Simulation Of Supercritical CO₂ Cooling Process For High Temperature Walls Of Scramjet

In the field of hypersonic vehicles,solid fuel scramjet has superior performance.However,solid-fuel scramjet lacks a cooling working medium.In the present work,the active cooling of the engine inner wall with supercritical CO₂was proposed.Starting from the design of the experimental device,the cooling effect of supercritical CO₂in the experimental section was studied by using MATLAB software and FLUENT simulation software.To meet the lightweight of the thermal protection system,the CO₂after cooling the engine was formed into a closed cooling cycle,and its numerical simulation analysis was carried out.The main work and conclusions are as follows:（1）For the designed experimental device,CEA software was used to calculate the combustion products,temperature,pressure,speed,and other parameters in each part of the designed experimental device.The results show that the gas temperature at the nozzle outlet is 2943K,the main products are H₂O,CO₂,CO,and O_2,and the surface characteristic velocity is 1657m/s.At the same time,the cooling water flow of the thrust chamber and isolation section was calculated,which is 1.3kg/s and2.2kg/s,respectively.（2）The simulation results of supercritical CO₂cooling in the experimental section show that:1)The higher the CO₂flow rate,the better the cooling effect on the inner wall surface of C/Si C,the lower the CO₂temperature rise,and the higher the pressure drop in the microtubular heat exchanger.When the CO₂flow rate is less than0.09kg/s,the temperature at the exit wall of the experimental section is higher than at the inlet.2)CO₂inlet pressure changes have little effect on the gas temperature and the average temperature of the inner wall surface of C/Si C,and changing the pressure does not affect the cooling performance.3)The lower the initial CO₂temperature,the better the cooling effect on the wall surface of C/Si C and the lower the pressure drop in the microtubular heat exchanger.（3）A supercritical CO₂closed cooling cycle was constructed and the effect of three cooling media（water,alcohol,and ammonia）on the performance of the simple cooling cycle was analyzed.The results show that:1)when water is used as the cooling media,the flow rate advantage of the closed cycle is obvious,but the cooling effect on the C/Si C is poor.2)when alcohol is used as the cooling media,the flow rate advantage of the closed-loop is more obvious only for higher CO₂flow rates.3)when ammonia is used as the cooling media,it can match the high CO₂flow rate,but the flow rate advantage is not as good as that of water.4)The simple cooling loop with water as the cooling medium is to be improved（by adding a set of pre-heaters）,which reduced the CO₂temperature at the inlet and had a beneficial effect on engine cooling.But introducing a preheater has no significant effect on reducing cooling water flow.