The hydrodynamic and flow noise generation mechanisms of XLUUV based on a numerical comparative study

As a key component of an underwater vehicle's propulsion system, the pump-jet propulsor (PJP) performance is also strongly related to the hull wake. There are mainly rotating hulls represented by an idealized submarine (SUBOFF) and non-rotating hulls represented by an Extra-large Unmanned Underwater Vehicle (XLUUV). This paper numerically investigates the hydrodynamics and flow noise of the PJP behind two typical hulls to analyze the influence of the hull wake flows on the PJP. The flow is obtained by the improved delay detached eddy simulation (IDDES) based on the wall-adapting local-eddy viscosity sub-grid scale model, and the flow noise is obtained by the Ffowcs Williams-Hawkings (FW-H) equation. The numerical results of the base case and the experimental results are in good agreement. The study shows that, owing to the hull shape, the non-rotating hull has higher frictional resistance and pressure difference resistance, rotating hull exhibits better resistance performance. However, the optimal propulsive efficiency of the non-rotating wake is 2% higher than that of the rotating hull. Uniquely, due to the complex low-speed flow generated by the four ribbings of the non-rotating hull, the thrust frequency domain distribution of the PJP behind it is more prominent at the quadruple axial frequency, and the flow noise at the characteristic point is 3.2 dB higher than that of the PJP behind the rotating hull. The rotating hull shows better acoustic stealth.