Control of a leading-edge separation bubble by bimodal disturbances

The leading-edge separation bubble of a blunt circular cylinder aligned with the main flow was forced by bimodal disturbances at Reynolds numbers of 0.69×105 and 1.38×105. The bimodal disturbances consisted of two sinusoidal components with different frequencies: one has the frequency F at which the minimal reattachment length was achieved by the single-frequency forcing, and the other has subharmonics or higher harmonics of this frequency. The reattachment length was found to most significantly depend on the phase difference between the two sinusoidal components for a particular combination of the frequencies F and 2F.