Pressure and Force Fluctuations on Isolated Roughened Circular Cylinders of Finite Height in Boundary Layer Flows

This paper presents spatio-temporal measurements of a #uctuating pressure "eld acting on isolated roughened cylinders of "nite height in simulated turbulent boundary layer #ows at subcritical Reynolds numbers. The cylinder surface is roughened by placing discrete roughness elements along the height at four circumferential locations. The resulting surface roughness con"guration helps to modify the #ow over the cylinder, which leads to the pressure "eld that exhibits characteristics similar to the transcritical Reynolds numbers. The space-time measurements of the random pressure "eld allowed computations of the mean and r.m.s. pressure coe$cients, power spectral density, spanwise and circumferential correlations, and their eigenfunction expansions. A manifold-pneumatic averaging technique was utilized to evaluate time varying area-averaged loads at various levels along the model height. The spatially averaged measurements of the pressure "eld over the roughened cylinder facilitated the estimation of local and mode-generalized alongwind and acrosswind aerodynamic force coe$cients, their spectral descriptions and multi-level force correlations. An increase in the turbulence level in#uences the #uctuating pressure "eld through modi"cations which take place in the structure of the boundary layer over the cylinder and the structure of the separated shear layers. ( 1999 Academic Press