Unsteady Flow Near a Circular Cylinder Oscillating Sinusoidally in a Uniform Flow : The Structure of the Boundary Layer and Flows Near the Separation Points

Abstract

The flow past a circular cylinder oscillating transversely in a uniform flow was investigated by flow visualization techniques. The frequency of the oscillating cylinder was set in the synchronized range in which the vortex sheds periodically with the same frequency as the oscillating cylinder. The experimental conditions were Re=1100, and A/D=0.2, where Re is the Reynolds number based on the diameter D, and A is the amplitude of the oscillation of the cylinder. The characteristic values (the displacement thickness, the shape factor, and the velocity at the outer edge of the boundary layer) were measured using the hydrogen bubble techniques. From the values, the local skin friction on the cylinder was estimated with the oscillating phase angle during a cycle. The characteristics of the unsteady boundary layer near the separation points, where the dye filaments separate from the cylinder, are discussed in comparison with those of a steady one.