핀틀 분사기의 형상 변수에 따른 분무 특성

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 윤영빈.Recently, as interest in low-cost reusable launch vehicles has increased with the micro-satellite market, soft-landing techniques have become important. A pintle injector can help realize this because it is capable of thrust control. After being devised by TRW, it has been developed and researched since the early 2000s. However, published literature and information are limited and still lacks in the design of the geometry. In particular, the pintle injector has many geometric parameters that affect its performance, so research on these is essential. This study examined the relationship between main geometric parameters and spray characteristics. Since the spray characteristics of the pintle injector are closely related to the combustion efficiency, it was analyzed through cold test. First of all, internal flow passage design was carried out to evenly inject the fluids for small thruster with a thrust ratio of 5:1. Various geometry cases were designed to maintain the axial concentricity of the drive part, and optimal geometry condition was derived through experiments and numerical analysis. Afterwards, the effects of the gap distance (G), a factor related to the control of annular flows orifice area, on the spray characteristics were investigated. When G decreased at the same throttling level, the spray angle decreased because the momentum of the annular flow became relatively large. When G was fixed, the spray angle was almost constant even though the throttling level was changed. Droplet diameter also had a proportional relationship with G. Through the relationship between SMD and Weber number (We) and momentum flux ratio (J), it was found that pintle injector has two main atomization mechanisms. At the pintle tip, when the radial and annular flows collided vertically, there was breakup of the liquid sheet due to the difference in momentum, and additional breakup due to the shear force at the interface of the two fluids. The experimental correlations for the spray angle and SMD were obtained, and through this, the control range of G to maintain a specific SMD in all thrust levels was derived. Cold test was also performed on another important geometric factor, skip distance. As the skip distance increased, the spray angle and SMD had a proportional relationship. While annular flow moved along the pintle surface, the velocity decreased due to the interaction between friction and the ambient air. Due to this, the momentum loss rate increased and such a tendency appeared. Change rate in the spray characteristics due to the skip distance became larger under the low thrust level, and showed the maximum change especially under the throttling level of 20%. In order to analyze these trends in more detail, numerical analysis of the axial direction velocity of the annular flow near the pintle surface was carried out. In all throttling levels, developed region with a similar velocity profile was observed after a potential core where the velocity remained constant from the orifice exit to a certain distance. In particular, it was found that the potential core region was the shortest and the velocity decay rate was the highest under the throttling level of 20%. As a result, the change rate of the spray angle and SMD seemed to be largest at the throttling level of 20%. Through the decay rate of velocity according to the skip distance, variation rates of the spray angle and SMD were obtained. Finally, from the design perspective, appropriate skip distance was proposed in consideration of the standard deviation between each throttling level. From this study, databases on the important geometric parameters were obtained. These results are expected to help understand the relationship between the skip distance and spray characteristics. In addition, it can be used to design a thrust control system to improve the spray efficiency as a reference for setting the orifice area control range of annular flow. In the future, the presented findings may provide guidance for the design of effective injectors to be used in throttleable engines.