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系統識別號 U0026-2307201821552100
論文名稱(中文) 凹槽機構之幾何參數對於超音速流場影響之數值模擬分析
論文名稱(英文) Numerical simulations of the effect of geometry parameters of cavity mechanism on a supersonic flow field
校院名稱 成功大學
系所名稱(中) 航空太空工程學系
系所名稱(英) Department of Aeronautics & Astronautics
學年度 106
學期 2
出版年 107
研究生(中文) 陳家禾
研究生(英文) Jia-He Chen
學號 P46054058
學位類別 碩士
語文別 中文
論文頁數 178頁
口試委員 指導教授-江滄柳
口試委員-劉正芳
口試委員-袁曉峰
中文關鍵字 超音速燃燒  液態燃料噴注  凹槽機構  數值模擬  弓形震波 
英文關鍵字 Supersonic combustion  Liquid fuel injection  Cavity  Numerical simulation  Bow Shock 
學科別分類
中文摘要 超燃衝壓發動機為目前吸氣式發動機中飛行速度最快之發動機,其特點在於自由流能維持在超音速的狀態下進入燃燒室中。由於自由流速度為超音速,液態燃料需要經過破碎、霧化及蒸發等過程,並與氧化劑混合後才能產生燃燒反應。這些諸多因素,造成燃燒室內部之點火不易、燃料與空氣難以充分混合影響著燃燒效率。因此,本研究加入凹槽駐焰機構針對其幾何外型的變化,使用ANSYS FLUENT進行一系列的數值計算模擬分析。藉由數值計算軟體探討凹槽機構之幾何形狀變化,對於超音速之流場結構的影響,並能夠模擬出明確的流場結構、氣態煤油分佈、燃燒室溫度分佈等重要參數,以提供實驗設備難以觀測之物理現象,有利於減少實驗昂貴的支出及提升人員的安全性。
首先,本研究根據Gruber等人之文獻,建立相同條件之二維超音速燃燒室,並藉由本研究設定之數值方法與其數值計算之流場進行比對,結果顯示本研究成功模擬出Gruber等人計算之穩態流場結構,同時驗證了本研究數值方法之可靠度及精確性。在幾何模型的部份,建立兩組不同凹槽長深比(L/D)值分為3.0及6.0,且後壁面傾角分為16度及30度之燃燒室模型。首先,觀察在尚未注入液態燃料之凹槽機構內部流場,發現到儘管為左右對稱之幾何模型,流場仍存在不對稱性,在一連串的測試下,發現加入凹槽機構,其內部產生之迴流區彼此間會有交互作用會造成流場不穩定的現象。因此,具凹槽機構中之流場不容易呈現對稱流場形態。凹槽機構的設置會造成自由流有小幅度之下傾現象,使得燃料流入凹槽機構中,增加燃料駐留於燃燒室中之質量。而不論L/D值為3.0或6.0的模型,後壁面傾角16度之自由流下傾角度皆大於後壁面傾角30度之自由流下傾角度,也代表著後壁面傾角16度之幾何外型能夠使燃料駐留質量較多。而自由流流經凹槽後壁面時,由於幾何型形狀改變影響流場面積縮小,造成流場速度減慢、壓力提升,而在後壁面產生後緣弓形震波的現象。最後,氣態煤油S型擺動方面,平板燃燒室會因前方液態燃料與自由流撞擊產生之弓形震波,會造成自由流發生擾動,使得氣態煤油有小幅度之S型擺動;具凹槽機構燃燒室,由於凹槽機構內部產生之迴流區,迴流區彼此間之交互作用,會造成流場產生不穩定性進而造成氣態煤油擺動現象更加顯著,而迴流區的個數增加,則會造成交互作用更加劇烈,流場的不穩定性更加嚴重,氣態煤油擺動則有愈劇烈的趨勢。
關鍵字:超音速燃燒、液態燃料噴注、凹槽機構、數值模擬、弓形震波
英文摘要 In order to investigate the detailed effects of a cavity flame holder on a supersonic flow field, the computational fluid dynamics (CFD) software ANSYS FLUENT was used to conduct a numerical simulation of the geometry parameters of a cavity mechanism on a supersonic flow field with a liquid kerosene injection. First of all, following Gruber et al., we established two two-dimensional cavity mechanism with the same boundary conditions and according to our numerical simulation results, successfully simulated a similar steady flow field structure, for which the accuracy and reliability were verified.
