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I.Z. Naqavi 1 , E. Savory 1 & R.J. Martinuzzi 2 1 Advanced Fluid Mechanics Research Group

Flow Characterization of Inclined Jet in Cross Flow for Thin Film Cooling via Large Eddy Simulation. 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

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I.Z. Naqavi 1 , E. Savory 1 & R.J. Martinuzzi 2 1 Advanced Fluid Mechanics Research Group

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  1. 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

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

  3. 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.

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

  5. 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.

  6. 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.

  7. Large Eddy Simulation: • In LES spatially filtered unsteady Navier Stokes equation are solved numerically.

  8. 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.

  9. 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.

  10. Results

  11. Average Vorticity Field: Average stream-wise vorticity at different y-z planes

  12. Streamlines overlaid on average stream-wise vorticity on a y-z plane at x=5D showing counter rotating vortex pair.

  13. Average wall normal vorticity at the bottom x-z plane Average span-wise vorticity at the central x-y plane

  14. Instantaneous Vorticity Field: Instantneous stream-wise vorticity at different y-z planes

  15. Instantaneous wall normal vorticity at the bottom x-z plane

  16. Instantaneous span-wise vorticity at the central x-y plane

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

  18. Coherent structures for inclined jet in cross flow (Laminar)

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

  20. 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

  21. Thank you

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