[MasterCooler]

Dear openFoam-Community,

I am just analyzing flows through porosities and thereby I have found out that the flow speed within the porosity seems to have a strange and unexpected characteristic.

For example in the case attached (see picture, x direction flow speed in lila with values on the left vertical axes, pressure in black with values on the right vertical axes, picture of the porosity in x direction in the top part in order to show the cell resolution) the flow through the porosity is in x-direction only. Flows in y and z dirction are very close to 0. So I would expect that the flow through the porosity is at constant level and independly from the x coordinate.

But the result from plot over a line shows another behaviour whereby the flow speed degreases first and come only back to a stable behaviour (as expected) after 4 or 5 cells in x direction. Briefly before the flow leaves the porosity a similar beahviour can be observed. At the same time velocities in y and z direction are very close to 0 (not shown in the picture) what also seems to be a conflict in continuity from my point of view. On the other side pressure behaviour is close to the expectations.

At the beginning I assumed that that resolution of my porosity wasn't fine enough and only the first cell in x direction would be affect so to speak as a transition effect but now I have refined the mesh and can see that the effect doesn't depend from the mesh fineness too much.

Therefore I want to kindly ask the following questions:
1) How can the observed effect be explained?
2) What about law of continuity conservation, is it violated?
3) Can I trust in the flow speed values reached in the center of the porosity or which flow speed can be seen as representative?

Many thanks in advance for your helping!

Cheers
Ben Theobald