Numerical Particle Tracing Research Of Rayleigh-Taylor Instability Induced Complex Flow And Mixing

Rayleigh-Taylor-instability(RTI)induced flow and mixing are of great im-portance both in nature and engineering scenarios,including the invasion of salt-water in the coastal area,the mixing of materials in chemical engineering,and the successful ignition of inertial confinement fusion.As a simplified and easy-to-implement framework,the single-fluid model has been widely utilized in RTI research.However,this model is not capable of capturing complex flow details and mixing of different components,which makes it hard for further RTI mix-ing investigation.Therefore,a novel method is desired to compensate for this inaccessibility of single-fluid modelFirstly,a single-fluid discrete Boltzmann method is utilized to model fluid flow kinetically and simulate the single fluid(miscible)RTI.Meanwhile,one-way coupled point particles are introduced as tracers for the complex flow and mixing process.The tracer particles make possible to observe finer structures with clear interfaces in the late mixing stage.One can clearly observe the flow field evolu-tion and distinguish tracer particles from the heavy or light fluids clearly.In this way,tracer particle successfully delineates detailed morphological information of the flow field.Also combining with the image of the thermodynamic nonequilib-rium behavior around the interfaces provided by particle tracking,tracer particles provide a new investigating angle for RTI.Via the defined local mixedness,from densities of two kinds of particles,we quantitatively describe the mixing status of the system,and capture the appearance position of as well as indicate the in-tensity of Kelvin-Helmholtz instability.Finally,the effects of compressibility and viscosity on mixing are investigated separately.Both of them show two-stage effects on the mixing process.The underlying mechanism of these two-stage ef-fects is interpreted as that a "hard" system with low compressibility and/or high viscosity is beneficial to the development of large structures at the initial stage and a“soft”system with high compressibility and/or low viscosity is favorable for the generation of small structures at the late stage.At the late stage,for a fixed time,the field averaged mixedness exponentially decreases with the viscosity,which indicates the existence of a characteristic viscosity ?0 during the instability development.Results in this paper help understand the mechanism of complex compressible flow and mixing under Rayleigh-Taylor instability scope and present references for related particle tracking experiments.