Abstract
Inflow turbulence-induced broadband force spectra of a pump-jet are investigated numerically. The turbulence-generating grid and Fourier synthesis method are employed to produce inflow turbulence with spatial flow structure and temporal fluctuation. These methods are combined with Large Eddy Simulation (LES) to obtain the unsteady broadband force spectra of a pump-jet. The characteristics of unsteady force spectra and velocity spectra of the pump-jet are compared with those of a single rotor and a ducted propeller to reveal the influences of the duct and the pre-swirl stator. The results show that averaged unsteady force spectra show obvious broadband characteristic in the low frequency range, and appear discrete components at BPF and its multiples. The presence of the pre-swirl stator superimposes the spatial non-uniform flow field to the original unsteady inflow, and increases the proportion of periodic component. As a result, the amplitudes of the unsteady broadband force spectra for the rotor of the pump-jet are higher than the ducted propeller and propeller, but the humps are not as obvious as them. The research is helpful to provide ideas for the vibration and noise reduction of the pump-jet.
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