半圓柱阻礙物對重力驅動顆粒流場之影響; The effect of semi-circular cylinder obstacle on gravity-driven granular flow

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题名:	半圓柱阻礙物對重力驅動顆粒流場之影響;The effect of semi-circular cylinder obstacle on gravity-driven granular flow
作者:	邱上育;Shang-yu Chiu
贡献者:	機械工程研究所
关键词:	顆粒流;崩塌流場;阻礙物;顆粒體積佔有率;阻流;choked flow;granular flow;avalanche;obstacle;solid fraction
日期:	2011-07-20
上传时间:	2012-01-05 12:30:08 (UTC+8)
摘要:	本論文主要以傾斜矩形流槽探討重力驅動的顆粒崩塌流場，並在流槽中設置半圓柱阻礙物，以實驗的方式研究不同實驗控制參數(流槽傾角、儲槽開口高度以及半圓柱半徑)對顆粒流撞擊阻礙物之運動行為以及相關物理機制的影響。為了觀察顆粒流體自由表面、側面與底層表面運動時的情形，在透明壓克力製成的滑道上下兩側架設鏡子，從側面拍攝以同時取得三面影像，並使用流體自由表面與底面的速度場來修正側面的速度場，以求得到更準確的體積流率，以及顆粒體積佔有率。實驗結果顯示阻礙物對流場的影響(如流體深度、速度以及顆粒體積佔有率)程度會隨著上游福祿數增加而增加，且上游福祿數高於某一臨界值後，阻礙物對流場的影響變化會急遽上升；而隨著半圓柱半徑的增加，阻礙物的影響也隨之增加。在低上游福祿數時，流場發生阻流(choked flow)的現象，我們也探討在此流態中的各種運動行為。 The aim of this work is to examine the dynamic behavior of granular flows with granular hydraulic-jumps. The jump is produced by using a fixed semi-circular cylinder obstacle in a rectangular sliding chute. Three different inclined angles combining with three different sizes of the obstacles and four different heights of container opening are tested. Two slender mirrors are installed at the top and the bottom of the transparent chute to reflect the free surface flow and the basal flow image simultaneously to the photographic recording system. Together with the side wall view, image/PIV analysis for the three visible flow fields is performed. With the extra flow profiles and a proposed linear interpolation scheme, we are able to calculate the solid volume fraction along the stream-wise direction in a cost-effective way. The results show that the effect of the obstacle on the flow field increase both with increasing the Froude number of the upstream flow and the size of obstacle, and rapidly increase when Froude number of the upstream larger than critical value. Moreover, choked flow is occurred at lower Froude number of the upstream flow. The dynamic behaviors in this state are also discussed.
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