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I.Z. Naqavi 1, E. Savory 1 & R.J. Martinuzzi 2 1 Advanced Fluid Mechanics Research Group Department of Mechanical and Materials Engineering The University of Western Ontario 2 Mechanical and Manufacturing Engineering University of Calgary Flow Characterization of Inclined Jet in Cross Flow for Thin Film Cooling via Large Eddy Simulation
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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 (Durbin, 2000) Cold fluid Holes for film cooling on turbine blade. Thin Film Cooling: 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. Hot fluid Cooling film
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Background: Four major structures have been identified i.e. horse shoe vortex, jet shear-layer vortex, counter rotating vortex pair and wake vortices. Horseshoe vortices Jet shear-layer vortices Counter rotating vortex pair Wake vortices Wall
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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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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 3 rd 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. Large Eddy Simulation (cont.):
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Re D =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 x=5D 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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Coherent structures for inclined jet in cross flow (Turbulent) Hairpin structures Stream-wise structure
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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
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