Numerical Study On Transpiration Cooling Of The Strut In The Combustion Chamber Of Scramjet Engine

With rapid development of hypersonic vehicles,advanced power devices are needed to provide power.Struts in the combustion chamber of the devices play an important role in improving the combustion effect of the combustion chamber.But the huge thermal load formed by the high-temperature and high-speed mainstream will cause the strut to lose its efficacy,so effective thermal protection measures must be taken.As an advanced cooling method,transpiration cooling has a high cooling efficiency.In this work,transpiration cooling,an active thermal protection method,used for the strut thermal protection is studied.By the means of numerical simulation,a flow and heat transfer model of transpiration cooling is established to reveal the thermal protection mechanism of transpiration cooling and the factors that influence the cooling effect,and provide a reference for the later design of reasonable thermal protection system.Numerical simulations are carried out respectively for the flow field with and without transpiration cooling,and the thermal protection efficiency of the flow field when the strut is protected by transpiration cooling is analyzed.It shows that the velocity boundary layer on the surface of the strut with the transpiration cooling is significantly thicker than that without the transpiration cooling,which avoids the direct stagnation of the mainstream on the surface of the strut.The seepage of the coolant at the stagnation point will push the bow shock wave generated by the mainstream away from the strut,which can reduce the force and heat load formed by the mainstream on the strut.At the same time,the accumulation of the coolant downstream improves the cooling efficiency.The flow rate of the coolant inside the strut is affected by the local pressure which gradually increases as the coolant approaches the outlet.Numerical investigations are carried out concerning the influence of different coolants,the inlet temperature and mass flow rate of the coolant,and other factors on the cooling effect.Studies show that the specific heat capacity of the coolant is the main factor affecting the cooling effect.Compared with methane and air,helium has a larger specific heat capacity and a lower density,so that it has a higher cooling efficiency and a better blowing effect.Comparing and analyzing the cooling effect of different inlet temperatures of the coolant,the coolant at lower temperature has greater cooling potential.The increase of the mass flow rate will enhance the heat exchange between the coolant and solid structure,and form a thicker layer of coolant on the strut surface,leading to an improved cooling efficiency.Numerical investigations are also carried out to study the flow field in which the inclination angles of the strut are different.The results show that with the increase of the inclination angle of the strut,the thermal load on the front edge of the strut is reduced.The influence of the characteristics of the porous medium on the cooling effect is numerically investigated.The results show that the increase of porosity and particle size in the porous medium will cause the decrease of the internal heat exchange area of the porous medium and reduce the heat transfer.But,increasing the Reynolds number inside the coolant channel will enhance the heat transfer.The increase of the thermal conductivity of the porous medium will improve the heat transfer between the frameworks,so that the heat in the local high temperature zone will be released,and the temperature of the front edge of the strut will be reduced.