Large-Eddy Simulation of a Supersonic Inlet-Isolator

The isolator is an important flow section in a dual-mode scramjet engine that provides stable compressed flow to the combustor. However, if the combustor-induced backpressure exceeds a limiting value, the compression structure inside the isolator could be disgorged, leading to inlet unstart. Numerical tools that can predict unstart would be valuable in the design of robust scramjet engines. Here, the predictive capability of the large-eddy-simulation methodology is assessed by validating against experimental studies of isolator unstart. A conservative finite-difference-based large-eddy-simulation approach incorporating immersed-boundary methodology has been developed for this purpose. Using a variety of numerical schemes, subfilter models, and computational grids, it is demonstrated that large-eddy simulation is able to predict fully started flow quite accurately. Further simulations of unstart configurations indicate that large-eddy simulation is able to capture the large-scale features of the unstart process remarkably well, exhibiting unsteady flow structures nearly identical to the experiment. Quantitatively, large-eddy simulation overpredicts boundary-layer separation that leads to faster shock propagation as compared to experiments.