolution is also investigated by increasing the number of vertical levels, without moving the top of the model. The vertical resolution is increased up to 41 levels, using two kinds of level distribution. For the first, the increase in vertical resolution concerns especially the troposphere (with 22 levels in the troposphere, and the second treats the whole atmosphere in a homogeneous way (with 15 levels in the troposphere; the standard version of 31 levels has 10 levels in the troposphere. A comparison is made between the dynamical aspects of the simulations. The zonal wind and precipitation are presented and compared for each resolution. A positive impact is found with the finer tropospheric resolution on the precipitation in the mid-latitudes and on the westerly stratospheric jet, but the general impact on the model climate is weak, the physical parameterizations used appear to be mostly independent to the
Sphere Drag and Heat Transfer.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-20
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
Coulomb drag in quantum circuits
Levchenko, Alex; Kamenev, Alex
2008-01-01
We study drag effect in a system of two electrically isolated quantum point contacts (QPC), coupled by Coulomb interactions. Drag current exhibits maxima as a function of QPC gate voltages when the latter are tuned to the transitions between quantized conductance plateaus. In the linear regime this behavior is due to enhanced electron-hole asymmetry near an opening of a new conductance channel. In the non-linear regime the drag current is proportional to the shot noise of the driving circuit,...
Concannon, Thomas
2016-01-01
The time it takes to fall down a tunnel through the center of the Earth to the other side takes approximately 42 minutes, but only when given several simplifying assumptions: a uniform density Earth; a gravitational field that varies linearly with radial position; a non-rotating Earth; a tunnel evacuated of air; and zero friction along the sides of the tunnel. Though several papers have singularly relaxed the first three assumptions, in this paper we relax the final two assumptions and analyze the motion of a body experiencing these types of drag forces in the tunnel. Under such drag forces, we calculate the motion of a transport vehicle through a tunnel of the Earth under uniform density, under constant gravitational acceleration, and finally under the more realistic Preliminary Reference Earth Model (PREM) density data. We find the density profile corresponding to a constant gravitational acceleration better models the motion through the tunnel compared to the PREM density profile, and the uniform density m...
Shell selection of hermit crabs is influenced by fluid drag
Casillas, Barbara; Ledesma, Rene; Alcaraz, Guillermina; Zenit, Roberto
2010-11-01
The flow around gastropod shells used by hermit crabs (Calcinus californiensis) was visualized experimentally. These crabs choose their shells according to many factors; we found that the choice of shell (shape and weight) is directly related to the drag caused over them by the exposure to wave action. Tests were conducted in a wind tunnel to investigate flow differences for shells of various shapes. A particle image velocimetry (PIV) system was used to visualize the flow field. The images above show the flow field around two types of shells (Thais speciosa and Nerita scabircosta) for Reynolds numbers of O(10^5). Using a control volume analysis, the drag coefficient was inferred. Several shell geometries, orientations and mean flow velocities were tested. In this talk, the flow and drag force will be shown for the different arrangements. A discussion of the relation between drag and shape will be presented.
Energy Technology Data Exchange (ETDEWEB)
Roberts, David C [Los Alamos National Laboratory
2008-01-01
The article considers the dramatic phenomenon of seemingly frictionless flow of slow-moving superfluids. Specifically the question of whether an object in a superfluid flow experiences any drag force is addressed. A brief account is given of the history of this problem and it is argued that recent advances in ultracold atomic physics can shed much new light on this problem. The article presents the commonly held notion that sufficiently slow-moving superfluids can flow without drag and also discusses research suggesting that scattering quantum fluctuations might cause drag in a superfluid moving at any speed.
Drag characteristics of competitive swimming children and adults.
Kjendlie, Per-Ludvik; Stallman, Robert Keig
2008-02-01
The aims of this study were to compare drag in swimming children and adults, quantify technique using the technique drag index (TDI), and use the Froude number (Fr) to study whether children or adults reach hull speed at maximal velocity (vmax). Active and passive drag was measured by the perturbation method and a velocity decay method, respectively, including 9 children aged 11.7+/-0.8 and 13 adults aged 21.4+/-3.7. The children had significantly lower active (kAD) and passive drag factor (kPD) compared with the adults. TDI (kAD/kPD) could not detect any differences in swimming technique between the two groups, owing to the adults swimming maximally at a higher Fr, increasing the wave drag component, and masking the effect of better technique. The children were found not to reach hull speed at vmax, and their Fr were 0.37+/-0.01 vs. the adults 0.42+/-0.01, indicating adults' larger wave-making component of resistance at vmax compared with children. Fr is proposed as an evaluation tool for competitive swimmers.
Using Wind Setdown and Storm Surge on Lake Erie to Calibrate the Air-Sea Drag Coefficient
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. PMID:23977309
Using wind setdown and storm surge on Lake Erie to calibrate the air-sea drag coefficient.
Directory of Open Access Journals (Sweden)
Carl Drews
Full Text Available 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.
Intershell resistance in multiwall carbon nanotubes: A Coulomb drag study
DEFF Research Database (Denmark)
Lunde, Anders Mathias; Flensborg, Karsten; Jauho, Antti-Pekka
2005-01-01
We calculate the intershell resistance R-21 in a multiwall carbon nanotube as a function of temperature T and Fermi level epsilon(F) (e.g., a gate voltage), varying the chirality of the inner and outer tubes. This is done in a so-called Coulomb drag setup, where a current I-1 in one shell induces...... effects for the Coulomb drag between different tubes due to selection rules combined with mismatching of wave vector and crystal angular momentum conservation near the Fermi level. This gives rise to orders of magnitude changes in R-21 and even the sign of R-21 can change depending on the chirality...
Practical evaluation of the drag of a ship for design and optimization
Institute of Scientific and Technical Information of China (English)
YANG Chi; HUANG Fuxin
2013-01-01
We consider two major components of the drag of a ship, the“friction drag”and the“wave drag”, that are related to vis-cous friction at the hull surface and wavemaking, and mostly depend on the Reynolds number and the Froude number, respectively. We also consider the influence of sinkage and trim, viscosity, and nonlinearities on the drag. The sum of the friction drag given by the classical ITTC friction formula and the wave drag predicted by the modification, called Neumann-Michell (NM) theory, of the classical Neumann-Kelvin theory of ship waves is found to be within about 10%of experimental drag measurements for four ship hulls for which theoretical predictions and experimental measurements are compared. The sum of the ITTC friction drag and the NM wave drag can then be expected to yield realistic practical estimates that can be useful for routine applications to design and hull-form optimization of a broad range of displacement ships. Furthermore, we note several simple extensions of this highly simplified approach that can be expected to significantly improve accuracy.
Nonlocal Drag of Magnons in a Ferromagnetic Bilayer
Liu, Tianyu; Vignale, G.; Flatté, Michael E.
2016-06-01
Quantized spin waves, or magnons, in a magnetic insulator are assumed to interact weakly with the surroundings, and to flow with little dissipation or drag, producing exceptionally long diffusion lengths and relaxation times. In analogy to Coulomb drag in bilayer two-dimensional electron gases, in which the contribution of the Coulomb interaction to the electric resistivity is studied by measuring the interlayer resistivity (transresistivity), we predict a nonlocal drag of magnons in a ferromagnetic bilayer structure based on semiclassical Boltzmann equations. Nonlocal magnon drag depends on magnetic dipolar interactions between the layers and manifests in the magnon current transresistivity and the magnon thermal transresistivity, whereby a magnon current in one layer induces a chemical potential gradient and/or a temperature gradient in the other layer. The largest drag effect occurs when the magnon current flows parallel to the magnetization; however, for oblique magnon currents a large transverse current of magnons emerges. We examine the effect for practical parameters, and find that the predicted induced temperature gradient is readily observable.
Re-examination of compliant wall experiments in air with water substrates. [for drag reduction
Hefner, J. N.; Weinstein, L. M.
1976-01-01
A possible alternative explanation is proposed for compliant wall drag reductions measured in previous investigations. Standing waves were observed to form on the surfaces of compliant wall models in air with water substrates as the freestream velocity was increased from 15 to 30 m/s. These waves resembled sine waves with half of the wave protruding over the upstream portion of the model and the other half being recessed over the downstream end of the model. These data coupled with results of recent drag reduction experiments suggest that standing waves could have caused a shift in the model center of gravity creating a bending moment that was interpreted as a reduction in the skin friction drag.
Aerodynamic Drag and Gyroscopic Stability
Courtney, Elya R
2013-01-01
This paper describes the effects on aerodynamic drag of rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that a bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by the experiments reported here. Measured ballistic coefficients were compared with gyroscopic stabilities computed using the Miller Twist Rule for nearly solid metal bullets with uniform density and computed using the Courtney-Miller formula for plastic-tipped bullets. The experiments reported here also demonstrate a decrease in aerodynamic drag near Sg = 1.23 +/- 0.02. It is hypothesized that this decrease in drag over a narrow band of Sg values is due to a rapid damping of coning motions (precession and nutation). Observation of this drag decrease at a consistent value of Sg demonstrates the relati...
Drag Reduction of Bacterial Cellulose Suspensions
Directory of Open Access Journals (Sweden)
Satoshi Ogata
2011-01-01
Full Text Available Drag reduction due to bacterial cellulose suspensions with small environmental loading was investigated. Experiments were carried out by measuring the pressure drop in pipe flow. It was found that bacterial cellulose suspensions give rise to drag reduction in the turbulent flow range. We observed a maximum drag reduction ratio of 11% and found that it increased with the concentration of the bacterial cellulose suspension. However, the drag reduction effect decreased in the presence of mechanical shear.
Analytical calculation of the drag force near drag crisis of a falling sphere
Assis, Armando V D B; Branco, N S
2010-01-01
We obtain analitically the $v^2$ dependence of the drag force on a falling sphere close to the drag crisis, as well as the drag coefficient at the drag crisis, with excellent agreement with experiment. We take into account the effects of viscosity in creating a turbulent boundary layer and perform the calculations using the Navier-Stokes equation.
Temperature dependence of coulomb drag between finite-length quantum wires.
Peguiron, J; Bruder, C; Trauzettel, B
2007-08-24
We evaluate the Coulomb drag current in two finite-length Tomonaga-Luttinger-liquid wires coupled by an electrostatic backscattering interaction. The drag current in one wire shows oscillations as a function of the bias voltage applied to the other wire, reflecting interferences of the plasmon standing waves in the interacting wires. In agreement with this picture, the amplitude of the current oscillations is reduced with increasing temperature. This is a clear signature of non-Fermi-liquid physics because for coupled Fermi liquids the drag resistance is always expected to increase as the temperature is raised.
Variation of the drag coefficient and its dependence on sea state
Geernaert, G. L.; Katsaros, K. B.; Richter, K.
1986-01-01
Using a Gill propeller vane anemometer and resistance wave wires over a water column depth of 15 m, simultaneous measurements of the momentum flux and sea surface wave spectra were acquired from the Pisa mast, 28 km offshore in the German Bight during autumn and winter 1979. These data were analyzed to identify the relationship between wind stress and surface waves. It was found that wind stresses for wind speeds above 15 m/s were regularly higher than open ocean wind stresses as reported by Smith (1980) and by Large and Pond (1981) for the same mean wind speed. These results, when described in terms of the drag coefficient, compared closely with the results of Sheppard et al. (1972), who collected surface layer statistics over Lough Neagh, Northern Ireland. After modeling the surface waves of the North Sea as a function of wave saturation (or wave age), it became evident that variations in the magnitude of the drag coefficient could be explained by coincident variations in the surface wave energy spectrum. By applying the wave dependent roughness length model described by Kitaigorodskii (1973), the North Sea drag coefficient was predicted to be larger than drag coefficients reported from the open sea.
Variation of the drag coefficient and its dependence on sea state
Geernaert, Gerald L.; Katsaros, Kristina B.; Richter, Karl
1986-06-01
Using a Gill propeller vane anemometer and resistance wave wires over a water column depth of 15 m, simultaneous measurements of the momentum flux and sea surface wave spectra were acquired from the Pisa mast, 28 km offshore in the German Bight during autumn and winter 1979. These data were analyzed to identify the relationship between wind stress and surface waves. It was found that wind stresses for wind speeds above 15 m/s were regularly higher than open ocean wind stresses as reported by Smith (1980) and by Large and Pond (1981) for the same mean wind speed. These results, when described in terms of the drag coefficient, compared closely with the results of Sheppard et al. (1972), who collected surface layer statistics over Lough Neagh, Northern Ireland. After modeling the surface waves of the North Sea as a function of wave saturation (or wave age), it became evident that variations in the magnitude of the drag coefficient could be explained by coincident variations in the surface wave energy spectrum. By applying the wave dependent roughness length model described by Kitaigorodskii (1973), the North Sea drag coefficient was predicted to be larger than drag coefficients reported from the open sea.
Vapor layers reduce drag without the crisis
Vakarelski, Ivan; Berry, Joseph; Chan, Derek; Thoroddsen, Sigurdur
2016-11-01
The drag of a solid sphere moving in fluid is known to be only a function of the Reynolds number, Re and diminishes rapidly at the drag crisis around Re 3 ×105. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect, can occur over a wide range of Re, from as low as 600. The Navier slip model with a viscosity dependent slip length captures the observed drag reduction and wake shape.
Turbulent drag reduction by polymers
Energy Technology Data Exchange (ETDEWEB)
Bonn, Daniel [Van der Waals-Zeeman Instituut, University of Amsterdam, Valckenierstraat 65 1018, XE Amsterdam (Netherlands); Amarouchene, Yacine [CPMOH, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence cedex (France); Wagner, Christian [Institut fuer Experimentalphysik, Universitaet des Saarlandes, Saarbruecken (Germany); Douady, Stephane [Laboratoire de Physique Statistique de l' ENS, 24 rue Lhomond, 75231 Paris cedex 05 (France); Cadot, Olivier [ENSTA, Chemin de la Huniere, 91761 Palaiseau cedex (France)
2005-04-13
The reduction of turbulent energy dissipation by addition of polymers is studied experimentally. We first address the question of where the action of the polymers is taking place. Subsequently, we show that there is a direct correlation of drag reduction with the elongational viscosity of the polymers. For this, the reduction of turbulent energy dissipation by addition of the biopolymer DNA is studied. These results open the way for a direct visualization study of the polymer conformation in a turbulent boundary layer.
Drag Effects in Charm Photoproduction
Norrbin, E
1999-01-01
We have refined a model for charm fragmentation at hadron colliders. This model can also be applied to the photoproduction of charm. We investigate the effect of fragmentation on the distribution of produced charm quarks. The drag effect is seen to produce charm hadrons that are shifted in rapidity in the direction of the beam remnant. We also study the importance of different production mechanisms such as charm in the photon and from parton showers.
Island-trapped Waves, Internal Waves, and Island Circulation
2015-09-30
Island-trapped waves , internal waves , and island circulation T. M. Shaun Johnston Scripps Institution of Oceanography University of California...topography. As strong flows encounter small islands, points, and submarine ridges, it is expected that wakes, eddies, and arrested internal lee waves ...form drag, lee waves , eddy generation) over small-scale topographic features and (ii) fundamentally nonlinear processes (turbulent island wakes
Research of low boom and low drag supersonic aircraft design
Institute of Scientific and Technical Information of China (English)
Feng Xiaoqiang; Li Zhanke; Song Bifeng
2014-01-01
Sonic boom reduction will be an issue of utmost importance in future supersonic trans-port, due to strong regulations on acoustic nuisance. The paper describes a new multi-objective optimization method for supersonic aircraft design. The method is developed by coupling Seebass-George-Darden (SGD) inverse design method and multi-objective genetic algorithm. Based on the method, different codes are developed. Using a computational architecture, a concep-tual supersonic aircraft design environment (CSADE) is constructed. The architecture of CSADE includes inner optimization level and out optimization level. The low boom configuration is gener-ated in inner optimization level by matching the target equivalent area distribution and actual equivalent area distribution. And low boom/low drag configuration is generated in outer optimiza-tion level by using NSGA-II multi-objective genetic algorithm to optimize the control parameters of SGD method and aircraft shape. Two objective functions, low sonic boom and low wave drag, are considered in CSADE. Physically reasonable Pareto solutions are obtained from the present optimization. Some supersonic aircraft configurations are selected from Pareto front and the optimization results indicate that the swept forward wing configuration has benefits in both sonic boom reduction and wave drag reduction. The results are validated by using computational fluid dynamics (CFD) analysis.
Research of low boom and low drag supersonic aircraft design
Directory of Open Access Journals (Sweden)
Feng Xiaoqiang
2014-06-01
Full Text Available Sonic boom reduction will be an issue of utmost importance in future supersonic transport, due to strong regulations on acoustic nuisance. The paper describes a new multi-objective optimization method for supersonic aircraft design. The method is developed by coupling Seebass–George–Darden (SGD inverse design method and multi-objective genetic algorithm. Based on the method, different codes are developed. Using a computational architecture, a conceptual supersonic aircraft design environment (CSADE is constructed. The architecture of CSADE includes inner optimization level and out optimization level. The low boom configuration is generated in inner optimization level by matching the target equivalent area distribution and actual equivalent area distribution. And low boom/low drag configuration is generated in outer optimization level by using NSGA-II multi-objective genetic algorithm to optimize the control parameters of SGD method and aircraft shape. Two objective functions, low sonic boom and low wave drag, are considered in CSADE. Physically reasonable Pareto solutions are obtained from the present optimization. Some supersonic aircraft configurations are selected from Pareto front and the optimization results indicate that the swept forward wing configuration has benefits in both sonic boom reduction and wave drag reduction. The results are validated by using computational fluid dynamics (CFD analysis.
A diagnostic model to estimate winds and small-scale drag from Mars Observer PMIRR data
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.
Institute of Scientific and Technical Information of China (English)
YAO Yan; LU Chuan-jing; SI Ting; ZHU Kun
2011-01-01
Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted. A suit of traveling wavy wall device is developed. The drag forces of the traveling wavy wall with various wave speeds ( c ) are measured under different water speeds (U) in the K15 cavitation water tunnel and are compared with that of the flat plate. The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed.Under different flow speeds, when traveling wave wall reached to the minimum of drag force, the corresponding the ratio of the wall motion phase speed c to flow speed U, c/U is slightly different. Within the parameters of the experiment, when c/U reaches a certain value, the drag force of the traveling wavy wall can be less than that of the flat plate. The drag reduction can be up to 42％.Furthermore, as the value of c / U increases, the traveling wavy wall can restrain the separation and improve the quality of flow field.
Ship Hull Form Optimization by Evolutionary Algorithm in Order to Diminish the Drag
Institute of Scientific and Technical Information of China (English)
Hassan Zakerdoost; Hassan Ghassemi; Mahmoud Ghiasi
2013-01-01
This study presents a numerical method for optimizing hull form in calm water with respect to total drag which contains a viscous drag and a wave drag.The ITTC 1957 model-ship correlation line was used to predict frictional drag and the corrected linearized thin-ship theory was employed to estimate the wave drag.The evolution strategy (ES) which is a member of the evolutionary algorithms (EAs) family obtains an optimum hull form by considering some design constraints.Standard Wigley hull is considered as an initial hull in optimization procedures for two test cases and new hull forms were achieved at Froude numbers 0.24,0.316 and 0.408.In one case the ES technique was ran for the initial hull form,where the main dimensions were fixed and the only variables were the hull offsets.In the other case in addition to hull offsets,the main dimensions were considered as variables that are optimized simultaneously.The numerical results of optimization procedure demonstrate that the optimized hull forms yield a reduction in total drag.
Transformance: reading the gospel in drag.
McCune, Jeffrey Q
2004-01-01
Despite the large body of scholarship on drag and its performance of misogyny, mimicry, and masculinity, little attention has been paid to the role of musical genres in Black drag performance and its reception. This essay explores drag performances of gospel music and its relationship with the spectator at the Biology Bar, a Black gay drag site in Chicago. By examining the shift from the club "space" to the church "place," this research locates several possibilities for queer gospel performances. Through the introduction of a theory of transformance, this essay highlights the contradictions, complications, and complexities of the relationship between the Black church and the Black gay community.
DOE Project on Heavy Vehicle Aerodynamic Drag
Energy Technology Data Exchange (ETDEWEB)
McCallen, R; Salari, K; Ortega, J; Castellucci, P; Pointer, D; Browand, F; Ross, J; Storms, B
2007-01-04
Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At highway speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; (2) Develop innovative drag reducing concepts that are operationally and economically sound; and (3) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices. The studies described herein provide a demonstration of the applicability of the experience developed in the analysis of the standard configuration of the Generic Conventional Model. The modeling practices and procedures developed in prior efforts have been applied directly to the assessment of new configurations including a variety of geometric modifications and add-on devices. Application to the low-drag 'GTS' configuration of the GCM has confirmed that the error in predicted drag coefficients increases as the relative contribution of the base drag resulting from the vehicle wake to the total drag increases and it is recommended that more advanced turbulence modeling strategies be applied under those circumstances. Application to a commercially-developed boat tail device has confirmed that this restriction does not apply to geometries where the relative contribution of the base drag to the total drag is reduced by modifying the geometry in that region. Application to a modified GCM geometry with an open grille and radiator has confirmed that the underbody flow, while important for underhood cooling, has little impact on the drag
Extensibility enables locomotion under isotropic drag
Pak, On Shun
2011-01-01
Anisotropic viscous drag is usually believed to be a requirement for the low Reynolds number locomotion of slender bodies such as flagella and cilia. Here we show that locomotion under isotropic drag is possible for extensible slender bodies. After general considerations, a two-ring swimmer and a model dinoflagellate flagellum are studied analytically to illustrate how extensibility can be exploited for self-propulsion without drag anisotropy. This new degree of freedom could be useful for some complex swimmer geometries and locomotion in complex fluid environments where drag anisotropy is weak or even absent.
Improvements of evaporation drag model
Institute of Scientific and Technical Information of China (English)
LI Xiao-Yan; XU Ji-Jun
2004-01-01
A special visible experiment facility has been designed and built, and an observable experiment is performed by pouring one or several high-temperature particles into a water pool in the facility. The experiment result has verified Yang's evaporation drag model, which holds that the non-symmetric profile of the local evaporation rate and the local density of vapor would bring about a resultant force on the hot particle so as to resist its motion. However, in Yang's evaporation drag model, radiation heat transfer is taken as the only way to transfer heat from hot particle to the vapor-liquid interface, and all of the radiation energy is deposited on the vapor-liquid interface and contributed to the vaporization rate and mass balance of the vapor film. In improved model heat conduction and heat convection are taken into account. This paper presents calculations of the improved model, putting emphasis on the effect of hot particle's temperature on the radiation absorption behavior of water.
A relationship between wave steepness and wave age for wind waves in deep water
Institute of Scientific and Technical Information of China (English)
LIU Bin; DING Yun; GUAN Changlong
2007-01-01
Studying the relationship between wave steepness and wave age is import ant for describing wind wave growth with energy balance equation of significant waves. After invoking the dispersion relation of surface gravity wave in deep water, a new relationship between wave steepness and wave age is revealed based on the "3/2-power law" (Toba, 1972), in which wave steepness is a function of wave age with a drag coefficient as a parameter. With a given wave age, a larger drag coefficient would lead to larger wave steepness. This could be interpreted as the result of interaction between wind and waves.Comparing with previous relationships, the newly proposed one is more consistent with observational data in field and laboratory.
Numerically modelling tidal dissipation with bottom drag in the oceans of Titan and Enceladus
Hay, Hamish C. F. C.; Matsuyama, Isamu
2017-01-01
Icy satellites that contain subsurface oceans require sufficient thermal energy to prevent the liquid portion of their interiors from freezing. We develop a numerical finite difference model to solve the Laplace Tidal Equations on a sphere in order to simulate tidal flow and thermal energy dissipation in these oceans, neglecting the presence of an icy lid. The model is applied to Titan and Enceladus, where we explore how Rayleigh (linear) and bottom (quadratic) drag terms affect dissipation. The latter drag regime can only be applied numerically. We find excellent agreement between our results and recent analytical work. Obliquity tide Rossby-wave resonant features become independent of ocean thickness under the bottom drag regime for thick oceans. We show that for Titan, dissipation from this Rossby-wave resonance can act to dampen the rate of outward orbital migration by up to 40% for Earth-like values of bottom drag coefficient. Gravity-wave resonances can act to cause inward migration, although this is unlikely due to the thin oceans required to form such resonances. The same is true of all eccentricity tide resonances on Enceladus, such that dissipation becomes negligible for thick oceans under the bottom drag regime.
DEFF Research Database (Denmark)
Ibsen, Lars Bo
2008-01-01
Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many t...
Seagrass blade motion under waves and its impact on wave decay
Luhar, M.; Infantes, E.; Nepf, H.
2017-05-01
The hydrodynamic drag generated by seagrass meadows can dissipate wave-energy, causing wave decay. It is well known that this drag depends on the relative motion between the water and the seagrass blades, yet the impact of blade motion on drag and wave-energy dissipation remains to be fully characterized. In this experimental study, we examined the impact of blade motion on wave decay by concurrently recording blade posture during a wave cycle and measuring wave decay over a model seagrass meadow. We also identified a scaling law that predicts wave decay over the model meadow for a range of seagrass blade density, wave period, wave height, and water depth scaled from typical field conditions. Blade flexibility led to significantly lower drag and wave decay relative to theoretical predictions for rigid, upright blades. To quantify the impact of blade motion on wave decay, we employed an effective blade length, le, defined as the rigid blade length that leads to equivalent wave-energy dissipation. We estimated le directly from images of blade motion. Consistent with previous studies, these estimates showed that the effective blade length depends on the dimensionless Cauchy number, which describes the relative magnitude of the wave hydrodynamic drag and the restoring force due to blade rigidity. As the hydrodynamic forcing increases, the blades exhibit greater motion. Greater blade motion leads to smaller relative velocities, reducing drag, and wave-energy dissipation (i.e., smaller le).
Drag Coefficient of Thin Flexible Cylinder
Subramanian, Chelakara; Gurram, Harika
2015-11-01
Measurements of drag coefficients of thin flexible cylindrical wires are described for the Reynolds number range between 250 - 1000. Results indicate that the coefficient values are about 20 to 30 percent lower than the reported laminar flow values for rigid cylinders. Possible fluid dynamics mechanism causing the reduction in drag will be discussed.
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 ...
Polymer flexibility and turbulent drag reduction
Gillissen, J.J.J.
2008-01-01
Polymer-induced drag reduction is the phenomenon by which the friction factor of a turbulent flow is reduced by the addition of small amounts of high-molecular-weight linear polymers, which conformation in solution at rest can vary between randomly coiled and rodlike. It is well known that drag redu
DRAG ON SUBMICRON NANOPARTICLE AGGREGATES
Institute of Scientific and Technical Information of China (English)
F.; Einar; Kruis
2005-01-01
A new procedure was developed for estimating the effective collision diameter of an aggregate composed of primary particles of any size. The coagulation coefficient of two oppositely charged particles was measured experimentally and compared with classic Fuchs theory, including a new method to account for particle non-sphericity. A second set of experiments were performed on well-defined nanoparticle aggregates at different stages of sintering, i.e. from the aggregate to the fully sintered stage. Here, electrical mobility was used to characterize the particle drag. The aggregates are being built from two different size-fractionated nanoparticle aerosols, the non-aggregated particles are discarded by an electrofilter and then they are passed through a furnace at concentrations low enough not to induce coagulation.
Ultrafast photon drag detector for intersubband spectroscopy
Sigg, Hans; Graf, Stephan; Kwakernaak, Martin H.; Margotte, Bernd; Erni, Daniel; Van Son, Peter; Köhler, Klaus
1996-03-01
The photon drag effect of a 2D electron gas is measured using the ps infrared pulses of the wavelength-tunable free electron laser source FELIX. The pulsed photon drag response is found to depend critically on the coupling characteristics of the electrical circuit. We therefore developed an impedance and velocity matched photon drag detector. It consists of a GaAs/AlGaAs multi quantum well sample which forms an integral part of a microstrip line. A Ge-prism enables incoupling at the critical total reflection angle. This novel transmission line integrated photon drag detector (TIP-detector) generates signal transients below 10 ps rise and fall times. Its continuous spectral response through the intersubband resonance is investigated at room temperature and at T=100 K. An analysis of the spectral lineshape of the photon drag current response yields information about the momentum relaxation times of the electrons in the ground and excited subbands.
Drag Reduction by Microvortexes in Transverse Microgrooves
Directory of Open Access Journals (Sweden)
Bao Wang
2014-07-01
Full Text Available A transverse microgrooved surface was employed here to reduce the surface drag force by creating a slippage in bottom layer in turbulent boundary layer. A detailed simulation and experimental investigation on drag reduction by transverse microgrooves were given. The computational fluid dynamics simulation, using RNG k-ε turbulent model, showed that the vortexes were formed in the grooves and they were a main reason for the drag reduction. On the upside of the vortex, the revolving direction was consistent with the main flow, which decreased the flow shear stress by declining the velocity gradient. The experiments were carried out in a high-speed water tunnel with flow velocity varying from 17 to 19 m/s. The experimental results showed that the drag reduction was about 13%. Therefore, the computational and experimental results were cross-checked and consistent with each other to prove that the presented approach achieved effective drag reduction underwater.
Giant Frictional Drag in Double Bilayer Graphene Heterostructures
Lee, Kayoung; Xue, Jiamin; Dillen, David C.; Watanabe, Kenji; Taniguchi, Takashi; Tutuc, Emanuel
2016-07-01
We study the frictional drag between carriers in two bilayer graphene flakes separated by a 2-5 nm thick hexagonal boron nitride dielectric. At temperatures (T ) lower than ˜10 K , we observe a large anomalous negative drag emerging predominantly near the drag layer charge neutrality. The anomalous drag resistivity increases dramatically with reducing T , and becomes comparable to the layer resistivity at the lowest T =1.5 K . At low T the drag resistivity exhibits a breakdown of layer reciprocity. A comparison of the drag resistivity and the drag layer Peltier coefficient suggests a thermoelectric origin of this anomalous drag.
Numerical simulation for the influence of injected laser power on plasma drag reduction
Energy Technology Data Exchange (ETDEWEB)
Liu, Z; Fang, J [Department of Postgraduates, Academy of Equipment Command and Technology, 3380 Post box, Huairou Beijing 101416 (China); Dou, Z G; Huang, H, E-mail: liuzhun0@gmail.com [Department of Basic Theories, Academy of Equipment Command and Technology, 3380 Post box, Huairou Beijing 101416 (China)
2011-02-01
Laser plasma drag reduction is a new method to reduce the wave drag of hypersonic flight. Inject laser power is an important parameter. An appropriate laser power should be chosen when laser power was injected to achieve the best drag reduction effect via the minimum laser power. The effect of inject laser power on the performance of laser plasma drag reduction when incoming flight Mach number is 6.5 and at 30km altitude was simulated numerically. The result indicates that the drag can be effectively reduced by energy injection in the upstream flow. The larger the inject power is, the smaller the drag of the blunt body obtained. The energy injection can also influence the pressure and temperature on the surface of blunt body. When laser energy injected, high pressure region on the surface moves to the back of the hemisphere, the pressure of stagnation point decreased. There are two peaks of temperature on the blunt surface, one is the stagnation point and the other is the high pressure region. Temperature of the surface after high pressure region is lower comparison to the condition that no energy injected.
On the Minimum Induced Drag of Wings
Bowers, Albion H.
2011-01-01
Of all the types of drag, induced drag is associated with the creation and generation of lift over wings. Induced drag is directly driven by the span load that the aircraft is flying at. The tools by which to calculate and predict induced drag we use were created by Ludwig Prandtl in 1903. Within a decade after Prandtl created a tool for calculating induced drag, Prandtl and his students had optimized the problem to solve the minimum induced drag for a wing of a given span, formalized and written about in 1920. This solution is quoted in textbooks extensively today. Prandtl did not stop with this first solution, and came to a dramatically different solution in 1932. Subsequent development of this 1932 solution solves several aeronautics design difficulties simultaneously, including maximum performance, minimum structure, minimum drag loss due to control input, and solution to adverse yaw without a vertical tail. This presentation lists that solution by Prandtl, and the refinements by Horten, Jones, Kline, Viswanathan, and Whitcomb.
The role of drag in insect hovering.
Wang, Z Jane
2004-11-01
Studies of insect flight have focused on aerodynamic lift, both in quasi-steady and unsteady regimes. This is partly influenced by the choice of hovering motions along a horizontal stroke plane, where aerodynamic drag makes no contribution to the vertical force. In contrast, some of the best hoverers--dragonflies and hoverflies--employ inclined stroke planes, where the drag in the down- and upstrokes does not cancel each other. Here, computation of an idealized dragonfly wing motion shows that a dragonfly uses drag to support about three quarters of its weight. This can explain an anomalous factor of four in previous estimates of dragonfly lift coefficients, where drag was assumed to be small. To investigate force generation and energy cost of hovering flight using different combination of lift and drag, I study a family of wing motion parameterized by the inclined angle of the stroke plane. The lift-to-drag ratio is no longer a measure of efficiency, except in the case of horizontal stroke plane. In addition, because the flow is highly stalled, lift and drag are of comparable magnitude, and the aerodynamic efficiency is roughly the same up to an inclined angle about 60 degrees , which curiously agrees with the angle observed in dragonfly flight. Finally, the lessons from this special family of wing motion suggests a strategy for improving efficiency of normal hovering, and a unifying view of different wing motions employed by insects.
Coulomb drag between helical Luttinger liquids
Kainaris, N.; Gornyi, I. V.; Levchenko, A.; Polyakov, D. G.
2017-01-01
We theoretically study Coulomb drag between two helical edges with broken spin-rotational symmetry, such as would occur in two capacitively coupled quantum spin Hall insulators. For the helical edges, Coulomb drag is particularly interesting because it specifically probes the inelastic interactions that break the conductance quantization for a single edge. Using the kinetic equation formalism, supplemented by bosonization, we find that the drag resistivity ρD exhibits a nonmonotonic dependence on the temperature T . In the limit of low T ,ρD vanishes with decreasing T as a power law if intraedge interactions are not too strong. This is in stark contrast to Coulomb drag in conventional quantum wires, where ρD diverges at T →0 irrespective of the strength of repulsive interactions. Another unusual property of Coulomb drag between the helical edges concerns higher T for which, unlike in the Luttinger liquid model, drag is mediated by plasmons. The special type of plasmon-mediated drag can be viewed as a distinguishing feature of the helical liquid—because it requires peculiar umklapp scattering only available in the presence of a Dirac point in the electron spectrum.
Orographic drag uncertainties impact forecast skill
Sandu, Irina; Zadra, Ayrton; Wedi, Nils; Bacmeister, Julio
2017-04-01
Despite their importance for the large-scale circulation, to date the representation of drag processes remains a major source of uncertainty in global models. Among the different drag processes the representation of orographic drag is particularly challenging. This has been recently highlighted by the WMO Working Group on Numerical Experimentation (WGNE) 'Drag project' which demonstrated that the main NWP and climate models differ significantly in representation of the total parameterized surface stress and in the partitioning of surface stress among various physical processes, particularly in regions with orography. Here we discuss how uncertain is the representation of orographic drag in models, and we illustrate how this uncertainty affects the skill of medium range weather forecasts. Namely we show how different is the representation of the resolved orography even in models with similar headline horizontal resolution. We also use the results of the WGNE 'Drag project' to illustrate how much models differ in terms of the total parameterized surface stress and its partition among various processes. Finally, we use the Integrated Forecasting System of ECMWF to demonstrate how much these intermodel differences either in the resolved orography or the representation subgrid drag affect the forecast skill.
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...
Two—parameter—dependent Drag Coefficient Over Sea Surface by Turbulent Modeling
Institute of Scientific and Technical Information of China (English)
JiachunLI; ZifanZHANG
1999-01-01
A new model accounting for both turbulence and sea state effects has been proposed in the current paper to describe momentum exchange through air-sea interface.While long wave components mainly change air flow profile,short wave components exert their influences on the momentum exchange via turbulent stress,which leads to the growth of drag coefficients by a factor of two in young wave age circumstances,As a typical case study,we have considered neutral ABL over a representative regular wave with roughness due to short capillary wves riding over it.The results by the pressent model are in reasonable agreement with Maat's analysis numerically fitted by HEXMAX data and Janssen's results.Two parameter dependence of drag coefficient can resolve the existing discrepency between theory and observations.
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.
Drag Reduction by Leidenfrost Vapor Layers
Vakarelski, Ivan U.; Marston, Jeremy O.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.
2011-05-01
We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.
Frame-Dragging from Charged Rotating Body
Dubey, Anuj Kumar
2016-01-01
In the present paper, we have considered the three parameters: mass, charge and rotation to discuss their combined effect on frame dragging for a charged rotating body. If we consider the ray of light which is emitted radially outward from a rotating body then the frame dragging shows a periodic nature with respect to coordinate $\\phi$ (azimuthal angle). It has been found that the value of frame dragging obtains a maximum at, $ \\phi =\\frac{\\pi}{2}$ and a minimum at $ \\phi =\\frac{3 \\pi}{2}$.
Drag Reduction by Leidenfrost Vapor Layers
Vakarelski, Ivan Uriev
2011-05-23
We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.
Reynolds-dependence of turbulent skin-friction drag reduction induced by spanwise forcing
Gatti, Davide
2015-01-01
This paper examines how increasing the value of the Reynolds number $Re$ affects the ability of spanwise-forcing techniques to yield turbulent skin-friction drag reduction. The control strategy is the streamwise-travelling waves of spanwise wall velocity (Quadrio {\\em et al. J. Fluid Mech.}, vol. 627, 2009, pp. 161--178). The study builds upon an extensive drag-reduction database created with Direct Numerical Simulation of a turbulent channel flow for two, 5-fold separated values of $Re$, namely $Re_\\tau=200$ and $Re_\\tau=1000$. The sheer size of the database, which for the first time systematically addresses the amplitude of the forcing, allows a comprehensive view of the drag-reducing characteristics of the traveling waves, and enables a detailed description of the changes occurring when $Re$ increases. The effect of using a viscous scaling based on the friction velocity of either the non-controlled flow or the drag-reduced flow is described. In analogy with other wall-based drag reduction techniques, like ...
Observation and numerical experiments for drag coefficient under typhoon wind forcing
Cao, Huiqiu; Zhou, Liangming; Li, Shuiqing; Wang, Zhifeng
2017-02-01
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 ( C d ) 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.
Kyle, H. C.
1976-01-01
The Analytic Drag Control (ADC) entry guidance has been developed and baselined for the space shuttle orbiter entry. A method is presented which corrects the orbiter entry guidance commanded bank angle for biases between navigated drag and guidance computed reference drag. This is accomplished by an integral feedback technique, which uses the drag bias information to adjust the difference between navigated and reference altitude rate used by the ADC guidance. The method improves the capability of the ADC guidance system by compensating for any error source which causes a bias between the navigated drag and reference drag profile. These errors include navigated altitude rate errors, atmosphere dispersions, and roll attitude deadband effects. A discussion of the method and results of digital computer entry simulations is presented.
Bubble Drag Reduction Requires Large Bubbles
Verschoof, Ruben A.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef
2016-09-01
In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.
Bubble drag reduction requires large bubbles
Verschoof, Ruben A; Sun, Chao; Lohse, Detlef
2016-01-01
In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.
Methods of reducing vehicle aerodynamic drag
Energy Technology Data Exchange (ETDEWEB)
Sirenko V.; Rohatgi U.
2012-07-08
A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.
Drag sails for space debris mitigation
Visagie, Lourens; Lappas, Vaios; Erb, Sven
2015-04-01
The prudence for satellites to have a mitigation or deorbiting strategy has been brought about by the ever increasing amount of debris in Earth orbit. Drag augmentation is a potentially passive method for de-orbiting in LEO but its collision risk mitigation efficiency is sometimes underestimated by not taking all the relevant factors into account. This paper shows that using drag augmentation from a deployable drag-sail to de-orbit a satellite in LEO will lead to a reduction in collision risk. In order to support this finding, the models that are needed in order to evaluate the collision risk of a decaying object under drag conditions are presented. A comparison is performed between the simpler Area-Time-Product (ATP) and more precise collision risk analysis, and the effects that are overlooked in the simple ATP calculation are explained.
Integrated lift/drag controller for aircraft
Olcott, J. W.; Seckel, E.; Ellis, D. R. (Inventor)
1974-01-01
A system for altering the lift/drag characteristics of powered aircraft to provide a safe means of glide path control includes a control device integrated for coordination action with the aircraft throttle. Such lift/drag alteration devices as spoilers, dive brakes, and the like are actuated by manual operation of a single lever coupled with the throttle for integrating, blending or coordinating power control. Improper operation of the controller is inhibited by safety mechanisms.
Flow drag and heat transfer characteristics of drag-reducing nanofluids with CuO nanoparticles
Wang, Ping-Yang; Wang, Xue-Jiao; Liu, Zhen-Hua
2017-02-01
A new kind of aqueous CuO nanofluid with drag-reducing performance was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CuO nanoparticles added and has both special effects of drag-reducing and heat transfer enhancement. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube with an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag reducing fluid and new drag-reducing nanofluid. However, their heat transfer characteristics were obvious different. The heat transfer characteristics of the new drag-reducing nanofluid significantly depend on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be applied to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.
Flow drag and heat transfer characteristics of drag-reducing nanofluids with CuO nanoparticles
Wang, Ping-Yang; Wang, Xue-Jiao; Liu, Zhen-Hua
2016-05-01
A new kind of aqueous CuO nanofluid with drag-reducing performance was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CuO nanoparticles added and has both special effects of drag-reducing and heat transfer enhancement. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube with an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag reducing fluid and new drag-reducing nanofluid. However, their heat transfer characteristics were obvious different. The heat transfer characteristics of the new drag-reducing nanofluid significantly depend on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be applied to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.
Bioinspired surfaces for turbulent drag reduction.
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'.
Cotunneling Drag Effect in Coulomb-Coupled Quantum Dots
Keller, A. J.; Lim, J. S.; Sánchez, David; López, Rosa; Amasha, S.; Katine, J. A.; Shtrikman, Hadas; Goldhaber-Gordon, D.
2016-08-01
In Coulomb drag, a current flowing in one conductor can induce a voltage across an adjacent conductor via the Coulomb interaction. The mechanisms yielding drag effects are not always understood, even though drag effects are sufficiently general to be seen in many low-dimensional systems. In this Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot and, through both experimental and theoretical arguments, identify cotunneling as essential to obtaining a correct qualitative understanding of the drag behavior.
