軸流式風扇之流場模擬與實驗｜國立臺灣科技大學博碩士論文系統

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研究生：	林重安 Chung-an Lin
論文名稱：	軸流式風扇之流場模擬與實驗 Computational and Experimental Investigations of Axial Fan
指導教授：	黃榮芳 Rong Fung Huang
口試委員:	張家和 Chir Ho Chang 陳明志 Ming Jyh Chern 孫珍理 Chen Li Sun 唐永新 Yeong Shin Tarng 劉昌煥 Chang Huan Liu 葉啟南 Chi Nan Yeh 揚騰芳 Ten Fang Yang
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：	2007
畢業學年度：	95
語文別：	中文
論文頁數：	196
中文關鍵詞：	軸流式風扇、質點影像速度儀、風扇性能、數值模擬
外文關鍵詞：	Axial flow fan, PIV, Fan-performance, Numerical simulation
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散熱一直都是現今電子產業所關切的問題，風扇經常被用來作為散熱系統的裝置之ㄧ，而散熱效率的良窳與風扇的性能曲線(壓力與風量的關係)有關。在進行風扇的設計或改良時，通常需要使用計算擬的方法預測風扇的性能曲線。由於以往數值模擬的結果相對於實驗量測的風扇性能仍有明顯的誤差存在。因此，本研究利用計算流體動力學(Computational Fluid Dynamics, CFD)軟體STAR-CD，針對軸流風扇研發出一套與傳統不同的計算程序，經AMCA 210標準程序實驗驗證的結果，此一方法可計算出極為接近實驗量測之風扇性能曲線，大大的改良了與傳統方法計算產生較大不準度的問題。藉由所計算出的風扇流場，探討風扇內部葉片與葉片間及出入口流場在軸向與徑向平面的特性。使用靜態網格與動態網格方法所得到的計算結果均能準確預測風扇性能曲線，準確度達98%以上(傳統計算模擬法的誤差通常可達20%以上，在失速區的誤差甚至可能超過30%)，兩者在流場的分佈特性預測上並無明顯的差異。經分析計算出來的絕對與相對速度場的結果，風扇性能曲線在產生失速時，是由於風扇葉片設計不良，在吸力面的尾端靠近風扇出口處產生渦漩而阻礙了流量的發展；在高靜壓區，葉片壓力面會產生大型的渦漩阻礙流量的發展。

This study uses the STAR-CD, a commercial code of Computational Fluid Dynamics, to calculate and analyze the flow field characteristics and performance curve of an axial fan. Both the static and moving grids are employed in the computation. A new computational approach other than the conventional simulation method, which is popularly adopted by investigators, is developed. The new approach uses the “added impedance” method to improve the prediction of the pressure, flow rate, and velocity distribution. The results show at least three emphases. Firstly, the deviation of the calculated fan performance curve by using the new approach from the experimental results can attain a level less than 2%, which is a drastic improvement over that obtained by using the convention method. The conventional method usually would cause an inaccuracy higher than 20%. In the region where the stall occurs, the inaccuracy of conventional method may even exceed 30%. Secondly, usage of the static and moving grids for the computation is not the issue. Both the static and moving grids show almost identical results. Thirdly, the stall occurs when the aerodynamic contour of the fan blade is inappropriately designed for the mid and high back-pressure operations. Under this situation, recirculation bubble would appear around the trailing edge of the suction surface of the fan blade, and therefore reduces the development of the flow. At deep stall, large recirculation flow structure may even appear around the pressure surface and block the passage between the neighboring fan blades. The flow rate is hence reduced.

