水流墩前湧波之探討

Bow wave and Hydraulic jump induced by cylindrical piers in open channel flows

劉力維(Li-Wei Liu)

指導教授 ： 周憲德 ； 吳祚任

國立中央大學/工學院/土木工程學系/碩士(2008年)

摘要

本文以實驗及數值計算分析超臨界流況下，橋墩受水流沖擊所造成的墩前湧波，探討橋墩尺度對振幅、頻率的影響；實驗於亞臨界流況下，利用超音波速度剖面儀(UVP)量測墩前速度場分佈，進一步探討墩前射流之分離位置及流場中頻率的特性，並透過數值模Truchas分析墩前射流位置及渦流分佈。實驗結果顯示，沖擊高度與上游福祿數呈正比之關係；UVP 能有效量測邊界層厚度及墩前渦流尺寸；透過數值模式，能進一步分析細部流場變化，如：渦度分佈、底床剪應力。本研究之結果可幫助於瞭解亞、超臨界流況中墩前沖擊高度與上游福祿數的關係，可供相關工程設計之參考。

關鍵字

超臨界流 ； 墩前湧波 ； 沖擊高度 ； 底床剪應力 ； 頻譜分析

並列摘要

Bow waves in front of cylindrical piers under different flow conditions, especially supercritical flows, are explored in this study by employing both flume experiments and 3D numerical simulation. An ultrasonic velocity profiler (UVP) is used to measure the downward/upward flow right in front of the pier, and the downward flow and the stagnation point along the profile are also measured. The magnitudes and the frequencies of bow waves are analyzed by image analysis. The vortex sizes are mainly determined by pier diameter alone. The dimensionless amplitude of bow waves is proportional to the square of upstream Froude numbers. The numerical simulations for piers in shallow water show that the shear stresses on the floor exhibit maximum value at the downstream sides, which is due to pier-induced surface drawdown and wake separation.

並列關鍵字

Spectrum analysis. ； Bed shear stress ； Surge height ； Bow wave ； Supercritical Flow

參考文獻

2.胡富雁(2007) ，「波狀水躍流場之水理分析」，碩士論文，國立中央大學土木工程學系，中壢。

10.Blevins., (1990) “Flow-Induce Vibration”, VAN NOSTRAND REINHOLD.

6.Ahmed, F and Rajaratnam, N. (1998) “Flow around bridge piers” J. Hydraulic Engineering., vol.124, No.3, pp.288-300.

8.Baker, C.J. (1979) “The Laminar Horseshoe Vortex”, J. Fluid Mech., Vol.95, pp.347-367.

9.Ballio, F., Bettoni, C. and Frsnzetti, S. (1998) “ A Survey of Time-Averaged Characteristics of Laminar and Turbulent Horseshoe Vortices ,” J. Fluids Engineering, Vol.120, pp.233-242.