Hydrodynamic Drag on Streamlined Projectiles and Cavities
Jetly, Aditya
2016-04-19
The air cavity formation resulting from the water-entry of solid objects has been the subject of extensive research due to its application in various fields such as biology, marine vehicles, sports and oil and gas industries. Recently we demonstrated that at certain conditions following the closing of the air cavity formed by the initial impact of a superhydrophobic sphere on a free water surface a stable streamlined shape air cavity can remain attached to the sphere. The formation of superhydrophobic sphere and attached air cavity reaches a steady state during the free fall. In this thesis we further explore this novel phenomenon to quantify the drag on streamlined shape cavities. The drag on the sphere-cavity formation is then compared with the drag on solid projectile which were designed to have self-similar shape to that of the cavity. The solid projectiles of adjustable weight were produced using 3D printing technique. In a set of experiments on the free fall of projectile we determined the variation of projectiles drag coefficient as a function of the projectiles length to diameter ratio and the projectiles specific weight, covering a range of intermediate Reynolds number, Re ~ 104 – 105 which are characteristic for our streamlined cavity experiments. Parallel free fall experiment with sphere attached streamlined air cavity and projectile of the same shape and effective weight clearly demonstrated the drag reduction effect due to the stress-free boundary condition at cavity liquid interface. The streamlined cavity experiments can be used as the upper bound estimate of the drag reduction by air layers naturally sustained on superhydrophobic surfaces in contact with water. In the final part of the thesis we design an experiment to test the drag reduction capacity of robust superhydrophobic coatings deposited on the surface of various model vessels.
Solute drag on perfect and extended dislocations
Sills, R. B.; Cai, W.
2016-04-01
The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction ?, and the dislocation character angle ?, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.
Tuned liquid dampers with a Keulegan-Carpenter number-dependent screen drag coefficient
Hamelin, J. A.; Love, J. S.; Tait, M. J.; Wilson, J. C.
2013-11-01
The amplitude-dependent damping associated with a tuned liquid damper (TLD) equipped with slat-type screens produces a device that performs optimally at a targeted response amplitude. Increasing the slat height produces a screen whose drag coefficient is dependent on the Keulegan-Carpenter number (KC), which may improve the TLD performance. This new type of TLD is modeled as an equivalent mechanical model with damping that is dependent on both KC and the response amplitude. An experimental shake table testing program is undertaken to study the influence of KC on the TLD response and to validate the model. A power fit is performed on the experimentally determined screen drag coefficient and KC values to express the drag coefficient as a function of KC and the steady flow drag coefficient. Predicted frequency response plots of sloshing forces and energy dissipation per cycle are in agreement with experimental results. A structure-TLD system model is developed to theoretically study the performance of this new TLD. Nonlinear shallow water wave theory is used to validate the output of the mechanical model. Results indicate that a KC-dependent screen drag coefficient produces a more robust TLD whose performance is maintained over a broader range of structural response amplitudes.
On the horseshoe drag of a low-mass planet. I - Migration in isothermal disks
Casoli, J
2009-01-01
We investigate the unsaturated horseshoe drag exerted on a low-mass planet by an isothermal gaseous disk. In the globally isothermal case, we use a formal- ism, based on the use of a Bernoulli invariant, that takes into account pressure effects, and that extends the torque estimate to a region wider than the horse- shoe region. We find a result that is strictly identical to the standard horseshoe drag. This shows that the horseshoe drag accounts for the torque of the whole corotation region, and not only of the horseshoe region, thereby deserving to be called corotation torque. We find that evanescent waves launched downstream of the horseshoe U-turns by the perturbations of vortensity exert a feed-back on the upstream region, that render the horseshoe region asymmetric. This asymmetry scales with the vortensity gradient and with the disk's aspect ratio. It does not depend on the planetary mass, and it does not have any impact on the horseshoe drag. Since the horseshoe drag has a steep dependence on the width...
Lift and Drag Measurements of Superhydrophobic Hydrofoils
Sur, Samrat; Kim, Jeong-Hyun; Rothstein, Jonathan
2015-11-01
For several years, superhydrophobic surfaces which are chemically hydrophobic with micron or nanometer scale surface features have been considered for their ability to reduce drag and produce slip in microfluidic devices. More recently it has been demonstrated that superhydrophobic surfaces reduce friction coefficient in turbulent flows as well. In this talk, we will consider that modifying a hydrofoil's surface to make it superhydrophobic has on the resulting lift and drag measurements over a wide range of angles of attack. Experiments are conducted over the range of Reynolds numbers between 10,000hydrofoil is made superhydrophobic. The hydrofoils are coated Teflon that has been hot embossed with a 325grit stainless steel woven mesh to produce a regular pattern of microposts. In addition to fully superhydrophobic hydrofoils, selectively coated symmetrical hydrofoils will also be examined to study the effect that asymmetries in the surface properties can have on lift and drag. Partially funded by NSF CBET-1334962.
Locomotion and drag in wet and dry granular media
Goldman, Daniel; Kuckuk, Robyn; Sharpe, Sarah
2015-03-01
Many animals move within substrates such as soil and dry sand; the resistive properties of such granular materials (GM) can depend on water content and compaction, but little is known about how such parameters affect locomotion or the relevant physics of drag and penetration. We developed a system to create homogeneous wet GM of varying moisture content and compaction in quantities sufficient to study the burial and subsurface locomotion of the Ocellated skink (C. ocellatus) a desert-generalist lizard. X-ray imaging revealed that in wet and dry GM the lizard slowly buried (~ 30 seconds) propagating a wave from head to tail, while moving in a start-stop motion. During forward movement, the head oscillated, and the forelimb on the convex side of the body propelled the animal. Although body kinematics (and ``slip'') were similar in both substrates, the burial depth was smaller in wet GM. Penetration and drag force experiments on smooth cylinders revealed that wet GM was ~ 3 × more resistive than dry GM, suggesting that during burial the lizard operated near its maximum force producing capability and was thus constrained by environmental properties. work supported by NSF PoLS.
Induce Drag Reduction of an Airplane Wing
Directory of Open Access Journals (Sweden)
Md. Fazle Rabbi
2015-06-01
Full Text Available This work describes the aerodynamic characteristics for aircraft wing model with and without slotted winglet. When an aircraft moves forward with a high speed then a small circulatory motion of air is created at the wingtip due to the pressure difference between the upper and lower surface of the wing is called vortices. This circulatory fluid tends to leak from lower to upper surface of wing which causes downward motion is called “downwash” and generates a component of the local lift force in the direction of the free stream called induced drag. Downwash causes reduction of lift and contribute induced drag to the total drag. Drag reduction for aerial vehicles has a range of positive ramifications: reduced fuel consumption, larger operational range, greater endurance and higher achievable speeds. An experimental study is conducted to examine the potentiality of slotted winglet for the reduction of induced drag, and for the improvement of lift coefficient without increasing the span of aircraft wing. The model composed of a swept wing built from NACA 0012 airfoil. The test conducted in subsonic wind tunnel of 1m×1m rectangular test section at flow speed 25m/s placing the wing without winglet, wing with winglet at 30° inclination, wing with winglet at 60° inclination, and wing with winglet at 70° inclination at angle of attack ranging from 0 to 16 degree. The test result shows 20- 25% reduction in drag coefficient and 10-20% increase in lift coefficient by using slotted winglet.
Barotropic Turbulence on a Beta-Plane with Quadratic Bottom Drag
Kong, H.; Jansen, M.
2016-12-01
Geostrophic turbulent eddies are crucial in the oceans because they play a major role in transporting and mixing physical quantities and chemical constituents. However, it would be too computationally expensive for current IPCC-class models to fully resolve them, calling for proper parameterizations. Many of the key properties of geostrophic turbulence are captured by barotropic (2D) turbulence, which thus serves as a useful model to develop a fundamental understanding of meso-scale turbulence in the ocean. Although barotropic turbulence has received significant attention in the literature, the arguably most realistic case of beta-plane turbulence with quadratic bottom drag remains unexplored. The beta-effect and bottom drag both affect the halting scale of the inverse energy cascade - while quadratic drag can halt the cascade by removing eddy kinetic energy (EKE) out of the system, the beta effect introduces a wave-turbulence crossover and causes a channeling of energy into zonal jets. The characteristics of the flow are governed by a single non-dimensional parameter, which can be expressed as the ratio of the frictional halting scale and the wave-turbulence crossover scale. In a regime most relevant to Earth's ocean, we find that the eddy mixing length is significantly suppressed by the beta-effect and well approximated by the Rhines scale. The EKE level instead remains controlled by the bottom drag. This allows us to derive a parameterization for the eddy diffusivity which agrees well with the eddy diffusivity diagnosed from our model.
Balancing acts: drag queens, gender and faith.
Sullivan-Blum, Constance R
2004-01-01
While engaged in research on the same-sex marriage debate in mainline denominations, I interviewed 23 LGBT Christians, four of whom were drag queens. While it is not possible to generalize from such a small sample, the drag queens in this study insist on maintaining their identity as Christians despite the hegemonic discourse that renders faith and LGBT identities mutually exclusive. They developed innovative approaches to reconciling their gender and sexual identities with their spirituality. Their innovations are potentially liberating not just for them personally, but for LGBT people generally because they challenge Christianity's rigid dichotomies of gender and sexuality.
New drag laws for flapping flight
Agre, Natalie; Zhang, Jun; Ristroph, Leif
2014-11-01
Classical aerodynamic theory predicts that a steadily-moving wing experiences fluid forces proportional to the square of its speed. For bird and insect flight, however, there is currently no model for how drag is affected by flapping motions of the wings. By considering simple wings driven to oscillate while progressing through the air, we discover that flapping significantly changes the magnitude of drag and fundamentally alters its scaling with speed. These measurements motivate a new aerodynamic force law that could help to understand the free-flight dynamics, control, and stability of insects and flapping-wing robots.
Lateral-drag Casimir forces induced by anisotropy
Nefedov, Igor S
2016-01-01
We predict the existence of lateral drag forces near the flat surface of an absorbing slab of an anisotropic material. The forces originate from the fluctuations of the electromagnetic field, when the anisotropy axis of the material forms a certain angle with the surface. In this situation, the spatial spectra of the fluctuating electromagnetic fields becomes asymmetric, different for positive and negative transverse wave vectors components. Differently from the case of van der Waals interactions in which the forward-backward symmetry is broken due to the particle movement or in quantum noncontact friction where it is caused by the mutual motion of the bodies, in our case the lateral motion results merely from the anisotropy of the slab. This new effect, of particular significance in hyperbolic materials, could be used for the manipulation of nanoparticles.
Lateral-drag propulsion forces induced by anisotropy.
Nefedov, Igor S; Rubi, J Miguel
2017-07-21
We predict the existence of lateral drag forces near the flat surface of an absorbing slab made of an anisotropic material. The forces originate from the fluctuations of the electromagnetic field, when the anisotropy axis of the material forms a certain angle with the surface. In this situation, the spatial spectra of the fluctuating electromagnetic fields becomes asymmetric, different for positive and negative transverse wave vectors components. Differently from the case of van der Waals interactions in which the forward-backward symmetry is broken due to the particle movement, in our case the lateral motion results merely from the anisotropy of the slab. This new effect, of particular significance in hyperbolic materials, could be used for the manipulation of nanoparticles.
Diffusion equation and spin drag in spin-polarized transport
DEFF Research Database (Denmark)
Flensberg, Karsten; Jensen, Thomas Stibius; Mortensen, Asger
2001-01-01
We study the role of electron-electron interactions for spin-polarized transport using the Boltzmann equation, and derive a set of coupled transport equations. For spin-polarized transport the electron-electron interactions are important, because they tend to equilibrate the momentum of the two-spin...... species. This "spin drag" effect enhances the resistivity of the system. The enhancement is stronger the lower the dimension is, and should be measurable in, for example, a two-dimensional electron gas with ferromagnetic contacts. We also include spin-flip scattering, which has two effects......: it equilibrates the spin density imbalance and, provided it has a non-s-wave component, also a current imbalance....
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.
ABM Drag_Pass Report Generator
Fisher, Forest; Gladden, Roy; Khanampornpan, Teerapat
2008-01-01
dragREPORT software was developed in parallel with abmREPORT, which is described in the preceding article. Both programs were built on the capabilities created during that process. This tool generates a drag_pass report that summarizes vital information from the MRO aerobreaking drag_pass build process to facilitate both sequence reviews and provide a high-level summarization of the sequence for mission management. The script extracts information from the ENV, SSF, FRF, SCMFmax, and OPTG files, presenting them in a single, easy-to-check report providing the majority of parameters needed for cross check and verification as part of the sequence review process. Prior to dragReport, all the needed information was spread across a number of different files, each in a different format. This software is a Perl script that extracts vital summarization information and build-process details from a number of source files into a single, concise report format used to aid the MPST sequence review process and to provide a high-level summarization of the sequence for mission management reference. This software could be adapted for future aerobraking missions to provide similar reports, review and summarization information.
Turbulent drag reduction in dilute polymer solutions
Sreenivasan, K. R.; White, Christopher M.
1998-11-01
It is well known that the addition of small amounts of flexible polymers reduces drag in turbulent pipe flows. However, the underlying physics is still poorly understood. This paper will consider two aspects: The dependence of the onset of drag reduction on polymer concentration, and the so-called maximum drag reduction asymptote. The latter defines the maximum drag reduction possible for any polymer at a given Reynolds number, independent of the polymer concentration and detailed polymeric structure [1]. It is shown tentatively that a modest reworking of de Gennes' theory [2] is compatible with available experimental data. The principal element of the theory is that the polymers do not get stretched fully, but that the partially extended polymers store elastic energy and interfere with cascade mechanisms in turbulence. A conclusive understanding requires experiments in which the polymer properties that go into the theory are directly measured. [1] P.S. Virk, AIChE J., 21, 625 (1975) [2] P.G. de Gennes, Introduction to Polymer Dynamics, University of Cambridge (1990)
Drag reduction using slippery liquid infused surfaces
Hultmark, Marcus; Stone, Howard; Smits, Alexander; Jacobi, Ian; Samaha, Mohamed; Wexler, Jason; Shang, Jessica; Rosenberg, Brian; Hellström, Leo; Fan, Yuyang
2013-11-01
A new method for passive drag reduction is introduced. A surface treatment inspired by the Nepenthes pitcher plant, previously developed by Wong et al. (2011), is utilized and its design parameters are studied for increased drag reduction and durability. Nano- and micro-structured surfaces infused with a lubricant allow for mobility within the lubricant itself when the surface is exposed to flow. The mobility causes slip at the fluid-fluid interface, which drastically reduces the viscous friction. These new surfaces are fundamentally different from the more conventional superhydrophobic surfaces previously used in drag reduction studies, which rely on a gas-liquid interface. The main advantage of the liquid infused surfaces over the conventional surfaces is that the lubricant adheres more strongly to the surface, decreasing the risk of failure when exposed to turbulence and other high-shear flows. We have shown that these surfaces can reduce viscous drag up to 20% in both Taylor-Couette flow and in a parallel plate rheometer. Supported under ONR Grants N00014-12-1-0875 and N00014-12-1-0962 (program manager Ki-Han Kim).
Explicitly Stochastic Parameterization of Nonorographic Gravity-Wave Drag
2010-01-01
τb exp [ − (c− coff ) 2 c2w ] , (1) τb = τ ∗ b F (φ, t), (2) with a phase-speed width cw = 30 m s −1. τb is the “background” momentum flux and is...equispaced distribution of ground-based horizontal phase speeds cj = coff + j∗∆c, (3) j∗ = −nc,−nc + 1, . . .+ nc − 1,+nc = j − nc + 1, (j∗ ∈ Z, nc ∈ N...distribution is symmetric about coff and thus samples (1) symmetrically about it’s peak. In the Garcia et al. (2007) formulation, coff = Usrc = |Usrc|, where
Nacelle drag reduction: An analytically-guided experimental program
Smetana, F. O.
1975-01-01
Modifications are proposed to standard estimating procedures, as well as the BODY computer program, which predict that the drag of two nacelles will equal the drag of the fuselage. A preliminary computer analysis that considers increased dimensions for the nacelle forebody so that the noise is relatively less blunt indicates a reduction in form drag much greater than the increase in skin friction drag attributable to increased surface area.
Navier slip model of drag reduction by Leidenfrost vapour layers
Berry, Joseph D; Vakarelski, Ivan U.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.
2016-01-01
Recent experiments found that a hot solid sphere that is able to sustain a stable Leidenfrost vapour layer in a liquid exhibits significant drag reduction during free fall. The variation of the drag coefficient with Reynolds number shows substantial deviation from the characteristic drag crisis behavior at high Reynolds numbers. Results obtained with liqiuds of different viscosities show that onset of the drag crisis depends on the viscosity ratio of the vapor to the liquid. The key feature o...
Investigation into the Mechanism of Polymer Thread Drag Reduction
1990-01-01
drag reducers than polyacrylamides of equal molecular weight. The drag reduction increases as the Re or Cm increases. The concentrations of polymer...wall region, 10 < y’ < 100, for drag reduction to occur. The normalized distance from the wall is defined as y* = yut/v; u, is the friction velocity...AP 30, a polyacrylamide solution, with a 5000 ppm concentration on the centerline of a water flow in a glass tube, they achieved drag reduction up to
14 CFR 25.697 - Lift and drag devices, controls.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Lift and drag devices, controls. 25.697....697 Lift and drag devices, controls. (a) Each lift device control must be designed so that the pilots....101(d). Lift and drag devices must maintain the selected positions, except for movement produced by an...
14 CFR 25.699 - Lift and drag device indicator.
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Lift and drag device indicator. 25.699....699 Lift and drag device indicator. (a) There must be means to indicate to the pilots the position of each lift or drag device having a separate control in the cockpit to adjust its position. In addition...
Innovative Flow Control Concepts for Drag Reduction
Lin, John C.; Whalen, Edward A.; Eppink, Jenna L.; Siochi, Emilie J.; Alexander, Michael G.; Andino, Marlyn Y.
2016-01-01
This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wing's leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs
Research on Drag Torque Prediction Model for the Wet Clutches
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equivalent radius is a function of clutch speed and flow rate. The drag torque achieves its peak at a critical speed. Above this speed, drag torque drops due to the shrinking of the oil film. The model also points out that viscosity and flow rate effects on drag torque. Experimental results indicate that the model is reasonable and it performs well for predicting the drag torque peak.
Analytically Derived Wind Wave Growth Relations
Institute of Scientific and Technical Information of China (English)
管长龙; 孙群
2002-01-01
By the use of the 3/2 power law presented by Toba combined with the significant wave energy balance equation forwind wave, wind wave growth at a limited fetch is analytically investigated. The new wind wave growth relations(WWGRs) are analytically derived with sheltering coefficient and wind drag coefficient as parameters. The geometricalaverage of observational values of sheltering coefficient and the arithmetic average of observational values of wind drag co-efficient are applied to determine the new WWGRs. Comparisons with existing empirical WWGRs are made.
The other optimal Stokes drag profile
Montenegro-Johnson, Thomas D
2014-01-01
The lowest drag shape of fixed volume in Stokes flow has been known for some 40 years. It is front-back symmetric and similar to an American football with ends tangent to a cone of 60 degrees. The analogous convex axisymmetric shape of fixed surface area, which may be of interest for particle design in chemistry and colloidal science, is characterized in this paper. This "other" optimal shape has a surface vorticity proportional to the mean surface curvature, which is used with a local analysis of the flow near the tip to show that the front and rear ends are tangent to a cone of angle 30.8 degrees. Using the boundary element method, we numerically represent the shape by expanding its tangent angle in terms decaying odd Legendre modes, and show that it has 11.3% lower drag than a sphere of equal surface area, significantly more pronounced than for the fixed-volume optimal.
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......) is evaluated using diagrammatic techniques. The transresistivity is given by an integral over energy and momentum transfer weighted by the product of the screened interlayer interaction and the phase space for scattering events. We demonstrate, by a numerical analysis of the transresistivity, that for well...
Drag Reduction by Polymeric and Nonpolymeric Additives
White, Christopher; Sreenivasan, K. R.
1997-11-01
To investigate the ``self-healing'' property of drag reducing surfactant micelles we have conducted a comparative study between high polymers and surfactants in six turbulent pipe flows (Reynolds numbers between 2000 and 90,000) with varying intensities o f secondary flow. Friction factor values are measured in a straight pipe of 185 diameters; three pipes, each turning through four 90 degree elbows, of lengths 1085 diameters, 875 diameters, and 600 diameters; and a twice-turned coiled pipe, radius of curv ature of 24 diameters and length of 290 diameters. All the flows are gravity driven to prevent degradation effects caused by pump impellers. The large stresses set up by the secondary flows degrade the fragile polymers, thus reducing their effectivness as a drag reducer. The ``self-healing'' of the micelles enables the surfactant to maintain its effectivness. We will present the ``self-healing'' characteristics of the surfactant micelles using the polymer data as the datum.
Investigation on Drag Reduction of Trucks
Institute of Scientific and Technical Information of China (English)
QI Xiao-ni; LIU Zhen-yan
2008-01-01
A study of the mechanism of fences was given to reduce drag by means of theoretical analysis, numerical simulation and experimental research. A 3D mathematical model has been developed based on computational fluid dynamics software Phoenics that was capable of handling steady state, 3D flow to simulate the flow field around the truck. The experiment made in a low speed wind tunnel is used as references for validation. By analyzing the results of calculation and experiment, the flowing mechanism of the flow field around the container truck and the drag-reducing mechanism of #-shaped fences on the truck are unveiled, which provides theoretical guidance to the aerodynamic formation designing and amelioration.
1D-1D Coulomb drag in a 6 Million Mobility Bi-layer Heterostructure
Bilodeau, Simon; Laroche, Dominique; Xia, Jian-Sheng; Lilly, Mike; Reno, John; Pfeiffer, Loren; West, Ken; Gervais, Guillaume
We report Coulomb drag measurements in vertically-coupled quantum wires. The wires are fabricated in GaAs/AlGaAs bilayer heterostructures grown from two different MBE chambers: one at Sandia National Laboratories (1.2M mobility), and the other at Princeton University (6M mobility). The previously observed positive and negative drag signals are seen in both types of devices, demonstrating the robustness of the result. However, attempts to determine the temperature dependence of the drag signal in the 1D regime proved challenging in the higher mobility heterostructure (Princeton), in part because of difficulties in aligning the wires within the same transverse subband configuration. Nevertheless, this work, performed at the Microkelvin laboratory of the University of Florida, is an important proof-of-concept for future investigations of the temperature dependence of the 1D-1D drag signal down to a few mK. Such an experiment could confirm the Luttinger charge density wave interlocking predicted to occur in the wires. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL8500.
Drag-free Spacecraft Technologies: criticalities in the initialization of geodesic motion
Zanoni, Carlo
2016-01-01
Present and future space missions rely on systems of increasingly demanding performance for being successful. Drag-free technology is one of the technologies that is fundamental for LISA-Pathfinder, an ESA mission whose launch is planned for the end of September 2015. A purely drag-free object is defined by the absence of all external forces other than gravity. This is not a natural condition and thus requires a proper design of a spacecraft, whose core is an object in free-fall, called test mass (TM). The purity of the drag-free orbit depends on the spacecraft capability of protecting the TM from disturbances, which indeed has limitations. According to a NASA study, such a concept provides substantial economies for LEO satellites. At the same time, a drag-free motion is required in many missions of fundamental physics. eLISA is an ESA concept mission aimed at opening a new window to the universe, black holes, and massive binary systems by means of gravitational waves. LISA-Pathfinder is in charge of proving ...
What happens to turbulent skin-friction drag reduction at high $Re$?
Gatti, Davide
2012-01-01
We address one of the capital problems in the field of turbulent skin-friction drag reduction, i.e. the performance of the known techniques at high values of the Reynolds number $Re$. We limit ourselves to considering open-loop techniques based on spanwise forcing (oscillating wall, streamwise-travelling waves), and explore via Direct Numerical Simulations (DNS) how quickly the drag reduction and net energy savings decrease when the friction Reynolds number is increased. We suggest an unexpected and interesting scenario where the performance of the drag-reduction technique degrade with $Re$ with a markedly different rate depending on the parameters. In particular, the known optimal region turns out to be such at low-$Re$ only, since there drag reduction degrades quite fast with $Re$, in line with available results. However, other regions are much less sensitive to $Re$, or insensitive at all. If one considers that the energy required to create the forcing presents a slightly favorable trend with $Re$, the pos...
Gunther, Neil J
2012-01-01
The electrical power consumed by typical magnetic hard disk drives (HDD) not only increases linearly with the number of spindles but, more significantly, it increases as very fast power-laws of speed (RPM) and diameter. Since the theoretical basis for this relationship is neither well-known nor readily accessible in the literature, we show how these exponents arise from aerodynamic disk drag and discuss their import for green storage capacity planning.
Satellite Formation Control Using Atmospheric Drag
2007-03-01
all cases tested, and the eccentricity-minimizing control law was able to maintain the position within 4.17 feet. More recently, Wedekind considered...three different formations, in-plane, in-track, and circular, was considered. Wedekind achieved favorable results for these three formations when the...and Kluwer Academic Publishers, 2004. 23. Wedekind , James T. Characterizing and Controlling the Effects of Differential Drag on Satellite Formations
Drag Reduction, from Bending to Pruning
Lopez, Diego; Michelin, Sébastien; de Langre, Emmanuel
2013-01-01
Most plants and benthic organisms have evolved efficient reconfiguration mechanisms to resist flow-induced loads. These mechanisms can be divided into bending, in which plants reduce their sail area through elastic deformation, and pruning, in which the loads are decreased through partial breakage of the structure. In this work, we show by using idealized models that these two mechanisms or, in fact, any combination of the two, are equally efficient to reduce the drag experienced by terrestrial and aquatic vegetation.
Satellite Attitude Control Using Atmospheric Drag
2007-03-01
Astronautics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In...yaw axes and provide magnetic damping on both the pitch and yaw axes. The satellite resem- bles a shuttlecock used in badminton (see Figure 2.2). The...Control Using Atmospheric Drag Guettler, David B., Captain, USAF Air Force Institute of Technology Graduate School of Engineering and Management (AFIT
Phonon-drag effects on thermoelectric power
Wu, M. W.; Horing, N. J. M.; Cui, H. L.
1995-01-01
We carry out a calculation of the phonon-drag contribution $S_g$ to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to the weakly nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation times due to phonon-phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at hi...
Stokes’ and Lamb's viscous drag laws
Eames, I.; Klettner, C. A.
2017-03-01
Since Galileo used his pulse to measure the time period of a swinging chandelier in the 17th century, pendulums have fascinated scientists. It was not until Stokes' (1851 Camb. Phil. Soc. 9 8-106) (whose interest was spurred by the pendulur time pieces of the mid 19th century) treatise on viscous flow that a theoretical framework for the drag on a sphere at low Reynolds number was laid down. Stokes' famous drag law has been used to determine two fundamental physical constants—the charge on an electron and Avogadro's constant—and has been used in theories which have won three Nobel prizes. Considering its illustrious history it is then not surprising that the flow past a sphere and its two-dimensional analog, the flow past a cylinder, form the starting point of teaching flow past a rigid body in undergraduate level fluid mechanics courses. Usually starting with the two-dimensional potential flow past a cylinder, students progress to the three-dimensional potential flow past a sphere. However, when the viscous flow past rigid bodies is taught, the three-dimensional example of a sphere is first introduced, and followed by (but not often), the two-dimensional viscous flow past a cylinder. The reason why viscous flow past a cylinder is generally not taught is because it is usually explained from an asymptotic analysis perspective. In fact, this added mathematical complexity is why the drag on a cylinder was only solved in 1911, 60 years after the drag on a sphere. In this note, we show that the viscous flow past a cylinder can be explained without the need to introduce any asymptotic analysis while still capturing all the physical insight of this classic fluid mechanics problem.
Space Age Swimsuit Reduces Drag, Breaks Records
2008-01-01
A space shuttle and a competitive swimmer have a lot more in common than people might realize: Among other forces, both have to contend with the slowing influence of drag. NASA s Aeronautics Research Mission Directorate focuses primarily on improving flight efficiency and generally on fluid dynamics, especially the forces of pressure and viscous drag, which are the same for bodies moving through air as for bodies moving through water. Viscous drag is the force of friction that slows down a moving object through a substance, like air or water. NASA uses wind tunnels for fluid dynamics research, studying the forces of friction in gasses and liquids. Pressure forces, according to Langley Research Center s Stephen Wilkinson, dictate the optimal shape and performance of an airplane or other aero/hydro-dynamic body. In both high-speed flight and swimming, says Wilkinson, a thin boundary layer of reduced velocity fluid surrounds the moving body; this layer is about 2 centimeters thick for a swimmer.
Modelling LARES temperature distribution and thermal drag
Nguyen, Phuc H
2015-01-01
The LARES satellite, a laser-ranged space experiment to contribute to geophysics observation, and to measure the general relatistic Lense-Thirring effect, has been observed to undergo an anomalous along-track orbital acceleration of -$0.4\\ pm/s^2$ (pm := picometer). This "drag" is not surprising; along track drag has previously been observed with the related LAGEOS satellites (-$3.4\\ pm/s^2$). It is hypothesized that the drag is due to anisotropic thermal radiation from the satellite's exterior. We report the results of numerical computations of the along-track orbital decay of the LARES satellite during the first 105 days after launch. The results depend to a significant degree on the visual and IR absorbance $\\alpha$ and emissivity $\\epsilon$ of the fused silica cube-cornered laser retroreflectors (CCRs). We present results for two values of $\\alpha_{IR}$ = $\\epsilon_{IR}$: 0.82, a standard number for "clean" fused silica; and 0.60, a possible value for silica with slight surface contamination subjected to ...
Picosecond response of a photon drag detector
Energy Technology Data Exchange (ETDEWEB)
Kimmitt, M.F. [Univ. of Essex (United Kingdom)
1995-12-31
The primary use of photon drag detectors has been with CO{sub 2} lasers at 10{mu}m. Cornmercially-available devices are limited to response times of < 0.5-1ns and voltage responsivities of <0.5{mu}V W{sup -1}. This poster paper will describe the first photon drag detector specifically designed for very fast response. Using the free-election laser FELIX at the FOM Institute in the Netherlands, a rise time of <50ps has been demonstrated, using a 5mm{sup 2} area detector with a responsivity of >1{mu}V W{sup -1} over the wavelength range 10-25{mu}m. The figure shows the clear resolution of the micropulse structure of the laser. The actual width of each pulse is a few picosecoods, with a micropulse spacing of Ins. The advantages or photon drag detectors are room-temperature operation, linear response to intensifies greater than 10{sup 6}MW cm{sup -2} and very high damage threshold. These detectors are cheap to manufacture and, using different semiconductors, can be designed for any wavelength from 1 {mu}m-5mm.
Effects of Polymer Parameters on Drag Reduction.
Safieddine, Abbas Mohammad
The effects of polymer parameters on fluid drag reduction using polyethylene oxide (PEO), polyacrylamide (PAM), guar gum (GG) and hydroxyethyl cellulose (HEC) were investigated. Due to the unavailability of high molecular weight (MW) water-soluble polymers having narrow molecular weight distribution (MWD), an aqueous preparative size exclusion chromatography (SEC) system capable of fractionating over wide MW ranges was constructed. An online low shear viscometer, coupled to the SEC, measured the instantaneous intrinsic viscosity of the eluting polymer solution and, therefore, served as a MW detector since Mark-Houwink "K" and "a" values for all four polymers were known. With the aid of the viscometer, the SEC system was calibrated. The preparative nature of the chromatography system allowed the collection of large volumes of nearly monodisperse fractions (MWD SEC approach allowed drag reduction (DR) experiments using well-characterized, narrowly dispersed polymer solutions under controlled tube flow conditions. Correlations of drag reduction performance with primary polymer parameters (i.e., concentration, intrinsic viscosity ((eta)), volume fraction (c(eta)), number of chain links (N), and combinations thereof) were used to test the validity of several theoretical DR models. Walsh's energy model, as well as the Deborah argument, did not completely account for drag reduction behavior under all experimental conditions. Within each of the flexible or rigid polymer groups, the extensional viscosity model was successful in correlating c(eta) N with DR under all turbulent conditions. However, it failed to account for the differences in chemical structure between the two polymer groups. However, when the cellulosic repeat unit was used instead of the carbon-carbon bond as the chain link for the rigid polymers (GG and HEC), all DR versus c (eta) N curves under all turbulent conditions collapsed into a single function. This has been predicted by the recent "yo-yo" model of
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.
Drag of Clean and Fouled Net Panels – Measurements and Parameterization of Fouling
Gansel, Lars Christian; Plew, David R.; Endresen, Per Christian; Olsen, Anna Ivanova; Misimi, Ekrem; Guenther, Jana; Jensen, Østen
2015-01-01
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. PMID:26151907
Afterbody Drag. Volume 3. Literature Survey.
1980-06-01
34 AGARD, Otta- wa, June 1955. 34. Faru, I., "Experimental Determination of Base Pressures at Supersonic Velocities." Bumblebee Report 106, Johns ...Taylor Model Basin Aero Report 857, January 1954. 68. Pietrangeli, G.J., "The Determination of Afterbody Drag at Transonic Speeds." Johns Hopkins...34 NASATND-7095, 1972. Coltrane , L.C., "Investigation of Two Bluff Shapes in Axial Free Flight Over a Mach Number Range from 0.35 to 2.15." NACARM L58A16
Coulombic dragging of molecular assemblies on nanotubes
Kral, Petr; Sint, Kyaw; Wang, Boyang
2009-03-01
We show by molecular dynamics simulations that polar molecules, ions and their assemblies could be Coulombically dragged on the surfaces of single-wall carbon and boron-nitride nanotubes by ionic solutions or individual ions moving inside the nanotubes [1,2]. We also briefly discuss highly selective ionic sieves based on graphene monolayers with nanopores [3]. These phenomena could be applied in molecular delivery, separation and desalination.[3pt] [1] Boyang Wang and Petr Kral, JACS 128, 15984 (2006). [0pt] [2] Boyang Wang and Petr Kral, Phys. Rev. Lett. 101, 046103 (2008). [0pt] [3] Kyaw Sint, Boyang Wang and Petr Kral, JACS, ASAP (2008).
Gravitational Capture of Asteroids by Gas Drag
Directory of Open Access Journals (Sweden)
E. Vieira Neto
2009-01-01
captured by the planet got its velocity reduced and could been trapped as an irregular satellite. It is well known that, depending on the time scale of the gas envelope, an asteroid will spiral and collide with the planet. So, we simulate the passage of the asteroid in the gas envelope with its density decreasing along the time. Using this approach, we found effective captures, and have a better understanding of the whole process. Finally, we conclude that the origin of the irregular satellites cannot be attributed to the gas drag capture mechanism alone.
Drag phenomena from holographic massive gravity
Baggioli, Matteo; Brattan, Daniel K.
2017-01-01
We consider the motion of point particles in a strongly coupled field theory with broken translation invariance. We obtain the energy and momentum loss rates and drag coefficients for a class of such particles by solving for the motion of classical strings in holographic massive gravity. At low temperatures compared to the graviton mass the behaviour of the string is controlled by the appearance of an exotic ground state with non-zero entropy at zero temperature. Additionally, we find an upper bound on the diffusion constant for a collection of these particles which is saturated when the mass of the graviton goes to zero.
Drag phenomena from holographic massive gravity
Baggioli, Matteo
2015-01-01
We consider the motion of point particles in a strongly coupled field theory with broken translation invariance. We obtain the energy and momentum loss rates and drag coefficients for a class of such particles by solving for the motion of classical strings in holographic massive gravity. At low temperatures compared to the graviton mass the behaviour of the string is controlled by the appearance of an exotic ground state with non-zero entropy at zero temperature. Additionally we find an upper bound on the diffusion constant for a collection of these particles which is saturated when the mass of the graviton goes to zero.
On Nature of Plasmonic Drag Effect
Durach, Maxim
2016-01-01
Light-matter momentum transfer in plasmonic materials is theoretically discussed in context of the modified plasmonic pressure mechanism, taking into account electron thermalization process. We show that our approach explains the observed in experiments relationship between the photoinduced electromotive force and absorption, emphasizes the quantum nature of plasmon-electron interaction, and allows one to correctly calculate the magnitude of the plasmon drag emf in flat metal films for the first time. We extend our theory on the films with modulated profiles and show that simple relationship between plasmonic energy and momentum transfer holds for the case of laminar electron drift and relatively small amplitudes of height modulation.
Karkowski, Janusz; Malec, Edward; Pirog, Michal; Xie, Naqing
2016-01-01
We consider stationary, axially symmetric toroids rotating around spinless black holes, assuming the general-relativistic Keplerian rotation law, in the first post-Newtonian approximation. Numerical investigation shows that the angular momentum accumulates almost exclusively within toroids. It appears that various types of dragging (anti-dragging) effects are positively correlated with the ratio $M_\\mathrm{D}/m$ ($M_\\mathrm{D}$ is the mass of a toroid and $m$ is the mass of the black hole) - moreover, their maxima are proportional to $M_\\mathrm{D}/m$. The horizontal sizes of investigated toroids range from c. 50 to c. 450 of Schwarzschild radii $R_\\mathrm{S}$ of the central black hole; their mass $M_\\mathrm{D} \\in (10^{-4}m, 40m)$ and the radial size of the system is c. 500 $R_\\mathrm{S}$. We found that the relative strength of various dragging (anti-dragging) effects does not change with the mass ratio, but it depends on the size of toroids. Several isoperimetric inequalities involving angular momentum are s...
Drag prediction method of powered-on civil aircraft based on thrust drag bookkeeping
Directory of Open Access Journals (Sweden)
Zhang Yufei
2015-08-01
Full Text Available A drag prediction method based on thrust drag bookkeeping (TDB is introduced for civil jet propulsion/airframe integration performance analysis. The method is derived from the control volume theory of a powered-on nacelle. Key problem of the TDB is identified to be accurate prediction of velocity coefficient of the powered-on nacelle. Accuracy of CFD solver is validated by test cases of the first AIAA Propulsion Aerodynamics Workshop. Then the TDB method is applied to thrust and drag decomposing of a realistic aircraft. A linear relation between the computations assumed free stream Mach number and the velocity coefficient result is revealed. The thrust losses caused by nozzle internal drag and pylon scrubbing are obtained by the isolated nacelle and mapped on to the in-flight whole configuration analysis. Effects of the powered-on condition are investigated by comparing through-flow configuration with powered-on configuration. The variance on aerodynamic coefficients and pressure distribution is numerically studied.
Dittmar, J. H.
1984-01-01
Previous comparisons between calculated and measured supersonic helical tip speed propeller noise show them to have different trends of peak blade passing tone versus helical tip Mach number. It was postulated that improvements in this comparison could be made first by including the drag force terms in the prediction and then by reducing the blade lift terms at the tip to allow the drag forces to dominate the noise prediction. Propeller hub to tip lift distributions were varied, but they did not yield sufficient change in the predicted lift noise to improve the comparison. This result indicates that some basic changes in the theory may be needed. In addition, the noise predicted by the drag forces did not exhibit the same curve shape as the measured data. So even if the drag force terms were to dominate, the trends with helical tip Mach number for theory and experiment would still not be the same. The effect of the blade shock wave pressure rise was approxmated by increasing the drag coefficient at the blade tip. Predictions using this shock wdave approximation did have a curve shape similar to the measured data. This result indicates that the shock pressure rise probably controls the noise at supersonic tip speed and that the linear prediction method can give the proper noise trend with Mach number.
An Analytical Method for Positioning Drag Anchors in Seabed Soils
Institute of Scientific and Technical Information of China (English)
张炜; 刘海笑; 李新仲; 李清平; 曹静
2015-01-01
Positioning drag anchors in seabed soils are strongly influenced not only by the properties of the anchor and soil, but also by the characteristics of the installation line. The investigation on the previous prediction methods related to anchor positioning demonstrates that the prediction of the anchor position during dragging has inevitably introduced some key and unsubstantiated hypotheses and the applicability of these methods is limited. In the present study, the interactional system between the drag anchor and installation line is firstly introduced for the analysis of anchor positioning. Based on the two mechanical models for embedded lines and drag anchors, the positioning equations for drag anchors have been derived both for cohesive and noncohesive soils. Since the drag angle at the shackle is the most important parameter in the positioning equations, a novel analytical method that can predict both the variation and the exact value of the drag angle at the shackle is proposed. The analytical method for positioning drag anchors which combines the interactional system between the drag anchor and the installation line has provided a reasonable theoretic approach to investigate the anchor behaviors in soils. By comparing with the model flume experiments, the sensitivity, effectiveness and veracity of the positioning method are well verified.
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....... 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...
Bionic Research on Bird Feather for Drag Reduction
Directory of Open Access Journals (Sweden)
Beibei Feng
2015-02-01
Full Text Available To reduce friction drag with bionic method in a more feasible way, the surface microstructure of bird feather was analyzed attempting to reveal the biologic features responding to skin friction drag reduction. Then comparative bionic surface mimicking bird feather was fabricated through hot-rolling technology for drag reduction. The microriblet film was formed on a PVC substrate through a self-developed hot-rolling equipment. The bionic surface with micron-scale riblets formed spontaneously due to the elastic-plastic deformation of PVC in high temperature and high pressure environment. Comparative experiments between micro-structured bionic surface and smooth surface were performed in a wind tunnel to evaluate the effect of bionic surface on drag reduction, and significant drag reduction efficiency was obtained. Numerical simulation results show that microvortex induced in the solid-gas interface of bionic surface has the effect of shear stress reduction and the small level of an additional pressure drag resulting from pressure distribution deviation on bird feather like surface, hence reducing the skin friction drag significantly. Therefore, with remarkable drag reduction performance and simple fabrication technology, the proposed drag reduction technique shows the promise for practical applications.
Drag reduction properties of superhydrophobic mesh pipes
Geraldi, Nicasio R.; Dodd, Linzi E.; Xu, Ben B.; Wells, Gary G.; Wood, David; Newton, Michael I.; McHale, Glen
2017-09-01
Even with the recent extensive study into superhydrophobic surfaces, the fabrication of such surfaces on the inside walls of a pipe remains challenging. In this work we report a convenient bi-layered pipe design using a thin superhydrophobic metallic mesh formed into a tube, supported inside another pipe. A flow system was constructed to test the fabricated bi-layer pipeline, which allowed for different constant flow rates of water to be passed through the pipe, whilst the differential pressure was measured, from which the drag coefficient (ƒ) and Reynolds numbers (Re) were calculated. Expected values of ƒ were found for smooth glass pipes for the Reynolds number (Re) range 750-10 000, in both the laminar and part of the turbulent regimes. Flow through plain meshes without the superhydrophobic coating were also measured over a similar range (750 superhydrophobic coating, ƒ was found for 4000 superhydrophobic mesh can support a plastron and provide a drag reduction compared to a plain mesh, however, the plastron is progressively destroyed with use and in particular at higher flow rates.
