Active flow control of a delta wing at high incidence using segmented piezoelectric actuators

The separated flow around a 60° degrees sweep, semi-span delta wing at high angle-of-attack was controlled using zero-mass-flux periodic excitation, generated by cavity-installed Piezo-electric actuators. The excitation emanated from a segmented slot at the sharp leading edge. Normal and tangential forces, together with pitching and rolling moments, were measured by means of a four-component balance. The boundary layer on the wind tunnel wall, upstream of the delta wing, was removed using suction, with little effect on the forces and moments measured on the semi span model. Amplitude modulation (AM) and burst mode (BM) signals were used to generate reduced frequencies (scaled with the free stream velocity and the root chord) in the range O(1) to O(10) relative to the high resonance frequency of the actuators that is of O(100) based on the same scaling. A parametric investigation, studying the effects of AM frequency, BM duty cycle and frequency, excitation momentum, its location along the leading edge and the optimal phase between the actuators as well as the Reynolds number, is reported and discussed. Upper surface pressures and PIV data supplements the force and moment data. The comprehensive data-set indicates that frequencies of O(1) are most effective for increasing the normal force generated by the delta wing. Burst mode with a duty cycle as low as 5% was more effective than amplitude modulated signal with the same peak velocity but an order of magnitude larger momentum input. Based on the current findings it is not shown that the enhanced performance is related either to delay of vortex breakdown or to vortex enhancement prior to breakdown, but perhaps to a quasi-2D mechanism, enhancing the momentum transfer across the shear layer and generating a streamwise vortex of size commensurable to the local wing span.