Estimation Of Drag Coefficient Research Articles

Anisotropic reflection effect on satellite, Ajisai

A model for the anisotropic reflection force acting on Ajisai is presented which includes the variable reflectivity coefficient and the force in the direction perpendicular to the incident light. This model significantly reduces the along-track orbit errors of Ajisai and smoothes the spike-like variation in the estimated drag coefficients from analysis of Ajisai laser ranging data. The model produces 17% smaller range residual RMS values in a one-year arc analysis of 1993 data, and a smaller residual RMS for a short-arc analysis in mid-year, the period from May to August, 1993.

Drag and Sediment Dispersion Over Sand Waves

Estimates of the drag coefficient over sand waves during calm weather in the southern North Sea have been obtained from measurements of the water slope and currents at different heights ( z) above the sea-bed using the log profile and momentum balance methods. An observed phase difference between principal terms in the momentum balance equation is examined theoretically. Drag coefficient estimates are found to agree broadly with previous studies. Owing to bedform asymmetry, average drag coefficient values obtained at z=1 m ( C 100) are found to be 0·0021 and 0·0029 for flood and ebb tides, respectively. Systematic changes in bed roughness are not detected. Using a momentum balance approach, the average drag coefficient value ( C d ) at z=10 m is found to be 0·0056. Changes in 10-min average C d values over sand waves during the tidal cycle are found to be small with bedform asymmetry having no detectable effect. Correlation between C d and C 100is found to be poor and separation of skin friction and form drag terms is not possible with existing measurements. The inclusion of form drag in C 100values at the present site leads to over-estimation of the bed shear stress ({q) available to mobilize and transport sediment. Mobile sediment, detected through the use of tracers and a transmissometer, was not found to have any measurable effect on either C d or C 100in calm weather conditions.

Estimation of drag coefficient over the western desert sector of the Indian summer monsoon trough

In the estimation of momentum fluxes over land surfaces by the bulk aerodynamic method, no unique value of the drag coefficient (C D) is found in the literature. The drag coefficient is generally estimated from special observations at different parts of the world. In this study an attempt is made to estimate drag coefficient over the western desert sector of India using data sets of Monsoon Trough Boundary Layer Experiment (MONTBLEX) during the summer monsoon season of 1990. For this purpose, the fast and slow response data sets obtained simultaneously from a 30 m high micro-meteorological tower at Jodhpur are used. All the observations used in this study are confined to a wind speed regime of 2.5–9.0 ms−1. A comparison of momentum fluxes computed by eddy correlation (direct estimation) with profile and bulk aerodynamic (C D = 3.9 × 10−3, Garratt, 1977) methods revealed that though the nature of variation of the fluxes by all these methods is almost similar, both the indirect methods give an under-estimated value of the fluxes. The drag coefficient is estimated as a function of wind speed and surface stability by a multiple regression approach. An average value of the estimated drag coefficient is found to be of the order of 5.43 × 10−3. The estimated value ofC D is validated with a set of independent observations and found to be quite satisfactory. The recomputed momentum fluxes by bulk aerodynamic method using the estimated drag coefficient are in close agreement with the directly estimated fluxes.

Effect of particle shape on viscous attenuation of ultrasound in concentrated clay suspensions

Acoustic wave propagation in concentrated suspensions is analyzed using a modified coupled‐phase modeling approach. The particle, size, shape, and orientation are taken into account for estimation of viscous drag coefficient of spheroid particles over wide ranges of frequency and particle concentration. The study deals with frequency‐dependent and concentration‐dependent ultrasound attenuation coefficient of clay suspensions, with particular attention to the effect of particle size and shape distributions. For clay suspensions, the major loss of acoustic energy results from the viscous dissipation arising from the relative particle–fluid motion. Predicted results of sound‐speed and attenuation coefficient based on consideration of particle shape factors agree well with the measurements available in literature for frequencies of 0.10–5.0 MHz and solid concentrations up to 40 vol%. Experimental results of attenuation spectra of plate‐shaped kaolin clay slurries with solid concentrations of 0.6 to 16.9 vol% over 3 to 60 MHz are obtained using a newly developed AcoustoPhor System 8000. These attenuation spectra are interpreted in terms of realistic particle size and shape distributions. The effects of nonsphericity become dominant as particle concentrations and operating frequencies are increased. Realistic size‐dependent shape factors are shown to explain the measured spectra.

