# How to calculate the average velocity over a surface through time using paraview?

My problem is a little more complex, but here is a simplified similar model.

Let us consider a fire source inside a box and the hot gases (burnt or unburnt) from the combustion are going out of the exhaust (white surface) at a certain velocity. We have the velocity field of the entire domain and can be visualized using ParaView. We also have density and temperature fields among others.

Now, using ParaView I would like to calculate the average velocity of the gases coming out of this surface (white) over time (unsteady regime).

Note: The individual boundaries are not loaded in ParaView. That is outlet as a separate surface, the domain as a separate surface. The entire volume is treated as a single entity with specified boundary conditions.

Any help to calculate this is appreciated.

• Hi Uday. Are you asking how to calculate the average velocity using ParaView -strictly- or how to do in a framework? The first one is a little bit out of scope and you may not get an answer. – Abdullah Ali Sivas Sep 4 '20 at 3:04
• Hello Sivas, Yes, I want to calculate using ParaView. Isn't it possible to do by adding a probe in the location where I want to measure the velocity and then integrate it? – Uday C K Sep 4 '20 at 6:58
• If your question is just how to do that in ParaView, I think their Discourse is more appropriate. That being said, did you try extracting the surface and then doing the integral? – nicoguaro Sep 8 '20 at 13:34