1 research outputs found

    λ ˆμ΄μ € λ™μ‹œ 계츑을 μ΄μš©ν•œ Puffed ν™”μ—Όμ˜ ꡬ쑰와 νŠΉμ„±μ— κ΄€ν•œ μ‹€ν—˜μ  연ꡬ

    Get PDF
    ν•™μœ„λ…Όλ¬Έ (석사)-- μ„œμšΈλŒ€ν•™κ΅ λŒ€ν•™μ› : κ³΅κ³ΌλŒ€ν•™ 기계항곡곡학뢀, 2019. 2. 윀영빈.μ—΄ λ°©μΆœλŸ‰κ³Ό ν™”μ—Όλ©΄ μ‚¬μ΄μ—λŠ” 일련의 관계가 μ‘΄μž¬ν•˜κΈ° λ•Œλ¬Έμ— μ—°μ†ŒλΆˆμ•ˆμ •μ— λŒ€ν•œ μ˜ˆμΈ‘μ„ μœ„ν•΄μ„œλŠ” ν™”μ—Ό ꡬ쑰에 κ΄€ν•œ 연ꡬ가 ν•„μš”ν•˜λ‹€. μ—°μ†ŒλΆˆμ•ˆμ •μ€ 이λ₯Ό κ΅¬μ„±ν•˜λŠ” μ„Έ 가지 섭동이 μ–‘μ„± ν”Όλ“œλ°± 루프λ₯Ό ν˜•μ„±ν•˜μ˜€μ„ λ•Œ λ°œμƒ 및 μ¦ν­ν•˜κΈ° λ•Œλ¬Έμ— 각각의 μ„Έ 가지 섭동에 λŒ€ν•΄ μžμ„Ένžˆ κ³ λ €ν•  ν•„μš”κ°€ μžˆλ‹€. λ³Έ μ—°κ΅¬μ—μ„œλŠ” μ—°μ†ŒλΆˆμ•ˆμ •μ— κ΄€ν•œ μ—°κ΅¬μ˜ μΌν™˜μœΌλ‘œ puffed 화염이라 λΆˆλ¦¬λŠ” 특이 ν™”μ—Ό ꡬ쑰에 κ΄€ν•œ 연ꡬλ₯Ό μˆ˜ν–‰ν•˜μ˜€λ‹€. 이전 μ—°κ΅¬μ—μ„œ, κΉ€ λ“±[1]은 νŠΉμ • 주파수 및 μž…λ ₯ 속도 섭동 μ˜μ—­μ—μ„œ puffed 화염이 λ°œμƒν•˜λŠ” 것을 ν™•μΈν•˜μ˜€λ‹€. λ”°λΌμ„œ λ³Έ μ—°κ΅¬μ—μ„œλŠ” μ΄λŸ¬ν•œ puffed 화염에 κ΄€ν•œ λ°œμƒ 원인과 응닡 νŠΉμ„±μ— κ΄€ν•΄ μ—°κ΅¬ν•˜μ˜€λ‹€. 그에 따라, OH-PLIF 와 PIV λ™μ‹œ 계츑을 μˆ˜ν–‰ν•˜μ˜€λ‹€. μ‹€ν—˜μ€ ν™•μ‚° ν™”μ—Όμ˜ ν•œ μ’…λ₯˜μΈ, μ—°λ£Œ λΆ„μΆœ 속도와 μ‚°ν™”μ œ λΆ„μΆœ 속도가 μ„œλ‘œ λ™μΌν•œ 버크 슈만 화염에 κ΄€ν•΄ μ§„ν–‰ν•˜μ˜€λ‹€. 메탄과 μˆ˜μ†Œμ˜ ν˜Όν•©κΈ°κ°€ μ—°λ£Œλ‘œ μ‚¬μš©λ˜μ—ˆκ³  μ‚°ν™”μ œλ‘œλŠ” μƒμ˜¨ 곡기가 μ‚¬μš©λ˜μ—ˆλ‹€. μ—°μ†ŒλΆˆμ•ˆμ • ν˜„μƒμ„ λͺ¨μ‚¬ν•˜κΈ° μœ„ν•œ μ™ΈλΆ€ 음ν–₯ 가진은 100 Hz λΆ€ν„° 180 Hz κΉŒμ§€ 20 Hz κ°„κ²©μœΌλ‘œ μΈκ°€λ˜μ—ˆλ‹€. λ˜ν•œ μž…λ ₯ 속도 섭동 진폭은 0.1μ—μ„œ 0.5 κΉŒμ§€ 0.1의 κ°„κ²©μœΌλ‘œ μ μš©λ˜μ—ˆλ‹€. λ ˆμ΄μ € λ™μ‹œ 계츑에 μ˜ν•΄ 속도μž₯, strain rateμž₯, OH λΆ„ν¬λŠ” λ™μ‹œμ— κ³„μΈ‘λ˜μ—ˆλ‹€. λ™μ‹œ κ³„μΈ‘μ˜ 결과둜 ν™”μ—Όμ˜ 응닡 νŠΉμ„±κ³Ό μœ λ™μ˜ 거동은 같은 μ‹œκ°„λŒ€μ— λŒ€ν•΄ λΆ„μ„λ˜μ—ˆλ‹€. OH-PLIF 계츑을 μ΄μš©ν•˜μ—¬ ν™”μ—Ό ꡬ쑰λ₯Ό ν™•μΈν•˜μ˜€μœΌλ©° 이 μ™Έμ˜ λ‹€λ₯Έ μ •λŸ‰μ  계츑은 PIV 계츑을 μ΄μš©ν•˜μ—¬ μˆ˜ν–‰ν•˜μ˜€λ‹€. λ™μΌν•œ μ™ΈλΆ€ 음ν–₯ 가진 주파수 μ˜μ—­μ—μ„œλŠ” νŠΉμ • μž…λ ₯ 속도 μ΄μƒμ—μ„œ flame puffed ν˜„μƒμ΄ λ°œμƒλ˜μ—ˆλ‹€. μ™ΈλΆ€ 음ν–₯ 가진 μ£ΌνŒŒμˆ˜κ°€ μ¦κ°€ν•˜λŠ” κ²½μš°μ—λŠ” 화염을 λΆ„λ¦¬ν•˜κΈ° μœ„ν•΄ 더 큰 μž…λ ₯ 속도 섭동이 ν•„μš”ν•˜μ˜€λ‹€. μ΄λŠ” 화염이 μ €μ—­ ν•„ν„° λΌλŠ” 것을 λ‹€μ‹œ ν•œ 번 μ•Œ 수 있게 ν•˜μ˜€λ‹€. λ˜ν•œ flame puffed ν˜„μƒμ€ μ™ΈλΆ€ 음ν–₯ 가진 μ£ΌνŒŒμˆ˜μ— 따라 주기적으둜 λ°œν˜„λ¨μ„ 확인할 수 μžˆμ—ˆλ‹€. PIV와 OH-PLIF의 λ™μ‹œ 계츑을 톡해 높은 strain rate 와 μ‚°ν™”μ œμ˜ μœ μž…μ΄ ν™”μ—Όμ˜ μ ˆλ‹¨ 과정에 μžˆμ–΄ μ£Όμš”ν•œ 원인이 됨을 νŒŒμ•…ν•˜μ˜€λ‹€. μ‹€ν—˜ 결과에 따라, 높은 strain rateκ°€ μž‘μš©ν•˜λ©΄ 화염면이 μ„­λ™ν•˜κ³  ν™”μ—Όλͺ©μ΄ λ”μš± μ’μ•„μ§€κ²Œ λœλ‹€. λ˜ν•œ flame puffed 과정이 진행됨에 따라, 점점 더 높은 strain rate κ°€ 화염면에 μž‘μš©ν•˜λŠ” 것을 ν™•μΈν•˜μ˜€λ‹€. Flame puffed κ³Όμ •μ˜ λ§ˆμ§€λ§‰ λ‹¨κ³„μ—μ„œ μΌλ°˜μ μ΄μ§€ μ•Šμ€ κΈ‰κ²©ν•œ λ³€ν™”λ₯Ό λ³΄μ΄λŠ” μœ λ™μ΄ κ³„μΈ‘λ˜μ—ˆκ³  이둜 인해 λ”μš± 높은 strain rate κ°€ 화염면에 μž‘μš©ν•˜μ˜€λ‹€. 