Slow non‐newtonian flow through packed beds: Effect of zero shear viscosity

AbstractThe slow non‐Newtonian (inelastic) flow through packed beds of mono‐size spherical particles has been simulated by solving the equations of motion numerically. The inter‐particle interactions have been modelled by using a simple cell model. Theoretical estimates of pressure, friction and total drag coefficients as function of the pertinent physical (l≥n≥ 0.2; 0.3 ≤ e ≤ 0.5) and kinematic parameters (0.01 ≤ '≤ 100) for a fixed value of Reynolds number {Re = 0.001) have been obtained. The theoretical predictions reported herein have been validated using the suitable experimental results available in the literature, and the importance of including the zero shear viscosity in analyses for the creeping flow problems is convincingly demonstrated.

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

Ascent modeling of scientific balloon missions is particularly sensitive to accurate knowledge of the balloon lifting gas mass. Transient distortions of the balloon body effectively increase drag beyond classical solid body data. Further, experimenters have reported an increase in virtual mass with developing flow relative to the accepted inviscid determination at incipient flow. In support of the National Aeronautics and Space Administration (NASA) Balloon Program, small scale balloons (175 m 3) were flown with varying lifting gas and total system mass. Stow Away Special (SAS) instrument packages were developed to measure and record acceleration and temperature data during these tests. Top fitting and instrument payload accelerations were measured from launch to steady state ascent and through ballast drop transients. The development of the small (5×7.5×15 m 3), light weight (.5 kg.), self-powered SAS is discussed along with mathematical models developed to determine gas mass, drag and virtual mass coefficients.

The Large-Scale Inflow-Layer Structure of Hurricane Frederic (1979)

Abstract Aircraft, rawinsonde, satellite, ship, and buoy data collected over a 40-h period were composited to analyze the inflow-layer structure of Hurricane Frederic (1979) within a radius of 10° latitude of the storm center. To improve the quality of the composite analyses, the low-level cloud-motion winds (CMWs) employed in this study were assigned a level of best fit (LBF). An LBF was assigned to each CMW by determining the level at which the closest agreement existed between CMW and ground-truth wind data (e.g., rawinsonde, aircraft, ship, and buoy). The CMWs were then adjusted vertically to uniform analysis levels, combined with ground-truth wind data, and objectively analyzed. These objectively analyzed wind fields were used to obtain kinematically derived fields of vorticity, divergence, and vertical velocity. An angular-momentum budget was also computed to obtain estimates of surface drag coefficients. The low-level CMWs in this study were found to have LBFs ranging from 300 to 4000 m. It was sho...

Slow power law fluid flow relative to an array of infinite cylinders

The creeping flow of incompressible power law fluids past arrays of infinite cylinders has been investigated theoretically. The intercylinder interactions have been modeled using a free surface cell model. While, for the parallel flow, the momentum equation has been integrated numerically to obtain the estimates of drag coefficient for the assemblage, the well-known variational principles have been used to analyze the cross-flow configuration. The resulting upper and lower bounds on drag coefficient are very close to each other under most conditions of practical interest. preliminary comparisons with the scant data available in the literature are satisfactory.

The Profile Drag of A Hawk’s Wing, Measured by Wake Sampling in A Wind Tunnel

ABSTRACT The distribution of dynamic pressure behind a Harris’ hawk’s wing was sampled using a wake rake consisting of 15 pitot tubes and one static tube. The hawk was holding on to a perch, but at an air speed and gliding angle at which it was capable of gliding. The perch was instrumented, so that the lift developed by the wing was known and the lift coefficient could be calculated. The mean of 92 estimates of profile drag coefficient was 0.0207, with standard deviation 0.0079. Lift coefficients ranged from 0.51 to 1.08. Reynolds numbers were nearly all in the range 143000–194000. The estimates of profile drag coefficient were reconcilable with previous estimates of the wing profile drag of the same bird, obtained by the subtractive method, and also with values predicted by the ‘Airfoil-ii’ program for designing aerofoils, based on a digitized wing profile from the ulnar region of the wing. The thickness of the wake suggested that the boundary layer was mostly or fully turbulent in most observations and separated in some, possibly as an active means of creating drag for control purposes. It appears that the bird could momentarily either increase or decrease the profile drag of specific parts of the wing, by active changes of shape, and it appeared to use the carpo-metacarpal region especially for such control movements. Further investigation in a low-turbulence wind tunnel would help to resolve doubts about the possible influence of airstream turbulence on the behaviour of the boundary layer.

