The application of bionic vortex generator on the duct of a pump-jet propulsor and mechanism for its flow control

The pump-jet propulsor (PJP) has a low noise level, but its prominent low-frequency line spectrum noise makes it easily locked and recognized, and suppressing unsteady forces is an effective way to reduce it. The vortex generator (VG) improves the flow characteristics by generating controllable vortexes, but it has not been applied to the PJP yet. Based on the bionic principle, we design a VG imitating the dorsal fin of a dolphin, two VGs as one group, and install ten groups on the PJP duct. Based on the hybrid Reynolds-Averaged Navier-Stokes and Large Eddy Simulation method, a high-fidelity flow field is established to explore the influence of VG on the hydrodynamics, unsteady forces, wake fluctuations and flow characteristics of the PJP. The results reveal that at the self-propulsion point J = 0.8, VGs reduce the total thrust coefficient K_T by 0.89 %, but reduce the unsteady force at the stator-passing frequency f_s by 30 %. VGs decrease the velocity and pressure standard deviations by 25 % and 40 % respectively. The velocity at the shaft-frequency f_n is decreased by 53.3 %, at the rotor-passing frequency f_r by 45.4 %, and at f_s by 32.6 %. The pressure at f_r is reduced by 57.5 %, and at f_s by 73.1 %. At high advance coefficients, VG leading edge vortex, root vortex, wingtip vortex and leeward vortex appear. The leeward vortex promotes the dissipation of rotor tip vortex, reduces its frequency peaks, and suppresses the flow separation and duct shedding vortex. The bionic VG offers new concepts for optimizing the unsteady forces of PJPs.