Originally Posted by The Don
Well it is a sudden expansion and I remember sitting in my Fluid Dynamics Labs and measuring pressure losses in sudden expansions and contractions. So for me it is just taking the outlet energy we have and throwing some away for no good reason.
I understand what you are getting at but although jet turbine and ducted fans are both "reaction" type engines, they are different in that the turbine jet benefits from the expansion of hot gases which doesn't exist with the ducted fan. But then again, it's been over 2 decades since my aerospace engineering days in college and almost a decade since I last worked in the industry, so I am a bit rusty.