Spanwise Differences in Static and Dynamic Stall on a Pitching Rotor Blade Tip Model

An experimental investigation of static and dynamic stall on a rotor blade tip model with an aspect ratio of 6.2 at a chord Reynolds number of 900,000 and a Mach number of 0.16 is presented. The spatiotemporal behavior of the flow separation was analyzed using unsteady surface pressure measurements and high-speed particle image velocimetry. The maximum effective angle of attack prior to stall is shifted to approximately two-thirds of the span outboard because of an increasing geometric angle of attack of the model toward the tip. Different stages of flow separation for static angles of attack were identified, including the occurrence of two stall cells. During dynamic stall, the leading edge vortex formation starts near the spanwise position of the static stall onset. The subsequent spanwise evolution of the vortex formation results in two Ω vortices for deep stall conditions, covering the same spanwise areas as the two static stall cells.