[Beowulf] Gas Flow Simulations was Moores Law is dying

Ian Pascoe softy.lofty.ilp at btinternet.com
Mon Apr 13 08:52:05 PDT 2009

Hi all

Slightly wandering off the beaten track.

Does anyone know of any academic or industry R & D that have a simulator
that can handle pulse flows in a gas stream?

I'm aware of simulators that can handle things like jet and rocket engine
gas flows, but these are fairly constant - I'm particularly looking for the
pulse type, although I admit I'm not even sure if the math and physics have
been worked out for this flow type.

The reason?  One of the groups I am part of are looking at the development
of really old tech in the form of the reciprocating steam engine, and in
particular the exhaust system.  A lot of work has been done using constant
flow gas simulators, but as the exhaust beats increase so the flow dynamics
change.  So far experimentation has been done physically, and since RGB and
Jim's comments sounded whistles I thought I'd ask as the physical approach,
unsurprisingly, takes a lot of time!



-----Original Message-----
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org]On
Behalf Of Robert G. Brown
Sent: 10 April 2009 15:38
To: Lux, James P
Cc: Beowulf Mailing List
Subject: RE: [Beowulf] Moores Law is dying

On Fri, 10 Apr 2009, Lux, James P wrote:

> ...I don't know that they're harmonics, per se, but just the
> phenomenon of aerodynamic flutter, which was very poorly understood and
> is basically a resonance thing. (the nonlinearities in the state

Um, "basically a resonance thing" = "harmonics" in a linearization
around the resonance in question, right...;-)

> equation for air doesn't help with understanding, of course).  Flutter
> can occur at lower speeds, too (it's what sets Vne on some small
> planes), but at lower speeds, how to deal with it is easier to solve
> empirically AND it's testable by gradually creeping up on it and waiting
> for the evil moment.  When you get close to sonic speed (and actually,
> it's localized sonic speed over part of the airframe that's troubling),
> then you get very fast changes.  One needs to be a manly man test pilot.


> BTW, demonstrating sonic flow is easy.  Your run of the mill air
> nozzle is probably in "choked flow" with a shock wave in the throat.  If
> you have a usual shop air compressor, and the air is damp (bad for the
> tank, but good for the demo), and vent it through something like an 1/8"
> hole, you'll probably see a nice Mach cone, as the rapid change in
> pressure causes the water to condense.  An old style non-OSHA safe air
> blowing nozzle does nicely, so does a 1/4" or 1/2" ball valve feeding a
> pipe cap with a hole drilled in it.

I have no idea what you just said here, but it sounds very cool!  Maybe
I'll as my lab guy who does understand this sort of thing to look into
it for the appropriate part of physics 41.  (Well, OK, I do KINDA
understand, but not well enough to visualize what you're shooting for.)


Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
Durham, N.C. 27708-0305
Web: http://www.phy.duke.edu/~rgb
Book of Lilith Website: http://www.phy.duke.edu/~rgb/Lilith/Lilith.php
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