Quote:
Originally Posted by Pooft Lee
Do you know a good place to read on the reynolds numbers? My knowledge with aero so far is pretty existential. There's a lot of guessing by feel and checking the results if you don't have CFD and don't know the math. I thought the boundary layer would thicken and continue to drag along a surface until it had to contend with a change in direction. Is the the turbulence you're talking about from the boundary layer slowing to a crawl and falling apart?
As far as the bandaid thing, a lot of engineering is bandaids but I see where you're going with elegant design. An afterthought shouldn't be praised as a breakthrough. I was referring to the Audi photos posted earlier with significant dimples 2-4" across that have a clear defined shape. I haven't posted enough here quite yet to link the photos, I believe they were page 1. But they seem concentrated around boundaries. It looks like the interest is around the edges of the floorpan, and the gap for the exhaust and transmission.
In an application where you can't be scraping every speed bump with nice ducting and diffusers, using vortex generators to fence airflow boundaries without impacting ground clearance is pretty elegant engineering. I'd really like to know if that's their real game with those large dimples on the undertray. On a golf ball, dimples trip up the boundary layer to keep it moving, if you created turbulent, faster airflow in the right places it should do a good job dividing different areas so you don't have unwanted spill over different pressure boundaries
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I'll try a link here for Reynolds number
http://ecomodder.com/forum/showthrea...ion-14818.html
*The boundary layer does thicken,but there's nothing we can do about it.It's a viscosity phenomena,responsible for skin friction.No smoothing of the body can reduce it.
*Turbulence is caused by any perturbation to the flow,either by velocity change,deflection of flow,separation of flow,or introduced vorticity.Hucho warns us not to introduce any 'kinks' along the flow pathway,which would include vortices.
*If you create any kind of turbulence,the kinetic energy of the stream is lost to atmospheric heating.The energy lost can never be recovered as a pressure gain,to raise the base pressure behind the car.Since raising the base pressure is the entire foundation of streamlining,you're committing the greatest sin.
*If you can find a Tesla S,take a look underneath it to see what they've done.It is the lowest drag production car available to us.
*The Cd 0.21 GM EV 1 had a smooth bottom as well.
*None of the racing teams,with the world's lowest drag use anything but extremely smooth bellies.