Rayleigh-Taylor(RT)instability widely exists in nature and engineering fields.How to better understand the physical mechanism of RT instability is of great theoretical significance and practical value.At present,abund...Rayleigh-Taylor(RT)instability widely exists in nature and engineering fields.How to better understand the physical mechanism of RT instability is of great theoretical significance and practical value.At present,abundant results of RT instability have been obtained by traditional macroscopic methods.However,research on the thermodynamic non-equilibrium(TNE)effects in the process of system evolution is relatively scarce.In this paper,the discrete Boltzmann method based on non-equilibrium statistical physics is utilized to study the effects of the specific heat ratio on compressible RT instability.The evolution process of the compressible RT system with different specific heat ratios can be analyzed by the 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 y 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.展开更多
Kelvin–Helmholtz(KH)instability is a fundamental fluid instability that widely exists in nature and engineering.To better understand the dynamic process of the KH instability,the influence of the tangential velocity ...Kelvin–Helmholtz(KH)instability is a fundamental fluid instability that widely exists in nature and engineering.To better understand the dynamic process of the KH instability,the influence of the tangential velocity on the compressible KH instability is investigated by using the discrete Boltzmann method based on the nonequilibrium statistical physics.Both hydrodynamic and thermodynamic nonequilibrium(TNE)effects are probed and analyzed.It is found that,on the whole,the global density gradients,the TNE strength and area firstly increase and decrease afterwards.Both the global density gradient and heat flux intensity in the vertical direction are almost constant in the initial stage before a vortex forms.Moreover,with the increase of the tangential velocity,the KH instability evolves faster,hence the global density gradients,the TNE strength and area increase in the initial stage and achieve their peak earlier,and their maxima are higher for a larger tangential velocity.Physically,there are several competitive mechanisms in the evolution of the KH instability.(i)The physical gradients increase and the TNE effects are strengthened as the interface is elongated.The local physical gradients decrease and the local TNE intensity is weakened on account of the dissipation and/or diffusion.(ii)The global heat flux intensity is promoted when the physical gradients increase.As the contact area expands,the heat exchange is enhanced and the global heat flux intensity increases.(iii)The global TNE intensity reduces with the decreasing of physical gradients and increase with the increasing of TNE area.(iv)The nonequilibrium area increases as the fluid interface is elongated and is widened because of the dissipation and/or diffusion.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51806116 and 11875001)the Natural Science Foundation of Fujian Province(Grant No.2018J01654).
文摘Rayleigh-Taylor(RT)instability widely exists in nature and engineering fields.How to better understand the physical mechanism of RT instability is of great theoretical significance and practical value.At present,abundant results of RT instability have been obtained by traditional macroscopic methods.However,research on the thermodynamic non-equilibrium(TNE)effects in the process of system evolution is relatively scarce.In this paper,the discrete Boltzmann method based on non-equilibrium statistical physics is utilized to study the effects of the specific heat ratio on compressible RT instability.The evolution process of the compressible RT system with different specific heat ratios can be analyzed by the 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 y 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.
基金supported by the National Natural Science Foundation of China(Grant Nos.51806116 and 11875001)the Natural Science Foundation of Fujian Provinces(Grant Nos.2021J01652 and 2021J01655).
文摘Kelvin–Helmholtz(KH)instability is a fundamental fluid instability that widely exists in nature and engineering.To better understand the dynamic process of the KH instability,the influence of the tangential velocity on the compressible KH instability is investigated by using the discrete Boltzmann method based on the nonequilibrium statistical physics.Both hydrodynamic and thermodynamic nonequilibrium(TNE)effects are probed and analyzed.It is found that,on the whole,the global density gradients,the TNE strength and area firstly increase and decrease afterwards.Both the global density gradient and heat flux intensity in the vertical direction are almost constant in the initial stage before a vortex forms.Moreover,with the increase of the tangential velocity,the KH instability evolves faster,hence the global density gradients,the TNE strength and area increase in the initial stage and achieve their peak earlier,and their maxima are higher for a larger tangential velocity.Physically,there are several competitive mechanisms in the evolution of the KH instability.(i)The physical gradients increase and the TNE effects are strengthened as the interface is elongated.The local physical gradients decrease and the local TNE intensity is weakened on account of the dissipation and/or diffusion.(ii)The global heat flux intensity is promoted when the physical gradients increase.As the contact area expands,the heat exchange is enhanced and the global heat flux intensity increases.(iii)The global TNE intensity reduces with the decreasing of physical gradients and increase with the increasing of TNE area.(iv)The nonequilibrium area increases as the fluid interface is elongated and is widened because of the dissipation and/or diffusion.
