Control of a Karman vortex flow by rotational oscillations of a cylinder.

摘要

An effect of the rotation of a circular cylinder on its drag is investigated by numerical simulation. The cylinder axis is perpendicular to the direction of the flow which moves with a Reynolds number of 190, causing a Karman vortex street. The applied rotation of the cylinder is oscillatory, and can be described by rotation velocity as a function of time. The function {dollar}v(t)=a sgn(sinomega t) vertsinomega tvertsp{lcub}2sp{lcub}n{rcub}{rcub}{dollar} was chosen and its three-dimensional parameter space was searched for the set of parameters which cause the smallest drag. The search was performed with the help of a new optimization algorithm that is based on the Voronoi grid generation algorithm. Flow past the cylinder was calculated using an implicit, incompressible, two-dimensional finite element Navier-Stokes solver on unstructured triangular mesh. The flow solver was modified in order to implement cylinder rotations.; The search concentrated mostly on oscillations with frequencies similar to the natural shedding frequency. For flows in this parameter range, several relations and dependencies were found. In addition, flows past cylinders with constant rotational velocity and flows past cylinders oscillating with much higher and lower frequencies were investigated.