本文的目的是在探討矩形截面凸狀物在不同邊界條件下，回覆再接觸非定常之現象，實驗分別進行在雷諾數分別為2.54×104及5.09×104，使用之模型寬高比為4，且將模型置於距入口端X’= 10H及16H處，其中H為模型之高。再者將在模型前端放置砂網以增加流場之紊流強度，觀察回覆再接觸長度之變化。
實驗方法將利用Thermal tuft-MEMS熱膜感測器量測回覆再接觸區及使用熱線測速儀搭配熱膜感測器之相關性延遲分析了解手指結構之大小。同時使用套裝軟體FLUENT映證回覆再接觸區之準確性。實驗結果得知在兩個不同雷諾數及不同位置下，模型中央回覆再接觸區發生在X = 3H處，此結果與模擬結果十分接近，而模型兩側回覆再接觸區因受側向邊界及黏滯力之影響，回覆再接觸區相對較中央區域短。當流場紊流強度增強時，中央回覆再接觸區縮短至X = 1.6H及1.5H處，表示回覆再接觸區明顯受流場擾動而變化。在此情形下，透過熱線測速儀所量測之W速度分量得知，流場中央區域之速度分量往左右兩測偏移，因此模型之中央回覆再接觸長度短於兩側回覆再接觸長度，並且證實回覆再接觸現象之三維特性。此外藉由延遲相關性分析可知，手指結構大小為0.5H，當流場紊流強度增強時，手指結構縮小為0.3H。
由熱絲測速儀得知回覆再接觸非定常之特徵，當S4受到S3傳來的熱造成電壓值下降，反之S2電壓值上升，MEMS訊號值呈現明顯之反相位，同時也可發現熱線測速儀之U速度分量明顯下降、V速度分量呈上升趨勢而W速度分量不穩定擺動，由此可得知在非定常現象出現時，手指結構運動是脫離模型表面且左右來回擺動，熱線測速儀與MEMS熱膜感測器存在如此的關係，因此得知此回覆再接觸現象存在三維非定常之特徵。

The purpose of the research is to investigate the unsteady, three-dimensional behaviors of flow reattachment over a surface-mounted rectangular block under different boundary conditions. The aspect ratio of the rectangular block model, i. e., its width versus height (H), was 4. The model was located at 10H and 16H downstream from the inlet of the test section, respectively. Experiments were made for the Reynolds numbers at 2.54×104 and 5.09×104, with and without the incoming boundary layer roughened by a screen installed immediately upstream of the model.
The region of flow reattachment was clearly identified by the self-made thermal tuft MEMS sensors applied on the surface of the model. In addition, the phenomenon of flow separation and reattachment around the model was successfully simulated by a CFD method. Results show that the reattachment length at the centerline of the model is around 3H at the two different Reynolds numbers studied, irrespective of the locations of the model from the inlet. Similar results were obtained by the two-dimensional CFD analysis. On the other hand, it is noted that the large-scale 3-D flow at the junctions of the sidewalls and the model caused the reattachment lengths near the two sidewalls substantially shorter than that at the centerline of the model. In the case of the incoming boundary layer roughened by a screen upstream, the reattachment length was found significantly shortened, in a way that the reattachment length at the centerline of the model appeared to be shorter than those near the two sidewalls.
Cross-correlation analysis of the signals of the MEMS sensors and X-type hot-wire was performed to study the three-dimensional flow structures embedded in the flow reattachment region. As found, the characteristic spanwise lengths of the three-dimensional flow structures are about 0.5H and 0.3H, respectively, for the incoming boundary layers without and with roughened by a screen upstream of the model. It is further noted that the unsteady behaviors of flow reattachment were featured with the intermittent events remarkably noted in the streamwise (U) and vertical (V) velocity traces. Namely, at the moments when U gets decreased appreciably, V very likely appears positive and at high value. These events are attributed to the presence of unsteady, three-dimensional flow structures, which conceivably induce strong momentum mixing in the flow reattachment region and cause the reattachment length shortened substantially.

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