Boundary Layer Transition and Re-Laminarization in the Nozzle of a Shock Tunnel – a Numerical Study

The boundary layer behavior in hypersonic nozzle of a shock tunnel has been investigated by means of the computational fluid dynamics simulations. The state of boundary layer at the nozzle outlet can highly affect the downstream flow passing around the test model in the shock tunnel test section. The formation of shock and expansion wave systems towards the downstream diaphragm and the reflection and expansion waves towards the upstream shock tube were well-simulated after the diaphragm rupture. Focusing on the transitional boundary layer simulation, results of the optimal nozzle's steady-state flow indicate that the boundary layer enters the throat region, undergoes a phase transition, and then returns to a laminar state due to re-acceleration. The turbulence intensity in this region, coupled with the width of the transition zone, increases with higher upstream stagnation pressure. Furthermore, simulation of the unsteady starting flow shows that the passage time of unsteady waves and the quasi-steady region, have good agreement with the experimental results.