The drag force during the transient regime
Souza, P V S; de Oliveira, P M C
2015-01-01
In this paper, we analyze the drag force acting on a cylinder in a wind tunnel. The inspiration comes from an experimental result: a small, light ball falls on air; its speed increases, reaches a maximum, decreases and finally stabilizes. This surprising breaking behavior is due to the gradual formation of the so-called von K\\'arm\\'an street of air vortices behind the ball: while it is not completely formed, the transient drag force is smaller than the known steady state value and the ball can reach speeds higher than its final value. To show it, we treat the similar problem of a cylinder inside a wind tunnel suddenly switched on, by solving the Navier-Stokes dynamic equation. We use a finite difference method with successive relaxations on a grid. We also treat the case of a rotating cylinder, leading to the Magnus force. The novelty is the method we use to calculate these forces, which avoids the traditional surface integration of velocity gradients; the latter demands a very precise determination of the ve...
Drag Force Anemometer Used in Supersonic Flow
Fralick, Gustave C.
1998-01-01
To measure the drag on a flat cantilever beam exposed transversely to a flow field, the drag force anemometer (beam probe) uses strain gauges attached on opposite sides of the base of the beam. This is in contrast to the hot wire anemometer, which depends for its operation on the variation of the convective heat transfer coefficient with velocity. The beam probe retains the high-frequency response (up to 100 kHz) of the hot wire anemometer, but it is more rugged, uses simpler electronics, is relatively easy to calibrate, is inherently temperature compensated, and can be used in supersonic flow. The output of the probe is proportional to the velocity head of the flow, 1/2 rho u(exp 2) (where rho is the fluid density and u is the fluid velocity). By adding a static pressure tap and a thermocouple to measure total temperature, one can determine the Mach number, static temperature, density, and velocity of the flow.
Bag-breakup control of surface drag in hurricanes
Troitskaya, Yuliya; Zilitinkevich, Sergej; Kandaurov, Alexander; Ermakova, Olga; Kozlov, Dmitry; Sergeev, Daniil
2016-04-01
Air-sea interaction at extreme winds is of special interest now in connection with the problem of the sea surface drag reduction at the wind speed exceeding 30-35 m/s. This phenomenon predicted by Emanuel (1995) and confirmed by a number of field (e.g., Powell, et al, 2003) and laboratory (Donelan et al, 2004) experiments still waits its physical explanation. Several papers attributed the drag reduction to spume droplets - spray turning off the crests of breaking waves (e.g., Kudryavtsev, Makin, 2011, Bao, et al, 2011). The fluxes associated with the spray are determined by the rate of droplet production at the surface quantified by the sea spray generation function (SSGF), defined as the number of spray particles of radius r produced from the unit area of water surface in unit time. However, the mechanism of spume droplets' formation is unknown and empirical estimates of SSGF varied over six orders of magnitude; therefore, the production rate of large sea spray droplets is not adequately described and there are significant uncertainties in estimations of exchange processes in hurricanes. Herewith, it is unknown what is air-sea interface and how water is fragmented to spray at hurricane wind. Using high-speed video, we observed mechanisms of production of spume droplets at strong winds by high-speed video filming, investigated statistics and compared their efficiency. Experiments showed, that the generation of the spume droplets near the wave crest is caused by the following events: bursting of submerged bubbles, generation and breakup of "projections" and "bag breakup". Statistical analysis of results of these experiments showed that the main mechanism of spray-generation is attributed to "bag-breakup mechanism", namely, inflating and consequent blowing of short-lived, sail-like pieces of the water-surface film. Using high-speed video, we show that at hurricane winds the main mechanism of spray production is attributed to "bag-breakup", namely, inflating and
Covariance analysis of differential drag-based satellite cluster flight
Ben-Yaacov, Ohad; Ivantsov, Anatoly; Gurfil, Pini
2016-06-01
One possibility for satellite cluster flight is to control relative distances using differential drag. The idea is to increase or decrease the drag acceleration on each satellite by changing its attitude, and use the resulting small differential acceleration as a controller. The most significant advantage of the differential drag concept is that it enables cluster flight without consuming fuel. However, any drag-based control algorithm must cope with significant aerodynamical and mechanical uncertainties. The goal of the current paper is to develop a method for examination of the differential drag-based cluster flight performance in the presence of noise and uncertainties. In particular, the differential drag control law is examined under measurement noise, drag uncertainties, and initial condition-related uncertainties. The method used for uncertainty quantification is the Linear Covariance Analysis, which enables us to propagate the augmented state and filter covariance without propagating the state itself. Validation using a Monte-Carlo simulation is provided. The results show that all uncertainties have relatively small effect on the inter-satellite distance, even in the long term, which validates the robustness of the used differential drag controller.
Simplified Models for the Drag Coefficient of a Pitched Baseball
Kagan, David; Nathan, Alan M.
2014-01-01
The classic experiment to measure the drag coefficient involves dropping coffee filters. Wouldn't it be more fun to try something different? In fact, an experiment on the drag force is conducted nearly 4000 times a day during the baseball season and you have free access to this PITCHf/x data!
Drag reduction through self-texturing compliant bionic materials
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.
Bionic Research on Fish Scales for Drag Reduction
Institute of Scientific and Technical Information of China (English)
Zhaoliang Dou; Jiadao Wang; Darong Chen
2012-01-01
To reduce friction drag with bionic method in a more feasible way,the surface microstructure of fish scales was analyzed attempting to reveal the biologic features responding to skin friction drag reduction.Then comparable bionic surface mimicking fish scales was fabricated through coating technology for drag reduction.The paint mixture was coated on a substrate through a self-developed spray-painting apparatus.The bionic surface with micron-scale caves formed spontaneously due to the interfacial convection and deformation driven by interfacial tension gradient in the presence of solvent evaporation.Comparative experiments between bionic surface and smooth surface were performed in a water tunnel to evaluate the effect of bionic surface on drag reduction,and visible drag reduction efficiency was obtained.Numerical simulation results show that gas phase develops in solid-liquid interface of bionic surface with the effect of surface topography and partially replaces the solid-liquid shear force with gas-liquid shear force,hence reducing the skin friction drag effectively.Therefore,with remarkable drag reduction performance and simple fabrication technology,the proposed drag reduction technique shows the promise for practical applications.
Drag reduction in turbulent MHD pipe flows
Orlandi, P.
1996-01-01
This is a preliminary study devoted to verifying whether or not direct simulations of turbulent Magneto-Hydro-Dynamic (MHD) flows in liquid metals reproduce experimental observations of drag reduction. Two different cases have been simulated by a finite difference scheme which is second order accurate in space and time. In the first case, an external azimuthal magnetic field is imposed. In this case, the magnetic field acts on the mean axial velocity and complete laminarization of the flow at N(sub a) = 30 has been achieved. In the second case, an axial magnetic field is imposed which affects only fluctuating velocities, and thus the action is less efficient. This second case is more practical, but comparison between numerical and experimental results is only qualitative.
Lift and drag of cetacean flippers
Murray, Mark; Weber, Paul; Howle, Laurens; Fish, Frank
2008-11-01
Field observation and collection of biological samples has resulted in cetacean (whales, dolphins and porpoises) flipper geometry being known for most species. However, the hydrodynamic properties of cetacean flippers have not been rigorously tested and thus their performance characteristics are unknown. Here, conducting water tunnel testing using scale models of cetacean flippers derived via computed tomography (CT) scans, as well as computational fluid dynamic (CFD) simulations, we present a baseline work to determine the hydrodynamic characteristics of cetacean flippers. We found that flippers of similar planform shape had similar hydrodynamic performance characteristics. Furthermore, one group of flippers of planform shape similar to a modern swept wing was found to have lift coefficient versus angle of attack curves that were biphasic rather than linear in nature, which was caused by the onset of vortex-dominated lift. Drag coefficient versus angle of attack curves were found to be less dependant on planform shape.
Dancing droplets: Contact angle, drag, and confinement
Benusiglio, Adrien; Cira, Nate; Prakash, Manu
2015-11-01
When deposited on a clean glass slide, a mixture of water and propylene glycol forms a droplet of given contact angle, when both pure liquids spread. (Cira, Benusiglio, Prakash: Nature, 2015). The droplet is stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow from the border to the apex of the droplets. The apparent contact angle of the droplets depends on both their composition and the external humidity as captured by simple models. These droplets present remarkable properties such as lack of a large pinning force. We discuss the drag on these droplets as a function of various parameters. We show theoretical and experimental results of how various confinement geometries change the vapor gradient and the dynamics of droplet attraction.
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.
Air Flows in Gravity Sewers - Determination of Wastewater Drag Coefficient
DEFF Research Database (Denmark)
Bentzen, Thomas Ruby; Østertoft, Kristian; Vollertsen, Jes
2016-01-01
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......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...... 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...
Collisional Effects on Nonlinear Ion Drag Force for Small Grains
Hutchinson, I H
2013-01-01
The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.
Methods for Accurate Free Flight Measurement of Drag Coefficients
Courtney, Elya; Courtney, Michael
2015-01-01
This paper describes experimental methods for free flight measurement of drag coefficients to an accuracy of approximately 1%. There are two main methods of determining free flight drag coefficients, or equivalent ballistic coefficients: 1) measuring near and far velocities over a known distance and 2) measuring a near velocity and time of flight over a known distance. Atmospheric conditions must also be known and nearly constant over the flight path. A number of tradeoffs are important when designing experiments to accurately determine drag coefficients. The flight distance must be large enough so that the projectile's loss of velocity is significant compared with its initial velocity and much larger than the uncertainty in the near and/or far velocity measurements. On the other hand, since drag coefficients and ballistic coefficients both depend on velocity, the change in velocity over the flight path should be small enough that the average drag coefficient over the path (which is what is really determined)...
Effect of Off-Body Laser Discharge on Drag Reduction of Hemisphere Cylinder in Supersonic Flow
Kianvashrad, Nadia; Knight, Doyle; Wilkinson, Stephen P.; Chou, Amanda; Horne, Robert A.; Herring, Gregory C.; Beeler, George B.; Jangda, Moazzam
2017-01-01
The interaction of an off-body laser discharge with a hemisphere cylinder in supersonic flow is investigated. The objectives are 1) experimental determination of the drag reduction and energetic efficiency of the laser discharge, and 2) assessment of the capability for accurate simulation of the interaction. The combined computational and experimental study comprises two phases. In the first phase, laser discharge in quiescent air was examined. The temporal behavior of the shock wave formed by the laser discharge was compared between experiment and simulation and good agreement is observed. In the second phase, the interaction of the laser discharge with a hemisphere cylinder was investigated numerically. Details of the pressure drag reduction and the physics of the interaction of the heated region with the bow shock are included. The drag reduction due to this interaction persisted for about five characteristic times where one characteristic time represents the time for the flow to move a distance equal to the hemisphere radius. The energetic efficiency of laser discharge for the case with 50 mJ energy absorbed by the gas is calculated as 3.22.
Zhong, Shuixin; Chen, Zitong
2015-02-01
To improve the wind and precipitation forecasts over South China, a modified orographic drag parameterization (OP) scheme that considers both the gravity wave drag (GWD) and the mountain blocking drag (MBD) effects was implemented in the Global/Regional Assimilation and Prediction System Tropical Mesoscale Model (GRAPES_TMM). Simulations were performed over one month starting from 1200 UTC 19 June 2013. The initial and lateral boundary conditions were obtained from the NCEP global forecast system output. The simulation results were compared among a control (CTL) experiment without the OP scheme, a GWDO experiment with the OP scheme that considers only the GWD effect, and an MBD experiment with the modified OP scheme (including both GWD and MBD). The simulation with the modified OP scheme successfully captured the main features of precipitation, including its distribution and intensity, and improved the wind circulation forecast in the lower troposphere. The modified OP scheme appears to improve the wind forecast by accelerating the ascending air motion and reinforcing the convergence in the rainfall area. Overall, the modified OP scheme exerts positive impacts on the forecast of large-scale atmospheric fields in South China.
Institute of Scientific and Technical Information of China (English)
钟水新; 陈子通
2015-01-01
To improve the wind and precipitation forecasts over South China, a modifi ed orographic drag param-eterization (OP) scheme that considers both the gravity wave drag (GWD) and the mountain blocking drag (MBD) eff ects was implemented in the Global/Regional Assimilation and Prediction System Tropical Mesoscale Model (GRAPES−TMM). Simulations were performed over one month starting from 1200 UTC 19 June 2013. The initial and lateral boundary conditions were obtained from the NCEP global forecast system output. The simulation results were compared among a control (CTL) experiment without the OP scheme, a GWDO experiment with the OP scheme that considers only the GWD eff ect, and an MBD ex-periment with the modifi ed OP scheme (including both GWD and MBD). The simulation with the modifi ed OP scheme successfully captured the main features of precipitation, including its distribution and intensity, and improved the wind circulation forecast in the lower troposphere. The modifi ed OP scheme appears to improve the wind forecast by accelerating the ascending air motion and reinforcing the convergence in the rainfall area. Overall, the modifi ed OP scheme exerts positive impacts on the forecast of large-scale atmospheric fi elds in South China.
Performance losses of drag-reducing spanwise forcing at moderate values of the Reynolds number
Gatti, Davide; Quadrio, Maurizio
2013-12-01
A fundamental problem in the field of turbulent skin-friction drag reduction is to determine the performance of the available control techniques at high values of the Reynolds number Re. We consider active, predetermined strategies based on spanwise forcing (oscillating wall and streamwise-traveling waves applied to a plane channel flow), and explore via Direct Numerical Simulations (DNS) up to Reτ = 2100 the rate at which their performance deteriorates as Re is increased. To be able to carry out a comprehensive parameter study, we limit the computational cost of the simulations by adjusting the size of the computational domain in the homogeneous directions, compromising between faster computations and the increased need of time-averaging the fluctuating space-mean wall shear-stress. Our results, corroborated by a few full-scale DNS, suggest a scenario where drag reduction degrades with Re at a rate that varies according to the parameters of the wall forcing. In agreement with already available information, keeping them at their low-Re optimal value produces a relatively quick decrease of drag reduction. However, at higher Re the optimal parameters shift towards other regions of the parameter space, and these regions turn out to be much less sensitive to Re. Once this shift is accounted for, drag reduction decreases with Re at a markedly slower rate. If the slightly favorable trend of the energy required to create the forcing is considered, a chance emerges for positive net energy savings also at large values of the Reynolds number.
Experimental investigation of drag coefficients of gobi surfaces
Institute of Scientific and Technical Information of China (English)
董治宝; 屈建军; 刘小平; 张伟民; 王训明
2002-01-01
The response of gobi surfaces to the near-surface air flow can be characterized quantitatively by drag coefficients. By using wind tunnel tests, an attempt is made to define the relationship between the drag coefficients of gobi surfaces and gravel size and coverage. It is concluded that the drag coefficients of gobi surfaces tend to be constants when gravel coverage is over 40%-50%. Consequently, we think that the gobi deflation planes expanding vastly in the arid Northwestern China are aerodynamically stable, at least not the supplying sources of current dust storms, and therefore the emphasis on dust storm control should be paid on the so-called "earth gobi" that has low gravel coverage. The prediction model for drag coefficients of gobi surfaces has been developed by regressing drag coefficients on gravel size and coverage, the predicted results are in reasonably good agreement with wind tunnel results (R 2 = 0.94). The change of drag coefficients with gravel friction Reynolds number implies that the development extent of drag effect increases with gravel size and coverage.
Drag reduction in turbulent flows over superhydrophobic surfaces
Daniello, Robert J.; Waterhouse, Nicholas E.; Rothstein, Jonathan P.
2009-08-01
In this paper, we demonstrate that periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime. Superhydrophobic surfaces contain micro- or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to drag reductions approaching 50%. At a given Reynolds number, drag reduction is found to increase with increasing feature size and spacing, as in laminar flows. No observable drag reduction was noted in the laminar regime, consistent with previous experimental results for the channel geometry considered. The onset of drag reduction occurs at a critical Reynolds number where the viscous sublayer thickness approaches the scale of the superhydrophobic microfeatures and performance is seen to increase with further reduction in viscous sublayer height. These results indicate superhydrophobic surfaces may provide a significant drag reducing mechanism for marine vessels.
Characterization of aerodynamic drag force on single particles: Final report
Energy Technology Data Exchange (ETDEWEB)
Kale, S.R.
1987-10-01
An electrodynamic balance was used to measure the drag coefficient and also to record the size and shape of spheres, and coal and oil shale particles (100 ..mu..m to 200 ..mu..m in size). The electrodynamic balance consisted of a central, and two end electrodes. The resulting electric field stably suspended a charged particle. A suspended particle, back illuminated by a light emitting diode, was viewed by a video camera. The image was analyzed for particle position control and was calibrated to give the diameter of spheres, or the area equivalent diameter of nonspherical particles. The drag coefficient was calculated from the air velocity and the dc voltage required to keep the particle at the balance center. The particle Reynolds number varied from 0.2 to 13. Three particles each of coal and oil shale were captured and photographed by a scanning electron microscope and the motion of all the particles was recorded on video tape. Drag coefficient vs Reynolds number data for spheres agreed well with correlations. Data for thirteen particles each of coal and oil shale indicated a power law relationship between drag coefficient and Reynolds number. All these particles exhibited higher drag than spheres and were also observed to rotate. The rotation, however, did not affect the drag coefficient. The choice of characteristic dimension affects the drag characteristics of oil shale more strongly than for coal, owing to the flake-like shape of oil shale. 38 figs., 5 tabs.
Does Polishing a Rifle Bore Reduce Bullet Drag?
2012-01-17
thus lower drag. A Remington 700 5R Mil-Spec chambered in 300 Winchester Magnum was used. The bullets used were a 155.5 grain Berger Fullbore Boat...drag on the bullets. 15. SUBJECT TERMS Ballistic coefficient, aerodynamic drag, rifle bore, bore polishing, Remington 700 5R 16. SECURITY...A Remington 700 5R Mil-Spec chambered in 300 Winchester Magnum was used. The bullets used were a 155.5 grain Berger Fullbore Boat Tail and a 125
The Digital Drag and Drop Pillbox
Granger, Bradi B.; Locke, Susan C.; Bowers, Margaret; Sawyer, Tenita; Shang, Howard; Abernethy, Amy P.; Bloomfield, Richard A.; Gilliss, Catherine L.
2017-01-01
Objective: We present the design and feasibility testing for the “Digital Drag and Drop Pillbox” (D-3 Pillbox), a skill-based educational approach that engages patients and providers, measures performance, and generates reports of medication management skills. Methods: A single-cohort convenience sample of patients hospitalized with heart failure was taught pill management skills using a tablet-based D-3 Pillbox. Medication reconciliation was conducted, and aptitude, performance (% completed), accuracy (% correct), and feasibility were measured. Results: The mean age of the sample (n = 25) was 59 (36–89) years, 50% were women, 62% were black, 46% were uninsured, 46% had seventh-grade education or lower, and 31% scored very low for health literacy. However, most reported that the D-3 Pillbox was easy to read (78%), easy to repeat-demonstrate (78%), and comfortable to use (tablet weight) (75%). Accurate medication recognition was achieved by discharge in 98%, but only 25% reported having a “good understanding of my responsibilities.” Conclusions: The D-3 Pillbox is a feasible approach for teaching medication management skills and can be used across clinical settings to reinforce skills and medication list accuracy. PMID:28282304
Turbulent drag reduction through oscillating discs
Wise, Daniel J
2014-01-01
The changes of a turbulent channel flow subjected to oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations. The Reynolds number is $R_\\tau$=$180$, based on the friction velocity of the stationary-wall case and the half channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20%. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim to identify the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, computed by taking into account the power spent to actuate the discs. This may be positive and reaches 6%. The Rosenblat viscous pump flow is used to predict the power spent for disc motion in the turbulent channel flow and to estimate localized and transient regions over the disc surface subjected to the turbulent regenerative braking effect, for which the wall turbulence exerts work on the discs. The...
Directory of Open Access Journals (Sweden)
Cheslav Balash
Full Text Available For prawn trawling systems, drag reduction is a high priority as the trawling process is energy intensive. Large benefits have occurred through the use of multiple-net rigs and thin twine in the netting. An additional positive effect of these successful twine-area reduction strategies is the reduced amount of otter board area required to spread the trawl systems, which leads to further drag reduction. The present work investigated the potential of redirecting the drag-strain within a prawn trawl away from the wings and the otter boards to the centre line of the trawl, where top and bottom tongues have been installed, with an aim to minimise the loading/size of the otter boards required to spread the trawl. In the system containing the new 'W' trawl, the drag redirected to the centre-line tongues is transferred forward through a connected sled and towing wires to the trawler. To establish the extent of drag redirection to the centre-line tongues and the relative drag benefits of the new trawl system, conventional and 'W' trawls of 3.65 m headline length were tested firstly over a range of spread ratios in the flume tank, and subsequently at optimum spread ratio in the field. The developed 'W' trawl effectively directed 64% of netting-drag off the wings and onto the centre tongues, which resulted in drag savings in the field of ∼20% for the associated 'W' trawl/otter-board/sled system compared to the traditional trawl/otter-board arrangement in a single trawl or twin rig configuration. Furthermore, based on previously published data, the new trawl when used in a twin rig system is expected to provide approximately 12% drag reduction compared to quad rig. The twin 'W' trawl system also has benefits over quad rig in that a reduced number of cod-end/By-catch Reduction Device units need to be installed and attended each tow.
DEFF Research Database (Denmark)
Muller, Peter Barkholt; Barnkob, Rune; Jensen, Mads Jakob Herring;
2012-01-01
We present a numerical study of the transient acoustophoretic motion of microparticles suspended in a liquid-filled microchannel and driven by the acoustic forces arising from an imposed standing ultrasound wave: the acoustic radiation force from the scattering of sound waves on the particles...... parameters using a numerical particle-tracking scheme. The model shows the transition in the acoustophoretic particle motion from being dominated by streaming-induced drag to being dominated by radiation forces as a function of particle size, channel geometry, and material properties....
Directory of Open Access Journals (Sweden)
Hongru Zhao
2016-11-01
Full Text Available The vertical migration and accumulation of Microcystis is an important process in water blooms, and colony migration is influenced by colony size and wind-wave disturbance. The vertical migration of Microcystis colonies in turbulence can be simulated in a numerical model. In this study, we model such migration by coupling the colony size and hydrodynamics, including the gravity, colony buoyancy, and the viscous drag force of turbulence. The turbulence intensity was represented by the turbulent kinetic energy (KZ; the larger the KZ, the stronger the wind-wave disturbance. The simulated vertical distribution of Microcystis well agreed with the measured values in a laboratory experiment indicating that our model can simulate the vertical distribution of Microcystis under different hydrodynamic conditions. We also found a size-dependent critical turbulent kinetic energy (TKZ, such that if the turbulent kinetic energy of water exceeds the critical value (i.e., KZ > TKZ, the colonies sink under the drag forces of turbulence; conversely, if KZ < TKZ, the colonies can overcome the turbulent mixing and float. The TKZ of each colony was linearly related to colony diameter. The model is crucial for prediction and prevention of water blooms. The simulated threshold turbulent kinetic energy, at which water blooms disappear in Lake Taihu (a large freshwater lake in the Yangtze Delta, Jiangsu Province, China, was 55.5 cm2 s−2.
Electromagnetically-Induced Frame-Dragging around Astrophysical Objects
Ruiz, Andrés F Gutiérrez
2015-01-01
Frame dragging (Lense-Thirring effect) is generally associated with rotating astrophysical objects. However, it can also be generated by electromagnetic fields if electric and magnetic fields are simultaneously present. In most models of astrophysical objects, macroscopic charge neutrality is assumed and the entire electromagnetic field is characterized in terms of a magnetic dipole component. Hence, the purely electromagnetic contribution to the frame dragging vanishes. However, strange stars may posses independent electric dipole and neutron stars independent electric quadrupole moments that may lead to the presence of purely electromagnetic contributions to the frame dragging. Moreover, recent observations have shown that in stars with strong electromagnetic fields, the magnetic quadrupole may have a significant contribution to the dynamics of stellar processes. As an attempt to characterized and quantify the effect of electromagnetic frame-dragging in this kind of astrophysical objects, an analytic soluti...
Rotating cylinder drag balance with application to riblets
Hall, T.; Joseph, D.
2000-12-01
Experimental results are reported and discussed for a rotating cylinder drag balance designed to predict drag reduction by surfaces like riblets. The apparatus functions by measuring the torque applied to the inner cylinder by a fluid, such as water, that is set in motion by the controlled rotation of the outer cylinder. The instrument was validated by calibration for laminar flow and comparison of turbulent flow results to the those of G. I. Taylor. The ability to predict drag reduction was demonstrated by testing 114 m symmetric sawtooth riblets, which gave a maximum reduction of about 5% and an overall drag reduction range of 5
Jet Lag a Drag on Pro Baseball Players
... 163187.html Jet Lag a Drag on Pro Baseball Players Study found traveling across time zones linked ... might be more than just tiring for pro baseball players: The resulting jet lag may actually harm ...
Constraining the Drag Coefficients of Meteors in Dark Flight
Carter, R. T.; Jandir, P. S.; Kress, M. E.
2011-01-01
Based on data in the aeronautics literature, we have derived functions for the drag coefficients of spheres and cubes as a function of Mach number. Experiments have shown that spheres and cubes exhibit an abrupt factor-of-two decrease in the drag coefficient as the object slows through the transonic regime. Irregularly shaped objects such as meteorites likely exhibit a similar trend. These functions are implemented in an otherwise simple projectile motion model, which is applicable to the non-ablative dark flight of meteors (speeds less than .+3 km/s). We demonstrate how these functions may be used as upper and lower limits on the drag coefficient of meteors whose shape is unknown. A Mach-dependent drag coefficient is potentially important in other planetary and astrophysical situations, for instance, in the core accretion scenario for giant planet formation.
Experimental study of drag reduction in flumes and spillway tunnels
Institute of Scientific and Technical Information of China (English)
Ying-kui WANG; Chun-bo JIANG
2010-01-01
Experiments in an open flume model and spillway tunnel model were carried out using drag reduction techniques.Two drag reduction techniques were adopted in the experiments:polymer addition and coating.The drag reduction effect of a polyacrylamide(PAM)solution and dimethyl silicone oil coating were studied in the flume model experiments,and the results were analyzed.Experiments were then carried out with a model of the Xiluodu Hydropower Station,the second largest dam in China.In order to reduce the resistance,the spillway tunnels were internally coated with dimethyl silicone oil.This is the first time that these drag reduction techniques have been applied to so large a hydraulic model.The experimental results show that the coating technique can effectively increase flood discharge.The outlet velocity and the jet trajectory distance are also increased,which enhances the energy dissipation of the spillway tunnel.
Development of Drag Reducing Polymer of FDR-SPC
Lee, Inwon; Park, Hyun; Chun, Ho Hwan
2015-11-01
In this study, a novel FDR-SPC (Frictional Drag Reduction Self-Polishing Copolymer) is first synthesized in this study. The drag reducing functional radical such as PEGMA (Poly(ethylene) glycol methacrylate) has been utilized to participate in the synthesis process of the SPC. The release mechanism of drag reducing radical is accounted for the hydrolysis reaction between the FDR-SPC and seawater. The types of the baseline SPC monomers, the molecular weight and the mole fraction of PEGMA were varied in the synthesis process. The resulting SPCs were coated to the substrate plates for the subsequent hydrodynamic test for skin friction measurement. A significant reduction in Reynolds stress was observed in a range of specimen, with the maximum drag reduction being 15.9% relative to the smooth surface for PRD3-1.
Collecting responses through Web page drag and drop.
Britt, M Anne; Gabrys, Gareth
2004-02-01
This article describes how to collect responses from experimental participants using drag and drop on a Web page. In particular, we describe how drag and drop can be used in a text search task in which participants read a text and then locate and categorize certain elements of the text (e.g., to identify the main claim of a persuasive paragraph). Using this technique, participants respond by clicking on a text segment and dragging it to a screen field or icon. We have successfully used this technique in both the argument element identification experiment that we describe here and a tutoring system that we created to teach students to identify source characteristics while reading historical texts (Britt, Perfetti, Van Dyke, & Gabrys, 2000). The implementation described here exploits the capability of recent versions of Microsoft's Internet Explorer Web browser to handle embedded XML documents and drag and drop events.
Separability of drag and thrust in undulatory animals and machines
National Research Council Canada - National Science Library
Bale, Rahul; Shirgaonkar, Anup A; Neveln, Izaak D; Bhalla, Amneet Pal Singh; MacIver, Malcolm A; Patankar, Neelesh A
2014-01-01
.... 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...
Nature of the Venus thermosphere derived from satellite drag measurements (solicited paper)
Keating, G.; Theriot, M.; Bougher, S.
2008-09-01
density, scale height, inferred temperature, pressure, and other parameters as a function of altitude. 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 thermospheric drag effects in over 30 years. The Venus Express accelerometer drag experiment is very similar to accelerometer experiments aboard Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter which orbit Mars. The Venus Express drag measurements of the polar region will allow a global empirical model of the thermosphere to emerge. Previous drag measurements have been made principally near the equator. The experiment may help us understand on a global scale, tides, winds, gravity waves, planetary waves, and the damping of waves. Comparisons will be made between low and high latitude results; between the middle and upper atmosphere; and with other instruments that provide information from current and previous measurements. The character of the sharp temperature gradient near the day/night terminator needs to be studied at all latitudes. The cryosphere we discovered on the nightside needs to be studied at high latitudes. The rotating vortex dipole over the North Pole surrounded by a colder "collar" needs to be analyzed to identify how wave activity extends into the polar thermosphere. We have already discovered super-rotation in the equatorial thermosphere, but we need to study 4-day super-rotation at higher latitudes to obtain a global picture of the thermosphere. The super-rotation may affect escape rates and the evolution of the atmosphere. References: [1] Keating, G. M., et al: Venus Thermosphere and Exosphere: First Satellite Drag Measurements of an Extraterrestrial Atmosphere. Science, Vol. 203, No. 4382, 772-774, Feb. 23, 1979. [2] Keating, G. M. and Bougher, S.W.: Isolation of Major Venus Cooling Mechanism and Implications for Earth and Mars, Journal of Geophysical Research, Vol. 97, 4189
Automated design of minimum drag light aircraft fuselages and nacelles
Smetana, F. O.; Fox, S. R.; Karlin, B. E.
1982-01-01
The constrained minimization algorithm of Vanderplaats is applied to the problem of designing minimum drag faired bodies such as fuselages and nacelles. Body drag is computed by a variation of the Hess-Smith code. This variation includes a boundary layer computation. The encased payload provides arbitrary geometric constraints, specified a priori by the designer, below which the fairing cannot shrink. The optimization may include engine cooling air flows entering and exhausting through specific port locations on the body.
Drag force in a charged N = 4 SYM plasma
Energy Technology Data Exchange (ETDEWEB)
Caceres, Elena [Facultad de Ciencias, Universidad de Colima, Bernal Diaz del Castillo 340, Colima (Mexico); Gueijosa, Alberto [Departamento de Fisica de Altas Energias, Instituto de Ciencias Nucleares, Universidad Autonoma de Mexico, Apdo. Postal 70-543, D.F. 04510 (Mexico)
2006-11-15
Following recent developments, we employ the AdS/CFT correspondence to determine the drag force exerted on an external quark that moves through an N = 4 super-Yang-Mills plasma with a non-zero R-charge density (or, equivalently, a non-zero chemical potential). We find that the drag force is larger than in the case where the plasma is neutral, but the dependence on the charge is non-monotonic.
Separability of drag and thrust in undulatory animals and machines
Bale, R; Shirgaonkar, AA; Neveln, ID; Bhalla, APS; MacIver, MA; Patankar, NA
2014-01-01
For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers...
TURBULENCE TRANSPORT OF SURFACTANT SOLUTION FLOW DURING DRAG REDUCTION DEGENERATION
Institute of Scientific and Technical Information of China (English)
GU Wei-guo; WANG De-zhong
2012-01-01
Turbulence transport of surfactant solution flow during drag reduction degeneration is investigated experimentally in a two-dimensional channel.Particle Image Velocimetry (P1V) system is used to take two-dimensional velocity frames in the streamwise and wall-normal plane.The additive of surfactant is cetyltrimethyl ammonium chloride (CTAC) with the mass concentration of 25 ppm.Drag reduction degeneration happens in the CTAC solution flow,exhibiting the maximal drag reduction at Re =25000and losing drag reduction completely at Re =40 000.The velocity frames are statistically analyzed in four quadrants which are divided by the u -axis and v-axis.It is found that the phenomenon of“Zero Reynolds shear stress” is caused by the decrease of wallnormal fluctuations and its symmetrical distribution in quadrants.The increase of Reynolds number leads to the enhancement of turbulence burst phenomenon.During thc drag reduction degeneration,the CTAC solution flow contains both high turbulence intensity and drag reduction states.
CME propagation: Where does the solar wind drag take over?
Sachdeva, Nishtha; Colaninno, Robin; Vourlidas, Angelos
2015-01-01
We investigate the Sun-Earth dynamics of a set of eight well observed solar coronal mass ejections (CMEs) using data from the STEREO spacecraft. We seek to quantify the extent to which momentum coupling between these CMEs and the ambient solar wind (i.e., the aerodynamic drag) influences their dynamics. To this end, we use results from a 3D flux rope model fit to the CME data. We find that solar wind aerodynamic drag adequately accounts for the dynamics of the fastest CME in our sample. For the relatively slower CMEs, we find that drag-based models initiated below heliocentric distances ranging from 15 to 50 $R_{\\odot}$ cannot account for the observed CME trajectories. This is at variance with the general perception that the dynamics of slow CMEs are influenced primarily by solar wind drag from a few $R_{\\odot}$ onwards. Several slow CMEs propagate at roughly constant speeds above 15--50 $R_{\\odot}$. Drag-based models initiated above these heights therefore require negligible aerodynamic drag to explain their...
Drag Torque Prediction Model for the Wet Clutches
Institute of Scientific and Technical Information of China (English)
HU Jibin; PENG Zengxiong; YUAN Shihua
2009-01-01
Reduction of drag torque in disengaged wet clutch is one of important potentials for vehicle transmission improvement. The flow of the oil film in clutch clearance is investigated. A three-dimension Navier-Stokes(N-S) equation based on laminar flow is presented to model the drag torque. Pressure and speed distribution in radial and circumferential directions are deduced. The theoretical analysis reveals that oil flow acceleration in radial direction caused by centrifugal force is the key reason for the shrinking of oil film as constant feeding flow rate. The peak drag torque occurs at the beginning of oil film shrinking. A variable is introduced to describe effective oil film area and drag torque after oil film shrinking is well evaluated with the variable. Under the working condition, tests were made to obtain drag torque curves at different clutch speed and oil viscosity. The tests confirm that simulation results agree with test data. The model performs well in the prediction of drag torque and lays a theoretical foundation to reduce it.
Lukerchenko, N. (Nikolay); Keita, I. (Ibrahima); Chára, Z. (Zdeněk); Vlasák, P. (Pavel)
2010-01-01
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The dimensionless drag force, Magnus force, and drag torque coefficients were determined from the comparison of the calculated translational and angular velocities and trajectory with experimental ones for the rough particle. The proper value of the correction coefficients were established from condition of the best fittin...
Lukerchenko, N. (Nikolay); Keita, I. (Ibrahima); Kvurt, Y.; Miles, J.
2010-01-01
The drag torque, drag force and Magnus force acting on a spheroid rotating around its axis of symmetry and moving perpendicularly to this axis in initially quiescent water were studied using experimental data and numerical simulation. The prolate spheroid with ratio of the axes 4/3 was speeded up in special device, which ensured the required rotational and translational velocity in the given plane. A video system was used to record the spheroid motion in water. Using the video records the sph...
Nation Drag: Uses of the Exotic
Directory of Open Access Journals (Sweden)
Micol Seigel
2009-02-01
Full Text Available In Uneven Encounters, the forthcoming book from which this article is excerpted, Micol Seigel chronicles the exchange of popular culture between Brazil and the United States in the years between the World Wars, and she demonstrates how that exchange affected ideas of race and nation in both countries. From Americans interpreting advertisements for Brazilian coffee or dancing the Brazilian maxixe, to Rio musicians embracing the “foreign” qualities of jazz, Seigel traces a lively, cultural back-and-forth. Along the way, she shows how race and nation are constructed together, by both non-elites and elites, and gleaned from global cultural and intellectual currents as well as local, regional, and national ones. Seigel explores the circulation of images of Brazilian coffee and of maxixe in the United States during the period just after the imperial expansions of the early twentieth century. Exoticist interpretations structured North Americans’ paradoxical sense of self as productive “consumer citizens.” Some people, however, could not simply assume the privileges of citizenship. In their struggles against racism, Afro-descended citizens living in the cities of Rio de Janeiro, São Paulo, New York, and Chicago encountered images and notions of each other, and found them useful. Seigel introduces readers to cosmopolitan Afro-Brazilians and African Americans who rarely traveled far but who absorbed ideas from abroad nonetheless. African American vaudeville artists saw the utility of pretending to “be” Brazilian to cross the color line on stage. Putting on “nation drag,” they passed not from one race to another but out of familiar racial categories entirely. Afro-Brazilian journalists reported intensively on foreign, particularly North American, news and eventually entered into conversation with the U.S. black press in a collaborative but still conflictual dialogue. Seigel suggests that projects comparing U.S. and Brazilian racial
Wave-Current Conditions and Navigation Safety at an Inlet Entrance
2015-06-26
Wind wave generation and growth, diffraction, reflection, dissipation due to bottom friction , white-capping and breaking, wave-current interaction...the Coriolis force, wind stress, wave stress, bottom stress, vegetation flow drag, bottom friction , wave roller, and turbulent diffusion. Governing...H s , m), spectral peak period ( pT , sec ) and mean wave direction ( , deg), wave steepness ( /H Ls p , where L p is the spectral peak wavelength
Indian Academy of Sciences (India)
Balla Venukumar; K P J Reddy
2007-02-01
Substantial aerodynamic drag, while ﬂying at hypersonic Mach number, due to the presence of strong standing shock wave ahead of a large-angle bluntcone conﬁguration, is a matter of great design concern. Preliminary experimental results for the drag reduction by a forward-facing supersonic air jet for a 60° apex-angle blunt cone at a ﬂow Mach number of 8 are presented in this paper. The measurements are carried out using an accelerometer-based balance system in the hypersonic shock tunnel HST2 of the Indian Institute of Science, Bangalore. About 29% reduction in the drag coefﬁcient has been observed with the injection of a supersonic gas jet.
2010-07-01
waves occur over the Himalayas , the drag that these waves produce occurs as a result of wave-breaking above the subtropical jet maximum. As climate...positive ρ̄u′w′ is observed only in the Indian and African monsoon regions. Westward winds are dominant in the lower stratosphere of this region. Gravity
Active Drag-Reducing Technique Using Bumps on Transonic Wings%跨音速机翼采用鼓包主动减阻技术研究
Institute of Scientific and Technical Information of China (English)
2012-01-01
Research on shock wave drag-reducing using two dimensional and three dimensional bumps is performed, including comparisons on wings of large aircraft. The mechanism of bump drag-reducing is researched via supercritical airfoil profile, and geometrical shape and location of bump are optimized. The research results show that location, shape and serial distribution of bump have significant effects on drag-reducing for wings. Finally, the drag-reducing technique using bumps is applied to the large aircraft. As a result, the presented technique reduces shock wave drag to a great extent, increases the ratio of lift to drag, and improves aerodynamic efficiency of the aircraft.%对二维、三维鼓包进行激波控制减阻，并在大型客机的机翼上进行了对比研究。在研究鼓包减阻的机理时，采用了超临界翼型，鼓包的几何形状及鼓包位置的优化也进行了研究。研究结果表明，鼓包位置、形状及串列式分布对机翼的减阻影响较大。最后把得到的研究结果应用到大型飞机的激波减阻上，结果表明，该方法能较大程度地减小激波阻力，进而提高飞机的升阻比，提高飞机的气动效率。
A Clustering Genetic Algorithm for Cylinder Drag Optimization
Milano, Michele; Koumoutsakos, Petros
2002-01-01
A real coded genetic algorithm is implemented for the optimization of actuator parameters for cylinder drag minimization. We consider two types of idealized actuators that are allowed either to move steadily and tangentially to the cylinder surface (“belts”) or to steadily blow/suck with a zero net mass constraint. The genetic algorithm we implement has the property of identifying minima basins, rather than single optimum points. The knowledge of the shape of the minimum basin enables further insights into the system properties and provides a sensitivity analysis in a fully automated way. The drag minimization problem is formulated as an optimal regulation problem. By means of the clustering property of the present genetic algorithm, a set of solutions producing drag reduction of up to 50% is identified. A comparison between the two types of actuators, based on the clustering property of the algorithm, indicates that blowing/suction actuation parameters are associated with larger tolerances when compared to optimal parameters for the belt actuators. The possibility of using a few strategically placed actuators to obtain a significant drag reduction is explored using the clustering diagnostics of this method. The optimal belt-actuator parameters obtained by optimizing the two-dimensional case is employed in three-dimensional simulations, by extending the actuators across the span of the cylinder surface. The three-dimensional controlled flow exhibits a strong two-dimensional character near the cylinder surface, resulting in significant drag reduction.
Agitator tank device and drag reduction agent evaluation
Institute of Scientific and Technical Information of China (English)
张帆; 肖博元; 汤养浩; 罗旗荣
2008-01-01
The device that consists of tank and disk agitator for evaluation drag reduction agents(DRA) was established.The effect of DRA was defined by testing the changes of agitator torque that drives the disk rotation.The HG-DRA for oil pipeline from Linyi to Puyang was studied by agitator tank device.The relationships between the drag reduction rate and Reynolds number,concentration,balance time were studied.The best concentration and the highest Renords number for the best drag reduction rate were confirmed.The results show that the drag reduction rate tested in agitator tank is close to that in pipeline.The maximum error of drag reduction rate between pipeline and agitator tank is 18.3%,which indicates that the agitator tank device is available to evaluate the effect of DRA for pipeline and it also has the advantages of simple,easy to be operated and using small volume of oil.Those are very helpful for operaters to know the properties of DRA and operate pipeline well.
