I am not sure I totally understand you. The way I understand it is that as you neck down the intake. Air velocity will increase. Also, in a perfect world, pressure would not necessarily increase due to the increase in air velocity. Yes this does happen to some extent due to inefficiencies in the duct design. Air can't move through it quickly enough so pressure builds. The same thing would happen if you went from a 4" hole down to a 1/32" hole.
I keep going back and rereading your post. You have to be very careful with the wording. Because if said backwards, it's wrong. If you have air traveling through a duct with an area of 30 sq. cm. And at some point to duct begins to transition down to 15 sq. cm. Air velocity will increase and pressure will also increase. But this has some limitations, if there is enough drag in the surface, or the duct is very poorly designed, the air velocity would decrease and air pressure would severly increase.
But lets say you have another duct that has an area of 30 sq. cm. And at some point the duct transitions up to an area of 120 sq. cm. Air velocity will decrease and air pressure will decrease. And there isn't much in the way of design that will change this outcome. Unless after some period the duct transitioned down to 30 sq. cm. At that point the air pressure will increase again. And if the whole duct goes from 30 to 120 to 30, there will most likely be a pressure increase in the section with an area of 120 sq. cm. Right
Just because air velocity decreases doesn't mean the pressure will increase.
I am also not sure where your going with the whole boundary layer thing. But boundary layer drag is the reason I decided to stay away from sticking more things into the intake duct.
I should also point out that I do not claim to be any kind of expert in this area. I am simply applying what seems logical to me. If it doesn't work, and it may not, then fine. But at least I eleminated the option.
I just looked at the duct system for BVM's F-4 phantom, and I fail to see how his design is any different that what I am trying to do. Could you please explain.