單體透水性筐網與不透水圓柱於定床之流場差異探討

Flow-field Comparison around a Single Cylinder with Porous or Non-porous Material

10.29417/JCSWC.201106_42(2).0002

黃進坤(Chin-Kun Hu)；許少華(Shao-Hua Marko Hsu)；劉建榮(Chien-Jung Liu)；周峻暐(Chun-Wei Chou)

透水性 ； 緩流促淤 ； 筐網圓柱 ； porous ； slowing flow for deposition ； porous cylinder

中華水土保持學報

42卷2期（2011 / 06 / 01）

93 - 106

繁體中文

防治河岸沖刷的工法需隨河岸曲直、水流強度、保護標的…等來設計或放置不同的剛性（不透水）與柔性（透水性）保護工法，以達到減輕河岸遭洪水衝擊以及緩流促淤造灘的目的。本文主要針對具透水性與導流性之筐網圓柱以室內水工試驗進行初步的研究與分析，探討於定床條件下水流流經具透水性筐網圓柱與不透水圓柱後下游流場的差異。結果發現，圓柱透水性愈差，圓柱下游卡曼渦流的影響愈明顯，橫向流速會因尾跡渦流強度增大而有週期性的振盪。此外，透水性筐網圓柱有穿越流抑制尾流效應，可降低柱體下游的流速與渦流效應使下游流場穩定性較高。圓柱直徑不同所造成的下游流場變化幅度遠小於透水性不同所造成的影響，故於設計透水性筐網圓柱時應以透水性高但結構強度足夠抵抗水流沖擊為主要考量。

The design of river-bank protection depends on the local situation of the protected site, including the curvature of the river, flow strength, and the protected objects. The protection may combine rigid (non-porous) and flexible (porous) elements for reducing the impact of flood flow and creating regions that slow the flow of deposition around the bank. In this study, flume experiments were conducted for investigating the flow fields around a porous cylinder. The emphasis was on the comparison between a porous cylinder and a non-porous one. The degree of porosity was also a focus. Karman vortex shedding becomes stronger with periodic oscillation for a non-porous cylinder. With [breed/debris??] flow through the porous cylinder, the flow behind the cylinder becomes stabilized and the vortex shedding disappears. The effect of cylinder diameter is smaller than the degree of porosity. In conclusion, designing a highly porous protection work with sufficient strength in the frame of structure to resist being deformed by strong flow is an important issue for river engineering.