Spatiotemporal evolution and instability of the mixing layer in supersonic ejector based on large eddy simulation

In this paper, the spatiotemporal evolution and the instability of the turbulence mixing layer in a supersonic ejector are deeply studied based on large eddy simulation. Time-averaged distributions and transient results are discussed based on mixed fluids. In particular, the general flow characteristics are identified through the examination of the spatiotemporal evolution of temperature, entropy, Mach number, and density gradient fields. A thin shear layer is gradually formed, and several ring vortices are effectively captured at the lip of the nozzle. Surprisingly, the annular vortex gradually evolves into a V-shaped vortex with time evolution, which reveals that the transition of turbulence occurs in the first half of the mixing chamber. It is found that the supersonic mixing layer exhibits slow growth initially, and a significant increase in velocity is effectively captured at the throat position based on time averaged velocity profiles. A similar trend is also evident in the transition region of the supersonic ejector throat. The mixing of motive flow and suction flow is effectively enhanced by a shock train generated within the diffusion chamber. A recirculation region is created, which leads to a narrowing of the potential core of the jet, and the symmetry of the flow is broken due to the shock location. It is further found that the instability of the main jet is the dominant factor in the fluid mixing process by studying the power spectrum of the pressure signal and characteristic frequency inside the mixing chamber. It further provides important physical insights into understanding the spatiotemporal evolution of internal turbulence and the mixing mechanism in the supersonic steam ejector.