Time-Dependent Flow Around a Circular Cylinder Accelerated Uniformly From One Steady Speed to Another

Unsteady flow around a circular cylinder accelerated from one steady speed to another was investigated experimentally using flow visualization techniques.The experiment was carried out in a water tank.The initially prescribed Reynolds number was varied between 19 and 89, and the dimensionless acceleration between 1.0X10 2 and 3.0X10 4 The following facts were found.Immediately after the cylinder is given an acceleration, an inviscid flow pattern appears near the cylinder and the initial vortices are left downstream.Then the new twin vortex formation begins immediately behind the cylinder, and the secondly formed vortices develop downstream in a manner similar to the case of start from rest.The change of the flow pattern is characterized by the initially prescribed Reynolds number and the applied acceleration.