High velocity outlet BC

Luk

Hi all, I have following problem. I am trying to model very simple situation: a pipe with the water. The pipe outflows free to air. Since there is very high pressure at the inlet BC the water reaches velocity of approx. 200m/s near the outlet. Everything seems to be ok, however I notice about 25% of overestimation of flow rate comparing to measurements. I guess that there is a mistake in setting pressure to 0.0 at the outlet (which I was thinking is adequate for free outlet). I thing that there should be some pressure loss factor due to fragmentation of the flow into droplets etc. (which one I dont want to model since my interest is in flow rate and behavior inside a pipe). Anybody can help?

Luk