View Single Post
Old 07-31-2019, 11:21 PM   #98 (permalink)
EcoModding Apprentice
Join Date: Apr 2012
Location: Charlotte, NC
Posts: 130

TBD - '17 Toyota Corolla LE
90 day: 34 mpg (US)
Thanks: 87
Thanked 108 Times in 46 Posts
Originally Posted by aerohead View Post
This scale is too small. The airspeed required for proper Reynolds number would be beyond MACH-1.You'd be in compressible flow.It just won't work!
Yoshi has 50+ years in wind tunnel development. He's one of the automotive scale wind tunnel testing pioneers. He built NPTi's rolling road scale wind tunnel from nothing (starting in the very late 70s) and developed all the relevant techniques that led to multiple IMSA GTP championships for Nissan. In those days they used very small scales, 10-14%.

Yoshi's done the verification work, comparing model results to the full scale results, conducting tests in both, and found the trends are indeed translatable, even if the force absolutes are not. Remember his target was CFD; and a scale model tunnel will still beat the pants off of CFD in the amount of iterations/data it can generate.

The idea is to establish trends, within reasonable testing parameters. Even testing at 50% scale, we'd still need to be running at wind/road speeds much higher than we are running (or capable of) in order to match full scale Reynolds numbers. Yet we're in the tunnel day in, day out, producing tangible results for the track. To be honest, in my modest 20+ years, I'm not sure I've ever seen a scale tunnel produce proper Reynolds numbers! Yet the scale rolling road wind tunnel is still the go-to development tool because what are your options?
  Reply With Quote
The Following 2 Users Say Thank You to woodstock74 For This Useful Post:
aerohead (08-07-2019), Snax (08-01-2019)