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Old 06-22-2020, 11:52 PM   #1 (permalink)
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A Non scientific everyday Aero Observation

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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Old 06-23-2020, 01:48 AM   #2 (permalink)
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I don't have any answers, but to add to your observations. When on my motorcycle if you don't expect it semis can push me away from the wake (when traveling in opposite directions). I feel PU's and SUV's usually driving by. I don't ever remember feeling it from a car.

I have felt the same in my car as well. I can't say I've ever noticed it when I'm the one moving (equal and opposite reactions?). Even when I drive my van.
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Old 06-24-2020, 11:27 AM   #3 (permalink)
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bow and stern waves

Quote:
Originally Posted by j-c-c View Post
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.
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.
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Last edited by aerohead; 06-24-2020 at 11:27 AM.. Reason: typing correct
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Old 06-24-2020, 12:05 PM   #4 (permalink)
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It may be possible a pickup feels like less wake in passing because it's like 2 wakes separated by 5-8 feet. Where the small SUV has just one wake concentrated behind it. Overall better but a sharp shove vs a long push.

Also on something really long like a semi with trailer, you feel that push from the cab but actually doesn't much of that air settle down and reattach along the trailer? So it's just the 2nd suck back that's the real drag.
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Old 06-25-2020, 05:20 PM   #5 (permalink)
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One could strap an anemometer to a roadside post and point a camera so it captures the display and each passing vehicle.

Automating the video analysis is above my pay grade.
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Old 06-26-2020, 11:29 PM   #6 (permalink)
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Yeah, one positive thing you can say about pickups is that they're less far away from the template than SUVs are.
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Old 06-27-2020, 03:57 PM   #7 (permalink)
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Interesting replies, but has/will/does anybody had this experience of passing vehicle wakes that they remember and can share/verify my shared observation?

Seems like if trying to measure, the observer's car might also play a role, and since it is so quick of an impulse, it would best be recorded for later review, and with a device with a rather quick response and no/little overshoot qualities.

Last edited by j-c-c; 06-27-2020 at 07:32 PM..
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Old 06-27-2020, 08:03 PM   #8 (permalink)
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So I just stumbled on this maybe related learned source, page 99, anybody read it? Bus passing a parked car aero effects.

https://ecomodder.com/forum/showthre...ers-38382.html
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Old 06-27-2020, 11:23 PM   #9 (permalink)
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Old 06-28-2020, 03:07 PM   #10 (permalink)
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Thanks, the suspense is killing me.

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