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Showing papers on "Drag coefficient published in 1984"


Proceedings ArticleDOI
01 Feb 1984
TL;DR: In this paper, a basic ground vehicle type of bluff body, the time averaged wake structure is analyzed for low and high wake flow for the low drag and high drag configurations is described.
Abstract: For a basic ground vehicle type of bluff body, the time averaged wake structure is analysed. At a model length based reynolds number of 4.29 million, detailed pressure measurements, wake survey and force measurements were done in a wind tunnel. Some flow visualisation results were also obtained. Geometric parameter varied was base slant angle. A drag breakdown revealed that almost 85% of body drag is pressure drag. Most of this drag is generated at the rear end. Wake flow exhibits a triple deck system of horseshoe vortices. Strength, existence and merging of these vortices depend upon the base slant angle. Characteristic features of the wake flow for the low drag and high drag configurations is described. Relevance of these phenomena to real ground vehicle flow is addressed.

936 citations


Proceedings ArticleDOI
01 Jan 1984
TL;DR: In this article, the effect of rib details on the riblet drag reduction performance was investigated in boundary layers having different upstream histories and at higher Reynolds numbers than previously reported, and it was found that the drag reduction was dependent on the height and spacing of riblets in law of the wall variables regardless of the free-stream Reynolds number or upstream boundary-layer history.
Abstract: Riblet surfaces have been tested in boundary layers having different upstream histories and at higher Reynolds numbers than previously reported. The drag reduction for the riblet surfaces was found to be dependent on the height and spacing of the riblets in law-of-the-wall variables regardless of the free-stream Reynolds number or upstream boundary-layer history. Micro-photographs of the actual riblet geometries are examined to determine the effect of rib details on the riblet drag-reduction performances. To further increase drag-reduction performance, riblet surfaces are combined with another drag-reduction concept, the large-eddy breakup device (LEBU). In addition, the yaw sensitivity of riblets is evaluated, as well as the characteristics of riblet surfaces manufactured out of a thin vinyl sheet.

289 citations


Journal ArticleDOI
TL;DR: In this article, an analysis of mean and periodical motion in the near-wake flow is performed around a finite circular cylinder on a flat plate, where the slenderness parameter of the cylinder is in a range of l/d=1∼8.
Abstract: Some flow visualization experiments and measurements of surface pressure, Strouhal number, etc. around a finite circular cylinder on a flat plate have been performed in order to study the effect of a three-dimensional flow. The slenderness parameter of the cylinder is in a range of l/d=1∼8, where the slenderness parameter influences remarkably the flow behavior. From an analysis of mean and periodical motion in the near-wake flow, the following results are obtained. (1) The separation velocity at the side wall is lower than that of a two-dimensional cylinder, and this decreases the drag coefficients. (2) A pair of trailing vortices exist right below the free-end. (3) Down-wash flow and the trailing vortex near the free-end dominate the behavior of Karman vortex shedding. Finally, based on these results, the flow models around the finite height cylinder are presented.

241 citations


Journal ArticleDOI
TL;DR: In this paper, fluid-dynamic instability of a smooth circular cylinder, free to oscillate laterally against linear springs in the wake from an identical stationary neighbouring body, was investigated.
Abstract: Measurements are presented of fluid-dynamic instability of a smooth circular cylinder, free to oscillate laterally against linear springs in the wake from an identical stationary neighbouring body. The observations also encompassed determination of static forces on the downstream cylinder as functions of relative position of the cylinder pair. Most of the experiments were performed under two conditions of free-stream turbulence. Static tests indicated that both the drag coefficient and the Strouhal number of the downstream body are continuous functions of its relative position. The drag forces were found to be negative at small gaps. It was observed that the transverse extent of the force field increases with increasing streamwise gap.In the dynamic experiments, depending on the cylinders’ separation and structural damping, the cylinder exhibited a vortex-resonance, or a galloping, or a combined vortex-resonance and galloping, or a separated vortex-resonance and galloping. Whilst the characteristics of wake-excited motion were found to be essentially unaffected by a limited change in free-stream turbulence intensity, the galloping amplitudes were observed to be sensitive to the cylinders’ aspect ratio. An increase in the stability parameter caused significant effects on the cylinder response in amplitude domain. Wake observations behind the oscillating body indicated that in vortex lock-in the frequency of vortex-shedding locked to vibration frequency, but during small-amplitude galloping motion the shedding frequency behaved as if the cylinder was stationary.

