Hi, I am working with a problem of expansion and uniform flow. The problem is that I want to uniform the flow when the expansion end, for this reason I put a porous media zone in the end of the expansion, but I have recirculation in this zone, I don't know if somebody know how to simulate the uniform flow when I have expansion?

(1). The flow separation is controlled by the expansion. So, with the geometry fixed, you will see the flow recirculation. (2). But if you put the porous media or flow straightener at some distance downstream of the end of the expansion, it is possible to make the flow more uniform. (3). The suggestion is : move it further downstream, and check the results. It is not a good idea to put the porous media zone in the middle of the flow separation, put it behind it.

Thanks for your suggestion, but in this case I can't move the flow straightener, because it is a physical condition. In your experience do you know another way different to porous media to simulate flow starightener like a grid or tubes bank?

(1). If the expansion is smooth (not a sudden expansion), then , in principle, you can put in some guide vanes to keep the flow attached through the expansion section. (2-D, or annular, depending on the duct or pipe section) (2). In this way, you can eliminate the flow separation in the expansion section.