CFD Pressure/Airload Correlation with Experimental Data on a Slowed Mach-Scaled Rotor at High Advance Ratios

Slowing down the rotor RPM is a viable method to alleviate the compressibility effect at the advancing side of a rotor in forward flight, which is proved effective in raising the cruise speed limitation of a compound helicopter. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel, and some basic understandings were gained on the high advance ratio aerodynamic phenomena, such as thrust reversal and dynamic stall in reverse flow region. In one of the wind tunnel tests, the rotor blades were instrumented with pressure sensors and strain gauges at 30% radius, and enough pressure data was acquired to calculate the integrated sectional airloads. Further, the experimental results of rotor performance, control angles, blade airloads and structural loads were correlated with the predictions of comprehensive analysis as well as CFD/CSD coupled analysis. Furthermore, the paper focuses on the comparison between experimental surface pressure and airload data and the CFD/CSD results for cases with various collective and shaft tilt settings. Overall, the data correlation was found satisfactory for these cases, and this study provided some insights into the aerodynamic mechanisms that affect the rotor airload and performance.