Why fibers are better turbulent drag reducing agents than polymers
Boelens, Arnout; Muthukumar, Murugappan
2016-11-01
It is typically found in literature that fibers are not as effective as drag reducing agents as polymers. However, for low concentrations, when adding charged polymers to either distilled or salt water, it is found that polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. In this study, using hybrid Direct Numerical Simulation with Langevin dynamics, a comparison is performed between polymer and fiber stress tensors in turbulent flow. The stress tensors are found to be similar, suggesting a common drag reducing mechanism in the onset regime. Since fibers do not have an elastic backbone, this must be a viscous effect. Analysis of the viscosity tensor reveals that all terms are negligible, except the off-diagonal shear viscosity associated with rotation. Based on this analysis, we are able to explain why charged polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. Additionally, we identify the rotational orientation time as the unifying time scale setting a new time criterion for drag reduction by both flexible polymers and rigid fibers. This research was supported by NSF Grant No. DMR-1404940 and AFOSR Grant No. FA9550-14-1-0164.
Drag reduction of flow boiling with polymer additives
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The drag-reducing effect of polymer additive aqueous solution was investigated in flow boiling, and the polymer additives were two kinds of polyacrylamide (PAM) with relative molecular mass about 2.56×106 and 8.55×106. The frictional pressure drop was calculated according to the measured total pressure drop. The results show that the flow drag of flow boiling is reduced by adding a small amount of PAM to water when heat flux is in the range of 15.1 kW*m-2 to 47.0 kW*m-2, when the mass fraction of PAM is higher than 2.0×10-5, the drag-reducing effect is obvious. Drag-reducing effect of PAM, whose relative molecular mass is 8.55×106, is slightly better than that of 2.56×106 at the same mass fraction, and the greater the flow rate of the additive solution, the better the effect of the drag reduction.
Biomimetic Drag Reduction Study on Herringbone Riblets of Bird Feather
Institute of Scientific and Technical Information of China (English)
Huawei Chen; Fugang Rao; Xiaopeng Shang; Deyuan Zhang; Ichiro Hagiwara
2013-01-01
Birds have gradually formed various excellent structures such as streamlined shape and hollow shaft of feather to improve their flying performance by millions of years of natural selection.As typical property of bird feather,herringbone riblets align along the shaft of each feather,which is caused by perfect link of barbs,especially for the primary and secondary feathers of wings.Such herringbone riblets of feather are assumed to have great impact on drag reduction.In this paper,microstructures of secondary feathers of adult pigeons are investigated by SEM,and their structural parameters are statistically obtained.Based on quantitative analysis of feather structure,novel biomimetic herringbone riblets with narrow smooth edge are proposed to reduce surface drag.In comparison with traditional microgroove riblets and other drag reduction structures,the drag reduction rate of the proposed biomimetic herringbone riblets is experimentally clarified up to 16％,much higher than others.Moreover,the drag reduction mechanism of herringbone riblets are also confirmed and exploited by CFD.
Summary of the Fourth AIAA CFD Drag Prediction Workshop
Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Rider, Ben; Zickuhr, Tom; Levy, David W.; Brodersen, Olaf P.; Eisfeld, Bernhard; Crippa, Simone; Wahls, Richard A.; Morrison, Joseph H.; Mavriplis, Dimitri J.; Murayama, Mitcuhiro
2010-01-01
Results from the Fourth AIAA Drag Prediction Workshop (DPW-IV) are summarized. The workshop focused on the prediction of both absolute and differential drag levels for wing-body and wing-body-horizontal-tail configurations that are representative of transonic transport air- craft. Numerical calculations are performed using industry-relevant test cases that include lift- specific flight conditions, trimmed drag polars, downwash variations, dragrises and Reynolds- number effects. Drag, lift and pitching moment predictions from numerous Reynolds-Averaged Navier-Stokes computational fluid dynamics methods are presented. Solutions are performed on structured, unstructured and hybrid grid systems. The structured-grid sets include point- matched multi-block meshes and over-set grid systems. The unstructured and hybrid grid sets are comprised of tetrahedral, pyramid, prismatic, and hexahedral elements. Effort is made to provide a high-quality and parametrically consistent family of grids for each grid type about each configuration under study. The wing-body-horizontal families are comprised of a coarse, medium and fine grid; an optional extra-fine grid augments several of the grid families. These mesh sequences are utilized to determine asymptotic grid-convergence characteristics of the solution sets, and to estimate grid-converged absolute drag levels of the wing-body-horizontal configuration using Richardson extrapolation.
A Conventional Liner Acoustic/Drag Interaction Benchmark Database
Howerton, Brian M.; Jones, Michael G.
2017-01-01
The aerodynamic drag of acoustic liners has become a significant topic in the design of such for aircraft noise applications. In order to evaluate the benefits of concepts designed to reduce liner drag, it is necessary to establish the baseline performance of liners employing the typical design features of conventional configurations. This paper details a set of experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of a number of perforate-over-honeycomb liner configurations at flow speeds of M=0.3 and 0.5. These conventional liners are investigated to determine their resistance factors using a static pressure drop approach. Comparison of the resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 Hz at source sound pressure levels of 140 and 150 dB. Educed impedance and attenuation spectra are used to determine the interaction between acoustic performance and drag.
Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries
Howerton, Brian M.; Jones, Michael G.
2016-01-01
Interest in characterization of the aerodynamic drag of acoustic liners has increased in the past several years. This paper details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of centerline flow Mach number equals 0.3 and 0.5. Various perforate geometries and orientations are investigated to determine their resistance factors using a static pressure drop approach. Comparison of these resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 hertz at source sound pressure levels of 140 and 150 decibels. Educed impedance and attenuation spectra are used to determine the impact of variations in perforate geometry on acoustic performance.
CubeSat testing of Coulomb drag propulsion
Janhunen, Pekka; Toivanen, Petri; Rauhala, Timo; Haeggström, Edward; Grönland, Tor-Arne
2016-01-01
In Coulomb drag propulsion, a long high voltage tether or system of tethers gathers momentum from a natural plasma stream such as solar wind or ionospheric plasma ram flow. A positively polarised tether in the solar wind can be used for efficient general-purpose interplanetary propellantless propulsion (the electric solar wind sail or E-sail), whereas a negatively polarised tether in LEO can be used for efficient deorbiting of satellites (the plasma brake). Aalto-1 is a 3-U cubesat to be launched in May 2016. The satellite carries three scientific experiments including 100 m long Coulomb drag tether experiment. The tether is made of four 25 and 50 micrometre diameter aluminium wires that are ultrasonically bonded together every few centimetre intervals. The tether can be charged by an onboard voltage source up to one kilovolt positive and negative. The Coulomb drag is measured by monitoring the spin rate.
Fatal truck-bicycle accident involving dragging for 45 km.
Klintschar, M; Darok, M; Roll, P
2003-08-01
Vehicle-bicycle accidents with subsequent dragging of the rider over long distances are extremely rare. The case reported here is that of a 16-year-old mentally retarded bike rider who was run over by a truck whose driver failed to notice the accident. The legs of the victim became trapped by the rear axle of the trailer and the body was dragged over 45 km before being discovered under the parked truck. The autopsy revealed that the boy had died from the initial impact and not from the dragging injuries which had caused extensive mutilation. The reports of the technical expert and the forensic pathologist led the prosecutor to drop the case against the truck driver for manslaughter.
Does an active adjustment of aerodynamic drag make sense?
Maciejewski, Marek
2016-09-01
The article concerns evaluation of the possible impact of the gap between the tractor and semitrailer on the aerodynamic drag coefficient. The aim here is not to adjust this distance depending on the geometrical shape of the tractor and trailer, but depending solely on the speed of articulated vehicle. All the tests have form of numerical simulations. The method of simulation is briefly explained in the article. It considers various issues such as the range and objects of tests as well as the test conditions. The initial (pre-adaptive) and final (after adaptation process) computational meshes have been presented as illustrations. Some of the results have been presented in the form of run chart showing the change of value of aerodynamic drag coefficients in time, for different geometric configurations defined by a clearance gap between the tractor and semitrailer. The basis for a detailed analysis and conclusions were the averaged (in time) aerodynamic drag coefficients as a function of the clearance gap.
Separability of drag and thrust in undulatory animals and machines
Bale, Rahul; Neveln, Izaak D; Bhalla, Amneet Pal Singh; MacIver, Malcolm A; Patankar, Neelesh A
2014-01-01
For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal- istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation fram...
Self-burrowing seeds: drag reduction in granular media
Jung, Wonjong; Choi, Sung Mok; Kim, Wonjung; Kim, Ho-Young
2014-11-01
We present the results of a combined experimental and theoretical investigation of drag reduction of self-burrowing seeds in granular media. In response to environmental changes in humidity, the awn (a tail-like appendage of seed) of Pelargonium carnosum exhibits coiling-uncoiling deformation which induces the thrust and rotary motions of the head of the seed against the surface of the soil. Using various sizes of glass beads that mimic the granular soil, we measure the thrust forces required for the seed of Pelargonium carnosum to penetrate into granular media with and without rotation. Our quantitative measurements show that the rotation of the seed remarkably reduces the granular drag as compared to the drag against the non-spinning seed. This leads us to conclude that the hygroscopically active awns of Pelargonium carnosum enables its seed to dig into the relatively coarse granular soils.
EFFECT OF AERATOR ON HYDRAULIC DRAG ACTING ON A CHUTE
Institute of Scientific and Technical Information of China (English)
NI Han-gen; LI Xin; ZHOU Jing; JIN Qiao
2005-01-01
The formulae used to calculate the friction in the non-uniform flow chute were examined with the experimental data, and the results show that the accuracy of the formula is enough for engineering applications. A comparison between the results of friction respectively from the uniform flow assumption and the non-uniform flow approximation indicates that the former is an order of magnitude larger than the latter in the case of steep chute. The hydraulic drag on a steep chute with aerators was measured on the hydraulic model directly and the coefficient of the aerator effect on the drag was obtained. The variation patterns of the wall shear just downstream of the aerators were investigated and the mechanism of the increase in the drag by aerator were analyzed qualitatively with the measured water-depths just downstream the aerators.
Gravity wave driving of the QBO estimated from satellite observations and ERA-Interim
Ern, Manfred; Preusse, Peter; Kalisch, Silvio; Ploeger, Felix; Riese, Martin
2015-04-01
The quasi-biennial oscillation (QBO) of the zonal wind in the tropical stratosphere is an important process in atmospheric dynamics. The QBO has effect on atmospheric dynamics over a large range of altitudes and latitudes. Effects of the QBO are found, for example, in the mesosphere, and selective filtering of upward propagating waves plays an important role for the stratopause semiannual oscillation (SAO). The QBO also influences the extratropics and even surface weather and climate. Still, climate models have large difficulties in reproducing a realistic QBO. Atmospheric waves play an important role in the driving of the QBO. Both global scale waves and mesoscale gravity waves (GWs) contribute. We derive GW temperature variances, GW momentum fluxes and potential GW drag from three years of High Resolution Dynamics Limb Sounder (HIRDLS) and from 11 years of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. These observations are compared with the drag that is still missing in the tropical momentum budget of the ECMWF ERA-Interim (ERAI) reanalysis after considering zonal wind tendency, Coriolis force, advection terms, and the drag due to resolved global-scale waves. Being strongly constrained by data assimilation, the meteorological fields of ERAI are quite realistic. Therefore this missing drag can be attributed to small scale GWs not resolved by the model. We find good qualitative agreement between observed GW drag and the missing drag due to waves not resolved in ERAI. During eastward QBO wind shear even the magnitude of observed and ERAI missing drag are in good agreement. During westward shear, however, observed drag is much weaker than the ERAI missing drag. This asymmetry might hint at uncertainties in the advection terms of ERAI. Further, observed GW spectra indicate that QBO-related GW dissipation is mainly due to critical level filtering.
Optical Clock and Drag-Free Requirements for a Shapiro Time-Delay Mission
Ashby, Neil
2011-01-01
In the next decade or two, extremely accurate tests of general relativity under extreme conditions are expected from gravitational wave observations of binary black hole mergers with a wide range of mass ratios. In addition, major improvements are planned in both strong and weak equivalence principle tests; clock measurements based on the ACES program on the ISS; more accurate light-bending measurements; and other new types of tests. However, whether these tests are all consistent with general relativity or not, it still appears desirable to proceed with a much improved measurement of the Shapiro time delay. A suggested approach is based on using a high-quality optical clock in a drag-free spacecraft near the sun-earth L1 point and a smaller drag-free transponder spacecraft in a two-year period solar orbit. Laser phase travel-time measurements would be made between the two spacecraft over a period of 10 or 20 days around the time when the line of sight passes through the Sun. The requirements on the optical c...
A framework for understanding drag parameterizations for coral reefs
Rosman, Johanna H.; Hench, James L.
2011-08-01
In a hydrodynamic sense, a coral reef is a complex array of obstacles that exerts a net drag force on water moving over the reef. This drag is typically parameterized in ocean circulation models using drag coefficients (CD) or roughness length scales (z0); however, published CD for coral reefs span two orders of magnitude, posing a challenge to predictive modeling. Here we examine the reasons for the large range in reported CD and assess the limitations of using CD and z0 to parameterize drag on reefs. Using a formal framework based on the 3-D spatially averaged momentum equations, we show that CD and z0 are functions of canopy geometry and velocity profile shape. Using an idealized two-layer model, we illustrate that CD can vary by more than an order of magnitude for the same geometry and flow depending on the reference velocity selected and that differences in definition account for much of the range in reported CD values. Roughness length scales z0 are typically used in 3-D circulation models to adjust CD for reference height, but this relies on spatially averaged near-bottom velocity profiles being logarithmic. Measurements from a shallow backreef indicate that z0 determined from fits to point measurements of velocity profiles can be very different from z0 required to parameterize spatially averaged drag. More sophisticated parameterizations for drag and shear stresses are required to simulate 3-D velocity fields over shallow reefs; in the meantime, we urge caution when using published CD and z0 values for coral reefs.
The no-drag frame for anomalous chiral fluid
Stephanov, Mikhail A
2015-01-01
We show that for an anomalous fluid carrying dissipationless chiral magnetic and/or vortical currents there is a frame in which a stationary obstacle experiences no drag, but energy and charge currents do not vanish, resembling superfluidity. However, unlike ordinary superfluid flow, the anomalous chiral currents do transport entropy in this frame. We show that the second law of thermodynamics completely determines the amounts of these anomalous non-dissipative currents in the "no-drag frame" as polynomials in temperature and chemical potential with known anomaly coefficients. These general results are illustrated and confirmed by a calculation in the chiral kinetic theory and quark-gluon plasma at high temperature.
Drag reduction in electro-osmosis of polymer solutions
Chang, Feng-Ming; Tsao, Heng-Kwong
2007-05-01
Electro-osmosis is the preferred transport mechanism in microfluidic systems. Drag reduction in electro-osmosis of polymer solutions is observed due to polymer depletion in the electric double layer (EDL). The well-known Helmholtz-Smoluchowski (HS) equation indicates that the electro-osmosis mobility is inversely proportional to the solution viscosity. For low molecular weight the polymer size (R) is smaller than the EDL thickness (λ) and the HS equation is valid. For high molecular weight (R>λ) the chains in the EDL are partially sheared and the effective viscosity is smaller than the solution viscosity. Salt addition reduces λ and can enhance drag reduction substantially.
Rotation of slender swimmers in isotropic-drag media
Koens, Lyndon
2016-01-01
The drag anisotropy of slender filaments is a critical physical property allowing swimming in low-Reynolds number flows, and without it linear translation is impossible. Here we show that, in contrast, net rotation can occur under isotropic drag. We first demonstrate this result formally by considering the consequences of the force- and torque-free conditions on swimming bodies and we then illustrate it with two examples (a simple swimmers made of three rods and a model bacterium with two helical flagellar filaments). Our results highlight the different role of hydrodynamic forces in generating translational vs.~rotational propulsion.
Drag and lift coefficients evolution of a Savonius rotor
Chauvin, A.; Benghrib, D.
1989-10-01
The lift and drag coefficients of the rotating Savonius wind machine are determined from the pressure difference measured between the upper plane and the lower plane of a blade. Pressure measurements have been performed for two sets of experiments; the first one for U ∞ = 10 m/s and the second one for U ∞ = 12.5 m/s. In each case it is to be noted that a negative lift effect is present for low values of the tip speed ratio λ. The lift coefficient becomes positive when λ increases. The drag coefficient is of course always negative.
Development of reduced drag concepts for acoustic liners using experimental methods
Jasinski, Christopher
2016-11-01
Commercial aircraft have used acoustic liners to reduce engine noise for many years, although their drag production has been largely unstudied. The next generation of aircraft may benefit from additional surface area covered by acoustic liner, thus understanding their drag production mechanism is crucial for future designs. An accurate direct aerodynamic drag measurement technique has been developed using a force balance with linear air bearings. Using 3D-printed and conventional liners, low-drag designs are being developed. This paper will investigate the underlying fluid mechanics governing the drag production in acoustic liners and describe new attempts to reduce aerodynamic drag.
A Coupled Mesoscale-Model Fourier Method for Mountain Waves Over Hawaii
2010-01-01
2008a; Eckermann et al, 2009). As Smith et al (2007) note 3 in their overview of mountain waves observed over the Pyrenees during the Mesoscale Alpine...smaller than the FT/WRF wave drag values. Given that the two wave-flux peaks above the downslope of Mauna Loa and Mauna Kea were governed by
Self-consistent theory of capillarity-wave generation by small moving objects
Chepelianskii, A D; Chevy, F; Raphaël, E
2009-01-01
We investigate theoretically the onset of capillary-gravity waves created by a small object moving at the water-air interface. It is well established that, for straight uniform motion, no steady waves appear at velocities below the minimum phase velocity $c_\\text{min} = 23 {\\rm cm/s}$. At higher velocities the emission of capillary-gravity waves creates an additional drag force. The behavior of this force near the critical velocity is still poorly understood. A linear response theory where the object is replaced by an effective pressure source predicts a singular behavior for the wave drag. However, experimental data tends to indicate a more continuous transition. In this article, we show that a proper treatment of the flow equations around the obstacle can regularize wave emission, even in the linear wave approximation, thereby ensuring a continuous behavior of the drag force.
Large photon drag effect of intrinsic graphene induced by plasmonic evanescent field
Luo, Ma; Li, Zhibing
2016-12-01
A large photon drag effect of the massless Dirac fermions in intrinsic graphene is predicted for a graphene-on-plasmonic-layer system. The surface plasmons in the plasmonic layer enlarge the wave number of the photon hundreds times more than in vacuum. The evanescent field of the surface plasmons generates a directional motion of carriers in the intrinsic graphene because of the large momentum transfer from the surface plasmon to the excited carriers. A model Hamiltonian is developed on the assumption that the in-plane wavelength of the surface plasmons is much smaller than the mean free path of the carriers. The time evolution of the density matrix is solved by perturbation method as well as numerical integration. The nondiagonal density matrix elements with momentum transfer lead to a gauge current, which is an optically driven macroscopic direct current. The dependence of the macroscopic direct current on the incident direction and intensity of the laser field is studied.
Nichols, David A; Zhang, Fan; Zimmerman, Aaron; Brink, Jeandrew; Chen, Yanbei; Kaplan, Jeffrey D; Lovelace, Geoffrey; Matthews, Keith D; Scheel, Mark A; Thorne, Kip S
2011-01-01
When one splits spacetime into space plus time, the Weyl curvature tensor (vacuum Riemann tensor) gets split into two spatial, symmetric, and trace-free (STF) tensors: (i) the Weyl tensor's so-called "electric" part or tidal field, and (ii) the Weyl tensor's so-called "magnetic" part or frame-drag field. Being STF, the tidal field and frame-drag field each have three orthogonal eigenvector fields which can be depicted by their integral curves. We call the integral curves of the tidal field's eigenvectors tendex lines, we call each tendex line's eigenvalue its tendicity, and we give the name tendex to a collection of tendex lines with large tendicity. The analogous quantities for the frame-drag field are vortex lines, their vorticities, and vortexes. We build up physical intuition into these concepts by applying them to a variety of weak-gravity phenomena: a spinning, gravitating point particle, two such particles side by side, a plane gravitational wave, a point particle with a dynamical current-quadrupole mo...
Effect of Radiation Drag on Hoyle-Lyttleton Accretion
Nio, T; Fukue, J; Nio, Tomomi; Matsuda, Takuya; Fukue, Jun
1998-01-01
Hoyle-Lyttleton type accretion is investigated, by taking account of not only the effect of radiation pressure but the effect of radiation drag. We calculate the trajectories of particles for three cases: only the effect of gravity is considered (case A); the effect of radiation pressure is taken into account (case B); the effect of radiation drag as well as radiation pressure is taken into account (case C). The accretion radii for former two cases are $2GM/v_{\\infty}^2$ for case A and $2GM(1-\\Gamma)/v_{\\infty}^2$ for case B, where M is the mass of the accreted object, $v_{\\infty}$ the relative velocity, and Gamma the normalized luminosity of the accreted object. We found that the accretion radius for case C is in between those of cases A and B under the present approximation; i.e., the accretion radius decreases due to radiation pressure while it increases due to radiation drag. In addition, the accretion radius for case C becomes larger as the incident velocity becomes fast. The effect of radiation drag bec...
Spacecraft Re-Entry Impact Point Targeting Using Aerodynamic Drag
Omar, Sanny R.; Bevilacqua, Riccardo
2017-01-01
The ability to re-enter the atmosphere at a desired location is important for spacecraft containing components that may survive re-entry. While impact point targeting has traditionally been initiated through impulsive burns with chemical thrusters on large vehicles such as the Space Shuttle, and the Soyuz and Apollo capsules, many small spacecraft do not host thrusters and require an alternative means of impact point targeting to ensure that falling debris do not cause harm to persons or property. This paper discusses the use of solely aerodynamic drag force to perform this targeting. It is shown that by deploying and retracting a drag device to vary the ballistic coefficient of the spacecraft, any desired longitude and latitude on the ground can be targeted provided that the maneuvering begins early enough and the latitude is less than the inclination of the orbit. An analytical solution based on perturbations from a numerically propagated trajectory is developed to map the initial state and ballistic coefficient profile of a spacecraft to its impact point. This allows the ballistic coefficient profile necessary to reach a given target point to be rapidly calculated, making it feasible to generate the guidance for the decay trajectory onboard the spacecraft. The ability to target an impact point using aerodynamic drag will enhance the capabilities of small spacecraft and will enable larger space vehicles containing thrusters to save fuel by more effectively leveraging the available aerodynamic drag.
Towards unified drag laws for inertial flow through fibrous materials
Yazdchi, K.; Luding, S.
2012-01-01
We give a comprehensive survey of published experimental, numerical and theoretical work on the drag law correlations for fluidized beds and flow through porous media, together with an attempt of systematization. Ranges of validity as well as limitations of commonly used relations (i.e. the Ergun an
Rheological and drag reduction properties of hydroxypropyl xanthan gum solutions☆
Institute of Scientific and Technical Information of China (English)
Meng Tian; Bo Fang; Leiping Jin; Yongjun Lu; Xiaohui Qiu; Hao Jin; Kejing Li
2015-01-01
Hydroxypropyl xanthan gum (HXG) was prepared from xanthan gum (XG) and propylene oxide under alkaline condition. Rheological and drag reduction properties of different concentrations of aqueous HXG and XG solution were studied. The micro-structure network of HXG and XG solutions was investigated by Cryo-FESEM. The re-sults showed that HXG and XG solutions could exhibit shear thinning property. The apparent viscosity of 6 g·L−1 HXG solution was 1.25 times more than that of 6 g·L−1 XG solution. The storage modulus G′and the loss modulus G″of HXG solutions were greater than those of XG solutions, and thixotropic and viscoelastic prop-erties were more significant in HXG solutions. The HXG and XG solutions reduced the pressure drop of straight pipe, and the maximum drag reduction of 1 g·L−1 HXG and XG in smooth tube reached 72.8%and 68.1%, respec-tively. Drag reduction rate was increased as the concentration increased. The HXG solution may become a new polymeric drag reducer.
Superhydrophobic drag reduction in laminar flows: a critical review
Lee, Choongyeop; Choi, Chang-Hwan; Kim, Chang-Jin
2016-12-01
A gas in between micro- or nanostructures on a submerged superhydrophobic (SHPo) surface allows the liquid on the structures to flow with an effective slip. If large enough, this slippage may entail a drag reduction appreciable for many flow systems. However, the large discrepancies among the slippage levels reported in the literature have led to a widespread misunderstanding on the drag-reducing ability of SHPo surfaces. Today we know that the amount of slip, generally quantified with a slip length, is mainly determined by the structural features of SHPo surfaces, such as the pitch, solid fraction, and pattern type, and further affected by secondary factors, such as the state of the liquid-gas interface. Reviewing the experimental data of laminar flows in the literature comprehensively and comparing them with the theoretical predictions, we provide a global picture of the liquid slip on structured surfaces to assist in rational design of SHPo surfaces for drag reduction. Because the trapped gas, called plastron, vanishes along with its slippage effect in most application conditions, lastly we discuss the recent efforts to prevent its loss. This review is limited to laminar flows, for which the SHPo drag reduction is reasonably well understood.
A Phenomenological Drag Law in Blast-Soil Interaction
2013-01-16
mentioned work coming from the sedimentation and fluidization UNCLASSIFIED: Distribution Statement A. Approved for public release 4 studies [Gidaspow, 1994...with Fluidization . Academic Press. [Loth, 2008] Loth, E. (2008). Compressibility and rarefaction effects on drag of a spherical particle. AIAA, 46(9
Exploring the Aerodynamic Drag of a Moving Cyclist
Theilmann, Florian; Reinhard, Christopher
2016-01-01
Although the physics of cycling itself is a complex mixture of aerodynamics, physiology, mechanics, and heuristics, using cycling as a context for teaching physics has a tradition of certainly more than 30 years. Here, a possible feature is the discussion of the noticeable resistant forces such as aerodynamic drag and the associated power…
Single Gradientless Light Beam Drags Particles as Tractor Beams
DEFF Research Database (Denmark)
Novitsky, Andrey; Qiu, Cheng-Wei; Wang, Haifeng
2011-01-01
is the strong nonparaxiality of the light beam, which contributes to the pulling force owing to momentum conservation. The nonparaxiality of the Bessel beam can be manipulated to possess a dragging force along both the radial longitudinal directions, i.e., a "tractor beam" with stable trajectories is achieved...
Interactive point cloud blending by drag-and-drop
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
With the rapid development of 3D digital photography and 3D digital scanning devices, massive amount of point samples can be generated in acquisition of complex, real-world objects, and thus create an urgent need for advanced point-based processing and editing. In this paper, we present an interactive method for blending point-based geometries by dragging-anddropping one point-based model onto another model's surface metaphor. We first calculate a blending region based on the polygon of interest when the user drags-and-drops the model. Radial basis function is used to construct an implicit surface which smoothly interpolates with the transition regions. Continuing the drag-and-drop operation will make the system recalculate the blending regions and reconstruct the transition regions. The drag-and-drop operation can be compound in a constructive solid geometry (CSG) manner to interactively construct a complex point-based model from multiple simple ones. Experimental results showed that our method generates good quality transition regions between two raw point clouds and can effectively reduce the rate of overlapping during the blending.
DRAG REDUCTION EFFECT OF COUPLING FLEXIBLE TUBES WITH TURBULENT FLOW
Institute of Scientific and Technical Information of China (English)
CAI Shu-peng; JIN Guo-yu; LI Da-mei; Yang Lin
2008-01-01
To analyze the mechanism of drag reducing effect by coupling flexible tubes with turbulent flow, based on experimental examination of more obvious turbulent drag reduction effect in flexible tubes than in rigid tubes, experimental investigation was performed on the effect of turbulent drag reduction, fluctuating vibration characteristics of flexible tube and the correlations by using a double-tube system and laser displacement sensor. The results are as follows: with the decrease of the thickness of the flexible tubes, the root mean square of fluctuating amplitude of the outer wall of the tubes increases, and the non-dimensional burst period increases, resulting in the increase of the reduction rate of drag coefficient by coupling flexible tubes with turbulent flow. At applied pressure-balanced air on the outer wall and the Reynolds number of about 1.75 104, the non-dimensional burst periods of the flexible tubes with the thickness of 2 mm, 3 mm, 4 mm are 141, 126, 105, respectively.
Some Remarks on CFD Drag Prediction of an Aircraft Model
Peng, S. H.; Eliasson, P.
Observed in CFD drag predictions for the DLR-F6 aircraft model with various configurations, some issues are addressed. The emphasis is placed on the effect of turbulence modeling and grid resolution. With several different turbulence models, the predicted flow feature around the aircraft is highlighted. It is shown that the prediction of the separation bubble in the wing-body junction is closely related to the inherent modeling mechanism of turbulence production. For the configuration with an additional fairing, which has effectively removed the separation bubble, it is illustrated that the drag prediction may be altered even for attached turbulent boundary layer when different turbulence models are used. Grid sensitivity studies are performed with two groups of subsequently refined grids. It is observed that, in contrast to the lift, the drag prediction is rather sensitive to the grid refinement, as well as to the artificial diffusion added for solving the turbulence transport equation. It is demonstrated that an effective grid refinement should drive the predicted drag components monotonically and linearly converged to a finite value.
Frictional drag between quantum wells mediated by phonon exchange
DEFF Research Database (Denmark)
Bønsager, M.C.; Flensberg, Karsten; Hu, Ben Yu-Kuang;
1998-01-01
lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation...
A coating of passively oscillating flexible cilia to reduce drag
Revell, Alistair; Harwood, Adrian; O'Connor, Joseph; Sanchez, Jonathan; Favier, Julien
2016-11-01
We present results related to the reduction of wake drag by the coordinated action of a layer of passively oscillating flexible cilia. Inspired by the pop-up of bird feathers, this configuration is shown to self-adapt to the surrounding flow, leading to a stabilization of the wake, a reduction of the mean drag and of lift oscillations. The study is performed using Lattice Boltzmann method, coupled to a recent version of the immersed boundary method. We will present the physical analysis of the coupling between multiple beating cilia and an incoming fluid flow. The modal behaviour of the cilia dynamics will be discussed, as well as their effect on an archetype of unsteady separated boundary layer (first the oscillating channel flow and then the circular cylinder). In the latter case results demonstrate an optimal drag occurs for a particular stiffness, compared to the control case where the same cilia are fixed. It appears that the optimal results are due to a reconfiguration of the elastic coating according to the local vorticity of the flow, and a frequency lock-in, which leads to more stable wake and reduced drag. The structural parameters of the layer will be varied. Results from the PEL-SKIN project: funded by EU Grant #334954.
Effect of swim cap model on passive drag.
Gatta, Giorgio; Zamparo, Paola; Cortesi, Matteo
2013-10-01
Hydrodynamics plays an important role in swimming because even small decreases in a swimmer's drag can lead to performance improvements. During the gliding phases of a race, the head of a swimmer is an important point of impact with the fluid, and the swim cap, even if it covers only a small portion of the swimmer's body, can have an influence on drag. The purpose of this study was to investigate the effects on passive drag (Dp) of wearing 3 different types of swim caps (LSC: a lycra cap; CSC: a silicone cap; HSC: a silicone helmet cap without seams). Sixteen swimmers were tested at 3 velocities (1.5, 1.7, 1.9 m·s), and the Dp measurements were repeated at each condition 5 times. A statistical analysis revealed significant differences in drag (p swim cap is the most rigid, the most adherent to the swimmer's head, and does not allow the formation of wrinkles compared with the other 2 investigated swim caps. Therefore, the following conclusions can be made: (a) swimmers should take care when selecting their swim cap if they want to improve the fluid dynamics at the "leading edge" of their body and (b) because Dp is affected by the swim cap model, care should be taken when comparing data from different studies, especially at faster investigated speeds.
The Mercury-Drag Effect, a Demonstration of Transport Phenomena
Martin, D. H.; Teese, R. B
1969-01-01
The mercury-drag effect is demonstrated when mercury vapor diffuses through nitrogen gas at low pressure, passing through tubes of different radii to liquid nitrogen-cooled cold traps. The pressure changes of the nitrogen gas on the mercury-deficient side of the cold traps are observed and compared with theoretical and experimental valves from the…
Separability of drag and thrust in undulatory animals and machines.
Bale, Rahul; Shirgaonkar, Anup A; Neveln, Izaak D; Bhalla, Amneet Pal Singh; MacIver, Malcolm A; Patankar, Neelesh A
2014-12-10
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.
Drag force and surface roughness measurements on freshwater biofouled surfaces.
Andrewartha, J; Perkins, K; Sargison, J; Osborn, J; Walker, G; Henderson, A; Hallegraeff, G
2010-05-01
The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m x 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.
Laminar Drag Reduction in Microchannels Using Ultrahydrophobic Surfaces
Ou, Jia; Perot, Blair; Rothstein, Jonathan
2003-11-01
In devices where the fluid flow is laminar, there are currently no methods for reducing drag. We will present a series of experiments which demonstrate a 20-30% drag reduction for the flow of water through microchannels using hydrophobic surfaces with micron sized roughness. These 'ultrahydrophobic' surfaces are fabricated using photolithography to etch microposts and microridges with specific size, spacing and arrangement into silicon. The surfaces are then reacted with an organosilane to make them hydrophobic. The resulting surfaces have contact angles greater than 150 degrees. Pressure drop measurements are made for a series of ultrahydrophobic surface patterns, flow rates and microchannel heights. Pressure drop measurements across hydrophobic smooth surfaces are found to correlate precisely with theory while the drag reduction observed for the flow across these ultrahydrophobic surfaces is found to increase with increasing micropost spacing and decreasing micropost area. A physical model will be presented which explains the drag reduction in terms of a shear-free air-water interface between microposts supported by surface tension. Confirmation of the model will be presented with optical measurements of the displacement of the air-water interface under flow.
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...
FY2003 Annual Report: DOE Project on Heavy Vehicle Aerodynamic Drag
Energy Technology Data Exchange (ETDEWEB)
McCallen, R C; Salari, K; Ortega, J; DeChant, L J; Roy, C J; Payne, J J; Hassan, B; Pointer, W D; Browand, F; Hammache, M; Hsu, T; Ross, J; Satran, D; Heineck, J; Walker, S; Yaste, D; Englar, R; Leonard, A; Rubel, M; Chatelain, P
2003-10-24
Objective: {sm_bullet} Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles. {sm_bullet} Establish a database of experimental, computational, and conceptual design information, and demonstrate potential of new drag-reduction devices.
Numerical Research on Drag Reduction Characteristics of Supercavitating Body of Revolution
Institute of Scientific and Technical Information of China (English)
FUHui-ping; LUChuan-jing; LIJie
2004-01-01
Drag reduction characteristics of supercavitating body of revolution was researched numerically with a bubble two-phase flow model embodied in commercial CFD code Fluent 6.0.The work included the effects of body shape on drag coefficient and supercavity sizes; supercavity control; drag coefficient Cd as a function of cavitation number; and the effect of the ratio of length L to diameter D on drag reduction rate. Research on drag reduction mechanism of supercavitation shows that supercavitation can reduce not only the friction drag coefficient but also the pressure drag coefficient. There may be a best combination among body shape, the ratio L/D, cavitation number, engineering feasibility and so on, which makes the drag reduction ratehighest.
Quantifying drag on wellbore casings in moving salt sheets
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.
Reducing drag of a commuter train, using engine exhaust momentum
Ha, Dong Keun
The objective of this thesis was to perform numerical investigations of two different methods of injecting fluid momentum into the air flow above a commuter train to reduce its drag. Based on previous aerodynamic modifications of heavy duty trucks in improving fuel efficiency, two structural modifications were designed and applied to a Metrolink Services commuter train in the Los Angeles (LA) County area to reduce its drag and subsequently improve fuel efficiency. The first modification was an L-shaped channel, added to the exhaust cooling fan above the locomotive roof to divert and align the exhaust gases in the axial direction. The second modification was adding an airfoil shaped lid over the L-shape channel, to minimize the drag of the perturbed structure, and thus reduce the overall drag. The computational fluid dynamic (CFD) software CCM+ from CD-Adapco with the ?-? turbulence model was used for the simulations. A single train set which consists of three vehicles: one locomotive, one trailer car and one cab car were used. All the vehicles were modeled based on the standard Metrolink fleet train size. The wind speed was at 90 miles per hour (mph), which is the maximum speed for the Orange County Metrolink line. Air was used as the exhaust gas in the simulation. The temperature of the exhausting air emitting out of the cooling fan on the roof was 150 F and the average fan speed was 120 mph. Results showed that with the addition of the lid, momentum injection results in reduced flow separation and pressure recovery behind the locomotive, which reduces the overall drag by at least 30%.
Aerodynamic drag from two tubes in side-by-side arrangement for different tube shapes
Directory of Open Access Journals (Sweden)
Олександр Михайлович Терех
2016-06-01
Full Text Available Experimental investigations of aerodynamic drag from two tubes in side-by-side arrangement for different tube shapes in the range of Reynolds numbers from 4000 to16000 are performed. Comparison of experimental data is executed. It is set, that the tubes of drop-shaped form have less aerodynamic drag and the tubes of flat-oval and dumb-bell forms have greater drag as compared to drag of circular tubes
2011-08-22
... Madness Drag Boat Race, Mattaponi River, Wakema, VA AGENCY: Coast Guard, DHS. ACTION: Temporary Final rule. SUMMARY: The Coast Guard will establish special local regulations during the Mattaponi Madness Drag ] Boat... events titled the ``Mattaponi Madness Drag Boat Event.'' The power boat races will be held on the...
Drag-free Small Satellite Platforms for Future Geodesy Missions
Conklin, J. W.; Hong, S.; Nguyen, A.; Serra, P.; Balakrishnan, K.; Buchman, S.; De Bra, D. B.; Hultgren, E.; Zoellner, A.
2013-12-01
Continuous satellite geodesy measurements lasting into the foreseeable future are critical for the understanding of our changing planet. It is therefore imperative that we explore ways to reduce costs, while maintaining science return. Small satellite platforms represent a promising path forward if ways can be found to reduce the size, weight, and power of the necessary instrumentation. One key enabling technology is a precision small-scale drag-free system under development at the University of Florida and Stanford University. A drag-free satellite (a) contains and shields a free-floating test mass from all non-gravitational forces, and (b) precisely measures the position of the test mass inside the satellite. A feedback control system commands thrusters to fly the 'tender' spacecraft with respect to the test mass. Thus, both test mass and spacecraft follow a pure geodesic in spacetime. By tracking the relative positions of low Earth orbiting drag-free satellites, using laser interferometry for example, the detailed shape of geodesics, and through analysis, the higher order harmonics of the Earth's geopotential can be determined. Drag-free systems can be orders of magnitude more accurate that accelerometer-based systems because they fundamentally operate at extremely low acceleration levels, and are therefore not limited by dynamic range like accelerometers. Since no test mass suspension force is required, larger gaps between the test mass and satellite are possible, which reduces the level of unwanted disturbing forces produced by the satellite itself. The small satellite platform also enables cost-effective constellations, which can increase the temporal resolution of gravity field maps by more-frequently observing given locations on the Earth. Mixed-orbit constellations can also markedly enhance observational strength, decorrelate gravity coefficient estimates, and help address the fundamental aliasing problem that exists with previous missions. The
Pendergraft, O. C., Jr.; Schmeer, J. W.
1972-01-01
Twin-jet afterbody models were investigated by using two balances to measure the thrust-minus-total drag and the afterbody drag, separately, at static conditions and at Mach numbers up to 2.2 for an angle of attack of 0 deg. Hinged-flap convergent-divergent nozzles were tested at subsonic-cruise- and maximum-afterburning-power settings with a high-pressure air system used to provide jet-total-pressure ratios up to 20. Two nozzle lateral spacings were studied, using afterbodies with similar interfairing shapes but with different longitudinal cross-sectional area distributions. Alternate, blunter, interfairings with different shapes for the two spacings, which produced afterbodies having identical cross-sectional area progressions corresponding to an axisymmetric minimum wave-drag configuration, were also tested. The results indicate that the wide-spaced configurations improved the flow field around the nozzles, thereby reducing drag on the cruise nozzles; however, the increased surface and projected cross-sectional areas caused an increase in afterbody drag. Except for a slight advantage with cruise nozzles at subsonic speeds, the wide-spaced configurations had the higher total drag at all other test conditions.
Acceleration Noise Considerations for Drag-free Satellite Geodesy Missions
Hong, S. H.; Conklin, J. W.
2016-12-01
The GRACE mission, which launched in 2002, opened a new era of satellite geodesy by providing monthly mass variation solutions with spatial resolution of less than 200 km. GRACE proved the usefulness of a low-low satellite-to-satellite tracking formation. Analysis of the GRACE data showed that the K-Band ranging system, which is used to measure the range between the two satellites, is the limiting factor for the precision of the solution. Consequently, the GRACE-FO mission, schedule for launch in 2017, will continue the work of GRACE, but will also test a new, higher precision laser ranging interferometer compared with the K-Band ranging system. Beyond GRACE-FO, drag-free systems are being considered for satellite geodesy missions. GOCE tested a drag-free attitude control system with a gravity gradiometer and showed improvements in the acceleration noise compensation compared to the electrostatic accelerometers used in GRACE. However, a full drag-free control system with a gravitational reference sensor has not yet been applied to satellite geodesy missions. More recently, this type of drag-free system was used in LISA Pathfinder, launched in 2016, with an acceleration noise performance two orders of magnitude better than that of GOCE. We explore the effects of drag-free performance in satellite geodesy missions similar to GRACE-FO by applying three different residual acceleration noises from actual space missions: GRACE, GOCE and LISA Pathfinder. Our solutions are limited to degree 60 spherical harmonic coefficients with biweekly time resolution. Our analysis shows that a drag-free system with acceleration noise performance comparable to GOCE and LISA-Pathfinder would greatly improve the accuracy of gravity solutions. In addition to these results, we also present the covariance shaping process used in the estimation. In the future, we plan to use actual acceleration noise data measured using the UF torsion pendulum. This apparatus is a ground facility at
An active attitude control system for a drag sail satellite
Steyn, Willem Herman; Jordaan, Hendrik Willem
2016-11-01
The paper describes the development and simulation results of a full ADCS subsystem for the deOrbitSail drag sail mission. The deOrbitSail satellite was developed as part of an European FP7 collaboration research project. The satellite was launched and commissioning started on 10th July 2015. Various new actuators and sensors designed for this mission will be presented. The deOrbitSail satellite is a 3U CubeSat to deploy a 4 by 4 m drag sail from an initial 650 km circular polar low earth orbit. With an active attitude control system it will be shown that by maximising the drag force, the expected de-orbiting period from the initial altitude will be less than 50 days. A future application of this technology will be the use of small drag sails as low-cost devices to de-orbit LEO satellites, when they have reached their end of life, without having to use expensive propulsion systems. Simulation and Hardware-in-Loop experiments proved the feasibility of the proposed attitude control system. A magnetic-only control approach using a Y-Thomson spin, is used to detumble the 3U Cubesat with stowed sail and subsequently to 3-axis stabilise the satellite to be ready for the final deployment phase. Minituarised torquer rods, a nano-sized momentum wheel, attitude sensor hardware (magnetometer, sun, earth) developed for this phase will be presented. The final phase will be to deploy and 3-axis stabilise the drag sail normal to the satellite's velocity vector, using a combined Y-momentum wheel and magnetic controller. The design and performance improvements when using a 2-axis translation stage to adjust the sail centre-of-pressure to satellite centre-of-mass offset, will also be discussed, although for launch risk reasons this stage was not included in the final flight configuration. To accurately determine the drag sail's attitude during the sunlit part of the orbit, an accurate wide field of view dual sensor to measure both the sun and nadir vector direction was developed for
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.
Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids
Vakarelski, Ivan U.; Berry, Joseph D.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.
2016-09-01
The drag coefficient CD of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re ˜3 ×1 05 . A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ˜600 to 1 05. The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape.
Wind tunnel experiment of drag of isolated tree models in surface boundary layer
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
For very sparse tree land individual tree was the basic element of interaction between atmosphere and the surface. Drag of isolated tree was preliminary aerodynamic index for analyzing the atmospheric boundary layer of this kind of surface. A simple pendulum method was designed and carried out in wind tunnel to measure drag of isolated tree models according to balance law of moment of force. The method was easy to conduct and with small error. The results showed that the drag and drag coefficient of isolated tree increased with decreasing of its permeability or porosity. Relationship between drag coefficient and permeability of isolated tree empirically was expressed by quadric curve.
Li, Shi-bin; Wang, Zhen-guo; Barakos, George N.; Huang, Wei; Steijl, Rene
2016-10-01
Waverider will endure the huge aero-heating in the hypersonic flow, thus, it need be blunt for the leading edge. However, the aerodynamic performance will decrease for the blunt waverider because of the drag hoik. How to improve the aerodynamic performance and reduce the drag and aero-heating is very important. The variable blunt radii method will improve the aerodynamic performance, however, the huge aero-heating and bow shock wave at the head is still serious. In the current study, opposing jet is used in the waverider with variable blunt radii to improve its performance. The three-dimensional coupled implicit Reynolds-averaged Navier-Stokes(RANS) equation and the two equation SST k-ω turbulence model have been utilized to obtain the flow field properties. The numerical method has been validated against the available experimental data in the open literature. The obtained results show that the L/D will drop 7-8% when R changes from 2 to 8. The lift coefficient will increase, and the drag coefficient almost keeps the same when the variable blunt radii method is adopted, and the L/D will increase. The variable blunt radii method is very useful to improve the whole characteristics of blunt waverider and the L/D can improve 3%. The combination of the variable blunt radii method and opposing jet is a novel way to improve the whole performance of blunt waverider, and L/D can improve 4-5%. The aperture as a novel way of opposing jet is suitable for blunt waverider and also useful to improve the aerodynamic and aerothermodynamic characteristics of waverider in the hypersonic flow. There is the optimal P0in/P0 that can make the detached shock wave reattach the lower surface again so that the blunt waverider can get the better aerodynamic performance.
Mechanically Robust Superhydrophobic Surfaces for Turbulent Drag Reduction
Golovin, Kevin; Boban, Mathew; Xia, Charlotte; Tuteja, Anish
2014-11-01
Superhydrophobic surfaces (SHS) resist wetting by keeping a thin air layer within their texture. Such surfaces have been shown to reduce skin friction during laminar and transitional flows. However, turbulent boundary layer flows exhibit high shear stresses that damage the fragile microstructure of most SHS, and it is yet unclear to what extent these surfaces can reduce drag. Moreover, the increasing pressure fluctuations and decreasing wall unit length experienced during turbulent flow makes designing mechanically robust SHS with the correct roughness scales a challenge. In this work we evaluate many different SHS in terms of their hydrophobicity, mechanical durability and roughness. Whereas even commercially available SHS lose their superhydrophobic properties after slight mechanical abrasion, our novel coatings survive up to 200x longer. Moreover, we evaluate how the roughness of such surfaces changes with mechanical abrasion, and we design SHS with the correct roughness to display optimal drag reduction in turbulent boundary layer flows. Funding from ONR.
Detection of gravitational frame dragging using orbiting qubits
Lanzagorta, Marco; Salgado, Marcelo
2016-05-01
In this paper we propose information theoretic and interferometric techniques to detect the effect of gravitational frame dragging on orbiting qubits. In particular, we consider the Kerr spacetime geometry and spin-\\tfrac{1}{2} qubits moving in equatorial circular orbits. We ignore the { O }({\\hslash }) order effects due to spin-curvature coupling, which allows us to consider the motion of the spin-\\tfrac{1}{2} particles as Kerr geometry geodesics. We derive analytical expressions for the infinitesimal Wigner rotation and numerical results for their integration across the length of the particle’s trajectory. To this end, we consider the bounds on the finite Wigner rotation imposed by Penrose’s cosmic censorship hypothesis. Finally we propose how the Wigner rotation strictly due to frame dragging could be observed using interferometry and other quantum metrology techniques.
Drag-shield drop tower residual acceleration optimisation
Figueroa, A.; Sorribes-Palmer, F.; Fernandez De Pierola, M.; Duran, J.
2016-07-01
Among the forces that appear in drop towers for microgravity experiments, aerodynamic drag plays a crucial role in the residual acceleration. Buoyancy can also be critical, especially at the first instances of the drop when the low speed of the experimental platform makes the aerodynamic drag small compared with buoyancy. In this paper the perturbation method is used to formulate an analytical model which has been validated experimentally. The experimental test was conduced by undergraduate students of aerospace engineering at the Institute of Microgravity ‘Ignacio Da Riva’ of the Technical University of Madrid (IDR/UPM) microgravity tower. The test helped students to understand the influence of the buoyancy on the residual acceleration of the experiment platform. The objective of the students was to understand the physical process during the drop, identify the main parameters involved in the residual acceleration and determine the most suitable configuration for the next drop tower proposed to be built at UPM.
Ion drag force in plasmas at high electronegativity.
Denysenko, I; Yu, M Y; Stenflo, L; Xu, S
2005-07-01
The electric as well as the positive- and negative-ion drag forces on an isolated dust grain in an electronegative plasma are studied for large negative-ion densities, when the negative ions are not Boltzmann distributed. The investigation is carried out for submicrometer dust particles, so that the theory of Coulomb scattering is applicable for describing ion-dust interaction. Among the forces acting on the dust grain, the negative-ion drag force is found to be important. The effects of the negative-ion density, neutral-gas pressure, and dust-grain size on the forces are also considered. It is shown that by increasing the density of the negative ions one can effectively manipulate the dust grains. Our results imply that both dust voids and balls can be formed.
Bioinspired superhydrophobic, self-cleaning and low drag surfaces
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.
Simultaneous drag and flow measurements of Olympic skeleton athletes
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.
Substructure drag effects and recrystallization textures in aluminium
Energy Technology Data Exchange (ETDEWEB)
Higginson, R. [Univ. of Sheffield (United Kingdom). Dept. of Engineering Materials; Bate, P. [Doncasters plc, Melbourne (United Kingdom)
1999-03-10
Many important recrystallization texture components in metals such as aluminium originate from nuclei in which the mobile high-angle boundary exists prior to, or is formed in the early stages of, annealing. Nucleation can then occur by a process known as strain-induced boundary migration (SIBM). It is possible that this process will involve several growing subgrains, and the drag from that substructure can then have a significant effect. A simple model is used to demonstrate how changes in the overall driving force for recrystallization and Zener drag can affect recrystallization textures when SIBM is involved. This is discussed in relation to experimental observations and the evidence for this process is reviewed.
Observation of light dragging in rubidium vapor cell
Strekalov, D V; Yu, N; Maleki, L; Strekalov, Dmitry; Matsko, Andrey B.; Yu, Nan; Maleki, Lute
2003-01-01
We report on the experimental demonstration of light dragging effect due to atomic motion in a rubidium vapor cell. We found that the minimum group velocity is achieved for light red-shifted from the center of the atomic resonance, and that the value of this shift increases with decreasing group velocity, in agreement with the theoretical predictions by Kocharovskaya, Rostovtsev, and Scully [Phys. Rev. Lett. {\\bf 86}, 628 (2001)].
Lift and Drag Performance of Odontocete Cetacean Flippers
2009-01-01
Cooper et al., 2008). The cross-section of a typical flipper is similar to that of a modern engineered air/ hydrofoil (Fish, 2004; Miklosovic et al., 2004...to modern engineered hydrofoils , which have hydrodynamic properties such as lift coefficient, drag coefficient and associated efficiency. Field...study are differentiated by whether or not their lift curves are linear. An engineered hydrofoil with linear behavior in the non-stall region was also
Alleviation of fuselage form drag using vortex flows: Final report
Energy Technology Data Exchange (ETDEWEB)
Wortman, A.
1987-09-15
The concept of using vortex generators to reduce the fuselage form drag of transport aircraft combines the outflow from the plane of symmetry which is induced by the rotational component of the vortex flow with the energization of the boundary layer to reduce the momentum thickness and to delay or eliminate flow separation. This idea was first advanced by the author in 1981. Under a DOE grant, the concept was validated in wind tunnel tests of approximately 1:17 scale models of fuselages of Boeing 747 and Lockheed C-5 aircraft. The search for the minimum drag involved three vortex generator configurations with three sizes of each in six locations clustered in the aft regions of the fuselages at the beginning of the tail upsweep. The local Reynolds number, which is referred to the length of boundary layer run from the nose, was approximately 10{sup 7} so that a fully developed turbulent boundary layer was present. Vortex generator planforms ranged from swept tapered, through swept straight, to swept reverse tapered wings whose semi-spans ranged from 50% to 125% of the local boundary layer thickness. Pitch angles of the vortex generators were varied by inboard actuators under the control of an external proportional digital radio controller. It was found that certain combinations of vortex generator parameters increased drag. However, with certain configurations, locations, and pitch angles of vortex generators, the highest drag reductions were 3% for the 747 and about 6% for the C-5, thus confirming the arguments that effectiveness increases with the rate of upsweep of the tail. Greatest gains in performance are therefore expected on aft loading military transports. 10 refs., 11 figs., 1 tab.
Measuring the Effects of Lift and Drag on Projectile Motion
Cross, Rod
2012-01-01
The trajectory of a projectile through the air is affected both by gravity and by aerodynamic forces. The latter forces can conveniently be ignored in many situations, even when they are comparatively large. For example, if a 145-g, 74-mm diameter baseball is pitched at 40 ms[superscript -1] (89.5 mph), it experiences a drag force of about 1.5 N.…
Drag force in wind tunnels: A new method
Souza, P. V. S.; Girardi, D.; de Oliveira, P. M. C.
2017-02-01
A rigid object of general shape is fixed inside a wind tunnel. The drag force exerted on it by the wind is determined by a new method based on simple basic Physics concepts, provided one has a solver, any solver, for the corresponding dynamic Navier-Stokes equation which determines the wind velocity field around the object. The method is completely general, but here we apply it to the traditional problem of a long cylinder perpendicular to the wind.
Thermal lift generation and drag reduction in rarefied aerodynamics
Pekardan, Cem; Alexeenko, Alina
2016-11-01
With the advent of the new technologies in low pressure environments such as Hyperloop and helicopters designed for Martian applications, understanding the aerodynamic behavior of airfoils in rarefied environments are becoming more crucial. In this paper, verification of rarefied ES-BGK solver and ideas such as prediction of the thermally induced lift and drag reduction in rarefied aerodynamics are investigated. Validation of the rarefied ES-BGK solver with Runge-Kutta discontinous Galerkin method with experiments in transonic regime with a Reynolds number of 73 showed that ES-BGK solver is the most suitable solver in near slip transonic regime. For the quantification of lift generation, A NACA 0012 airfoil is studied with a high temperature surface on the bottom for the lift creation for different Knudsen numbers. It was seen that for lower velocities, continuum solver under predicts the lift generation when the Knudsen number is 0.00129 due to local velocity gradients reaching slip regime although lift coefficient is higher with the Boltzmann ES-BGK solutions. In the second part, the feasibility of using thermal transpiration for drag reduction is studied. Initial study in drag reduction includes an application of a thermal gradient at the upper surface of a NACA 0012 airfoil near trailing edge at a 12-degree angle of attack and 5 Pa pressure. It was seen that drag is reduced by 4 percent and vortex shedding frequency is reduced due to asymmetry introduced in the flow due to temperature gradient causing reverse flow due to thermal transpiration phenomena.
Reducing Aerodynamic Drag on Empty Open Cargo Vehicles
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.
Asymptotic analytical methods in fluid mechanics related to drag prediction
Inger, G. R.
1975-01-01
Some recent theoretical work of a purely analytical nature is described which promises to provide engineering predictions for the important drag-related phenomena of flow in the stall regime. This analytical work deals with rigorous asymptotic studies of the complete Navier-Stokes equations that govern the viscous flow around any aerodynamic body under conditions where boundary layer separation takes place from the body surface.
Simulation of the Clustering Phenomenon in a Fast Fluidized Bed： The Importance of Drag Correlation
Institute of Scientific and Technical Information of China (English)
李佑楚
2004-01-01
Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has, however, not been thoroughly investigated. In this article, a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization, including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles. Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation. The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds. This drag force correlation, based on a simple averaging assumption, could give some basic insights about the magnitude of the drag reduction.
5th Drag Reduction in Engineering Flows Meeting
1991-01-01
The European Drag Reduction Meeting has been held on 15th and 16th November 1990 in London. This was the fifth of the annual European meetings on drag reduction in engineering flows. The main objective of this meeting was to discuss up-to-date results of drag reduction research carried out in Europe. The organiser has adopted the philosophy of discussing the yesterday's results rather than the last year's results. No written material has therefore been requested for the meeting. It was only after the meeting the submission of papers was requested to the participants, from which 16 papers were selected for this proceedings volume. The meeting has attracted a record number of participants with a total of 52 researchers from seven European countries, U. K. , France, Germany, the Netherlands, Italy, Switzerland and U. S. S. R. as well as from Japan, Canada and Australia. The subjects covered in this proceedings volume include riblets, LEBUs (Large Eddy Break-Up device), surface roughness, compliant surfaces and p...
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.
Frame-dragging Effect in Strong Gravity Regime
Chakraborty, Chandrachur
2016-01-01
The exact frame-dragging (or Lense-Thirring (LT) precession) rates for Kerr, Kerr-Taub-NUT (KTN) and Taub-NUT spacetimes have been derived. Remarkably, in the case of the `zero angular momentum' Taub-NUT spacetime, the frame-dragging effect is shown not to vanish, when considered for spinning test gyroscope. In the case of the interior of the pulsars, the exact frame-dragging rate monotonically decreases from the center to the surface along the pole and but it shows an `anomaly' along the equator. Moving from the equator to the pole, it is observed that this `anomaly' disappears after crossing a critical angle. The `same' anomaly can also be found in the KTN spacetime. The resemblance of the anomalous LT precessions in the KTN spacetimes and the spacetime of the pulsars could be used to identify a role of Taub-NUT solutions in the astrophysical observations or equivalently, a signature of the existence of NUT charge in the pulsars.
Effects of drag factor on physiological aspects of rowing.
Kane, D A; Jensen, R L; Williams, S E; Watts, P B
2008-05-01
This study examined the effects of two resistances, or "drag factors" on selected physiological variables during incremental progressive rowing tests (seven 3-min stages) on a Concept2 ergometer. Subjects were seven male and seven female university club rowers. Their mean age, body mass and height were 19.6 +/- 1.5 years, 72.7 +/- 8.0 kg, and 172.2 +/- 7.5 cm, respectively. Progressive tests were conducted using drag factors 100 (D100) and 150 (D150) before the spring racing season. Values were determined for the following physiological variables: ventilation (V.E), oxygen uptake (V.O2), heart rate (HR), blood lactate concentration (BLC), respiratory exchange ratio (R) and rowing economy (W/V.O2). Comparisons across all six submaximal stages showed no significant difference between D(100) and D(150) for any of the variables measured (p > .05). Maximal V.E(max) was significantly greater at D100 than D150 (p D100 than at D150, though not significantly so. The mean D100-D150 differences in V.E and SR for each stage were significantly correlated (r = 0.76, p < .01), suggesting drag factor may affect V.E via SR.
Effect of The Swimmer's Head Position on Passive Drag.
Cortesi, Matteo; Gatta, Giorgio
2015-12-22
The aim of this study was to investigate the effect of the head position on passive drag with a towing-line experiment in a swimming pool. The tests were performed on ten male swimmers with regional level swimming skills and at least 10 years of competitive swimming experience. They were towed underwater (at a depth of 60 cm) at three speeds (1.5, 1.7 and 1.9 m/s) and in two body positions (arms above the swimmer's head and arms alongside the body). These two body positions were repeated while the swimmer's head was positioned in three different ways: head-up, head-middle and head-down in relation to the body's horizontal alignment. The results showed a reduction of 4-5.2% in the average passive drag at all speeds when the head was down or aligned to the swimmer's arms alongside the body, in comparison to the head-up position. A major significant decrease of 10.4-10.9% (p < 0.05) was shown when the head was down or aligned at the swimmer's arms above the swimmer's head. The passive drag tended to decrease significantly by a mean of 17.6% (p < 0.001) for all speeds examined with the arms alongside the body position rather than with the arms above the head position. The swimmer's head location may play an important role in reducing hydrodynamic resistance during passive underwater gliding.
Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity.
Bhushan, Bharat
2011-01-01
The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as lotus (Nelumbo nucifera) leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical surface roughness and presence of a wax layer. In addition to a self-cleaning effect, these surfaces with a high contact angle and low contact angle hysteresis also exhibit low adhesion and drag reduction for fluid flow. An aquatic animal, such as a shark, is another model from nature for the reduction of drag in fluid flow. The artificial surfaces inspired from the shark skin and lotus leaf have been created, and in this article the influence of structure on drag reduction efficiency is reviewed. Biomimetic-inspired oleophobic surfaces can be used to prevent contamination of the underwater parts of ships by biological and organic contaminants, including oil. The article also reviews the wetting behavior of oil droplets on various superoleophobic surfaces created in the lab.
A Comparison of Experimental and Analytical Procedures to Measure Passive Drag in Human Swimming.
Directory of Open Access Journals (Sweden)
Tiago M Barbosa
Full Text Available The aim of this study was to compare the swimming hydrodynamics assessed with experimental and analytical procedures, as well as, to learn about the relative contributions of the friction drag and pressure drag to total passive drag. Sixty young talented swimmers (30 boys and 30 girls with 13.59±0.77 and 12.61±0.07 years-old, respectively were assessed. Passive drag was assessed with inverse dynamics of the gliding decay speed. The theoretical modeling included a set of analytical procedures based on naval architecture adapted to human swimming. Linear regression models between experimental and analytical procedures showed a high correlation for both passive drag (Dp = 0.777*Df+pr; R2 = 0.90; R2a = 0.90; SEE = 8.528; P<0.001 and passive drag coefficient (CDp = 1.918*CDf+pr; R2 = 0.96; R2a = 0.96; SEE = 0.029; P<0.001. On average the difference between methods was -7.002N (95%CI: -40.480; 26.475 for the passive drag and 0.127 (95%CI: 0.007; 0.247 for the passive drag coefficient. The partial contribution of friction drag and pressure drag to total passive drag was 14.12±9.33% and 85.88±9.33%, respectively. As a conclusion, there is a strong relationship between the passive drag and passive drag coefficient assessed with experimental and analytical procedures. The analytical method is a novel, feasible and valid way to gather insight about one's passive drag during training and competition. Analytical methods can be selected not only to perform race analysis during official competitions but also to monitor the swimmer's status on regular basis during training sessions without disrupting or time-consuming procedures.
An optical readout system for the drag free control of the LISA spacecraft
de Rosa, R.; di Fiore, L.; Garufi, F.; Grado, A.; La Rana, A.; Milano, L.
2011-01-01
LISA is an ESA-NASA joint project for the realization of a space interferometric gravitational wave (GW) antenna. LISA is designed for the measurement of GWs in a very low frequency band (0.1-100 mHz). The antenna is composed by three spacecraft (SC) in suitable heliocentric orbits placed at the corners of a huge equilateral triangle, each side being 5 million km long. The SCs are linked by lasers, forming a sort of optical transponder. By means of phase locking techniques, any round-trip phase delay change gives a measurement of a change in the SC distance (measured as light transit time), due to incoming GWs. An essential requirement is that the SCs are set as close as possible to pure geodetic motion, in the measurement frequency band. This is hardly fulfilled because the SCs are disturbed by several external forces, like solar radiation pressure, cosmic rays etc. In each SC there are two free falling proof masses (PM) that are as much isolated as possible by all external force but gravity. The relative position between each PM and the SC is measured, in six degrees of freedom, by the so-called inertial sensor (IS). The IS signal is then used for drag-free servo-loops that force the SC to follow the geodetic motion of the PMs. The current solution for the IS is the adoption of capacitive sensing. This gives a reliable device but poses several limitations due to back action and cross couplings. In this work, we present an optical lever sensor as an alternative solution. In particular we analyze the potential sensitivity and discuss the advantages in terms of relaxed specifications for the drag free control loops. We also report on bench-top measurements that confirm the performance in the required frequency band.
A design and analysis approach for drag reduction on aircraft with adaptive lifting surfaces
Cusher, Aaron Anthony
Adaptive lifting surfaces, which can be tailored for different flight conditions, have been shown to be beneficial for drag reduction when compared with conventional non-adaptive surfaces. Applying multiple trailing-edge flaps along the wing span allows for the redistribution of lift to suit different flight conditions. The current approach uses the trailing-edge flap distribution to reduce both induced- and profile- components of drag with a trim constraint. Induced drag is reduced by optimally redistributing the lift between the lifting surfaces and along the span of each surface. Profile drag is reduced through the use of natural laminar flow airfoils, which maintain distinct low-drag-ranges (drag buckets) surrounding design lift values. The low-drag-ranges can be extended to include off-design values through small flap deflections, similar to cruise flaps. Trim is constrained for a given static margin by considering longitudinal pitching moment contributions from changes in airfoil section due to individual flap deflections, and from the redistribution of fore-and-aft lift due to combination of flap deflections. The approach uses the concept of basic and additional lift to linearlize the problem, which allows for standard constrained-minimization theory to be employed for determining optimal flap-angle solutions. The resulting expressions for optimal flap-angle solutions are presented as simple matrix equations. This work presents a design and analysis approach which is used to produce flap-angle solutions that independently reduce induced, profile, and total drag. Total drag is defined to be the sum of the induced- and profile-components of drag. The general drag reduction approach is adapted for each specific situation to develop specific drag reduction schemes that are applied to single- and multiple-surface configurations. Successful results show that, for the application of the induced drag reduction schemes on a tailless aircraft, near-elliptical lift
Wave-induced dynamics of flexible blades
Luhar, M
2015-01-01
We present an experimental and numerical study that describes the motion of flexible blades, scaled to be dynamically similar to natural aquatic vegetation, forced by wave-induced oscillatory flows. For the conditions tested, blade motion is governed primarily by two dimensionless variables: (i) the Cauchy number, $Ca$, which represents the ratio of the hydrodynamic forcing to the restoring force due to blade stiffness, and (ii) the ratio of the blade length to the wave orbital excursion, $L$. For flexible blades with $Ca \\gg 1$, the relationship between drag and velocity can be described by two different scaling laws at the large- and small-excursion limits. For large excursions ($L \\ll 1$), the flow resembles a unidirectional current and the scaling laws developed for steady-flow reconfiguration studies hold. For small excursions ($L \\gg 1$), the beam equations may be linearized and a different scaling law for drag applies. The experimental force measurements suggest that the small-excursion scaling applies...
Collisions and drag in debris discs with eccentric parent belts
Löhne, T.; Krivov, A. V.; Kirchschlager, F.; Sende, J. A.; Wolf, S.
2017-08-01
Context. High-resolution images of circumstellar debris discs reveal off-centred rings that indicate past or ongoing perturbation, possibly caused by secular gravitational interaction with unseen stellar or substellar companions. The purely dynamical aspects of this departure from radial symmetry are well understood. However, the observed dust is subject to additional forces and effects, most notably collisions and drag. Aims: To complement the studies of dynamics, we therefore aim to understand how the addition of collisional evolution and drag forces creates new asymmetries and strengthens or overrides existing ones. Methods: We augmented our existing numerical code Analysis of Collisional Evolution (ACE) by an azimuthal dimension, the longitude of periapse. A set of fiducial discs with global eccentricities ranging from 0 to 0.4 was evolved over gigayear timescales. Size distribution and spatial variation of dust were analysed and interpreted. We discuss the basic impact of belt eccentricity on spectral energy distributions and images. Results: We find features imposed on characteristic timescales. First, radiation pressure defines size cut-offs that differ between periapse and apoapse, resulting in an asymmetric halo. The differences in size distribution make the observable asymmetry of the halo depend on wavelength. Second, collisional equilibrium prefers smaller grains on the apastron side of the parent belt, reducing the effect of pericentre glow and the overall asymmetry. Third, Poynting-Robertson drag fills the region interior to an eccentric belt such that the apastron side is more tenuous. Interpretation and prediction of the appearance in scattered light is problematic when spatial and size distribution are coupled.
Studies of compressible shear flows and turbulent drag reduction
Orszag, S. A.
1981-04-01
Compressible shear flows and drag reduction were examined and three methods are addressed: (1) the analytical and numerical aspects of conformal mapping were summarized and a new method for computation of these maps is presented; (2) the computer code SPECFD for solution of the three dimensional time dependent Navier-Stokes equations for compressible flow on the CYBER 203 computer is described; (3) results of two equation turbulence modeling of turbulent flow over wavy walls are presented. A modified Jones-Launder model is used in two dimensional spectral code for flow in general wavy geometries.
Drag flow analysis of Oldroyd eight constant fluid
Directory of Open Access Journals (Sweden)
A.M. Siddiqui
2016-09-01
Full Text Available This article presents the steady drag flow problems. The incompressible Oldroyd eight constant fluid flow is considered between two infinite parallel plates. Three flow problems including the Couette flow, Poiseuille flow and Couette–Poiseuille flow are modeled. The source term appearing in the nonlinear differential equation for each case is simplified with the application of modified homotopy perturbation method, and thus the general solution is obtained. The validity of second order approximate analytic solutions is tested with the aid of a numerical technique. The order of accuracy has been obtained in tabular form and the graphs are presented to demonstrate the difference between the three flow regimes.
The drag of inflatable rubber de-icers
Robinson, Russell G
1938-01-01
Force tests on rubber de-icer models of several different profiles, at approximately one-third full scale, been carried out in the NACA 8-foot high speed wind tunnel. The conventional de-icer installation, deflated, added about 15 percent to the smooth-wing drag and, inflated, added about 100 percent. An improved installation with flash attaching strips added about 10 percent, deflated. The bulging, or ballooning, of de-icers from the wing surface is described and some remedies are discussed.
Giant Surface-Plasmon-Induced Drag Effect in Metal Nanowires
Durach, Maxim; Rusina, Anastasia; Stockman, Mark I.
2009-10-01
Here, for the first time we predict a giant surface-plasmon-induced drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. In nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ˜105-106V/cm. The giant SPIDER is an ultrafast effect whose bandwidth for nanometric wires is ˜20THz. It opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.
Giant surface plasmon induced drag effect (SPIDEr) in metal nanowires
Durach, Maxim; Rusina, Anastasia; Stockman, Mark I.
2009-08-01
Here, for the first time we predict a giant surface plasmon-induced drag effect (SPIDEr), which exists under conditions of the extreme nanoplasmonic confinement. Under realistic conditions, in nanowires, this giant SPIDEr generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ~ 105 ~ 106 V/cm. The SPIDEr is an ultrafast effect whose bandwidth for nanometric wires is ~ 20 THz. The giant SPIDEr opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.
Ad/dressing the nation: drag and authenticity in post-apartheid South Africa.
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.
Spatially distributed control for optimal drag reduction of the flow past a circular cylinder
Poncet, Philippe; Hildebrand, Roland; Cottet, Georges-Henri; Koumoutsakos, Petros
We report high drag reduction in direct numerical simulations of controlled flows past circular cylinders at Reynolds numbers of 300 and 1000. The flow is controlled by the azimuthal component of the tangential velocity of the cylinder surface. Starting from a spanwise-uniform velocity profile that leads to high drag reduction, the optimization procedure identifies, for the same energy input, spanwise-varying velocity profiles that lead to higher drag reduction. The three-dimensional variations of the velocity field, corresponding to modes A and B of three-dimensional wake instabilities, are largely responsible for this drag reduction. The spanwise wall velocity variations introduce streamwise vortex braids in the wake that are responsible for reducing the drag induced by the primary spanwise vortices shed by the cylinder. The results demonstrate that extending two-dimensional controllers to three-dimensional flows is not optimal as three-dimensional control strategies can lead efficiently to higher drag reduction.
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.
Study on Drag and Sonic Boom of Supersonic Bi-Directional Flying Wing%双向飞翼超声速客机激波阻力和声爆研究
Institute of Scientific and Technical Information of China (English)
李占科; 张旭; 冯晓强; 关晓辉
2014-01-01
基于超声速双向飞翼构型，采用CFD方法进行阻力计算，采用F-BOOM程序进行声爆计算，研究翼型、平面形状和EFCE激波阻力优化算法对双向飞翼激波阻力和声爆的影响。计算结果表明，平底构型可以明显降低双向飞翼超声速客机的超声速巡航的声爆，却很大程度上增加了巡航阻力，而对称构型却恰好相反；细长的平面几何形状对降低双向飞翼激波阻力和声爆都有作用，尤其对降低对称构型的声爆效果明显；EFCE激波阻力优化算法对降低双向飞翼激波阻力有明显作用，但同时会带来声爆方面的不利影响。因此，超声速客机的减阻设计和低声爆设计需要进行权衡研究。%Based on SBiDir-FW ( supersonic bi-directional flying wing ) , CFD ( Computational Fluid Dynamics ) method is used to calculate the drag and F-BOOM method is applied to compute the sonic boom;this study focuses on how the airfoil, flat shape and EFCE shock wave drag optimization algorithm affect the drag and sonic boom of SBiDir-FW. The results and their analysis show preliminarily that: ( 1 ) flat bottom configuration can reduce the cruise sonic boom of SBiDir-FW remarkably, but it greatly increases the cruising drag, while the opposite phenome-non can be detected in symmetrical configuration;(2)slender flat shape can reduce drag and sonic boom of SBiDir-FW, especially for reducing the sonic boom of symmetrical configuration;(3)EFCE shock wave drag optimization algorithm can reduce the shock wave drag of SBiDir-FW obviously, but will also bring adversely effect on sonic boom. Therefore, the balance should be weighed when considering the design of low drag and low sonic boom for supersonic aircraft.
Drag force in a string model dual to large-N QCD
Talavera, P
2007-01-01
We compute the drag force exerted on a quark and a di-quark systems in a background dual to large-N QCD at finite temperature. We find that appears a drag force in the former setup with flow of energy proportional to the mass of the quark while in the latter there is no dragging as in other studies. We also review the screening length.
Drag force in a string model dual to large-N QCD
Energy Technology Data Exchange (ETDEWEB)
Talavera, Pere [Departament de Fisica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Jordi Girona 1-3, E-08034 Barcelona (Spain)
2007-01-15
We compute the drag force exerted on a quark and a di-quark systems in a background dual to large-N QCD at finite temperature. We find that appears a drag force in the former setup with flow of energy proportional to the mass of the quark while in the latter there is no dragging as in other studies. We also review the screening length.
Invariant Type-B characteristics of drag-reducing microalgal biopolymer solutions
Gasljevic, K.; Hall, K.; Chapman, D.; Matthys, E. F.
2017-05-01
The drag-reducing properties of polysaccharides from marine microalgae were investigated. They were compared to two drag-reducing additives studied extensively in the past, synthetic poly(ethylene) oxide, one of the most effective drag-reducing additives; and Xanthan Gum, another biopolymer often considered a model polymer for chemical and rheological research. Compared to Xanthan Gum, the most effective polymers from our microalgae show a higher drag-reducing efficiency in terms of necessary concentration to achieve a given level of drag reduction. In addition, they show a striking Type-B drag reduction behavior, which may be a very useful quality in most drag reduction applications, thanks to the independence of the drag reduction level on flow conditions such as velocity, shear stress, and tube diameter. With these polymers from microalgae we did not see evidence of Type-A behavior over the wide range of conditions studied (including pipe diameters up to 52 mm). Importantly, this suggests that the Drag Reduction coefficient in pipe flow for ideal drag-reducing solutions such as the polysaccharides investigated here is invariant at a given additive concentration of flow or solution parameters like ionic strength and can be used as a solution property to predict its drag reduction effectiveness over a wide range of conditions. On the contrary, Xanthan Gum showed evidence of both Type-A behavior in large diameter pipes and Type-B behavior in smaller ones. The polymers from microalgae also showed high resistance to degradation. Considering that these microalgae are very effective producers of polysaccharides (both extracellular and intracellular), they appear to be very promising additives for drag reduction applications.
Estimating the Instantaneous Drag-Wind Relationship for a Horizontally Homogeneous Canopy
Pan, Ying; Chamecki, Marcelo; Nepf, Heidi M.
2016-07-01
The mean drag-wind relationship is usually investigated assuming that field data are representative of spatially-averaged metrics of statistically stationary flow within and above a horizontally homogeneous canopy. Even if these conditions are satisfied, large-eddy simulation (LES) data suggest two major issues in the analysis of observational data. Firstly, the streamwise mean pressure gradient is usually neglected in the analysis of data from terrestrial canopies, which compromises the estimates of mean canopy drag and provides misleading information for the dependence of local mean drag coefficients on local velocity scales. Secondly, no standard approach has been proposed to investigate the instantaneous drag-wind relationship, a critical component of canopy representation in LES. Here, a practical approach is proposed to fit the streamwise mean pressure gradient using observed profiles of the mean vertical momentum flux within the canopy. Inclusion of the fitted mean pressure gradient enables reliable estimates of the mean drag-wind relationship. LES data show that a local mean drag coefficient that characterizes the relationship between mean canopy drag and the velocity scale associated with total kinetic energy can be used to identify the dependence of the local instantaneous drag coefficient on instantaneous velocity. Iterative approaches are proposed to fit specific models of velocity-dependent instantaneous drag coefficients that represent the effects of viscous drag and the reconfiguration of flexible canopy elements. LES data are used to verify the assumptions and algorithms employed by these new approaches. The relationship between mean canopy drag and mean velocity, which is needed in models based on the Reynolds-averaged Navier-Stokes equations, is parametrized to account for both the dependence on velocity and the contribution from velocity variances. Finally, velocity-dependent drag coefficients lead to significant variations of the calculated
Drag Coefficients of Low Altitude Stationary Flight Test Airship Estimated from Flight Tests
Okuyama, Masahiro; Matsumoto, Takashi
Flight tests were carried out to obtain aerodynamic characteristics of the low altitude stationary flight test airship. The deceleration test method was used in a flight experiment to obtain the drag coefficient. Combining with the deceleration test result, the minimum drag coefficient was acquired by equating a thrust force with the corresponding drag force at the steady level flight. As a result, 0.044±0.002 were obtained on the minimum drag coefficient of the airship. Modifications of the deceleration test data analysis are proposed to be applicable to test data obtained under non-zero attack angle etc. in the paper.
Cyclist drag in team pursuit: influence of cyclist sequence, stature, and arm spacing.
Defraeye, Thijs; Blocken, Bert; Koninckx, Erwin; Hespel, Peter; Verboven, Pieter; Nicolai, Bart; Carmeliet, Jan
2014-01-01
In team pursuit, the drag of a group of cyclists riding in a pace line is dependent on several factors, such as anthropometric characteristics (stature) and position of each cyclist as well as the sequence in which they ride. To increase insight in drag reduction mechanisms, the aerodynamic drag of four cyclists riding in a pace line was investigated, using four different cyclists, and for four different sequences. In addition, each sequence was evaluated for two arm spacings. Instead of conventional field or wind tunnel experiments, a validated numerical approach (computational fluid dynamics) was used to evaluate cyclist drag, where the bicycles were not included in the model. The cyclist drag was clearly dependent on his position in the pace line, where second and subsequent positions experienced a drag reduction up to 40%, compared to an individual cyclist. Individual differences in stature and position on the bicycle led to an intercyclist variation of this drag reduction at a specific position in the sequence, but also to a variation of the total drag of the group for different sequences. A larger drag area for the group was found when riding with wider arm spacing. Such numerical studies on cyclists in a pace line are useful for determining the optimal cyclist sequence for team pursuit.
Drag Moderation by the Melting of an Ice Surface in Contact with Water
Vakarelski, Ivan U.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.
2015-07-01
We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re ˜2 ×104- 3 ×105 and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface.
Drag reduction by linear viscosity model in turbulent channel flow of polymer solution
Institute of Scientific and Technical Information of China (English)
吴桂芬; 李昌烽; 黄东升; 赵作广; 冯晓东; 王瑞
2008-01-01
A further numerical study of the theory that the drag reduction in the turbulence is related to the viscosity profile growing linearly with the distance from the wall was performed.The constant viscosity in the Navier-Stokes equations was replaced using this viscosity model.Some drag reduction characteristics were shown comparing with Virk’s phenomenology.The mean velocity and Reynolds stress profiles are consistent with the experimental and direct numerical simulation results.A drag reduction level of 45% was obtained.It is reasonable for this linear viscosity model to explain the mechanism of turbulence drag reduction in some aspects.
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.
Drag Moderation by the Melting of an Ice Surface in Contact with Water
Vakarelski, Ivan Uriev
2015-07-24
We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re∼2×104–3×105 and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface.
Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin
2016-08-01
The relationship between the frictional drag and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The frictional drag encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag.
Drag material change in hot runner injection molding
Institute of Scientific and Technical Information of China (English)
蒋炳炎; 黄伯云
2001-01-01
Quick material change is often encountered for the different colors or kinds of polymer in hot runner injecting molding process. Time-costing and incompleteness of material change process often affects the quality and productivity of products. In the practical production, multi-injection or white material as the transition material is often adopted for quick material change. Based on the rheological behavior of the new and the previous plastic melt, the researches on the related problems were carried out. The concept of drag material change was originally presented. The physical and mathematical model on the simultaneous flow process of the new and the previous plastic melt in hot runner were built up, which can well explain the influence of the injection speed, pressure, viscosity difference, temperature and mold structure on the drag material change efficiency. When temperature in different position in the mold was increased and adjusted, the viscosity difference between the two kinds of melt can be controlled. Therefore the material change ability can be greatly improved during the whole material change process, getting rid of more and more difficult changing in the late stage.
Data base for the prediction of inlet external drag
Mcmillan, O. J.; Perkins, E. W.; Perkins, S. C., Jr.
1980-01-01
Results are presented from a study to define and evaluate the data base for predicting an airframe/propulsion system interference effect shown to be of considerable importance, inlet external drag. The study is focused on supersonic tactical aircraft with highly integrated jet propulsion systems, although some information is included for supersonic strategic aircraft and for transport aircraft designed for high subsonic or low supersonic cruise. The data base for inlet external drag is considered to consist of the theoretical and empirical prediction methods as well as the experimental data identified in an extensive literature search. The state of the art in the subsonic and transonic speed regimes is evaluated. The experimental data base is organized and presented in a series of tables in which the test article, the quantities measured and the ranges of test conditions covered are described for each set of data; in this way, the breadth of coverage and gaps in the existing experimental data are evident. Prediction methods are categorized by method of solution, type of inlet and speed range to which they apply, major features are given, and their accuracy is assessed by means of comparison to experimental data.
Lift and drag performance of odontocete cetacean flippers.
Weber, Paul W; Howle, Laurens E; Murray, Mark M; Fish, Frank E
2009-07-01
Cetaceans (whales, dolphins and porpoises) have evolved flippers that aid in effective locomotion through their aquatic environments. Differing evolutionary pressures upon cetaceans, including hunting and feeding requirements, and other factors such as animal mass and size have resulted in flippers that are unique among each species. Cetacean flippers may be viewed as being analogous to modern engineered hydrofoils, which have hydrodynamic properties such as lift coefficient, drag coefficient and associated efficiency. Field observations and the collection of biological samples have resulted in flipper geometry being known for most cetacean species. However, the hydrodynamic properties of cetacean flippers have not been rigorously examined and thus their performance properties are unknown. By conducting water tunnel testing using scale models of cetacean flippers derived via computed tomography (CT) scans, as well as computational fluid dynamic (CFD) simulations, we present a baseline work to describe the hydrodynamic properties of several cetacean flippers. We found that flippers of similar planform shape had similar hydrodynamic performance properties. Furthermore, one group of flippers of planform shape similar to modern swept wings was found to have lift coefficients that increased with angle of attack nonlinearly, which was caused by the onset of vortex-dominated lift. Drag coefficient versus angle of attack curves were found to be less dependent on planform shape. Our work represents a step towards the understanding of the association between performance, ecology, morphology and fluid mechanics based on the three-dimensional geometry of cetacean flippers.
Evidence of sublaminar drag naturally occurring in a curved pipe
Noorani, A.; Schlatter, P.
2015-03-01
Steady and unsteady flows in a mildly curved pipe for a wide range of Reynolds numbers are examined with direct numerical simulation. It is shown that in a range of Reynolds numbers in the vicinity of Reb ≈ 3400, based on bulk velocity and pipe diameter, a marginally turbulent flow is established in which the friction drag naturally reduces below the laminar solution at the same Reynolds number. The obtained values for friction drag for the laminar and turbulent (sublaminar) flows turn out to be in excellent agreement with experimental measurements in the literature. Our results are also in agreement with Fukagata et al. ["On the lower bound of net driving power in controlled duct flows," Phys. D 238, 1082 (2009)], as the lower bound of net power required to drive the flow, i.e., the pressure drop of the Stokes solution, is still lower than our marginally turbulent flow. A large-scale traveling structure that is thought to be responsible for that behaviour is identified in the instantaneous field. This mode could also be extracted using proper orthogonal decomposition. The effect of this mode is to redistribute the mean flow in the circular cross section which leads to lower gradients at the wall compared to the laminar flow.
Tucker, V A
2000-12-01
Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(-)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously
Waves and instability in a one-dimensional microfluidic array
Liu, Bin; Feng, Yan
2012-01-01
Motion in a one-dimensional (1D) microfluidic array is simulated. Water droplets, dragged by flowing oil, are arranged in a single row, and due to their hydrodynamic interactions spacing between these droplets oscillates with a wave-like motion that is longitudinal or transverse. The simulation yields wave spectra that agree well with experiment. The wave-like motion has an instability which is confirmed to arise from nonlinearities in the interaction potential. The instability's growth is spatially localized. By selecting an appropriate correlation function, the interaction between the longitudinal and transverse waves is described.
