Quote:
Originally Posted by s_t
I found the following presentation useful in reinforcing some of the concepts I've read on this forum (though got a bit lost in the last quarter or so).
http://www.bakker.org/dartmouth06/engs150/11-bl.pdf
In other threads I've seen comments about achieve better milage figures after a clean/detail. How sensitive is turbulence and separation to surface finish, in objects of car/motorhome size? Roughly what sized Reynolds number is involved?
Whatever I build is going to be 'homebuilt', and I haven't been planning on having to get it mirror smooth! Motorhomes/caravans have windows on the sides, which involves surface irregularities of a few mm. I'm planning polycarbonate sealed solar panels on the top, which are of about 3mm thickness (1/8"). I was just planning on gluing them on as is, leaving the 3mm vertical edge around each panel.
Will these kind of surface imperfections have no/little effect, or be beneficially tripping the boundary layer and causing minor turbulence that assists laminar flow beyond that (like a golf ball, or slide 20 in that presentation link above), or just destroy laminar flow and mess up aero properties? |
The mechanism which rules the transition from a laminar,to,turbulent boundary layer,occurs at a scale smaller than the surface roughness of glossy paint.
It's called 'critical surface roughness' and there's nothing to be done about it.
Even on a Messerschmitt fighter aircraft,the difference between a polished surface and flat paint makes no difference to performance.
On a laminar airfoil it would,but only at flight conditions,at very high distance from the ground,in calm air.
You won't have any laminar boundary layer on your vehicle,and that's actually a good thing.
Minor surface defects may be embedded within the thickness of the boundary layer,not affecting the laminar inviscid flow outside the boundary layer.
For the hard edge on the PVs,you could soften that with caulk.