Large eddy simulation of vortex structure evolution, flow, and heat transfer characteristics in hydrocarbon fuel boundary layer combustion

Hypersonic flight increases the aerodynamic-thermal loads on propulsion systems, representing a principal bottleneck to performance advancement. Film-boundary-layer combustion using large-molecule hydrocarbon fuels, which simultaneously provides film cooling and combustion-induced drag reduction, is a promising technology to overcome this limitation. This study employs large-eddy simulation to examine C10H22 film-boundary-layer combustion at a mainstream (Ma = 1.75) and coolant (Ma = 1.22). Drag-reduction performance, vortex-structure evolution, and heat-transfer characteristics are contrasted between cases with and without film combustion, and the effects of dynamic pressure ratios of 0.11, 0.15, and 0.17 on these metrics are evaluated. Results show that boundary-layer combustion reduces turbulent kinetic energy in the mixing layer and decreases the wall skin-friction coefficient by roughly 20% relative to the non-reacting case. Vortex structures are zonally organized: near-wall regions are dominated by quasi-streamwise vortices, the outer layer by Ω-shaped vortices, and a transitional mid-layer exhibits multiscale vortex coexistence. Oxidative-cracking chemistry produces zonal wall-temperature responses: an initial region with negligible change, a cracking-dominated endothermic cooling region, and an oxidation-dominated region with slight warming but overall enhanced cooling. Within a certain range, increasing the dynamic pressure ratio aids drag reduction but weakens film cooling; a ratio of 0.15 achieves the best trade-off.