FLOW CHARACTERISTICS OF SETTLING SUSPENSIONS AND FLUIDIZED BEDS OF SPHERICAL PARTICLES

Abstract The complete Navier-Stokes equations together with the free surface cell model have been solved numerically to obtain the theoretical estimates of drag coefficients of particle assemblages moving through an incompressible Newtonian liquid. The results reported herein have been expressed in terms of the constant rate sedimentation velocities for concentrated suspensions and voidage-velocity behaviour for particulately fluidized liquid-solid systems. Theoretical results have been validated by carrying out detailed comparisons with the widely used correlations available in the literature. Bearing in mind the experimental uncertainty in this field, the agreement between theory and experiments is satisfactory in the range of variables, (0.3 ≤ e ≤ 0.9) and (10−3 ≤ Re ≤ 100), studied in this work.

Station-Holding by three Species of Benthic Fishes

ABSTRACT Station-holding performance was determined on a smooth substratum and on a grid substratum for three species of benthic fishes differing in body shape, surface texture, density, friction coefficient and behavioural repertoire. The grid was made of wires parallel to the flow, which raised fish into the free stream. Limited observations were also made on the benthopelagic cod. Station-holding performance was evaluated at two speeds. The first was defined as the slip speed, above which activities such as swimming, fin-beating, body arching, body clamping and gripping the substratum were required to hold position on the substratum. The second was defined as the swim speed, when fish began swimming out of ground contact. Cod and lasher started swimming when they began slipping, so that slip and swim speeds were the same, averaging 6cms−1 for cod and 32cms−1 for lasher on the smooth surface. Body postures and fin-beating delayed swimming from a slip speed of about 20 cm s−1 to swim speeds of 47–58 cm s−1 for plaice and rays. The grid had relatively little effect on slip and swim speeds of plaice and rays. Lasher grasped the grid with their pectoral fins, increasing swim speeds to 55cms−1. Amputation of the posterior portion of the median fins of plaice reduced swim speeds on the smooth surface to 36cms−1. Amputation of the pectoral fins of lasher reduced the swim speed on the grid to 38cms−1. Estimates of drag coefficients for fish were made using published data for blisters. These were used to determine lift coefficients and the effects of grasping the substratum on the friction coefficient. Comparison of lift coefficients of rays on the smooth substratum with those on the grid showed that flow beneath the body reduced lift. Amputation of the posterior of the median fins of plaice and the rarity of body posturing by plaice and rays on the grid showed that the major role of this station-holding behaviour was reduction of lift through induction of flow beneath the body. Lashers were able to hold station at speeds comparable to plaice and rays when they could utilize the small amount of surface structure of the grid to increase friction. Benthic fishes tend to have either ‘flattened’ plaice-or ray-like forms with low drag coefficients but high lift coefficients, or more fusiform lasher-like forms with high drag coefficients and low lift coefficients. High-lift forms use behaviour to reduce lift coefficients, whereas high-drag forms use behaviour to increase friction.

Sediment Entrainment and Deposition Measurements in Long Island Sound

Entrainment and deposition fluxes were measured in Central Long Island Sound. Data were collected with a 3‐MHz acoustic transceiver range gated to sample the sediment concentration in 1‐cm intervals in the bottom 70 cm of the water column. Horizontal and vertical velocities were sampled 68 cm above the bottom. A turbulent control volume derivation was used to estimate the fluxes and their variation over one 3.5‐hr deployment and a second deployment that spanned a tidal cycle. Time histories of three measures of the shear stress as well as the turbulent and wave kinetic energy were correlated with the entrainment fluxes. Turbulent and wave kinetic energy was the most reliable correlate with entrainment while the Reynolds' stress and drag coefficient estimates fared less well, the former failing at ebb tide, and the latter during periods of low average velocity.

Estimation of fluxes from wind and temperature profiles in the marine atmospheric surface boundary layer

Daytime hourly measurements on wind profile at a station 7°40'N, 78°26' 131, and wind and temperature profiles at 12°35' N, 80°48'E, were made in the 3-6 m layer above sea surface, using sensors fitted at six levels on a 3,2 m mast which was projected forward of the bow of the research vessel “R.V. Gaveshoni” during her cruise in May 1983 when she was halted at these stations, on 16 and 20 May respectively, for observations.
 Drag coefficient was estimated from wind profiles on 16th, Wind profiles on 20th were corrected for diabetic effects using the corresponding temperature profiles and the estimated drag coefficient, momentum and sensible heat flux are presented.

