The drag and lift characteristics of a cylinder placed near a plane surface

Abstract

Surface pressure, drag and lift coefficients have been experimentally determined for a right circular cylinder located near a plane surface and placed in a cross flow of air. Parametric studies were carried out for Reynolds numbers varying from 90,000 to 250,000, three plate lengths and a variety of cylinder to plate spacings. The variation of the drag coefficient as a function of gap size was found to exhibit an interesting and unexpected trend. The drag was a minimum when the cylinder was resting on the plate and was a maximum at a gap size of approximately one cylinder radius. Flow visualization studies together with detailed measurements of the vortex shedding frequency in the cylinder wake indicate that the plate interferes with the formation of the vortex street in the cylinder wake when it is located within a cylinder radius of the cylinder. This interference disturbs the cylinder base pressure which in turn influences the magnitude of the drag coefficient.