EXPERIMENTAL AND NUMERICAL-SIMULATION ON OSCILLATING AIRFOIL IN 2D FLOW OF THE HELICOPTER ROTOR BLADE DYNAMIC STALL

This work concerns the experimental and numerical simulation of the ai rfoil dynamic stall in a 2D unsteady flow. The flow unsteadiness is si mulated by means of a combined motion of the airfoil in translation/pi tch, which produces simultaneous variations of velocity V and incidenc e ct around the airfoil. The cycles (V, alpha) are selected to be repr esentative of the actual stall conditions encountered by the rotor bla de sections. From experiments, the overall and local analysis of the O A209 airfoil response to the (V, alpha) cycles of the combined motion, exhibits the influence of the additional velocity variations V = V (o mega t) on the pitching motion alpha = alpha (omega t). The increase i n the oscillating parameters values induces a sharp increase in the am plitude of the lift hysteresis loops, which reflects the fact that the dynamic stall processes generated by the combined motion are differen t from those generated by the incidence variations alone. The data so obtained in pitching and combined motions are then used to improve and Validate two stall calculation models of semi-empirical nature (INDIC E and GBCN). The improvements brought to the optimisation of the set o f constants to be introduced in the GBCN code, have here provided an e xcellent prediction of the hysteresis loops determined by experiments in combined motion.