! Thank you! My problem is when I add source of a species, the velocity vector is changed, but in my case, when add the source of a species, I do not want the velocity vector is changed. I mean that before adding source, I have to run the velocity field from Inlet, then I add source of a species and want the velocity from the flow field bring species to the whole domain, but in my results, it seems that when I add source of a species, it looks like I am adding the velocity as well, so this is why the velocity vector is changed between before adding source and after adding source. You can see my results of velocity vector as the following:n1/ Velocity vector before adding sourcen2/ Velocity vector after adding source of a speciesnThank you very much for your time! I am always here to get your advice!n