232 citations


Journal ArticleDOI
TL;DR: The analysis of Cox and Brenner as mentioned in this paper for the particle motion in a nonporous duct is extended to include the effect of the wall porosity, and particle trajectories and concentrations profiles are calculated for a plane Poiseuille flow with one porous wall.

193 citations


Patent
27 Dec 1984
TL;DR: In this paper, a system of flow control devices which result in reduced skin friction on aerodynamic and hydrodynamic surfaces is described, which results in a substantial reduction in skin friction drag.
Abstract: The invention is a system of flow control devices which result in reduced skin friction on aerodynamic and hydrodynamic surfaces The devices cause a breakup of large-scale disturbances in the boundary layer of the flow field Referring to FIGS 1 and 2, the riblet device 10 acts to reduce disturbances near the boundary layer wall by the use of longitudinal striations forming vee-shaped grooves These grooves are dimensional on the order of the wall vortices and turbulent burst dimensions 31 depicted in FIG 3 The large-eddy breakup device 41, depicted in FIGS 4 and 5, is a small strip or airfoil which is suspended in the upper region of the boundary layer Various physical mechanisms cause a disruption of the large-scale vortices The combination of the devices of this invention result in a substantial reduction in skin friction drag

107 citations


Journal ArticleDOI
TL;DR: In this paper, a series of radiosondes along a 150-km track starting at the ice edge of the Antarctic marginal ice zone (MIZ) was used to investigate the influence of atmospheric boundary layer (ABL) on the deceleration of surface roughness.
Abstract: During a traverse of the Antarctic marginal ice zone (MIZ) near the Greenwich Meridian in October 1981, we launched a series of radiosondes along a 150-km track starting at the ice edge. Since the wind was from the north, off the ocean, these radiosonde profiles showed profound modification of the atmospheric boundary layer (ABL) as the increasing surface roughness decelerated the flow. The primary manifestation of this modification was a lifting of the inversion layer with increasing distance from the ice edge by the induced vertical velocity. But there was also a cooling of the stably stratified mixed layer below the inversion and a consequent flux of sensible heat to the surface that averaged over 200 W/m2. The magnitude of this flux suggests that atmospheric heat transport plays a significant role in the destruction of ice in the Antarctic MIZ. Using the rising of the inversion and ABL similarity theory, we estimated the change in the neutral stability drag coefficient, CD, across the MIZ. CD increased from its open ocean value, 1.2×10−3, at the ice edge to 4.0×10−3 at 80–90% ice concentration. We present an equation for this dependence of drag on ice concentration that should be useful for modeling the surface stress in marginal ice zones.

94 citations


Journal ArticleDOI
TL;DR: In this article, an experimental and theoretical examination of the settling, entrainment and overturning of 176 valves representing 16 common Northwest European marine bivalve species, together with a comparative study of 15 plastic models in the form of segments from cylindrical tubes, was made.
Abstract: An experimental and theoretical examination has been made of the settling, entrainment and overturning of 176 valves representing 16 common Northwest European marine bivalve species, together with a comparative study of 15 plastic models in the form of segments from cylindrical tubes. Settling behaviour in both stagnant and moving water depends on particle mass, symmetry and concavo-convexity. Separated empty bivalve shells spin and spiral while settling and, if sufficiently elongated, also pitch. At the observed Reynolds numbers, the shells and models fall concave-up, the terminal fall velocity increasing as the square root of the unit immersed mass or weight. The drag coefficient is independent of Reynolds number but increases with surface roughness and, particularly, particle elongation. Turbulence slightly lowers the critical elongation for pitching. A separation vortex lies captive on the upper side of each descending particle. Consequently, an empty bivalve shell traversing a suspension of sand traps grains on its upper side at a rate proportional to their volume concentration and terminal fall velocity. This process, increasing the effective shell mass, is limited only by the capacity of the shell and grain spillage due to the possible onset of pitching. The ratio (non-dimensional) of a quantity proportional to the applied fluid force and the particle unit immersed weight consistently describes the entrainment of concave-up and convex-up particles, and also the immediate overturning of a valve on settling concave-up to the bed. These thresholds vary in relative magnitude with bed-particle friction and particle concavo-convexity. In general, convex-up particles are the most stable; the concave-up entrainment and overturning thresholds are of a substantially lower but similar magnitude. The high frequency of concave-up bivalve attitudes in turbidites is understandable largely in terms of the ability of a settling valve to increase in effective mass by grain entrapment. Convex-up attitudes in the lower parts of turbidites may record currents stronger than the overturning threshold.

