研究生: |
劉思賢 Szu-hsien Liu |
---|---|
論文名稱: |
前傾式離心風扇之模擬與實驗 Computational and Experimental Investigations of a Forward-curved Blades Centrifugal Fan |
指導教授: |
黃榮芳
Rong-Fung Huang |
口試委員: |
楊鏡堂
Jing-Tang Yang 趙振綱 Ching-Kong Chao 陳明志 Ming-Jyh Chern 牛仰堯 Yang-Yao Niu 沈澄宇 Cherng-Yeu Shen |
學位類別: |
博士 Doctor |
系所名稱: |
工程學院 - 機械工程系 Department of Mechanical Engineering |
論文出版年: | 2011 |
畢業學年度: | 99 |
語文別: | 中文 |
論文頁數: | 287 |
中文關鍵詞: | 前傾式離心風扇 、DFR 、風扇性能曲線 、風扇流場 |
外文關鍵詞: | Forward-curved blades centrifugal fan, DFR, Fan flow, Fan performance curve |
相關次數: | 點閱:278 下載:6 |
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現今投影機相關產業受惠於視訊與影音技術之突破而蓬勃發展,但是光機產生的廢熱儼然成為設計挑戰,受限於光機外形結構,唯採用離心式風扇才能克服系統流阻並供給所需風量,相關風扇選用則必頇藉由風扇性能曲線匹配系統流阻來決定。針對投影機散熱需求,本文選定小型前傾式離心風扇做為研究標的。然而,現行數值模擬方法無法在風扇開發初期正確計算出與量測結果相接近之性能曲線,為改善當前預測風扇特性準確性較低之缺點,本研究使用計算流體動力學(Computational Fluid Dynamics, CFD)軟體STAR-CD,發展出一套有別於傳統方法之計算程序,該方法將AMCA標準量測設備內噴嘴的阻抗曲線以下游離散式多孔性阻抗區的模式導入計算模型,並據此稱為DFR方法(downstream flow resistance)。求解過程中,DFR方法將阻抗區上下游的靜壓差轉換成阻抗動量源併入動量守恆方程式,遵循噴嘴阻抗約束方程反覆運算壓力和流速等計算變量,確保通過阻抗區之流量與阻抗區上下游的靜壓差滿足噴嘴阻抗關係式,並使風扇出口靜壓值更接近實際情況。經比對依照AMCA標準程序實驗所量測的風扇特性,發現採用DFR方法可將預測結果的精確度提高至97%以上,然而傳統方法計算模擬的最大誤差卻高達62%。此外,使用DFR方法搭配靜態網格和動態網格所計算的性能曲線幾乎一致,這將有助於風扇設計者以DFR方法與靜態網格縮短產品開發時程。當背壓升高時,蝸殼出口區由傳統方法所計算的流速分佈明顯受堵無法順利流出轉而趨向舌部,這表示傳統方法未能正確計算風扇流場,導致預測流量值偏低,比對由DFR方法模擬之流場則無此現象並較為正確。
The progress in the video related technologies fueled the projector industry to a flourish. However, heat dissipations from the optical engine became a design challenge. The fan selection for lamp cooling must be designed according to the interaction between fan performance curve and system impedance. Unfortunately, the existent simulation methods cannot predict the fan curve close to the measured results during the design stage. To improve the obvious defects of conventional methods, a newly developed computational approach by using the commercial code (STAR-CD) of computational fluid dynamics is employed. The main purpose is to study the fan flow and performance curve of the forward-curved blades centrifugal fan. The new approach, which is termed the “downstream flow resistance” (DFR) method, engaged the flow resistances of nozzles of the AMCA test rig in the downstream area of the computational domain. The engaged flow resistance is treated as the distributed momentum sources in a specific porous region. The static pressure at the fan exit is iteratively corrected to real values. By using the DFR method, the maximum deviation of the calculated fan curve from the measured results can attain a level less than 3%. This progress presents a dramatic improvement over the maximum deviation of about 62% obtained by using the conventional method. The improvement is due to the appropriate prediction of the fan flow by properly adjusted pressure drops across the porous region. Future designers will benefit from the high accuracy of fan performance prediction and shorter design cycle time by utilizing the DFR method with the static-grid scheme.
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