Diagnostics of 3D Dynamic Stall on Rotor Blades
Technical rept. 1 Jun 2004-31 Mar 2008
GEORGIA INST OF TECH ATLANTA GA OFFICE OF CONTRACT ADMINISTRATION
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This project investigated the nature of the velocity field behind the separation line in dynamic stall on rotor blades, particularly the centrifugal effects and radial velocity field. Initial experiments were performed using a single-bladed rotor in hover with transient stall induced by an inflow obstructor. A 2-bladed teetering rotor setup was then constructed in the Georgia Tech 7 x 9 tunnel. PIV measurements confirmed the finding of discrete quasi-periodic streamwise vortical structures in the radial flow behind the separation line in both experiments. Co-rotating structures suggest that the free shear layer formed at stall rolls up into discrete cells. The spanwise spacing of structures is approximately the height of the separated flow region. The presence of these structures helps explain the nature of the radial flow variation from root to tip in the separated flow region. Measurements of the variance in the radial velocity profile suggest that the breakup into discrete structures originates in the region of radial acceleration rather than at the outer edge of the separated flow.