Effects Of Knudsen Numbers And Perturbed Interfaces On RT Instability

Rayleigh-Taylor(RT)instability exists widely in nature and engineering,such as the inertial confinement fusion,the Z-pinch plasma,the quantum magnetized plasma,the colloid admixture.It is well known that the RT instability in fluid mechanics still has many problems to be solved.Some specific images and laws can be well obtained through the theoretical study.But it requires specific assumptions,and the consideration is relatively simple,resulting in a great difference between the obtained laws and the actual situation.However,the experimental methods often encounter such as the high price of experimental equipment,the poor repeatability,and even the high risk of operation.With the rapid development of computing science,numerical simulation which has the advantages of less investment,short cycle and reproducibility,has become the favor of the majority of researchers and engineers.For this reason,the effects of Knudsen number,amplitude,and transition layer on RT instability are studied by the mesoscopic numerical simulation.The main research contents are as follows:In chapter 1,the research status of the RT instability at home and abroad is reviewed,and the development history and application progress of the discrete Boltzmann method(DBM)used in this paper is also reviewed.In chapter 2,the derivation process of the DBM model which is used to study the RT instability and the mathematical description of the nonequilibrium information extraction are given.This model can not only describe the macroscopic hydrodynamic behavior,but also study the thermodynamic nonequilibrium effect which is closely related to the fluid flow behavior in detail.In chapter 3,the Knudsen number(₂)effect on the RT instability in compressible fluid is studied.The results show that₂has an inhibitory effect on the RT instability,and the larger the value of₂,the more obvious the later developed Kelvin-Helmholtz instability,the faster the mushroom-like shape appears,and the more significant the ther-modynamic nonequilibrium effect.Due to the the initial settings,the total thermodynamic nonequilibrium strength of the system decreases first,then increases exponentially,and then increases slowly.At a place far from the disturbed interface,the nonequilibrium strength is basically zero,and the nonequilibrium effect is mainly concentrated on both sides of the interface,which is closely related to the gradient of macroscopic quantities.The study of this part is helpful to understand the physical nature of nonlinear multi-scale nonequilibrium of Knudsen number effect on the RT instability.In chapter 4,the amplitude effect on the RT instability of compressible fluid is studied.The effects of different initial amplitudes on the RT instability are shown as follows:firstly,the larger the initial amplitude is,the larger overall density gradient is.At the later stage of evolution,the density gradient of the system becomes smaller with the increase of the initial amplitude.Secondly,the proportion of the nonequilibrium region of the system shows a change law similar to the density gradient of the system.Moreover,the results also show that the density gradient at a certain moment has an exponential function relationship with the initial amplitude,and the proportion of the thermodynamic nonequilibrium region of the system also shows a similar trend with the initial amplitude.These results can help us to better understand the internal kinetic mechanism of amplitude effect on the RT instability of compressible fluids,and provide a physical reference for promoting or suppressing the RT instability.In chapter 5,the effect of transition layer on the RT instability of compressible fluid is studied.The influence of different initial transition layers on the RT instability is shown as follows:firstly,in the early stage of system evolution,the larger the initial transition layer,the smaller the density gradient,at the later stage of evolution,the larger the initial transition layer,the larger the density gradient of the system.Secondly,the nonequilibrium area ratio of the system shows a similar trend to the density gradient of the system.Furthermore,the density gradient at a certain moment has a quadratic function relation with the initial transition layer,and the proportion of nonequilibrium region in the system also has a quadratic function relation with the initial transition layer.These results enrich our physical understanding of the transition layer effect,and provide theoretical reference and scientific basis for the improvement of existing macroscopic continuous modeling,and the application of inertial confinement fusion,and other related national defense projects.In chapter 6,a general summary of the research work is summarized,and the future research work on the correlation of the compressible RT instability is prospected.