Learning Forum

[mona2022]

Hi all,

I am doing a transient simulation with a need to get the time averaged velocity field using the "arithmetic average" set in CFX-Pre.

But, when I check the time average results, I have found that for the nearly unchanged transient velocity profile which was extracted far upstream from the separation bubble and thus remains almost steady there (which has been checked from the transient data), its resulted time-averaged profile differ greatly from it.

In particular, unlike the transient one which is smooth, the time-averaged profile oscillates a lot and is, further more , discontinuous along the normal direction (y) . This phenomenon can be found from the attached figures called "u_trnavg changes" and "u_unchange".

[Surya Deb]

Hello,
It seems like you are using the "Velocity" variable as a vector for the Output control. Is that correct? Do you want to average the velocity magnitude or velocity along a specific coordinate?
Regards SD

[mona2022]

Hi sdeb I want to average the velocity along each coordinates, namely velocity u, velocity v and velocity w, in order to get the mean velocity field.
With using "Velocity" as a vector in this transient statistics, I got the "Velocity u.Trnavg", "Velocity v.Trnavg" and "Velocity w.Trnavg" respectively, which I think is the very thing I need.
Is there something wrong with my above operation which you think has resulted in this weird phenomenon?
Look forward to your replying and thank you in advance!
Best regards Mona.

[Surya Deb]

Hello,
The operation looks all right to me. Can you double check the start iteration?
Also check the smoothness at other locations as well.
Do you see any dependence on mesh resolution?
Regards SD