Numerical Simulation Of Heat Transfer Of N-decane Under Supercritical Pressure In Horizontal Scramjet-engine Cooling Channels

The scramjet engine provides reliable power source for the high Mach number flight of hypersonic vehicles.The cooling problem of the combustion chamber is one of the key issues that need to be solved to achieve hypersonic flight.Regenerative cooling technology is currently widely used and has a high cooling efficiency.This technology uses hydrocarbon fuel as the coolant,mainly to "regeneratively" cool the combustion chamber through the heat transfer and the cracking heat absorption of the fuel.Because hydrocarbon fuels are often under supercritical pressure,the physical properties and transportation parameters change drastically.Considering the effect of chemical reaction,the flow and heat transfer process is very complex.Therefore,it is very important to use numerical methods to predict the flow and heat transfer in the cooling channels.Herein,we choose the n-decane in the supercritical pressure horizontal channels as the research object.First,a numerical model for calculating the heat transfer in the horizontal channels is established,and its accuracy is verified.Then by using this numerical method,we calculate the heat transfer phenomenon of n-decane in the supercritical pressure horizontal channels considering the effect of buoyancy and cracking endothermic reaction.The main research contents are as follows:(1)The numerical simulation study on the flow and heat transfer of n-decane in horizontal rectangular cooling channels under supercritical pressure is mainly to explore the effect and mechanism of buoyancy on the heat transfer of n-decane.The results indicate that the buoyancy force gives rise to the secondary flow causing an apparent difference in the distribution of temperature and heat fluxes at different locations in the combustion chamber;the buoyancy enhances the heat exchange capacity of wall surfaces;The heat transfer performance of the cooling channel with the same heat and gravity direction is the most improved;the modified Jackson & Hall empirical formula has higher accuracy without considering the buoyancy condition,but the empirical formula cannot characterize the influence of buoyancy to the heat transfer between the fluid and cooling channel walls.(2)The numerical simulation of the heat transfer of n-decane in the horizontal round channel under supercritical pressure considering cracking endotherm is carried out.The influence of buoyancy and other parameters on cracking endotherm and heat transfer is mainly investigated.The results show that the buoyancy in the round channel not only causes a significant difference in temperature and heat fluxes distribution in walls,but also changes the cracking position in the round channel because of the temperature,and the buoyancy will inhibit the cracking reaction;increasing the solid thermal conductivity of the round channel makes the wall temperature distribution more uniform,but also suppresses the cracking reaction;changing the inlet speed can significantly change the flow field distribution and heat transfer characteristics and increasing the fluid inlet velocities can suppress the occurrence of n-decane cracking reaction in the round channel.