粒子圖像測速技術開發 - 探討基礎理論與應用

許多學校都有在發展粒子圖像測速法(PIV)的技術，淡江大學也有風洞實驗室，也常常在做風的受力，但是皆利用模型表面壓力或是基底剪力彎矩探討受力的變化。但時常會出現一些無法解釋的原因，因此須從流場的角度去觀察是否為流場造成的。由於淡江大學風工程研究中心(WERC)引進了高速攝影機，連續型雷射，煙霧產生器等等的設備，為了對流場的進一步的了解，可以藉此機會嘗試風洞PIV之架構，來解釋受力的情況。本研究主要將PIV理論整合成一套系統(MyPIV)，其中理論包含二維相關平面計算、二維相關平面平移、高斯擬合位移、偵測錯誤向量、向量修正及高通濾波等等的理論。接著利用MyPIV將照片分析深寬比為7二維矩柱周圍的流場，且在上游1公分，2公分處放置直徑為1毫米的圓柱。除了利用OpenPIV對照其一致性，也將上、中、下游三區域資料接合並且探討於矩柱上游1、2公分增加圓柱造成紊流對於整體流場的影響。本研究數據分析時，於上游無圓柱，圓柱於矩柱上游1、2公分的這三個案例中。在相對風速方面可以明顯看出高、低風速區。由於下游為不同天量測，因此風速有落差，且上、中游之間由於重疊區域不夠多，因此造成數據中斷。在分離流泡方面，上游放置圓柱且越往上游移動時分離流泡最大位置有往上游移動、也有縮小的趨勢。另外，於找尋再接觸位置時只能於上游無圓柱的案例中看到再接觸的現象，其餘兩個案例因為剪切層小於詢問窗口的大小，因此無法判斷再接觸位置。然而，於分析再接觸的三個案例中，發現到於矩柱前緣點上游0.15D皆發現到縮流現象，但是圓柱於矩柱上游2公分這個案例中，由於圓柱較矩柱中心偏下，因此縮流現象較無明顯。

關鍵字

二維矩柱；粒子圖像測速法；風洞實驗；頓體空氣動力學； OpenPIV

並列摘要

In Taiwan, many schools are developing particle image velocimetry (PIV) technology. Tamkang University also has a wind tunnel laboratory and often does base force experiments for models. However, all of them use the model surface pressure or base shear bending moment to investigate the force changes. But often there are unexplained reasons, therefore, it is necessary to observe whether it is caused by the flow field. So, the Wind Engineering Research Center (WERC) of Tamkang University has introduced high-speed cameras, lasers, smoke generators, and other equipment, to further understand the flow field. With these state-of-art equipment, we’re trying to develop the framework of PIV. The works focuses on the integrating the basic theories of PIV into a system (MyPIV), which includes the concept of two-dimensional correlation, Gaussian peak fit, outlier identification, and optional high-pass filter. Measurements of the velocity field were conducted around a two-dimensional rectangular prism of 7 cm streamwise depth and 1 cm in width. The velocity field obtained from the current framework (MyPIV) is compared to the results obtained from OpenPIV. In additional to the rectangular model, an optional 1 mm diameter cylinder were placed at 1 cm and 2 cm upstream to investigate the effect of the upstream perturbation of the flow field. In the three cases being examined, higher wind speeds are observed outside the shear layer while low wind speed are observed inside the separation bubble. Since the measurements of downstream field of view (FOV) were conducted at several days after the measurements of middle and upstream FOVs, velocity discontinuity observed in overlapped region were due to slightly different setups and external meteorology on different testing days. The experimental results show that the position of the maximum separation bubble height tends to move upstream and become smaller when the cylinder is placed upstream at shorter distance. When looking for the reattachment point, the reattachment phenomenon can only be seen in the case where there is no upstream cylinder. In the other two cases, the reattachment point cannot be determined because the shear layer is smaller than the size of the interrogation window. The presence of the body leading edge causes contracted and accelerated flow outside the shear near the corner. However, the flow acceleration is less pronounced when the perturbation cylinder is placed upstream.

並列關鍵字

Two-dimensional column ； Particle Image Velcimetry ； OpenPIV ； wind tunnel experiment ； bluff body aerodynamic

參考文獻

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