Study On Phase Transition Effects On Hypersonic Flows

The study on the two-phase flow with phase transition originated from the devel-opment of industrial steam turbines. Subsequently, a part of the air dynamics experts began to pay attention to the problem of water vapor condensation in a supersonic wind tunnel (or nozzle) which has been partially solved in the last century. In recent years, along with the development of combustion-heated tunnel technology, the research into the effect of phase transition on hypersonic flow has entered a new stage. In this stage, the study of the effect of phase transition has different characteristics from the previ-ous studies:the combustion-heated tunnel has such characteristics as large expansion ratio and high Mach number; the vitiated airflow of the wind tunnel contains a large amount of water vapor, carbon dioxide and other components. Furthermore, the high temperature gas effect of the experimental airflow in the expansion of the acceleration process cannot be ignored. From a view of the research results, there are only a handful of research literatures in this area. And the main parts of the research are the study of the water vapor condensation in the combustion wind tunnel which is mainly based on the numerical simulation. In addition, when the high-speed airflow with droplets from the wind tunnel exit go through the surface of aerocraft model, the heat absorption ef-fect and the added mass effect during droplet evaporation have a significant impact on the aerodynamic parameters of the model surface. There is little research on this aspect at present. Based on these, this thesis carries out the following research work on such three aspects as the influence of the water vapor condensation in the combustion-heated tunnel, the effect of evaporation in the hypersonic flow and the influence of the nitrogen condensation, which is specifically described as follows:Firstly, the theoretical model of water vapor condensation influence in combustion-heated tunnel is constructed. By analyzing the physical process of the water vapor condensation in the combustion-heated tunnel, the specialty of the water vapor conden-sation is obtained. On this basis, the process is decoupled into an isentropic expansion process and the water vapor condensation process, and the virtual concept of isentropic expansion interface and condensation interface are proposed. By establishing the rela-tionship between the two interface parameters, the theoretical model of the influence of water vapor condensation is established and verified. This model takes into account both the effect of high temperature gas and the effects of phase transition. Applying the theoretical model, a method for quickly evaluating the influence of condensation on the flow parameter of wind tunnel can be obtained.Secondly, apply the methods of numerical simulation and theoretical model to s-tudy the influence of the high-speed flow with droplets on the aerodynamic parameters of wedge surface. The numerical simulation results show that the relaxation process of droplet evaporation in post-shock region is related to the intensity of shock wave, and influence the uniformity of aerodynamic parameters of the model surface. Among them, the largest unevenness appears at the deflection angle in the right moment when the droplets evaporate totally in the whole shock downstream region. According to the coupling characteristics between the droplet evaporation and shock wave, on this basis, the process is decoupled into the interaction process of airflow and shock wave and the process of droplet evaporation. Then the virtual concepts of shock interface and evapo-ration interface are proposed. By establishing the relationship between the two interface parameters, the theoretical evaluation model of the influence of droplet evaporation in hypersonic flow is established and verified.Finally, the numerical calculation program for evaluating the nitrogen condensa-tion in conventional hypersonic wind tunnel is developed and verified. In the light of the development of numerical methods and the latest research results of nitrogen conden-sation model, on the basis of the ASCE2D program, this thesis develops the numerical calculation code for evaluating nitrogen condensation. The code is applied to inves-tigate the effect of nitrogen condensation on the flow parameters of hypersonic wind tunnel.In summary, through the research, we can obtain the following meaningful re-search results:A theoretical model of the influence of water vapor condensation in the combustion-heated tunnel is constructed, which provides a quick evaluation method for the condensation effect of the combustion-heated tunnel; the physical evaporation pro-cess of the high speed airflow with droplet through the wedge is discussed in detail; the judgment basis of the maximum nonuniformity of the aerodynamic parameter of the model surface is given, a theoretical evaluation model of the effect of water vapor e-vaporation in hypersonic flow is established; in view of nitrogen condensation effect in the conventional hypersonic wind tunnel, the numerical calculation code for evaluating nitrogen condensation is developed.