Performance Validation of CFD/CSD for Active and Passive Rotor Systems

With the recent dramatic increase of computing power, first principal based CFD/CSD tools are becoming more routinely used in the rotorcraft industry. This study performed validation of current CFD/CSD tools in terms of rotor performance to assess its prediction capability for various rotor concepts using a consistent simulation approach. Correlated experimental data include UH-60A NFAC test, UH-60A slowed rotor, UH-60A individual blade control, S-434 with active trailing-edge flap, and flight test data of UH-60M with advanced blade tip design. The root shank impact was added as the post-processing step using a relevant drag coefficient. It was found that the current tools could predict performance within 10% in most cases. The peak L/De and stall boundary of UH-60A rotor were well predicted. The performance benefits from active control rotors using individual blade control and active flap were captured very well with good agreement in active control phase and magnitude. The high advance ratio flight condition was also well predicted even though highly unsteady flow features are present. Error increased at the high-thrust high-speed condition, but the absolute error was still within a reasonable range considering uncertainty in measurements and the root-shank effect. Good correlation was obtained for the UH-60M at low and moderate speeds. However, predictions showed earlier gradual stall at high-thrust and high-speed conditions. The impact of different flight conditions and grid resolution was studied, but only limited improvement was obtained. Further investigation is suggested to address the discrepancy.