인젝터 출구유속에 따른 Vortex Flow Pancake 하이브리드 로켓의 연소 특성 연구 = (A) Study on the Combustion Characteristics of Vortex Flow Pancake Hybrid Rocket with the Injector Exit Mass Flux

다국어 초록 (Multilingual Abstract)

In this thesis, a semi-empirical regression rate model of Vortex Flow Pancake (VFP) hybrid rocket is developed and assessed.
The proposed model is based on the Marxman’s boundary layer combustion model and Volchkov’s vortex chamber aerodynamic model. The regression rate is the function of circumferential mass flux at the chamber periphery G_k. The G_k is substituted by the injector exit mass flux G_inj, and also the H/d ratio is introduced, which is a semi-empirical variable representing the expansion of oxidizer jet from injector orifice. The experimental data obtained from lab-scale firing test are fitted to the proposed regression rate model. The regression rates are divided into three differing groups based on the range of H/d ratio. Under equal G_inj, a low regression rate is observed for high H/d ratio group. This is believed to be caused by the nature of jet developing from the injector exit: as the H/d ratio increases, the area expansion ratio of jet prior to attachment and the corresponding momentum loss increase, which results in the decrease of the circumferential mass flux at the periphery and the fuel regression rate.
The proposed regression rate model is validated through three approaches. Firstly, the post-combustion surface of fuel grain is qualitatively analyzed. A whirlpool-shaped profile indicating both circumferential and radial flow traces is observed. It exhibits a high similarity to the end-wall layer streamline of Volchkov’s vortex chamber aerodynamic model, demonstrating the high feasibility of using vortex chamber model for VFP hybrid. Secondly, the conventional and current regression rate models are compared in statistics. The current model demonstrates a lower Mean Absolute Error (MAE) and a narrower Gaussian error distribution, attributed to it’s low variance. It is verified that the current model improves the precision and reliability of regression rate prediction compared to the conventional model. Finally, it is assessed whether the proposed model can reproduce the results of previous studies. The previous studies were performed under low G_inj and narrow H/d ratio. While the previous studies showed that the regression rate was hardly affected by chamber height, a significant effect is observed in the present study. Within the range of consistent with previous studies, the regression rate dependency on the chamber height (and H/d ratio) is also mitigated in this study. Furthermore, a narrow range of H/d ratio may increase the likelihood that data are grouped into a single curve, as the regression rate curve is distinguished by the range of H/d ratio. From these findings, it is verified that the proposed regression rate model can partially reproduce the regression behavior reported from previous studies.

목차 (Table of Contents)

• 제 1 장 서론 1
• 1.1 연구 배경 1
• 1.2 연구 동향 5
• 1.3 연구 목표 및 개요 7
• 제 2 장 이론적 모델링 8
• 2.1 경계층 연소 모델 8
• 2.2 VFP 후퇴율 모델 11
• 제 3 장 실험장치 및 조건 20
• 3.1 연소시험 설비 20
• 3.2 Lab-scale VFP 모터 21
• 3.3 실험 조건 22
• 제 4 장 결과 및 분석 23
• 4.1 인젝터 출구유속에 따른 후퇴율 23
• 4.2 연소 후 연료 표면 형상 분석 26
• 4.3 산화제 유속에 따른 후퇴율 27
• 4.4 후퇴율 모델의 비교 31
• 4.5 선행연구와의 비교 32
• 제 5 장 결론 34
• 참고문헌 36
• 영문초록 39