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12.23.2 Postprocessing Turbulent Flow Statistics

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 root-mean-square (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 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  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.

Figure 12.23.1: Postprocessing Choices for Unsteady Wall Statistics...

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 $\rightarrow$ set $\rightarrow$ data-sampling

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 re-initialize the flow statistics.

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© Fluent Inc. 2006-09-20