Here are top and bottom views of my cowl at angles of attack of 0, 4 and
8 degrees.

Something that should be borne in mind about venting into areas of low
pressure is that they are also areas of high velocity, and at some point
pressure recovery is going to take place, the velocity will drop, and
the tendency to separate will increase. Disturbing the high velocity
flow by injecting air from a heat exchanger into it may result in
earlier separation, or a thicker turbulent boundary layer, downstream,
and this may have an adverse effect on drag. This effect would be
difficult to quantify, I think, and it may be negligible. In the case of
Melmoth 2, the flow on the top of the cowling gets decelerated and then
re-accelerated by the windshield, and it's doubly difficult to guess
what effect, if any, the air outlets have on this process. The flow
attachment is pretty good over the canopy, however, judging from the
behavior of raindrops, and so I don't think anything too dreadful is
happening.

Peter Garrison

Peter, does this CFD take into consideration the spiral flow from
the prop?

Paul Lamar


I'm afraid that I failed to include a spectrum scale with my previous email, so
the magnitudes of the pressures were unspecified. here it is (this applies to
all six plots):

Peter Garrison