Effect of spanwise-varying local forcing on turbulent separated flow over a backward-facing step

Abstract

An experimental study was made of turbulent separated flows over a backward-facing step. A local forcing was given to the separated flow by means of a sinusoidally oscillating jet issuing from a thin slit near the separation line. To produce a spanwise-varying local forcing at the separation edge, a banded thin tape covered the slit. Effects of the spanwise-varying local forcings on the separated flow were scrutinized by altering the spatially banded blocking width (w) and the open slit distance (g). An optimal value of wig was sought, which led to the minimum reattachment length (x(R)). The effect of spanwise-varying local forcing on x(R) was found to be slight compared to the case of two-dimensional forcing (w = 0). The experiment was made at Re-H = 33000 and A(0) = 0.018 by changing the forcing frequency (0 less than or equal to St(H) less than or equal to 1.0).