Effects of sweep on the dynamics of active separation control

Abstract

AbstractA series of active flow control experiments were recently conducted at high Reynolds numbers on a wall mounted ‘Hump’. The model simulates the upper surface of a 20% thick Glauert-Goldschmied type airfoil at zero incidence. The flow over the model is turbulent since the tunnel sidewall boundary-layer flows over it, eliminating laminar-turbulent transition from the problem. The main motivation for the experiments was to generate a comprehensive data base for validation of unsteady numerical simulation as a first step in the development of a design tool, without which it would not be possible to effectively utilise the great potential of unsteady flow control. This paper focuses on the dynamics of several key features of the baseline as well as the controlled two- and three-dimensional flows.It was found that the two-dimensional separated flow contains unsteady waves centered on a reduced frequency (Strouhal number based on the length of the separated region and free-stream velocity) of 0·8, while in the three-dimensional separated flow, reduced frequencies of 0·3 and 1·0 are active. Several scenarios of resonant wave interaction take place over the separated shear-layer and in the pressure recovery regions. The unstable reduced frequency bands for periodic excitation are centered on 1·5 and 5, but these reduced frequencies are based on the length of the baseline bubble that shortens due to the excitation. The conventional swept wing-scaling works well for the coherent wave features. Reproduction of these dynamic effects by a numerical simulation would provide benchmark validation.