Numerical study on heat transfer and thermomechanical response characteristics of C/SiC Cooling Channel in RBCC combustor

Carbon fiber-reinforced silicon carbide (C/SiC) composites combine low density with excellent high-temperature resistance, making them promising candidates for regenerative cooling structures, where thermal endurance and weight reduction are critical. This study investigates the flow and heat transfer and thermomehanical response of single channels in the regenerative cooling system of a rocket-based combined cycle (RBCC) engine, considering different solid materials (GH3536 and C/SiC) and structural configurations. Results show that C/SiC-based channel designs demonstrate clear advantages in both thermal protection and thermomechanical reliability. Under the present operating conditions, replacing GH3536 with C/SiC raises the maximum allowable heated-wall temperature from about 1273 K to about 2073 K, increasing the thermal safety margin from 21.45% to 39.70%, which corresponds to an improvement of nearly 20 percentage points. More importantly, in the C/SiC+GH3536 hybrid structure, the relatively low radial thermal conductivity of C/SiC reshapes the wall heat-flux distribution through a fin-effect-driven thermal regulation mechanism, thereby lowering the temperature of the outer GH3536 layer while simultaneously promoting coolant cracking, increasing the convective heat transfer coefficient, and improving utilization of the coolant chemical heat sink. When the radial thermal conductivity difference is about 8 W/(m·K), the wall heat-flux variation reaches about 0.05 MW/m², resulting in a temperature reduction of nearly 50 K in the GH3536 region; moreover, a 28.57% increase in radial thermal conductivity difference doubles the maximum wall heat-flux difference. In addition, unlike pure C/SiC channels, the hybrid configuration effectively suppresses stress concentration and allows the outer GH3536 layer to serve as the primary load-bearing structure.