Energy Technology Data Exchange (ETDEWEB)
Ahmed, K.; Tonks, M.; Zhang, Y.; Biner, B.
2016-09-28
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.
Drag reduction by wing tip slots in a gliding Harris' hawk, Parabuteo unicinctus
Tucker
1995-01-01
The anterior-most primary feathers of many birds that soar over land bend upwards and separate vertically to form slotted wing tips during flight. The slots are thought to reduce aerodynamic drag, although drag reduction has never been demonstrated in living birds. Wing theory explains how the feathers that form the tip slots can reduce induced drag by spreading vorticity horizontally along the wing and by acting as winglets, which are used on aircraft to make wings non-planar and to spread vorticity vertically. This study uses the induced drag factor to measure the induced drag of a wing relative to that of a standard planar wing with the same span, lift and speed. An induced drag factor of less than 1 indicates that the wing is non-planar. The minimum drag of a Harris' hawk gliding freely in a wind tunnel was measured before and after removing the slots by clipping the tip feathers. The unclipped hawk had 7090 % of the drag of the clipped hawk at speeds between 7.3 and 15.0 m s-1. At a wing span of 0.8 m, the unclipped hawk had a mean induced drag factor of 0.56, compared with the value of 1.10 assumed for the clipped hawk. A Monte Carlo simulation of error propagation and a sensitivity analysis to possible errors in measured and assumed values showed that the true mean value of the induced drag factor for the unclipped hawk was unlikely to be more than 0.93. These results for a living bird support the conclusions from a previous study of a feathered tip on a model wing in a wind tunnel: the feathers that form the slotted tips reduce induced drag by acting as winglets that make the wings non-planar and spread vorticity both horizontally and vertically.
Photon mass drag and the momentum of light in a medium
Partanen, Mikko; Häyrynen, Teppo; Oksanen, Jani; Tulkki, Jukka
2017-06-01
Conventional theories of electromagnetic waves in a medium assume that the energy propagating with the light pulse in the medium is entirely carried by the field. Thus, the possibility that the optical force field of the light pulse would drive forward an atomic mass density wave (MDW) and the related kinetic and elastic energies is neglected. In this work, we present foundations of a covariant theory of light propagation in a medium by considering a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces between the induced dipoles and the electromagnetic field. We show that a light pulse having a total electromagnetic energy ℏ ω propagating in a nondispersive medium transfers a mass equal to δ m =(n2-1 ) ℏ ω /c2 , where n is the refractive index. MDW, which carries this mass, consists of atoms, which are more densely spaced inside the light pulse as a result of the field-dipole interaction. We also prove that the transfer of mass with the light pulse, the photon mass drag effect, gives an essential contribution to the total momentum of the light pulse, which becomes equal to the Minkowski momentum pM=n ℏ ω /c . The field's share of the momentum is the Abraham momentum pA=ℏ ω /(n c ) , while the difference pM-pA is carried by MDW. Due to the coupling of the field and matter, only the total momentum of the light pulse and the transferred mass δ m can be directly measured. Thus, our theory gives an unambiguous physical meaning to the Abraham and Minkowski momenta. We also show that to solve the centenary Abraham-Minkowski controversy of the momentum of light in a nondispersive medium in a way that is consistent with Newton's first law, one must account for the mass transfer effect. We derive the photon mass drag effect using two independent but complementary covariant models. In the mass-polariton (MP) quasiparticle approach, we consider the light pulse as a coupled state between the photon and matter, isolated from
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.
2016-04-12
enhanced dissipation rates over rough topography, indicative of internal tide dissi- pation. They compared these rates with the low-mode internal tide power... Ponte and Klein 2015). c. Energetics We analyze globally and regionally integrated and time-mean barotropic and baroclinic energy balances for the...Ray 2001; Simmons et al. 2004a; Kang and Fringer 2012), where f g indicates the area integral or area averaging, P is the tidal energy input, C is the
Optimizing Internal Wave Drag in a Forward Barotropic Model with Semidiurnal Tides
2015-01-23
42–55 49scale factor than the simulations with the spatially varying scalar SAL (Table 2), the position of the parabola of the JSL scheme rela- tive to...the position of the parabola of the reduced Nycander scalar does not change substantially before and after iterating the SAL. This implies that we
Computer code to interchange CDS and wave-drag geometry formats
Johnson, V. S.; Turnock, D. L.
1986-01-01
A computer program has been developed on the PRIME minicomputer to provide an interface for the passage of aircraft configuration geometry data between the Rockwell Configuration Development System (CDS) and a wireframe geometry format used by aerodynamic design and analysis codes. The interface program allows aircraft geometry which has been developed in CDS to be directly converted to the wireframe geometry format for analysis. Geometry which has been modified in the analysis codes can be transformed back to a CDS geometry file and examined for physical viability. Previously created wireframe geometry files may also be converted into CDS geometry files. The program provides a useful link between a geometry creation and manipulation code and analysis codes by providing rapid and accurate geometry conversion.
Use of Leading Edge Waves to Increase Lift/Drag Ratio Project
National Aeronautics and Space Administration — One of the goals of NASA's Fundamental Aeronautics "Subsonic Fixed Wing" project is to reduce fuel burn by 25% 5% by 2018. This corresponds approximately to an...
Towards a climatology of orographic induced wave drag in the stable boundary layer over real terrain
Kleczek, M.A.; Steeneveld, G.J.; Nappo, C.J.; Holtslag, A.A.M.
2012-01-01
The stable boundary layer (SBL) is of particular interest for numerous environmental issues as air quality, aviation, fog forecasting, wind energy engineering, and climate modelling. Unfortunately the current understanding of the SBL is still rather poor, and progress is slow. The relatively poor un
Inserting Tides and Topographic Wave Drag into High-resolution Eddying Simulations
2014-07-01
Executive Services and Communications Directorate (0704-0188). Respondents should be aware that notwithstanding any other provision of law, no person ...RESPONSIBLE PERSON 19b. TELEPHONE NUMBER (Include area code) Special Issue: High Resolution Ocean Climate Modelling No.65 (Vol 19 No.2) July 2014...Rodriguez, 2012: SWOT : The Surface Water and Ocean Topography Mission, Jet Propulsion Laboratory JPL-Publication 12-05, 228 pp Garner, S.T., 2005: A
The energy balance of wind waves and the remote sensing problem
Hasselmann, K.
1972-01-01
Measurements of wave growth indicate an energy balance of the wave spectrum governed primarily by input from the atmosphere, nonlinear transfer to shorter and longer waves, and advection. The pronounced spectral peak and sharp low frequency cut-off characteristic of fetch-limited spectra are explained as a self-stabilizing feature of the nonlinear wave-wave interactions. The momentum transferred from the atmosphere to the wind waves accounts for a large part of the wind drag. These findings are relevant for remote microwave sensing of the sea surface by backscatter and passive radiometry methods.
On the propagation of sound waves in a stellar wind traversed by periodic strong shocks
Pijpers, F. P.
1994-01-01
It has been claimed that in stellar winds traversed by strong shocks the mechanism for driving the wind by sound wave pressure cannot operate because sound waves cannot propagate past the shocks. It is shown here that sound waves can propagate through shocks in one direction and that this is a sufficient condition for the sound wave pressure mechanism to work. A strong shock amplifies a sound wave passing through it and can drag the sound wave away from the star. It is immaterial for the soun...
Electron and phonon drag in thermoelectric transport through coherent molecular conductors
DEFF Research Database (Denmark)
Lü, Jing-Tao; Wang, Jian-Sheng; Hedegård, Per
2016-01-01
there are at least two phonon degrees of freedom. After deriving expressions for the linear drag coefficients, obeying the Onsager relation, we further investigate their effect on nonequilibrium transport. We show that the drag effect is closely related to two other phenomena: (1) adiabatic charge pumping through...
Turbulent Taylor-Couette flow over riblets: drag reduction and the effect of bulk fluid rotation
Greidanus, A. J.; Delfos, R.; Tokgoz, S.; Westerweel, J.
2015-05-01
A Taylor-Couette facility was used to measure the drag reduction of a riblet surface on the inner cylinder. The drag on the surfaces of the inner and outer cylinders is determined from the measured torque when the cylinders are in exact counter-rotation. The three velocity components in the instantaneous flow field were obtained by tomographic PIV and indicate that the friction coefficients are strongly influenced by the flow regimes and structures. The riblet surface changes the friction at the inner-cylinder wall, which generates an average bulk fluid rotation. A simple model is proposed to distinguish drag changes due to the rotation effect and the riblet effect, as a function of the measured drag change and shear Reynolds number . An uncorrected maximum drag reduction of 5.3 % was found at that corresponds to riblet spacing Reynolds number . For these conditions, the model predicts an azimuthal bulk velocity shift of 1.4 %, which is confirmed by PIV measurements. This shift indicates a drag change due to a rotation effect of -1.9 %, resulting in a net maximum drag reduction of 3.4 %. The results correspond well with earlier reported results and demonstrate that the Taylor-Couette facility is a suitable and accurate measurement tool to characterize the drag performance of surfaces.
Sign reversal of drag in bilayer systems with in-plane periodic potential modulation
DEFF Research Database (Denmark)
Alkauskas, A.; Flensberg, Karsten; Hu, Ben Yu-Kuang;
2002-01-01
We develop a theory for describing frictional drag in bilayer systems with in-plane periodic potential modulations, and use it to investigate the drag between bilayer systems in which one of the layers is modulated in one direction. At low temperatures, as the density of carriers in the modulated...
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....
The form drag due to vegetated weir-like obstacles interpreted as expansion losses
Ali, S.; Uijttewaal, W.S.J.
2009-01-01
The Objective of this study is to estimate the form drag due to vegetated weir- like obstacles. Head loss due to submerged vegetated dikes and groins has been modeled by expansion loss form drag model (Energy and momentum balance principles) and it has been compared with experimental data. An experi
Skin-friction drag analysis from the forced convection modeling in simplified underwater swimming.
Polidori, G; Taïar, R; Fohanno, S; Mai, T H; Lodini, A
2006-01-01
This study deals with skin-friction drag analysis in underwater swimming. Although lower than profile drag, skin-friction drag remains significant and is the second and only other contribution to total drag in the case of underwater swimming. The question arises whether varying the thermal gradient between the underwater swimmer and the pool water may modify the surface shear stress distribution and the resulting skin-friction drag acting on a swimmer's body. As far as the authors are aware, such a question has not previously been addressed. Therefore, the purpose of this study was to quantify the effect of this thermal gradient by using the integral formalism applied to the forced convection theory. From a simplified model in a range of pool temperatures (20-30 degrees C) it was demonstrated that, whatever the swimming speeds, a 5.3% reduction in the skin-friction drag would occur with increasing average boundary-layer temperature provided that the flow remained laminar. However, as the majority of the flow is actually turbulent, a turbulent flow analysis leads to the major conclusion that friction drag is a function of underwater speed, leading to a possible 1.5% reduction for fast swimming speeds above 1m/s. Furthermore, simple correlations between the surface shear stress and resulting skin-friction drag are derived in terms of the boundary-layer temperature, which may be readily used in underwater swimming situations.
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 Study of Drag Resistance using a Laboratory Scale Rotary Set-Up
DEFF Research Database (Denmark)
Weinell, Claus Erik; 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...
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.
The Drag Induced Resonant Capture for Kuiper Belt Objects
Jiang, I G; Jiang, Ing-Guey; Yeh, Li-Chin
2004-01-01
It has been an interesting question that why there are one-third of Kuiper Belt Objects (KBOs) trapped into the 3:2 resonance but, in contrast, only several KBOs are claimed to be associated with the 2:1 resonance. In a model proposed by Zhou et al. (2002), the stochastic outward migration of the Neptune could reduce the number of particles in the 2:1 resonance and thus the objects in the 3:2 resonance become more distinct. As a complementary study, we investigate the effect of proto-stellar discs on the resonance capture. Our results show that the gaseous drag of a proto-stellar disc can trap KBOs into the 3:2 resonance rather easily. In addition, no objects are captured into the 2:1 resonance in our simulation.
Intertial Frame Dragging in an Acoustic Analogue spacetime
Chakraborty, Chandrachur; Majumdar, Parthasarathi
2015-01-01
We report an incipient exploration of the Lense-Thirring precession effect in a rotating {\\it acoustic analogue black hole} spacetime. An exact formula is deduced for the precession frequency of a gyroscope due to inertial frame dragging, close to the ergosphere of a `Draining Bathtub' acoustic spacetime which has been studied extensively for acoustic Hawking radiation of phonons and also for `superresonance'. The formula is verified by embedding the two dimensional spatial (acoustic) geometry into a three dimensional one where the similarity with standard Lense-Thirring precession results within a strong gravity framework is well known. Prospects of experimental detection of this new `fixed-metric' effect in acoustic geometries, are briefly discussed.
Computational analysis of methods for reduction of induced drag
Janus, J. M.; Chatterjee, Animesh; Cave, Chris
1993-01-01
The purpose of this effort was to perform a computational flow analysis of a design concept centered around induced drag reduction and tip-vortex energy recovery. The flow model solves the unsteady three-dimensional Euler equations, discretized as a finite-volume method, utilizing a high-resolution approximate Riemann solver for cell interface flux definitions. The numerical scheme is an approximately-factored block LU implicit Newton iterative-refinement method. Multiblock domain decomposition is used to partition the field into an ordered arrangement of blocks. Three configurations are analyzed: a baseline fuselage-wing, a fuselage-wing-nacelle, and a fuselage-wing-nacelle-propfan. Aerodynamic force coefficients, propfan performance coefficients, and flowfield maps are used to qualitatively access design efficacy. Where appropriate, comparisons are made with available experimental data.
Turbulent drag reduction with liquid-infused surfaces
Smits, Alexander; van Buren, Tyler
2016-11-01
We present turbulent skin friction reduction over liquid-impregnated surfaces in Taylor-Couette flow. The surface of the inner cylinder of the facility contains square grooves, with widths from 100 μm to 800 μm and a fixed liquid area of half the total area. Alkane liquids are infused in the surface with viscosities from 1/3 to 2 times that of water. For Reynolds numbers up to Red =10,500 corresponding to a flow shear of τ=50 Pa, we achieve drag reduction exceeding 30%, three times higher than ever reported for liquid-infused surfaces. Supported by the ONR through MURI Grant Nos. N00014-12-1-0875 and N00014-12-1-0962.
Bluff body drag manipulation using pulsed jets and Coanda effect
Barros, Diogo; Noack, Bernd R; Spohn, Andreas; Ruiz, Tony
2015-01-01
We analyze the effects of unsteady forcing on the wake and drag of a square back blunt body. In combination with a Coanda effect, shear-layer forcing by periodic blowing of wall bounded jets allows to recover over 30 % of the base pressure. The actuation frequency is an order of magnitude higher than the natural shear-layer instabilities. High frequency Coanda blowing leads to a thinner time-averaged wake. The effect of this form shaping is analyzed by pressure taps on the rear side of the model in combination with PIV measurements. Velocity components of the mean field indicate a pressure recovery and favorable mean curvature effects across the separated shear layers in the region close to the rear end of the blunt body when actuation is applied. The wake dynamics further downstream, however, remains very similar to the unforced oscillatory wake mode.
Effect of Gravitational Frame Dragging on Orbiting Qubits
Lanzagorta, Marco
2012-01-01
In this paper we discuss the effect of gravitational frame dragging on orbiting qubits. In particular, we consider the Kerr spacetime geometry and spin-1/2 qubits moving in an equatorial radial fall with zero angular momentum and equatorial circular orbits. We ignore the ${\\cal O}(\\hbar)$ order effects due to spin-curvature coupling, which allows us to consider the motion of the spin-1/2 particles as Kerr geometry geodesics. We derive analytical expressions for the infinitesimal Wigner rotation and numerical results for their integration across the length of the particle's trajectory. To this end, we consider the bounds on the finite Wigner rotation imposed by Penrose's cosmic censorship hypothesis.
Drag and propulsive forces in electric sails with negative polarity
Sanchez-Torres, Antonio
2016-02-01
An electric solar sail (E-sail) is a recent propellantless propulsion concept for a direct exploration of the Solar System. An E-sail consists of a set of bare, conductive tethers at high positive/negative bias, prone to extract solar wind momentum by Coulomb deflection of protons. Additionally, a negatively biased E-sail has been proposed as a concept for de-orbiting space debris with drag forces produced in Low Earth Orbit (LEO). The present work focuses on the negative-bias case with a sheath that must be correctly modeled for a flowing plasma ambient. Ion scattering within the sheath and the resulting force are determined for several plasma conditions. Since the plasma flow does reduce the effective range for the ion scattering within the sheath, the resulting force is then reduced. Tethers at very high negative bias should be required for extremely high plasma flow.
Fluid Mechanics, Drag Reduction and Advanced Configuration Aeronautics
Bushnell, Dennis M.
2000-01-01
This paper discusses Advanced Aircraft configurational approaches across the speed range, which are either enabled, or greatly enhanced, by clever Flow Control. Configurations considered include Channel Wings with circulation control for VTOL (but non-hovering) operation with high cruise speed, strut-braced CTOL transports with wingtip engines and extensive ('natural') laminar flow control, a midwing double fuselage CTOL approach utilizing several synergistic methods for drag-due-to-lift reduction, a supersonic strut-braced configuration with order of twice the L/D of current approaches and a very advanced, highly engine flow-path-integrated hypersonic cruise machine. This paper indicates both the promise of synergistic flow control approaches as enablers for 'Revolutions' in aircraft performance and fluid mechanic 'areas of ignorance' which impede their realization and provide 'target-rich' opportunities for Fluids Research.
Effect of Swim Cap Surface Roughness on Passive Drag.
Gatta, Giorgio; Cortesi, Matteo; Zamparo, Paola
2015-11-01
In the last decade, great attention has been given to the improvements in swimming performance that can be obtained by wearing "technical swimsuits"; the technological evolution of these materials only marginally involved swim caps production, even if several studies have pointed out the important role of the head (as main impact point with the fluid) on hydrodynamics. The aim of this study was to compare the effects on passive drag (Dp) of 3 swim cap models: a smooth silicon helmet cap (usually used during swimming competitions), a silicon helmet cap with "dimples," and a silicon helmet cap with "wrinkles." Experiments were performed on 10 swimmers who were towed underwater (at a depth of 60 cm) at 3 speeds (1.5, 1.7, and 1.9 m·s) and in 2 body positions: LA (arms above the swimmer's head) and SA (arms alongside the body). The Dp values obtained in each trial were divided by the square of the corresponding speed to obtain the speed-specific drag (the k coefficient = Dp/v). No differences in k were observed among swim caps in the LA position. No differences in k were observed between the smooth and dimpled helmets also in the SA position; however, the wrinkled swim cap helmet showed a significant larger k (4.4%) in comparison with the model with dimples, when the swimmers kept their arms alongside the body (in the SA position). These data suggest that wearing a wrinkled swim cap helmet can be detrimental to performance at least in this specific position.
Experimental Study on Physical Mechanism of Drag Reduction of Hydrophobic Materials in Laminar Flow
Institute of Scientific and Technical Information of China (English)
YU Yong-Sheng; WEI Qin-Ding
2006-01-01
We experimentally study the physical mechanism of the drag reduction of hydrophobic materials in the macroscopic scale. The experiment includes the drag and velocity measurements of laminar boundary layer Sow over flat plates, and the observation of air bubbles on the surfaces. The plate surfaces have different wetting and roughness properties. In the drag measurements, the plates with bubbles on the surfaces lead to drag reduction, but not for those without bubbles. Velocity measurement confirms that the flow is laminar and gives apparent fluid slip on the plate wall with bubbles. In observation, air bubbles in macroscopic size emerge and enlarge on hydrophobic surfaces but not on hydrophilic surfaces. Therefore, the drag reduction of hydrophobic materials is explained by the generation of air bubbles of macroscopic size that cause the apparent velocity slip.
Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids
Vakarelski, Ivan Uriev
2016-09-08
The drag coefficient CD of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re∼3×105. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ∼600 to 105. The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape. © 2016 American Physical Society.
Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium
Kuan, Pei-Chen; Chan, Wei Sheng; Kosen, Sandoko; Lan, Shau-Yu
2016-01-01
As one of the most influential experiments on the development of modern macroscopic theory from Newtonian mechanics to Einstein's special theory of relativity, the phenomenon of light dragging in a moving medium has been discussed and observed extensively in different types of systems. To have a significant dragging effect, the long duration of light travelling in the medium is preferred. Here we demonstrate a light-dragging experiment in an electromagnetically induced transparent cold atomic ensemble and enhance the dragging effect by at least three orders of magnitude compared with the previous experiments. With a large enhancement of the dragging effect, we realize an atom-based velocimeter that has a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. Such a demonstration could pave the way for motional sensing using the collective state of atoms in a room temperature vapour cell or solid state material.
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.
Lu, Tongli; Li, Hongkui; Zhang, Jianwu; Hao, Hongtao
2016-01-01
The objective of this paper is to improve the performance of the synchronizer control strategy by considering the effect of clutch drag torque. The research of synchronization process in wet dual clutch transmission is performed in this paper. The significant effect of clutch drag torque is analyzed by adding a complex clutch drag torque module to synchronizer model. This paper focuses on the development of original estimation method of clutch drag torque. The estimation method offers an effective way to obtain accurate clutch drag torque, and it is applied to develop a new supervisor control strategy. Results have demonstrated that the estimation method has satisfied efficiency and accuracy and the control strategy improves the performance of the synchronizer mechanism significantly.
Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium
Kuan, Pei-Chen; Huang, Chang; Chan, Wei Sheng; Kosen, Sandoko; Lan, Shau-Yu
2016-10-01
As one of the most influential experiments on the development of modern macroscopic theory from Newtonian mechanics to Einstein's special theory of relativity, the phenomenon of light dragging in a moving medium has been discussed and observed extensively in different types of systems. To have a significant dragging effect, the long duration of light travelling in the medium is preferred. Here we demonstrate a light-dragging experiment in an electromagnetically induced transparent cold atomic ensemble and enhance the dragging effect by at least three orders of magnitude compared with the previous experiments. With a large enhancement of the dragging effect, we realize an atom-based velocimeter that has a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. Such a demonstration could pave the way for motional sensing using the collective state of atoms in a room temperature vapour cell or solid state material.
DOE Project on Heavy Vehicle Aerodynamic Drag FY 2005 Annual Report
Energy Technology Data Exchange (ETDEWEB)
McCallen, R C; Salari, K; Ortega, J; Castellucci, P; Eastwood, C; Paschkewitz, J; Pointer, W D; DeChant, L J; Hassan, B; Browand, F; Radovich, C; Merzel, T; Plocher, D; Ross, J; Storms, B; Heineck, J T; Walker, S; Roy, C J
2005-11-14
Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At high way speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; and (2) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices.
Drag reduction by reconfiguration of a full tree in a wind tunnel
de Langre, Emmanuel; Tadrist, Loic; Leclercq, Tristan; Hemon, Pascal; Amandolese, Xavier; Saudreau, Marc; Marquier, Andre; Knapp, Graham; Flamand, Olivier
2015-11-01
The results of drag measurements performed on a full 3 m-tall cherry tree in an atmospheric wind tunnel are presented. The drag on the trunk alone is shown to increase quadratically with the velocity of the flow, as expected, but the drag on the whole tree with branches and leaves follows a smaller power law with velocity, after the reconfiguration of most leaves. The transition from the quadratic law to a linear increase of the drag of the leaves with the magnitude of the flow is observed. Data is also obtained on moment loading on the base of the tree showing also an effect of the reconfiguration. Finally, these results are compared with current models of drag reduction by reconfiguration.
Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium.
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.
A Study of Two-Dimensional Unsteady Breaking Waves in Finite-Depth Water
2010-01-01
1880). [8] J. H. Duncan, “An experimental investigation of breaking waves produced by a towed hydrofoil ,” Proc. R. Soc. London, Ser. A 377, 331(1981...measured the drag per unit length due to quasi-steady breaking waves generated with a submerged hydrofoil . His measurements illustrated that the... hydrofoil . Proc. R. Soc. London Ser. A 377, 331-348. DUNCAN, J. H. 1983 The breaking and non-breaking wave resistance of a two- dimensional hydrofoil . J
Introduction of parameterized sea ice drag coefficients into ice free-drift modeling
Institute of Scientific and Technical Information of China (English)
LU Peng; LI Zhijun; HAN Hongwei
2016-01-01
Many interesting characteristics of sea ice drift depend on the atmospheric drag coefficient (Ca) and oceanic drag coefficient (Cw). Parameterizations of drag coefficients rather than constant values provide us a way to look insight into the dependence of these characteristics on sea ice conditions. In the present study, the parameterized ice drag coefficients are included into a free-drift sea ice dynamic model, and the wind factorα and the deflection angleθ between sea ice drift and wind velocity as well as the ratio ofCa toCw are studied to investigate their dependence on the impact factors such as local drag coefficients, floe and ridge geometry. The results reveal that in an idealized steady ocean,Ca/Cw increases obviously with the increasing ice concentration for small ice floes in the marginal ice zone, while it remains at a steady level (0.2–0.25) for large floes in the central ice zone. The wind factorα increases rapidly at first and approaches a steady level of 0.018 whenA is greater than 20%. And the deflection angleθ drops rapidly from an initial value of approximate 80° and decreases slowly asA is greater than 20% without a steady level likeα. The values of these parameters agree well with the previously reported observations in Arctic. The ridging intensity is an important parameter to determine the dominant contribution of the ratio of skin friction drag coefficient (Cs’/Cs) and the ratio of ridge form drag coefficient (Cr’/Cr) to the value of Ca/Cw,α, andθ, because of the dominance of ridge form drag for large ridging intensity and skin friction for small ridging intensity among the total drag forces. Parameterization of sea ice drag coefficients has the potential to be embedded into ice dynamic models to better account for the variability of sea ice in the transient Arctic Ocean.
DEFF Research Database (Denmark)
This book is dedicated to various aspects of electromagnetic wave theory and its applications in science and technology. The covered topics include the fundamental physics of electromagnetic waves, theory of electromagnetic wave propagation and scattering, methods of computational analysis...
Wave kinematics and response of slender offshore structures. Vol 5: Wave forces and responses
Energy Technology Data Exchange (ETDEWEB)
Pedersen, L.M.; Riber, H.J.
1999-08-01
A load measuring system (LMS) and a wave measuring system (WMS) has been used on the North Sea platform Tyra. The LMS consists of an instrumented pipe placed vertically in the crest zone of high and steep waves. The WMS consists of an unique sonar system placed on the sea floor. Simultaneous measurements are carried out of the kinematics of waves and currents and the response of the instrumented pipe during a period of five month in the winter 1994/95. Numerical calculations with LIC22 are carried out of the response of the LMS applying the measured wave and current kinematics. The responses are compared to the measured responses of the LMS. The comparison is based on the statistical main properties of the calculated and measured response as the kinematic field is measured 150 metres away from the instrumented pipe. From the analyses the main parameters (reduced velocity V{sub R} and correlation length l{sub c}) for vortex induced vibrations (VIV) are calibrated and the main environmental conditions for VIV are determined. The hydrodynamic coefficients determining the wave and current forces on slender structures are studied (drag coefficient C{sub D} and added mass coefficient C{sub M}). Further, the effect on the drag coefficient due to air blending in the upper part of the wave is determined. (au)
Shih, Ching-Hsiang
2012-01-01
Software technology is adopted by the current research to improve the Drag-and-Drop abilities of two people with multiple disabilities and minimal motor control. This goal was realized through a Dynamic Drag-and-Drop Assistive Program (DDnDAP) in which the complex dragging process is replaced by simply poking the mouse wheel and clicking. However,…
Shih, Ching-Hsiang
2012-01-01
Software technology is adopted by the current research to improve the Drag-and-Drop abilities of two people with multiple disabilities and minimal motor control. This goal was realized through a Dynamic Drag-and-Drop Assistive Program (DDnDAP) in which the complex dragging process is replaced by simply poking the mouse wheel and clicking. However,…
Numerical Simulation of High Drag Reduction in a Turbulent Channel Flow with Polymer Additives
Dubief, Yves
2003-01-01
The addition of small amounts of long chain polymer molecules to wall-bounded flows can lead to dramatic drag reduction. Although this phenomenon has been known for about fifty years, the action of the polymers and its effect on turbulent structures are still unclear. Detailed experiments have characterized two distinct regimes (Warholic et al. 1999), which are referred to as low drag reduction (LDR) and high drag reduction (HDR). The first regime exhibits similar statistical trends as Newtonian flow: the log-law region of the mean velocity profile remains parallel to that of the Newtonian ow but its lower bound moves away from the wall and the upward shift of the log-region is a function of drag reduction, DR. Although streamwise fluctuations are increased and transverse ones are reduced, the shape of the rms velocity profiles is not qualitatively modified. At higher drag reductions, of the order of 40-50%, the ow enters the HDR regime for which the slope of the log-law is dramatically augmented and the Reynolds shear stress is small (Warholic et al. 1999; Ptasinski et al. 2001). The drag reduction is eventually bounded by a maximum drag reduction (MDR) (Virk & Mickley 1970) which is a function of the Reynolds number. While several experiments report mean velocity profiles very close to the empirical profile of Virk & Mickley (1970) for MDR conditions, the observations regarding the structure of turbulence can differ significantly. For instance, Warholic et al. (1999) measured a near-zero Reynolds shear stress, whereas a recent experiment (Ptasinski et al. 2001) shows evidence of non-negligible Reynolds stress in their MDR flow. To the knowledge of the authors, only the LDR regime has been documented in numerical simulations (Sureshkumar et al. 1997; Dimitropoulos et al. 1998; Min et al. 2001; Dubief & Lele 2001; Sibilla & Baron 2002). This paper discusses the simulation of polymer drag reduced channel ow at HDR using the FENE-P (Finite Elastic non
CAN 8-WEEKS OF TRAINING AFFECT ACTIVE DRAG IN YOUNG SWIMMERS?
Directory of Open Access Journals (Sweden)
Daniel A. Marinho
2010-03-01
Full Text Available The aim of this study was to assess the effects of 8-weeks of training on active drag in young swimmers of both genders. Eight girls and twelve boys' belonging to the same swimming team and with regular competitive participation in national and regional events for the previous two seasons participated in this study. Active drag measurements were conducted in two different evaluation moments: at the beginning of the season and after 8 weeks of training (6.0 ± 0.15 training units per week, 21.00 ± 3.23 km per week and 3.50 ± 0.23 km per training unit. The maximal swimming velocity at the distance of 13 m, active drag and drag coefficient were measured on both trials by the method of small perturbations with the help of an additional hydrodynamic body. After 8 weeks of training, mean active drag (drag force and drag coefficient decreased in girls and boys, although no significant differences were found between the two trials. It seems that 8 weeks of swimming training were not sufficient to allow significant improvements on swimming technique
Comparison of predicting drag methods using computational fluid dynamics in 2d/3d viscous flow
Institute of Scientific and Technical Information of China (English)
ZHU; ZiQiang; WANG; XiaoLu; LIU; Jie; LIU; Zhou
2007-01-01
As a result of the necessity of aircraft engineering design and the progress of computational fluid dynamics (CFD), techniques of accurately predicting aerodynamic drag are being increasingly explored. According to the momentum balance, the drag can be represented by an integral over a cross-flow plane (called wake integration method) at an arbitrary distance behind the configuration. A formulation to reduce the size of the wake cross plane region required for calculating the drag is developed by using cutoff parameters of vorticity and entropy. This increases the calculation accuracy and decreases the computation time required. Numerical experiments are made to obtain the threshold values of these cutoff parameters. The wake integration method is applied to predict drags of some examples including airfoil, a variety of wings and wing-body combination. Numerical results are compared with those of traditional surface integration method, showing that the predicting drag values with the wake integration method are closer to the experimental data. The results also show that drag prediction within engineering accuracy is possible by using CFD and the numerical drag optimization of complex aircraft configurations is possible, too.
On the Minimum Induced Drag of Wings -or- Thinking Outside the Box
Bowers, Albion H.
2011-01-01
Of all the types of drag, induced drag is associated with the creation and generation of lift over wings. Induced drag is directly driven by the span load that the aircraft is flying at. The tools by which to calculate and predict induced drag we use were created by Ludwig Prandtl in 1903. Within a decade after Prandtl created a tool for calculating induced drag, Prandtl and his students had optimized the problem to solve the minimum induced drag for a wing of a given span, formalized and written about in 1920. This solution is quoted in textbooks extensively today. Prandtl did not stop with this first solution, and came to a dramatically different solution in 1932. Subsequent development of this 1932 solution solves several aeronautics design difficulties simultaneously, including maximum performance, minimum structure, minimum drag loss due to control input, and solution to adverse yaw without a vertical tail. This presentation lists that solution by Prandtl, and the refinements by Horten, Jones, Kline, Viswanathan, and Whitcomb.
Improving the durability of a drag-reducing nanocoating by enhancing its mechanical stability.
Cheng, Mengjiao; Zhang, Songsong; Dong, Hongyu; Han, Shihui; Wei, Hao; Shi, Feng
2015-02-25
The durability of superhydrophobic surface is a major problem to restrict industrial application of superhydrophobic materials from laboratory research, which can be attributed to a more general issue of mechanical stability for superhydrophobic coatings. Therefore, in order to handle this issue, we have fabricated a mechanically stable drag-reducing coating composed of elastic polydimethylsiloxane (PDMS) and hydrophobic copper particles on model ships, which can resist mechanical abrasion and has displayed a durable drag-reducing effect. In comparison with normal Au superhydrophobic coatings, the as-prepared PDMS/copper coatings showed durable drag reduction performance with a similar drag-reducing rate before (26%) and after (24%) mechanical abrasion. The mechanism for the enhanced mechanical stability and maintained drag reduction of the superhydrophobic surfaces was investigated through characterizations of surface morphology, surface wettability, and water adhesive force evaluation before and after abrasion. This is the first demonstration to realize the application of durable drag reduction by improving the mechanical stability of superhydrophobic coatings. We do believe that superhydrophobic surfaces with good resistance to mechanical abrasion or scratching may draw wide attention and gain significant applications with durable drag-reducing properties.
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.
Numerical simulation on drag reduction of revolution body through bionic riblet surface
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Numerical simulations of flow fields on the bionic riblet and the smooth revolution bodies were performed based on the SST k-ω turbulence model in order to explain the mechanisms of the skin friction drag reduction, base drag reduction on the riblet surface, and flow control behaviors of riblet surface near the wall. The simulation results show that the riblet surface arranged on the rearward of the revolution body can reduce the skin friction drag by 8.27%, the base drag by 9.91% and the total drag by 8.59% at Ma number 0.8. The riblet surface reduces the skin friction drag by reducing the velocity gradient and turbulent intensity, and reduces the base drag by weakening the pumping action on the dead water region which behind the body of revolution caused by the external flow. The flow control behavior on boundary layer shows that the riblet surface can cut the low-speed flow near the wall effectively, and restrain the low-speed flow concentrating in span direction, thus weaken the instability of the low speed steaks produced by turbulent flow bursting.
Drag and Lift Force Acting on a Rotational Spherical Particle in a Logarithmic Boundary Flow
Institute of Scientific and Technical Information of China (English)
XU Wei-jiang; CHE De-fu; XU Tong-mo
2006-01-01
The drag and lift forces acting on a rotational spherical particle in a logarithmic boundary flow are numerically studied. The effects of the drag velocity and rotational speed of the sphere on the drag force are examined for the particle Reynolds number from 50 to 300 and for the dimensionless rotational angular speed of 0≤Ω≤1.0. The influence of dimensionless roughness height z0of the wall is also evaluated for z0≤10. The results show that the drag forces on a sphere both in a logarithmic flow and in a uniform unsheared flow increase with the increase of the drag velocity. For 50≤Rep≤300, the drag coefficient (-C)D increases with decreased roughness height z0. The time-averaged drag coefficient is also significantly affected by rotational speed of the sphere and roughness height z0 . The lift coefficient -CL increases with increased rotational speed and decreases with increased roughness height.
Iqbal, Azmat; Khan, Naveed; Bacha, Bakht Amin; Rahman, Amin Ur; Ahmad, Afaq
2017-09-01
Recently, a considerable enhancement has been observed in the celebrated Fresnel-Fizeau light drag by innovative experimental and theoretical approaches because of its fundamental and practical interest in the emerging technology of quantum optics and photonics. We present a semiclassical density matrix approach on the demonstration of light drag in a slow-light moving medium comprising five-level single tripod atomic configuration. To accomplish this, we introduce Kerr-type nonlinearity that leads to electromagnetically-induced transparency amplification under resonance conditions. By switching ON Kerr-type nonlinearity effect, we observe a prominent transparency window in probe field's absorption spectrum whose width and amplitude can be controlled further by the intensity of Kerr field and control field. The incorporation of Kerr field also switches light propagation from superluminal to subluminal domain. We predict a significant enhancement both in the lateral and the rotary photon drag owing to drag of light linear polarization state subjected to translation and rotation of the host medium, respectively. Consistent with earlier results, light drag considerably depends on both transverse and angular velocity of the host medium. In regime of subluminal propagation, light polarization state drags along the medium motion while in the superluminal propagation region it drags opposite to the medium motion.
DOE's effort to reduce truck aerodynamic drag through joint experiments and computations.
Energy Technology Data Exchange (ETDEWEB)
Salari, Kambiz (Lawrence Livermore National Laboratory); Browand, Fred (University of Southern California); Sreenivas, Kidambi (University of Tennessee, Chattanooga); Pointer, W. David (Argonne National Laboratory); Taylor, Lafayette (University of Tennessee, Chattanooga); Pankajakshan, Ramesh (University of Tennessee, Chattanooga); Whitfield, David (University of Tennessee, Chattanooga); Plocher, Dennis (University of Southern California); Ortega, Jason M. (Lawrence Livermore National Laboratory); Merzel, Tai (University of Southern California); McCallen, Rose (Lawrence Livermore National Laboratory); Walker, Stephen M (NASA Ames Research Center); Heineck, James T (NASA Ames Research Center); Hassan, Basil; Roy, Christopher John (Auburn University); Storms, B. (NASA Ames Research Center); Ross, James (NASA Ames Research Center); Englar, Robert (Georgia Tech Research Institute); Rubel, Mike (Caltech); Leonard, Anthony (Caltech); Radovich, Charles (University of Southern California); Eastwood, Craig (Lawrence Livermore National Laboratory); Paschkewitz, John (Lawrence Livermore National Laboratory); Castellucci, Paul (Lawrence Livermore National Laboratory); DeChant, Lawrence Justin.
2005-08-01
Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million gal/year. Objectives are: (1) In support of DOE's mission, provide guidance to industry in the reduction of aerodynamic drag; (2) To shorten and improve design process, establish a database of experimental, computational, and conceptual design information; (3) Demonstrate new drag-reduction techniques; and (4) Get devices on the road. Some accomplishments are: (1) Concepts developed/tested that exceeded 25% drag reduction goal; (2) Insight and guidelines for drag reduction provided to industry through computations and experiments; (3) Joined with industry in getting devices on the road and providing design concepts through virtual modeling and testing; and (4) International recognition achieved through open documentation and database.
Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Levy, David; Zickuhr, Tom; Mavriplis, Dimitri J.; Wahls, Richard A.; Morrison, Joseph H.; Brodersen, Olaf P.; Eisfeld, Bernhard; Murayama, Mitsuhiro
2008-01-01
Recently acquired experimental data for the DLR-F6 wing-body transonic transport con figuration from the National Transonic Facility (NTF) are compared with the database of computational fluid dynamics (CFD) predictions generated for the Third AIAA CFD Drag Prediction Workshop (DPW-III). The NTF data were collected after the DPW-III, which was conducted with blind test cases. These data include both absolute drag levels and increments associated with this wing-body geometry. The baseline DLR-F6 wing-body geometry is also augmented with a side-of-body fairing which eliminates the flow separation in this juncture region. A comparison between computed and experimentally observed sizes of the side-of-body flow-separation bubble is included. The CFD results for the drag polars and separation bubble sizes are computed on grids which represent current engineering best practices for drag predictions. In addition to these data, a more rigorous attempt to predict absolute drag at the design point is provided. Here, a series of three grid densities are utilized to establish an asymptotic trend of computed drag with respect to grid convergence. This trend is then extrapolated to estimate a grid-converged absolute drag level.
Investigation of drag reduction through a flapping mechanism on circular cylinder
Asif, Md. Asafuddoula; Gupta, Avijit Das; Rana, M. D. Juwel; Ahmed, Dewan Hasan
2016-07-01
During flapping wing, a bird develops sufficient lift force as well as counteracts drag and increases its speed through different orientations of feathers on the flapping wings. Differently oriented feathers play a significant role in drag reduction during flying of a bird. With an objective to investigate the effect of installation of such flapping mechanism as a mean of drag reduction in case of flow over circular cylinder, this concept has been implemented through installation of continuous and mini flaps, made of MS sheet metal, where flaps are oriented at different angles as like feathers of flapping wings. The experiments are carried out in a subsonic wind tunnel. After validation and comparison with conventional result of drag analysis of a single cylinder, effects of flapping with Reynolds number variation, implementation of different orientations of mini flaps and variation of different interspacing distance between mini flaps are studied to find the most effective angle of attack of drag reduction on the body of circular cylinder. This research show that, installation of continuous flap reduces value of drag co-efficient, CD up to 66%, where as mini flaps are found more effective by reducing it up to 73%. Mini flaps of L/s=6.25, all angled at 30O, at the 30O angular position on the body of circular cylinder has been found the most effective angle of attack for drag reduction in case of flow over circular cylinder.
Drag reduction by means of dimpled surfaces in turbulent boundary layers
van Nesselrooij, M.; Veldhuis, L. L. M.; van Oudheusden, B. W.; Schrijer, F. F. J.
2016-09-01
Direct force measurements and particle image velocimetry (PIV) were used to investigate the drag and flow structure caused by surfaces with patterns of shallow spherical dimples with rounded edges subject to turbulent boundary layers. Drag reduction of up to 4 % is found compared to a flat surface. The largest drag reduction was found at the highest tested Reynolds number of 40,000 (based on dimple diameter). A favorable trend promises further improvements at higher Reynolds numbers. PIV revealed the absence of significant separation inside the dimples but did show the existence of a converging/diverging flow in the upstream and downstream dimple half, respectively. This leads to the rejection of theories proposed by other authors concerning the mechanism responsible for drag reduction. Instead, a fundamental dependence on pattern orientation is observed. Furthermore, preliminary Reynolds-averaged Navier-Stokes (RANS) simulations have been compared with the PIV data. Although the large-scale mean flows show good agreement, the numerical simulation predicts no drag reduction. As the RANS approach is inherently incapable of resolving effects on the behavior of small-scale turbulence structure, the origin of drag reduction is attributed to effects on the small-scale turbulence, which is not resolved in the simulations. It is argued that dimples, when placed in well-designed patterns to create the necessary large-scale flow structure, lead to drag reduction by affecting the turbulent structures in the boundary layer, possibly in a way similar to spanwise oscillations of the wall.
