Buoyancy-driven secondary flows and coke particle transport dynamics in heated curved channels

Curved cooling channels are unavoidable geometric constraints in hypersonic scramjet engines, where their spatial orientation dictates the thermofluid behavior of Rocket Propellant-3 aviation kerosene. This study systematically elucidates the driving mechanisms of buoyancy within curved channels under various layouts, revealing its regulatory effects on spatiotemporal thermal-fluid fields and macroscopic coking characteristics. The results show that the circumferential wall temperature exhibits an S-shaped non-uniform profile. Heat transfer deterioration in the horizontal-horizontal (HH) and horizontal-upward (HU) configurations occurs along the inner and top walls, respectively. Conversely, the horizontal-downward (HD) configuration undergoes a restructuring of internal thermal fields, significantly enhancing overall heat transfer and alleviating regional deterioration.Hydrodynamic analysis indicates that the HD configuration induces a stronger radial secondary flow, optimizing fluidic mixing. However, this intensive radial perturbation causes the dimensionless radial forces on discrete coke particles to escalate sharply, contributing up to 0.5 of the net force, which degrades the streamward velocity coupling and leads to a tracking lag where the Stk/Stk NG exceeds 1.2. At the microscopic level, this intensive secondary flow disrupts the spatial focus of granular transport, avoiding preferential accumulation, and suppresses particle agglomeration through hydrodynamic shear stripping. Macrostructurally, while HH and HU exhibit comparable coking magnitudes, the HD configuration yields the lowest total coke mass, proving its prominence in proactive coking mitigation. Crucially, when the buoyancy parameter recedes below Gr b /Gr th < 30, its regulatory dominance over flow, heat transfer, and particle transport diminishes markedly across all layouts. Ultimately, this work provides precise mechanistic guidance for cooling network optimization and safeguards the high-Mach long-endurance flight of hypersonic vehicles.