90 citations


Journal ArticleDOI
TL;DR: In this article, a simple stress model was developed to explain the observations of reduced drag when small gas bubbles are introduced into a turbulent boundary layer, which is caused by a combination of density reduction and turbulence modification.
Abstract: A simple stress model has been developed to explain the observations of reduced drag when small gas bubbles are introduced into a turbulent boundary layer. The drag reduction is caused by a combination of density reduction and turbulence modification. The maximum reduction is obtained when the gas volume fraction approaches the bubble packing limit; the medium viscosity also increases markedly in this limit and becomes the important factor in restricting further reduction in drag. The derived analytical expression represents experimental data well.

77 citations


Proceedings ArticleDOI
12 Jan 1984
TL;DR: In this article, experimental measurements of the ice shapes and resulting drag increases were measured in the NASA-Lewis Icing Research Tunnel, and additional results were given which are helpful in understanding the ice structure and the way it forms, and in improving the ice accretion modeling theories.
Abstract: Experimental measurements of the ice shapes and resulting drag increases were measured in the NASA-Lewis Icing Research Tunnel. The measurements were made over a large range of conditions (e.g., airspeed and temperature, drop size and liquid water content of the cloud, and the angle of attack of the airfoil). The measured drag increase did not agree with the existing correlation. Additional results were given which are helpful in understanding the ice structure and the way it forms, and in improving the ice accretion modeling theories. There are data on the ice surface roughness, on the effect of the ice shape on the local droplet catch, and on the relative importance of various parts of the ice shape on the drag increase. Experimental repeatability is also discussed.

76 citations


Journal ArticleDOI
TL;DR: The effects of the aerodynamic drag reduction on the behavior of both pitched and batted balls is significant, and may explain several features of the game of baseball which previously have been unexplained or attributed to other causes as mentioned in this paper.
Abstract: At Reynolds numbers above about 105 the aerodynamic drag force on a sphere drops sharply as the flow begins to become turbulent in the boundary layer. For baseballs, this ‘‘drag crisis’’ may occur at speeds which are typical for pitched or batted balls. The effects of the drag reduction on the behavior of both pitched and batted balls is significant, and may explain several features of the game of baseball which previously have been unexplained or attributed to other causes. In particular, the drag reduction may help to explain why pitched fastballs appear to rise, why pitched curve balls appear to drop sharply, and why home run production has increased since the introduction of the alleged ‘‘lively ball.’’ Calculations suggest that aerodynamic forces are as important a factor in fastpitch softball as in baseball, and that they are a critical factor in a number of other ball games.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the drag on a sphere moving horizontally through stably stratified salt water and found that ΔCD has both positive and negative values attributable respectively to lee-wave drag and suppression of turbulence in the wake.
Abstract: The drag on a sphere moving horizontally through stably stratified salt water is measured in laboratory experiments. The increment ΔCD in drag coefficient due to the stratification is obtained as a function of a stratification parameter κ and, in principle, the usual Reynolds number R. In these experiments, where R ranges from 150 to 5000, ΔCD is insensitive to R. But, as a function of κ, ΔCD has both positive and negative values attributable respectively to lee-wave drag and to suppression of turbulence in the wake. An observed delay in flow separation also apparently results from the lee-wave drag.

