Computational Analysis and Flow Physics of a Ducted Rotor in Edgewise Flight

This study examines the performance of the ducted rotor in hover and edgewise flight conditions. The flow over a three-dimensional model of a ducted rotor was simulated using the Spalart-Allmaras RANS model implemented in a stabilized finite element method. A sliding mesh was used to conveniently account for the large-scale motion associated with rotor revolutions. The simulation results were analyzed to understand the flow physics and quantify the contributions of the rotor and various sections of the duct interior surfaces on the total aerodynamic forces (thrust, drag and side force) and moments (pitching and rolling). In edgewise flight, freestream flow separates off the front of the duct inlet causing a region of recirculating flow and upwash in the rotor plane. The upwash region biases rotor thrust production to the front of the disk. The swirl velocity further biases the region of flow separation over the inlet and upwash at the front of the rotor towards the retreating side of the disk. The shift of thrust production on the rotor and duct towards the front produces a strong nose up pitching moment on the ducted rotor. The rear of the diffuser is a significant contributor to the total drag, this force as incudes a nose down pitch moment which partially negates the moment from the duct inlet. The rotor is the primary source of vertical vibratory forces as well as vibratory pitching and rolling moments. The small tip clearance of the rotor causes a local interaction between the blade tip and duct that is the dominant contributor to in-plane vibratory forces on the ducted rotor.