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    Title: 渦流對三維背階流效應探討
    Other Titles: Vortex effects on three dimensional backward-facing step flows
    Authors: 蘇士傑;Su, Shih-jie
    Contributors: 淡江大學航空太空工程學系碩士班
    陳增源;Chen, Tzeng-yuan
    Keywords: 背向階梯;熱傳;渦流;Backward-facing step;heat transfer;Vortex Effects
    Date: 2007
    Issue Date: 2010-01-11 06:44:46 (UTC+8)
    Abstract: 本研究以實驗量測方式探討背階入口不同渦流強度對於三維背階流場特性與熱傳效應的影響。使用一小型風洞系統用來產生均勻流之空氣進入管道入口,另一個不同高度的測試管道連接形成一展弦比為4,擴張比1.33,背階高1.75cm的背階管道,於背階後使用厚度0.1mm的不鏽鋼片貼於加熱表面,將三角翼渦流產生器置於管道入口以產生不同渦流強度的入口條件,流場雷諾數介於500至15000之間,包含層流、過渡流及紊流。使用都卜勒雷射測速儀(LDV)及T型熱電偶線量測速度及溫度,量測內容包涵:(1)再接觸長度的量測及背階下游斷面的流場結構。(2)近熱傳面的流場特性,如對流效應、二次流效應及紊流效應。(3)熱傳面的熱傳效應分布。
    研究結果顯示,在層流時再接觸長度隨雷諾數增加而增加,過渡流時再接觸長度隨雷諾數增加而減少,紊流時再接觸長度幾乎不隨雷諾數變化,加裝渦流場生器時會使再接觸長度變短,也加快使流體發展成過渡流與紊流。加裝渦流產生器也使得近壁面之對流強度及紊流效應增加,也因此增加了熱傳效應,其中紊流效應為影響熱傳效應的主因。最大熱傳效應發生於再接觸點附近。
    The research experimentally investigates the effects of vortex intensity on the flow and heat transfer characteristics in three-dimensional backward-facing step flows. A wind tunnel system is used to generate a uniform flow at an inlet duct. Another test duct of different height is connected to the inlet duct to form a backward-facing step duct of aspect ratio 4, expansion ratio 1.33, and step height of 1.75 cm. A 0.1 mm thick stainless steel foil is attached to the step wall to serve as the heat transfer surface. Vortex generator is placed inside the inlet duct, and used to generate different levels of vortex on the inlet free-stream. The Reynolds number is between 500 and 17000, which cover the laminar, transitional and turbulent flows. The velocity and temperature measurements were conducted using laser Doppler velocimetry, and Type-T thermocouples, respectively. Specifically, the measurements include (1) the reattachment length, and the flow structures at different duct cross-sections downstream of the step wall; (2) the flow characteristics near the heat transfer surface, such as the convective mean velocity, the secondary flow and the turbulent kinetic energy; (3) the heat transfer distributions on the heat-transfer surface. Results of this study show that the reattachment length increases with Reynolds number in the laminar flow region, decreases with Reynolds number in the transitional flow region, and almost remains constant with Reynolds number in the turbulent flow region. The vortex generator much reduce the reattachment length, and the Reynolds numbers for the onset of the transitional and turbulent flows. This study also indicates that the vortex increase the convective mean velocity, and turbulent kinetic energy near the transfer surface, and cause the increase in heat transfer rate. The flow turbulent kinetic energy plays the most important role in heat transfer distributions. The maximum heat transfer rate occurs near in the reattachment point.
    Appears in Collections:[航空太空工程學系暨研究所] 學位論文

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