The Effect of Pitch Location on Dynamic Stall

Abstract

This paper reports the results of theoretical and wind-tunnel studies of the effect of pitch location on dynamic stall for an airfoil pitching at constant rate. A modified momentum-integral method was used to predict the effect of pitch location and rate on the delay in quarter-chord separation. The wind-tunnel study involved the collection of time-varying pressure readings from 16 locations on an NACA 0015 airfoil that were subsequently used to determine lift, pressure-drag, and moment coefficients as functions of angle of attack for 140 test cases, covering 28 dynamic airspeed/pitch-rate/pitch-location combinations. Dynamic-stall effects of change (from steady flow) in the angle of attack at which separation occurs at the quarter chord (for comparison with the momentum-integral results), and change in the angle of attack at which stall occurs were extracted from these data and found to collapse best onto a non-dimensional pitch rate given by the chord times the pitch rate divided by two times the free-stream velocity. An adjusted non-dimensional rate formed by replacing one half the chord with the fraction of the chord corresponding to the pitch location was also examined and found not to be the proper non-dimensional variable for collapsing the data. The quarter-chord separation data compared favorably with the theoretical predictions.