Trade-off between propulsive performance and structural integrity in a scramjet under fluid–thermal–structural interaction

The pursuit of high thrust performance in scramjet engines, which are intense thermochemical reactors for hypersonic propulsion, is inherently constrained by the structural integrity of combustor walls under extreme heat loads. This study investigates the fundamental trade-off between propulsive performance and structural durability in a scramjet combustor, focusing on the role of the fuel equivalence ratio (ER). Through high-fidelity numerical simulations of a coated and actively cooled combustor at ERs of 0.1, 0.21, and 0.3, we reveal that the fluid–thermal–structural interaction (FTSI) process, dominated by wall temperature rise, significantly intensifies combustion. This enhancement is evident as a transition to stable combustion at ER = 0.1 and an upstream shift of the shock system at higher ERs. Crucially, the resulting thermal loads dictate the structural response: deformation is primarily driven by thermal expansion, with material nonlinearities (plasticity and creep) becoming severe near the cavity at ER = 0.3. We demonstrate a critical trade-off where the highest specific thrust at ER = 0.3 is accompanied by a high risk of material failure in the substrate. These findings underscore that the operational envelope of such high-intensity energy conversion systems is fundamentally defined by multiphysics coupling. The study provides a critical framework for optimizing the thermal management and fuel strategy of advanced propulsion systems, balancing energy efficiency with structural durability.