機車引擎散熱罩與風扇之流場與散熱效果改良：實驗與計算分析

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研究生：	吳啟榮 Chi-jung Wu
論文名稱：	機車引擎散熱罩與風扇之流場與散熱效果改良：實驗與計算分析 Control of Heat Dissipation in a Motorcycle Engine via Flow Modulation
指導教授：	黃榮芳 Rong-fung Huang
口試委員:	葉啟南 none 蘇裕軒 none 孫珍理 none 陳明志 none
學位類別：	碩士 Master
系所名稱：	工程學院 - 機械工程系 Department of Mechanical Engineering
論文出版年：	2005
畢業學年度：	93
語文別：	中文
論文頁數：	210
中文關鍵詞：	散熱罩、風扇、計算模擬
外文關鍵詞：	flow-directing cover, fan, STAR-CD
相關次數：	點閱：280 下載：0
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為了改良一部四行程單缸氣冷式引擎之散熱機構，以提升其散熱效果，本研究利用數值計算並結合實驗的方式，針對散熱機構進行調整，調整過程可分為兩部份：一、提升散熱機構之風量，以降低汽缸壁周圍的溫度；二、針對散熱機構之風量分配，以改善汽缸壁之溫度均勻度。本研究先以數值計算的方式，對散熱機構之相關流道進行模擬，並藉由數值計算之結果，歸納出幾個修正方向包括風扇本體、風扇蝸殼流道、散熱罩流道等等相關流道，以供後續實驗之進行。在實驗方面，改良風扇本體與風扇蝸殼流道，對提升風量及降低汽缸壁溫度，確實有很大的幫助，經實驗結果顯示，在汽缸壁周圍平均溫度相較於未修正前下降約18 oC。而當風量獲得提升後，再針對散熱罩流道進行修正，修正方式為在散熱罩內設置氣流分配板，希望能藉此達到分配氣流之效用，以改善汽缸壁的溫度均勻度，並盡可能減小因氣流分配板所造成的流量損失。於實驗結果顯示，因氣流分配板有效分配氣流，並減小氣流直接衝擊汽缸迎風面，使該處的溫度不至於太低，所以溫度均勻度較未修正前改善許多。另外，經各項修正後，引擎扭力、馬力、油耗等等性能並未下降。

To improve the heat dissipation performance of a single-cylinder, four-stroke-cycle, air-cooled engine, the cooling fan, the scroll housing, the inlet, and the flow-directing cover are experimentally and numerically studied and optimized. The commercial code, STAR-CD is employed to analyze the velocity distributions between the fan blades, in the scroll, in the flow-directing cover, and through the engine fin in order to factor out the design parameters. Experimental study and optimization are conducted in two phases: the flow rate measurements and the around-cylinder temperature measurements. The flow measurements are completed by using the AMCA 210 standard fan test rig. While the temperature measurements are done by attaching 40 K-type thermocouples with 250 mm bead diameter to circumferential positions around the cylinder. The strategy of the optimization process is maximizing the fan flow rate first by modifying the fan inlet as well as the position and shape of the scroll. Then proceed to minimize the circumferential temperature distribution of the cylinder by optimizing a specially designed flow distributing plate, which is installed in the proper position and orientation of the flow-directing cover. It is found that the inlet diameter should be kept as large as that of the fan hub so that the fan flow rate is maximized. There is a specific design position for locating the cut-off. Deviating from the optimized design location, the flow rate deteriorates significantly. The flow rate is increased by about 25% compared with the original design after optimization. With this increased flow rate the circumferentially averaged temperature is decreased by about 19oC. However, the maximum temperature difference around the cylinder, i.e., the index for the temperature nonuniformility, attains 39oC. By properly installing the flow distributing plate, the flow rate is increased by about 22% compared with the original design after optimization. With this increased flow rate the circumferentially averaged temperature is decreased by about 16oC. However, the maximum temperature difference around the cylinder, i.e., the index for the temperature nonuniformility, attains 23.3oC.

中文摘要.................................................i
Abstract................................................ii
誌謝...................................................iii
目錄....................................................iv
符號索引...............................................vii
表圖目錄................................................ix
第一章 緒論..............................................1
        1.1 研究動機.....................................1
        1.2 文獻回顧.....................................2
        1.3 研究構想與戰略...............................5
第二章 計算分析..........................................7
        2.1計算流力軟體的簡介............................7
        2.2統御方程式....................................9
           2.2.1紊流模式................................10
        2.3數值方法.....................................12
           2.3.1離散化方程式............................13
           2.3.2 SIMPLE解法理論.........................14
           2.3.3收斂標準................................16
        2.4數值模擬.....................................17
           2.4.1計算網格................................17
           2.4.2邊界條件與初始條件......................18
        2.5結果分析.....................................19
           2.5.1原始散熱罩之流場........................19
           2.5.2風扇背面的間隙修正之流場................20
           2.5.3風扇段蝸殼之舌部修正....................21
           2.5.4風扇段蝸殼之蝸形修正....................23
           2.5.5散熱段流道修正..........................23
               2.5.6散熱風扇修正........................24
第三章 實驗方法、設備與儀器.............................26
        3.1實驗方法.....................................26
        3.2實驗設備與儀器...............................26
        3.2.1引擎.......................................27
        3.2.2動力計.....................................27
           3.2.3油耗量測設備............................27
           3.2.4廢氣量測設備............................28
           3.2.5空氣流量量測設備........................28
           3.2.6風量量測系統............................29
           3.2.7溫度量測系統............................31
第四章 風扇段蝸殼流道的改良.............................33
        4.1原始散熱風扇及蝸殼，並搭配原始散熱罩的汽缸壁
           溫度分佈及蝸殼入口風量.......................34
        4.2風扇背面與ACG頂部之間隙修正..................35
        4.3風扇蝸殼流道之舌部位置修正...................35
第五章 風扇段蝸殼入口的改良.............................37
        5.1入口直徑修正.................................37
        5.2入口形狀修正.................................38
        5.3蝸殼入口表面與風扇頂面之間隙修正.............39
        5.4蝸殼入口的柵欄修正...........................39
第六章 導流段散熱罩的改良...............................41
        6.1改良前分析...................................41
        6.2散熱罩流道之轉角與底部修正...................42
        6.3散熱罩流道內安置氣流分配板...................43
           6.3.1氣流分配板之上游距離調整................43
           6.3.2氣流分配板之上、下游高度調整............46
           6.3.3弧形氣流分配板之上游α角度與下游高度的
                調整....................................50
           6.3.4引擎性能比較............................53
        6.4總結.........................................54
第七章 風扇的改良.......................................55
        7.1原始風扇-風扇0(前傾式).......................56
        7.2風扇修正-風扇A(前傾式).......................56
        7.3風扇修正-風扇B1、B2 、B3 (後傾式)............57
第八章 結論與建議.......................................59
        8.1 結論........................................59
        8.2 建議........................................60
參考文獻................................................62

                                

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