Influence Of The Specific Heat Ratio And Acceleration On The Non-equilibrium Rayleigh-Taylor Instability

Rayleigh-Taylor(RT)instability phenomenon exists widely in nature and engineering fields.There are complex thermodynamic and hydrodynamic non-equilibrium effects in the process of its occurrence.It is of great theoretical significance and practical value to clearly understand the physical mechanism of the RT instability.However,accurately describing the complex physical phenomena in fluid system evolution poses great challenges to traditional models.In this paper,we use the discrete Boltzmann method(DBM)to study the RT instability,and its main contents are as follows:In Chapter 1,the research background and development history of RT instability are introduced.And we discuss the development of the discrete Boltzmann method,describe the modeling idea and solution method of it,and then explain its advantages compared with traditional fluid model.In Chapter 2,the modeling process of DBM is briefly introduced.DBM is a mesoscopic kinetic method based on statistical physics.Its modeling process includes three steps: simplification of collision terms,dispersion of particle velocities,and extraction of thermodynamic non-equilibrium information.Through these steps,unextractable information can be stratified and quantitatively studied.In Chapter 3,the RT instability under different specific heat ratios are simulated by using the DBM,and the evolution process of the compressible RT system under different specific heat ratios was further clarified by analyzing the global temperature gradient and the proportion of the non-equilibrium region.Firstly,as a result of the competition between the macroscopic magnitude gradient and the non-equilibrium region,the average TNE intensity first increases and then reduces,and it increases with the specific heat ratio decreasing;the specific heat ratio has the same effect on the global strength of the viscous stress tensor.Secondly,the moment when the total temperature gradient in direction deviates from the fixed value can be regarded as a physical criterion for judging the formation of the vortex structure.Thirdly,under the competition between the temperature gradients and the contact area of the two fluids,the average intensity of the non-equilibrium quantity related to the heat flux shows diversity,and the influence of the specific heat ratio is also quite remarkable.In Chapter 4,the evolution of the RT instability under different acceleration are studied.The effects of acceleration on RT instability is as follows: First,in the early stage of,the greater the acceleration,the greater the global temperature gradient of the fluid system.Furthermore,the relationship between the acceleration and global average temperature gradient is exponential.And in the later stage,the temperature gradient will be smaller.Secondly,with the increase of acceleration,the maximum Mach number increases in the early stage and decreases in the later stage.What’s more,it can be seen from the2 D contour diagram that the Mach number in the middle and two sides of the system is the largest.Finally,the non-equilibrium strength of the system also decreases with the increase of the acceleration and the relationship between the two increases exponentially in the early stage,similarly,there is an opposite trend in the late stage.In Chapter 5,the compressible RT instability with random multimode initial perturbations at continuous interfaces is numerically investigated by means of the DBM.The results show that with the influence of temperature gradient,the thermodynamic nonequilibrium strength related to heat flux firstly increases and then decreases.Under the action of thermal diffusion,the thermodynamic non-equilibrium strength at the interface firstly decreases and then increases,which affects the time evolution of proportion of the thermodynamic non-equilibrium region.In this respect,effects of temperature gradient and thermal diffusion on the time evolution trend of non-equilibrium strength at the interface are the same.Finally,we analyze the time evolution of the global average thermodynamic non-equilibrium strength,and find that under the joint action of macroscopic physical gradients and thermodynamic non-equilibrium area,the global average thermodynamic non-equilibrium strength firstly increases,then decreases,and finally tends to be stable.On the one hand,the increase(decrease)of the area of thermodynamic nonequilibrium region will increase(decrease)the strength of thermodynamic non-equilibrium.On the other hand,the increase(decrease)of physical gradients at the material interface also has the same effect on the global average thermodynamic non-equilibrium strength.The two physical mechanisms interact and compete with each other.In Chapter 6,the paper summarized the above research,the lack of research nowadays is reflected,and then the future research work is envisaged.