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Student Number 88323062
Author Rei-Qi Su(蘇瑞期)
Author's Email Address No Public.
Statistics This thesis had been viewed 1329 times. Download 933 times.
Department Mechanical Engineering
Year 2000
Semester 2
Degree Master
Type of Document Master's Thesis
Language zh-TW.Big5 Chinese
Title 自由傳播預混焰與紊流尾流交互作用﹔火焰拉伸率和燃燒速率之量測
Date of Defense 2001-07-17
Page Count 107
Keyword
  • premixed flame
  • stretch rate
  • turbulent wake
  • Abstract This research uses a self-designed turbulent wake burner to investigate a downward propagating premixed flame interacting with a turbulent wake. Since the interaction of flame and wake can produce the so-called flame stretching effects. To study the stretching effects and ST, we apply high-speed laser tomography and particle image velocimetry (PIV), use research-grade methane or propane -air mixtures, and conduct a series of experiments. Basically, there are two types of wake vortices, a compressive strain (counter-rotating) vortex pair and an extensive strain vortex pair. It is found that flame-wake interactions in compressive strain vortices are more intense than in extensive strain vortices. This is because the compressive strain vortex pair can engulf directly the flame into the clockwise-rotating vortex core. Burning starts at the vortex core and through layers and layers radially. The other half, counter-rotating vortex has slower burning rates. This asymmetry of burning is due to the facts that the axis of the vortex pair is not perpendicular to the flame front and the buoyancy effect matters.
    We calculate the local flame stretching rate (including the curvature rate and the aerodynamic strain rate) along the wrinkled flame front at different times using laser tomography and PIV techniques. For the extensive strain vortex pair, values of the stretching rate increase along the wrinkled flame front from the vortex tip to the position which is close to the vortex core. This result is similar to that of Driscoll et al. (1994) using a single axisymmetric vortex pair interacting with a premixed flame. It is found that the curvature term is much more important than the strain rate term. Thus, the stretching rate may be approximated by the curvature term alone. From the probability density function of the stretching rate, we found that the stretching rate changes with time , indicating that the unsteady effect cannot be neglected.
    In order to measure the effect of turbulent intensity to ST, we put the thin disturbance slices with different heights on the edge of the sliding plate. The results are then compared with previous experimental and theoretical results. It is found that the present ST measurements are much higher than our previous data using a cruciform burner which can produce a near-isotropic turbulent flow field. This may be because in the 3-D near-isotropic turbulent flow field many flame-flame collisions and annihilations are frequently observed. Therefore, the increase of the total flame area is not linearly proportional to the turbulent intensity, values of ST obtained in 3-D near-isotropic turbulence field using the cruciform burner are found to be much less than that of the present measurements for 2-D flame-wake interactions. However, the latter is not stationary and must be viewed with caution.
    Table of Content 摘要...............................................................................................................I
    英文摘要.................................................................................................... II
    誌謝.............................................................................................................III
    目錄.............................................................................................................IV
    圖表目錄....................................................................................................VI
    符號說明.....................................................................................................X
    第一章 前言.................................................................................................1
    1.1 動機.....................................................................................................1
    1.2 問題所在............................................................................................2
    1.3 解決提案和論文架構.......................................................................4
    第二章 文獻回顧........................................................................................7
    2.1 薄碎焰(Flamelet)理論........................................................................7
    2.2 預混紊流燃燒區域圖.......................................................................8
    2.3 拉伸效應對預混焰的影響.............................................................12
    2.3.1 拉伸的基本定義................................................................12
    2.3.2 正拉伸與負拉伸................................................................13
    2.4 預混焰流力和擴散不穩定性........................................................15
    2.5 非定常火焰拉伸效應.....................................................................17
    第三章 實驗設備和量測方法.................................................................24
    3.1 紊流尾流燃燒設備介紹.................................................................24
    3.2 紊流尾流...........................................................................................27
    3.3 雷射斷層攝影術..................................................................................29
    3.4 影像處理...............................................................................................32
    3.5 質點影像測速儀..................................................................................33
    3.6 拉伸率之計算..................................................................................... 34
    3.6.1 曲率項之計算...............................................................................34
    3.6.2 空氣動力應變項及膨脹率之計算............................................35
    3.7紊流強度和紊流燃燒速度之量測估算...........................................35
    3.8實驗誤差評估......................................................................................37
    3.8.1 雷射斷層攝影術..........................................................................37
    3.8.2 PIV之量測精確度........................................................................38
    第四章 預混焰與尾流之非定常拉伸分析...........................................48
    4.1火焰動態傳播分析,應用雷射斷層攝影術...............................48
    4.2拉伸率與膨脹率之關係..................................................................51
    4.3拉伸率、應變率及曲率之間的關係............................................55
    4.4拉伸率、應變率、曲率及膨脹率之機率密度函數分佈.........57
    第五章 紊流燃燒速度估算.....................................................................83
    5.1 紊流強度對燃燒速度的影響........................................................83
    5.2 相關實驗理論與結果之比較........................................................85
    第六章 結論與未來工作..........................................................................98
    6.1 結論....................................................................................................98
    6.2 未來工作.........................................................................................100
    參考文獻...................................................................................................102
    附錄A-曲率之計算..................................................................................107
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  • Shenqyang Shy(施聖洋)
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    Date of Submission 2001-07-17

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