Active Control of the Flow Around a Barchan Sand Dune Model

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Active Control of the Flow Around a Barchan Sand
Dune Model

• Applied National Research Project
• By
• Dr. Shibl, Dr. Zedan, and Dr. Al-Saif

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Seminar Contents

• Barchan Dune and its Migration.
• Dune Migration Control.
• Research Methodology.
• Experimental Work.
• Static pressure Five Hole probe Hot Wire
  Anemometer
• Conclusion.

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Barchan Dunes
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Effects of Winds

• Winds erode, transport, and deposit sand
• Large sand grains are carried in Saltation (one
  meter above ground)
• Smaller ones are in suspension

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A Barchan Dune ( 3 m high)
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BARCHAN DUNE
Crest
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Mechanism of Dune Migration

• Barchan dune moves with self-preserving shape,
  i.e. equilibrium of erosion and sand deposition
  rates.
• Sand is transported from the stoss to the dune
  lee side causing the dune to migrate.
• The main mechanism is saltation ( 75 of sand
  transport.) and surface creep (rolling)
• The crest becomes unstable and sand avalanches
  occur down the slip face.

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DUNE MIGIRATION CONTROL

• Flow Field Modification around dunes
• -Turbulence manipulators along the dune stoss.
• - Provoking separation along the stoss (wind can
  dump some of its burden in the separation region
  before crest.

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Control by Surface Conditioning

• Oil Spraying. (expensive and temporary)
• Differential oiling (strips), for dune
  destruction.
• Destroying the streamline symmetry of the dune
• Increasing the surface roughness (spreading
  fishing nets, microorganisms to form rigid
  crusts).

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Wind Breakers and Fences.

• Modifying the upstream wind characteristics by
  setting up windbreaks using fences,
• turbulence manipulators,
• vortex generatorsetc.

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Combined Control

• To Achieve Effective Migration Control
• By Combining Stabilization and Fences.
• By Combining Turbulence Manipulation, Vortex
  generators and Roughness .
• By Combining Differential oiling (strips) and
  windbreaks..

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Research Methodology

• Study experimentally the flow around 2-D model of
  Barchan dune,
• Flow modification using fences and turbulence
  manipulators positioned selectively along the
  stoss.
• Using pressure tapping, five-hole probe and hot
  wire anemometer.

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RESULTS

• Results are compared, to facilitate finding the
  optimum fence and manipulator locations.
• The comparisons involve
• -Pressure distribution and pressure drag.
• -Shear stress.
• -Power spectrum.
• -Mean and turbulent velocity profiles.

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Summary of Experimental Work

• Control using a fence either downstream or
  upstream of dune model,
• Upstream Velocity Uo 28.2 m/sec 0.4 and
  Upstream Re 8.65 X 105

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Control using manipulators (d/H0.06) along dune
stoss
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Static Pressure Measurements

• Pressure Distribution Along Dune Surface With
  and Without control.
• Percentage Uncertainty within 2.5
• (95 Confidence Level)

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Press with and without Fence
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Pressure with and without Manipulator
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Pressure Distribution With Manipulators
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Five Hole Probe Measurements

• Velocity Profile With and Without Control in
  the Vicinity of Dune Crest
• Percentage Uncertainty within 1.5
• (95 Confidence Level) Away From Separation in
  the Dune Lee Side

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Velocity profile without control
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Velocity profile with upstream 120o fence
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Hot Wire Measurements

• Longitudinal Mean Velocity and its
  Turbulence Intensity With and Without Control
• Percentage Uncertainty within 2
• (95 Confidence Level) Away From Separation in
  Dune Lee Side.

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Longitudinal Mean Velocity and its Turbulence
Intensity Without any Fences or Manipulators.
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Longitudinal Mean Velocity and its Turbulence
Intensity at Station 1 With and Without
Manipulator (d/H0.06) on Dune Crest
(X/H4.06).
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Spectrum Distribution

• Relation between Amplitude Ratio and Distance
  from Dune Surface For Different Frequencies.

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Spectrum Distribution at St.1Without Fence or
Manipulators
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Spectrum Distribution at St.1with Manipulator at
Crest
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Conclusion

• It is possible to modify the flow around sand
  dune with the aim of hindering its migration
  using fences and manipulators.
• The most effective location for fence and
  manipulators is in the vicinity before dune
  crest.
• There is need for experimentation and numerical
  simulation of 3-D Barchan sand dune model in
  presence of flow control.