Research On The Mechanisms Of Cavitation-Excited Forces And It’s Stablities Control In A Waterjet Pump

The waterjet pumps are usually operating in the context of non-uniform inflow,such as the ship wakes,appendage wakes,and pipe suction flows etc.The cavitation itself on rotating blade would present many instabilities,which would interact with the non-uniform inflow to trigger severe cavitation dynamics and resultant loading pulsation to perform an significant impact on the operating stabiliies of pump.Combined with experiments,numerical simulation and spectral feature extraction method,this work studies the balde cavitation dynamics,excited-force characteristics,and achieves the localization of tonal,broadband,and transient excitation source for a waterjet pump with inlet guide vans(IGVs)to reveal the mechanisms of cavitationexcited force.Based on the above research,two passive control methods,obstacles and bionic tubercle,are specifically employed to stably control blade cavitation within the waterjet pump.The main contents of this work are summarized as follows:(1)The studies on cavitation dynamics,excitation source of loading pulsation and excited-force mechanisms for a waterjet pump with IGVs are conducted.As illuminated,the blade cavitation would globally perform a typical periodic oscillations as each blade passes through the IGVs wake in sequence,which are largely attributable to the nonuniform and periodic distribution of incidence angles.Based on the studies on the loading oscillation of blade cavitation with the aid of spectral feature extraction method of m POD and MRDMD,it is found that the leading edge where cavitation dynamically develops majorly contribute to the excited force.The tonal component is triggered by the determinstic IGVs passing frequency,and the broadband somponent is caused by the cavitation-induced random loadings,the non-uniformly developed cavitation is mainly responsible for the transients of loading pulsations.(2)Base on the study of blade cavitation dynamics and excited-force mechanism in the waterjet pump,the work designs obstacle bars to attach on the blade suction surface to control cavitation,and meanwhile investigats obstacles blade cavitation dynamics,control mechanism,excitation source characteristics and excited-force stability.The results show that the blade leading-edge remains cavity-free,and the obstacles meanwhile trigger turbulent shear cavitation.The cavitation depression mechanisms attribute to the upstream raised high pressure and the decelerating effects induced by obstacle.The analysis with the help of spectral feature extraction methods indicate that the wake regimes of obstacle cavitation play a prominent role to affect the laoding oscillations that also induce the broadband and transient excitation source.By comparing the energy level of different frequency bands for original and obstacle balde,it is found that the cavitation-induced force pulsations regarding IGVs passing frequency would be effectively degraded.(3)The bionic tubercle is employed to control the blade cavitation oscillations,the mechanisms of cavitation dynamics,control mechanisms,excitation source,and excited-force stabilities for bionic tubercle balde are studied.The results show that,at the equivalent cavitation developing stage with original pump,the cavities on the bionic blades are stably attaching in the trough of tubercle and the cavitation oscillations triggered by the IGVs wakes are depressed to a great degree.The control mechanism is demonstrated as that the pressure alternations make the cavities constantly attach in tubercle troughs.Relying on the spectral feature extraction methods,the analysis on the loading pulsations inside the bionic pump indicate that the the excitation source are mainly concentrating around the tubercle and middle regimes of blade leading edge where cavitation develops.The pulsation energy regarding different frequency bands for the bionic water-jet pump are closing to that of original pump,which suggests that the depreesion of cavitation-excited force need to be further studied.This work sheds light on the mechanisms of blade cavitation dynamics and excited force under non-uniform inflow perturbations and rotating modulation.The studies on the pump cavitation control confirm the advantages of obstacle and tubercle pump to enhance the cavitation stabilities,which is meaningful to facilitate a positive guide for the cavitation control inside fluid machinery.