Actuator Surface Model with Computational-Fluid-Dynamics-Convected Wake Model for Rotorcraft Applications

Abstract

An actuator surface model has been developed that couples an aerodynamics model to a computational fluid dynamics solver. The model is designed for simulation of rotors in complex operating environments, and it advances a recently developed actuator surface model through the addition of two new elements: a computational fluid dynamics (CFD)-convected wake model, and an improved coupling algorithm. The wake model uses Lagrangian particle tracking to determine the geometry of the rotor wake from the CFD solution. Prior study of the influence of the maximum wake age in the model led to the conclusion that only 45 deg of wake is required for accurate resolution of air loads. The S-76 rotor in hover and the UH-60A rotor in forward flight are used for validation. Thrust coefficients, torque coefficients, and figures of merit over a range of collective settings agree well with experimental data for the S-76 rotor. Sectional normal force coefficients in forward flight are compared with experimental data, results from resolved-blade simulations, and other rotor models: again showing good agreement. These results suggest the new actuator surface model can predict time-accurate rotor loads where accurate resolution of the near-blade flowfield and high-frequency loads, such as blade–vortex interactions, are not critical.