How can full size cars be accurately tested in the so narrow A2 wind tunnel?

[DasKleineWunder]

Weren't cars or models supposed to occupy only a small fraction of the wind tunnel cross sectional area?
Yet in the A2 wind tunnel

http://www.a2wt.com/

cars use about 1/3 of the tunnel width and height

How do they avoid interference from the tunnel walls?
I read somewhere that they adjust the tunnel ceiling height or shape to the shape of the vehicle.
How do they calculate the adjustments needed?

 

[DasKleineWunder]

Some tunnels use a moving ground or floor boundary layer suction.
Would boundary layer suction also be useful for the tunnel walls and ceiling?
How to calculate the size of the wall holes and pump size/flow required for this suction?

​

 

[Sparweb]

What makes you think they are concerned with gaining valid data?
Wouldn't a different theory, one that proposes that they are helping the drag racers dispose of excess sums of money, be equally plausible?



STF

 

[btrueblood]

All wind tunnels have blockage effects, and wall influences. There are known and published methods to account for same (see Rae et. al., Low Speed Wind Tunnel Testing). Prof. Rae was my aero teacher and operated the Kirsten Wind Tunnel at U of Wash. for many years.

 

[IRstuff]

Weren't cars or models supposed to occupy only a small fraction of the wind tunnel cross sectional area?

cars use about 1/3 of the tunnel width and height

1/3 of width and height is 1/9 of area, so it is technically a small fraction of the cross sectional area.

TTFN
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[KENAT]

From their website they claim "We utilize a passive boundary layer system" though if you read closer that appears to only be on the floor. I'm going to guess this is not as good as a moving floor - especially if it doesn't allow for tire rotation.

They may be pushing it a little on the wall clearances but perhaps not too bad to get data good enough for what they want - plus like Btrue says corrections can be made.

They also don't appear to have guide vanes on the fans, I realize it appears to be sucking the air from behind rather than blowing from the front but being firmly subsonic I'd still be concerned at the vortexes messing things up a little.

Reading their bio it seems like their intent is to be relatively 'cheap and cheerful' and that one consequence of that is that the wind tunnels aren't as high tech/performance as most large modern AC wind tunnels would be.

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[IRstuff]

They have a mesh in front of the fans; that's probably not enough to diffuse the air flow:

As for the cross-sectional area, the majority of the work related to the topside of the vehicle, for which there is adequate clearance:

TTFN
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