Sure, that wikipedia quote is correct - for
small, smooth spheres where the comparison is between a low Reynolds number regime (laminar) against turbulent flow.
But you're skipping over the important point that at
high Reynolds numbers, for large objects like cars, the change in speed does
not significantly affect Cd. Which is what was said in the three sources quoted.
Here's a fourth:
Quote:
|
cD ... remains nearly constant for large Re#'s in the laminar region and approaches a constant value after the transitional region. As a car is very wide compared to something like a tennis ball, the Reynolds number is high - very high in fact (on order of 10^6 @ 55mph and 10^5 at ~3mph). - source
|
And a fifth:
Quote:
|
In general, the dependence of [production cars'] drag coefficients on Reynolds number is very small and sudden changes do not occur. This demonstrates that the predominant part of the drag of these vehicles is pressure drag. (Source: Aerodynamics of Road Vehicles, Hucho Ed., 1998)
|