이와 λ™μ‹œμ—, ν™”μ—ΌμœΌλ‘œμ˜ μ‚°ν™”μ œμ˜ μœ μž…μ€ ν™”μ—Ό μ ˆλ‹¨ ν˜„μƒμ˜ 또 λ‹€λ₯Έ 원인이라 ν•  수 μžˆμ—ˆλ‹€. Flame puffed 과정이 μ§„ν–‰λ˜λ©΄μ„œ μ£Όμœ„ 곡기가 점차 ν™”μ—Ό 쀑간 μ˜μ—­μœΌλ‘œ μΉ¨μž…ν•˜μ˜€μœΌλ©° 이둜 인해 κ²°κ΅­μ—” 화염이 μ™„μ „νžˆ λΆ„λ¦¬λ˜κ³  μ‚°ν™”μ œκ°€ ν•΄λ‹Ή μ˜μ—­ μ€‘κ°„μœΌλ‘œ μ™„λ²½ν•˜κ²Œ μΉ¨νˆ¬λœλ‹€. Flame puffed ν˜„μƒμ΄ λ°œμƒν•˜λ©΄ ν™”μ—Όμ˜ 응닡 νŠΉμ„±μ€ 음ν–₯ 가진을 μΈκ°€ν•˜μ§€ μ•Šμ€ κ²½μš°μ™€ μ™„μ „νžˆ 달라진닀. ν™”μ—Όμ˜ 길이와 면적은 보닀 μ§§μ•„μ§€κ²Œ λ˜λ‚˜ ν™”μ—Όμ˜ 길이 및 면적 섭동은 큰 폭으둜 μ¦κ°€ν•œλ‹€. 즉, flame puffed ν˜„μƒμ΄ λ°œμƒν•˜λŠ” κ²½μš°μ— 화염은 보닀 λΆˆμ•ˆμ •ν•œ μƒνƒœκ°€ λœλ‹€κ³  ν•  수 μžˆλ‹€.To predict combustion instability, the study of the flame surface is necessary because there is a relationship between the heat release rate and the flame surface. Combustion instability is occurred and amplified when the three components of the perturbation constitute a positive feedback. Thus each of three components should be considered carefully. In order to predict the combustion instability, in this paper, the unique flame structure, called as the puffed flame, was investigated. In the previous work, Kim et al. [1] discovered the puffed flame structure at the specific forcing frequency and the velocity perturbation region. In this paper, therefore, we revealed the causes and the dynamic characteristics of the puffed flame. Thus, simultaneous OH-PLIF and PIV measurements were conducted. In case of the flame, the burke-schumann flame, a special case of the non-premixed flame, was considered. The mixture of the methane and hydrogen was used as the fuel, and the air was used as the oxidizer. The acoustic forcing was applied for the several frequency regionfrom 100 Hz to 180 Hz with 20 Hz steps. Also incoming velocity perturbation amplitude was varied from 0.1 to 0.5 with 0.1 steps. The velocity, strain rate, and the distribution of the OH radical were measured at the same time due to the simultaneous laser diagnostics. From these results, the response characteristics and the flow behavior were found at the exact same time. Flame structure was captured from the OH-PLIF measurement and the other quantitative results such as velocity vector and strain rate field were measured from the PIV. In the same forcing frequency region, the flame puffed phenomenon was occurred over the specific velocity perturbation amplitude. If the forcing frequency became higher, the more velocity perturbation amplitude was necessary for the flame puffed. With this results, we could realize that the flame acts as a low pass