Modification And Application Of Cavitation Model Considering Thermodynamic Effect

Cavitation is the phenomenon that the liquid vaporizes into vapour when the local pressure of liquid is lower than the vapour pressure in the process.The latent heat of vaporization is absorbed by liquid with vaporization,resulting the temperature difference between vapour and liquid,which will affect the formation and development of bubbles,namely the thermodynamic effect of cavitation.In the design of liquid rocket turbopump,due to the difficulty in carrying out low temperature tests,the normal method under water is used to design and test at present,which results the actual flow state and cavitation characteristics of it can't be predicted accurately.Therefore,mastering the numerical calculation method of water and liquid hydrogen cavitation flow and establishing the qualitative and quantitative relationship between liquid hydrogen and water cavitation characteristics have practical application value for the development of cavitation simulation technology and important engineering significance for improving the design level of hydrogen inducer.Mainly based on the data of Cervone's cavitation test and taking NACA0015 airfoil as the research object,this thesis studies the applicability of different cavitation models in water and liquid hydrogen and the influence of temperature,flow parameters and the thermodynamic effect on water and liquid hydrogen under considering thermodynamic effect.Based on the thermal equilibrium of single bubble and the Fourier law of the temperature boundary layer,developing a method of modifying the bubble radius by thermodynamic effects.And a method of correcting the local saturated vapour pressure by thermodynamic effects was developed based on the thermal balance of the two phases and the B factory theory.The second development of CFX software are carried out using CEL language then two thermodynamically modified Zwart cavitation models are established and are used to simulate the cavitation flow around the NACA0015 hydrofoil in water at 343.15 K.The cavitation flow simulation results show that the two modified methods can effectively characterize the influence of the thermodynamic effect in the cavitation process and have a good consistency.The first method is only applicable to the cavitation model with the change rate of cavitation radius in the cavitation source term.So we use the second method to modify different cavitation models.Taking NACA0015 airfoil as the research object,the applicability of Zwart,Merkle,Schnerr-Sauer and Kunz modified by thermodynamic effect in water cavitation flow wasanalyzed.Based on the test data of Hord's hydrogen cavitation and taking the test hydrofoil as the research object,the applicability of the above four cavitation models considering thermodynamic effect in hydrogen cavitation flow was analyzed.The results show that only Kunz model can predict liquid hydrogen cavitation flow.According to the data of liquid hydrogen cavitation test carried out by Hord,the coefficients of Zwart,Merkle and Schnerr-Sauer are modified.On this basis,the difference between the four cavitation model in liquid hydrogen cavitation flow is analyzed and the applicability of each model in water and hydrogen is compared.The Merkle model has the smallest simulation error and the highest calculation efficiency in water cavitation flow.It is the most adaptable to the water cavitation simulation.In liquid hydrogen cavitation flow,the error of pressure simulation of Merkle model is slightly larger than that of Kunz model,but it is also has good applicability.The Kunz model is not applicable to water cavitation flow simulation but in the liquid hydrogen cavitation flow it has the smallest simulation error and the strongest applicability.The Zwart model has the stronger applicability in water cavitation flow but in the liquid hydrogen cavitation flow it has the largest simulation error,the lowest calculation efficiency and the worest applicability.The Schnerr-Sauer model has the largest simulation error,the longest calculation time and the worest applicability in water cavitation flow.It also has the higher simulation error and poor applicability in liquid hydrogen cavitation flow.Based on the simulation results of liquid hydrogen and water with different cavitation model considering thermodynamic effect,it is found that Merkle model has good applicability in both liquid hydrogen and water.Merkle cavitation model which has good applicability in both liquid hydrogen and water was selected to calculate the cavitation flow of water and liquid hydrogen around NACA0015 hydrofoil.The difference of the influence of temperature,flow parameters and thermodynamic effect on the cavitation flow of liquid hydrogen and water was analyzed in this study.The results show that when the temperature change is small,the inlet cavitation number can approximately represent the degree of cavitation,and the variation law each parameter in liquid hydrogen and water with cavitation number is similar.The thermodynamic effect increases with the increase of temperature.The liquid hydrogen cavitation flow phenomenon is similar to high-temperature water and the liquid hydrogen shows more obvious thermodynamic effect in cavitation flow.