Numerical Investigation of Pre-evacuation Influences of Second Throat Exhaust Diffuser

In this paper, the influences of regional pre-evacuation of an altitude test facility on starting time of a second throat supersonic exhaust diffuser are numerically investigated. Detailed numerical studies have been carried out to evaluate the physics of the flow and starting time of the diffuser for different pre-evacuation zones along the diffuser and the test chamber. Unsteady axisymmetric compressible Navier–Stokes equations, incorporated with the two equation kω-SST turbulence model are solved, with density-based solver to extract the current flow features. The numerical method is properly validated with the measured data available in the literature. Our investigations show that the amount of pre-evacuation volume has strong effects on starting time of the diffuser. As we extend pre-evacuation zone along the diffuser, the smaller starting time of diffuser is resulted. However, the increasing of pre-evacuated test chamber size causes the increasing of starting time of the diffuser.