Supersonic wind tunnel is an important ground experimental equipment for the research of hypersonic aircraft and engines. For a hypersonic wind tunnel system, one of its core components is the supersonic nozzle which can transform the airflow from subsonic state to a supersonic state. Due to the long-term scouring of high-speed, high-temperature and oxygenated flow, the wall heat flux at the throat of supersonic nozzle is very high, which brings great challenges to the normal operation of the hypersonic wind tunnel, and many thermal protections method for the nozzle also came into being.
Studies have shown that film cooling has the advantages of simple structure, high cooling efficiency, and reusability. Thus, film cooling has great application prospects in hypersonic wind tunnel nozzles. However, the flow and heat transfer characteristics of the film in supersonic and large curvature wall environment are not clear. The cooling efficiency of the film and the influence of the introduction of the film on the quality of the airflow at nozzle outlet are also unclear. Therefore, it is urgent to systematically study the film cooling characteristics and flow mechanism of supersonic nozzles. In this paper, based on the Reynolds-Average method and the SST k-ω turbulence model, the flow characteristics, wall thermal load characteristics and outlet airflow quality of the Mach 6 hypersonic nozzle with the gas film are numerical studied. The main contents and conclusions are:
In the first part, the two-dimensional flow and heat transfer characteristics of film cooling in supersonic nozzle are numerically studied. The nozzle wall was cooled by the way of parallel air injection through a slot. The numerical results show that the air film can effectively reduce the heat flux at the nozzle wall, especially at the throat. When the air film flow rate only accounts for 3.53% of the mainstream, the heat flux at the throat decreases by 30.1%. The introduction of gas film will not significantly affect the distribution of Mach number at the nozzle outlet, but only has a small effect on the total temperature distribution at the nozzle outlet, which makes the temperature boundary layer thicker. At the same time, under the same air film flow condition, the change of slot height, step thickness, and jet distance has little effect on the cooling efficiency of the nozzle throat.
In the second part, the three-dimensional flow and heat transfer characteristics of film cooling in supersonic nozzle are numerically studied. The nozzle wall is cooled by a porous air injection, and the effects of parameters such as jet angle, film flow rate, and film aperture on the cooling efficiency and the airflow quality of the nozzle outlet are studied. The results show that the gas film can effectively reduce the overall heat flux of the nozzle. When the jet angle is 30° and the film flow only accounts for 3.07% of the main flow, the average heat flux of the throat drops by 31.1%. Due to the film hole spacing, the nozzle throat heat flow distribution is periodically distributed. The heat flux is the lowest in the opposite position of the film hole. And has the peak value in the center of the adjacent film hole. Moreover, studies have found that when the jet angle is too large, the air film is easier to separate from the wall, which makes the cooling efficiency drop sharply, having a greater impact on the quality of the airflow at the nozzle outlet. When the jet angle is small, the air film adheres to the wall and has less impact on the quality of the airflow at the nozzle outlet.