Discrete-Blade, Navier-Stokes Computational Fluid Dynamics Analysis of Ducted-Fan Flow

The application of overset grid methods to studying the flowfield of the FANTAIL antitorque system of the RAH-66 rotorcraft is described. The FANTAIL itself and the experimental program used to design it are described first. Then, OVERFLOW-D, an overset grid-based, Navier-Stokes computational fluid dynamics code is reviewed, and its adaptation to the ducted fan geometry of the FANTAIL is explained. The modeling of the FANTAIL using OVERFLOW-D, including grids and boundary conditions, is explained in detail. The results of numerical studies of the hovering FANTAIL are presented and are shown to compare well with experiment. Flowfield visualizations are presented and are used to explain how the blade tip vortices combine with the adverse pressure gradient beneath the rotor disk to impact flow along the duct wall beneath the disk.