역류제트를 이용한 센터바디 디퓨져의 성능특성에 관한 연구

Abstract

This thesis describes research on verification of performance characteristics of center-body diffusers and counter-flow jet injection of center-body diffusers in high-altitude simulation facilities. The supersonic exhaust diffusers are generally used for rocket engine testing in high-altitude simulation facilities. They can be classified into the constant-area exhaust diffuser, the second throat exhaust diffuser, and the center-body diffuser. The center-body diffuser, compared to the constant-area exhaust diffuser and the second throat exhaust diffuser, can reduce the cost of a high-altitude simulation facility. However, since it is disadvantageous in terms of the cooling system and the aerodynamic heating, it is only used for p4.1 facility of DLR. Therefore, this thesis proposed an efficient thermal protection system of the center-body diffuser with counter-flow jet injection. The performance characteristics of the center-body diffuser and the counter-flow jet injection in the center-body diffuser were analyzed by analytical and the numerical methods. The counter-flow jet injection in the flow field of center-body diffuser was calculated with axisymmetric two-dimensional Navier-Stokes equation, with k-ε and S-A turbulence model. The center-body diffuser was compared with the second throat exhaust diffuser in terms of the starting pressure, the ratio of vacuum pressures, and the design parameters. The performance characteristics are related with design parameters such as cone half-angle, position, and blunt-cone of the center-body. This is closely related to the loss of total pressure according to the change of cone half-angle and blunt-cone of the center-body. The counter-flow jet injection in the center-body diffuser was applied for the thermal protection system on the cone-tip of the center-body. The temperature of the cone-tip was reduced proportionate to the increase of pressure of the counter-flow jet. The cone-tip temperature of approximately 3400k was reduced to approximately 500k with the counter-flow jet injection compared to without the counter-flow jet injection in the flow field of the center-body diffuser. The flow phenomenon of LPM and SPM was confirmed to depend on the total pressure of counter-flow jet, the speed of flow field, and the shape of blunt-cone. Finally, the counter-flow jet system was confirmed to be effective for thermal protection of the center-body diffuser. It was verified that the starting pressure of the center-body diffuser changed according to the cone shape. These results will be applicable to the development on the counter-flow jet system to improve the performance of the center-body diffuser.