Quote:
Originally Posted by j-c-c
So I got over 3+million miles on the road over the decades, that means I have sat on the side of the road, or stopped in a turning lane while nearby traffic whizzed by often. This observation I have encountered thousands of times, but today I first organized my question on that observation.
So when sitting still in your vehicle, say in a left hand turning lane waiting for the arrow to turn, everybody I am sure has felt the aero wake energy as cars pass you at normal traffic speed on the right. Today, traffic was plentiful, and I was puzzled as to the extreme (IMO) variation in that aero shock effect as they passed. I had no way or real interest in making any measurements, but there was no obvious reason I could by eye, observe why there was such a variation in their wakes. I'm accounting for speed, distance from my vehicle, size of passing car, shape of passing car, following distance between passing cars, any noticeable variation of ambient crosswinds. The differences were significant, and not intuitive, like a small aero SUV had a bigger "wake" then a full size PU. Of course there could be small variations with ideal combinations that might explain, unknown to me, my observation. I also do not believe in "magic", so something is the basis for this. And I am thinking the observed "wakes" have some relation to the cars aero efficiency, since it is wasted energy(?), but then I wonder if what I am feeling as a shock wake, is really just a positive pressure quickly followed by a negative pressure, from an efficient low drag car design.
Sorry for my babbling, but not sure I have ever read any comments on this subject.
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This phenomena is experienced especially in closed test section wind tunnels.
Really 'dirty' shapes can actually cause flow separation on the walls and ceiling of the wind tunnel, whereas, really 'clean', low-drag vehicles create no appreciable effect at these boundaries.
At Monaco, during Formula-1 Grand Prix racing, these Cd 1.0+ race cars demonstrate flow field perturbation 30-feet away, top and sides.
A Volkswagen XL1 wouldn't really register. Nor the 1993, 183-mph, GM EV1/ Impact BEV land speed record car.