Suscripción a Biblioteca: Guest
Seventh International Symposium on Turbulence and Shear Flow Phenomena
July, 28-31, 2011, Ottawa Convention Centre, Ottawa, Canada

DOI: 10.1615/TSFP7

THE DECAY OF HOMOGENEOUS TURBULENCE GENERATED BY MULTI-SCALE GRIDS

pages 1-6
DOI: 10.1615/TSFP7.530
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SINOPSIS

An experimental investigation of freely decaying homogeneous, quasi-isotropic turbulence generated by a low-blockage space-filling fractal square grid is presented. We find good agreement with previous work by Mazellier & Vassilicos ["Turbulence without the Richardson-Kolmogorov cascade", Phys. Fluids 22, 075101 (2010)] but also extend the length of the assessed decay region and consolidate the results by repeating the experiments with a second probe of increased spatial resolution. It is confirmed that this moderately high Reynolds number turbulence (150 < Reλ < 400) does not follow the classical high Reynolds number scaling of the dissipation rate ε ~ u'3/L which is in fact equivalent to a proportionality between the Taylor-based Reynolds number Reλ and the ratio of integral scale L to Taylor micro-scale λ. Instead we observe a constant ratio L/λ whilst Reλ decays during free turbulence decay. Alternative reasons for this non-classical behaviour are discussed, including various ways in which the turbulence may fall into a self-preserving, single-length-scale state. It is also shown that the measured 3D energy spectra can be reasonably collapsed using a single length-scale over the entire decay region even though the Reynolds number is high enough for conventional decaying turbulence to display spectra with two-scale (inner and outer) Kolmogorov scaling.

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