Three-Dimensional Transient Simulation of Supercritical RP-3 Pyrolysis and Flow Maldistribution in Parallel Regenerative Cooling Channels

To investigate transient flow instabilities in parallel-channel regenerative cooling systems subjected to nonuniform heat flux, a three-dimensional transient numerical model was developed to couple variations in supercritical fluid thermophysical properties with endothermic pyrolysis kinetics. The spatiotemporal evolution of RP-3 fuel within parallel channels was analyzed, and the role of a midstream interconnection structure in mitigating flow maldistribution was clarified. During the initial heating stage, the viscosity reduction of the supercritical fuel produced a drag-reduction effect that temporarily maintained a nearly uniform flow distribution. As the wall temperature increased and the pseudocritical region approached, the sharp decrease in density markedly increased the acceleration pressure drop, disrupting the pressure balance between channels. In combination with the progressive accumulation of pyrolysis products, this process led to a positive feedback loop characterized by flow rate reduction, insufficient heat absorption, and increasing flow resistance. The introduction of a midstream interconnection enabled pressure-driven lateral mass transfer between channels. The resulting crossflow was directed predominantly from the high-heat-flux channel toward the low-heat-flux channel, providing a release path for overheated, low-density, and strongly cracked fluid in the high-heat-flux channel and thereby weakening the downstream accumulation of thermal and compositional nonuniformities as well as the associated resistance amplification. Compared with the configuration without interconnection, the stage-averaged maximum flow-deviation coefficient decreased by 17.4% during the pseudocritical transition stage and by 48.3% during the deep-pyrolysis stage.