Topic
Drag coefficient
About: Drag coefficient is a research topic. Over the lifetime, 14471 publications have been published within this topic receiving 303196 citations. The topic is also known as: drag factor.
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Patent•
31 Oct 1989
TL;DR: In this article, an improvement in the lift and drag characteristics of a lifting surface is achieved by attaching a serrated panel to the trailing edge of the lifting surface, with a 60° included angle between adjacent serrations.
Abstract: An improvement in the lift and drag characteristics of a lifting surface is achieved by attaching a serrated panel to the trailing edge of the lifting surface. The serrations may have a saw-tooth configuration, with a 60° included angle between adjacent serrations. The serrations may vary in shape and size over the span-wise length of the lifting surface, and may be positioned at fixed or adjustable deflections relative to the chord of the lifting surface.
174 citations
TL;DR: In this paper, the aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment, and the results indicated that the effects of both wind direction and the non-uniformity of the heights of buildings on urban aerodynamic parameters vary greatly with the roughness packing density.
Abstract: The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic parameters characterising arrays—the drag coefficient (C
d
), roughness length (z
o) and displacement height (d)—are used for analysis. C
d
is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63 arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated C
d
and z
o of the staggered arrays peak against the plan area index (λ
p
) and frontal area index (λ
f
), in contrast with values for the square arrays, which are less sensitive to λ
p
and λ
f
. In addition, the square arrays with a wind direction of 45° have a considerably larger C
d
, and the wind direction increases z
o/H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z
o is more remarkable when λ
f
exceeds 20%, and the discrepancy in z
o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C
d
is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity of the heights of buildings on urban aerodynamic parameters vary greatly with λ
p
and λ
f
; hence, these effects should be taken into account by considering the roughness packing density.
174 citations
TL;DR: In this paper, a finite difference approximation to the vorticity transport equation on an expanding spherical polar grid system is obtained by constructing a finite-difference approximation of the transport equation with second order accuracy both in time and space.
Abstract: Numerical solutions of the transient uniform flow around a sphere are obtained. The transition takes place between an initial potential flow and a fully developed viscous field. The fluid is incompressible, homogeneous, and its flow is governed by the complete Navier‐Stokes equations. The range of Reynolds number studied is Re = 1–1000 where a recirculatory wake appears and the nonlinear terms are essential, that is, they cannot be neglected or approximated. The flow is assumed to be axisymmetric throughout this range. A time‐dependent stream function‐vorticity formulation is adopted. The solution is obtained by constructing a finite difference approximation to the vorticity transport equation on an expanding spherical polar grid system. Central differencing of second‐order accuracy both in time (Dufort‐Frankel) and space is utilized. Experiments with numerical stability show an appreciable deviation from linearized stability analysis due to the large gradients of vorticity in the field. Quantitative physical results are obtained. The geometrical parameters characterizing the recirculatory wake compare favorably with those recorded in physical experiments. The detailed distribution of the vorticity on the sphere agrees with results obtained via the steady‐state approach at Re = 10, 40, and 100. The computed drag coefficient CD agrees well with the standard drag curve over the range of Reynolds numbers investigated.
174 citations
TL;DR: Using video microscopy coupled with particle tracking routines, the Brownian fluctuations of micrometer-sized particles were analyzed to yield a quantitative measurement of the diffusion coefficients parallel and perpendicular to the nematic director.
Abstract: The Stokes-Einstein relation relates the diffusion coefficient of a spherical Brownian particle in a viscous fluid to its friction coefficient. For a particle suspended in anisotropic liquid, theory predicts that the drag coefficient should also be anisotropic. Using video microscopy coupled with particle tracking routines, the Brownian fluctuations of micrometer-sized particles were analyzed to yield a quantitative measurement of the diffusion coefficients parallel and perpendicular to the nematic director. The experimental values agree quite well with recent numerical calculations that take into account the distortions of the director field in the vicinity of the particles.
173 citations