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apetr26542 (Structural)
13 May 06 8:56
I am curious as to the relationship of drag coefficient and speed for a vehicle. I calculated an object moveing at 55mph having a Reynolds of 3.2*10^6. I think this puts it beyong the transition where drag coefficient drops significantly. However at 10mph it is before this transition.
But I've only seen data on spheres and cylinders, any hard data out there for vehicles? People I talk to say for vehicles the drag coeff. is pretty constant, but I would like to see something to that effect. thanks
GregLocock (Automotive)
13 May 06 19:49
Drag coefficient is not constant, for cars.
Try looking in Hucho - Aerodynamics of Road Vehicles. I'm not sure if it is discussed there but it sounds like a good place to start.
Having said that, over the speed range at which it matters, for public roads, it is reasonably constant. 字串8
If you have a vehicle with a truly efficient shape then the laminar to turbulent transition does move forward with speed, so that has a significant effect in the speed range we are talking about.
However for real cars the effects of crosswinds etc are far more important. Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
SparWeb (Aerospace)
18 May 06 14:31
Try Hoerner's Fluid Dynamic Drag
FAQ2-919
You can also find used copies on the internet, and it may also be available at Darcorp.
Steven Fahey, CET
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