Parametric Actuator-Based Numerical Investigation of Rotor-Ground Interaction

This study models the interaction of a two-bladed 14" propeller with the ground under different configurations using actuator disk method (ADM) where the rotor is modeled using unsteady momentum sources distributed over the entire disk. While ADM has been extensively used for standard rotorcraft analysis, it's performance in unconventional operating conditions remains an open question. Exhaustive experiments conducted at DEVCOM Army Research Laboratory are compared with ADM to evaluate the inexpensive method's ability to predict rotor loads for parametric variations in rotor-ground interaction scenarios. Partial ground effect (part of the rotor operating IGE), side-by-side rotors in ground effect and variation in IGE pitch attitude are specifically considered in this study. ADM generally predicts the thrust increase in partial ground effect (PGE) as the rotor goes from OGE to IGE although the increase is somewhat earlier and milder than measured in experiments. Side-by-side rotors in ground effect are predicted remarkably well by ADM which captures the fountaining flow between the rotor wakes as well as reduction in thrust seen compared to IGE in experiments. Finally, pitch attitude variation cases showed reasonably good agreement in trend at lower angles although ADM shows a more gradual drop in thrust at higher angles (beyond 15◦) compared to the sharper drop seen in experiments.