I.Z. Naqavi1, E. Savory1

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Flow Characterization of Inclined Jet in Cross
Flow for Thin Film Cooling via Large Eddy
Simulation
I.Z. Naqavi1, E. Savory1 R.J.
Martinuzzi2 1Advanced Fluid Mechanics Research
Group Department of Mechanical and Materials
Engineering The University of Western
Ontario 2Mechanical and Manufacturing
Engineering University of Calgary
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Overview

• Jets in Cross Flow
• Thin Film Cooling
• Background
• Current Work
• Large Eddy Simulation
• Results
• Conclusions

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Jets in Cross Flow

• A flow configuration representing a variety of
  industrial and environmental flows.
• A jet is introduced from the wall at a certain
  angle to the main stream.
• Used in VTOL, thin film cooling, pollutant
  dispersion etc.

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Thin Film Cooling
Hot fluid
Cooling film
Cold fluid
Thin film cooling (Durbin, 2000)
Holes for film cooling on turbine blade.

• Separation of a hot fluid from a wall by a cold
  fluid, in form of a thin layer ejecting from
  wall, is called thin film cooling.

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Background
Counter rotating vortex pair
Jet shear-layer vortices
Horseshoe vortices
Wake vortices
Wall

• Four major structures have been identified i.e.
  horse shoe vortex, jet shear-layer vortex,
  counter rotating vortex pair and wake vortices.
  

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Current Work

• In this work LES is performed for inclined jet
  in cross flow.
• Effort is being made to introduce a cross flow
  with true turbulence.
• Previous LES simulations lack effective
  turbulence specification at the inlet. In this
  work a real turbulent field is specified at the
  inlet.
• This will enhance the understanding of the
  effect of background turbulence on the jet in
  cross flow.

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Large Eddy Simulation

• In LES spatially filtered unsteady Navier Stokes
  equation are solved numerically.

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Large Eddy Simulation (cont.)

• A fractional step scheme (Moin, 1982) is used to
  solve Navier Stokes equations.
• A semi implicit time advancement scheme is used
  where convection terms are discretized explicitly
  with 3rd order Runge-Kutta scheme and diffusion
  terms are discretized implicitly with
  Crank-Nicolson scheme.
• Resulting set of linear system is approximately
  factorized and solved using Tri-diagonal matrix
  algorithm.
• To solve pressure poisson equation fourier
  decomposition is applied in span-wise direction
  and resulting system of equation is solved using
  cyclic reduction method.

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Large Eddy Simulation (cont.)

• ReD 3500
• Domain size

• Grid size
• At inlet a true turbulent velocity field is
  specified for that purpose a separate channel
  flow code is run and velocities are saved at a
  plane for some 150 flow through time.

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Results
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Average Vorticity Field
Average stream-wise vorticity at different y-z
planes
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Streamlines overlaid on average stream-wise
vorticity on a y-z plane at x5D showing counter
rotating vortex pair.
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Average wall normal vorticity at the bottom x-z
plane
Average span-wise vorticity at the central x-y
plane
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Instantaneous Vorticity Field
Instantneous stream-wise vorticity at different
y-z planes
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Instantaneous wall normal vorticity at the bottom
x-z plane
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Instantaneous span-wise vorticity at the central
x-y plane
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Coherent Structure

• Coherent structures can be represented by
  iso-surfaces of pressure poisson.

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Coherent structures for inclined jet in cross
flow (Laminar)
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Hairpin structures
Stream-wise structure
Coherent structures for inclined jet in cross
flow (Turbulent)
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Conclusions

• Instantaneous flow picture is presenting a very
  strong interaction of cross flow with jet.
• Vortical structures coming from upstream
  interact with the jet.
• Such interactions can have strong influence on
  heat transfer.

http//www.eng.uwo.ca/research/afm/default.htm
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Thank you