Heejang Moon

Linear Stability Analysis for Combustion Instability in Solid Propellant Rocket

Corresponding author. E-mail: hjmoon@kau.ac.krABSTRACT Linear stability analysis for combustion instability within a cylindrical port of solid rocket motor has been conducted. The analysis of acoustic energy has been perfor med by a commercial COMSOL code to obtain the mode function associated to each acoustic mode pr ior to the calculation of stability alpha. An instability diagnosis based on the linear stability a nalysis of Culick is performed where special interests have been focused on 5 stability factors(alph a) such as pressure coupling, nozzle damping, particle damping and additionally, flow turning effect and viscous damping to take into account the flow and viscosity effect near the fuel surface. The instability decay characteristics depending on the particle size is also analyzed.초 록 본 연구에서는 고체로켓 모터의 연소 불안정성을 예측하고 분석 할 수 있는 해석도구의 개발을 위해 음향에너지의 분석과 선형 안정성 해석을 수행하였다. 음향 해석의 경우 상용 프로그램인 COMSOL을 이용하여 단면적이 일정한 실린더 형상의 연소실 음향 해석 및 모드 해를 도출하였다. Culick에 의해 정립된 고체추진 로켓의 선형 안정성 해석에 기초하여 연소 불안정성을 진단하였으며 압력결합, 노즐감쇠, 입자감쇠의 안정성 요소(stability alpha) 외에 유동방향변환(flow turning) 요소와 점성감쇠(viscous loss) 요소를 추가하여 연료 표면 근처의 유동 및 점성효과를 포함하는 연소 불안정의 경향을 파악하였다. 또한 입자의 크기에 따른 주파수 영역별 연소 불안정 감쇠 특성을 파악하였다.Key Words: Solid Rocket(고체로켓), Acoustic(음향학), Combustion Instability(연소 불안정), Linear Stability Analysis(선형 안정성 해석), Stability Alpha(안정성 요소)Nomenclature : speed of sound

The Nonlinear Combustion Instability Prediction of Solid Rocket Motors

The prediction of combustion instability is important to avoid an obvious threat to the structural safety and the motor performance because it affects the apparent response function of the propellant, the burning rate, and a mean flow Mach number at the local surface. The combustion instability occurs in case acoustic waves were coupled with the combustion/flow dynamic frequency. In this paper, an acoustic instability model is derived from the nonlinear wave equation for analysing acoustic dynamics in solid rocket motors. The chamber pressure and burning rate effects on combustion instability have been investigated.

Trade-off Evaluation due to Application of Mixing Chamber for Hybrid Rocket-Propulsion System

The intermediate mixing chamber is one of various methods for improving the regression rate and combustion efficiency of the hybrid rocket. The mixing chamber with its non-combustible material makes the propulsion performance increase, but it leads to a low fuel-loading density in the combustion chamber; therefore, this performance-related trade-off between the mixing chamber and the low fuel-loading density was studied. In this study, the trade-off was conducted by comparing the intermediate-mixing-chamber case with a w/o-mixing-chamber case. The small hybrid-sounding rocket is designed with internal ballistics for comparing the rocket length to the weight. In addition, an external ballistic analysis was conducted for comparing the performances of the w/and w/o-mixing-chamber cases. As a result, the intermediate-mixing-chamber case shows that the length and the weight were decreased to 12 % and 8 %, respectively; furthermore, when compared with the normal cases, the estimated altitude result of the w/-mixing-chamber case was increased to approximately 75 m.

Effect of Particle Size Distribution on the Sensitivity of Combustion Instability for Solid Rocket Motors

Prediction of combustion instability within a solid-propellant rocket motor has been conducted with the classical acoustic analysis. The effect of particle size distribution on the instability has been analyzed by comparing the log-normal distribution to the fixed mono-sized particle followed by a survey of motor length scale effect between the baseline model and small scale model. Particle damping effect was more efficient for the small scale motor which has a relatively high unstable mode frequencies. It was also revealed that the prediction results by considering the particle size distribution show an overall attenuation of fluctuating pressure amplitude with respect to the mono-sized case.

Effect of Diaphragm Thickness on Regression Rate Improvement in Hybrid Rocket Motor

In this work, a study was conducted to investigate the effect of diaphragm thickness on the regression rate of the hybrid rocket motor. To observe the flow pattern and the recirculation zone, visualizations of combustion chambers with different diaphragm thickness (5mm, 10mm) were performed. It was found that the case with 5 mm thickness had a larger recirculation zone and therefore, had a higher regression rate than the case with 10mm thickness due to the increased residence time and heat transfer toward the fuel surface. Finally, it was concluded that the thickness of diaphragm can be a critical parameter for the enhancement of the regression rate.

Thrust Control of Hybrid Propulsion System for Lunar Exploration

ABSTRACT A feasibility study of thrust control of hybrid propulsion sy stem for lunar exploration is presented. The thrust control experiments were performed by controlling th e oxidizer mass flow rate where the thrust modulation is carried by using a ball valve and a stepping motor. The gaseous oxygen (GOX) and the HDPE (High Density PolyEthylene) were used for the oxid izer and solid fuel, respectively. It was found that the thrust levels were stable without much fluctuation during the modulation period, and that the thrust was exactly controlled with target thrust m odulation ratio of 53% and 32%.초 록 본 연구는 달 탐사 적용을 위한 하이브리드 추진 시스템의 기초 연구로서 산화제 유량 제어를 통한 추력제어 연구를 수행하였다. 산화제 유량 제어를 위해 볼밸브(ball valve)와 스텝 모터(stepping motor)를 이용하여 유량 제어 시스템을 구축하였으며, 산화제 및 연료는 각각 기체 산소(gas oxygen)와 고밀도 폴리에틸렌(High Density PolyEthylene)을 사용하였다. 실험 결과 산화제 유량 제어를 통해 목표 추력 제어 비율(53%, 32%)로 추력제어가 이루어 졌으며, 각각의 구간 내에서 추력이 일정하게 유지 되는 것을 확인 하였다. Key Words: Lunar Exploration(달 탐사), Hybrid Propulsion System(하이브리드 추진 시스템), Thrust Control(추력제어), Oxidizer Flow Rate Control(산화제 유량 제어)