摘要	i
Abstract	ii
目錄	iii
符號索引	vii
表圖索引	x
第一章 緒論	1
1 研究動機	1
2 文獻回顧	1
3 研究目的與方法	6
第二章 計算模擬之模型與實驗方法	8
1 計算流力軟體簡介	8
2 統御方程式	10
2.1 穩態模式(Steady state)	10
2.2 暫態模式(Transient)	12
3 紊流方法	12
4 數值模擬	15
4.1 計算網格	15
4.2 邊界條件與初始條件	16
4.3  CFD 1與CFD 2出口邊界條件設定	18
5 數值方法	18
5.1 離散化方程式	18
5.2 穩態模式與暫態模式數值方法	20
5.3  SIMPLE與PISO解法理論	20
5.4 收斂標準	26
6 實驗方法	27
6.1 實驗設備與儀器	28
第三章 標的風扇與其性能	31
1 風扇結構	31
2 風扇性能	32
Part I Static Grid Results	33
第四章 靜態網格之計算結果與討論	33
1  CFD 1計算方法之結果與討論	33
1.1  CFD 1之性能曲線與靜壓效率結果	33
2  CFD 2 Static grid計算方法之結果與討論	34
2.1  CFD 2 Static grid之性能曲線與靜壓效率結果	35
3  CFD 1與 CFD 2 Static grid之葉片間流場結構	36
3.1  CFD 1之葉片間流場結構	36
3.2  CFD 2 Static grid之葉片間流場結構	38
3.3  徑向平面之葉片間流場結構	41
3.3.1 取像截面於z/H = 0	42
3.3.2 取像截面於z/H = 0.25	43
3.3.3 取像截面於z/H = 0.5	43
3.3.4 取像截面於z/H = 0.75	44
3.3.5 取像截面於z/H = 1.0	45
4  CFD 2 Static grid之速度分佈	45
4.1  絕對徑向速度分佈	46
4.2  相對徑向速度分佈	48
4.3  軸向速度分佈	48
4.4  軸向速度分佈場	50
5  CFD 2 Static grid之渦度分佈	51
5.1  取像截面於z/H = 0	52
5.2  取像截面於z/H = 0.25	52
5.3  取像截面於z/H = 0.5	53
5.4  取像截面於z/H = 0.75	53
5.5  取像截面於z/H = 1.0	53
6  CFD 2 Static grid之壓力分佈	53
6.1  葉片間壓力分佈	54
6.2  徑向平面之葉片間壓力分佈	55
第五章 風扇入口流場	57
1 風扇入口之軸向流場結構	57
2 風扇入口之徑向流場結構	57
3 風扇入口之速度分佈	58
3.1  軸向速度分佈	58
3.2  徑向速度分佈	59
4 風扇入口之渦度分佈	59
4.1  軸向渦度分佈	59
4.2  徑向渦度分佈	60
第六章 風扇出口流場	61
1 風扇出口之軸向流場結構	61
1.1  取像截面於Y/Din = 0	61
1.2  取像截面於Y/Din = 0.25	62
1.3  取像截面於Y/Din = 0.5	63
2 風扇出口之徑向流場結構	63
2.1 取像截面於Z/H = 0.5	63
2.2 取像截面於Z/H = 1.0	64
2.3 取像截面於Z/H = 1.5	64
2.4 取像截面於Z/H = 2.0	64
3 風扇出口之速度分佈	65
3.1 軸向速度分佈	66
3.1.1 取像截面於Y/Din = 0	66
3.1.2 取像截面於Y/Din = 0.25	66
3.1.3 取像截面於Y/Din = 0.5	67
3.2 徑向速度分佈	67
3.2.1 取像截面於Z/H = 0.5	67
3.2.2 取像截面於Z/H = 1.0	67
3.2.3 取像截面於Z/H = 1.5	68
3.2.4 取像截面於Z/H = 2.0	68
4 風扇出口之渦度分佈	68
4.1 軸向渦度分佈	68
3.1.1 取像截面於Y/Din = 0	68
3.1.2 取像截面於Y/Din = 0.25	69
3.1.3 取像截面於Y/Din = 0.5	69
4.2 徑向渦度分佈	69
4.2.1 取像截面於Z/H = 0.5	69
4.2.2 取像截面於Z/H = 1.0	69
4.2.3 取像截面於Z/H = 1.5	70
4.2.4 取像截面於Z/H = 2.0	70
Part II Moving Grid Results	71
第七章 動態網格之計算結果與討論	71
1  CFD 2 Moving grid計算方法之結果與討論	71
1.1  CFD 2 Moving grid之性能曲線與靜壓效率結果	71
1.2  葉片間瞬時流場結構	72
Part III Discussion	76
第八章 討論	76
1  CFD 1與 CFD 2 Static grid之結果比較	76
1.1 葉片間流場結構	76
2  CFD 2 Static grid與 CFD 2 Moving grid之結果比較	78
2.1 葉片間流場結構	78
2.2 葉片間速度分佈	80
2.2.1 徑向速度分佈	80
2.2.2 軸向速度分佈	81
2.2.3 等速度分佈	81
第九章 結論	82
參考文獻	83

                                

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