Effect mechanisms of leading-edge tubercle on blade cavitation control in a waterjet pump

The bio-inspired leading-edge tubercles (LET) are specifically designed and exploited to control the blade cavitation dynamics under the inlet guide vans (IGVs) wake impacts in a waterjet pump. The experiments, nu-merical simulation, and modal analysis are jointly carried out to elaborate on the effects mechanisms and cavitation oscillations of the LET pump. It is observed that the tubercle blade cavitation is stably confined in the troughs with a tubular-like pattern and the spanwise coherent development is broken. The tubercles drive the flow turbulent and then form low pressure in the troughs to give rise to cavities. Weak counter-rotating vortex pairs can be identified in the tubercle trough. The analysis of vortex transportation demonstrates that vortex stretching and dilatation would be induced by tubercle cavitation. The loading instabilities obtained by Dynamic Mode Decomposition (DMD) indicate that the dominant oscillations emerge around the tubercles in the blade middle part regarding heavy loading. Due to the large-scale cavities depression by the tubercles, the thrust ex-tremes in some revolutions could be efficiently avoided. In comparison with smooth and tubercle pumps, the thrust energy regarding the tonal and broadband frequency for a single blade and impeller are closing, which need to be further studied to degrade excited force instabilities. This work fundamentally investigates the cavitation instabilities and mechanisms in a tubercle waterjet pump, which could provide a guide on pump design to stabilize cavitation oscillations under uncertain inflow perturbations.

Automated summary

The effects mechanisms and cavitation oscillations of bio-inspired leading-edge tubercles in a waterjet pump were investigated through experiments, numerical simulation, and modal analysis. It was found that the tubercle design could confine the blade cavitation in the troughs with stable tubular-like patterns and break the spanwise coherent development. The tubercles induced turbulent flow, formed low pressure in the troughs, and caused cavities. Vortex stretching and dilatation due to tubercle cavitation were also observed. The loading instabilities around the tubercles were found to be responsible for dominant oscillations in the blade middle part. The large-scale cavities depression by the tubercles effectively avoided thrust extremes. The thrust energy between smooth and tubercle pumps for a single blade and impeller were found to be similar, indicating the need for further research to mitigate excited force instabilities.