Journal ArticleDOI
TL;DR: In this paper, the authors used the boundary element method to obtain a fully numerical solution for comparison with the theoretical predictions of Chhabra and Uhlherr, and they also presented a simple empirical relation which gave a good first approximation to the drag force.
Abstract: In the report of Chhabra and Uhlherr [1], a theoretical formulation for the drag force on a sphere in a fluid governed by the Carreau viscosity equation was presented. The formulation gave a good representation of the drag force when compared with experimental measurements, although the experiments were carried out on fluids exhibiting both shear-thinning and elastic behaviour. In the present work the ‘boundary element method’ has been used to obtain a fully numerical solution for comparison with the theoretical predictions. The two sets of results agree closely. We also present a simple empirical relation which gives a good first approximation to the drag force (∼ 10%).

Journal ArticleDOI
TL;DR: The Navier-Stokes and energy equations have been solved numerically for a pair of spheres in tandem at Re = 40 for two different spacings using bispherical coordinates as discussed by the authors.

01 May 1984
TL;DR: In this article, a flapped natural-laminar flow airfoil, NLF(1)-0414F, was designed for 0.70 chord laminar flow on both surfaces at a lift coefficient of 0.40.
Abstract: Experimental results have been obtained for a flapped natural-laminar-flow airfoil, NLF(1)-0414F, in the Langley Low-Turbulence Pressure Tunnel. The tests were conducted over a Mach number range from 0.05 to 0.40 and a chord Reynolds number range from about 3.0 x 10(6) to 22.0 x 10(6). The airfoil was designed for 0.70 chord laminar flow on both surfaces at a lift coefficient of 0.40, a Reynolds number of 10.0 x 10(6), and a Mach number of 0.40. A 0.125 chord simple flap was incorporated in the design to increase the low-drag, lift-coefficient range. Results were also obtained for a 0.20 chord split-flap deflected 60 deg.

Journal ArticleDOI
TL;DR: In this article, the evolution of two-and three-dimensional non-stationary viscous-fluid flows in a plane channel is simulated by means of efficient computational algorithms for direct integration of the Navier-Stokes equations.
Abstract: Two- and three-dimensional non-stationary viscous-fluid flows in a plane channel are considered. By means of efficient computational algorithms for direct integration of the incompressible Navier-Stokes equations the evolution of these flows over large time intervals is simulated. Classes of two- and three-dimensional non-stationary flows with stationary integral characteristics (the flow rate, mean pressure gradient, total energy of pulsations etc.) were found. Such flows are called secondary flows. Two-dimensional secondary flows have only qualitative similarity to turbulent flows observed in experiments. Three-dimensional secondary flows agree very well, even quantitatively, with turbulent flows. The principal characteristics of turbulent flows such as drag coefficient, mean-velocity profile, the distributions of the pulsation velocity components and some others are reproduced in three-dimensional secondary flows with good accuracy.

Journal ArticleDOI
TL;DR: In this paper, the response of a rigid two-dimensional elastically mounted smooth cylinder, with oscillations restricted to a plane normal to the incident flow, as influenced by the vicinity of an identical fixed body placed inside the wake, was investigated.
Abstract: Experiments were conducted to investigate the response of a rigid two-dimensional elastically mounted smooth circular cylinder, with oscillations restricted to a plane normal to the incident flow, as influenced by the vicinity of an identical fixed body placed inside the wake. The static lift and drag coefficients, as well as the vibration amplitude and frequency of the upstream cylinder as functions of relative position of the pair of cylinders are given. Most measurements were carried out under two conditions of free-stream turbulence. Whilst turbulence decreased the magnitude of drag coefficients, it had no appreciable effect on lift coefficients. The forces on the upstream body were found to be influenced by the proximity to the downstream one in a significant way only when the streamwise spacing is less than two diameters.In the dynamic tests, two kinds of instability, namely a vortex-resonance and galloping, were observed, with the latter only occurring when the downstream cylinder was well submerged in the near wake of the upstream one. The vortex-shedding frequency was always found to lock to oscillation frequency. Whereas the vibration characteristics remained essentially unaffected with changing turbulence intensity, the galloping amplitudes were observed to be sensitive to cylinders’ aspect ratio. A quasi-steady theory was developed to predict the galloping behaviour.

