DSMC simulation of instability of plane supersonic jet in coflow

The Direct Simulation Monte Carlo (DSMC) method is used for numerical simulation, at the molecular-kinetic level, of instability development in a plane supersonic jet exhausting into a coflow. The flowfields obtained in computations with a large number of test particles after their averaging over a small time interval almost coincide with the data of continuum simulations. The results show that sinuous instability is developed at subsonic convective Mach numbers, which means that disturbances of the antisymmetric mode are the most unstable ones. Typical nonlinear interactions of vortices are observed in the form of their roll-up around each other and pairwise merging. The mean velocity profiles reveal that mixing layers rapidly merge together, after which the jet velocity decreases and the jet width increases. By the end of the computational domain the velocity at the jet axis decreases approximately by a factor of 1.5, and the mean velocity profile becomes bell-shaped, which is typical for a developed jet flow. In the case of a supersonic convective Mach number, the sinuous instability corresponding to the antisymmetric mode is also excited. The structures formed in this case are sufficiently larger, and the jet breakup occurs at smaller distances from the nozzle exit. The flow dynamics is significantly affected by shock waves formed near vortices moving with a supersonic velocity with respect to the coflow.