12.17.2 Postprocessing Turbulent Flow Statistics

As described in this section (in the separate Theory Guide), 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 Run Calculation dialog box, ANSYS FLUENT gathers data for time statistics while performing the simulation. The statistics that ANSYS FLUENT collects at each sampling interval (which consists of the mean and the root-mean-square (RMS) values) can be postprocessed by selecting Unsteady Statistics... in any of the postprocessing dialog boxes. 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 dialog boxes, you can view wall statistics such as Mean Pressure Coefficient, Mean Wall Shear Stress, Mean X-Wall Shear Stress, Mean Y-Wall Shear Stress, Mean Z-Wall 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  26.12.4 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, go to

Run Calculation Sampling Options...

The sampling Options dialog box will open, where you can enable or disable the statistics shown in Figure  12.17.1.

Figure 12.17.1: Sampling Options Dialog Box

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