| The hypersonic aircraft is currently a hotspot in the development of near-space vehicles,and the active regenerative cooling technology of the scramjet engine in hypersonic aircraft is one of the key and difficult points of research.Understanding and utilizing the heat transfer characteristics of hydrocarbon fuels is an important aspect of achieving effective hightemperature cooling.Revealing the inherent laws of heat transfer processes and understanding the influencing mechanism of related factors are the main objectives of studying the heat transfer characteristics of hydrocarbon fuel regenerative active cooling in hypersonic scramjet engines.Therefore,this paper uses OpenFOAM for secondary development to numerically simulate the convective heat transfer characteristics of RP-3 under supercritical pressure.The main research contents and conclusions are as follows:(1)Using OpenFOAM for secondary development,the internal heat transfer solver was modified to solve the problem of sharp changes in properties under supercritical pressure using a lookup table method.The results were compared and verified with experimental data,and it was found that the modified solver had high accuracy and was able to simulate the convective heat transfer of RP-3 under supercritical pressure.(2)Simulations of convective heat transfer of RP-3 under supercritical pressure in a 2 mm microchannel were conducted using OpenFOAM with modified internal heat transfer solver.The obtained data includes velocity field,turbulence kinetic energy field,and temperature field,from which non-dimensional parameters were calculated to reveal their variations.Results show that before reaching the pseudo-critical region,the fluid density variation is small in the cross-section of the tube,and the secondary flow induced by the density difference is weak,with negligible temperature difference between the upper and lower walls.In the pseudo-critical region,the upper wall temperature reaches the highest value,reaching the pseudo-critical temperature first,while the near-wall fluid along the tube circumference successively reaches the pseudo-critical temperature,with the main flow temperature being the lowest and reaching the pseudo-critical temperature last.The uneven distribution of temperature in the cross-section leads to a large difference in fluid density,with low-temperature high-density fluid near the center of the tube flowing downward and hightemperature low-density fluid near the lower wall flowing upward along the wall,eventually accumulating near the upper wall,resulting in heat transfer deterioration.This secondary flow leads to strong flow near the lower wall with high heat transfer coefficient and weak flow near the upper wall with low heat transfer coefficient.(3)The effects of factors such as heat flux density,mass flow rate,inlet temperature,and gravity acceleration on the flow and heat transfer characteristics of RP-3 under supercritical pressure were studied by setting 10 different working conditions and conducting simulations.Comparative analysis was performed to determine the impact of different factors.The results show that as the heat flux density increases and the mass flow rate decreases,the temperature difference between the upper and lower wall surfaces becomes larger,resulting in a greater difference in the heat transfer coefficient between the two surfaces,and the position of the maximum temperature difference moves forward.Different inlet temperatures only cause a difference in the starting position of changes in fluid thermal properties and do not affect the overall trend of heat transfer.The effect of gravity acceleration on flow and heat transfer is more significant.As the gravity acceleration increases,the buoyancy effect becomes more apparent,resulting in a larger temperature difference between the upper and lower wall surfaces and a greater difference in the heat transfer coefficient between the two surfaces.The heat transfer deterioration on the upper wall surface becomes more severe,while the heat transfer enhancement on the lower wall surface becomes more apparent. |