민간 주도의 우주 발사체 시장 성장과 함께 초소형 위성 시장이 커짐에 따라 상업 발사 서비스 시장 경쟁이 치열해지면서 발사 비용을 낮추기 위한 차세대 발사체 개발이 활발히 이루어지고 있다. 재사용 발사체는 저비용 발사 임무를 실현하기 위한 중요 기술로, 지상 또는 해상 착륙 시 엔진 회수를 위한 소프트 랜딩 기술이 매우 중요하게 여겨진다. 소프트 랜딩은 발사체 엔진의 추력을 조절함으로써 실현 가능하며, 이를 위한 몇 가지 기술들 중 추진제 오리피스 면적 제어를 이용한 방식이 신뢰성 있다고 여겨지고 있다. 핀틀 분사기는 면적 조절을 통한 추력 제어 방식의 대표적 시스템이다. 미국 TRW 사에 의해 고안된 후, 2000년대 초반부터 국내외에서 핀틀 분사기에 대한 개발 및 연구가 수행되고 있으나, 공개된 문헌 및 정보가 한정적이며 제한적이기 때문에 설계에 있어 여전히 어려움이 존재한다. 특히, 핀틀 분사기는 성능에 영향을 미치는 여러 형상 변수들을 가지기 때문에 이에 대한 연구가 필수적이다. 따라서 본 연구에서는 중요 형상 변수들과 분무 특성과의 관계를 살펴보았다. 핀틀 분사기의 분무 특성은 연소 성능과 밀접하게 관련되어 있기 때문에 수류 실험을 통해 이를 분석하고자 하였다. 먼저, 핀틀 분사기의 최적 설계를 위한 데이터베이스 마련을 위해 5:1의 추력비를 가지는 소형 액체로켓엔진용 핀틀 분사기에 대해 유체를 고르게 분무하기 위한 내부 유로 설계를 수행하였다. 추력이 변하는 동안 구동 장치의 축 방향 동심도를 유지하기 위해 다양한 형상 케이스를 고안하였고 수치해석 및 실험을 통해 최적 형상 조건을 모색하였다. 이후 annular flow의 오리피스 면적 조절과 관련된 인자인 gap distance (G)를 바꿔가며 분무 특성에 미치는 영향을 살펴보았다. 실험 결과, 동일 추력 레벨에서 G가 감소할 경우, annular flow의 운동량이 상대적으로 커지기 때문에 분무각은 감소하였다. G가 고정되어 있을 경우에는 추력 레벨이 변하더라고 분무각은 거의 일정하였다. 액적 직경의 경우도 G가 감소함에 따라 작아지는 경향을 보였다. SMD와 분열과 관련된 무차원수인 We 및 J와의 관계를 살펴본 결과, 핀틀 분사기가 크게 두 가지 미립화 과정을 가지는 것을 알 수 있었다. 초기 핀틀 끝 단에서 radial flow와 annular flow가 수직 충돌 시 두 유체의 운동량 차로 인한 액막 분열과 함께 두 유체 표면에서의 전단력으로 인한 추가 분열이 진행되는 것으로 분석되었다. 분무각 및 SMD에 대한 실험식을 구하였고, 이를 통해 전 추력 구간에서 특정 SMD를 유지하기 위한 G의 제어 범위를 도출하였다. 핀틀 분사기의 또 다른 중요 형상 변수인 skip distance에 대해서도 수류 실험을 수행하였고, skip distance의 증가에 따라 분무각 및 SMD가 비례 관계를 가지는 것을 확인하였다. Annular flow가 핀틀 표면을 따라 이동하면서 마찰 및 대기와의 상호작용으로 인해 유속이 감소하게 되고 이에 따른 운동량 손실률 증가 등으로 인해 이러한 경향이 나타났다. Skip distance에 따른 분무 특성 변화율은 저 추력 조건으로 갈수록 커졌고, 특히 20% 조건에서 가장 큰 폭을 보였다. 이러한 경향성을 좀 더 자세히 분석하기 위해 핀틀 표면 부근에서 annular flow의 축 방향 속도 분포를 수치적으로 분석하였다. 전 추력 조건에서 오리피스 출구 시작점으로부터 일정 거리까지 속도가 일정하게 유지되는 potential core와 속도 프로파일이 유사성을 가지는 developed region이 관찰되었다. 특히, 20% 추력 조건에서 potential core 영역이 가장 짧았고 최대 속도 감소율도 가장 높은 것으로 나타났다. 이로 인해 20% 추력 조건에서 분무각과 SMD가 가장 크게 변화된 것으로 보였다. Skip distance에 따른 속도 감소율을 통해 분무각 및 SMD 변화율을 얻었고, 마지막으로 설계 관점에서 각 추력 레벨간의 표준 편차를 고려하여 적절한 skip distance가 제안되었다. 본 연구를 통해 핀틀 분사기 설계 단계에서 고려돼야 할 주요 형상 변수들에 대한 자료를 확보하였다. 이러한 결과는 skip distance와 분무 특성과의 관계를 이해하는데 도움이 될 것으로 기대된다. 또한, annular flow의 오리피스 면적 제어 범위 설정을 위한 참고 자료로서 분무 성능 향상을 위한 추력 제어 시스템 설계에 활용 가능하다. 향후 가변추력용 엔진을 위한 효과적인 분사기 설계에 대한 기초자료로서 이용될 것으로 기대된다.CHAPTER 1 INTRODUCTION 1 CHAPTER 2 DESIGN OF PINTLE INJECTOR 8 2.1 Specifications and Basic Parameters 8 2.2 Design of Radial Flow Passage 13 2.3 Design of Annular Flow Passage 19 CHAPTER 3 EXPERIMENTAL METHODS AND SETUPS 24 3.1 Spray Imaging 24 3.2 Droplet Size (SMD) 25 3.3 Spray Pattern 27 CHAPTER 4 EFFECTS OF GAP DISTANCE ON SPRAY CHARACTERISTICS 31 4.1 Objectives 31 4.2 Experimental Conditions 31 4.3 Results and Discussion 34 4.3.1 Spray Structure 34 4.3.2 Droplet Size (SMD) 42 4.3.3 Spray Uniformity 46 4.3.4 Relationship between Spray Angle and SMD 50 4.3.5 Variations in Gap Distance and Spray Angle with SMD 51 CHAPTER 5 SPRAY CHARATERISCIS WITH SKIP DISTANCE 54 5.1 Background and Objectives 54 5.2 Experimental Conditions 57 5.3 Numerical Conditions and Setups 59 5.4 Results and Discussion 60 5.4.1 Spray Angle 60 5.4.2 Droplet Size (SMD) 63 5.4.3 Distribution of Gas Velocity 65 5.4.4 Correlations of Spray Characteristics with Decay Rate 74 5.4.5 Trends of Average Spray Angle and SMD with Standard Deviation 79 CHAPTER 6 CONCLUSION 81 REFERENCES 84 ABSTRACT IN KOREAN 92Docto

