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.

Motion of Waves in Shallow Water. Interaction between Waves and Sand Bottoms

Abstract: The loss of energy of a travelling water wave, due to the mechanism of the formation of sand ripples and water vortices on a sandy bed, becomes of practical importance when models are used to predict full-scale foreshore movements. On the assumption that the bottom-water oscillation is nearly simply harmonic, the mechanism was studied by oscillating a section of bed through still water. The pitch, p, of the sand ripple formed was found to vary as the square root of the grain diameter, independently of the speed and of the grain density, for amplitudes, R, of water motion exceeding this pitch. But for smaller amplitudes the pitch shortens with decreasing amplitude of movement. The mean drag coefficient, k, in the case of artificial rigid ripples, was measured directly. For R/p less than unity, k remains constant. For R/p greater than unity, k was found to vary as (R/p)-0$^{\cdot}$75. These results are compared with the case of steady flow. The critical water speeds and amplitudes for first disturbance of grains on a smoothed surface was also measured, over a wide range of grain diameters and densities. The results conform closely to a simple empirical expression.

The velocity of rise of distorted gas bubbles in a liquid of small viscosity

Abstract: The terminal velocity of rise of small, distorted gas bubbles in a liquid of small viscosity is calculated. Small viscosity means that the dimensionless group gμ4/ρT3 where g is the acceleration of gravity, μ the viscosity, ρ the density and T the surface tension, is less than 10−8. It is assumed—and the numerical accuracy of the assumption is discussed—that the distorted bubbles are oblate ellipsoids of revolution. The drag coefficient is found by extending the theory given recently (Moore 1963) for the boundary layer on a spherical gas bubble. The results are in reasonable quantitative agreement with the experimental data.

Sphere Drag and Settling Velocity Revisited

Abstract: Sphere drag data from throughout the twentieth century are available in tabular form. However, much of the data arose from experiments in small diameter cylindrical vessels, where the results might have been influenced by the wall effect. Wall effect corrections developed by others were applied to 178 of the 480 data points collected. This corrected data set is believed to be free of the influence of wall effects. Existing drag and settling velocity correlations were compared to this data set. In addition, new correlations of the same forms were developed using the corrected data. Two new correlations of sphere terminal velocity are proposed, one applicable for all Reynolds numbers less than 2310 5 , and the other designed to predict settling velocities with exceptional accuracy for terminal Reynolds numbers less than 4,000, a region that contains almost all applications of interest in environmental engineering. The trial and error solution for settling velocity using the Fair and Geyer equation for drag should be retired in favor of the direct calculation available from these new correlations.

Influence of surface roughness on the cross-flow around a circular cylinder

Abstract: The influence of surface roughness on the cross-flow around a circular cylinder is the subject of the present experimental work. The investigations were carried out in a high-pressure wind tunnel, thus high Reynolds numbers up to Re = 3 × 106 could be obtained. Local pressure and skin friction distributions were measured. These quantities were evaluated to determine the total drag coefficient and the percentage of friction as functions of Reynolds number and roughness parameter. In addition the local skin friction distribution yields the angular position of boundary-layer transition from laminar to turbulent flow and the location of boundary-layer separation.