Three-Dimensional Numerical Study on Flow around a Circular Cylinder in Oscillatory Flow. 2nd Report. The Characteristics of Fluid-Dynamic Force.

Abstract

Flow around a circular cylinder in oscillatory flow was studied by a numerical simulation using a finite-volume method. The computations were carried out by assuming 3-dimensional (3-d), unsteady, incompressible and viscous flow through Keulegan-Carpenter number (KC) in the range of 3≤KC≤25 at Stokes number (β)=95. The distribution of transverse force coefficient CL corresponds well to the shape of spanwise cell structure formed on a cylinder surface at KC=3, 4. At KC=20, there appear many peaks of dominant frequencies in the power spectrum of in-line force coeffient CF and there also appears the decrease of spanwise correlation coefficient of CL, which cause to decrease the rms values of in-line and transverse force coefficients CFrms and CLrms. The drag and inertia coefficients of Morison equation CD and CM and CLrms are compared with the measured ones and their results are in good agreement. It was found that CD is the maximum value and CM the minimum when twin-vortices are formed.