Starting transient flows in a chevron ejector-diffuser system

The vacuum ejector-diffuser system has been widely used in many applications such as refrigeration systems, high altitude test facilities and fluid transportation devices. We simulated the starting transient flows of a supersonic vacuum ejector-diffuser system and its performance characteristics and analyzed by the numerical methods. Newly designed chevron lobes were installed at the inlet of the primary stream of the vacuum ejector-diffuser system for the purpose of its performance improvement. A CFD method based on transient scheme was applied to simulate the equilibrium flow behavior inside the secondary chamber. Primary numerical analysis results show that the performance of the vacuum ejector-diffuser system is considerably improved under chevron effects. Compared to the conventional ejector-diffuser system with a convergent nozzle, the updated system with a chevron nozzle leads to a lower equilibrium pressure inside the secondary chamber with less starting time. The flow characteristics obtained from the numerical results highlight the importance of the vortex generation effects of the chevron nozzle. The generation process of the longitudinal vortexes and its effects on the ejector-diffuser performance has been discussed in detail.