We established two three-dimensional cavity mechanisms, with L/D=3.0 and 6.0, where L was the cavity center length, and D was the cavity depth. The two L/D values were studied with two aft ramp angles: θ=16 degrees and θ=30 degrees. All cavity flows were of the open type. Initially, we observed two high pressure regions in the combustor. One was the high pressure region formed by the collision of the liquid jet with the free stream, and the other was the high pressure region formed by the change of the flow field due to the geometric change. These high pressure regions were all bow shock. When a free stream flows over the cavity mechanism, the compression wave causes the free stream to separate into shear vortices that enter the cavity mechanism with a slight lean angle. In this case, because the aft wall ramp angle was smaller, the lean angle was larger, and the kerosene fuel content inside the cavity was greater. Regardless of whether L/D=3.0 or L/D=6.0, the lean angle of the aft ramp angle at 16 degrees was greater than the lean angle of aft ramp angle at 30 degrees. Finally, during the kerosene vapor oscillation, due to the bow shock generated by the collision between the liquid injection and the free stream, the free steam flowing though the bow shock causes a deviation in the free stream velocity. As a result, the kerosene vapor exhibits an S-type oscillation phenomenon. Different L/D values for the cavity can affect the internal recirculation structure of the cavity, and the interaction between each recirculation process causes instability in the flow field, which makes the kerosene vapor more extreme.
Keywords: Supersonic combustion, Liquid fuel injection, Cavity, Numerical simulation, Bow Shock.
論文目次 摘要 .........................................I
致謝 .........................................XII
目錄 .........................................XIV
表目錄 .........................................XVII
圖目錄 .........................................XVIII
符號索引 .........................................XXXII
第一章 導論......................................1
§1-1 前言......................................1
§1-2 文獻回顧...................................3
§1-3 研究動機與目的.............................13
第二章 數學與物理模型..............................15
§2-1 基本假設...................................16
§2-2 連續相流場之統御方程式......................17
§2-3 紊流模型之統御方程式........................22
§2-4 邊牆函數...................................24
§2-5 離散相流場之統御方程式......................27
第三章 數值方法...................................43
§3-1 控制體積轉換之傳輸方程式....................43
§3-2 壓力耦合演算法求解器........................44
§3-3 二階上風法.................................45
§3-4 離散相計算流程..............................46
§3-5 鬆弛因子...................................47
§3-6 收斂標準...................................48
第四章 結果與討論.................................49
§4-1 二維超音速燃燒室之網格模型與邊界條件..........51
§4-2 二維超音速燃燒室之網格獨立測試...............52
§4-3 選用模型驗證及二維超音速燃燒室流場分析........53
§4-4 三維超音速燃燒室網格模型與邊界條件............55
§4-5 三維超音速燃燒室之網格獨立測試................57
§4-6 超音速流場不對稱性之流場分析..................59
§4-7 具凹槽機構之超音速燃燒室後壁面高壓形成成因.....62
§4-8 L/D=3.0之超音速燃燒室冷流場分析..............64
§4-9 L/D=6.0之超音速燃燒室冷流場分析..............68
§4-10 具凹槽機構之超音速燃燒室與平板機構之相互比較...73
第五章 結論與未來建議..............................77
§5-1 結論.......................................77
§5-2 未來建議....................................81
參考文獻............................................83
表 附錄.............................................88
圖 附錄.............................................90
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