Multi-fidelity Scramjet Unstart Predictions: From Detailed Numerical Discontinuous Galerkin Simulations to Reduced-Order Models

StableĀair-breathingĀhypersonic flight, at Mach numbers greater than 5, is a promising technology that is poised to have a transformative impact on national security, and beyond. The propulsion systemĀmust operate over a broad range of conditions and, for the low-to-mid range of the hypersonic corridor (Mach numbers between 5 and 15), supersonic combustion ramjets, orĀscramjets,Āprovide superior theoretical propulsion efficiency when compared toĀother air-breathing engines orĀrockets. To broaden the Mach number that a fixed air-breathing engine geometry can fly, it must be able to transition between subsonic (ramjet) and supersonic (scramjet) combustion. The key feature of this dual-modeĀengine is the isolator: a constant-area duct between inlet and combustor. During ram-to-scramjet operationĀa series of reflected oblique shocks,Āknown as a shock train, forms in the isolator. Choking downstream in the combustor can destabilize the shock train and cause it to propagate upstream to the inlet. This process, known as unstart, disrupts the supersonic flow and can cause catastrophic failure. To realize the proposed multi-fidelity prediction approach, tools for high-fidelity scramjet simulations must be developed. Such simulations entail challenges with regards to (i)Āthe incorporation of detailed chemical kinetics; (ii)Āmeshing complex geometries; and (iii)Āefficient computation on heterogeneous machines at exascale. This proposal outlines a multi-fidelity approachĀto build a simulation framework that addresses these challenges. This project will demonstrate the feasibility of this approach by (i) developing a flamlet subgrid model; (ii) performing a high-fidelity simulation of scramjet unstart using the MIRGE-Com library; andĀ(iii) developingĀa reduced-order model of scramjet unstart to facilitate multi-fidelity modeling useful for scramjet design.