Acoustic characteristics of water-jet propulsion with screw mixed-flow pump under quasi-submerged state

As a key point of the stealth performance, acoustic characteristics of a screw mixed water-jet pump were investigated under the quasi-submerged state. The relationships between thrust and rotation speed of screw-mixed pump, drag, and submerged velocity of water-jet propulsion were obtained from the flume tests and numerical simulation. Based on the results of the unsteady flow field calculation with the detached eddy simulation (DES), the sound radiation fields of the screw mixed water-jet propulsion at different rotation speeds were investigated by the finite element method (FEM) coupled with the vibro-acoustic method. The flow-induced dipole source noise of every flow passage component increases with the increasing of rotation speed. The mathematical relations of the flow-induced noise at impeller between different rotation speeds were established. The maximum sound pressure level (SPL) of every flow passage component appears at the impeller blade-passing frequency (BPF). In the medium-high frequency domain, dipole source induced noise from the impeller is the main external noise field during the propulsion process. At the first-order BPF, the ratio of SPL of the impeller is equal to the 0.5 power of the rotation speed in the phase of 0 degrees, 90 degrees, 180 degrees, and 270 degrees. At the sixthorder BPF, the ratio of SPL of the impeller is directly proportional to the reciprocal power of rotation speed ratio in the phase of 0 degrees, 90 degrees, 180 degrees, and 270 degrees.