Open Vessel simulation
 

Dear All,
I am simulating a hydrocyclone submerged into an open vessel which is allowed to overflow. What is the best way to simulate this?
At the moment I am setting the top of the vessel as a flow-split outlet, the results converge however I am getting a pressure lower than atmospheric at the top of the vessel which is impossible. This is leading to reverse flow problems. I have extended the outlet but this makes little difference.

Any help would be greatly appreciated.

Rhodri