FLUENT - Using a User Defined Function (UDF) to obtain unsteady statistics of dependent variables in a time-dependent calculation


In a time dependent FLUENT calculation, you may want to obtain unsteady statistics (mean values and RMS values) of dependent variables. This solution provides a method to do this via a User-Defined Function (UDF).
The following UDF shows how this can be done.
Inside the UDF, make sure that the header file "models.h" is included.


#############
#define RMS(mean_accum, rms_accum, n, nsq)
sqrt(fabs(rms_accum/n - SQR(mean_accum)/nsq))
u_m = C_STORAGE_R(c,t,SV_U_MEAN)/delta_time_sampled
... V_MEAN
... W_MEAN
u_rms = RMS(C_STORAGE_R(c,t, SV_U_MEAN), C_STORAGE_R(c,t, SV_U_RMS),
delta_time_sampled, SQR(delta_time_sampled));
###############





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