Numerical Simulation And Experimental Research On High Enthalpy And Pressure Air Heater

High enthalpy and pressure air heater is employed primarily in the free-jet test system of scramjet. It is characterized by high total temperature, high total pressure, high Mach number, high air flow rate and high wall heat flux. Technical difficulty involves combustion management and heat transfer control. An air heater based on the chamber of liquid rocket engine (LRE) is investigated by numerical simulation and experimental technology to test the performance of atomization, combustion and heat transfer, and to acquire the influences of structural or operating parameters on the performances of the air heater.At first, the discharge and atomization characteristics of the tripropellant coaxial injectors applied in the air heater were researched through the experimental method, and the influences of injector configurations and test operation parameters on the discharge and atomization characteristics are discussed in detail. The results indicate that, the discharge coefficient of injector is affected obviously by the pressure drop of air, recess of injectors and liquid stimulant. Likewise, the spray cone angles, SMD and velocity of droplet are affected distinctly by pressure drop of air and recess of injectors. The better atomization performance is generally attributed to the decline of pressure drop of air, and the increasing recess can increase the spray cone angles, decrease the SMD of droplet. However, it does not affect much on the droplet distribution.Moreover, a physical model available in the high enthalpy and pressure air-heater was developed to simulate its spray combustion and heat transfer processes. In addition, the hot-fire tests of air-heater were performed, where a total temperature rake was developed to measure the total temperature distribution on the nozzle exit. Experimental results were compared with numerical results. The effects of numerical scheme on the results were evaluated, and the influences of structural and operating parameters on the combustion flow field were investigated in detail. Results indicate that the mesh style play significant role on the combustion flow field prediction, the characteristic length of chamber and the parameters of injectors influence the performance of the air heater, and the increase of air velocity helps to accelerate the mixing and combustion, which can improve the uniformity of nozzle exit. The length of flame is discrepant greatly when the oxygen status changes from liquid to gaseous, and this discrepancy is irrelevant to the characteristic length. Air heater adopting gaseous oxide can produce higher total temperature and more uniform temperature filed at exit comparing to liquid oxide.Finally, the heat transfer process of air heater was studied by the numerical technology to analyze the reliability of cooling system. The influence of different boundary conditions is estimated to assess the accuracy of the result of simulation. The result shows that it will lead to significant error if the calculation of thermo-equilibrium is adopted as the boundary condition. Moreover, the temperature and heat flux of the chamber wall are affected obviously by the coolant discharge, structure of cooling channel and the flow-mode of coolant. Finally, the minimal coolant flowrate that that keeps reliable air heater cooling is obtained.