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研究生:吳宗瀚
研究生(外文):Zong-Han Wu
論文名稱:以力元理論觀點探討真實果蠅懸停之氣動力機制
論文名稱(外文):The Unsteady Aerodynamics of Real FruitFly from the Perspective of a Force Element Theory
指導教授:朱錦洲
口試委員:張家歐謝政達宮村斐
口試日期:2013-07-20
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:應用力學研究所
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2013
畢業學年度:101
語文別:中文
論文頁數:104
中文關鍵詞:非常定空氣動力學果蠅:懸停
外文關鍵詞:Unsteady AerodynamicsFruitFlyhovering
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本論文主要是以張建成教授於1992年所發表之力元理論,來分析低雷諾數下果蠅懸停撲拍之非定常氣動力特性。力元理論可檢視流場中非零渦度流元與物體受力之間關係,同時可將物體運動時之受力中提煉出勢流力以及其它具有物理意義之受力貢獻。本文將分別檢視三種不同懸停模式(對稱、超前與延遲)下各個升力元素之變化,同時與二維簡化模式下(Hsieh, Chang & Chu, 2009, vol. 623, pp. 121–148)進行比對。不同於二維假設,在所探討之三種運動模式中附加質量力皆具升力貢獻,而翅膀主要升力來源來自於環境渦度。
為了進一步探討翅膀三個運動階段包括:撲拍中期、翻轉前期與翻轉後期之前緣渦、翼尖渦、後緣渦與根部渦漩等三維渦漩結構與翅膀高升力之間的關係。透過以翅膀旋轉軸做為中心,將流場以同心圓進行環狀切割,分別探討各個環狀切割流場中之升力元素變化。吾人更進一步發現在複雜三維翅膀翻轉階段時之流場中所存在之高升力機制。貼附於翅膀前緣端之前緣渦撲拍中期時之升力來源,即動態失速機制。當翅膀於翻轉前期,翼尖渦、後緣渦與根部渦漩相連成渦環狀並向尾流脫落,前緣渦沿著翅膀表面朝向翼尖方向運動。當翅膀於翻轉後期時,翅膀將有兩次騎乘升力元素機制,原本由三個渦漩組成之渦環結構提供升力,而前一週期之前緣渦平貼於翅膀迎風面上卻提供負升力元素,當翅膀持續加速時,原前緣渦將會因翅膀旋轉朝向翅膀翼尖與後緣端,並與新生成之後緣渦融合產生額外之正升力貢獻。三種撲拍模式翻轉時刻的不同將引致兩個騎乘升力元素機制之發生時間點不同。
此外,將流場沿著翼展方向進行傳統壓力積分法(Pressure Force Analysis, PFA)與流元的渦度與物體受力作連結(Vorticity Force Analysis, VFA)進行二維特性之探討(Lee, Hsieh, Chang & Chu; 2012)。透過比較VFA與PFA在不同截面之間的差異,提供不同於過去三維真實流場卻以二維分析方法之新見解。


In this study, the force element theory proposed by Prof. Chang C. C. (1992) is used to analyze three-dimensional unsteady aerodynamics for hovering flapping flight of fruit-fly at low-Reynolds-number flows. The theory enables us to quantify the contributions to the forces exerted on the wing in terms of fluid elements with non-zero vorticity, and extract potential forces such as added mass and inertial forces from the total forces. The variations of the lift force and its constituent components for three different type motions, including symmetric, advanced and delayed rotations, are carefully examined. In conjunction with the previous results of Hsieh, Chang and Chu (J. Fluid Mech, 2009, vol. 623, pp. 121–148), we further compare each force contribution with the results under simplified two-dimensional assumptions. It is shown that the lift is almost supported by vorticity in the flow field, and the added-mass forces have positive contribution for these three-type motions.To understand the lift force generation relative to three-dimensional vortex structures, such as leading-edge vortex (LEV), trailing-edge vortex (TEV), tip vortex (TV) and Root vortex (RV) during different hover motion stages, we divide whole flow domain into annularity column regions with same center of circle, which is the rotation center of the wing. Except a well-known high lift mechanism generated, the delayed-stall vortex, during the midstroke for three different types of rotation, the insect wing will take advantage of wake vortices to gain extra lift force, termed as “riding on lift elements” at two different time instant, as performing turning stage.
Besides, the line of force analysis of the pressure force analysis (PFA) and the vorticity force analysis (VFA) is pursued by dividing flow domain into some regions along spanwise direction of the wing. From comparison of differences between PAF and VFA, we could isolate two-dimension characteristics from three dimensional flows, further survey feasibility of two-dimensional analyses on flapping motions in unsteady flow.


CONTENTS

口試委員會審定書 #
誌謝 i
中文摘要 ii
ABSTRACT iii
CONTENTS iv
LIST OF FIGURES vii
LIST OF TABLES xi
Chapter 1 Introduction 1
1.1 背景簡介與研究動 1
1.2 非常定空氣動力學 2
1.2.1 Wagner效應(Magus effect) 2
1.2.2 動態失速機制 3
1.2.3 旋轉升力 4
1.2.4 尾跡捕獲機制 6
1.3 力元理論 8
1.4 文獻回顧 9
1.5 全文概述 12
Chapter 2 控制方程式與數值方法 13
2.1 簡介 13
2.2 網格產生 13
2.2.1 網格品質 14
2.3 控制方程式 15
2.3.1 質量守恆方程式 15
2.3.2 動量守恆方程式 16
2.4 數值方法 16
2.4.1 分離求解器 16
2.4.2 空間離散 17
2.4.3 時間離散 22
2.4.4 壓力-速度偶合關係的處理 24
2.5 UDF介紹 30
2.5.1 網格資料結構 30
2.5.2 解釋與編譯UDF 33
2.5.3 DEFINE巨集與UDF之定義 34
2.5.4 求解器資料連結 41
2.5.5 使用者自訂標量(UDS&UDM) 41
2.5.6 UDF執行流程 43
Chapter 3 力元理論 45
3.1 簡介 45
3.2 輔助勢流 46
3.3 力元理論推導 47
Chapter 4 果蠅懸停撲翅數值結果 52
4.1 前言 53
4.2 爭議性問題 53
4.3 數值結果驗證 。
4.4 流場與運動參數 55
圖一 (a)水平拍動的速度與無因次化時間 ; (b)三種模式之攻角變化 ; (c)三種撲翅模式示意圖。 56
4.5 力元因子分析 57
4.5.1 升阻力總和 57
4.5.2 力元因子分布圖 60
4.5.3 力元因子 之影響 64
4.6 騎渦效應 85
4.7 區域切割分析 91
Chapter 5 結論與未來展望 98
REFERENCE 102


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