Airspeed question

[Andrew W. Macfadyen]

Your think of lamina flow no at that kind of velocity the flow would be likely
to be fully developed turbulent flow with very thin turbulent boundar layer.
The velocity profile would be more or less consant as the boundary layers might
only be fractions of mm thick Turbulent flow  boundary lairs are thin because
so much mixing is going on due to eddies that the boundary layer is continually
re-energised by robbing energy from the main flow causing "blockage",
eventually no matter how much pressure you apply the venturi won't flow any
more air.

It is likely that some of airflow through the venturi and around the butter fly
is going supersonic as at that kind of velocity at the pressure you would find
in the contraction of the venturi  you willl start to run into
compressibillity. (aka the sound barrier)

I once worked on a casscade wind tunnel for testing turbine blades that was
next to a tiny supersonnic wind tunnel (ex WW2 German and still in use in
1991!) and when they ran that that  screamed like a banshee.

Gary Derian wrote:

> I have never heard that air whistles only at over 300 mph.  Even if this
> were true, the ports could have some local eddies that cause whistling even
> though the velocity in the middle of the port is much less.
> Gary Derian <gderian at cybergate.net>
>
> -----Original Message-----
> From: Robert Humphris <r.humphris at indigo-avs.com>
>
> >Fellow EFi'ers
> >
> >As the techincal advisor of the Renault 5 GT Turbo owners club, I have
> >often heard some strange tales, many of which turn out to be utter
> >rubish.  But last night I heard something that I cannot decide upon, and
> >I would like to ask the amassed knowledge in this list their opinion.
> >
> >Now we all know that flow is important in NA engines, with Turbo engines
> >airspeed is just as important if not more so.   So with this in mind one
> >of the members was asking a porting shop about their mods to carb and
> >manifold.  They said that they were 70% up on standard flow... which
> >they claim to be able to prove, so we will leave it at that...  The bit
> >that I am not sure about is on the subject of airflow, when questioned
> >they said that "When you put the carb and manifold on the flowbench it
> >whistles.  Air only starts to whistle at 300mph, so we know that the
> >airspeed is greater than 300mph..."
> >
> >Now this seems to be quite a claim... And I have never heard such a
> >thing before.  Is this true?  or not true, if so why?
> >
> >Obviously I have a mission to trash any bogus claims from tuning
> >companies as the members of the club shouldn't be tricked into parting
> >with their cash, so you advice will be received greatfully.
> >
> >Cheers
> >
> >Rob Humphris