A Method to Generate Propulsor Side Forces

Abstract

A computational study was performed to investigate a method to generate vehicle maneuvering forces from a propulsor alone. A ducted, preswirl propulsor was configured with an upstream stator row and downstream rotor. During normal operation, the upstream stator blades are all situated at the same pitch angle and preswirl the flow into the propulsor while generating a roll moment to counter the moment produced by the rotor. By varying the pitch angles of the stator blade about the circumference, it is possible to both generate a mean stator side force and subsequently vary the axial velocity and swirl that is ingested into the propulsor. The rotor then generates a side force in response to the inflow. Both potential flow and fully viscous 3D Reynolds averaged Navier–Stokes (RANS) computations were used to predict the stator forces, velocity field, and rotor response. Potential flow methods were used for initial examination of a wide variety of stator configurations. The most promising were then modeled using RANS. The RANS inflow was then computed and used as velocity boundary conditions during rotor blade design using potential flow methods. Blade parameters including blade number, rake, skew, and a combination of the two were varied to characterize their effects. RANS was used to then validate the final propulsor design. Computations demonstrated that total side force coefficients on the order of 0.1 and moment coefficients about the stator leading edge of 0.066 could be generated by the propulsor alone. This translates to an additional 50% control authority at 3 kn for current Navy 21″ unmanned undersea vehicles.