Design of a novel nozzle for rocket engines with full flow at sea level

Abstract

To prevent flow separation under overexpanded conditions in traditional large-area-ratio nozzles of rocket engines at sea level, the method of characteristics for wall pressure control is adopted. This method, which is based on thrust-optimized contours, can be implemented to redesign the latter half of a divergent contour to ensure that the wall pressure of the new contour is not less than the critical separation pressure of 0.03 MPa. The newly generated nozzle is named the full-flow nozzle. Then, the design method is verified by simulations, and the performance of full-flow nozzles is evaluated. The results show that the method of wall pressure control can achieve the intended purpose, and the newly generated contour ensures that the nozzle is not only in the full-flow state at sea level but also able to withstand combustion chamber or ambient pressure fluctuations. The combustion chamber pressure is 8.5 MPa, and the specific heat ratio of hot gas is 1.144. Compared with the thrust-optimized contour with an area ratio of 40, in which the flow tends to separate at sea level, the full-flow nozzle can increase the area ratio to 60. Thus, the vacuum specific impulse can be increased by approximately 5.24 s. Compared with the thrust-optimized contour nozzle with an area ratio of 60, the vacuum specific impulse of the full-flow nozzle with an equal area ratio is decreased by 1.57 s.