In this paper,the two-dimensional Rayleigh-Taylor(RT) instability is directly simulated using the moving particle semiimplicit(MPS) method,which is based on the fully Lagrangian description.The objectives of this paper are to investigate preliminarily the effect of viscosity and finite size domain on the evolution of the RT instability.The simulation results demonstrate that(1) the mushroom-like vortex motions are formed in late time due to fluid viscosity,which give rise to the secondary shear flow instability,(2) the finite thickness of the fluid layer limits the development of the RT instability.The above results are consistent with the experiments and theoretical analyses.Meanwhile,the linear growth rate of the RT instability obtained from the numerical simulation is also in agreement with theoretical analyses.And the nonlinear threshold from the simulation result is comparable with the theoretical estimate.Two stages of the nonlinear evolution of the RT instability are revealed in the numerical simulation,nonlinear saturation and turbulent mixing.
