Time-frequency Characteristics Of Self-excited Suction Pulse Jet Under Variable Confining Pressure

Based on the present situation of serious siltation in the reservoir area of China's silt-laden rivers needs to be resolved urgently.Using the advantage of self-excited pulse jet in controlling sediment deposition in river reservoir area,the self-developed self-excited pulsed jet nozzle test system with low pressure and large flow under water was developed.Experimental study on jet impingement pressure pulsation of self-excited inspiratory pulse jet nozzle under submerged condition.Combined with the current research situation at home and abroad,time-frequency analysis method was adopted to study the impingement pressure pulsation signal of self-excited jet under different confining pressure and dimensionless structure parameters.The time-frequency characteristics and the energy spectrum distribution of the impinging pressure pulsation signal of the nozzle jet are obtained by analyzing the different confining pressure and different dimensionless structural parameters.Firstly,the present situation of reservoir siltation in China and the relative methods of desilting are briefly introduced,and the new water jet technology widely used,such as continuous jet,abrasive jet,cavitation jet and so on,is described in detail.At the same time,the present situation of domestic and international research and the application of water jet are summarized.Secondly,the basic structure and characteristics of submerged jet are introduced,the mechanism and technical characteristics of self-excited oscillating jet and self-excited inspiratory pulse jet are compared and analyzed,and the frequency characteristics of self-excited oscillating pulse jet are analyzed theoretically.The time-frequency analysis algorithm of jet pressure pulsation signal,its advantages and the comparison between different methods are also discussed.Finally,based on the time-domain waveform of pressure pulsation obtained from impact test,the time-frequency characteristics of impulse pressure pulsation signal of self-excited pulsed jet nozzle are studied by means of experimental study:(1)The time-frequency characteristics and energy spectrum distributionof impulse pressure pulsation signals of suction and unaspirated self-excited pulsed jet nozzles are studied.The results show that the amplitude and frequency of jet pressure pulsation signals are obtained after suction.Jet energy and impact increased significantly;(2)The amplitude,pulse frequency,jet energy and impact force of the impulse pressure pulsation signal of the self-excited inspiratory pulse jet nozzle under different confining pressure conditions and different dimensionless parameter ratios are compared and analyzed.The time-frequency characteristic and energy spectrum distribution of different confining pressure and different dimensionless parameter ratio are obtained,and the optimum confining pressure and dimensionless parameter ratio of pulse are obtained.The results of this paper provide the theoretical basis for the practical application of self-excited pulsed jet nozzles in high efficiency desilting of reservoirs.