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Instability of Cryogenic Swirl Flows under Subcritical to Supercritical Conditions : 아임계 및 초임계 조건에서 극저온 스월 유동의 불안정성
DC Field | Value | Language |
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dc.contributor.advisor | 윤영빈 | - |
dc.contributor.author | 조성호 | - |
dc.date.accessioned | 2017-07-13T06:17:38Z | - |
dc.date.available | 2017-07-13T06:17:38Z | - |
dc.date.issued | 2015-02 | - |
dc.identifier.other | 000000025071 | - |
dc.identifier.uri | https://hdl.handle.net/10371/118426 | - |
dc.description | 학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2015. 2. 윤영빈. | - |
dc.description.abstract | Instability characteristics of cryogenic swirl flows were experimentally investigated. The cryogenic liquid nitrogen was injected into a high-pressure chamber through a simplex swirl injector under subcritical to supercritical conditions of nitrogen. High-speed photography with backlight imaging was used to obtain images of the temporally changing flow. The set of images was analyzed by the image processing method. The instability frequency was measured by flow image processing and the laser beam diagnostics.
Surface instability of the flow under subcritical to supercritical condition was investigated. Comparing the flow images of the cryogenic and conventional swirl flows, different behaviors were noted, and it was hypothesized that the instability of the cryogenic swirl flow was dominated by the precessing vortex core in the central toroidal recirculation zone. When the ambient condition of the flow was changed from subcritical to supercritical, the phase change and subsequent density change of the injectant differed and flow actions, such as the behavior of the downstream flow, the spray angle, the wavelength, and the propagation velocity, changed drastically. When measuring the frequency of the flow instability, it was found to correspond to that of the precessing vortex core instability. The frequency decreased with the ambient pressure due to the decreasing flow velocity, but it did not change drastically when the surrounding conditions changed from subcritical to supercritical. This implies that the interface of the flow is highly affected by the density of the phase-changed injectant, but that the instability of the flow is determined by the flow in a liquid state. The dynamic characteristics of a cryogenic swirl flow under supercritical conditions were experimentally investigated using a mode decomposition method. Superposed instability structures and vortex ring structures were found in the instantaneous flow image. The spray angle was decreased under supercritical conditions because of the unusual phase change of the injectant inside the injector. Two kinds of modes were deduced by POD analysis of the flow images. The analysis showed that two types of modes exist: a symmetric/tilted-ring shaped mode and an anti-symmetric shaped mode. The Kelvin-Helmholtz instability mechanism generated the symmetric mode. The anti-symmetric structure was created by helical instability, which was generated by the instability of the liquid film inside the injector under subcritical conditions. However, under supercritical conditions, the precessing vortex core in the central toroidal recirculation zone determined the unstable behavior of the flow. A spatial and temporal analysis of the POD modes supported this explanation for the instability. Meanwhile, the spatial characteristics of the coherent structures became similar in the downstream region or under supercritical conditions, which implicates the strong influence of the state of the injectant in flow behavior. | - |
dc.description.tableofcontents | CHAPTER 1. INTRODUCTION 1
1.1 Background and Motivation 1 1.2 Survey of Relevant Literature 5 1.2.1 Characteristics of fluid under supercritical condition 5 1.2.2 Single and coaxial jet flow 6 1.2.3 Jet flow with external excitation 8 1.2.4 Simplex swirl flow 9 1.3 Scope of Study 10 CHAPTER 2. EXPERIMENTAL METHOD 11 2.1 Experimental Apparatus 11 2.1.1 Design procedure of swirl injector 11 2.1.2 High-pressure chamber 17 2.1.3 Cryogenic fluid feeding system 19 2.2 Flow Measurement 20 2.2.1 High-speed photography 21 2.2.2 Flow instability frequency measurement 23 CHAPTER 3. SURFACE INSTABILITY ON CRYOGENIC SWIRL FLOW UNDER SUB- TO SUPERCRITICAL CONDITIONS 24 3.1 Background and Objectives 24 3.2 Experimental Methods 27 3.2.1 Injector design 27 3.2.2 Experimental conditions 28 3.2.3 Experimental techniques 30 3.3 Results and Discussion 31 3.3.1 Characteristics of the cryogenic swirl flow 31 3.3.2 Effect of the ambient pressure on a cryogenic swirl flow surface 34 3.3.3 Instabilty analysis of a cryogenic swirl flow surface 43 CHAPTER 4. DYNAMIC CHARACTERISTICS OF A CRYOGENIC SWIRL FLOW UNDER SUPERCRITICAL CONDITIONS 46 4.1 Background and Objectives 46 4.2 Experimental Methods 48 4.2.1 Injector design 48 4.2.2 Experimental conditions 50 4.2.3 Experimental techniques 51 4.2.4 Proper Orthogonal Decompsition 51 4.3 Results and Discussion 54 4.3.1 Static characteristics of a cryogenic flow 54 4.3.2 POD analysis of flow image 57 4.3.3 Analysis of POD mode 69 CHAPTER 5. CONCLUSION AND FUTURE WORK 74 5.1 Conclusion 74 5.2 Recommendations for Future Work 76 APPENDIX. PROPER ORTHOGONAL DECOMPOSITION 77 A.1 Background 77 A.2 POD Analysis Procedure 77 BIBLIOGRAPHY 81 ABSTRACT IN KOREAN 87 | - |
dc.format | application/pdf | - |
dc.format.extent | 5778909 bytes | - |
dc.format.medium | application/pdf | - |
dc.language.iso | en | - |
dc.publisher | 서울대학교 대학원 | - |
dc.subject | Liquid Propellant Rocket Engine | - |
dc.subject | Simplex Swirl Injector | - |
dc.subject | Cryogenic Flow | - |
dc.subject | Supercritical Condition | - |
dc.subject | Flow Instability | - |
dc.subject | Proper Orthogonal Decomposition | - |
dc.subject.ddc | 621 | - |
dc.title | Instability of Cryogenic Swirl Flows under Subcritical to Supercritical Conditions | - |
dc.title.alternative | 아임계 및 초임계 조건에서 극저온 스월 유동의 불안정성 | - |
dc.type | Thesis | - |
dc.description.degree | Doctor | - |
dc.citation.pages | 88 | - |
dc.contributor.affiliation | 공과대학 기계항공공학부 | - |
dc.date.awarded | 2015-02 | - |
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