SINUSOIDAL FORCING OF A TURBULENT SEPARATION BUBBLE

A turbulent separation bubble is forced by single- and double-frequenc y sinusoidal disturbances, with the emphasis placed on the reattachmen t length as a function of the forcing amplitude and frequency. The sep aration bubble is that formed along the side of a blunt circular cylin der with a square leading edge. In single-frequency forcing, the reatt achment length attains a minimum at a particular forcing frequency, F, which scales with the frequency of shedding of vortices from the reat tachment region of the separated shear layer. A flow model is presente d to interpret the frequency F. Forcing of sufficiently high amplitude eliminates the recirculating region in a range of the forcing frequen cy. Flow visualization and a survey of the mean flow and turbulence pr operties demonstrate how the flow in the separated shear layer is modi fied by the forcing. In double-frequency forcing, the superposition of the F-component on its higher or subharmonic components is considered . A non-resonant combination of the two frequencies is also considered .