Structural Blade Loads of a Mach-Scaled Rotor During Dynamic Stall in Hover

This paper focuses on an experimental investigation of rotor loads during dynamic stall on a rotating pitching blade. In particular, the effect of rotor control parameters - rotor speed, collective pitch, and cyclic pitch - on the structural load dynamics of a rotor blade are analyzed in hover. The rotor platform used is the Mach-scaled, two-bladed Munich Experimental Rotor Investigation Testbed (MERIT) rotor at the Technical University of Munich (TUM). The dynamic stall cases selected vary in collective and cyclic pitch angles: 14^◦±6^◦, 14^◦±10^◦, and 20^◦±6^◦. Static and dynamic stall data are measured at three different rotor speeds: 900, 1200, and 1500 RPM with the highest corresponding tip Mach and Reynolds numbers of Ma_tip = 0.41 and Re_tip = 1.2·10⁶. Increasing pitch and rotor speed shows a considerable positive trend in the load overshoot, and hysteresis of the blade root moments of most cases. Cycle-to-cycle variations with bifurcation occur in some load graphs of light dynamic stall cases and are not restricted to reattachment regions.