Measurement of instantaneous velocities in separated flow around a bluff body using laser Doppler anemometry.

At high Reynolds numbers the flow around a square edged plate separates from the leading edge corner, reattaches downstream and gives rise to regions of concentrated vorticity embedded in irrotational fluid. Work at C.S.I.R.O. has shown that the large scale structures shed from the separation bubble have a strong tendency to combine and further that the rate of shedding and the tendency to combine into paired structures can be regulated by the introduction of sound induced velocity perturbations was used. The paper describes the use of a single component. Laser Doppler anemometer, in conjunction with sound induced velocity perturbations, to measure two dimensional velocity vectors in the region of the separation bubble by conditionally sampling with respect to the acoustic frequency.