LAMINAR FLOW PAST AN OSCILLATING CIRCULAR CYLINDER IN CROSS FLOW

The present study numerically investigates the two-dimensional laminar flow past a circular cylinder forced to oscillate transverse to the free-stream. The numerical simulations are performed at a various range of cylinder oscillation frequency ranged between 0.8 and 1.2 of the natural vortex shedding frequency, and the oscillation amplitude extended up to 50% of the cylinder diameter at one Reynolds number of 185 showing the typical two-dimensional vortex shedding. The immersed boundary method is used to handle the oscillating cylinder in a rectangular grid system using the finite volume method. The primary vortex shedding frequency has the same value with the exciting frequency. When the exciting frequency exceeds the natural vortex shedding frequency, the secondary vortex shedding frequency appeared with the value less than the natural shedding frequency. The time sequence of the wake structures near the cylinder at the extreme upper position reveals that a single vortex or a pair of vortices appears according to the time. A pair of vortices is composed of two saddle points and two centers of vortices, showing the occurrence of vortex switching phenomenon. The quantitative information about the flow variables such as the distribution of wall vorticity on the cylinder surface, drag and lift coefficients is highlighted.