| In recent years,with the expansion and the development of China's energy industry,Liquefied Natural Gas(LNG),as a new type of industry,has achieved rapid development.LNG submersible pump is widely used in the process of production,transportation and utilization of LNG.Its rotational speed is very high and the medium is cryogenic fluids,so that the cavitation is very easy to occur in the pump which affects the performance of the LNG submersible pump.The cavitation of the LNG submersible pump improves the higher requirements of the performance,and the design of LNG submersible pumps is difficult.Besides,the problem of the cryogenic fluid cavitation is also the key scientific problem concerned in the production,storage and transport system of cryogenic fluids related to liquefied natural gas.It is of great theoretical significance and engineering application value to further reveal the mechanism of the cavitation in cryogenic fluids and to master the flow characteristics.This research in this paper was supported by the National Natural Science Foundation of China(51776087)and the Key Research and Development Project of Jiangsu Provincial(Key Project)(BE2015001-3).This research focused on the mechanism of the effect of thermodynamic effect on the cavitation,and a modified cavitation model was used to study the flow characteristics of cavitation with different working temperatures and different media.The main work and innovation of this paper are as followed:(1)The modification and verification of cavitation models considering the thermodynamic effectThis paper focused on the effect of the thermodynamic effect on the cavitation.Based on the current cavitation models and combining the B factor theory and the thermodynamic equilibrium hypothesis,and using the Antoine equation,the modified cavitation models considering the thermodynamic effect was derived,which based on the Rayleigh-Plesset equation and can be used to calculate the cavitation two-phase flow.The loading of the cavitation models in the numerical simulation solver was realized by using the CEL language.(2)The effect of thermodynamic effect on the cavitation in water at different temperaturesThree typical cavitation models of Zwart,Merkle,Singhal and their corresponding modified cavitation models considering the thermodynamic effect were used to simulate the cavitation flow around the NACA0015 hydrofoil in water at temperature 25?,50?and 70?,respectively,the simulation results were compared with the experimental data.From the root mean square error analysis and comprehensive evaluation of the simulation results,it is found that the simulation results with the Merkle model and the modified Merkle model are close to the experimental values,and the applicability of that is stronger.It is verified that the applicability of the cavitation models and the feasibility of modified method about the cavitation models considering the thermodynamic effect in the numerical simulation of cavitation which occurs in different temperature water.The numerical simulation results show that,compared with the isothermal condition,when the thermodynamic effect is considered,the saturated vapor pressure reduces because of the decrease of the temperature in the cavity in the water under different temperature,which result in the weakening of the cavitation intensity and the shortening of the cavity length mainly due to source term about the effect of the thermodynamic effects added to the cavitation model.At the same time,with the increase of water temperature,the temperature depression in the cavity decreases,the pressure depression increases,and the corresponding cavitation intensity decreases and the cavity length shorten.Although the corresponding far field cavitation number?_?of the three are same,the local cavitation number?_c in the corresponding cavity increases with the increase of water temperature,which is the better representation of the differences in the cavitation intensity.In the process of interphase mass transfer,the mass of evaporation increases and the mass of condensation decreases with the increase of temperature,which more truly reflects the effect of thermodynamic effect on the cavitation in different temperature water.(3)The effect of thermodynamic effect on the cavitation in cryogenic fluids and the mechanism of cryogenic cavitation flowThree typical cavitation models of Zwart,Merkle,Singhal and the Merkle modified cavitation models considering the thermodynamic effect were also used to simulate the cavitation flow around the hydrofoil in the liquid nitrogen at 83.06K and77.64K,respectively,the simulation results were compared with the experimental data.From the comprehensive evaluation of the error of numerical simulation and experimental results,it is also found that the simulation results with the Merkle model and the modified Merkle cavitation model are close to the experimental values.The numerical simulation of the pressure and temperature distribution of the hydrofoil surface is more consistent with the experimental data and the law of the experimental phenomena,and the accuracy of the modified cavitation model is verified.It is also verified that the applicability of the cavitation models and the feasibility of modified method about the cavitation models considering the thermodynamic effect in the numerical simulation of cavitation which occurs in cryogenic fluids.The numerical simulation results show that,compared with the isothermal condition,when the thermodynamic effect is considered,the saturated vapor pressure reduces because of the decrease of the temperature in the cavity in the liquid nitrogen under different temperature,which result in the weakening of the cavitation intensity,the shortening of the cavity length,the mass of the evaporation is increased and the mass of condensation is reduced.Meanwhile compared with that at 77.64K,the temperature depression in the cavity is more,the corresponding pressure depression is larger,the cavitation intensity is relatively weaker,the shortening of the cavity length is more and the vapor volume fraction in the cavity is lower in the liquid nitrogen at 83.06K,but the local cavitation number?_c is higher than that of the liquid nitrogen at 77.64K,which is the better representation of the differences in the cavitation intensity than the far field cavitation number?_?.At the same time,the more temperature depression in the cavity in the liquid nitrogen at 83.06K that makes the value of additional source term about the thermodynamics effect larger,the corresponding decrease of condensation mass more in the interphase mass transfer and the gradient of condensation mass greater than that at 77.64K,which well reflects the effect of thermodynamic effect on the cavitation in cryogenic fluids.The results of this paper have a good understanding of the thermodynamic effect in the cavitation,and it has a relatively high reference value for accurately predicting the cavitation characteristics of the cryogenic fluids,and lays a good foundation for the study of the cavitation occurring in the fluid machinery of cryogenic fluids,such as the LNG submersible pump,and has a good value for promotion and application. |
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