Retreating blade stall control on a NACA 0015 aerofoil by means of a trailing edge flap
Trailing edge flaps may provide a mechanism for alleviating retreating blade stall. In the present investigation numerical simulations were conducted involving a NACA 0015 aerofoil section fitted with a plain trailing edge (TE) flap. All simulations were conducted using DIVEX, a tool being developed at the University of Glasgow, Department of Aerospace Engineering. In summary, the code uses a surface shedding discrete vortex method (DVM) for the simulation of 2-D incompressible flows around pitching aerofoils. The aero-foil is oscillating in pitch about its quarter chord axis and the clap undergoes negative pitch inputs, i.e. upward. An interesting feature appears to be that the cause of the severe nose down pitching movement introduced during dynamic stall is due to the cortical pair of the DSV and TEV where it is shown that the former feeds the latte in the case of the clean aerofoil for the range of reduced frequencies varying between k = 0.128 and k = 0.180. This fact suggests that manipulation of the vorticity in the vicinity of the trailing edge may be a mechanism for modification of the dynamic stall vortex (DSV) trajectory. This was found to relieve the aerofoil from severe pitching moment undershoot occurring during dynamic stall under appropriately phased flap actuations. Results obtained so far encourage the employment of a flap with fairly small size, 15% of the aerofoil chord. A parametric study is described which identifies the proper aerodynamic and actuation parameters for the current problem. In addition a simple open loop control scheme is developed based purely on rotor and flap related quantities.