Journal ArticleDOI
TL;DR: In this article, the effects of corner radius on the hydrodynamic forces experienced by cylindrical bluff bodies in oscillatory flow over the Keulegan Carpenter number range from 1 to 100.

Journal ArticleDOI
TL;DR: In this article, the influence of an exterior cylindrical boundary is taken into account by making measurements with boundaries of different diameter and using an empirical correlation to extrapolate to infinite boundary diameter.
Abstract: Measurements are presented for the drag on a circular cylinder moving along its axis of rotational symmetry at low Reynolds number The influence of an exterior cylindrical boundary is taken into account by making measurements with boundaries of different diameter and using an empirical correlation to extrapolate to infinite boundary diameter The results for cylinders with length to diameter ratio (L/D) between 4 and 100 agree well with the calculated values of Youngren and Acrivos The results for disks (0019

Proceedings ArticleDOI
01 Feb 1984
TL;DR: In this article, the influence of the trunk length of a road vehicle on drag coefficient was measured in a wind tunnel on a 1.5-scale model and a method was shown for correlating to the aerodynamic drag data from wake survey.
Abstract: Measurements are presented showing the influence of the trunk length of a road vehicle on drag coefficient. The experiments were made in the ''Politecnico di Torino'' wind tunnel on a 1/5 scale model. Data from balance measurements, body-surface pressure and wake flow surveys are reported. A method is shown for correlating to the aerodynamic drag data from wake survey.

Journal ArticleDOI
TL;DR: In this article, the hydrodynamics and heat/mass transport associated with condensation on a moving drop have been investigated for the intermediate Reynolds-number range of drop motion (Re = O(100)).
Abstract: The hydrodynamics and heat/mass transport associated with condensation on a moving drop have been investigated for the intermediate Reynolds-number range of drop motion (Re = O(100)). The drop environment is a mixture of saturated vapour and a non-condensable. The formulation entails a simultaneous solution of the quasi-steady elliptic partial differential equations that describe the flow field and transport in the gaseous phase, and the motion inside the liquid drop. The heat transport inside the drop is treated as a transient process. Results are reported for the interfacial velocities, drag, external and internal flow structure, heat flux, drop growth rate and temperature–time history inside the drop. The results obtained here have been compared with experimental data where available, and these show excellent agreement.The results reveal several novel features. The surface-shear stress increases with condensation. The pressure level in the rear of the drop is higher. As a consequence, the friction drag is higher and the pressure drag is lower. The total drag coefficient increases with condensation rate for small values of drop size or temperature differential, and it decreases for large values of these parameters. The volume of the separated-flow region in the rear of the drop decreases with condensation. At very high rates of condensation, the recirculatory wake is completely suppressed. Condensation also delays the appearance of the weak secondary internal vortex motion in the drop. The heat and mass fluxes are significantly affected by the presence of the non-condensable in the gaseous phase and by the circulation inside the drop.

Proceedings ArticleDOI
01 Jun 1984
TL;DR: In this paper, the passive shock wave/boundary layer control for reducing the drag of 14 percent-thick supercritical airfoil was conducted in the 3 in. x 15.4 in. RPI Transonic Wind Tunnel at transonic Mach numbers.
Abstract: An investigation of the passive shock wave/boundary layer control for reducing the drag of 14 percent-thick supercritical airfoil was conducted in the 3 in. x 15.4 in. RPI Transonic Wind Tunnel at transonic Mach numbers. Various porous surfaces with a cavity beneath it was positioned on the area of the airfoil, mounted on the test section bottom wall, where the shock wave occurs. The static pressure distributions over the airfoil, the wake impact pressure survey for determining the profile drag and the Schlieren photographs for porous surfaces are presented and compared with the results for solid surface airfoil. With a uniform porosity surface the normal shock wave for solid surface was changed to a lambda shock wave, and the wake impact pressure data indicated an appreciable drag reduction at transonic Mach numbers. For a free stream Mach number of 0.81 the profile drag coefficient for the airfoil top surface with uniform porosity was 46 percent lower than for the solid surface airfoil.

