Computational Analysis of Isolated and Embedded Ducted Rotors in Edgewise Flight

This study examines the performance of an isolated and embedded-in-body ducted rotor in edgewise flight conditions. The flow over a three-dimensional model of ducted rotor configurations 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). Performance comparisons were made between the isolated and embedded configurations. In cruise, the isolated duct configuration was shown to have a larger region of separated flow off the front inlet. The separation region in both configurations induces upwash through the front of the disk resulting in higher thrust production in that region but this effect is reduced in the embedded configuration. The front inlet and the rear diffuser are the major contributors to duct H-force but the embedded duct configuration produces lower total H-force. Both the duct and rotor contribute to a nose-up pitching moment, both of which are weaker for the embedded configuration. The rotor is the primary source of vertical vibratory forces as well as vibratory pitching moment. The small tip clearance of the rotor causes a local interaction between the blade tip and duct that is the dominant contributor to H-force vibratory forces on the ducted rotor. The embedded configuration was shown to significantly reduce the magnitude of the H-force and pitching moment vibrations, while vertical vibrations were largely the same for both configurations.