Steam Non-equilibrium Condensation Process

For hypersonic vehicle technology research, the ground simulation test is an important way to understand the hypersonic flight mechanism. At present,the hypersonic vehicle ground simulation tests in China, especially the large scale and high enthalpy tests were carried out in the combustion-heated hypersonic wind tunnel.The gastemperature will reduce rapidly during the expansion process of a hypersonic nozzle flow,which may cause steam condensation. This process will bring about the change of flow field parameters.In order to investigate the steam condensation process in a nozzle, one device was developed in place of nozzles in this dissertation. Combining the experiments and the numerical simulation,the influence of water vapor condensation on the flow parameters was obtained and analyzed. Furthermore, the influence of initial parameters on water vapor condensation were investigated. The results and conclusions are presented as follows:(1) Change of flow parameters along a nozzle is converted to the change with time in a certain position during the flow expansion process. Three different time scales,which correspond different nozzle dimensions,are actualized by adjusting the sectional area valve of the connection segment. The initial water vapor content is controlled by adjusting the water vapor pressure in the test section before the test. The steam condensation process is observed by planar laser scattering imaging. The water vapor concentration and temperature in the steam condensation process are obtained with Tunable Diode Laser Absorption Spectroscopy measurement system (TDLAS)based on water vapor spectral lines and methane spectral line. The results show that there exists obvious water vapor condensation in the test section under the experimental conditions, the condensation phenomena are captured by planar laser scattering imaging. It was also found that temperature evolutions have similar trends in experimental results with numerical simulation of nozzles, which is decreasing first then rising. Mole fraction of water vapor decreases rapidly and saturation reaches its peak when temperature trend changes, which are consistent with numerical simulation of the test section. The new experimental device can simulate the process of water vapor condensation in the wind tunnel flow for a certain extent.(2) The effects of time scale on water vapor condensation were studied using this system,which correspond different nozzle dimensions. The results show that temperature evolutions have similar trends in different time-scales experiments, which is decreasing first then rising. Mole fraction of water vapor decreases rapidly and saturation reaches its peak when temperature trend changes. For the same initial water vapor mole fraction, with the increase of the time scale, the condensation time puts off, but the condensation temperatures are very close, the decreased mole fraction and the saturation peak are also close.(3 )The effects of initial water vapor concentration on water vapor condensation were also studied using this system. The results show that the trends of temperaturemole fraction and saturation are similar for different initial water vapor concentration.But with the increase of water vapor content, the condensation time moves up, the condensation temperature increases and the saturation peak decreases.