Journal ArticleDOI
TL;DR: In this paper, the turbulent energy typically 1asted for about 50 s and showed a peak instantaneous −uw perturbation product of about 025 cm2 s−2 with a mean flow of about 3 cm s−1.
Abstract: Electromagnetic sensors have been used to measure the turbulent current fluctuations 50 cm above the sea bed at a depth exceeding 4000 m on an abyssal plain Bursts of turbulent energy typically 1asted for about 50 s and showed a peak instantaneous −uw perturbation product of about 025 cm2 s−2 The horizontal and vertical integral length scales were estimated to be around 150 and 30 cm, respectively, in a mean flow of about 3 cm s−1 The eddy correlation method gave estimates for the friction velocity of around 012 cm s−1 and the bottom drag coefficient was estimated to be 19 × 10−3 When normalized by variance, height above bottom and wave number the spectra agree with the similarity scaling suggested by Soulsby, and the statistics of the turbulence are consistent with existing results obtained from atmospheric and shallow water boundary layers

Journal ArticleDOI
01 Apr 1984
TL;DR: In this article, a bulk dynamic model for a vertically falling bathythernograph probe is proposed to predict fall speeds and depths as functions of time, and the theoretical results agree with recent observations and provide improved probe depth estimates in comparison with the manufacturer's empirical formula.
Abstract: Factors affecting the dynamics of expendable bathythernograph probes (SIPPICAN Corporation XBT types T-7 and T-4) are discussed, and a bulk dynamic model for a vertically falling probe is proposed. The model predicts fall speeds and depths as functions of time. The theoretical results agree with recent observations and provide improved probe depth estimates in comparison with the manufacturer's empirical formula. The model quantifies the relationships of probe mass, bulk drag coefficient, wire loss, and initial fall speed; consequently, it is suggested that these parameters should be considered when refined and accurate intercomparisons of XBT probes and conductivity-temperature-depth (CTD) profilers are made. Accurate determinations of the probe's hydrodynamic drag over its operational range of Reynolds number are needed for future refinements of the model.

Journal ArticleDOI
TL;DR: In this paper, pressure drop and void fraction measurements in two-phase (air-water) flow through porous beds of randomly packed spheres have been used to determine the interfacial gas-liquid drag and the gas-solid drag for the case of zero net liquid flux through the bed.
Abstract: Pressure drop and void fraction measurements in two-phase (air-water) flow through porous beds of randomly packed spheres have been used to determine the interfacial gas-liquid drag and the gas-solid drag for the case of zero net liquid flux through the bed. The results, presented for beds of 3.18-, 6.35-, and 12.7-mm spheres, show that the interfacial gas-liquid drag term is of the same order as the gas-solid drag term when the particle size is greater than 6 mm.

01 Jan 1984
TL;DR: In this article, the results of the wind tunnel investigation of untwisted, constant chord blades having four aspect ratios, with an NACA 4415 series airfoil section, at angles of attack ranging from -10 to 100 degrees are discussed.
Abstract: Wind Turbine blades operate over a wide angle of attack range. Unlike aircraft, a wind turbine's angle of attack range extends deep into stall where the three dimensional performance characteristics of air foils are not generally known. Peak power predictions upon which wind turbine components are sized, depend on a good understanding of a blade's post stall characteristics. The results of the wind tunnel investigation of untwisted, constant chord blades having four aspect ratios, with an NACA 4415 series airfoil section, at angles of attack ranging from -10 to 100 degrees are discussed. Tests were conducted for aspect ratios of 6, 9, 12 and infinity at four Reynolds numbers ranging from one-quarter million to one million. The results on the same family of airfoil section but with varying thickness ratio are given. Results of force and pitching moment measurements over the angle of attack range for all combinations of Reynolds numbers and aspect ratios, and the effects of boundary layer tripping, are presented. Both initial and secondary stall are presented. The maximum drag coefficient is found to occur an an angle of attack of 90 degrees. The pitching moment is unstable beyond stall. The lift and post-stall drag-coefficients decrease with decreasing aspect ratio. The boundary layer tripping is observed to decrease the lift curve slope and stalling angle of attack. The drag coefficient (with tripping) is significantly affected only at low aspect ratio. Beyond secondary stall, the lift to drag ratio is independent of aspect ratio. The maximum lift to drag ratio for the infinite aspect ratio blade is roughly twice that of the blade with an aspect ratio of six. This effect is independent of Reynolds number in the range studied.

