An evaluation on the laminar effect of buoyancy-driven supercritical hydrocarbon fuel flow and heat transfer characteristics

To ameliorate the thermal management of a cooling system in an advanced engine, the heat transfer characteristics affected by the buoyancy-driven supercritical hydrocarbon fuel flow in a rectangular channel are numerically explored in detail. Several common buoyancy criteria (Gr/Re², Gr/Re^2.7 and Gr_q/Gr_th) are established and a three-dimensional numerical model is simulated with a verified SST k-ω turbulence model at real working conditions. The test results demonstrate that the buoyancy force, essentially induced by the relatively large density gradient under the severe thermal stratification environment, dramatically redistributes the flow structure and temperature distribution. The buoyancy-aided flow accelerates the formation of secondary flow, which exerts the positive role in promoting the transitional trend towards laminar flow from the initial developed turbulent state. Besides, it decreases the wall shear stress and thermal diffusion in near-wall fluid as the thickness of thermal boundary layer increases. In particular, the laminar-like flow is considered to be responsible for the occurrence of the typical 1st HTD (Heat transfer deterioration) and the 2nd HTD. In addition, a local EHT (Enhanced Heat Transfer) behavior can be regarded as a consequence of a very slight recovery of Gr_q/Gr_th and Gr/Re^2.7 with a sharply increase in the wall shear stress and Nusselt number.