Combined Experimental/Numerical Development of Propulsor Evaluation Capability

This paper presents a method to combine computational fluid dynamics (CFD) modeling with subscale experiments to improve full-scale propulsor performance prediction. Laboratory experiments were conducted on subscale models of the NUWC Light underwater vehicle in the 0.3048 m × 0.3048 m water tunnel located at the Naval Undersea Warfare Center in Newport, Rhode Island. This model included an operational rim-driven ducted post-swirl propulsor. Laser Doppler Velocimetry was used to measure several velocity profiles along the hull. The experimental data were used in this project to validate the CFD models constructed using the commercial CFD software package, Fluent^®. Initially, axisymmetric two-dimensional simulations investigated the bare hull, hull only case, and a shrouded body without the propulsor. These models were selected to understand the axisymmetric flow development and investigate methods to best match the propulsor inflow. A variety of turbulence models were investigated and ultimately the numerical and experimental velocity profiles were found to match within 3%. Full 3D flow simulations were then conducted with an operating propulsor and compared with the corresponding subscale experimental data. Finally, simulations were conducted for full-scale tests and compared with actual open-water data. While the open-water data was limited to propulsor rpm and vehicle velocity, the operating advance ratio could be determined as well as the estimated vehicle thrust. This provided a method to utilize CFD/experiments to bridge the gap between subscale and full-scale tests. The predicted open-water advance ratio was 10.3% higher than the experimental value, as compared with the 28% difference previously found from a linear extrapolation of Reynolds number from model scale to full scale. This method was then applied to two different research propulsor geometries and led to agreement between computational and experimental advance ratios on the order of 2%.