Experimental Description of Combining Flows at an Open Channel Junction

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Experimental Description of Combining Flows at an
Open Channel Junction

• Eric Shumate

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Overview

• Problem Definition
• Previous Research
• Physical Description of Experiment
• Test Program
• Results
• Conclusions and Recommendations

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Project Goal

• Detailed Description of Open Channel Combining
  Flow
• Three-Dimensional Velocities and Turbulence
• Water Surface Mapping
• Junction Flow Characteristics

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Project Justification

• Benchmark Experimental Data Set for the
  Validation of Future Numerical Models
• Three-Dimensional Flow
• Free Water Surface
• Combining Flow Data for Hydraulic Structures
• Fish Passage Conveyance Structures
• Wastewater Treatment Facilities
• Irrigation Canals

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Junction Flow Characteristics
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Previous Research

• Subcritical and Transitional Junctions
• Depth Ratio Studies
• Empirical and Theoretical
• One-Dimensional Models
• Accuracy
• Empirical Relationships for Junction
  Characteristics

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Previous Research

• Small Experimental Facilities
• Minimal Velocity Data Collected
• One- or Two-Dimensional
• Measurements Taken at a Single Depth
• No Water Surface Mapping
• Dye Trace Delineation of Separation Zone

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Experimental Facility

• Identical, Rectangular Cross-Section for Main
  and Side Channels
• Junction Angle Adjustable Between 45? ? 90?
• Rolled Entrance Head Boxes with Flow Training
  Screens
• Adjustable Tailgate

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Experimental Facility
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Test Program

• Flow Designations
• Upstream Main Channel Flow, Qm
• Branch Channel Flow, Qb
• Total Combined Flow, Qt
• Flow Ratio, q Qm/Qt
• 90 Sharp-Edged Junction
• Downstream Froude Number constant, Fd 0.37
• All Distances Non-Dimensionalized by Width

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Test Program

• Flows Tested

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Data Collection

• Three Component Acoustic Doppler Velocimeter Used
  for Velocities and Turbulence
• 20 Cross-Sections
• Seven or Nine Vertical Profiles per Section
• 17 Points on Vertical Profile
• Approximately 2850 Data Points
• Point Gauge Used for Water Surface Mapping
• 3 x 3 Grid

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Data Collection
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u Contours
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u Contours
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u Contours
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u Contours
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u-v Vectors
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u-v Vectors
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u-v Vectors
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v-w Vectors
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v-w Vectors
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Relative Magnitude of w
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Relative Magnitude of w
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Turbulent Kinetic Energy
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Turbulent Kinetic Energy
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Turbulent Kinetic Energy
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Water Surface Map
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Water Surface Map
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Conclusions

• Quality Data Set Exists for the Validation of a
  Numerical Model of Open Channel Junction Flow
• Three-Dimensional Nature is Important to the
  General Flow Conditions in the Junction Region
• Surface and Near-Bed Flows Behave Differently
• Region of Highest Turbulence Occurs at the
  Downstream Portion of the Separation Zone
• Separation Zone Increases in Length Until a
  Threshold Value is Reached

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Recommendations

• Application of a Three-Dimensional, Free Water
  Surface CFD Code to the Open Channel Junction
• Detailed Experimental Investigations of Combining
  Flows with Junction Angles other than 90º
• Detailed Experimental Investigations of Combining
  Flows with Varying Downstream Froude Number