Theoretical Analysis of Control Mechanisms for Boundary-Layer Separation on Rotorcraft Blades
Final rept. 1 Jun 2003-30 Nov 2006
LEHIGH UNIV BETHLEHEM PA
Pagination or Media Count:
High maneuverability is one of the major goals in rotorcraft design. In practice, this goal is limited by unsteady dynamic stall near blade leading edges. Studies of three-dimensional boundary layer separation on a rotating blade are made. For hovering flight, the blade twist and downwash are included in the effective angle of attack. For forward flight, high angles of attack are used to simulate the most severe situation at the retreating blade. Because of the disparate scales of the leading edge radius and the blade span, separation is found to be quasi two-dimensional, and local singular behaviors at separation are very similar to the two-dimensional cases. Most of the results are obtained using an Eulerian approach, but a Lagrangian formulation is used to study the behavior near the separation singularity. Control mechanisms based on suction and blade oscillations are examined. It is found that oscillations, with a tuned frequency and amplitude, can delay separation. Leading edge suctioninjection is also effective in delaying separation for particular optimized slot locations.