Modelling of turbidity currents on Navy Submarine Fan, California Continental Borderland

ABSTRACTSeveral Holocene turbidites can be correlated across much of Navy Fan through more than 100 sediment core localities. The uppermost muddy turbidite unit is mapped throughout the northern half of the fan; its volume, grain‐size distribution and the maximum height of deposition on the basin slopes are known. These parameters can be related to the precise channel morphology and mesotopography revealed by deep‐tow surveys. Thus there is sufficient information to estimate detailed flow characteristics for this turbidity current as it moved from fan valley to distal basin plain.On the upper fan, the gradient and the increasing downstream width of the channel and only limited flow overspill suggest that the flow had a Froude number close to 1.0. The sediment associated with the channel indicates friction velocities of about 0.06 m s−1 and flow velocities of about 0.75 m s−1. Using this flow velocity and channel dimensions, sediment concentration (∼2×10−3) and discharge are estimated, and from a knowledge of the total volume of sediment deposited, the flow duration is estimated to be from 2 to 9 days. It is shown that the estimates of Froude number, drag coefficient, and sediment concentration are not likely to vary by more than a factor of 2.On the mid‐fan, the flow was much thicker than the height of the surface relief of the fan and it spread rapidly. The cross‐flow slope, determined from the horizontal extent of turbidite sediment, is used to estimate flow velocity, which is confirmed by consideration of both sediment grain size and rate of deposition. This again allows sediment concentration and discharge to be estimated. The requirements of flow continuity, entrainment of water during flow expansion, and observed sediment deposition provide checks on all these estimates, and provide an integrated picture of the evolution of the flow. The flow characteristics of this muddy turbidity current are well constrained compared to those for more sand‐rich late Pleistocene and early Holocene turbidity currents on the fan.

The limitations on stress parameterization imposed by intermittency in turbulent flow

The indirect dissipation technique is used to estimate 1-min averages of friction velocity u *in the surface layer over the tropical ocean. These estimates are compared to estimates of u *obtained using a drag coefficient and the relative difference between the two is examined in relation to stability and averaging time. Plumes and downdrafts are found to be responsible for an anomalous behavior of the drag coefficient estimates. Certain factors relating to plume properties, derived using conditional sampling as described in Khalsa (1980), are shown to be related to the variance between the two estimates of friction velocity. An investigation into the effects of increasing the averaging time reveals that plume spacing, which is dependent on stability, and the mean wind speed determine the minimum time for smoothing the influence of plumes and downdrafts.

A Gill Twin Propeller-Vane Anemometer for Flux Measurements During Moderate and Strong Winds

A wind velocity measuring system based on the Gill propeller anemometer is described. A method of calculating the vertical component, which allows for the non-cosine response and avoids the region of stall and nonlinear operation, is presented. A summary of the possible errors in Reynolds stress and drag coefficient estimates is given. A method of establishing the distance constant using field observations is presented. Finally, some preliminary results and some intercomparisons with other anemometers are described briefly.

Wind forces on and excitation of a 130-m concrete chimney

A field experiment concerned with wind forces on a large concrete chimney and the vibrations caused by these forces is presented. Some preliminary results concerning the consistency of the measurements are discussed, and some conclusions regarding chimney vibrations are given. A method for on-line dynamic calibration of wind pressure transducers is presented. The method has worked satisfactorily, but improvements concerning zero-pressure biases are needed. A universal mean-pressure distribution for the Stigsnaes chimney is presented. An estimated drag coefficient of 0.64 (independent of height above the ground) seems reasonable for transcritical Reynolds numbers. The roughness parameter of the sea for on-shore wind directions is found to be of the order of centimetres. A slight indication of increasing roughness with increasing wind speed is observed.

Wind stress on Arctic sea ice

Wind velocity fluctuations have been recorded with a sonic anemometer over sea ice at a number of locations in the Arctic Ocean and in Robeson Channel and used to compute surface stresses and drag coefficients. The wind drag coefficient is found to correlate well with the rms elevation of the ice and snow surface at wavelengths shorter than 13 meters. A formula for the estimation of drag coefficients from surface profiles is given. The form drag of ridges can be of similar magnitude to the measured surface drag and should be allowed for. Gust factors are examined. Spectra and other turbulence parameters are found to be in agreement with other boundary layer turbulence measurements over ice, water, and land.

Aerodynamic Design of a Land Speed Record Car

Over-all aerodynamic design considerations of The Blue Flame, a car which holds the world land-speed record, are discussed. Lift, drag, acceleration and deceleration characteristics are presented. Estimated drag coefficients and wind-tunnel results on a J^th scale model are compared with data measured during an actual speed run of The Blue Flame. Actual subsonic drag was found to be slightly lower than predicted.