But, semantics aside, yes, I agree,
lower exit pressure is what you are after and that does not always equate to
larger exit duct area. In fact, if the air heated by the core flows
through a nozzle it might even produce thrust and lower exit pressure using
a smaller exit. But, in general, I still believe that in most of our
cases, we are short of the level of duct design that would reliably permit
that. What we need is someone to invest in one of those $$$$ Computer
Fluid Flow software programs and see what they would reveal.
Ed
Ed,
I have to disagree with the big $$$ CFD
idea. Until I see proper exit ducts and every effort made to do things right
inlet wise....CFD is a waste of time. I have yet to see an installation at the
level of refinement where CFD would start to make sense. You can get to 90% of
optimum by following a few simple guidelines and some fairly simple math.
1.) do a heat balance at the cruise
condition to figure out how much air you need to ingest.
2.) Size your inlet
appropriately.
3.) Provide a real exit duct.
4.) Use a cowl flap.
5.) Do some testing with oil and tufts to
make improvements.
A properly done CFD will only get you
another 5% beyond these simple steps that are within reach of mere mortals. In
fact if the guy/gal doing the CFD work is not intimately familiar with the
situation and what sort of assumptions to make/conditions to assign it is very
likely that the results will be less successful that the empirical
method.
In other words CFD=decimal
dust.
Monty