Dynamic Stall Investigation on a Rotating semi-elastic Double-swept Rotor Blade at the Rotor Test Facility Göttingen

Experimental investigations of three-dimensional dynamic stall on a four-bladed Mach-scaled semi-elastic rotor with an innovative double-swept rotor blade planform are presented. The study focuses on the coupling between the aeroelastic behavior of the blade and the underlying aerodynamics. Blade bending moment and flap displacement measurements were conducted using strain gauges and optical tracking of blade tip markers. The aerodynamic behavior was characterized by means of unsteady surface pressure measurements using unsteady pressure-sensitive paint (iPSP) across the outer 65 % of the blade span and fast response pressure transducers at discrete locations. Different cyclicpitch settings were investigated at a rotation frequency of frotor = 23.6 Hz, that corresponds to blade tip Mach and Reynolds numbers of Mtip = 0.282 - 0.285 and Retip = 5.84 - 5.95 x 105. The findings reveal a detailed insight into the non-linear behavior in the flap movement during downstroke. iPSP and pressure transducer data indicates that this non-linear flap behavior is caused by a radially phase-shifted dynamic stall process at the forward and backward swept part of the blade.