Conditional filtering
From CFD-Wiki
A conditional filtering operation of a variable is defined as
where is a positive defined space filter with filter width
(see LES filters),
is a fine-grained probability density function,
which is taken as a Dirac delta
.
The probability density function
is a subgrid PDF and
is the sample space of the passive scalar
. In variable density flows, conditional density-weighted
(Favre) filtering is used,
,