河川潛板之渦流引致受力分析

Vorticity-induced forces on submerged vanes

賴哲弘(ZHE-HONG LAI)

指導教授 ： 林孟郁

中原大學/工學院/土木工程研究所/碩士(2016年)

https://doi.org/10.6840/cycu201600117

摘要

在河流流入彎道時，流體受到離心力和底床摩擦力的影響，導致河川垂直底床方向產生上下層的速度差，此速度差形成彎道二次流造成河床的破壞。潛沒式導流板(通稱潛板)為國外常見的一種改變河道底床工法，此工法將一薄平潛板放置於河川上游處，當流體通過潛板時，潛板下游處會產生一尾跡渦流，透過潛板設置的角度和位置，使產生的尾跡渦流可和彎道二次流相互抵消，達到保護河道的目的。
本研究應用三維非定常渦格法 (three-dimensional unsteady vortex lattice method)，建立簡化的潛板模式。將潛板分割成數個小板，在每個小板上都會產生一矩形邊界渦格環流量，計算每個時間點上，各個矩形邊界渦格環流量，進而推算出每個時間點上分離出來的，矩形尾跡渦格環流量。隨著時間變化，進行尾跡渦格端點位置的推移，模擬尾跡渦格隨時間的變化，並利用非定常的柏努力定理(Bernoulli theorem)，求解出各個小板上兩側的壓力差，進而找出每個時間點上潛板的受力情況。並藉由Odgaard and Wang(1991)的彎道床形模式計算出潛板下游底床床形變化。最後設定不同攻角、不同潛板板長和板高來進行潛板上的環流量、受力和潛板下游底床床形變化等分析。
研究結果顯示定量流通過潛板時，板長和攻角的增加都會造成環流量增加，尾跡渦的捲曲數量也隨之增加,且尾跡渦成形到穩定的時間變化不受板長和攻角改變的影響。潛板板長增加邊界渦環流量增加，則潛板下游床形變化隨之增加。潛板板長增加，潛板高長比降低，則潛板上的側向力相對降低。潛板攻角增加邊界渦環流量增加，造成潛板上側向力和阻力增加。

關鍵字

潛沒式導流板 ； 彎道二次流 ； 尾跡渦流 ； 柏努力定理

並列摘要

Flow in open-channel bends is affected by centrifugal force and basal friction force, inducing velocity gradient in vertical direction and generating secondary flow that may cause the erosion of riverbed. A submerged vane is an effective construction method for sediment management in alluvial rivers. Placing a thin flat submerged vane on the streambed at an angle to the flow may generate wake vortices. As a result, the secondary flow can be weakened and the shear stress on the channel bed is reduced.
In this study, a simplified numerical model for the flow induced by a submerged vane is established using a three-dimensional unsteady vortex lattice method. In this method, the vane is discretized into small panels. Each panel produces a little rectangular boundary circulation. By calculating the strengths of the boundary circulations and those of the separating wake circulations, the flow field and the bed shear stress induced by the wake of the submerged vane can be determined. The pressure distribution on the surface of the vane and the forces induced by the wake vortices can be calculated using Bernoulli theorem.
The computational results show that increasing the panel length and the angle of attack will increase the wake circulation and the strength of wake vortices. The period for the flow to achieve steady state is not affected by the length and the angle of the vane. Increasing the length of the vane may enhance the wake circulation and increase the depth variation of the streambed, and reduces the lateral force on the vane, Increasing the angle to the flow may enhance the wake circulation and also increase the forces on the vane.

並列關鍵字

submerged vanes ； secondary flow ； wake circulation ； Bernoulli theorem

參考文獻

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[30] 歐陽慧濤、賴進松、林政斌、羅元宏，"潛沒式導流板之形狀對交互作用現象的影響"，中華水土保持學報，第41卷第3期，第243-253頁 (2010)。

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