| As an important hydraulic power component,gear pump is widely used in hydraulic transmission and control system with many advantages,such as simple structure,small size,good self-priming performance,strong anti-pollution ability,reliable operation,low cost and convenient maintenance.However,cavitation is likely to occur in gear pump internal oil because of its low suction pressure,which resulting in the gas-liquid two phases coexisted in it.As we all know,the appearance of gas phase in internal flow field adversely affects the operation of gear pump,whereafter,which will hinder the gear pump's development direction with high speed,high pressure and large flow.Hence,study about dynamic evolution process and influence of gas phase in internal flow field of gear pump can provide important information for improvement of gear pump.Few studied about quantitative description of cavitation phenomenon of gear pump and the dynamic evolution of gas phase in the whole process of cavitation occur to damage the metal inner surface of gear pump and other components in its hydraulic system.Therefore,in the present study,the CB type involute external gear pump was taken as the research object.The dynamic evolution process and influence of the gas phase in internal flow field of gear pump were investigated with theoretical analysis,dynamic numerical simulation and experimental comparison analysis.The main research contents of this study as follows:(1)In order to facilitate the quantitative description of cavitation inside gear pump,we divided the internal flow field area of CB involute external gear pump into four regions,established the calculation model for numerical simulation and analyzed the reason of cavitation in gear pump flow field.Then,we verified the validity and reliability of numerical calculation models and methods were used in this study.(2)Based on CFD numerical simulation method,the cavitation of gear pump internal flow field under normal working condition was studied.Firstly,the pressure distribution,velocity distribution and air volume fraction distribution of gear pump internal flow field were analyzed with Fluent software.Secondly,the law of variation among total gas volume fraction in internal flow field of gear pump with rotation angle and rotation time changes were analyzed with PumpLinx software,and the gas phase dynamic evolution law in gear pump internal flow field was obtained.Finally,the influence of cavitation on flow quality of gear pump outlet was analyzed.(3)Three influence factors(oil suction pressure,rotating speed and oil temperature)on cavitation characteristics of gear pumps were studied by Fluent and PumpLinx numerical simulation methods.Firstly,the variation law of pressure,velocity and air volume fraction in local area of gear pump internal flow field was analyzed with Fluent software.Secondly,the variation law of total gas volume fraction F_T and volume flow q_c at gear pump outlet was analyzed with PumpLinx software.Finally,based on the volume flow deviation rate?and fluctuation rate?of gear pump outlet,the flow quality variation law of gear pump outlet was analyzed with theoretical calculation results and numerical simulation results.(4)Based on theoretical analysis and experimental comparison method,the oxidative deterioration of hydraulic oil around cavitation bubbles in gear pump internal flow field under compression was analyzed during the gas phase dynamic evolution in internal flow field of gear pump.Firstly,the reasons for heat generation of cavitation bubbles in internal flow field of gear pump were analyzed.Secondly,the basic composition and main performance parameters of hydraulic oil were described.Thirdly,the corrosivity of three kinds of hydraulic oils was tested under simulated cavitation heat generation environment of gear pump flow field.And the chemical properties of three kinds of hydraulic oils were analyzed in the simulated cavitation heat production environment.Finally,the thermogravimetric analysis were compared of two kinds of hydraulic oils under simulated cavitation heat generation environment,and the reason why hydraulic oils were oxidized to form solid carbon particles was clarified.(5)Based on theoretical analysis method,the mechanisms of cavitation damage caused by the evolution of cavitation bubbles on metal inner surface of gear pump and other components in its hydraulic system were studied in the process of gas phase dynamic evolution in internal flow field of gear pump.Firstly,the physical denudation effect of cavitation bubbles on small holes in floating side plate of gear pump was analyzed when cavitation bubbles moved in the flow field.Secondly,the negative effects of cavitation heat generation on internal surfaces of gear pump and other hydraulic components were analyzed when cavitation bubbles were compressed in the flow field,such as organic acid chemical corrosion and solid carbon particle scratching etc.Then,the hydraulic shock damage caused by high-speed jet to the inner surface of gear pump and other hydraulic components was analyzed when cavitation bubble was crushed in the flow field.Finally,the mechanisms of cavitation damage to metal inner surface of gear pump and other components in its hydraulic system during the dynamic evolution of cavitation bubbles in gear pump internal flow field were summarized.Results indicated that the CFD numerical calculation model and research method can accurately describe the cavitation of gear pump internal flow field(based on the CB type involute external gear pump).The cavitation degree of gear pump internal flow field would affect the flow output quality of gear pump.Appropriately increasing the suction pressure of gear pump will be beneficial to reduce the cavitation degree of gear pump internal flow field,thereby improving the cavitation damage resistance and flow output quality of gear pump.Increasing the rotational speed of gear pump will increase the cavitation degree of gear pump internal flow field,so that the cavitation damage resistance and flow output quality of gear pump will be both reduced.Controlling the temperature of hydraulic oil inside gear pump to a reasonable temperature range will be beneficial to reduce the cavitation degree of gear pump internal flow field,thereby improving the cavitation damage resistance and flow output quality of gear pump.The by-products of cavitation heat production include organic acids and solid carbon particles,which as an important cause of oxidative deterioration of hydraulic oils.The cavitation damage on metal inner surface of gear pump and other components in its hydraulic system during dynamic evolution is a comprehensive result of multiple damage mechanisms acting on the surface materials of hydraulic components.The mechanism is not a linear superposition of single damage,but is complex coupling of multiple non-linear damage mechanism.The contents and the conclusions from this study can provide important information on theoretical research and engineering application in structural design optimization,output flow quality improvement,cavitation damage prevention of gear pumps. |
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