Towards the control of blade cavitation in a waterjet pump with inlet guide vanes: Passive control by obstacles

The blade cavitation in a waterjet pump presents highly dynamic behaviors under the inflow non-uniformities and unsteadiness. This work designs a pair of tandem obstacles attached on the blade suction surface to control blade cavitation within the waterjet pump. The unsteady simulations and experimental observation of the cavitating flow in a water tunnel are jointly carried out to study the control mechanism and control effects of obstacles. It is observed that, the blade leading edge regimes before the obstacle are nearly free of cavities at the incipient, moderate developing and fully developed cavitation stages whereas the shear cavitation is triggered after each obstacle. The cavitation control mechanism of obstacles is substantially attributable to the raised absolute pressure and the flow deceleration imposed by the adverse pressure gradient (APG) alternations. In particular, the position-shifted cavitation effectively weakens the interactions of inlet guide vanes (IGVs) wake and blade cavitation and hence to avoid the dynamic loading impingement around the leading edge regimes although a 5.6% hydraulic efficiency reduction is introduced. As a result, the root mean square (RMS) of 10-300 Hz of the obstacle thrust spectra is degraded with a pronounced amount. In the following work, the geometries and positions of obstacles will be further optimized to improve the cavitation control effects.