| With the increasing Mach number of aircraft,scramjet used by aircraft is often in a harsh environment of high temperature and high pressure,so the problem of scramjet thermal management has to be solved.Considering the volume of aircraft,cost of fuel preparation and storage,conventional fuel is limited,and high-performance endothermic hydrocarbon fuel has a better development prospect.In scramjets,the fuel needs to be heated to extremely high temperatures in order for the fuel to be cracked in the cooling passage to further reduce the temperature of the engine combustion chamber wall and meet the requirements of the scramjet chemical reheat cycle.This kind of fuel absorbs heat from the combustion chamber wall through the cooling channel and is decomposed into hydrogen and small molecule hydrocarbons with better combustion performance,and then enters the combustion chamber to release the stored physical heat sink and chemical heat sink.This kind of regenerative cooling method effectively solves the thermal management problem of aero-engine.Based on the hydrocarbon fuel is decane in scramjet regenerative cooling channel and the flow of heat transfer and thermal cracking process as the research object,first of all,the supercritical is established by means of polynomial fitting is physical model of decane,for different inlet velocity and surface heat flow density under the condition of supercritical flow is decane heat transfer process in numerical simulation,The effects of different boundary conditions on the flow heat transfer characteristics of n-decane under supercritical pressure are discussed.Secondly,based on the PDD chemical cracking mechanism,a chemical solver without explicit source was used to simulate the endothermic cracking of n-decane.The flow and heat transfer under the condition of cracking and non-cracking were co MPared and analyzed.It was found that the wall temperature and fluid temperature at the outlet of the channel decreased by100 K and 85 K respectively after the cracking reaction occurred.The average temperature of the fluid also decreased,and the specific heat capacity at constant pressure decreased accordingly.The pyrolysis reaction produces small molecular groups such as methane and ethylene,which reduces the fluid density,further increases the fluid velocity and strengthens the convective heat transfer.Finally,a three-dimensional flow thermal coupling model of aero-engine regenerative cooling channel with V-ribs was established.The heat transfer enhancement of supercritical n-decane was investigated by numerical simulation and the pyrolysis process of n-decane in the v-rib channel was explored in detail.The flow and heat transfer performance of smooth channel and V-ribbed channel is co MPared and analyzed.It is found that the V-shaped rib structure can significantly reduce the temperature of the channel wall and improve the heat transfer capacity of the channel.On this basis,the best V-shaped rib size is determined through the optimization of the design of the rib height and the rib Angle and the comprehensive heat transfer factor. |
