IN-LINE AND TRANSVERSE FORCES ON SMOOTH AND SAND-ROUGHENED CYLINDERS IN OSCILLATORY FLOW

This report presents the results of an extensive experimental investi-gation of tl-e 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 from 1/800 1c 1/50. The drag and inertia coefficients have been determined through-he 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 t % the smooth cylinder; and that (c) the use of the 'frequency parameter' DbvT and the roughness Reynolds number Umk/v allow a new interpretation of the present as well as the previously obtained data. The work reported herein has been supported in part by The Nationa