Thermal and drag reduction performance evaluation of a cavity-based scramjet combustor cooled by distributed hydrocarbon film

Highly robust and efficient cooling methods are crucial to the thermal protection of cavity-based scramjet combustor. In this work, a novel distributed gas film cooling method using the reacting coolant, n-Decane is proposed for a cavity-based scramjet combustor. The effect of reacting film coolant distribution on thermal and drag reduction performance is comprehensively analyzed to provide deep insights into the intrinsic coupling relationship between chemical reactions, flow structure and boundary layer heat transfer processes. The findings indicate that compared with the non-reacting gas film, the reacting gas film using n-Decane renders much lower wall temperature as well as lower wall shear stress. The cooling efficiency increases by as much as 43% at the exit of the scramjet combustor for the reacting gas film. In order to evaluate the effectiveness of the distributed gas film cooling method, the cooling and drag reduction performances of the distributed gas film cooling cases are compared with the single-stage gas film cooling case. With a fixed mass flow rate of the gaseous coolant, the conventional single gas film stream is split up into two streams of gaseous film injected from two independent injectors located in the cavity and the main combustor, respectively. It is found that that the cooling performance and the drag reduction performance are both improved when the distributed film cooling method is used. For the optimized distributed gas film cooling case, the weighted cooling efficiency increases by 5.66% while the wall shear stress decreases by 10.87% when compared with the single-stage gas film cooling case although the same total amount of coolant is used. This work indicate that the distributed film cooling is feasible in realizing collaborative optimization of cooling and drag reduction for the scramjet combustor via flow field re-organization and coolant re-distribution.