Experimental investigation of separation control - Part 2: Zero mass-flux oscillatory blowing

The control of a separated flow over a wall-mounted hump, by means of two-dimensional zero mass-flux perturbations, was studied experimentally to generate a, data set for the development and evaluation of computational methods. The companion paper (Part 1) considered details of the baseline (uncontrolled) case and a steady-suction control case. The data set for a specific zero mass-flux control case comprised static surface pressures together with phase-averaged unsteady surface pressures and particle image velocimetry flowfield measurements. Additional surface pressures were acquired for a variety of control frequencies, control amplitudes and Reynolds numbers. Due consideration was given to characterizing the flow in the vicinity of the control slot, with and without external flow, and to perturbation two-dimensionality. Triple-decomposition of the fluctuating velocity and pressure fields was employed for presenting and analyzing the experimental data. This facilitated an assessment of the mechanism of separation control and the quantification of the coherent and turbulent surface pressures, Reynolds stresses, and energy fluxes. Spanwise surface pressures and phase-averaged stereoscopic particle image velocimetry data revealed an effectively two-dimensional flowfield despite highly three-dimensional instantaneous flow structures.