butterfly valve
 

I'm simulating a butterfly valve. multi phase
Testing was conducted in 18-inch water pressure drop is measured.
24 inches of water pressure in my simulation is achieved.
What causes this difference?

How was the pressure drop measured? Does the fluid goes to a reservoir or just recirculates back to the inlet? The pressure drop was measured just before and just after the valve? Or was the outlet and inlet pressure of a pump?

If you just setup the outlet pressure as 0 Pa, the software does not take in account the pressure drop of an expansion after the duct you are simulating.

What is the speed at the outlet? According to "Memento Des Pertes de Charge"
If the speed is around 2 m/s, it is already enough to cause the 6 inches of aditional pressure drop.

Also, multiphase flows are tricky

What exactly are you simulating?

This is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

The pressure drop was measured just before and after the valve.
i setup the outlet pressure as 0 Pa.
i do not have any information at outlet...
air was aspirated through the butterfly valve.Distilled water was introduced upstream of valve.

Better check the FAQ that Glenn suggested