Application of a Maneuvering Propulsor Technology to Undersea Vehicles

Previous computational and experimental studies that have demonstrated a method to generate vehicle maneuvering forces from a propulsor alone have been applied to a generic undersea vehicle. An open, 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 torque produced by the rotor. 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. The stator wake axial velocity and swirl that is ingested into the rotor produces a counter-force by the rotor. Optimal design of the rotor minimizes the unsteady force and redirects the rotor force vector in an orthogonal direction to minimize the counter force. The viscous, 3D Reynolds-averaged Navier-Stokes (RANS) commercial code FLUENT (R) was used to predict the stator forces, velocity fields, and rotor response. Radiated noise was computed for the rotor separately and the entire geometry utilizing the Ffowcs Williams-Hawkings module available in FLUENT. Two separate geometries were studied-the first with a maximum stator blade row diameter contained within the body diameter and a second that was allowed to exceed the body diameter. Side force coefficients were computed for the two maneuvering propulsor configurations and compared with currently used control surface forces. Computations predicted that the maneuvering propulsor generated side forces equivalent to those produced by conventional control surfaces with side force coefficients on the order of 0.3. This translates to 50% larger forces than can be generated by conventional control surfaces on 21 in. unmanned undersea vehicles. Radiated noise calculations in air demonstrated that the total sound pressure levels produced by the maneuvering propulsor were on the order of 5 dB lower than the control fin test cases.