scholarly journals COMPARISON OF TURBULENCE INTEGRAL LENGTH SCALE DETERMINATION METHODS

2020 ◽  
Author(s):  
ARSENII TRUSH ◽  
STANISLAV POSPÍŠIL ◽  
HRVOJE KOZMAR
Keyword(s):  
Integral Length Scale ◽  
Length Scale ◽  
Determination Methods

Lateral dispersion in random cylinder arrays at high Reynolds number

2008 ◽  
Vol 600 ◽  
pp. 339-371 ◽  
Author(s):  
YUKIE TANINO ◽  
HEIDI M. NEPF
Keyword(s):  
Turbulence Intensity ◽  
Turbulent Diffusion ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Laboratory Data ◽  
Integral Length Scale ◽  
Length Scale ◽  
Linear Superposition ◽  
Cylinder Diameter ◽  
The Mean

Laser-induced fluorescence was used to measure the lateral dispersion of passive solute in random arrays of rigid, emergent cylinders of solid volume fraction φ=0.010–0.35. Such densities correspond to those observed in aquatic plant canopies and complement those in packed beds of spheres, where φ≥0.5. This paper focuses on pore Reynolds numbers greater than Res=250, for which our laboratory experiments demonstrate that the spatially averaged turbulence intensity and Kyy/(Upd), the lateral dispersion coefficient normalized by the mean velocity in the fluid volume, Up, and the cylinder diameter, d, are independent of Res. First, Kyy/(Upd) increases rapidly with φ from φ =0 to φ=0.031. Then, Kyy/(Upd) decreases from φ=0.031 to φ=0.20. Finally, Kyy/(Upd) increases again, more gradually, from φ=0.20 to φ=0.35. These observations are accurately described by the linear superposition of the proposed model of turbulent diffusion and existing models of dispersion due to the spatially heterogeneous velocity field that arises from the presence of the cylinders. The contribution from turbulent diffusion scales with the mean turbulence intensity, the characteristic length scale of turbulent mixing and the effective porosity. From a balance between the production of turbulent kinetic energy by the cylinder wakes and its viscous dissipation, the mean turbulence intensity for a given cylinder diameter and cylinder density is predicted to be a function of the form drag coefficient and the integral length scale lt. We propose and experimentally verify that lt=min{d, 〈sn〉A}, where 〈sn〉A is the average surface-to-surface distance between a cylinder in the array and its nearest neighbour. We farther propose that only turbulent eddies with mixing length scale greater than d contribute significantly to net lateral dispersion, and that neighbouring cylinder centres must be farther than r* from each other for the pore space between them to contain such eddies. If the integral length scale and the length scale for mixing are equal, then r*=2d. Our laboratory data agree well with predictions based on this definition of r*.

Advancing drag crisis of a sphere via the manipulation of integral length scale

2011 ◽  
Vol 14 (1) ◽  
pp. 35-53 ◽  
Author(s):  
Niloofar Moradian ◽  
David S.K. Ting ◽  
Shaohong Cheng
Keyword(s):  
Integral Length Scale ◽  
Length Scale

The motion of fibres in turbulent flow

1998 ◽  
Vol 377 ◽  
pp. 47-64 ◽  
Author(s):  
JAMES A. OLSON ◽  
RICHARD J. KEREKES
Keyword(s):  
Turbulent Flow ◽  
Fibre Length ◽  
Integral Length Scale ◽  
Length Scale ◽  
Dispersion Coefficients ◽  
Turbulent Fluid ◽  
Mean Motion ◽  
Fluid Velocities

Equations of mean and fluctuating velocities in rotation and translation have been derived for rigid thin inertialess fibres moving in a turbulent fluid. The derived equations for mean motion are general to fluid velocities that vary nonlinearly along the length of the fibre. From the equations of fluctuating fibre velocity, rotational and translational dispersion coefficients were derived. The resulting dispersion coefficients were shown to decrease as the ratio of fibre length to Lagrangian integral length scale of the turbulence increased.

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