Low Reynolds Number Flows around an Impulsively Started Two-Dimensional Circular Cylinder with Rotation by a Vortex Method.

Abstract

There are two typical cases in the problem of the two-dimensional unsteady flow past a rotating circular cylinder which is impulsively started. (1) The circular cylinder is impulsively started with rotation from rest and (2) the rotating cylinder is impulsively started. The difference between these two cases is given by the far-field condition. A vortex method is powerful for these problems because the far-field condition is naturally imposed, so the hybrid vortex method combined with a panel method, whose numerical accuracy was tested on low Reynolds number flow around an impulsively started cylinder without rotation in the previous work, is used in the present paper. The detailed results of the flow around the rotating cylinder with a constant anticlockwise angular velocity are shown and we see that there is difference of flow between these initial conditions and its difference does not become clearly small with development of time in the case of high angular velocity, in particular, the difference in drag force does not become clearly small with time although it in lift force becomes small with time.