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Flow field topology of submerged jets with fractal generated turbulence

Cafiero, G., Discetti, S. and Astarita, T. (2015) Flow field topology of submerged jets with fractal generated turbulence Physics of Fluids, 27 (11), 115103.

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Fractal grids (FGs) have been recently an object of numerous investigations due to the interesting capability of generating turbulence at multiple scales, thus paving the way to tune mixing and scalar transport. The flow field topology of a turbulent air jet equipped with a square FG is investigated by means of planar and volumetric particle image velocimetry. The comparison with the well-known features of a round jet without turbulence generators is also presented. The Reynolds number based on the nozzle exit section diameter for all the experiments is set to about 15 000. It is demonstrated that the presence of the grid enhances the entrainment rate and, as a consequence, the scalar transfer of the jet. Moreover, due to the effect of the jet external shear layer on the wake shed by the grid bars, the turbulence production region past the grid is significantly shortened with respect to the documented behavior of fractal grids in free-shear conditions. The organization of the large coherent structures in the FG case is also analyzed and discussed. Differently from the well-known generation of toroidal vortices due to the growth of azimuthal disturbances within the jet shear layer, the fractal grid introduces cross-wise disturbs which produce streamwise vortices; these structures, although characterized by a lower energy content, have a deeper streamwise penetration than the ring vortices, thus enhancing the entrainment process.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Mechanical Engineering Sciences
Authors :
Discetti, S.
Astarita, T.
Date : 9 November 2015
DOI : 10.1063/1.4935185
Uncontrolled Keywords : Air; Flow fields; Fractals; Reynolds number; Shear flow; Topology; Turbulence; Velocity measurement; Vortex flow; Coherent structure; Entrainment process; Entrainment rates; Particle image velocimetries; Streamwise vortices; Toroidal vortices; Turbulence generators; Turbulence productions; Fighter aircraft
Depositing User : Clive Harris
Date Deposited : 12 May 2020 18:25
Last Modified : 12 May 2020 18:25

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