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Alessandro Capone, Alfredo Soldati Department of Energetics, University of Udine, Italy

Experimental investigations on secondary structures in a fully developed turbulent jet and extension to fibre-laden case. Cost Action FP1005 – Nancy 13 th October 2011. Alessandro Capone, Alfredo Soldati Department of Energetics, University of Udine, Italy Giampaolo Romano

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Alessandro Capone, Alfredo Soldati Department of Energetics, University of Udine, Italy

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  1. Experimental investigations on secondary structuresin a fully developed turbulent jet and extension to fibre-laden case Cost Action FP1005 – Nancy 13th October 2011 Alessandro Capone, Alfredo Soldati Department of Energetics, University of Udine, Italy Giampaolo Romano Department of Mechanics and Aeronautics, University of Rome La Sapienza, Italy

  2. Main aim Investigation on streamwise vorticity developing in a round jet and its effect on mixing processes

  3. Why secondary structures? Turbulence develops in 3D giving rise to so-called secondary structures Main feature is streamwise vorticity secondary structures Courtesy Prof. GP Romano Courtesy Prof. A.Soldati

  4. Why secondary structures? • Mixing and efficiency at entraining fluid is decisive in many industrial applications • Streamwise vorticity takes part to this process

  5. Experimental setup • Water, fully developed turbulent round jet. • Streamwise (up to x/D=7) and crosswiseacquisitions • Reynolds number: • 3000-30000

  6. Results: average fields Mean velocity field at x/D=1.5 and Reynolds number 4800 and 19300

  7. Instantaneous fields • Time evolution of secondary structures at x/D=4.5 and Reynolds number 4800

  8. Coherency spectra • Re=4800 • For x/D>2.5 peak vanishes

  9. Spatial correlation functions • Size decreases • Asymptotic behaviour for Re>14500

  10. Entrainment Rate • At low x/D (<1.5) vortex rings effect on entrainment is relevant

  11. Entrainment Rate • At x/D=4.5 sheer entrainment rate increase • Steady state shifts towards higher radii

  12. Fibre-laden case • Rod orientation contains information about velocity gradients tensor • Parsa et al.Rotation and alignment of rods in two-dimensional chaotic flowPhys. Fluids 23(2011) Synthetic plastic fibres (nylon)

  13. Fibre-laden case • Phase discrimination and orientation estimate

  14. Fibre-laden case • Experimental results from pipe flow: near wall mean orientation

  15. Conclusion and developments • Time-resolved PIV allowedstatistical and spectralanalysis • Streamwisevorticity take control of entrainmentas x/D and Re increase • The size of secondaryvorticalstructuresappears to be strictlyconnected to entrainment • Rodrotationcalculationsbringuseful info aboutvorticity

  16. Questions Thank you for your attention!

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