Numerical Investigation of Rotor/Wing Aerodynamic Interactions at High Advance Ratios

Rotor/wing aerodynamic interactions in forward flight up to high advance ratios are investigated through numerical simulations using a rotorcraft computational fluid dynamics solver, rFlow3D, developed at Japan Aerospace Exploration Agency (JAXA). Rotor/wing aerodynamic interaction is one of the key technology issues in developing an efficient compound helicopter design. A validation based on Leishman’s previous experimental study is performed to study the prediction accuracy of the numerical methods of computational fluid dynamics. Then, rotor/wing aerodynamic interaction at high advance ratios is investigated. A simplified computational model with a rotor and a wing is assumed. A rectangular wing model is considered for the UH-60A helicopter with the wing size specified for the original maximum takeoff weight. The UH-60A rotor blade is used, assuming it to be rigid. The isolated rotor and the isolated wing configurations are first simulated, and the results are then compared with the results of the rotor/wing combined configuration so that the effect of interaction can be identified. Two flight conditions, one at cruising speed and the other at maximum speed, are considered. The rotor speed is reduced to 75% RPM at the high-speed flight conditions. The results show that the total effective drag of the combined rotor/wing configuration is approximately 20% higher than the simple summation of the effective drags of the isolated models. The wing lift decreases because of rotor/wing aerodynamic interaction, and the required rotor thrust increases to maintain the same total lift. The sectional normal force on the wing has an asymmetric distribution. The sectional lift significantly reduces, and the sectional drag increases on the wing under the rotor advancing side. On the wing under the rotor retreating side, the rotor has little effect on the sectional lift and drag of the wing. It is observed that the rotor/wing aerodynamic interaction at high advance ratios has a significant influence on the aerodynamic performance of the winged compound helicopter.