tank with multiple vents and outlets
 

I have a tank with multiple vents at the top and multiple outlets at the bottom. I fill the tank to an initial fluid depth and height, set each of the inlets/outlets with a zero pressure boundary, and then run the scenario and watch how the fluid exits the tank. Pretty straightforward.

I've ran numerous scenarios so far with no problem but my latest has really got me stumped. Somehow fluid is flowing in from one of my vents at the top and I don't know how it's getting there since it's coming in higher than my initial fluid height and I have gravity going the proper direction.

Any ideas?

Check that f=0 at the vent.

Yes, my F fraction was zero.

I deleted the entire block and created a new one and for some reason it started working correctly again. Kept the same boundary conditions. Weird.