傾斜噴流衝擊於旋轉圓盤之流場研究

Abstract

衝擊噴流技術利用流體直接衝擊在物體表面以達到乾燥、加熱或冷卻等目的。噴流及旋轉相關參數皆會影響流場，本文以粒子影像測速儀將流場可視化，觀察不同實驗條件下，傾斜噴流於旋轉圓盤上的流場型態與速度分布，實驗分別從圓盤的側面及上方拍攝，得到兩不同平面的流場。實驗主要參數包含:噴嘴直徑 15.7 mm，圓盤直徑為 160 mm，噴流與衝擊面間距 40 mm，進氣流量分別為 2、8 SLM，衝擊角度 45-90°，圓盤轉速為 0-500 RPM，圓盤與環境的溫度差分別為 0、50 °C。研究結果顯示，傾斜角造成靜止圓盤徑向方向慣性力不均，於 45°衝擊時停滯點朝徑向方向偏移，然而圓盤旋轉後流場型態不受衝擊角度影響，僅由旋轉雷諾數與噴流雷諾數比值決定，當此值大於 53 為旋轉效應主導。此外於溫差 50 °C、流量 2 SLM 時，靜止圓盤流場受熱浮力作用形成渦流，但當葛拉曉夫數與噴流雷諾數平方的比值小於 1，熱浮力效應不存在。

Impinging jet directly hits the object surface to achieve drying, heating or cooling purpose. Jet flow and rotation parameters will affect the flow field. In this paper, the flow pattern and velocity distribution of the inclined jet on the rotating disk under different experimental conditions were observed. The investigated parameters included: inlet flow rate (2 and 8 SLM), jet angle (45°-90°), disk rotational speeds (0-500 RPM), and inlet air-to-disk temperature difference (0 and 50 °C). The result showed that inclination angle caused the uneven inertia force in the radial direction of the stationary disk, and the stagnation point was shifted along the radial direction. However, the flow pattern was not affected by the impact angle when the disk started rotating. The flow pattern can be distinguished by the ratio of the rotational Reynolds number and jet Reynolds number. When this ratio was greater than 53, the rotation effect dominated. In addition, the flow above the heated stationary disk was influenced by the vortex flow generated by the buoyancy force at smaller inlet flow rate. As the ratio of the Grashof number to the square of the jet Reynolds number was less than 1, the buoyancy effect on the flow field was not noticeable .