LES

Here i collect some very basic tools i used when performing basic LES computations in Fluent.

1) Custom field function for the Q criterion (q_crit.txt, to be renamed in .scm). Some Fluent versions (12, 13 and maybe 14) only have a "Normalized Q criterion" scalar, while previous ones simply don't have it at all. This custom field function is what i used in those dark days.

2) Several initialization routines (init*.c and scalefield.c) fully described in the files...

Let us suppose you have the following matrices:

x(nx,ny,nz): x coordinates of your grid

y(nx,ny,nz): y coordinates of your grid

z(nx,ny,nz): z coordinates of your grid

dudx(nx,ny,nz): x-wise derivative of x-wise velocity component

dudy(nx,ny,nz): y-wise derivative of x-wise velocity component
.
.
.
dwdz(nx,ny,nz): z-wise derivative of z-wise velocity component

This is, more or less, how i would...

A paper produced for a national conference. Some basic details of the LES in Fluent are covered, together with the main setup:

http://www.lamc.ing.unibo.it/aimeta2.../MEM-273-0.pdf

The lambda 2 criterion simply concerns the definition of the scalar lambda2 and how turbulent structures can be visualized by proper isosurfaces of lambda2 (like for the Q criterion). Hence, the real difference with the scalar Q is how you compute the scalar lambda2.

This is defined as the second (in magnitude) eigenvalue of the matrix:



where:

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