
As described in Section
12.9, LES involves the solution of a transient
flow field, but it is the mean flow quantities that are of interest from an engineering standpoint.
For all other turbulent flow, if
Data Sampling for Time Statistics is enabled in the
Iterate panel,
FLUENT gathers data for time
statistics while performing the simulation. The statistics that
FLUENT collects at each sampling interval (which consists of the mean and the rootmeansquare (RMS) values) can be postprocessed by selecting
Unsteady Statistics... in any of the postprocessing panels. You can view several variables that include, but are not limited to, shear stresses (
Resolved UV/UW/VW Reynolds Stress), flow heat fluxes (
Resolved UT/VT/WT Heat Flux), and species statistics (
RMS Mass Fraction of species and
Mean Mass Fraction of species). If you select
Unsteady Wall Statistics... in any of the postprocessing panels, you can view wall statistics such as
Mean Pressure Coefficient,
Mean Wall Shear Stress,
Mean XWall Shear Stress,
Mean YWall Shear Stress,
Mean ZWall Shear Stress,
Mean Skin Friction Coefficient,
Mean Surface Heat Flux,
Mean Surface Heat Transfer Coef.,
Mean Surface Nusselt Number,
Mean Surface Stanton Number. See Section
25.17.4 for details.

Note that
mean statistics are collected only in interior cells and not on wall surfaces. Therefore, when node or cell values of mean quantities are plotted on the wall surface, you are actually plotting values in nearby cells attached to the wall.

There may be cases when you want to control what set of variables are available for postprocessing. To enable or disable certain variables, use the following text command:
solve set datasampling
The text command prompts you with a set of questions that you will answer yes or no to depending on whether or not you want statistics collected on certain variables. The following example demonstrates using the text command when do not want to collect statistics on species:
Data Sampling for Time Statistics? [yes] Sampling interval [2] Collect statistics for flow shear stresses? [yes] Collect statistics for flow heat fluxes? [yes] Collect wall statistics? [yes] Collect statistics for ch3oh? [yes] no 

When including or excluding statistics on variables, it is recommended that you reinitialize the flow statistics.
