Experimental Verification of CFD Modeling of Turbulent Flow over Circular Cavities using FLUENT

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University of Western Ontario Department of
Mechanical Materials Engineering
Advanced Fluid Mechanics Research Group
Experimental Verification of CFD Modeling of
Turbulent Flow over Circular Cavities using FLUENT
Presented by Thomas Hering MESc Candidate
Jesse Dybenko Research Engineer
Eric Savory Associate Professor
May 23, 2006
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Overview

• General overview of experimental parameters
• CFD grid generation
• CFD solution procedure
• Results
• Key findings
• Future work
• (Elliptical Cavities)

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Background

• Cavities may lead to increased noise and
  drag on an object
• Main focus on Circular cavities
• Resulting asymmetric flow and significant
  increase in drag at
• h/D 0.5

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Experimental Data Collected

• Three cases of h/D ratio 0.2, 0.47, 0.7 were
  tested
• Pressure transducer data was taken to plot
  surface pressure contours on cavity walls and
  surrounding plane
• Hot Wire anemometry was used to examine the wake
  flow characteristics
• The free stream velocity during the experiments
  was 27 0.15 m/s
• The pressure coefficient was normalized using the
  tunnel static pressure and free stream velocity

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Boundary Conditions and Dimensions
Velocity Inlet
The inlet velocity was set to 25 m/s, which
resulted in a free stream velocity of 26.4 m/s at
the free stream reference point
Wall
Cavity
Outflow
Wall
32D
47.3D
Y
4D
X
Z
5.5D
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Simulation Grid
Cavity
Side View
Top View
The computation domain was broken up into several
volumes which were meshed using a structured
hexagonal cooper meshing scheme
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Solution Procedure

• The solution was first iterated using the k-e
  turbulence model
• After initial solution convergence the Reynolds
  Stress model was applied and further iterated
• The tunnel length was used to develop a similar
  boundary layer as measured in the experiments
• A steady state solution sought

Simulated Data
Experimental Data
Boundary Layer Parameters
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Pressure Distributions
Pressure Coefficient

• Due to simulated steady state solution, only the
  mean values were compared
• Surface pressure distributions, wake profiles and
  drag coefficients were compared

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Pressure Contours for h/D 0.7

Simulated results matched well with experimental
data
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Pressure Distributions along the Centreline for
h/D 0.7
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Pressure Contours for h/D 0.2
Similar trends along the centreline as for the
h/D 0.7 case, but the difference between
simulated and experimental data was larger
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Pressure Contours for h/D 0.47 (Asymmetric flow)

• Asymmetry is much weaker in the simulated results
• Vortex tube does not completely leave the cavity
  in the simulated results

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Comparison between Turbulence Models for h/D
0.47
Asymmetry is weaker when applying the k-e
turbulence model

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Resulting Wake Comparisons
The weak asymmetry can be seen in the wake for
h/D 0.47 case
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Drag coefficient Comparison

• Experimental drag coefficient calculated using
  pressure distributions along cavity wall
• Weaker asymmetry the cause of the lower drag
  coefficient at
• h/D 0.47

Drag increment due to presence of cavity
CD Drag coefficient (normalized by the cavity
planform area) cf Skin friction coefficient
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Key Findings

• The simulated results showed the correct flow
  physics involved in circular cavity flows
• The asymmetric flow for a symmetric geometry, a
  distinct feature of this type of flow, was
  apparent in the simulations
• The weaker asymmetry led to a lower drag
  coefficient
• The simulations constantly under predicted the
  pressure values for all three configurations
  tested
• The Reynolds Stress Turbulence model provided
  better results than the k-e Turbulence model when
  comparing the strength of the asymmetry at h/D
  0.47

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Elliptical Cavities h/D 0.47
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University of Western Ontario Department of
Mechanical Materials Engineering
Advanced Fluid Mechanics Research Group
http//www.eng.uwo.ca/research/afm/main.htm
Discussion and Questions are welcome
An Experimental Investigation of
Turbulent Boundary Layer Flow over
Surface-Mounted Circular Cavities J. Dybenko and
E. Savory, UWO 1220-1245 May 24, 2006 (Walker)