Russell Kent wrote:

Paul wrote:

I am still amazed. Everything I have read so far states that the tips
are below supersonic. I guess it is possible. Perhaps the main reason
the duct diverges is to increase the pressure but any increase in
pressure WILL result in a reduction in velocity.  Bernoulli's principle
states  as air loses speed it gains static pressure.  P1 X V1 = P2 X V2.

Assuming the temperature remains constant.  :-)
[<snip>]

Further quote page 152; "The velocity of the air at the front of the
compressor must be less than sonic for most present day compressors. In
order to achieve this goal the design of the inlet duct of the airplane
is of primary importance." I see no real difference in the tips of the
compressor blades compared to those of the fan blades.

Uh, I may be reaching the wrong conclusion here, but simply because the tips
are supersonic (at sea level pressure) does not mean that the *air* is
travelling at supersoinic speeds, right?  Also, modern jet engines are
designed for maximum efficiency at altitude.  What is the speed of sound at
30K MSL ?  Is it possible that the fan tips are subsonic then?

Russell Kent

That's a good point Russell. I also think, due to viscosity effects
the air flow ahead of the fan, in the duct, has some rotational velocity 
that reduces the the mach # the fan see's. In other words the 
air is partially going in the same direction as the fan. Possibly.
I know for sure it has some rotational component after leaving the 
fan.

I would like to see a 3D representation of the air flow in the entire
duct.

Paul Lamar
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org