| The self-excited cavitating waterjet capitalizes on the natural tendency of an axisymmetric jet to organize into large structures and could achieve extreme high excitation frequency with large amplitude even under high ambient pressure.The strong pressure oscillations associated with intensified cavitation greatly improve the jet's erosion and cleaning capabilities.These effects can be utilized in important applications such as well scale removal,deep hole drilling and mining in deep-sea.However,it is difficult to acquire the performance of self-excited cavitating waterjet under high ambient pressure,which results in its frequency and cavitation erosion characteristics are unclear,further limits its popularization application in deep-sea and well.First,self-excited cavitating waterjet's frequency and erosion characteristics were analyzed theoretically.Furthermore,a detection method based on the flow signal in a pipeline was proposed to uncover the waterjet's characteristics under high ambient pressure.On this basis,the evolution law and mechanism of the waterjet's frequency and cavitation erosion performance under ambient pressure were studied.Lastly,based on high-speed particle image velocimetry,a visualization study was carried out to reveal the characteristics of the waterjet's flow field and vortex shedding.The main research contents are as follows:(1)Firstly,the frequency characteristics and erosion behavior of self-excited cavitating waterjet under high ambient pressure were analyzed theoretically,and the waterjet's mechanism was clarified.The acoustic natural frequency model of the resonator was established based on hydroacoustics and transient flow theory.Theoretical analysis of the frequency characteristics including acoustic natural frequency,self-excited frequency,jet's structured frequency and cavitation noise frequency was carried out and the influencing factors of each frequency were studied.Based on the cavitation bubbles dynamics,boundary layer theory and cavitation theory,the cavitation and erosion mechanism of self-excited cavitating waterjet under high ambient pressure were analyzed,and the influencing factors of erosion behavior were preliminarily obtained.(2)To detect the frequency characteristics of self-excited cavitating waterjet under high ambient pressure,a detection method based on the flow signal in a pipeline was proposed,and a system for detecting self-excited cavitating waterjet's characteristics under high ambient pressure was built accordingly.The pressure sensors were transferred from within the high-pressure tank to the outside of the tank and were arranged in the front pipeline outside the tank to avoid the influence of high ambient pressure.Dual-pressure sensors were used to acquire the flow pressure oscillation signal,and signal-processing technology was used to suppress noise interference for enhancing the intensity of useful signals and accurately obtaining the pressure fluctuation information of the self-excited cavitating waterjet.(3)The self-excited cavitating waterjet's frequency characteristics and its influence parameters were studied by the signal analysis method.Based on the spectrum analysis method,the spectrum characteristics of the jet were analyzed,and the relationship between the spectrum structure and resonance state of the jet was obtained.On this basis,the acoustic natural frequencies of various resonator geometries were studied to obtain their evolution rules.The influencing factors of the jet's structured frequency characteristics under different ambient pressures were studied.The above research reveals the self-excited cavitating waterjet 's frequency characteristics under ambient pressure and realizes the regulation of the oscillating state of the jet.(4)Based on the noise analysis and erosion experiment,the erosion behavior of self-excited cavitating jet was studied experimentally,to research its relationship with pressure oscillation and cavitation characteristics.On this basis,under high ambient pressure,the influence of various factors such as the standoff distance,cavitation number,the resonator and outlet's geometries were studied.Finally,the influence law and mechanism of various factors were obtained,revealing the cavitation erosion behavior of self-excited cavitating waterjet under high ambient pressure(5)Based on the High-speed planar particle image velocimetry(PIV),an experimental system was built to obtain the vortex shedding information in the self-excited cavitating jet's boundary layer under various nozzle outlet geometries.Based on the flow field analysis method,the characteristics of the jet's average velocity field,turbulence field,instantaneous velocity field and coherent structure under different nozzle outlet geometries were studied.The influence law of nozzle outlet geometries on the flow field and vortex ring characteristics of self-excited cavitating jet's was explored,and the internal influence mechanism was revealed. |
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