Thrust Analysis by Length Reduction of an ED Nozzle with Fixed Expansion Ratio
Creators: name:  J. LEE 
name:   J. CHOI 
name:   H. HUH 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: PROPULSION PHYSICS

description: Conventional bell nozzles used in rocket engines have a fixed expansion ratio. Therefore, performance loss in the conventional bell nozzles is induced at all altitudes other than at the design point, where Pe=Pa. To improve this performance loss, an altitude compensating nozzle was proposed. Altitude compensating nozzles include expansion-deflection (ED) nozzle, dual-bell nozzle, and aerospike nozzle. Among them, the ED nozzle uses a pintle located in the center of the nozzle to prevent performance loss. Nozzle internal flow passes through the pintle and deflected to the nozzle wall, and the effective nozzle exit area changes. In addition, in the same performance, the length of the ED nozzle is shorter than the bell nozzle[1]. Therefore, the ED nozzle would offer weight reduction allowing increased payloads. For these reasons, various studies on the ED nozzle have been conducted in many countries. Previous studies mainly focused on nozzle internal flow behavior and the thrust performance of design variables of the ED nozzle. The geometry of the ED nozzle in previous studies was variable, limited to investigating the thrust of the ED nozzle with a reduced length. Therefore, it is necessary to investigate the thrust of the ED nozzle with reduced length using the same design conditions. This study is a preliminary study for the design of the upper stage engine of the launch vehicle, and the thrust of length reduction of the ED nozzle was analyzed numerically by applying the ED nozzle to the engine using methane. The ED nozzles are designed using the same expansion ratio and pintle design condition. Based on the ED nozzle designed using thrust-optimized contour (TOC) with a throat angle of the ED nozzle of 30, the length of the ED nozzle is reduced to 10%, 20%, 30%, and 40%. According to the contour of the TOC nozzle proposed by Rao, the length of the nozzle could be shortened by increasing the throat angle of the nozzle at the same expansion ratio. Therefore, the angle of the ED nozzle increased to 40, 50, and the length is shortened to 13% and 27%. For the numerical analysis conditions, LOx/LCH4 with a combustion chamber pressure of 2.0 MPa and mixing ratio of 3.4 derived from the NASA CEA code is used. As a result, the geometry of the ED nozzle is 27% and 30% shorter than the ED nozzle basic geometry, which is similar to the thrust of the ED nozzle basic geometry. The length of the ED nozzle was reduced by 10%, 13%, 20%, and the thrust was 2.0%, 6.9%, 0.9% less than the ED nozzle basic geometry. The thrust gradually improved as the length of the ED nozzle reduced by 10%. In conclusion, we confirmed that the length of the ED nozzle under the same design conditions could be shortened while maintaining the thrust. Therefore, the payload gain due to the reduction of the length of the ED nozzle is expected. Additional research on the ED nozzle length reduction geometry for validation of the numerical analysis will be conducted in future work.