Evaluation of Aerodynamic Drag and Torque for External Tanks in Low Earth Orbit.
Stone, William C; Witzgall, Christoph
2006-01-01
A numerical procedure is described in which the aerodynamic drag and torque in low Earth orbit are calculated for a prototype Space Shuttle external tank and its components, the "LO2" and "LH2" tanks, carrying liquid oxygen and hydrogen, respectively, for any given angle of attack. Calculations assume the hypersonic limit of free molecular flow theory. Each shell of revolution is assumed to be described by a series of parametric equations for their respective contours. It is discretized into circular cross sections perpendicular to the axis of revolution, which yield a series of ellipses when projected according to the given angle of attack. The drag profile, that is, the projection of the entire shell is approximated by the convex envelope of those ellipses. The area of the drag profile, that is, the drag area, and its center of area moment, that is, the drag center, are then calculated and permit determination of the drag vector and the eccentricity vector from the center of gravity of the shell to the drag center. The aerodynamic torque is obtained as the cross product of those vectors. The tanks are assumed to be either evacuated or pressurized with a uniform internal gas distribution: dynamic shifting of the tank center of mass due to residual propellant sloshing is not considered.
Development of a coupled wave-flow-vegetation interaction model
Beudin, Alexis; Kalra, Tarandeep; Ganju, Neil Kamal; Warner, John C.
2017-01-01
Emergent and submerged vegetation can significantly affect coastal hydrodynamics. However, most deterministic numerical models do not take into account their influence on currents, waves, and turbulence. In this paper, we describe the implementation of a wave-flow-vegetation module into a Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system that includes a flow model (ROMS) and a wave model (SWAN), and illustrate various interacting processes using an idealized shallow basin application. The flow model has been modified to include plant posture-dependent three-dimensional drag, in-canopy wave-induced streaming, and production of turbulent kinetic energy and enstrophy to parameterize vertical mixing. The coupling framework has been updated to exchange vegetation-related variables between the flow model and the wave model to account for wave energy dissipation due to vegetation. This study i) demonstrates the validity of the plant posture-dependent drag parameterization against field measurements, ii) shows that the model is capable of reproducing the mean and turbulent flow field in the presence of vegetation as compared to various laboratory experiments, iii) provides insight into the flow-vegetation interaction through an analysis of the terms in the momentum balance, iv) describes the influence of a submerged vegetation patch on tidal currents and waves separately and combined, and v) proposes future directions for research and development.
Development of a coupled wave-flow-vegetation interaction model
Beudin, Alexis; Kalra, Tarandeep S.; Ganju, Neil K.; Warner, John C.
2017-03-01
Emergent and submerged vegetation can significantly affect coastal hydrodynamics. However, most deterministic numerical models do not take into account their influence on currents, waves, and turbulence. In this paper, we describe the implementation of a wave-flow-vegetation module into a Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system that includes a flow model (ROMS) and a wave model (SWAN), and illustrate various interacting processes using an idealized shallow basin application. The flow model has been modified to include plant posture-dependent three-dimensional drag, in-canopy wave-induced streaming, and production of turbulent kinetic energy and enstrophy to parameterize vertical mixing. The coupling framework has been updated to exchange vegetation-related variables between the flow model and the wave model to account for wave energy dissipation due to vegetation. This study i) demonstrates the validity of the plant posture-dependent drag parameterization against field measurements, ii) shows that the model is capable of reproducing the mean and turbulent flow field in the presence of vegetation as compared to various laboratory experiments, iii) provides insight into the flow-vegetation interaction through an analysis of the terms in the momentum balance, iv) describes the influence of a submerged vegetation patch on tidal currents and waves separately and combined, and v) proposes future directions for research and development.
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.
A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces
Fukagata, Koji; Kasagi, Nobuhide; Koumoutsakos, Petros
2006-05-01
We present a theoretical prediction for the drag reduction rate achieved by superhydrophobic surfaces in a turbulent channel flow. The predicted drag reduction rate is in good agreement with results obtained from direct numerical simulations at Reτ≃180 and 400. The present theory suggests that large drag reduction is possible also at Reynolds numbers of practical interest (Reτ˜105-106) by employing a hydrophobic surface, which induces a slip length on the order of ten wall units or more.
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%.
Departure of microscopic friction from macroscopic drag in molecular fluid dynamics
Hanasaki, Itsuo; Fujiwara, Daiki; Kawano, Satoyuki
2016-03-01
Friction coefficient of the Langevin equation and drag of spherical macroscopic objects in steady flow at low Reynolds numbers are usually regarded as equivalent. We show that the microscopic friction can be different from the macroscopic drag when the mass is taken into account for particles with comparable scale to the surrounding fluid molecules. We illustrate it numerically by molecular dynamics simulation of chloride ion in water. Friction variation by the atomistic mass effect beyond the Langevin regime can be of use in the drag reduction technology as well as the electro or thermophoresis.
Drag coefficients of lattice masts from full-scale wind-tunnel tests
DEFF Research Database (Denmark)
Georgakis, Christos; Støttrup-Andersen, Ulrik; Johnsen, Marie;
2009-01-01
:5 scale section model tests performed at the National Physics Laboratory and the National Maritime Institute in the UK in the 1970´s. ESDU provides velocity-dependent drag coefficients equivalent to those obtained from the same series of tests. In all cases, the mast legs and diagonals are comprised......In this paper, the drag coefficients obtained from a series of full-scale section model wind-tunnel tests of several lattice mast configurations are presented and compared to those provided in Eurocode 3 and ESDU. The drag coefficients provided in Eurocode are conservative interpretations of 1...
Drag and distribution measurements of single-element fuel injectors for supersonic combustors
Povinelli, L. A.
1974-01-01
The drag caused by several vortex generating fuel injectors for scramjet combustors was measured in a Mach 2 to 3.5 airstream. Injector drag was found to be strongly dependent on injector thickness ratio. The distribution of helium injected into the stream was measured both in the near field and the far field of the injectors for a variety of pressure ratios. The far field results differed appreciably from measurements in the near field. Injection pressure ratio was found to profoundly influence the penetration. One of the aerowing configurations tested yielded low drag consistent with desirable penetration and spreading characteristics.
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......-zero off-diagonal component in rho(21)). We show that these arguments are specious, and in fact Hall drag can be observed at sufficiently high temperatures when the intralayer transport time tau has significant energy-dependence around the Fermi energy epsilon(F). The ratio of the Hall to longitudinal...
Arnaiz, H. H.
1975-01-01
As part of a NASA program to evaluate current methods of predicting the performance of large, supersonic airplanes, the drag of the XB-70 airplane was measured accurately in flight at Mach numbers from 0.75 to 2.5. This paper describes the techniques used to determine engine net thrust and the drag forces charged to the propulsion system that were required for the in-flight drag measurements. The accuracy of the measurements and the application of the measurement techniques to aircraft with different propulsion systems are discussed. Examples of results obtained for the XB-70 airplane are presented.
Low rotational drag in high-temperature superconducting bearings
Hull, J. R.; Mulcahy, T. M.; Uherka, K. L.; Abboud, R. G.
1994-10-01
Bearings consisting of permanent magnets stably levitated over high-temperature superconductors exhibit low rotational drag and have the potential to enable high-efficiency flywheel energy storage. The coefficient of friction mu for such storage systems is derived as a function of bearing parameters and is shown to be an appropriate figure of merit to describe bearing losses. Analysis shows that values of mu 10(exp -6) enable flywheel standby losses less than 0.1 %/hr for high-speed flywheels. A vacuum-chamber experimental apparatus has been constructed to measure values of (mu) for various experimental bearing designs. Experimental values for mu at low velocity have been as low as 3 x 10(exp-7) for a 89-mm-diameter ring permanent magnet stably levitated over an array of melt-textured Y-Ba-Cu-O. An important loss mechanism occurs from eddy currents induced in the rotating magnet due to the discrete nature of the superconductor array.
Octopus-inspired drag cancelation by added mass pumping
Weymouth, Gabriel; Giorgio-Serchi, Francesco
2016-11-01
Recent work has shown that when an immersed body suddenly changes its size, such as a deflating octopus during rapid escape jetting, the body experiences large forces due to the variation of added-mass energy. We extend this line of research by investigating a spring-mass oscillator submerged in quiescent fluid subject to periodic changes in its volume. This system isolates the ability of the added-mass thrust to cancel the bluff body resistance (having no jet flow to confuse the analysis) and moves closer to studying how these effects would work in a sustained propulsion case by studying periodic shape-change instead of a "one-shot" escape maneuver. With a combination of analytical, numerical, and experimental results, we show that the recovery of added-mass kinetic energy can be used to completely cancel the drag of the fluid, driving the onset of sustained oscillations with amplitudes as large as four times the average body radius. Moreover, these results are fairly independent of the details of the shape-change kinematics as long as the Stokes number and shape-change number are large. In addition, the effective pumping frequency range based on parametric oscillator analysis is shown to predict large amplitude response region observed in the numerics and experiments.
Drag reduction and improvement of material transport in creeping films
Energy Technology Data Exchange (ETDEWEB)
Scholle, M.; Rund, A.; Aksel, N. [University of Bayreuth, Department of Applied Mechanics and Fluid Dynamics, Bayreuth (Germany)
2006-01-01
It is widely accepted that for bodies in turbulent flows a reduction of skin friction can be reached if the surface of the body is provided with small ridges aligned in the local flow direction. This surprising and counterintuitive phenomenon is called the shark-skin effect, motivated from the dermal surface morphology of sharks. In the present article we examine the possibility of resistance reduction due to a rippled surface topography in Stokes flow. We especially analyse the influence of wall riblets perpendicular to the flow direction on the mean transport velocity in gravity-driven creeping film flows following the idea that eddies generated in the valleys of the riblets act like fluid roller bearings and hence may reduce drag. Using a theoretical treatment of the Stokes equations with complex function theory, parameter studies with varying flow rate, bottom amplitude and bottom shape are presented. For the given bottom shapes the maximum enhancement of transport velocity is found by optimising the film thickness. (orig.)
Surfactant aggregation and its application to drag reduction
Energy Technology Data Exchange (ETDEWEB)
Harwigsson, I.
1995-09-01
A number of different drag-reducing (DR) surfactants: nonionics, zwitterionics and ampholytics suitable for use in both cool and hot water solution are described. These surfactants have been tested under various conditions common in district energy distribution. The surfactants described are environmentally more acceptable than the organic salts of quaternary ammonium compounds which have so far dominated as DR surfactants. The micellar phase formed in water by the surfactant system cetylpyridinium chloride/sodium salicylate has been investigated with surfactant self-diffusion (NMR) measurements and cryo-transmission electron microscopy. Results from this study support the hypothesis that worm-like micellar systems form a network before the phase boundary, when the first liquid crystalline phase formed is a bicontinuous cubic phase. A series of surfactants similar to the one used in the DR experiments has been examined in dilute solutions. Critical micellar concentration and the size of these micelles are investigated as a function of the amphiphile concentration, the pH and salt concentration. Adsorption properties on silica of zwitterionic dodecyl-N,N-dimethylammonio alkanoates, with polymethylene interchange arms of different lengths, have been investigated with an in situ ellipsometry technique. The use of two-tone frequency modulation spectroscopy as a general method for the determination of water activity has been initiated. 173 refs, 6 figs
Effect of wind-induced drag on leaf shapes
Louf, Jean-Francois; Ntoh Song, Pierre; Zehnbauer, Tim; Jung, Sunghwan
2016-11-01
Under windy conditions everyone can see leaves bending and twisting. From a geometrical point of view, a leaf is composed of two parts: a large flat plate called the lamina, and a small beam called the petiole, connecting the lamina to the branch/stem. While the wind is exerting forces (e.g. drag) on the lamina, the petiole undergoes twisting and bending stresses. To survive in harsh abiotic conditions, leaves might have evolved to form in many different shapes, resulting from a coupling between the lamina and the petiole. In this study we measure the twisting modulus (G) of the petiole using a twisting setup, and its Young modulus (E) by performing tensile tests. Micro-CT scan is used to precisely measure the cross section of the petiole allowing us to calculate the second moment of inertia (I) and the second moment of area (J). We then use the non-dimensional number EI/GJ and compare it to a geometrical non-dimensional number (Lpetiole +Llamina/2)/W, where Lpetiole is the length of the petiole, Llamina the length of the lamina, and W the width of the lamina. We found a linear relation between the ratio of the bending to twisting rigidity and the leaf geometry.
Wagner-Reetz, Maik; Kasinathan, Deepa; Schnelle, Walter; Cardoso-Gil, Raul; Rosner, Helge; Grin, Yuri; Gille, Peter
2014-11-01
The thermoelectric properties of single-crystalline and polycrystalline FeGa3 are systematically investigated over a wide temperature range. At low temperatures, below 20 K, previously not known pronounced peaks in the thermal conductivity (400 -800 WK-1 m-1) with corresponding maxima in the thermopower (in the order of -16000 μ V K-1) were found in single-crystalline samples. Measurements in single crystals along [100] and [001] directions indicate only a slight anisotropy in both the electrical and thermal transports. From susceptibility and heat-capacity measurements, a magnetic or structural phase transition was excluded. Using density functional theory based calculations, we have revisited the electronic structure of FeGa3 and compared the magnetic (including correlations) and nonmagnetic electronic densities of states. Thermopower at fixed carrier concentrations is calculated using semiclassical Boltzmann transport theory, and the calculated results match fairly with our experimental data. The inclusion of strong electron correlations treated in a mean field manner (by LSDA + U ) does not improve this comparison, rendering strong correlations as the sole explanation for the low-temperature enhancement unlikely. Eventually, after a careful review, we assign the peaks in the thermopower as a manifestation of the phonon-drag effect, which is supported by thermopower measurements in a magnetic field.
Fresnel-Fizeau drag: Invisibility conditions for all inertial observers
Halimeh, Jad C.; Thompson, Robert T.
2016-03-01
It was recently shown [J. C. Halimeh et al., Phys. Rev. A 93, 013850 (2016), 10.1103/PhysRevA.93.013850] that as a result of the Doppler effect, inherently dispersive single-frequency ideal free-space invisibility cloaks in relative motion to an observer can only cloak light whose frequency in the cloak frame coincides with the operational frequency of the cloak, although an infinite number of such rays exist for any cloak motion. In this article, we show analytically and through ray-tracing simulations that even though this relationship can be relaxed by simplifying the ideal invisibility cloak into a broadband amplitude cloak, Fresnel-Fizeau drag uncloaks the phase of light in the inertial frame of the cloak thereby compromising its amplitude cloaking in all other inertial frames. In other words, only an invisibility device that perfectly cloaks both the amplitude and the phase of light in its own inertial frame will also (perfectly) cloak this light in any other inertial frame. The same conclusion lends itself to invisible objects that are not cloaks, such as the invisible sphere.
Fresnel-Fizeau drag: Invisibility conditions for all inertial observers
Halimeh, Jad C
2016-01-01
It was recently shown [Halimeh \\emph{et al.} arXiv:1510.06114 (to appear in Phys. Rev. A)] that as a result of the Doppler effect, inherently dispersive single-frequency ideal free-space invisibility cloaks in relative motion to an observer can only cloak light whose frequency in the cloak frame coincides with the operational frequency of the cloak, although an infinite number of such rays exist for any cloak motion. In this article, we show analytically and through ray-tracing simulations that even though this relationship can be relaxed by simplifying the ideal invisibility cloak into a broadband amplitude cloak, Fresnel-Fizeau drag uncloaks the phase of light in the inertial frame of the cloak thereby compromising its amplitude cloaking in all other inertial frames. In other words, only an invisibility device that perfectly cloaks both the amplitude and the phase of light in its own inertial frame will also (perfectly) cloak this light in any other inertial frame. The same conclusion lends itself to invisi...
Coulomb drag and tunneling studies in quantum Hall bilayers
Nandi, Debaleena
The bilayer quantum Hall state at total filling factor νT=1, where the total electron density matches the degeneracy of the lowest Landau level, is a prominent example of Bose-Einstein condensation of excitons. A macroscopically ordered state is realized where an electron in one layer is tightly bound to a "hole" in the other layer. If exciton transport were the only bulk transportmechanism, a current driven in one layer would spontaneously generate a current of equal magnitude and opposite sign in the other layer. The Corbino Coulomb drag measurements presented in this thesis demonstrate precisely this phenomenon. Excitonic superfluidity has been long sought in the νT=1 state. The tunneling between the two electron gas layers exihibit a dc Josephson-like effect. A simple model of an over-damped voltage biased Josephson junction is in reasonable agreement with the observed tunneling I -- V. At small tunneling biases, it exhibits a tunneling "supercurrent". The dissipation is carefully studied in this tunneling "supercurrent" and found to remain small but finite.
Estimated Drag Coefficients and Wind Structure of Hurricane Frances
Zedler, S. E.; Niiler, P. P.; Stammer, D.; Terrill, E.
2006-12-01
As part of the Coupled Boundary Layers Air Sea Transfer (CBLAST) experiment, an array of drifters and floats was deployed from an aircraft just ahead of Hurricane Frances during it's passage to the northwest side of the Caribbean Island chain in August, 2004. The ocean and surface air conditions prior to, during, and after Hurricane Frances were documented by multiple sensors. Two independent estimates of the surface wind field suggest different storm structures. NOAA H*WINDS, an objectively analyzed product using a combination of data collected at the reconnaissance flight level, GPS profilers (dropwindsondes), satellites, and other data, suggest a 40km radius of maximum wind. A product based on the radial momentum equation balance using \\ital{in-situ} surface pressure data and wind direction measurements from the CBLAST drifter array suggests that the radius of maximum winds was 15km. We used a regional version of the MITGCM model with closed boundaries and realistic temperature and salinity fields which was forced with these wind field products to determine which wind field leads to circulation and SST structures that are most consistent with observed sea surface temperature fields and float profile data. Best estimates of the surface wind structure are then used to estimate the appropriate drag coefficient corresponding to the maximum velocity. Our results are compared with those obtained previously.
Atmospheric Drag Perturbation in an Autonomous Orbit Determination for Satellite
Institute of Scientific and Technical Information of China (English)
XUE shen-fang; JIN Sheng-zhen; NING Shu-nian; SUN Cai-hong
2005-01-01
In this paper, an autonomous orbit determination method for satellite using a large field of view star sensor is presented. The simulation of orbit under atmospheric drag perturbation are given with expanded Kalman filtering.The large field of view star sensor has the same precision as star sensor and a sufficient filed of view. Therefore ,the refraction stars can be observed more accurately in real time. The geometric relation between the refracted starlight and the earth can be determined by tangent altitude of the refraction starlight. And then the earth enter can be determined in satellite body frame. The simulation shows that the precision of the mean square deviation of satellite's position and velocity is 5m and 0.01m/s respectively. The calculated decrement of the semi-major axis in one day is close to the theoretical result, and the absolute error is in the range of decimeter when the altitude of orbit is 750 km. The simulateion of orbit of different initial semi-major axis shows that the higher the altitude of orbit is, the smaller the decrement of the semi-major axis is, and when the altitude of orbit is 1700 km the decimeter of the semi-major axis is 10-7km.
Assessment of the importance of the current-wave coupling in the shelf ocean forecasts
Directory of Open Access Journals (Sweden)
G. Jordà
2006-10-01
Full Text Available The effects of wave-current interactions on shelf ocean forecasts is investigated in the framework of the MFSTEP (Mediterranean Forecasting System Project Towards Enviromental Predictions project. A one way sequential coupling approach is adopted to link the wave model (WAM to the circulation model (SYMPHONIE. The coupling of waves and currents has been done considering four main processes: wave refraction due to currents, surface wind drag and bo€ttom drag modifications due to waves, and the wave induced mass flux. The coupled modelling system is implemented in the southern Catalan shelf (NW Mediterranean, a region with characteristics similar to most of the Mediterranean shelves. The sensitivity experiments are run in a typical operational configuration. The wave refraction by currents seems to be not very relevant in a microtidal context such as the western Mediterranean. The main effect of waves on current forecasts is through the modification of the wind drag. The Stokes drift also plays a significant role due to its spatial and temporal characteristics. Finally, the enhanced bottom friction is just noticeable in the inner shelf.
Assessment of the importance of the current-wave coupling in the shelf ocean forecasts
Directory of Open Access Journals (Sweden)
G. Jordà
2007-07-01
Full Text Available The effects of wave-current interactions on shelf ocean forecasts is investigated in the framework of the MFSTEP (Mediterranean Forecasting System Project Towards Enviromental Predictions project. A one way sequential coupling approach is adopted to link the wave model (WAM to the circulation model (SYMPHONIE. The coupling of waves and currents has been done considering four main processes: wave refraction due to currents, surface wind drag and bottom drag modifications due to waves, and the wave induced mass flux. The coupled modelling system is implemented in the southern Catalan shelf (NW Mediterranean, a region with characteristics similar to most of the Mediterranean shelves. The sensitivity experiments are run in a typical operational configuration. The wave refraction by currents seems to be not very relevant in a microtidal context such as the western Mediterranean. The main effect of waves on current forecasts is through the modification of the wind drag. The Stokes drift also plays a significant role due to its spatial and temporal characteristics. Finally, the enhanced bottom friction is just noticeable in the inner shelf.
Numerical simulations and observations of surface wave fields under an extreme tropical cyclone
Fan, Y.; Ginis, I.; Hara, T.; Wright, C.W.; Walsh, E.J.
2009-01-01
The performance of the wave model WAVEWATCH III under a very strong, category 5, tropical cyclone wind forcing is investigated with different drag coefficient parameterizations and ocean current inputs. The model results are compared with field observations of the surface wave spectra from an airborne scanning radar altimeter, National Data Buoy Center (NDBC) time series, and satellite altimeter measurements in Hurricane Ivan (2004). The results suggest that the model with the original drag coefficient parameterization tends to overestimate the significant wave height and the dominant wavelength and produces a wave spectrum with narrower directional spreading. When an improved drag parameterization is introduced and the wave-current interaction is included, the model yields an improved forecast of significant wave height, but underestimates the dominant wavelength. When the hurricane moves over a preexisting mesoscale ocean feature, such as the Loop Current in the Gulf of Mexico or a warm-and cold-core ring, the current associated with the feature can accelerate or decelerate the wave propagation and significantly modulate the wave spectrum. ?? 2009 American Meteorological Society.
Wave-frequency flows within a near-bed vegetation canopy
Henderson, Stephen M.; Norris, Benjamin K.; Mullarney, Julia C.; Bryan, Karin R.
2017-09-01
We study water flows and wave dissipation within near-bed pneumatophore canopies at the wave-exposed fringe of a mangrove forest on Cù Lao Dung Island, in the Mekong Delta. To evaluate canopy drag, the three-dimensional geometry of pneumatophore stems growing upward from the buried lateral roots of Sonneratia caseolaris mangroves was reconstructed from photogrammetric surveys. In cases where hydrodynamic measurements were obtained, up to 84 stems per square meter were observed, with stem heights 0.1 Hz), and up to 90 degrees at lower frequencies. A model is developed for wave-induced flows within the vertically variable canopy. Scaling suggests that acceleration-induced forces and vertical mixing were negligible at wave frequencies. Consistent with theory, drag-induced vertical variability in velocity scaled with Λ =Tw / (2 πTf) , where Tw = wave period, Tf = 2 / (CD a | u |) is the frictional time scale, CD ≈ 2 is the drag coefficient, and | u | is a typical flow speed. For fixed wave conditions (| u | and Tw), theory predicts increasing dissipation with increasing vegetation density (i.e. increasing a), until a maximum is reached for order-one Λ. For larger Λ, within-canopy flow is so inhibited by drag that further increases in a reduce within-canopy dissipation. For observed cases, Λ ⩽ 0.38 at energetic wave frequencies, so wave dissipation near the forest edge is expected to increase with increasing pneumatophore canopy density. However, under different wave conditions, the most dense canopies may occasionally approach the dissipation maximum (Λ ≈ 1). Predicted dissipation by the pneumatophore canopy was sufficient to attenuate most wave energy over distances slightly less (more) than 100 m into the marsh in 1 m (2 m) water depth.
Optimally amplified large-scale streaks and drag reduction in turbulent pipe flow.
Willis, Ashley P; Hwang, Yongyun; Cossu, Carlo
2010-09-01
The optimal amplifications of small coherent perturbations within turbulent pipe flow are computed for Reynolds numbers up to one million. Three standard frameworks are considered: the optimal growth of an initial condition, the response to harmonic forcing and the Karhunen-Loève (proper orthogonal decomposition) analysis of the response to stochastic forcing. Similar to analyses of the turbulent plane channel flow and boundary layer, it is found that streaks elongated in the streamwise direction can be greatly amplified from quasistreamwise vortices, despite linear stability of the mean flow profile. The most responsive perturbations are streamwise uniform and, for sufficiently large Reynolds number, the most responsive azimuthal mode is of wave number m=1 . The response of this mode increases with the Reynolds number. A secondary peak, where m corresponds to azimuthal wavelengths λ_{θ}^{+}≈70-90 in wall units, also exists in the amplification of initial conditions and in premultiplied response curves for the forced problems. Direct numerical simulations at Re=5300 confirm that the forcing of m=1,2 and m=4 optimal structures results in the large response of coherent large-scale streaks. For moderate amplitudes of the forcing, low-speed streaks become narrower and more energetic, whereas high-speed streaks become more spread. It is further shown that drag reduction can be achieved by forcing steady large-scale structures, as anticipated from earlier investigations. Here the energy balance is calculated. At Re=5300 it is shown that, due to the small power required by the forcing of optimal structures, a net power saving of the order of 10% can be achieved following this approach, which could be relevant for practical applications.
OPTIMIZATION OF A WAVE CANCELLATION MULTIHULL SHIP USING CFD TOOLS
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
A simple CFD tool, coupled to a discrete surface representation and a gradient-based optimization procedure, is applied to the design of optimal hull forms and optimal arrangement of hulls for a wave cancellation multihull ship. The CFD tool, which is used to estimate the wave drag, is based on the zeroth-order slender ship approximation. The hull surface is represented by a triangulation, and almost every grid point on the surface can be used as a design variable. A smooth surface is obtained via a simplified pseudo-shell problem. The optimal design process consists of two steps. The optimal center and outer hull forms are determined independently in the first step, where each hull forms are determined independently in the first step, where each hull keeps the same displacement as the original design while the wave drag is minimized. The optimal outer-hull arrangement is determined in the second step for the optimal center and outer hull forms obtained in the first step. Results indicate that the new design can achieve a large wave drag reduction in comparison to the original design configuration.
Guidance Scheme for Modulation of Drag Devices to Enable Return from Low Earth Orbit
Dutta, Soumyo; Bowes, Angela L.; Cianciolo, Alicia D.; Glass, Christopher E.; Powell, Richard W.
2017-01-01
Passive drag devices provide opportunities to return payloads from low Earth orbits quickly without using onboard propulsive systems to de-orbit the spacecraft. However, one potential disadvantage of such systems has been the lack of landing accuracy. Drag modulation or changing the shape of the drag device during flight offer a way to control the de-orbit trajectory and target a specific landing location. This paper discusses a candidate passive drag based system, called Exo-brake, as well as efforts to model the dynamics of the vehicle as it de-orbits and guidance schemes used to control the trajectory. Such systems can enable quick return of payloads from low Earth orbit assets like the International Space Station without the use of large re-entry cargo capsules or propulsive systems.
A Simple Method for Predicting Drag Characteristics of the Wells Turbine
Institute of Scientific and Technical Information of China (English)
HUANG Zhong-zhou; YU Zhi; ZHENG Yong-hong
2006-01-01
The drag characteristics of the Wells turbine are difficult to be accurately predicted because of the influences of many variables. Detailed analyses about the effects of these variables on the drag characteristics educe that the most sensitive parameters to the drag characteristics are the turbine solidity of the turbine and incidence angle of airflow. In this paper, an experimental research is conducted on the pressure drop across the flat-plate rotor which is used to simulate the Wells turbine. After nondimensionalization and fitting of the experimental data, a common experiential formula is obtained. Compared with the experimental data from literature, the computational results are satisfactory. Thus, this report provides a simple and convenient method for predicting the drag characteristics of the Wells turbine and optimizing the match design between an oscillating water column and a chamber.
Drag coefficient for the air-sea exchange in hurricane conditions
Golbraikh, E
2013-01-01
The physical model is proposed for prediction of the non-monotonic drag coefficient variation with the neutral stability 10-m wind speed, U10. The model is based upon measurements of the foam coverage fraction and characteristic size of foam bubbles with U10, and on the drag coefficient approximation by the linearly weighted averaging over alternating foam-free and foam-covered portions of the ocean surface. The obtained drag coefficient is in fair agreement with that obtained by field measurements of the vertical variation of mean wind speed in Powell et al. (Nature, 2003) which discover reduction of the sea-surface drag with U10 rising to hurricane conditions.
Experimental Investigation of Tunnel Discharge Ability by Using Drag Reduction Techniques
Directory of Open Access Journals (Sweden)
Ying-kui WANG
2010-06-01
Full Text Available The experiments in an open flume model and in the spillway tunnel models were carried out by using drag reduction technique. The drag reduction experiments in open channel model adopted two techniques: polymer addition and coating. The drag reduction effect of polyacrylamide (PAM solution and the dimethyl silicone oil coating were studied by the flume model experiments, and the results were satisfied. Then the experiments were carried out in the model of a Hydropower station, which is the second largest dam in China. In order to reduce the resistance, the spillway tunnel models were coated inside with the dimethyl silicone oil. It is the first time that applying the drag reduction technique in the large hydraulic model. The experimental results show that the coating technique can effectively increase the ability of flood discharge. The outlet velocity and the jet trajectory distance were also increased, which is beneficial to the energy dissipation of the spillway tunnel.
Large-eddy simulation of a turbulent flow over a heavy vehicle with drag reduction devices
Lee, Sangseung; Kim, Myeongkyun; You, Donghyun
2015-11-01
Aerodynamic drag contributes to a considerable amount of energy loss of heavy vehicles. To reduce the energy loss, drag reduction devices such as side skirts and boat tails, are often installed to the side and the rear of a heavy vehicle. In the present study, turbulent flow around a heavy vehicle with realistic geometric details is simulated using large-eddy simulation (LES), which is capable of providing unsteady flow physics responsible for aerodynamic in sufficient detail. Flow over a heavy vehicle with and without a boat tail and side skirts as drag reduction devices is simulated. The simulation results are validated against accompanying in-house experimental measurements. Effects of a boat tail and side skirts on drag reduction are discussed in detail. Supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) Grant NTIS 1615007940.
Preparation of microencapsulated α-olefin drag reducing polymer used in oil pipeline transportation
National Research Council Canada - National Science Library
Li, Bing; Xing, Wenguo; Dong, Guilin; Chen, Xiangjun; Zhou, Ningning; Qin, Zhanbo; Zhang, Changqiao
2011-01-01
Microcapsules containing oil drag-reducing polymer particles were prepared by melting-scattering and condensing of polyethylene wax, in-situ polymerization of urea and formaldehyde, and interfacial...
Principles of operation and data reduction techniques for the loft drag disc turbine transducer
Energy Technology Data Exchange (ETDEWEB)
Silverman, S.
1977-09-01
An analysis of the single- and two-phase flow data applicable to the loss-of-fluid test (LOFT) is presented for the LOFT drag turbine transducer. Analytical models which were employed to correlate the experimental data are presented.
Dynamic drag of edge dislocation by circular prismatic loops and point defects
Energy Technology Data Exchange (ETDEWEB)
Malashenko, V.V., E-mail: malashenko@kinetic.ac.donetsk.u [Donetsk Institute for Physics and Engineering of NASU, 83114 Donetsk (Ukraine); Donetsk National Technical University, 83000 Donetsk (Ukraine)
2009-11-15
Motion of edge dislocation in the presence of prismatic loops and point defects is studied analytically. It is shown that at certain conditions, the velocity dependence of the drag force has two maximums and two minimums.
development of a new drag coefficient model for oil and gas
African Journals Online (AJOL)
eobe
determination is critical to determination is critical to ensuring effective transportation of the particles. ... the fluid, and an upward diffusion of the particles, caused by a .... drag correction expression in multiphase flows since many particles are ...
Scalable, Lightweight, Low-Cost Aero/Electrodynamic Drag Deorbit Module Project
National Aeronautics and Space Administration — The proposed effort will develop the "Terminator Tape Deorbit Module", a lightweight, low-cost, scalable de-orbit module that will utilize both aerodynamic drag...
Lubricant-impregnated surfaces for drag reduction in viscous laminar flow
Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team
2013-11-01
For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).
Estimation Methods for Determination of Drag Characteristics of Fly-by-Wire Aircraft
Directory of Open Access Journals (Sweden)
G. Girija
2001-01-01
Full Text Available "In this paper, several parameter/state estimation approaches for the determination of drag polars from flight data are described and evaluated for a fly-by-wire (FBW aircraft. Both model-based approaches (MBAs and non-model-based approaches (NMBAs are considered. Dynamic response data from roller coaster and wind- up-turn manoeuvres are generated in a FBW aircraft flight simulator at different flight conditions and the typical performance results are presented. A novel approach to estimate the drag polar has been evaluated. It has been found that the NMBAs perform better than the MBAs. Classically, the MBAs have been used for the determination of drag polars. The merits of an NMBA are that it does not require specification of the detailed model of the aerodynamic coefficients and it can be suitably used for online estimation of drag polars from the flight data of aerospace vehicles
Application of numerical optimization to the design of supercritical airfoils without drag-creep
Hicks, R. M.; Vanderplaats, G. N.
1977-01-01
Recent applications of numerical optimization to the design of advanced airfoils for transonic aircraft have shown that low-drag sections can be developed for a given design Mach number without an accompanying drag increase at lower Mach numbers. This is achieved by imposing a constraint on the drag coefficient at an off-design Mach number while the drag at the design Mach number is the objective function. Such a procedure doubles the computation time over that for single design-point problems, but the final result is worth the increased cost of computation. The ability to treat such multiple design-point problems by numerical optimization has been enhanced by the development of improved airfoil shape functions. Such functions permit a considerable increase in the range of profiles attainable during the optimization process.
Drag &Drop, Multiphysics & Neural Net-based Lab-on-Chip Optimization Software Project
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...
Real-Time Adaptive Least-Squares Drag Minimization for Performance Adaptive Aeroelastic Wing
Ferrier, Yvonne L.; Nguyen, Nhan T.; Ting, Eric
2016-01-01
This paper contains a simulation study of a real-time adaptive least-squares drag minimization algorithm for an aeroelastic model of a flexible wing aircraft. The aircraft model is based on the NASA Generic Transport Model (GTM). The wing structures incorporate a novel aerodynamic control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF). The drag minimization algorithm uses the Newton-Raphson method to find the optimal VCCTEF deflections for minimum drag in the context of an altitude-hold flight control mode at cruise conditions. The aerodynamic coefficient parameters used in this optimization method are identified in real-time using Recursive Least Squares (RLS). The results demonstrate the potential of the VCCTEF to improve aerodynamic efficiency for drag minimization for transport aircraft.
Wetting behavior and drag reduction of superhydrophobic layered double hydroxides films on aluminum
Zhang, Haifeng; Yin, Liang; Liu, Xiaowei; Weng, Rui; Wang, Yang; Wu, Zhiwen
2016-09-01
We present a novel method to fabricate Zn-Al LDH (layered double hydroxides) film with 3D flower-like micro-and nanostructure on the aluminum foil. The wettability of the Zn-Al LDH film can be easily changed from superhydrophilic to superhydrophobic with a simple chemical modification. The as-prepared superhydrophobic surfaces have water CAs (contact angles) of 165 ± 2°. In order to estimate the drag reduction property of the surface with different adhesion properties, the experimental setup of the liquid/solid friction drag is proposed. The drag reduction ratio for the as-prepared superhydrophobic sample is 20-30% at low velocity. Bearing this in mind, we construct superhydrophobic surfaces that have numerous technical applications in drag reduction field.
Zhang, Fan; Nichols, David A; Chen, Yanbei; Lovelace, Geoffrey; Matthews, Keith D; Owen, Robert; Thorne, Kip S
2012-01-01
When one splits spacetime into space plus time, the Weyl curvature tensor (which equals the Riemann tensor in vacuum) splits into two spatial, symmetric, traceless tensors: the tidal field $E$, which produces tidal forces, and the frame-drag field $B$, which produces differential frame dragging. In recent papers, we and colleagues have introduced ways to visualize these two fields: tidal tendex lines (integral curves of the three eigenvector fields of $E$) and their tendicities (eigenvalues of these eigenvector fields); and the corresponding entities for the frame-drag field: frame-drag vortex lines and their vorticities. These entities fully characterize the vacuum Riemann tensor. In this paper, we compute and depict the tendex and vortex lines, and their tendicities and vorticities, outside the horizons of stationary (Schwarzschild and Kerr) black holes; and we introduce and depict the black holes' horizon tendicity and vorticity (the normal-normal components of $E$ and $B$ on the horizon). For Schwarzschil...
Effect of Jet-nozzle-expansion Ratio on Drag of Parabolic Afterbodies
Englert, Gerald W; Vargo, Donald J; Cubbison, Robert W
1954-01-01
The interaction of the flow from one convergent and two convergent-divergent nozzles on parabolic afterbodies was studied at free-stream Mach numbers of 2.0, 1.6, and 0.6 over a range of jet pressure ratio. The influence of the jet on boattail and base drag was very pronounced. Study of the total external afterbody drag values at supersonic speeds indicated that, over most of the high-pressure-ratio range, increasing the nozzle design expansion ratio increased the drag even though the boattail area was reduced. Increasing the pressure ratio tended to increase slightly the total-drag increment caused by angle-of-attack operation.
Drag &Drop, Mixed-Methodology-based Lab-on-Chip Design Optimization Software Project
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...
CHARACTERISTICS OF WIND DEFLECTOR FOR REDUCING AERODYNAMIC DRAG OF VAN-BODY TRUCK
Institute of Scientific and Technical Information of China (English)
Du Guang-sheng; Lei Li; Zhou Lian-di
2003-01-01
In this paper, the differences in the characteristics of airflow around the van-body truck and of the aerodynamic drag, which were caused by the installation of a wind deflector, were studied by experimentally and numerically. The results show that after the installation of the deflector, the airflow around the top and bottom of the truck becoms smooth, the intensity of tail-vortex is weakened and its contribution area lessened. It also indicates that the aerodynamic characteristics of the airflow are changed distinctly and the aerodynamic drag is reduced considerably. The effect of the thin-wall deflector is better than the solid one in decreasing the drag. It is also concluded that proper design of the gap between the deflector bottom and the top of the driver cab can enhance the effect of the deflector in reducing drag.
Daniello, Robert; Rothstein, Jonathan P.
2007-11-01
The experimental results of fully-developed turbulent channel flow past a series of ultrahydrophobic surfaces will be presented. We have shown previously that these surfaces can produce significant drag reduction in laminar channel flow by supporting a shear-free air-water interface between hydrophobic microridges or microposts. In this talk, we will experimentally demonstrate that it is possible to utilize these micropatterned surfaces as a passive technique for achieving significant drag reduction in fully-developed turbulent flows. Two-dimensional velocity profiles as well as shear and Reynolds stress fields generated from particle image velocimetry will be presented. These measurements clearly demonstrate a reduction in drag along the ultrahydrophobic wall when compared to a smooth surface. Pressure drop measurements along the channel will also be presented. Discussion will include the influence of Reynolds number and surface geometry on the velocity profiles, Reynolds stresses and the resulting drag reduction.
Drag force of Anisotropic plasma at finite U(1) chemical potential
Energy Technology Data Exchange (ETDEWEB)
Cheng, Long; Ge, Xian-Hui [Shanghai University, Department of Physics, Shanghai (China); Wu, Shang-Yu [National Chiao Tung University, Department of Electrophysics, Yau Shing Tung Center, Hsinchu (China); National Center for Theoretical Science, Hsinchu (China)
2016-05-15
We perform the calculation of the drag force acting on a massive quark moving through an anisotropic N = 4 SU(N) Super Yang-Mills plasma in the presence of a U(1) chemical potential. We present the numerical results for any value of the anisotropy and arbitrary direction of the quark velocity with respect to the direction of the anisotropy. We find the effect of the chemical potential or charge density will enhance the drag force for our charged solution. (orig.)
On Turbulent Contribution to Frictional Drag in Wall-Bounded Turbulent Flow
Institute of Scientific and Technical Information of China (English)
LI Feng-Chen; KAWAGUCHI Yasuo; HISHIDA Koichi; OSHIMA Marie
2006-01-01
@@ We propose a simple model for turbulent contribution to the frictional drag in a wall-bounded turbulent flow based on the characteristic parameters of turbulent bursting events. It is verified on water and drag-reducing surfactant solution flows investigated by particle image velocimetry in experiments. It is obtained that the turbulent contribution to the skin friction factor is linearly proportional to the product of the spatial frequency and strength of turbulent bursts originated from the wall.
Continuum model for Couette-Poiseuille flow in a drag molecular pump
Skovorodko, P A
2004-01-01
A continuum one-dimensional model of the plane Couette-Poiseuille flow is developed to describe the pressure distribution in a drag stage of molecular pump of either the Gaede or Holweck type. In spite of its simplicity and approximate nature the model provides a good qualitative representation of the drag pump operation in the whole range of the regimes from the continuum to free molecular ones.
Drag reduction by surface treatment in turbulent Taylor-Couette flow
Greidanus, A. J.; Delfos, R.; Westerweel, J.
2011-12-01
We use a Taylor-Couette facility to study the drag reducing effects of commercial surface products at high shear Reynolds numbers (Res) under perfect couter-rotating conditions (riwi = -rowo). The correlation between torque contribution of the von Kármán flow and shear Reynolds number is investigated. At this moment no significant drag changes are found for the commercial products. However, further research is needed to exclude uncertainties and errors from the torque measurements.
Kevlar/PMR-15 reduced drag DC-9 reverser stang fairing
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.
Drag, but not buoyancy, affects swim speed in captive Steller sea lions
Directory of Open Access Journals (Sweden)
Ippei Suzuki
2014-04-01
Full Text Available Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (∼12–26% subcutaneous fat. Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag showed that swim speed was best predicted by two variables, drag and dive phase (AIC = −139. Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy.
