This page calculates the head loss of a fluid at an abrupt pipe entrance. The head loss coefficient at an abrubt duct exit is 1.0.
The head loss hL can be calculated as:
hL = kloss x (um2 / (2 x g) )
Where kloss is the head loss coefficient, um is the flow velocity in the pipe, and g is the gravitational acceleration. kloss is 1.0 for an abrupt pipe exit.
Idel'chik, I E. and Fried, Erwin., Flow Resistance, a Design Guide for Engineers, Taylor & Francis, Washington D.C. 1989. p 349.