Investigation Of Instantaneous Frequency Characteristics And Simulation Of Self-resonating Water Jet

Self-resonating Water Jet(SRWJ)is widely used in the field of deep-sea resource exploitation for the characteristics of strong cavitation.The frequency characteristics affect the cavitation effect directly and then affect the erosion characteristics of the SRWJ.However,in the complex deep-sea environment,the frequency characteristics of SRWJ in addition to the influenced by the surrounding environment,it is also affected by the unsteady instantaneous characteristics,which leading that the relationship between the frequency structure and the cavitation characteristics is unclear,so as to affects the further improvement of the cavitation effect of the SRWJ.In this paper,according to the instantaneous characteristics of the SRWJ,the research is focus on the frequency characteristics,time-frequency characteristics,cavitation characteristics and multi-physical field effects of the SRWJ.Firstly,the characteristics of the instantaneous flow and the frequency feature of the SRWJ was explained,besides,on the basis of the theory of hydro-acoustic characteristics and fluid transient flow,the characteristics of acoustic resonance frequency of the SRWJ are analyzed;and then based on the cavitation and bubble dynamics,the characteristics of the cavitation frequency in the flow field are discussed,and the characteristic frequency composition of the free vibration jet is obtained.Based on the above research,the whole flow field characteristic frequency composition of the SRWJ is obtained.Considering the high confining pressure in the deep-sea environment,combination with the multi-physical field experiment platform,and according to the frequency response of the SRWJ,the physical structure of the SWRJ is designed.The structure of the frequency domain is demodulated and analyzed of the organ-pipe type nozzle,the resonance frequency,and its harmonics,bubble cavity oscillation frequency,fixed Cavitation frequency and the coherent frequency formed by the interaction of these characteristic frequencies are extracted.On the basis of the modulation of the frequencies,the cavitation indication characteristics of the SRWJ are investigated,and the empirical formulas of the characteristic frequency composition of different cavitation states are given.On the basis of the modulation of the frequencies of the SRWJ,and considering the instantaneous characteristics of the pressure,a time-frequency analysis method is proposed to study the instantaneous frequency of the SRWJ signal.By coupling the Morlet wavelet transforms,synchrosqueezed wavelet transforms(SWT)and the modulus maximum methods together,a comparative study on the verified in feasibility,noise reduction performance,and engineering application are carried out.On the basis of above,the pressure fluctuation signal of the high confining pressure in the deep-sea environment is carried out to obtain the time-frequency characteristics and non-stationary characteristics of the SRWJ.In view of the characteristics of the unsteady transient flow,by employing the CFD numerical simulation method,a turbulence coupling of cavitation model of the SRWJ is established.The resonant frequency and harmonic of the SRWJ are used to verify the numerical simulation model.And then,the velocity distribution,pressure oscillation and cavitation characteristics of the flow field SRWJ are obtained.Based on the characteristics of the flow field,the source of cavitation noise is identified,the spatiotemporal evolution and periodic distribution of cavitation are obtained,and the erosion effect is studied.This study provides some theoretical guidance for the modulation of the feature frequency,the control of cavitation characteristics,and obtain different erosion modes in the high confining pressure of the deep-sea environment;as well as technical support for optimizing the nozzle structure,finding the optimal target distance and improving the impact effect.