The coupled heat transfer of supercritical-pressure $n$-decane in a concave heated, 90 deg bend, square channel was investigated numerically. Both the geometry and boundary conditions were close to those expected in active-cooled scramjet engines. The effect of secondary motions and wall thermal conductivity on heat transfer was studied. The flowfields obtained by the Spalart–Allmaras model and Reynolds stress model were compared. The secondary flow of Prandtl’s first kind caused by the crosswise pressure gradient in the curved section was 1.0% of the maximum axial velocity. The secondary flow of Prandtl’s second kind caused by Reynolds stress was one magnitude less than that of Prandtl’s first kind. The Spalart–Allmaras turbulence model produced reasonable results with less computational effort than the Reynolds stress model. Secondary flow improves heat transfer by enhancing the mixing of the fluid. Furthermore, higher wall thermal conductivity produces more uniformly distributed temperature and heat flux.

The feasibility of regenerative cooling technology in scramjet engines has been verified, while the heat transfer behavior involved in the process needs further study. This paper expounds on the necessity of coupled heat-transfer analysis and summarizes its research progress. The results show that the effect of pyrolysis on heat transfer in the cooling channel depends on the heat flux and coking rate, and the coupling relationship between combustion and heat transfer is closely related to the fuel flow rate. Therefore, we confirm that regulating the cooling channel layout according to the real heat-flux distribution, suppressing coking, and accurately controlling the fuel flow rate can contribute to accomplishing the optimal collaborative design of cooling performance and combustion performance. Finally, a conjugate thermal analysis model can be used to evaluate the performance of various thermal protection systems.

To investigate the combustion modes and unsteady characteristics during the condition transition of a scramjet combustor, a series of experiments were carried out under the condition of Mach 2.52 supersonic incoming flow, the corresponding stagnation pressure and temperature of which were 1.6 MPa and 1486 K, respectively. A fuel supply system that could dynamically adjust the injection pressure was adopted to simulate the condition transition stage of a scramjet. Based on the advanced combustion diagnosis technique, the transient chemiluminescence image and the wall pressure were recorded during the whole combustion process. Three typical modes of turbulent combustion occurred when the injection pressure drop gradually increased. The jet flame was stable after the condition transition when the injection pressure drop was relatively low. An unstable combustion phenomenon accompanied by intermittent local extinction and reignition could be found near the blowout limits. With a further increase in the injection pressure drop, the flame was blown out quickly during the transition process. In addition, the flame development characteristics during condition transition under stable combustion mode and the effect of injection pressure drop were studied in detail. During the process of switching between the two conditions, the area and light intensity of the flame decreased over time, and the wall pressure was accordingly reduced. As the increase in injection pressure dropped, the intensity of chemical reactions deceased obviously and the transition time became longer.