鹽水異重流頭端之局部渦流流場與運移特性探討

Analyzing the Local Eddies and Moving Behavior of the Head of Saline Density Currents

10.29417/JCSWC.201009_41(3).0002

劉建榮(Chien-Jung Liu)；許少華(Shao-Hua Marko Hsu)

鹽水異重流 ； 頭端 ； 局部環狀渦流 ； 移動座標 ； Saline density current ； Head ； Local close circular eddy ； Moving coordinate

中華水土保持學報

41卷3期（2010 / 09 / 01）

201 - 215

繁體中文

本研究以水槽試驗配合垂直二維數值模式對鹽水異重流頭端局部渦流進行模擬探討，以釐清異重流頭端形狀與捲水效應等現象。透過非均勻與MAC交錯網格以及大渦模擬(LES)計算紊流流場紊流黏滯係數，並利用局部流場之理查生數與許密士數的關係計算紊流擴散係數。可發現當入流鹽水濃度增加時，試驗與數值的異重流頭端平均移動速度皆有明顯增加的現象。由傳統固定座標觀點觀察數值模擬異重流頭端局部流場可發現，頭端上方與鼻端下方皆有一局部流場，分別造成捲水效應使濃度明顯下降，此爲試驗不易量測與觀察到的現象。而透過移動座標觀點觀察異重流頭端局部流場則發現，頭端本身會自成一環狀渦流，其環狀渦流的大小幾乎與頭端大小差不多，表示異重流頭端大小是由此自成區域的環狀渦流所形成。

A vertical 2-D numerical model verified by the experimental results was used to analyze the local eddies and moving behavior of the head of saline density currents. Large Eddy simulation (LES), and the relation between the Schmidt number (S(subscript c)) and local Richardson number (R(subscript i)) calculated by the local flow field were used to calculate the eddy viscosity and eddy diffusion. Based on the fixed coordinate to observe the local flow field around the head of the density current, there were two eddies above the head and under the nose, respectively, diluting the concentration of the head. This phenomenon was difficult to measure and observe by experiments. When the moving coordinate moved with the velocity of the nose of the head to observe the head, there was a close circular eddy in the head and the size of the close circular eddy was the same as the size of the head. This means the size of the head depends on the close circular eddy in the head.