Understanding ducted-rotor antitorque and directional control characteristics part II: Unsteady simulations

Understanding the dynamic relationship between the antitorque thrust moment and the applied collective pitch angle is crucial, especially for directional control sensitivity analyses. Although there are many studies in the literature on the steady-state behavior of the FANTAIL™, little is known about the transient response and thrust buildup, which is the primary focus of this paper. Computational fluid dynamics is used for the solutions here because it provides a more complete flow field prediction, especially in low-power, near edgewise conditions. The flowfield is assumed to be inviscid, and the Euler equations are solved with a blade-element model for the FANTAIL. The main rotor is excluded in this study. Solutions are obtained by modifying the computer code PUMA2 (Parallel Unstructured Maritime Aerodynamics) and using an unstructured grid of 2.8 million cells. The code was run on Beowulf PC clusters. Dynamic fan thrust and moment response to applied collective pitch in hover and forward flight are presented and discussed.