| The high-pressure water jet is widely used by many industries,such as cutting,fire engineering,drilling and cleaning,with the increasing pressure on working conditions,piping and high-pressure water pumps and other equipment requirements are increasingly harsh,resulting in a sharp increase in production costs.The self-excited oscillation nozzle due to its self-oscillation,which produces pulsed jet characteristics,has the potential to achieve high operating efficiency under low operating conditions.The academic and market value to carry out research work on self-excited oscillating nozzles is invaluable.However,the mechanism of the self-excited oscillation pulsed jet is still in a period of continuous improvement,and the application depth and breadth of the self-excited oscillation nozzle are significantly limited since the turbulent flow field inside the self-excited oscillation nozzle is exceptionally complex.Therefore,the self-excited oscillation nozzle is taken as the research object,and using the combination of CFD(Computational Fluid Dynamics)numerical simulation and experiment,three aspects of research work have been focused on the optimization of nozzle structure,the evaluation of the effect of pulse jet production,and the analysis of the cavitation characteristics inside the nozzle.The specific research work is as follows:(1)The current research progress of pulse jet generation methods at home and abroad is analyzed,and the research status of self-excited oscillation nozzles at home and abroad is summarized.A new type of dual-chamber self-oscillating nozzles is designed to improve the production of pulsed jets,and the key technical problems and main research contents are expounded.(2)The effect evaluation system of the self-excited oscillation nozzle pulse jet is established.With the help of FLUENT,the numerical simulation of internal flow field and external flow field of the single chamber self excited oscillation nozzle is completed.The characteristics of the flow field in the nozzle chamber are analyzed,the direct cause of the pulse jet is found,and the optimal structure ratio of the single chamber nozzle is found.At the same time,a fluid network model of the single chamber self excited oscillation nozzle is established.The frequency equation of the nozzle jet and the wave velocity equation of the pressure disturbance are derived,and the amplitude frequency characteristics of the nozzle are analyzed.(3)Based on the research of single-chamber self-oscillating nozzles,the feasibility of a series-type dual chamber self-excited oscillating nozzle is firstly demonstrated by using a pulse jet production effect evaluation system.Then FLUENT software is used to simulate the internal and external flow field of a double chamber self-excited oscillation nozzle.The characteristics of the internal flow field of the nozzle are studied,and the reasonable parameter ratio range of the double chamber nozzle is determined.Meanwhile,a fluid network model of dual chamber self oscillating nozzles is built.The amplitude frequency characteristics of single and double chamber nozzles were compared and analyzed by MATLAB.Through the comprehensive analysis,it is found that the double chamber self excited oscillation nozzle can produce the pulsed jet effectively,and the performance parameters of the operating conditions are all better than the single chamber structure.(4)The mechanism and influence factors of cavitation effect in self-excited oscillation nozzle are studied.The characteristics and development process of "cavitation air bag" in the inner chamber of the self excited oscillation nozzle and the outlet pipe flow channel are emphatically analyzed.Based on the cavitation characteristics in the flow channel of the outlet pipe,a structural optimization method that can effectively suppress the cavitation effect in the outlet pipe flow channel is proposed.On the basis of the previous research,a cluster-type dual chamber self-oscillating nozzle is designed.(5)The numerical simulation and Experimental Research on the external flow field of self-excited oscillation nozzles are carried out,which proves the rationality of the numerical simulation and the optimization design of nozzle structure.Finally,a summary of the the concrete works in this dissertation is proposed and the further research direction is suggested. |
PDF Full Text Request