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What is the difference between Time Average Output and Running Average Output?

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This type of output is a simple average. The value that is printed in the output file is computed as follows:UTimeAve = sum( U_n )/n, where n = the step number. The reset_frequency tells AcuSolve to start the time averaging procedure over by deleting the previous time averaged field, setting n=0, then starting the process out with a fresh set of values. Note that these values are not carried forward across restarts. So, every time you restart AcuSolve, the time average output is reinitialized. 


This type of output uses a weighted average to compute the output value. This is useful for cases where you may want to weight the initial time steps less as the flow field is developing. The value that is printed in the output file is computed as follows: URunAve = 1/N*U_n + (1-1/N)*URunAve_n-1. Where N = min(step,N_max), step= the current time step number, and N_max=running_average_steps. The running_average_steps parameter is set in the EQUATION command. So, setting the running_average_steps essentially defines an averaging "window" over which to compute the output. This value is carried forward across restarts, and may also be initialized using the NODAL_INITIAL_CONDITION command. Note that TIME_AVERAGE_OUTPUT is simply an output quantity, whereas the RUNNING_AVERAGE_OUTPUT field is used in other areas internal to AcuSolve such as the non-reflecting boundary conditions, and running_average_wall_function. 

Both types of output can be visualized using Fieldview, Ensight, and Paraview. They are included in the extended output variables when using acuTrans to convert nodal output. Here is an example: 

acuTrans -out -to fieldview -extout 

If either TIME_AVERAGE_OUTPUT or RUNNING_AVERAGE_OUTPUT are defined, their variables will be written into the output file.


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