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Experimental investigations on secondary structures
in a fully developed turbulent jet and extension to fibre-laden case
Alessandro Capone, Alfredo Soldati
Department of Energetics, University of Udine, Italy
Giampaolo Romano
Department of Mechanics and Aeronautics, University of Rome La Sapienza, Italy
Cost Action FP1005 – Nancy 13th October 2011
Main aim
Investigation on streamwise vorticity developing in a round jet and its effect on
mixing processes
• Turbulence develops in 3D giving rise to so-called secondary structures
• Main feature is streamwise vorticity
secondary structures
Courtesy Prof. A.Soldati Courtesy Prof. GP Romano
Why secondary structures?
• Mixing and efficiency at entraining fluid is decisive in many industrial applications
• Streamwise vorticity takes part to this process
Why secondary structures?
• Water, fully developed turbulent round jet.
• Streamwise (up to x/D=7) and crosswise acquisitions
• Reynolds number:
3000-30000
Experimental setup
• At x/D=4.5 sheer entrainment rate increase
• Steady state shifts towards higher radii
Entrainment Rate
Fibre-laden case
Synthetic plastic fibres (nylon)
• Rod orientation contains information about velocity gradients tensor
• Parsa et al. Rotation and alignment of rods in two-dimensional chaotic flow Phys. Fluids 23 (2011)
• Time-resolved PIV allowed statistical and spectral analysis
• Streamwise vorticity take control of entrainment as x/D and Re increase
• The size of secondary vortical structures appears to be strictly connected to entrainment
• Rod rotation calculations bring useful info about vorticity
Conclusion and developments