Numerical Evaluation Of Phase Transition Effects In Wind Tunnel Flowfield And Model Test

In recent years, along with the development of air-breathing hypersonic vehicle, combustion-heated wind tunnel has been received a great deal of attention owing to its attractive capability of powered engine tests.Combustion heating is an efficient way to achieve the flight-equivalent thermodynamic conditions in a combustion-heated wind tunnel,but it also can create water vapor, carbon dioxide and other components. Wa-ter vapor contaminants will experience condensation as the fluid expands to super-sonic conditions, while the condensed water will experience evaporation when it passes through the shock wave generated by compressible configurations. Therefore, in order to understand phase transition effects in a combustion-heated wind tunnel, a compress-ible multi-components fluid dynamics solver, in which both condensation and evapora-tion phase transition models are incorporated, is adopted to investigate water vapor con-densation in hypersonic nozzle flows and the influence of condensed water evaporation on flow parameters as well as aerodynamic forces of typical test model configurations (two-dimensional wedge, three-dimensional wedge, cone and pitot-pressure rake,etc).The effects of water vapor phase transition in nozzle flows of hydrogen-fueled combustion-heated wind tunnel are examined at first. The numerical simulation results show that condensation makes the flow parameters of nozzle outlet deviated from ideal state, such as Mach number and total pressure decreases, and increases in static pressure and static temperature; Moreover, phase transition significantly changes the flow field structure of the nozzle, in which condensation shock and compressive wave reflected are observable. As a result, the uniformity of the flow at the nozzle exit and the main test section is deteriorated.Futhermore, the scale effects of nozzle in combustion-heated wind tunnel are in-vestigated. Four nozzles with similar configuration and exit diameters of 300mm,600mm, 2400mm and 5000mm, respectively are examined. The numerical results show that with the size of nozzle increased, the droplet radius will be increased, but the droplet num-ber will be decreased. As a result, different nozzles have roughly the same liquid mass fraction. It illustrates that the effects of water condensation on the nozzles with similar configuration are nearly the same. Therefore the influence of scale effects of nozzle in combustion-heated wind tunnel is not significant.Finally, the influence of condensed water evaporation on flow parameters as well as aerodynamic forces of typical simplified model configurations (two-dimensional wedge, three-dimensional wedge, cone and pitot-pressure rake) is investigated. The results show that in nozzle flows of hydrogen-fueled combustion-heated wind tunnel, although the water vapor will experience more condensation under the condition of high expansion, the condensed water will be evaporated when it passes through the shock wave generated by compressible configurations. Even though condensation makes the flow parameters of nozzle outlet deviated from ideal state, the following evaporation will drive the parameters back to the ideal state. The degree of the recovering is deter-mined by the strength of the compression. In this investigation, the deviation of nozzle outlet parameters by condensation is somehow above 10%, while the flow parameters as well as aerodynamic forces can be recovered to above 95% of ideal state after a shock compression generated by a 12° wedge configuration. From this point of view, the effects of water vapor phase transition can be neglected.