[bejanyar]

Hello.
I want to compare a 12 inch butterfly valve to a 36 in butterfly valve and find what differences occurs only by changing size specially the discharge coefficient and cavitation index.

I use total pressure inlet and static pressure outlet boundaries.
I use static outlet pressure = 101325 pa ( 1 atm ) since my valve open to atmosphere and changing inlet pressure from 110000 pa to 300000 pa .
Now my question:

1-If i use some pressure for 36 inch valve what pressure should i use for 12 inch valve ??? The same pressure ?? Or change it by some none-dimensional number like Reynolds or something else ??

2-Is my pressure inlet suitable for this purpose ??? Or should I use another type boundary ??

3- I do simulation by constant pressure in two size and after getting result i saw that discharge coefficient and sigma don't change at all !!

What is the problem ??
Thanks for your helps.