Internal and Blade Surface Pressure Measurements of Centrifugal Flow Control on a Large Scale Rotor

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A large scale rotor test has been performed to evaluate concepts for improving the high thrust and high speed capabilities of an edgewise single rotor helicopter. The primary approach was to alleviate dynamic stall using centrifugally pumped steady blowing, referred to as Retreating Side Blowing (RSB). This concept was studied earlier for an airfoil with a flow control slot able to generate momentum coefficients of 0.03 to 0.05 using computational simulation and experiment. The current experiment uses a 28 ft diameter rotor having an inlet at the blade root, a hollow spar, and a series of flow control slots from 65% to 95% of the radius. It was tested at the Sikorsky Main Rotor Whirl Stand and at the National Full Scale Aerodynamic Complex. Rotor performance and structural load data were acquired for multiple configurations at advance ratios of 0.24 to 0.61. This paper focuses on the internal pressure measurements used to determine the performance of the centrifugal pumping system in hover and in forward flight, and on the external pressure measurements used to define the effect of the slot blowing on the dynamic stall characteristics. While the centrifugal flow control system generated the expected mass flow, the impact on blade dynamic stall characteristics and rotor performance was less than desired. The rotor results are compared to those from the airfoil test and to prior flow control rotor tests.