Journal ArticleDOI
TL;DR: In this article, the authors used three profiles of momentum flux and mean wind to calculate an air-ice drag coefficient CD of 3.0 ±.6 × 10−3 referenced to a 10m anemometer height.
Abstract: Turbulent flux measurements were made at four levels (42, 90, 195, and 340 m) by the NOAA P-3 aircraft over first-year sea ice in the northern Bering Sea during February 1982. Three profiles of momentum flux and mean wind were used to calculate an air-ice drag coefficient CD of 3.0 ± .6 × 10−3 referenced to a 10-m anemometer height. The boundary layer was slightly unstable (zi/L = −1.2, where zi, was the inversion height of 660 m and L the Monin-Obukhov length). The mean wind speed at the 42-m height was 17 m/s, and the air temperature was −20°C. From turbulent heat flux measurements the value of the bulk heat transfer coefficient CH was 0.73 ± 1.6 × 10−3, giving a CH/CD of 0.24. The Bowen ratio was greater than 2.8. Comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement, which increases confidence in the calculations. The geostrophic drag coefficient |u*|/|G|, where u* is the friction velocity and G is the geostrophic wind, was 0.047. The turning angle of the surface wind (measured by an anemometer at a height of 3 m on the ice) was 32°, and the ratio of surface wind speed to the geostrophic wind speed was 0.76.

Proceedings ArticleDOI
01 Jan 1984
TL;DR: In this paper, largeeddy alteration techniques were used to modify the drag characteristics of the turbulent boundary layer and local skin-friction coefficients were measured for single and multi-element arrays of thin plates suspended in a fully turbulent, flat plate, boundary layer at R(theta) = 3,000.
Abstract: Large-eddy alteration techniques were used to modify the drag characteristics of the turbulent boundary layer. Local skin-friction coefficients were measured for single and multi-element arrays of thin plates suspended in a fully turbulent, flat plate, boundary layer at R(theta) = 3,000. Effects of these devices were measured more than 300 boundary-layer thicknesses downstream to R(theta) = 17,000. It was found that although most of the devices reduced the local skin friction immediately downstream, this reduced skin-friction region persisted for only 100-120 delta-0, after which a rapid rise in skin-friction coefficient occurred, often exceeding flat plate values. Net drag reductions were obtained only for tandem configurations and these reductions were sensitive to device spacing and height. The maximum net drag reduction reported was approximately 7 percent with a device spacing of 10 delta-0 at a height of 0.8 delta-0.

01 Aug 1984
TL;DR: In this article, a discrete element model for turbulent flow over rough surfaces has been rigorously derived from basic principles, which includes surface roughness effects as a constitutent part of the partial differential equations which describe momentum and energy transport in turbulent flows.
Abstract: : A discrete element model for turbulent flow over rough surfaces has been rigorously derived from basic principles. This model includes surface roughness effects as a constitutent part of the partial differential equations which describe momentum and energy transport in turbulent flows. The model includes the necessary empirical information on the interaction between the roughness elements and the flow around and between the elements in a general way which does not require experimental data on each specific surface. This empirical information is input via algebraic models for the local element drag coefficient and Nusselt number. These models were calibrated by comparison with base data sets from surfaces with three-dimensional (distributed) roughness elements. Calculations using the present model have been compared with experimental data from 118 separate experimental runs. The results of these comparisons ranged from good to excellent. The calculations compared equally well with both transitionally rough and fully rough turbulent flow results without modification of the roughness model. (Author)

Journal ArticleDOI
TL;DR: In this article, an analytical integral expression for the integral drag force on the dislocation and evaluated explicitly for the low-velocity limit was derived for the linear, isotropic elastic case.
Abstract: An analytical expression is derived for the steady-state solute distribution about an edge or mixed dislocation moving at constant velocity. The result is derived for the linear, isotropic elastic case. An analytical integral expression is presented for the integral drag force on the dislocation and evaluated explicitly for the low-velocity limit. The results are compared to those of earlier numerical and approximate analytical derivations.