Numerical Study on the Non-Oscillatory Unstarted Flow in a Scramjet Inlet-Isolator Model

For successful scramjet engine operations, it is important to understand the mechanism of the inlet unstart phenomenon. Among various unstarted flow patterns in hypersonic inlets, the mechanism of low-amplitude oscillatory unstarted flow is still unclear. Therefore, in the present study, the flow characteristics of non-oscillatory unstarted flow in a scramjet inlet-isolator model are studied by using numerical analysis with the RANS-based OpenFOAM solver. In the numerical results, the amplitude of pressure oscillation and the average pressure near the model outlet are in good agreement with experimental results. In the detailed analysis of the results, it is found that the incoming flow within the boundary layers repeatedly changes direction due to the flow blockage at the end of the model. In these direction-changing processes, recirculation zones near the walls irregularly influence the choked flow zones at the rear part of the model. These irregular behaviors result in non-oscillatory unstarted flow. Additionally, the main differences between the high-amplitude oscillatory unstarted flow and non-oscillatory unstarted flow are addressed.