Here is a photo of our Mocal 44 row oil cooler
with diffuser. A K&M Streamline into a wedge.
Not sure of the dimensions of hand. The Mocal web
site will have specs so you could get a rough idea of size.
I tested this one recently with a leaf blower
approximating 100 knot air flow and in that test it was very
even.
Having said that, I tested our water radiator
wedge diffuser when I built it years ago and had it reasonably
even
measuring pressures across the exit face, but now
instrumenting it in flight its flow is vastly uneven.
I have found that the flow is dependant not only
on getting the diffuser shape right according to the various
papers (eg. K&W, London, Oblique Flow Diffusers -
Streamline )
But importantly the environment it ends up in. The
papers share data for ideal conditions with for example
unobstructed exit air paths.
My thoughts now are that this has a significant
impact on the performance and therefore the advantage of
instrumenting in flight and reshaping for actual conditions.
The data I collected yesterday of our H2O diffuser
reveals that the air flow in various points across the face
are very different.
Simplified, if I average the pressures at the five
points I measured, then comparatively the back is up 20%, the
centre up 25% and the front down 60% from that average figure.
I’m figuring a 20% difference is probably OK, but
my front to back/middle difference of ~80% down in the front
top of that radiator may hold significant room for
improvement.
Further, my data suggests that as IAS rises those
differences are amplified.
So I am now targeting the modifications for our
worst case conditions of WOT sea level ~200hp and initial
climb numbers of 115KIAS.
Cheers.
Steve Izett