Experimental And Numerical Simulation Of Cavitation Flow In Salt Water

Cavitation phenomenon widely exists in hydraulic machinery,which affects the safe and stable operation of hydraulic machinery.Liquid medium is an important factor affecting cavitation.Research shows that cavitation in non clean water environment is more likely to occur.Based on the engineering background of seawater backflow into coastal rivers and the hydraulic utilization of marine energy,this paper focuses on the non clear water medium environment containing salt in water,and carries out the research on the cavitation characteristics of salt water.Firstly,it is determined that the medium representative of salt water is sodium chloride(NaCl)solution,and the medium properties of NaCl solution with different mass fraction is studied.The density,viscosity and saturated vapor pressure of the medium are measured experimentally,the quantitative relationship between the medium parameters of NaCl solution and its mass fraction is obtained.Secondly,taking the cavitating flow in venturi tube as the research object,the experimental study of clean water and NaCl solution with different mass fraction is carried out.The cavitation phenomenon is recorded by high speed photography,and the cavitation characteristics under different medium and different flow conditions are obtained.The length of cavitation flow direction in venturi tube is used to reflect the degree of cavitation,the development and change law of cavitation at different times is analyzed,and the relationship between the occurrence and development of cavitation in Venturi tube and medium properties is studied.Then,the numerical simulation of cavitation in venturi tube is carried out.Complete the comparison and selection of turbulence models and determine the SST-CC model.Based on the ZGB cavitation model commonly used in engineering,the numerical results of cavitation flow field in clear water are obtained,which are consistent with the experiment.However,there is a deviation between the calculated results of cavitation flow field in NaCl solution and the experiment,and the difference is significant with the increase of solution mass fraction.The correction scheme of empirical coefficient of cavitation model is studied,and the quantitative relationship between evaporation coefficient Fvap of ZGB model and mass fraction of NaCl solution is constructed,which improves the prediction accuracy of cavitation in NaCl solution.The cavitation development characteristics in NaCl solution are obtained,which provides a calculation method for cavitation simulation in NaCl solution.Finally,using the ZGB cavitation model modified based on NaCl solution and taking the centrifugal pump as the research object,the numerical simulation of clean water and NaCl solution with different mass fraction is carried out.Comparing the energy characteristics of centrifugal pump in different fluid medium,with the increase of mass fraction of NaCl solution,the drop point of centrifugal pump head becomes earlier and the drop speed is faster.The characteristics of cavitation flow field in centrifugal pump in different fluid medium are analyzed.Under the same pump working condition,the cavitation area in the impeller increases with the increase of NaCl solution mass fraction.The salt in the water restricts the cavitation performance of the pump,the amplitude of pressure fluctuation decreases.The influence law of medium properties on cavitation of centrifugal pump is obtained by using the modified cavitation model,which provides a practical numerical calculation method for engineering application.The research results obtained in this paper lay a foundation for reasonably predicting the cavitation flow field in salt water,and have important scientific significance for revealing the mechanical cavitation characteristics of seawater medium or salt water.