以FLUENT三維模擬檢核馬鞍壩魚道本體之流場適合度

Examining the Flow Pattern Suitability of Fishway Design in Ma-Ann Dam by FLUENT 3-D Simulation

10.29417/JCSWC.201012_41(4).0006

許少華(Shao-Hua Marko Hsu)；劉建榮(Chien-Jung Liu)；葉治宏(Chih-Hung Yeh)

豎孔式魚道 ； FLUENT ； 數值模擬 ； 表面流 ； 上溯 ； vertical slot fishway ； pool type fishway ； FLUENT ； numerical simulation ； streaming flow ； sail upstream

中華水土保持學報

41卷4期（2010 / 12 / 01）

343 - 351

繁體中文

由於水壩或攔河堰的興建，造成上、下游魚類生態廊道的中斷，爲使魚類能順利往上或下游洄游移動以維持其後代基因的正常繁衍，故魚道設計顯得格外重要。本研究主要針對大甲溪流域的馬鞍壩水池式魚道，以三維數值模式FLUENT來模擬探討其魚道內部的流場。模擬結果發現，模擬網格間距必須小於魚道隔板開孔最短邊長度的一半，在模擬計算上方能達到足夠的精度，且上下游邊界條件會影響距其最近的4個隔板之流況。故於探討魚道內部流況時，至少需以10個魚道隔板來進行模擬，如此距上下游邊界最遠處的中間休息池流況方能不受上下游邊界影響較具代表性。由模擬結果可發現，魚道隔板各開孔之平均流速皆小於大甲溪魚類上溯之流速上限1.7m/s，且隔板間休息池未有足以影響魚類上溯之渦流與湧升流，僅於右側溢流頂坎(Ice Harbor Weir)流況爲較不適合魚類上溯之表面流(streaming flow)流況，但不影響其提供魚類上溯或下降之功能。

Most rivers in Taiwan are steep and fast flowing, with extremely different seasonal discharges due to unevenly distributed rainfall. For hydropower generation or water resource purposes, weirs across river are usually built to facilitate water intakes, which may block the pass of fishes. As a result, fishways are important to help fish species pass the constructed structures and maintain their population and good genes. Good design of the fishway is a key element to it being successful. In this study, a three dimensional flow simulation model, FLUENT, was employed to simulate flow patterns and its three-dimensional velocity fields in a particular fishway with pool type in a hydropower dam in Da-Jia river, central Taiwan. Measurement data, by other people, in a physical model was used for verification and comparison. To have a convergent numerical solution, local refinement of computational grid size around all openings, such as orifices, is needed. The grid size should at least be smaller than half the narrow width of each opening. The upper or lower boundary will affect the flow pattern up to its near-by four pools in sequence. Therefore, at least ten pools are required in the simulation to have a central pool which is unaffected by either the upstream or downstream boundary. The simulated results show the averaged velocities at all openings are less than the upper-limit design flow-velocity, which is 1.5 to 1.7 m/sec. Within the pool, the flow pattern is stable and no significant circulation or up-lifting flow occurs, which might make the fish in the pool lose their way. Only the free surface flow across the Ice Harbor Weir indicates a streaming flow pattern, which is not suitable for surface-type fish to rest after each jump. Enlarging the longitudinal distance does not improve this drawback.