Three-dimensional numerical simulation of flow around stream deflectors: The effect of obstruction angle and length

Fish habitat rehabilitation projects often use paired stream deflectors to increase bed shear stress and maintain a deep pool. Many of these projects have been unsuccessful, mainly because of the lack of knowledge of the complex three-dimensional (3D) flow dynamics created by the deflectors. A 3D numerical model was used to simulate the flow field around stream deflectors in a laboratory flume. Predicted velocities were successfully evaluated against laboratory measurements. Deflectors ranging from contraction ratios of 0.1 -0.35 oriented to flow at angles of 30-150° were used for the simulations. Results show that the upstream dynamic pressure maximum, upstream flow separation distance, upstream downwelling extent, and total downwelling distance all increase with deflector angles. However, local minimum dynamic pressure, nose velocity amplification, downstream downwelling extent, and flow contraction width are maximized at angles closer to 90°. In general, maximum downwelling magnitudes increase for longer deflectors, with the greatest values being found for the 135° deflectors. Increasing the length of the deflectors tends to amplify most of the flow parameters. These findings have important implications for the design of paired deflectors in fish habitat rehabilitation projects where the objective is to maximize the pool size downstream of the obstructions.

[1]  D. M. Thompson,et al.  The Development and Historic Use of Habitat Structures in Channel Restoration in the United States: The Grand Experiment in Fisheries Management , 2004 .

[2]  Albert Molinas,et al.  Shear Stress around Vertical Wall Abutments , 1998 .

[3]  Denis Dartus,et al.  THREE-DIMENSIONAL COMPUTATION OF FLOW AROUND GROYNE , 1997 .

[4]  Marian Muste,et al.  Scale Effects in Flume Experiments on Flow around a Spur Dike in Flatbed Channel , 2004 .

[5]  K. Babaeyan-Koopaei,et al.  Flow pattern in the scour hole around a cylinder , 2003 .

[6]  Nallamuthu Rajaratnam,et al.  Flow around bridge piers , 1998 .

[7]  K. Richards,et al.  The application of computational fluid dynamics to natural river channels: three-dimensional versus two-dimensional approaches , 1999 .

[8]  Sujit K. Bose,et al.  Clear water scour at circular piers : a model , 1995 .

[9]  Sanjiv K. Sinha,et al.  Analysis of flow past submerged vanes , 2000 .

[10]  G. Mathias Kondolf,et al.  Evaluating stream restoration projects , 1995 .

[11]  M. Lapointe,et al.  Three‐dimensional flow dynamics around deflectors , 2005 .

[12]  Derek B. Ingham,et al.  High‐resolution numerical modelling of three‐dimensional flows over complex river bed topography , 2002 .

[13]  K. Richards,et al.  Role of Bed Discordance at Asymmetrical River Confluences , 2001 .

[14]  Siow-Yong Lim,et al.  Equilibrium Clear-Water Scour around an Abutment , 1997 .

[15]  Daniel R. Parsons,et al.  A Framework for Model Verification and Validation of CFD Schemes in Natural Open Channel Flows , 2005 .

[16]  P. Biron,et al.  Three-Dimensional Numerical Modeling of Mixing at River Confluences , 2004 .

[17]  T F Kwan,et al.  A STUDY OF ABUTMENT SCOUR , 1988 .

[18]  Pascale M. Biron,et al.  Deflector Designs for Fish Habitat Restoration , 2004, Environmental management.

[19]  Derek B. Ingham,et al.  Numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment , 2004 .

[20]  R. J. White,et al.  Growth and development of North American stream habitat management for fish , 1996 .

[21]  A. Molinas,et al.  Finite element surface model for flow around vertical wall abutments , 2000 .

[22]  CHIN,et al.  Modeling of 3 D Flow and Scouring around Circular Piers , 2001 .

[23]  B. Zhu,et al.  A sigma coordinate 3D k–ε model for turbulent free surface flow over a submerged structure , 2002 .

[24]  D. Sear,et al.  Modelling three‐dimensional flow structures and patterns of boundary shear stress in a natural pool–riffle sequence , 2001 .

[25]  B. Melville.  PIER AND ABUTMENT SCOUR: INTEGRATED APPROACH , 1997 .

[26]  Jasim Imran,et al.  Numerical Modeling of Three-Dimensional Flow Field Around Circular Piers , 2004 .

[27]  Vijay Panchang,et al.  Three-Dimensional Simulation of Scour-Inducing Flow at Bridge Piers , 1998 .

[28]  U. C. Kothyari,et al.  Scour around spur dikes and bridge abutments , 2001 .

[29]  Othman A. Karim,et al.  Simulation of flow around piers , 2002 .

[30]  S. Lane,et al.  Flow in meander bends with recirculation at the inner bank , 2003 .

[31]  Stuart N. Lane,et al.  Investigation of controls on secondary circulation in a simple confluence geometry using a three-dimensional numerical model , 1998 .

[32]  Fotis Sotiropoulos,et al.  Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments , 2003 .

[33]  D. M. Thompson.  Channel-Bed Scour with High versus Low Deflectors , 2002 .

[34]  Carlos V. Alonso,et al.  Geometry of Scour Holes Associated with 90° Spur Dikes , 1999 .