本研究藉由實驗方法，探討小圓柱尾流衝擊平板時所形成之流場特徵與氣動力性能。藉由雷射光頁輔助煙霧可視化技術，觀察小直徑圓柱尾流之流場特徵以及衝擊平板時之流場特徵；使用熱線風速儀量測小直徑圓柱下游的時序訊號；以質點影像速度儀(PIV)量測受小直徑圓柱尾流衝擊時的平板上游流場結構，並與流場可視化之特徵比對；使用壓力掃描器量測平板上游的表面壓力，探討小直徑圓柱尾流衝擊平板時，對平板上游表面壓力的影響。改變雷諾數、小直徑圓柱直徑以及平板寬度，流場可視化、熱線風速儀量測、迎風面壓力量測及速度場的實驗結果顯示：當小圓柱直徑固定時，在雷諾數與平板寬度的場域內，受到不同模態(例如：creeping flow, standing vortices, unstable standing vortices, and Kármán-Bénard eddies)之小直徑圓柱尾流衝擊時，流場特徵模態可分為parallel flow (平行流)、 vorticity concentrated mode (兩個轉向相反且近似對稱的旋轉流)、vortex formation mode (蕈狀渦漩結構)、 transitional mode (蕈狀渦漩結構上游呈現一至三個小渦漩結構)、 unstable vortex mode (蕈狀渦漩結構呈現不規則的逸放行為)。當小圓柱直徑雷諾數Red  14且小圓柱直徑與平板寬度比值d/D  0.05時，才會有parallel flow出現；當小圓柱直徑雷諾數Red > 14且小圓柱直徑與平板寬度比值d/D < 0.05時，由於平板表面上游區的蕈狀渦漩結構的生成，橫風不會直接衝擊平板表面，使得平板上游表面壓力係數降低。

The flow characteristics around the upstream face of a laminar wake-impinged flat plate with a finite width were experimentally studied in a wind tunnel. The laminar wake was evolved from a small-diameter circular cylinder at the Reynolds number based on the cylinder diameter (0.5 and 1.0 mm) lower than 160. The Reynolds numbers based on the width of the flat plate (varied from 10 to 60 mm) was lower than 9606. The smoke flow patterns, velocity field, streamline patterns, vorticity distributions, and pressure coefficients were measured and discussed. The visual flow patterns were obtained by the laser-light sheet assisted smoke flow visualization method. The velocity field was measured by the particle image velocimetry. The streamline and vorticity distributions were calculated from the measured velocity data. The topological flow patterns were proposed according to the streamline patterns to assist understanding of the characteristic flow structures. The surface pressure distributions across the width of the flat plate were measured by installing the pressure taps on the plate surface. The pressure coefficients were calculated using the measured surface pressures to characterize the influence of the wake impingement on the aerodynamic force. The physical mechanism of vortex formation was discussed based on the measured flow patterns and vorticity distributions. Four characteristic flow modes (vorticity concentrated, vortex formation, transitional, and unstable vortex modes) were observed around the upstream face of the wake-impinged flat plate when the flat plate width was larger or equal to 20 mm at all Reynolds numbers Red based on the small cylinder diameter and the small cylinder diameter to flat plate width ratios d/D performed in the study. As the flat plate width was smaller or equal to 10 mm, parallel flow around the upstream region of the upstream face of the flat plate was observed (i.e., no vortical flow structure existed there) at Red  14 and d/D  0.05. These characteristic flow modes appeared in different regimes in the domain of the plate Reynolds number and cylinder diameter-to-plate width ratio, and were formed as the plate was impinged by different cylinder wake modes (i.e., creeping flow, standing vortices, unstable standing vortices, and Kármán-Bénard eddies). The cylinder wake presented velocity defects across the wake and persisted to the far downstream area. The velocity gradients of the velocity defects led to accumulation of vorticities in the vertical plane around the upstream face of the wake-impinged flat plate. When the wake flows approached the flat plate, the vorticities in the wake made the flows curved towards the center plane and induced a reverse flow going towards upstream. The upstream-going flow met the freestream and diverted laterally to form a counter-rotating mushroom type vortices which primarily dominated the flow field. The lateral vortex stretching effect induced by the finite width of the flat plate increased the vorticities in the counter-rotating vortices due to the angular momentum conservation. The pressure coefficients of the wake-impinged flat plate were reduced because the formation of the counter-rotating vortices avoided the direct impingement of the freestream on the flat plate.

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