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 #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.

Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods

“…Naumann and Quadflieg (1972) and Kareem and Cheng (1999) examined flow patterns and spatio-temporal pressure fluctuations on a cylinder when an additional pair of rods was used on the rear surface where the final separation of the shear layer occurs.…”

Effects of free-end corner shape on flow structure around a finite cylinder

“…Okamoto and Sunabashiri (1992) found that the wake behind FCs of small aspect ratio (L=D ¼ 122) is symmetric, but that the wake pattern becomes three dimensional when the aspect ratio exceeds L=D ¼ 4: Farivar (1981) investigated the effect of FC free end on the mean pressure, pressure fluctuations and drag force acting on FC of various aspect ratios exposed to a uniform flow. Regular vortex shedding disappeared for aspect ratios smaller than L=D ¼ 7:5: Kareem and Cheng (1999) investigated the pressure and drag fluctuations for FCs located in a simulated boundary layer. The lateral velocity fluctuations due to strong turbulence intensity of approaching shear flow made a large contribution to the pressure fluctuations, however, the contribution of vortex shedding from the FC was weak.…”

Identification of meaningful coherent structures in the wind-induced pressure on a prismatic body

“…Tamura et al, 1997;Holmes, 1990;Kareem and Cheng, 1999). Sometimes the results of the analyses appeared encouraging, but there is a general opinion that PCA modes is unable to identify physicallymeaningful CSs (e.g.…”