how can i make a quench tank correct simulation
 

I'm new in this forum, my greatest congratulations to the creators of the forum. My question is:
Im creating a quenching tank in 3d of 8x8x4 meters. as you can see is a very large simulation. I'm planning to make it on a 2d design. but in this design the solution doesnt converge. What Im doing is, putting a multiple inlet velicity correspondign to the agitators in the bottom surface and what i dont know is weather I have to put an outlet at the surface of the water or not. What do you think