Pressure Field Evolution on Rotor Blades at High Advance Ratio 2016-01-2010

The design of advanced rotorcraft requires knowledge of the flowfield and loads on the rotor blade at extreme advance ratios (ratios of the forward flight speed to rotor tip speed). In this domain, strong vortices form below the rotor, and their evolution has a sharp influence on the aero-dynamics loads experienced by the rotor, particularly the loads experienced at pitch links. To understand the load distribution, the surface pressure distribution must be captured. This has posed a severe problem in wind tunnel experiments. In our experiments, a 2-bladed teetering rotor with collective and cyclic pitch controls is used in a low speed subsonic wind tunnel in reverse flow. Stereoscopic particle image velocimetry is used to measure the three component spatial velocity field. Measurement accuracy is now adequate for velocity data, and can be converted to pressure both at and away from the blade surface. In this paper, the pressure field under the blade in reverse flow is derived from velocity data after interpolation to satisfy conservation of mass, using a Navier-Stokes solver. The validity of the pressure calculation is being established using a progression of experiments from attached and separated flow near a cylinder, as a simplification to the complex flow field observed in rotor cases. The paper shows state of the art technique for extracting the pressure in vortex dominated flow field while emphasizing the credibility of the results using cylinder results.