filter. Also, it was revealed that the flame puffed phenomenon was periodic process which was following the external acoustic excitation wave. With the simultaneous PIV and OH-PLIF results, we could find out the relative high strain rate and the oxidizer entrainment played important roles for the puffed process. High strain rate make flame wrinkle and flame throat more thinner. As the process proceeded, more higher strain rate was applied to the flame surface as well. At the final stage of the flame puffed phenomenon, highly irregular flow was generated, so that the strain rate became much higher. Meanwhile, oxidizer entrainment could be another reason for the puffed flame. During the process, surrounding air was continuously invaded into the middle of the flame. At last, flame was separated into two regions due to the entrainment of the surrounding air. When the flame puffed phenomenon was occurred, the dynamic characteristics became different from the non-excitation flame case. The flame length became more smaller and the flame surface area also decreased. However, flame length and the surface area perturbation were increased. In other words, when the flame puffed, we could say that the flame became more unstable.Contents Chapter 1 INTRODUCTION 1 1.1 Combustion instability 1 1.2 Strain rate 4 1.3 Previous research 8 Chapter 2 EXPERIMENTAL APPARATUS AND METHODS 12 2.1 Burke-schumann flame combustor 12 2.2 Test condition 15 2.3 Particle image velocimetry 20 2.4 OH Planar laser induced fluorescence 23 2.5 Simultaneous laser diagnostics 26 Chapter 3 Results and Discussion 28 3.1 OH-PLIF images for the puffed flame 28 3.1.1 OH-PLIF images for the various forcing frequencies 28 3.1.2 OH-PLIF images for the various velocity perturbation amplitudes 32 3.1.3 Averaged OH-PLIF images 35 3.2 Results of the simultaneous laser diagnostics 37 3.2.1 Radial velocity generation 37 3.2.2 The beginning of the flame surface wrinkling 41 3.2.3 Strain rate distribution near the critical region 43 3.2.4 Comparison of the strain rate distribution 49 3.2.5 The effect of the strain rate to the puffed flame throat 52 3.2.6 The maximum and the minimum strain rate 55 3.2.7 Surrounding air entrainment 61 3.3 Dynamic characteristics of the puffed flame 64 3.3.1 Flame length and surface area 65 3.3.2 Flame length and surface area perturbation 69 Chapter 4 CONCLUSION 71 Appendix A Theoretical understanding of resonance frequency 74 Bibliography 77 Abstract in Korean 83Maste
    corecore