Axial-Flow Pump/Intake Fluid Dynamic Interactions: Numerical Predictions of Outboard Dynamic-Inlet Waterjets Operating Under Inlet Distortion

Abstract The Outboard Dynamic-inlet Waterjet (ODW) has already proved to innovate marine propulsion, outperforming existing technologies during near-nominal operations. Representing the naval equivalent to aero-engines, ODWs operate independently, isolated from the ship. Therefore, as in aviation the propulsive performance strictly depends on the quality of the free-stream, a similar behaviour is expected on ODWs, potentially compromising its mission envelope. With the existing literature discussing the details of nominal operations, the present numerical study aims to address the issues occurring when the system experiences inlet distortion. A structured computational domain is generated around the full annulus geometry, derived by matching an axisymmetric inlet with an axial-flow pump. Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, coupled with κ-ω SST and Zwart models for turbulence and cavitation, respectively, are solved to simulate the flow past an ODW operating with a 16° free-stream incidence, as pump blades rotate at 1400 r pm. The solution indicates that the entering flow separates on the lower half of the propulsor, breaking into several vortical structures downstream. These vortexes time evolution obstructs the capture stream-tube, deteriorating its distribution. Pump non-uniform inflows affect the incidence on rotor blades, resulting in unbalanced loads and anticipated tip cavitation in the lower right quadrant.