how to calculate flow at particular boundary?
 

How to calculate flow at particular boundary (pressure outlet) in openfoam?

Do you mean the mass flow rate? Here's a link

http://www.cfd-online.com/Forums/ope...-boundary.html

You can find more ways by searching the forum for "mass flow rate", this is a subject which has been discussed extensively in the past. It should be relatively easy if you only want to calculate it on a boundary patch.