No Winglets: What a Drag...Argument for Adding Winglets to Large Air Force Aircraft
2008-01-01
22134-5068 MASTER OF MILITARY STUDIES NO WINGLETS : WHAT A DRAG... ARGUMENT FOR ADDING WINGLETS TO LARGE AIR FORCE AIRCRAFT ,SUBMITTED IN PARTIAL...currently valid OMB control number. 1. REPORT DATE 2008 2. REPORT TYPE 3. DATES COVERED 00-00-2008 to 00-00-2008 4. TITLE AND SUBTITLE No Winglets ...What a Drag...Argument for Adding Winglets to Large Air Force Aircraft 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR
[Application and development of suture-dragging therapy for anal fistula].
Wang, Chen; Yao, Yibo; Dong, Qingjun; Liang, Hongtao; Guo, Xiutian; Cao, Yongqing; Lu, Jingen
2015-12-01
Traditional Chinese surgical treatment "suture-dragging" therapy is based on medical thread therapy and tight seton drainage in combination of minimal invasive surgical principle. It can preserve the integrity of anal sphincter musculature involved in fistulous tract or abscess and maintain anal function. This article not only describes in detail about the operation points and mechanisms of "suture-dragging" therapy of anorectal fistula, but also reviews the application and modification of anorectal disease.
Swanson, DG
1989-01-01
Plasma Waves discusses the basic development and equations for the many aspects of plasma waves. The book is organized into two major parts, examining both linear and nonlinear plasma waves in the eight chapters it encompasses. After briefly discussing the properties and applications of plasma wave, the book goes on examining the wave types in a cold, magnetized plasma and the general forms of the dispersion relation that characterize the waves and label the various types of solutions. Chapters 3 and 4 analyze the acoustic phenomena through the fluid model of plasma and the kinetic effects. Th
Boussinesq modeling of wave-induced hydrodynamics in coastal wetlands
Chakrabarti, Agnimitro; Brandt, Steven R.; Chen, Qin; Shi, Fengyan
2017-05-01
In this paper, an improved formulation of the vegetation drag force, applicable for the fully nonlinear Boussinesq equations and based on the use of the depth-varying, higher-order expansion of the horizontal velocity, in the quadratic vegetation drag law has been presented. The model uses the same numerical schemes as FUNWAVE TVD but is based on the CACTUS framework. The model is validated for wave height and setup, against laboratory experiments with and without vegetation cover. The wave attenuation results using the improved formulation were compared with those using the first-order reference velocity as well as with analytical solutions using linear wave theory. The analytical solution using the depth-varying velocity, predicted by the linear wave theory, was shown to match the model results with the fully expanded velocity approach very well for all wave cases, except under near-emergent and emergent conditions (when the ratio of stem height to water depth is greater than 0.75) and when the Ursell (Ur) number is less than 5. Simulations during peak storm waves, during Hurricane Isaac, showed that vegetation is very effective in reducing setup on platforms and in reducing the wave energy within the first few hundred meters.
Compliant Materials for Drag Reduction of High-speed Submerged Bodies
Directory of Open Access Journals (Sweden)
N. Bane Jee
2005-01-01
Full Text Available This paper briefly discusses the possibility of employing the compliant materials on underwater bodies for the drag reduction. Recent studies in the area of hydrobionics all-over the world have drawn the attention of hydrodynamicists for using the compliant materials on underwater body surfaces, similar to that found in fast aquatic animals like dolphins, towards achieving drag reduction and increased speeds of underwater vehicles and weapons'. Some basic principles of hydrohionics in drag reduction have been presented with special emphasis on the control of turbulent boundary layer characteristics of flow over the compliant material surfaces and induce delay in transition. Various researchers have estimated that the use of such compliantmaterial surfaces can lead to an overall drag reductton of the order of 10-12 per cent over drag of the rigid surface. This is a considerable drag reduction and should arouse keen interest among the underwater weapon and vehicle designers as the next stage of technological advancement in underwater hydrodynamic technology.
Energy Technology Data Exchange (ETDEWEB)
Lei, Xianliang, E-mail: xianlianglei@mail.xjtu.edu.cn; Li, Huixiong; Guo, YuMeng; Zhang, Qing; Zhang, Weiqiang; Zhang, Qian
2016-05-15
Highlights: • The minimum drag coefficient phenomenon (MDC) has been observed and further investigated. • Effects of heat flux, mass flux and pressure to MDC have been discussed. • A series of comparisons between existing correlations and data have been conducted. • Two correlations of drag coefficient are proposed for isothermal and nonisothermal flow. - Abstract: Hydraulic resistance and its components are of great importance for understanding the turbulence nature of supercritical fluid and establishing prediction methods. Under supercritical pressures, the hydraulic resistance of the fluid exhibits a “pit” in the regions near its pseudo-critical point, which is hereafter called the minimum drag coefficient phenomenon. However, this special phenomenon was paid a little attention before. Hence systematical experiments have been carried out to investigate the hydraulic resistance of supercritical pressure water in both adiabatic and heated horizontal tubes. Parametric effects of heat flux, pressure and mass fluxes to drag coefficient are further compared. It is found that almost all of the existing correlations don’t agree well with the experimental data due to the insufficient consideration of thermal-properties near the pseudocritical point. Two correlations of the drag coefficients are finally proposed by introducing the new variable of the derivative of density with respect to temperature or Prandtl number, which can better predict the drag coefficient of isothermal and nonisothermal flow respectively.
Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface
Koplik, Joel; Maldarelli, Charles
2017-02-01
Measurements of the surface diffusivity of colloidal spheres translating along a vapor-liquid interface show an unexpected decrease in diffusivity, or increase in surface drag (from the Stokes-Einstein relation), when the particles situate further into the vapor phase. However, direct measurements of the surface drag from the colloid velocity due to an external force find the expected decrease with deeper immersion into the vapor. We perform molecular dynamics simulations of the diffusivity and force experiments for a nanoparticle with a small surface roughness at a vapor-liquid interface to examine the effect of contact line fluctuations. The drag calculated from both calculations agree and decrease as the particle positions further into the vapor. The surface drag is smaller than the bulk liquid drag due to the partial submersion into the liquid and the finite thickness of the interfacial zone relative to the nanoparticle size. We observe weak contact line fluctuations and transient pinning events, but these do not give rise to an anomalous increase in drag in this system.
EFFECTIVE DIFFUSION AND EFFECTIVE DRAG COEFFICIENT OF A BROWNIAN PARTICLE IN A PERIODIC POTENTIAL
Institute of Scientific and Technical Information of China (English)
Hongyun Wang
2011-01-01
We study the stochastic motion of a Brownian particle driven by a constant force over a static periodic potential.We show that both the effective diffusion and the effective drag coefficient are mathematically well-defined and we derive analytic expressions for these two quantities.We then investigate the asymptotic behaviors of the effective diffusion and the effective drag coefficient,respectively,for small driving force and for large driving force.In the case of small driving force,the effective diffusion is reduced from its Brownian value by a factor that increases exponentially with the amplitude of the potential.The effective drag coefficient is increased by approximately the same factor.As a result,the Einstein relation between the diffusion coefficient and the drag coefficient is approximately valid when the driving force is small.For moderately large driving force,both the effective diffusion and the effective drag coefficient are increased from their Brownian values,and the Einstein relation breaks down. In the limit of very large driving force,both the effective diffusion and the effective drag coefficient converge to their Brownian values and the Einstein relation is once again valid.
Drag measurements in laterally confined 2D canopies: Reconfiguration and sheltering effect
Barsu, Sylvie; Doppler, Delphine; Jerome, J. John Soundar; Rivière, Nicolas; Lance, Michel
2016-10-01
Plants in aquatic canopies deform when subjected to a water flow and so, unlike a rigid bluff body, the resulting drag force FD grows sub-quadratically with the flow velocity U ¯ . In this article, the effect of density on the canopy reconfiguration and the corresponding drag reduction is experimentally investigated for simple 2D synthetic canopies in an inclinable, narrow water channel. The drag acting on the canopy, and also on individual sheets, is systematically measured via two independent techniques. Simultaneous drag and reconfiguration measurements demonstrate that data for different Reynolds numbers (400-2200), irrespective of sheet width (w) and canopy spacing (ℓ), collapse on a unique curve given by a bending beam model which relates the reconfiguration number and a properly rescaled Cauchy number. Strikingly, the measured Vogel exponent V and hence the drag reduction via reconfiguration is found to be independent of the spacing between sheets and the lateral confinement; only the drag coefficient decreases linearly with the sheet spacing since a strong sheltering effect exists as long as the spacing is smaller than a critical value depending on the sheet width.
Drag reduction for external and internal boundary layers using riblets and polymers
Reidy, Laurel W.; Anderson, Greg W.
1988-01-01
The efficiency of riblets and a drag-reducing polymer solution (a polyacrylamide slurry) in high-speed water tunnels for reducing drag in turbulent boundary layers was investigated in two experiments. One was an external flow experiment, in which riblets were applied to a flat plate in a high-speed water tunnel and the skin friction drag was calculated from velocity profile data. The second was an internal flow experiment, in which riblets were applied to the inside of a 6-in diameter pipe and the friction factor was calculated from mass flow rate and pressure drop measurements. Both experiments used adhesive-backed vinyl riblet film with 0.003-in height and spacing of the symmetric V-grooves. For the flat plate test, free stream velocity and Re data indicated a maximum drag reduction of about 8.1 percent. With riblets in the pipe, however, there was about three times as much friction reduction. When the polymer slurry was used in conjunction with riblets in the pipe flow, the total drag reduction was approximately equal to the sum of the drag reductions of the two techniques used separately, with some dependence on Reynolds number.
Experiment about Drag Reduction of Bionic Non-smooth Surface in Low Speed Wind Tunnel
Institute of Scientific and Technical Information of China (English)
Tian Li-mei; Ren Lu-quan; Han Zhi-wu; Zhang Shi-cun
2005-01-01
The body surface of some organisms has non-smooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a non-smooth surface were made. In order to find a relationship be tween drag reduction and the non-smooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the non-smooth surface causes drag reduction and the distribution of non-smooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the non-smooth structure on the tail of the experimental model, the configuration of riblets, diameter/bottom width of 1 mm, height/depth of 0.5 mm, arranged in a rhombic formation. At the optimal combination mentioned above, the 99% confidence interval for drag reduction was 11.13 % to 22.30%.
Summary of Data from the First AIAA CFD Drag Prediction Workshop
Levy, David W.; Zickuhr, Tom; Vassberg, John; Agrawal, Shreekant; Wahls, Richard A.; Pirzadeh, Shahyar; Hemsch, Michael J.
2002-01-01
The results from the first AIAA CFD Drag Prediction Workshop are summarized. The workshop was designed specifically to assess the state-of-the-art of computational fluid dynamics methods for force and moment prediction. An impartial forum was provided to evaluate the effectiveness of existing computer codes and modeling techniques, and to identify areas needing additional research and development. The subject of the study was the DLR-F4 wing-body configuration, which is representative of transport aircraft designed for transonic flight. Specific test cases were required so that valid comparisons could be made. Optional test cases included constant-C(sub L) drag-rise predictions typically used in airplane design by industry. Results are compared to experimental data from three wind tunnel tests. A total of 18 international participants using 14 different codes submitted data to the workshop. No particular grid type or turbulence model was more accurate, when compared to each other, or to wind tunnel data. Most of the results overpredicted C(sub Lo) and C(sub Do), but induced drag (dC(sub D)/dC(sub L)(exp 2)) agreed fairly well. Drag rise at high Mach number was underpredicted, however, especially at high C(sub L). On average, the drag data were fairly accurate, but the scatter was greater than desired. The results show that well-validated Reynolds-Averaged Navier-Stokes CFD methods are sufficiently accurate to make design decisions based on predicted drag.
Flight-measured lift and drag characteristics of a large, flexible, high supersonic cruise airplane
Arnaiz, H. H.
1977-01-01
Flight measurements of lift, drag, and angle of attack were obtained for the XB-70 airplane, a large, flexible, high supersonic cruise airplane. This airplane had a length of over 57 meters, a takeoff gross mass of over 226,800 kilograms, and a design cruise speed of Mach 3 at an altitude of 21,340 meters. The performance measurements were made at Mach numbers from 0.72 to 3.07 and altitudes from approximately 7620 meters to 21,340 meters. The measurements were made to provide data for evaluating the techniques presently being used to design and predict the performance of aircraft in this category. Such performance characteristics as drag polars, lift-curve slopes, and maximum lift-to-drag ratios were derived from the flight data. The base drag of the airplane, changes in airplane drag with changes in engine power setting at transonic speeds, and the magnitude of the drag components of the propulsion system are also discussed.
2009-01-01
tropospheric eddies (e.g. Song and Robinson, 2004; Chen and Zorita-Gotor, 2008). Thus, in order to get the stratospheric and tropo - spheric responses to...2009). Similarly, eastward propagating gravity waves originating near 10◦–20◦N of the tropo - sphere propagate upward and slightly northward to reach...24852508. McFarlane, N. A., 1987: The effect of orographically excited gravity- wave drag on the circulation of the lower stratosphere and tropo
Superhydrophobic copper tubes with possible flow enhancement and drag reduction.
Shirtcliffe, Neil J; McHale, Glen; Newton, Michael I; Zhang, Yong
2009-06-01
The transport of a Newtonian liquid through a smooth pipe or tube is dominated by the frictional drag on the liquid against the walls. The resistance to flow against a solid can, however, be reduced by introducing a layer of gas at or near the boundary between the solid and liquid. This can occur by the vaporization of liquid at a surface at a temperature above the Leidenfrost point, by a cushion of air (e.g. below a hovercraft), or by producing bubbles at the interface. These methods require a continuous energy input, but a more recent discovery is the possibility of using a superhydrophobic surface. Most reported research uses small sections of lithographically patterned surfaces and rarely considers pressure differences or varying flow rates. In this work we present a method for creating a uniform superhydrophobic nanoribbon layer on the inside of round copper tubes of millimetric internal radius. Two types of experiments are described, with the first involving a simultaneous comparison of four tubes with different surface finishes (as received, as received with hydrophobic coating, nanoribbon, and nanoribbon with a hydrophobic coating) under constant flow rate conditions using water and water-glycerol mixtures. The results show that the superhydrophobic nanoribbon with a hydrophobic coating surface finish allows greater flow at low pressure differences but that the effect disappears as the pressure at the inlet of the tube is increased. The second experiment is a simple visual demonstration of the low-pressure behavior using two nominally identical tubes in terms of length and cross-section, but with one tube possessing a superhydrophobic internal surface finish. In this experiment a reservoir is allowed to feed the two tubes with open ends via a T-piece and it is observed that, once flow commences, it preferentially occurs down the superhydrophobic tube.
Heat Waves Dangers we face during periods of very high temperatures include: Heat cramps: These are muscular pains and ... having trouble with the heat. If a heat wave is predicted or happening… - Slow down. Avoid strenuous ...
DEFF Research Database (Denmark)
Kramer, Morten; Brorsen, Michael; Frigaard, Peter
Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....
Stochastic model for joint wave and wind loads on offshore structures
DEFF Research Database (Denmark)
Ditlevsen, Ove Dalager
2002-01-01
The stochastic wave load environment of offshore structures is of such a complicated nature that any engineering analysis requires extensive simplifications. This concerns both the transformation of the wave field velocities and accelerations to forces on the structure and the probabilistic...... and by integration over all sea states given $Q>q_0$, the distribution is obtained that is relevant for the free space design. However, for the forces on the members of the structure also the wave period is essential. Within the linear wave theory (Airy waves) the drag term in the Morison force formula increases...... and is therefore very difficult if not impossible to obtain by analytical mathematical reasoning. Keywords: Extreme wind driven sea waves, Local maxima and period properties of Gaussian process, Nataf model for wave and wind data, Offshore structure loads, Sea wave stochastics during wind storm, Wave and wind...
DEFF Research Database (Denmark)
Kofoed, Jens Peter; Frigaard, Peter; Sørensen, H. C.
1998-01-01
This paper concerns with the development of the wave energy converter (WEC) Wave Dragon. This WEC is based on the overtopping principle. An overview of the performed research done concerning the Wave Dragon over the past years is given, and the results of one of the more comprehensive studies......, concerning a hydraulic evaluation and optimisation of the geometry of the Wave Dragon, is presented. Furthermore, the plans for the future development projects are sketched....
A mathematical model and numerical simulation of pressure wave in horizontal gas-liquid bubbly flow
Institute of Scientific and Technical Information of China (English)
HUANG Fei; BAI Bofeng; GUO Liejin
2004-01-01
By using an ensemble-averaged two-fluid model,with valid closure conditions of interfacial momentum exchange due to virtual mass force,viscous shear stress and drag force,a model for pressure wave propagation in a horizontal gas-liquid bubbly flow is proposed.According to the small perturbation theory and solvable condition of one-order linear uniform equations,a dispersion equation of pressure wave is induced.The pressure wave speed calculated from the model is compared and in good agreement with existing data.According to the dispersion equation,the propagation and attenuation of pressure wave are investigated systemically.The factors affecting pressure wave,such as void fraction,pressure,wall shear stress,perturbation frequency,virtual mass force and drag force,are analyzed.The result shows that the decrease in system pressure,the increase in void fraction and the existence of wall shear stress,will cause a decrease in pressure wave speed and an increase in the attenuation coefficient in the horizontal gas-liquid bubbly flow.The effects of perturbation frequency,virtual mass and drag force on pressure wave in the horizontal gas-liquid bubbly flow at low perturbation frequency are different from that at high perturbation frequency.
DEFF Research Database (Denmark)
This book is dedicated to various aspects of electromagnetic wave theory and its applications in science and technology. The covered topics include the fundamental physics of electromagnetic waves, theory of electromagnetic wave propagation and scattering, methods of computational analysis......, material characterization, electromagnetic properties of plasma, analysis and applications of periodic structures and waveguide components, etc....
Towne, Dudley H
1988-01-01
This excellent undergraduate-level text emphasizes optics and acoustics, covering inductive derivation of the equation for transverse waves on a string, acoustic plane waves, boundary-value problems, polarization, three-dimensional waves and more. With numerous problems (solutions for about half). ""The material is superbly chosen and brilliantly written"" - Physics Today. Problems. Appendices.
Transonic Drag Prediction on a DLR-F6 Transport Configuration Using Unstructured Grid Solvers
Lee-Rausch, E. M.; Frink, N. T.; Mavriplis, D. J.; Rausch, R. D.; Milholen, W. E.
2004-01-01
A second international AIAA Drag Prediction Workshop (DPW-II) was organized and held in Orlando Florida on June 21-22, 2003. The primary purpose was to inves- tigate the code-to-code uncertainty. address the sensitivity of the drag prediction to grid size and quantify the uncertainty in predicting nacelle/pylon drag increments at a transonic cruise condition. This paper presents an in-depth analysis of the DPW-II computational results from three state-of-the-art unstructured grid Navier-Stokes flow solvers exercised on similar families of tetrahedral grids. The flow solvers are USM3D - a tetrahedral cell-centered upwind solver. FUN3D - a tetrahedral node-centered upwind solver, and NSU3D - a general element node-centered central-differenced solver. For the wingbody, the total drag predicted for a constant-lift transonic cruise condition showed a decrease in code-to-code variation with grid refinement as expected. For the same flight condition, the wing/body/nacelle/pylon total drag and the nacelle/pylon drag increment predicted showed an increase in code-to-code variation with grid refinement. Although the range in total drag for the wingbody fine grids was only 5 counts, a code-to-code comparison of surface pressures and surface restricted streamlines indicated that the three solvers were not all converging to the same flow solutions- different shock locations and separation patterns were evident. Similarly, the wing/body/nacelle/pylon solutions did not appear to be converging to the same flow solutions. Overall, grid refinement did not consistently improve the correlation with experimental data for either the wingbody or the wing/body/nacelle pylon configuration. Although the absolute values of total drag predicted by two of the solvers for the medium and fine grids did not compare well with the experiment, the incremental drag predictions were within plus or minus 3 counts of the experimental data. The correlation with experimental incremental drag was not
Wave attenuation charcteristics of tethered float system
Digital Repository Service at National Institute of Oceanography (India)
Vethamony, P.
with increase 04 0.8 I 0.9 I.‘0 I!1 I 1.2 I 1.3 11.4 11.5 I!6 1.7 R(m)- Fig 7 (a). Variation of wave power and drag power with float size. t t 0 I I I I I I I I I 2 X-x /x-x-x--* Q) a- aD d x/x’ b 0- X’ (D y/ u) 6 t, 0 IQ_ d :- ? 0 9, 0...
The photon drag effect: A fast FIR detector
Energy Technology Data Exchange (ETDEWEB)
Sigg, H.C. [Paul Scherrer Institut, Zuerich (Switzerland); Son, P.C. van; Wenckebach, W.Th. [Delft Univ. of Technology (Netherlands)
1995-12-31
The photon drag (PD) effect in solids is the electrical current generated along the path of the absorbed photons. It is a very direct transducer which is also very fast because the momentum relaxation times of the electrons are involved. We studied the PD effect in the 2D electron gas (2DEG) of a GaAs/AlGaAs multi-quantum well system using the free-electron laser source FELIX. The temporal response on a ps timescale has been observed, and the continuous spectral response through the intersubband resonance (ISR) is investigated. For high excitation intensities we observe saturation of both the PD effect and the ISR absorption. The experiments are performed on an MBE grown GaAs/AlGaAs sample with 30 8-nm-wide quantum wells, each containing 0.8 10{sup 12} electrons/cm{sup 2}. The light is coupled to the 2DEG through a single-pass internal reflection in a Ge prism pressed onto the sample surface, and the electrical signal is capacitively coupled out to a microstrip line. The measured temporal response to the 2-ps-long infrared micropulses is limited by the 34 GHz bandwidth of the sampling oscilloscope. The spectral response (ISR at 120 meV) and the saturation of the PD effect and of the optical absorption are measured real-time on the timescale of the FELIX macropulse (typically 2 {mu}). Two contributions to the PD signal an be distinguished in the spectral response: One is proportional to the absorption and the other is proportional to its derivative with respect to frequency. The relative strength of the contributions is related to the momentum relaxation times of the electrons in the lowest and first excited subbands. At high excitation intensities, the relative strength of the two contributions stays surprisingly constant, despite the strongly increased ISR linewidth and the saturation of the signal. This indicates that the limiting relaxation time relevant for the saturation of the PD effect is longer than the sub-picosecond momentum relaxation times.
Phonon and magnon heat transport and drag effects
Heremans, Joseph P.
2014-03-01
Thermoelectric generators and coolers constitute today's solid-state energy converters. The two goals in thermoelectrics research are to enhance the thermopower while simultaneously maintaining a high electrical conductivity of the same material, and to minimize its lattice thermal conductivity without affecting its electronic properties. Up to now the lattice thermal conductivity has been minimized by using alloy scattering and, more recently, nanostructuring. In the first part of the talk, a new approach to minimize the lattice thermal conductivity is described that affects phonon scattering much more than electron scattering. This can be done by selecting potential thermoelectric materials that have a very high anharmonicity, because this property governs phonon-phonon interaction probability. Several possible types of chemical bonds will be described that exhibit such high anharmonicity, and particular emphasis will be put on solids with highly-polarizable lone-pair electrons, such as the rock salt I-V-VI2 compounds (e.g. NaSbSe2). The second part of the talk will give an introduction to a completely new class of solid-state thermal energy converters based on spin transport. One configuration for such energy converters is based on the recently discovered spin-Seebeck effect (SSE). This quantity is expressed in the same units as the conventional thermopower, and we have recently shown that it can be of the same order of magnitude. The main advantage of SSE converters is that the problem of optimization is now distributed over two different materials, a ferromagnet in which a flux of magnetization is generated by a thermal gradient, and a normal metal where the flux of magnetization is converted into electrical power. The talk will focus on the basic physics behind the spin-Seebeck effect. Recent developments will then be described based on phonon-drag of spin polarized electrons. This mechanism has made it possible to reach magnitudes of SSE that are comparable
Offset of a Drag-Free Sensor from the Center of Gravity of Its Satellite
Starin, Scott R.
2003-01-01
The drag-free satellite is one that encloses a proof mass, shielding it from atmospheric drag and solar radiation pressure (SRP). By sensing the location of the proof mass in the body and using thrusters to force the spacecraft to follow the proof mass in a closed-loop fashion, the effects of drag and SRP may be eliminated from the spacecraft orbit. Thus, several benefits may be gained, including improved ephemeris propagation and reduced operational costs. The package including the proof mass and the location sensing equipment may be considered as a single sensor; if generalized, such a sensor could be manufactured and used more easily in satellite designs, similar to how current missions use, for example, rate gyros and magnetometers. The flight heritage of the technology has been such that the proof mass sensor is a primary facet of the mission, allowing it to dominate design considerations. In particular, this paper discusses the effects that may be expected if a generalized drag-free sensor is placed some distance away from the spacecraft center of gravity. The proof mass will follow a given gravitational orbit, and a separation from the spacecraft center of gravity places the spacecraft itself in a different orbit from the proof mass, requiring additional fuel just to maintain function of the drag- free sensor. Conclusions include some guiding principles for determining whether certain mission characteristics may restrict or preclude the use of drag-free sensors for that mission. These principles may be used both by mission planners considering drag-free missions and by hardware designers considering or pursuing the development of such generalized sensors.
Turbulent Drag Reduction: Studies of Feedback Control and Flow Over Riblets
Choi, Haecheon
The objective of this study is to explore concepts for control of turbulent boundary layers leading to skin -friction reduction using the direct numerical simulation technique. This report is divided into three parts where three different control methods are investigated; a passive control by longitudinal riblets, an active control by sensing and perturbing structures near the wall, and a feedback control procedure guided by control theory. In PART I significant drag reduction is achieved when the surface boundary condition is modified to suppress the dynamically significant coherent structures present in the wall region. The drag reduction is accompanied with significant reduction in the intensity of the wall -layer structures and reductions in the magnitude of Reynolds shear stress throughout the flow. Two essential drag reduction mechanisms are presented. In PART II mathematical methods of control theory are applied to the problem of control of fluid flow. The procedure of how to cast the problem of controlling turbulence into a problem in optimal control theory is presented through the formalism and language of control theory. Then a suboptimal control and feedback procedure are presented using methods of calculus of variations through the adjoint state and gradient algorithms. This suboptimal feedback control procedure is applied to the distributed and boundary controls of the stochastic Burgers equation. Most cases considered show significant reductions of the costs. In PART III direct numerical simulation is performed to analyze turbulent flow over longitudinal riblets, and to educe the mechanism of drag reduction by riblets. The computed drags on the riblet surfaces are in good agreement with the existing experimental data. Differences in the mean-velocity profile and turbulence quantities are found to be limited to the inner region of the boundary layer. Velocity and vorticity fluctuations as well as the Reynolds shear stresses above the riblets are
Tsamados, M.; Barbic, G.; Petty, A.; Schroeder, D.; Holland, P.; Feltham, D. L.
2016-12-01
A new drag parametrization accounting explicitly for form drag has been recently formulated and applied to the Arctic sea ice (Lupkes et al, 2012 and Tsamados et al, 2014). We summarizehere the fundamental elements of this formulation and we then adapt it to the Antarctic sea ice. Considering the general expression of the momentum balance of sea ice, we analyze thetotal (neutral) drag coefficients by studying separately air-ice and ocean-ice momentum fluxes, and by introducing the parameterization for both the atmospheric neutral drag coeffcient (ANDC)and the oceanic neutral drag coeffcient (ONDC). The two coefficients are calculated as a sum of their skin frictional contribution and form drag contribution, which comes from ridges and floeedges for the ANDC and keels and floe edges for the ONDC. Due to the contrasting geography of the two polar regions, there are important differences, both dynamic and thermodynamic, betweenArctic and Antarctic sea ice. In the Antarctic, sea ice is younger, less ridged (hence thinner and smoother). Due to the intense snowfalls, the snow cover is generally thicker than in theArctic, with values that vary significantly both seasonally and regionally and can affect the roughness of the surface and can lead to flooding of the ice. At the outer boundary of the SouthernOcean, the ice is unconstrained by land, divergent and subject to meridional advection, which leads to a much faster ice drift than in the Arctic. We show here how the new parameterization accountingfor form drag influences the Antarctic sea ice characteristics.
Aerodynamic drag of a transiting sphere by large-scale tomographic-PIV
Terra, W.; Sciacchitano, A.; Scarano, F.
2017-07-01
A method is introduced to measure the aerodynamic drag of moving objects such as ground vehicles or athletes in speed sports. Experiments are conducted as proof-of-concept that yield the aerodynamic drag of a sphere towed through a square duct in stagnant air. The drag force is evaluated using large-scale tomographic PIV and invoking the time-average momentum equation within a control volume in a frame of reference moving with the object. The sphere with 0.1 m diameter moves at a velocity of 1.45 m/s, corresponding to a Reynolds number of 10,000. The measurements in the wake of the sphere are conducted at a rate of 500 Hz within a thin volume of approximately 3 × 40 × 40 cubic centimeters. Neutrally buoyant helium-filled soap bubbles are used as flow tracers. The terms composing the drag are related to the flow momentum, the pressure and the velocity fluctuations and they are separately evaluated. The momentum and pressure terms dominate the momentum budget in the near wake up to 1.3 diameters downstream of the model. The pressure term decays rapidly and vanishes within 5 diameters. The term due to velocity fluctuations contributes up to 10% to the drag. The measurements yield a relatively constant value of the drag coefficient starting from 2 diameters downstream of the sphere. At 7 diameters the measurement interval terminates due to the finite length of the duct. Error sources that need to be accounted for are the sphere support wake and blockage effects. The above findings can provide practical criteria for the drag evaluation of generic bluff objects with this measurement technique.
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.
Energy Technology Data Exchange (ETDEWEB)
Yaste, David M (NASA Ames Research Center, Moffet Field, CA); Salari, Kambiz (Lawrence Livermore National Laboratory, Livermore, CA); Hammache, Mustapha (University of Southern California, Los Angeles, CA); Browand, Fred (University of Southern California, Los Angeles, CA); Pointer, W. David (Argonne National Laboratory, Argonne, IL); Ortega, Jason M. (Lawrence Livermore National Laboratory, Livermore, CA); McCallen, Rose (Lawrence Livermore National Laboratory, Livermore, CA); Walker, Stephen M (NASA Ames Research Center, Moffet Field, CA); Heineck, James T (NASA Ames Research Center, Moffet Field, CA); Hassan, Basil; Roy, Christopher John (Auburn University, Auburn, AL); Storms, B. (NASA Ames Research Center, Moffet Field, CA); Satran, D. (NASA Ames Research Center, Moffet Field, CA); Ross, James (NASA Ames Research Center, Moffet Field, CA); Englar, Robert (Georgia Tech Research Institute, Atlanta, GA); Chatalain, Philippe (Caltech, Pasadena, CA); Rubel, Mike (Caltech, Pasadena, CA); Leonard, Anthony (Caltech, Pasadena, CA); Hsu, Tsu-Ya (University of Southern California, Los Angeles, CA); DeChant, Lawrence Justin.
2004-06-01
At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the smart design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments, and discuss our future direction.
Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse
Energy Technology Data Exchange (ETDEWEB)
Grishkov, V. E.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
2017-03-15
Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron–ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.
The Impact of Moisture on Mountain Waves During T-REX
2009-11-01
can play a dual role in modifying mountain waves and wave drag. A moist layer that is adjacent to the topog- raphy tends to weaken mountain waves and...plays a crucial role in forcing the low- level flow into the downslope windstorm regime and provides a pathway to the foehn. The interaction be- tween a...observations of mountain waves in the troposphere and lower strato - sphere over the Alps (Smith et al. 2002) and the Sierra Mountains (Smith et al. 2008) for
Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei
2016-11-01
Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.
Accurate calculation of Stokes drag for point-particle tracking in two-way coupled flows
Horwitz, Jeremy
2015-01-01
In this work, we propose and test a method for calculating Stokes drag applicable to particle-laden fluid flows where two-way momentum coupling is important. In the point-particle formulation, particle dynamics are coupled to fluid dynamics via a source term that appears in the respective momentum equations. When the particle Reynolds number is small and the particle diameter is smaller than the fluid scales, it is common to approximate the momentum coupling source term as the Stokes drag. The Stokes drag force depends on the difference between the undisturbed fluid velocity evaluated at the particle location, and the particle velocity. However, owing to two-way coupling, the fluid velocity is modified in the neighborhood of a particle, relative to its undisturbed value. This causes the computed Stokes drag force to be underestimated in two-way coupled point-particle simulations. We develop estimates for the drag force error as function of the particle size relative to the grid size. We then develop a correct...
Drag and Diffusion of Heavy Quarks in a hot and anisotropic QCD medium
Srivastava, P K
2016-01-01
The propagation of heavy quarks (HQs) in a medium was quite often modeled by the Fokker-Plank (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 expansion in transverse directions are almost frozen, hence an anisotropy in the momentum space sets in. Since HQs are too produced in the same time therefore the study of the effect of momentum anisotropy on the drag and diffusion coefficients becomes advertently 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 ...
The Mechanism of Drag Reduction around Bodies of Revolution Using Bionic Non-Smooth Surfaces
Institute of Scientific and Technical Information of China (English)
Li-mei Tian; Lu-quan Ren; Qing-ping Liu; Zhi-wu Han; Xiao Jiang
2007-01-01
Bionic non-smooth surfaces (BNSS) can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been, well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.
Yan, Liuming; Shao, Changle; Ji, Xiaobo
2009-07-15
The electroosmotic drag coefficient of water molecules in hydrated sodium perfluorosulfonate electrolyte polymer is evaluated on the basis of the velocity distribution functions of the sodium cations and water molecules with an electric field applied using molecular dynamics simulations. The simulation results indicate that both velocity distribution functions of water molecules and of sodium cations agree well with the classic Maxwellian velocity distribution functions when there is no electric field applied. If an electric field is applied, the distribution functions of velocity component in directions perpendicular to the applied electric field still agree with the Maxwellian velocity distribution functions but with different temperature parameters. In the direction of the applied electric field, the electric drag causes the velocity distribution function to deviate from the Maxwellian velocity distribution function; however, to obey the peak shifted Maxwellian distribution function. The peak shifting velocities coincide with the average transport velocities induced by the electric field, and could be applied to the evaluation of the electroosmotic drag coefficient of water. By evaluation of the transport velocities of water molecules in the first coordination shells of sodium cations, sulfonate anion groups, and in the bulk, it is clearly shown that the water molecules in the first coordination shell of sodium cations are the major contribution to the electroosmotic drag and momentum transfer from water molecules within the first coordination shell to the other water molecules also contributes to the electroosmotic drag.
Lift vs. drag based mechanisms for vertical force production in the smallest flying insects.
Jones, S K; Laurenza, R; Hedrick, T L; Griffith, B E; Miller, L A
2015-11-01
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.
Directory of Open Access Journals (Sweden)
Li Dong Qing
2016-01-01
Full Text Available The breeze vibration duration of conductors is long, the vibration amplitude is strong and the frequency range is wide for electric power transmission lines in strong wind areas, which seriously affects the safe and stable operation of transmission lines. There are two design schemes of conductors which can achieve the purpose of reducing wind-induced disaster. One is enhancing the structural strength of conductors to withstand wind load, but the investment is enormous and the effect is limited. The other is developing drag reduced conductors to reduce wind load by changing conductor structure. This paper started from application feasibility analysis of drag reduced conductors and designed four drag reduced conductors by structure optimization of the conventional aluminium conductor steel reinforced JL/G1A-630/45-45/7, denoted as DFY630/45(45°-R3.5, DFY630/45(60°-R3.5, DFY630/45(45°–R3.2 and DFY630/45(60°-R3.2, respectively. The wind tunnel test was performed and the wind resistance coefficients in unit length of five conductors were compared. Result showed that the wind resistance coefficients in unit length of four drag reduced conductors were obviously lower than that of the conventional conductor. By controlling the manufacturing process, popularization and application of drag reduced conductors for transmission lines in strong wind areas can be realized.
Global effect of local skin friction drag reduction in spatially developing turbulent boundary layer
Stroh, A; Schlatter, P; Frohnapfel, B
2016-01-01
A numerical investigation of two locally applied drag reducing control schemes is carried out in the configuration of a spatially developing turbulent boundary layer (TBL). One control is designed to damp near-wall turbulence and the other induces constant mass flux in the wall-normal direction. Both control schemes yield similar local drag reduction rates within the control region. However, the flow development downstream of the control significantly differs: persistent drag reduction is found for the uniform blowing case whereas drag increase is found for the turbulence damping case. In order to account for this difference the formulation of a global drag reduction rate is suggested. It represents the reduction of the streamwise force exerted by the fluid on a finite length plate. Furthermore, it is shown that the far downstream development of the TBL after the control region can be described by a single quantity, namely a streamwise shift of the uncontrolled boundary layer, i.e. a changed virtual origin. B...
Developing a methodology for estimating the drag in front-crawl swimming at various velocities.
Narita, Kenzo; Nakashima, Motomu; Takagi, Hideki
2017-02-10
We aimed to develop a new method for evaluating the drag in front-crawl swimming at various velocities and at full stroke. In this study, we introduce the basic principle and apparatus for the new method, which estimates the drag in swimming using measured values of residual thrust (MRT). Furthermore, we applied the MRT to evaluate the active drag (Da) and compared it with the passive drag (Dp) measured for the same swimmers. Da was estimated in five-stages for velocities ranging from 1.0 to 1.4ms(-1); Dp was measured at flow velocities ranging from 0.9 to 1.5ms(-1) at intervals of 0.1ms(-1). The variability in the values of Da at MRT was also investigated for two swimmers. According to the results, Da (Da=32.3 v(3.3), N=30, R(2)=0.90) was larger than Dp (Dp=23.5 v(2.0), N=42, R(2)=0.89) and the variability in Da for the two swimmers was 6.5% and 3.0%. MRT can be used to evaluate Da at various velocities and is special in that it can be applied to various swimming styles. Therefore, the evaluation of drag in swimming using MRT is expected to play a role in establishing the fundamental data for swimming.
Drag coefficients for modeling flow through emergent vegetation in the Florida Everglades
Lee, J.K.; Roig, L.C.; Jenter, H.L.; Visser, H.M.
2004-01-01
Hydraulic data collected in a flume fitted with pans of sawgrass were analyzed to determine the vertically averaged drag coefficient as a function of vegetation characteristics. The drag coefficient is required for modeling flow through emergent vegetation at low Reynolds numbers in the Florida Everglades. Parameters of the vegetation, such as the stem population per unit bed area and the average stem/leaf width, were measured for five fixed vegetation layers. The vertically averaged vegetation parameters for each experiment were then computed by weighted average over the submerged portion of the vegetation. Only laminar flow through emergent vegetation was considered, because this is the dominant flow regime of the inland Everglades. A functional form for the vegetation drag coefficient was determined by linear regression of the logarithmic transforms of measured resistance force and Reynolds number. The coefficients of the drag coefficient function were then determined for the Everglades, using extensive flow and vegetation measurements taken in the field. The Everglades data show that the stem spacing and the Reynolds number are important parameters for the determination of vegetation drag coefficient. ?? 2004 Elsevier B.V. All rights reserved.
Effect of the Size Distribution of Nanoscale Dispersed Particles on the Zener Drag Pressure
Eivani, A. R.; Valipour, S.; Ahmed, H.; Zhou, J.; Duszczyk, J.
2011-04-01
In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction, which have been incorporated in the existing relationships. Microstructural observations indicated a clear correlation between the size distribution of dispersed particles and recrystallized grain sizes in the AA7020 aluminum alloy. However, the existing relationship to calculate the Zener drag pressure yielded a negligible difference of 0.016 pct between the two structures homogenized at different conditions resulting in totally different size distributions of nanoscale dispersed particles and, consequently, recrystallized grain sizes. The difference in the Zener drag pressure calculated by the application of the new relationship was 5.1 pct, being in line with the experimental observations of the recrystallized grain sizes. Mathematical investigations showed that the ratio of the Zener drag pressure from the new equation to that from the existing equation is maximized when the number densities of all the particles with different sizes are equal. This finding indicates that in the two structures with identical parameters except the size distribution of nanoscale dispersed particles, the one that possesses a broader size distribution of particles, i.e., the number densities of particles with different sizes being equal, gives rise to a larger Zener drag pressure than that having a narrow size distribution of nanoscale dispersed particles, i.e., most of the particles being in the same size range.
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.
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...
Wahle, Kathrin; Staneva, Joanna; Koch, Wolfgang; Fenoglio-Marc, Luciana; Ho-Hagemann, Ha T. M.; Stanev, Emil V.
2017-04-01
The coupling of models is a commonly used approach when addressing the complex interactions between different components of earth systems. We demonstrate that this approach can result in a reduction of errors in wave forecasting, especially in dynamically complicated coastal ocean areas, such as the southern part of the North Sea - the German Bight. Here, we study the effects of coupling of an atmospheric model (COSMO) and a wind wave model (WAM), which is enabled by implementing wave-induced drag in the atmospheric model. The numerical simulations use a regional North Sea coupled wave-atmosphere model as well as a nested-grid high-resolution German Bight wave model. Using one atmospheric and two wind wave models simultaneously allows for study of the individual and combined effects of two-way coupling and grid resolution. This approach proved to be particularly important under severe storm conditions as the German Bight is a very shallow and dynamically complex coastal area exposed to storm floods. The two-way coupling leads to a reduction of both surface wind speeds and simulated wave heights. In this study, the sensitivity of atmospheric parameters, such as wind speed and atmospheric pressure, to the wave-induced drag, in particular under storm conditions, and the impact of two-way coupling on the wave model performance, is quantified. Comparisons between data from in situ and satellite altimeter observations indicate that two-way coupling improves the simulation of wind and wave parameters of the model and justify its implementation for both operational and climate simulations.
Kruse, Karsten
2017-01-01
Traveling waves propagating along surfaces play an important role for intracellular organization. Such waves can appear spontaneously in reaction-diffusion systems, but only few general criteria for their existence are known. Analyzing the dynamics of the Min proteins in Escherichia coli, Levine and Kessler (2016 New J. Phys. 18 122001) now identified a new mechanism for the emergence of traveling waves that relies on conservation laws. From their analysis one can expect traveling waves to be a generic feature of systems made of proteins that have a cytoplasmic and a membrane-bound state.
2016-01-01
We show the existence of a family of waves that share a common interesting property affecting the way they propagate and focus. These waves are a superposition of twin waves, which are conjugate to each other under inversion of the propagation direction. In analogy to holography, these twin "real" and "virtual" waves are related respectively to the converging and the diverging part of the beam and can be clearly visualized in real space at two distinct foci under the action of a focusing lens...