소형 액체로켓 노즐의 성능해석과 형상설계

Abstract

A computational analysis of nozzle flow characteristics and plume structure is conducted to examine performance of the supersonic nozzle employed in a thruster for ground firing test. At first, comparisons between computational results and experimental data are performed in order to assess the performance of various turbulence models for the optimal analysis of supersonic converging-diverging nozzle. RANS equation is employed to simulate the nozzle flow, and one/two equation turbulence closures, such as Spalart-Allmaras, RNG k-ε and k-ω SST, are considered to evaluate. Computed results with turbulence models fairly well predicted the pressure distribution along the wall and shock structure; especially the k-ω SST model showed the best agreement to experiment among the models employed. Before designing the contour of the thruster nozzle for ground firing test, an analysis of the original thruster nozzle having area ratio of 50:1 is performed to figure out an effect of the flight altitude on nozzle flow characteristics. Thrust performance of the nozzle is exceedingly poor upto 10 km of flight altitude because of the irreversible phenomena such as shock and/or flow separation occurring inside the nozzle, whereas it is restored to the nominal value as the altitude is attained higher than 30 km. The original thruster nozzle is not desirable for the ground firing test because irreversible phenomena, which give rise to unwelcome effects, are occurred inside of the nozzle. To avoid those irreversible phenomena during the ground firing test, two type of thruster nozzles reduced their area ratio are newly designed for ground firing test. One of them is a cut-off nozzle which was cut the original nozzle off at point where the area ratio became 10:1. The other is extended nozzle having same area ratio of the cut off nozzle but different contour. A performance penalty caused by flow separation in a diverging section is observed in cut-off nozzle. The performance could be enhanced by the modification of the diverging section of nozzle contour.