本研究藉由實驗方法，探討小圓柱尾流衝擊平板時所生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區的速度分佈、紊流強度以及平板上游表面的速度分佈。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、下游的表面壓力，探討小直徑圓柱尾流衝擊平板時，對平板上、下游表面壓力的影響，並分析壓力係數以及阻力係數。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：當平板寬度固定時，在雷諾數與小圓柱直徑的場域內，流場特徵模態可分為穩態域(stable regime)與非穩態域(unstable regime)兩種，大約在雷諾數大於6000以及小圓柱直徑與平板寬度比值大於9/1000時，流場為非穩態；大約在雷諾數小於6000以及小圓柱直徑與平板寬度比值小於9/1000時，流場為穩態。穩態域中的流場特徵，為小圓柱尾流在接近平板表面的上游區引致流場特徵結構，可分成三個子模態：在低雷諾數區形成兩個轉向相反且近似對稱的迴流；在中雷諾數區形成一蕈狀渦漩結構；在高雷諾數區，蕈狀渦漩結構上游呈現一至三個小渦漩結構。在非穩態域中的流場特徵，平板表面的蕈狀渦漩結構不會穩定存在於平板上方，而是呈現不規則的逸放行為。在穩態域中，由於平板表面上游區的蕈狀渦漩結構的生成，因此避免橫風直接衝擊平板表面，使得平板上游表面壓力係數降低，阻力係數也隨之下降，且當平板上游表面出現多個蕈狀渦漩結構時，平板的阻力係數下降最明顯。

The effect of small-diameter circular cylinder wake impinging a flat plate on the flow characteristics and aerodynamic performance were experimentally studied in a wind tunnel. The aims were focused on improving the flow behavior and aerodynamic performance of the flat plate. The effects of varying the small-diameter circular cylinder diameter on the flow characteristics upstream the flat plate were observed by laser-assisted smoke flow visualization technique. The instantaneous velocities and turbulent intensities in the wake of the small-diameter circular cylinder were detected by a one-component hot-wire anemometer. By installing a few pressure taps on the front and rear surface of the flate plate, the pressure distributions on the pressure surfaces were measured by a home-made pressure scanner. The pressure coefficients were calculated by dividing the measured surface pressure by the dynamic pressure of freestream. The drag coefficients were subsequently obtained by integrating the pressure coefficients over the surface area of the flat plate. The particle image velocitry (PIV) was employed to measure the velocity field. The streamline patterns and turbulence properties were derived from the measured velocity data. Two characteristic flow regimes (stable and unstable) were identified in the domain of small circular cylinder diameter and the flat plate width by flow visualization. Three characteristic flow modes were found in the stable regime: two reverse flows appeared at low Reynolds numbers; mushroom type vortices appeared at mediate Reynolds numbers; one, two, or three small vortices appeared upstream the mushroom type vortices at large Reynolds numbers. The surface pressure coefficients on the upstream surface and drag coefficients of the flat plate were reduced. The drag coefficients of the flat plate decreased the most significantly when a mushroom type multi-vortex appeared near the upstream surface of the flat plate.

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