Flow Structure Analysis Around An Oscillating Circular Cylinder At Low KC Number: A Numerical Study

Flow fields around an oscillating circular cylinder are studied by solving the incompressible Navier--Stokes equations in primitive variable formulation. A finite volume method with a pressure predictor--corrector scheme is used and the solution procedure is accelerated by a local time stepping technique. Numerical tests are carried out at the Keulegan--Carpenter number KC ! 20 and Reynolds number Re ! 4000. For the symmetrical flow (at either very low KC or low Re), the vorticity decaying effect is dominant in the flow field. At higher Re, the vorticity convection becomes stronger, eventually leading to the inception of the asymmetrical flow pattern. It was found that within this critical regime the artificial disturbances imposed to the flow field play an important role in determining the flow patterns: if the flow falls into the symmetrical category, it remains symmetrical even with the artificial disturbances; while if the flow falls into the unsymmetrical category, the a..