PRESSURE AND FORCE FLUCTUATIONS ON ISOLATED ROUGHENED CIRCULAR CYLINDERS OF FINITE HEIGHT IN BOUNDARY LAYER FLOWS

Abstract

This paper presents spatio-temporal measurements of a fluctuating pressure field acting on isolated roughened cylinders of finite height in simulated turbulent boundary layer flows 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 configuration helps to modify the flow over the cylinder, which leads to the pressure field that exhibits characteristics similar to the transcritical Reynolds numbers. The space-time measurements of the random pressure field allowed computations of the mean and r.m.s. pressure coefficients, 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 field over the roughened cylinder facilitated the estimation of local and mode-generalized alongwind and acrosswind aerodynamic force coefficients, their spectral descriptions and multi-level force correlations. An increase in the turbulence level influences the fluctuating pressure field through modifications which take place in the structure of the boundary layer over the cylinder and the structure of the separated shear layers.