DYNAMIC SURFACE MEASUREMENTS ON A MODEL HELICOPTER ROTOR DURING BLADE SLAP AT HIGH ANGLES OF ATTACK

An investigation of dynamic rotor blade surface phenomena and the resulting far field impulsive noise from a model helicopter rotor at high angles of attack and low tip speeds has been conducted. The study was performed at the M.I.T. 5 by 7 1/2 foot anechoic wind tunnel. The blade surface data was acquired using flush, surface mounted, miniature hot-films and fast response pressure transducers. Blade vortex interactions (BVI) on both the advancing and retreating side of the rotor azimuth were observed and correlated with the far field impulsive noise. The resultant blade loading was observed to be highly localized. The model rotor BVI which occurred caused boundary layer separation and reattachment and/or a shift in the laminar/turbulent transition point, over a very small blade azimuth, on the order of 5°. This BVI resulted in blade slap. A significant increase in broadband noise was generated and modulated at the blade passage frequency. A simple, inexpensive and reliable method has been developed to permit transfer of pressure and hot-film data from a rotating frame to a stationary frame. The method requires no Instrumentation in the rotating frame other than the transducers themselves.