Marc Wiese wrote:

Date: Wed, 16 Jan 2002 15:13:55 -0800
From: Chris Krok <stingray@galcit.caltech.edu>
Subject: (rx7)[none] wind tunnel info

I'd love to hear more about the new AND old tunnels.

There is info on both at http://www.galcit.caltech.edu/awt/
The page is a bit crude and out of date, unfortunately...  I'm
responsible for both the web page and building the tunnel, and finishing
the tunnel gets me out of here and into a new (i.e., better paying) job!
:)

WOOHOO! Another REAL aero guy on the list! Tell me more about the
new wind tunnel, I'm assuming adaptive refers to the walls.
Low-speed tunnel? I'd love to see pictures of it.

Actually, my thesis was on hydrogen combustion phenomena, but us aero
guys are pretty versatile.  :)  (Honestly, I had only used a wind tunnel
once before this, in undergrad fluid mechanics lab.)  The new tunnel is
a closed loop, and  fills a 30'x90' room.  The test section is 6' wide
by 5' high, and 25' long.  We're shooting for a max speed of 175 mph.
The side walls are rigid, but the top and bottom walls are made of
roughly 0.3" thick fiberglass.  The flex walls are flexed by
stepper-driven screw actuators, 20 stations on each wall, with one pair
of actuators at each station.  (Each pair runs in synch; we're just
adapting in 2-D.)  They can be flexed up to 1' from their resting
position (i.e., the tunnel height can expand from 5' to 7').

The purpose of the flexible walls is to remove confinement effects found
in a "rigid" test section.  When an object moves through the air
outdoors, the air has effectively infinite space to adjust to the
presence of the object.  When you put that object in a wind tunnel, the
air flowing around the object also has to deal with the walls.  One of
the main effects is that the model creates an area reduction, and the
air must speed up to maintain mass/volume flowrate through the reduced
area.  As a result, test data must be corrected for wall interference.
With the adaptive walls, measurements taken along the surface of the
walls are used to determine what shape they should be.  The walls are
adjusted to conform to the airflow around the object, and the air no
longer "sees" the walls.  In a standard wind tunnel, the model is
usually limited to 6% of the tunnel's cross-sectional area.  In our
tunnel, we should be able to go to 20% area blockage.

I forgot to mention before, we also tested a recent generation of the
Oscar Mayer Wienermobile.  But we try not to bring that up too often.

Thanks for the interest!

Chris

- --
Dr. J. Christopher Krok
John Lucas Adaptive Wind Tunnel
Caltech MS 205-45, Pasadena, CA 91125

Marc Wiese

 
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