變量流流況下非均勻縱列雙橋墩局部沖刷之研究

Local Scour around Two Non-uniform Circular Piers in Streamwise Direction with Various Flow Hydrographs

王傳益(Chuan-Yi Wang) ； 黃奕超(Yi-Chao Huang) ； 施漢鵬(Han-Peng Shih) ； 鄭人豪(Jen-Hao Cheng)

《農業工程學報》 57卷1期 (2011/03) Pp. 35-45

https://doi.org/10.29974/JTAE.201103.0003

摘要

本研究利用水工試驗模擬前峰型變量流作用下，非均勻縱列雙橋墩（墩徑比D/D(上標 *)=0.4）於4種橋墩間距（L(下標 d)=1.25D(上標 *)、2D(上標 *)、3D(上標 *)及4D(上標 *))及3種覆土高度下進行試驗，藉以瞭解縱列雙橋墩之局部沖刷深度與沖刷歷程變化。縱列雙橋墩橋墩間距L(下標 d)≥3D(上標 *)時，兩橋墩之間產生明顯之淤積堆。
當橋墩間距爲3D(上標 *)時，上游橋墩墩後之泥砂對下游橋墩具有屏蔽效應或回填下游沖刷坑，以致下游橋墩墩前沖刷深度有减小之現象，爲較理想之橋墩配置間距。當橋墩間距L(下標 d)≤1.25D(上標 *)時，因橋墩間距較短，當水流通過上游橋墩後，上游來流與馬蹄型渦流結合下游橋墩之向下射流交互作用而產生更爲紊亂之流場，造成較大之橋墩沖刷，爲較不理想之橋墩配置間距。

關鍵字

前峰型變量流 ； 非均勻縱列雙橋墩 ； 局部沖刷深度

並列摘要

This research uses hydraulic models to investigate the time variation of local scour depth for two streamwise, consecutive non-uniform circular piers under unsteady flows with advanced peak hydrographs. The upper and lower pier diameters are 20 mm and 50 mm, respectively, i.e. the pier diameter ratio is a constant (D/D(superscript *) 0.4). In addition, there arc four different longitudinal intervals between the two consecutive piers (L(subscript d)=1.25, 2, 3 and 4D(superscript *)), and 3 different initial bed levels in the experimental design. When L(subscript d)≥ 3D(superscript *), significant sand deposition occurs between the two consecutive piers. When L(subscript d)≥3D, the scour depth in front of the downstream pier decreases because the sand at the back of upstream pier fills downstream scour hole or the sheltering effect. Therefore, a smaller scour depth will occur and it is an ideal arrangement. When L(subscript d)≤ 1.25D(superscript *), the longitudinal interval between the two consecutive piers is short, the horseshoe vortex combines upstream flow and the downflow so that the flow field becomes more turbulent. Therefore, a bigger scour depth will occurs and it is not an ideal arrangement.

並列關鍵字

Unsteady flows with advanced peak hydrographs ； Consecutive non-uniform circular piers ； Local scour depth