TEST RESEARCH FOR ACTIVE CONTROL OF AIRFOIL REVERSE FLOW DYNAMIC STALL BASED ON TRAILING EDGE FLAP

In order to solve the issues such as unsteady load, increased drag and negative lift caused by reverse flow dynamic stall in reverse flow regime of helicopters, a test research which focused on the control of airfoil reverse flow dynamic stall was carried out using an airfoil test model with trailing edge flap. Dynamic pressure measurement was combined with integral of airfoil surface pressure to analyze the influence of different oscillating phase offset, amplitude and reduced frequency of trailing edge flap on reverse flow dynamic stall control, and the difference between dynamic pitching and fixed deflection of the trailing edge flap was compared. The test Reynolds number was Re = 3.5 × 10⁵. The results show that the flow separation at the blunt geometric leading edge during reverse flow dynamic stall can be improved when dynamic pitching trailing edge flap oscillating in the same frequency with airfoil model and the phase offset between dynamic pitching trailing edge flap and airfoil model is set to 0°, negative lift coefficient can be reduced by 21.2%, drag coefficient can be reduced by 37.5%, hysteresis area of pitching moment coefficient can be reduced by 44.6% under typical test condition. The control effect of dynamic pitching trailing edge flap on reverse flow dynamic stall raises with the increase of oscillation amplitude, but further increasing the oscillation amplitude has limited impact on the improvement of control effectiveness. When reduced frequency was increased, the control effect of dynamic pitching trailing edge flap on the drag in the reverse flow regime will be more obvious. Both dynamic pitching and fixed deflection of trailing edge flap can improve the unsteady aerodynamic performance in reverse flow, but dynamic pitching trailing edge flap has better adaptability than fixed deflection trailing edge flap during different angle of attack. Better unsteady load control and better drag and negative lift improvement was also observed when trailing edge flap was dynamic pitching.