Main Chamber and Preburner Injector Technology

This document reports the experimental and analytical research carried out at the Penn State Propulsion Engineering Research Center in support of NASA's plan to develop advanced technologies for future single stage to orbit (SSTO) propulsion systems. The focus of the work is on understanding specific technical issues related to bi-propellant and tri-propellant thrusters. The experiments concentrate on both cold flow demonstrations and hot-fire uni-element tests to demonstrate concepts that can be incorporated into hardware design and development. The analysis is CFD-based and is intended to support the design and interpretation of the experiments and to extrapolate findings to full-scale designs. The research is divided into five main categories that impact various SSTO development scenarios. The first category focuses on RP-1/gaseous hydrogen (GH2)/gaseous oxygen (GO2) tri-propellant combustion with specific emphasis on understanding the benefits of hydrogen addition to RP-1/oxygen combustion and in developing innovative injector technology. The second category investigates liquid oxygen (LOX)/GH2 combustion at main chamber near stoichiometric conditions to improve understanding of existing LOX/GH2 rocket systems. The third and fourth categories investigate the technical issues related with oxidizer-rich and fuel-rich propulsive concepts, issues that are necessary for developing the full-flow engine cycle. Here, injector technology issues for both LOX/GH2 and LOX/RP-1 propellants are examined. The last category, also related to the full-flow engine cycle, examines injector technology needs for GO2/GH2 propellant combustion at near-stoichiometric conditions for main chamber application

NASA Propulsion Engineering Research Center, Volume 2

This is the second volume in the 1994 annual report for the NASA Propulsion Engineering Research Center's Sixth Annual Symposium. This conference covered: (1) Combustors and Nozzles; (2) Turbomachinery Aero- and Hydro-dynamics; (3) On-board Propulsion systems; (4) Advanced Propulsion Applications; (5) Vaporization and Combustion; (6) Heat Transfer and Fluid Mechanics; and (7) Atomization and Sprays

Fifth International Symposium on Liquid Space Propulsion

Contents include the fiollowing: Theme: Life-life Combustion Devices Technology. Technical Sessions: International Perspectives. System Level Effects. Component Level Processes. Material Considerations. Design Environments -- Predictions. Injector Design Technology. Design Environments -- Measurements. Panel Discussion: Views on future research and development needs and Symposium observations. Aquarium Welcome and Southern Belle Riverboat Recognition Banquet evening events

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This issue of the Index Section contains entries for 3386 patent and application for patent citations covering the period May 1969 through June 1978. The Index Section contains five indexes --- subject, inventor, source, number, and accession number

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 04)

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NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 10)

Abstracts for 3089 patents and applications for patent entered in the NASA scientific and information system for the period covering May 1969 through December 1976 are indexed by subject, inventor, source, NASA case or U.S. patent number, and accession number in the NASA system

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 12)

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