Quote:
Originally Posted by 3-Wheeler
Hi Aerohead,
Do you have an equation that shows the relation between generated Reynolds number for full size objects and those of 1/24th scale?
Just off the top, 480 mph seems too fast for some reason. At a Mach value of 0.3 (225 mph), the air is starting to reach the "non-compressible" zone.
I know I've read here that the turbulent zone is fully established at speeds of only 20 mph or so for full size objects.
Jim.
|
Jim,I think it's just a scale relationship,or 'verisimilitude' as I think Don Sherman referred to it.
If the typical full-scale auto length/velocity @ 20 mph establishes the proper Reynolds number then,
*1/2-scale requires 40-mph
*1/4-scale 80-mph
*1/8-scale 160-mph
*1/16-scale 320-mph
*1/24-scale 420-mph
-------------------------------------------------------------------------
Lower air velocities can be used and a 'fudge-factor' arrived at.
When GM uses the Guggenheim tunnel at Cal Tech the Cds come out as much as 30% lower than what will happen in full-scale.
As long as a relationship is determined between the model test and full-scale results,a 'confidence' can be arrived at when predicting full-scale numbers.
Paul Jaray wrote about this issue back in the 20s.He used 1/10-scale models.
--------------------------------------------------------------------------
Without the correction factor you could end up with disappointing Cds as did Ledwinka with the Tatra,Tremulis with the Tucker,Breer with the Airflow,others I'm sure.
