In-line and transverse forces on smooth and sand-roughened cylinders in oscillatory flow at high Reynolds numbers

Abstract

This report presents the results of an extensive experimental investigation of the in-line and transverse forces acting on smooth and sand- roughened circular cylinders placed in oscillatory flow at Reynolds numbers up to 1,500,000, Keulegan-Carpenter numbers up to 100, and relative sand- roughnesses form 1/800 to 1/50. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least-squares method. The transverse force (lift) has been analysed in terms of its maximum, semi peak-to-peak, and root-mean-square values. In addition, the frequency of vortex shedding and the Strouhal number have been determined. The results have shown that (a) for smooth cylinders, all of the coefficients cited above are functions of the Reynolds and Keulegan-Carpenter numbers, particularly for Reynolds numbers larger than about 20,000; (b) for rough cylinders, the force coefficients also depend on the relative roughness k/D and differ significantly from those corresponding to the smooth cylinder; and that (c) the use of the 'frequency parameter' D sq/nu T and the roughness Reynolds number U sub m k/nu allow a new interpretation of the present as well as the previously obtained data.