[demirmvc]

In the control dictionary file, there are entries for 'U' and 'UMean'. What are the differences between these two terms?

const volVectorField& U = mesh.lookupObject<volVectorField>("U");
U
{
mean on;
prime2Mean off;
base time;
}
Could someone explain the differences?

I know 'U' represents the instantaneous velocity field in a CFD simulation.
'UMean' the time-averaged velocity field.
Is UMean used to find the average over the entire duration? In other words, is the UMean used to calculate u'?

[Severus]

Hello,
To see how UMean and UPrime2Mean is calculated, check here: https://www.openfoam.com/documentati...ldAverage.html

Yes, U is instantaneous velocity, UMean is time averaged velocity and UMean is needed to calculate UPrime2Mean. The averaging need not always be for the entire duration (see the Usage section in the above link).

By default you average for the entire duration if you don’t specify anything.
However, you can provide the start time (timeStart) and end time (timeEnd) for averaging, so that you will only perform the averaging within that specified time window and not for the entire duration.

Thanks