Postswirl Maneuvering Propulsor

Abstract

This research examines the novel use of a postswirl propulsor to generate side forces sufficient for undersea vehicle control. Numerical simulations using the commercial computational fluid dynamics (CFD) code Fluent® were used to predict the side forces for open and ducted, post-swirl propulsors configured with an upstream rotor and movable downstream stator row. By varying the pitch angles of the stator blade about the circumference, it is possible to generate a mean stator side force that can be used to maneuver the vehicle while generating sufficient roll to counter the torque produced by the rotor. A simple geometric configuration was used to minimize body geometry effects to better understand the flow physics with simulations conducted in a water tunnel environment. Flow computations highlighted the component forces and were used to characterize the velocity fields between the rotor and stator blade rows as well as the velocity field in the stator wake. There was significant coupling between the rotor and stator blade rows as demonstrated by the rotor wake velocity profiles. While the flow fields were coupled, there was not a significant difference in rotor axial or side forces except for the largest pitch amplitudes. Predictions showed that the maneuvering propulsor generated side forces predominantly by the stator and body that significantly exceeded those produced by conventional undersea vehicle control surfaces with side force coefficients on the order of 0.5. These forces are approximately three times larger than those generated by conventional control surfaces on 21 in. unmanned undersea vehicles (UUV's). Even for zero flow velocities, side forces were produced due to the induced flow produced by the rotor over the stator, further demonstrating the potential for this technology to be used for undersea vehicle maneuvering.