Preswirl Maneuvering Propulsor

Abstract

Recent concept studies have demonstrated the potential to utilize a preswirl propulsor configuration with adjustable upstream stator blades to generate propulsor side forces. These studies led to a set of experiments and corresponding computations to validate this concept. Ducted and open preswirl propulsors were 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 rotor. The rotor then generates side forces in response to the modified inflow. Wind tunnel experiments were conducted to measure the steady, spatially varying stator wake flows for various stator geometric configurations using stereoscopic particle image velocimetry. Water tunnel experiments were conducted to measure the forces produced. Experimental data were used to validate computations, which utilized fully viscous 3-D [Reynolds averaged Navier-Stokes (RANS)] computations to predict the stator forces, velocity field, and rotor response. Both methods provided insight into the underlying mechanisms of side force generation. Optimized rotor designs were specifically investigated to isolate the blade forces as well as the induced body forces. In this way, RANS provided high fidelity performance predictions of the final propulsor design. Experimental and computational data demonstrated that total side force coefficients on the order of 0.26 could be generated by the open propulsor. This amount of control authority exceeds current control surface capabilities for Navy 21 (0.5334 m) unmanned undersea vehicles and is comparable to novel thrust-vectored designs.