<VV> GM Wind Tunnel (Very long)

[AeroNed at aol.com]

I was extremely luck to use some of my work contacts to find a guy that  knew 
a guy that knew a guy that knew the guy that runs the GM wind tunnel. Since  
we were already going to be on the GM Tech Center property for the convention  
car show, I wrangled a tour of the GM wind tunnel. The MG WT test engineer is 
a  really great guy and has a picture of the Spyder and Monza GT being built 
in the  GM design studio in 1961 hanging in his office.
 
The plan was for me to catch a GM shuttle bus from the car show to the  
tunnel just before noon. I parked my car and walked around the Corvairs for a  
couple hours. I returned to my car to lock up my camera to get ready to head  over 
to the tunnel. Seconds after closing the door of my car, I turned around  and 
there was a guy with a GM badge standing there. I looked at his badge and it  
was the wind tunnel guy,. I said hi and introduced myself. It was total 
chance  that we ran into each other, and right next to my car. He wanted to see my 
car  and then we walked around the other Corvairs. He was very impressed by 
all the  Corvairs.
 
We ended up walking over to the tunnel. We had a great conversation during  
the walk. He told me all about the different buildings at the Tech Center. It  
turns out, it is a big engineer city, since the corporate headquarters moved  
down town. We walked by the Performance Engineering building where the cool 
"go  fast" stuff was being worked on and the Design Center where they were 
working on  the cars of tomorrow.
 
We got to the tunnel a few minutes late. My new friend introduced me to the  
tour guide. He was a bit worried about me going on the tour because I might  
point out his mistakes. He became real worried when he found out the boss was  
also going. He started off with a little background on the tunnel. We started  
the tour in the control room. It was very impressive because it was extremely 
 modern compared to most of the tunnels I've worked in. Next we moved into 
the  test section. It is 18 feet high, 34 feet wide and 70 feet long. That is 
much  bigger than any tunnel I've ever been in before. I was told about the 
sound in  the tunnel, but wasn't really prepared. There was no echo at all, the 
walls are  covered with sound insulation. It was kind of strange, almost 
uncomfortable.  This is so they can isolate the wind noise around the test car. There 
are two  sets of balances, one for full scale vehicles and one for models. 
There was a  full scale clay model in the tunnel that was covered and that's all 
I'll say  about that. Each balance contact is three non concentric circles 
that can  accommodate just about any wheel base and track. They measure the 
three forces  and three moments.
 
We walked around the circuit. At each corner there are turning vanes to  help 
the air around the 90 degree turns. These are also covered in acoustic  
material. As the tour went though the vanes, we couldn't hear him talking  anymore. 
We finally got to the backside and the fan. It is huge, 43 foot  diameter. 
The six blades are made out of spruce. The motor is a direct drive and  the 
guide showed how easily the blades could be rotated by hand. The maximum  speed of 
the fan is just 270 RPM which gives a blade tip speed of 415 MPH. The  
maximum air speed in the test section is 138  MPH. The electric motor to do  this is 
also huge, 4500 HP, 3400 kW, that is not a typo. (It might work to cool  a 
Corvair motor :^) )
 
All of that energy heats the air quite a bit. That is no a good thing from  
aerodynamic and practical reasons. Since many of the vehicles are clay bodies,  
they need to keep the air cool. There is a huge heat exchanger that keep the 
air  around 72 degrees. Finally we reached the bottom of the bell mouth, the 
largest  cross section of the tunnel. There is a very impressive flow 
straightening  stainless steel screen. I like to try to climb the bell mouth to the 
test  section. We couldn't do that here because there was no door through the 
screen.  It would have been very difficult because it is a 5 to 1 reduction in 
area,  very, very steep.
 
There is also an underground tunnel from the Design Center to the  wind 
tunnel for moving vehicles away from prying eyes. They also test the  competition. 
While I couldn't take any pictures, I did get some official  publicity shots. 
They include the outside, test section during a flow vis run  and the engine. 
I also have a general spec sheet. I can forward these to anyone  interested.
 
Ned
 



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