A Non scientific everyday Aero Observation

[aerohead]

Originally Posted by j-c-c

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.

1) as in overtaking a vehicle from the rear?
2) or a 'head-on' encounter?
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In 2014, in Utah,near Monticello, on the way to DARKO, in a very strong crosswind, I encountered a cattle-hauler at 140-mph closing velocity, which destroyed the front, articulated, driver's side wheel skirt. This is the worst case I can remember, other than the remnant of Hurricane Katrina, which sucked the leeward side front skirt off the truck, east of Tucson, Arizona.

[freebeard]

Quoth the OP

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.

Which episode when the trailer lifted clear into the air?

[aerohead]

Originally Posted by freebeard

Quoth the OP

Which episode when the trailer lifted clear into the air?

1) sitting in traffic, as the big vehicle passes, the air is displaced into a crude venturi, accelerates, and loses pressure, as per Bernoulli's Theorem, with the less massive car rolling on its chassis into this low pressure, then relaxing once the air resumes local barometric pressure after the truck rides into the sunset, with the credits rolling.
2) somewhere, east of Eiesenhower Tunnel, on I-70, a pressure ridge spanned the entire lane, and the little trailer wheels acted as if on a Vail ski jump, sending Viking airborne, in a curve, then jerking back into train as the wheels touched down. Very disconcerting!

[j-c-c]

I think the sitting still and observing a passing vehicles interaction is lot different then different two cars passing head on at speed. I suspect the increase in complexity, and understanding is nearly insurmountable when only in an observation mode.

[freebeard]

Really? The car rocks in roll instead of yaw, the Δ in closing speed halves. Fineness ratio and Reynolds number work the same.

A big dirty vehicle moving at high speed in a high crosswind might throw a lightweight vehicle into the ditch. I extrapolate from strings of boxcars blown off railroad trestles in high winds.

[j-c-c]

My opening post, as an observer sitting still, I suspect there was a yaw component, and if observed at double speed in head on passing, yaw interaction would be likely twice as fast and not humanly discernible. Also, in my opening comment, to restate, a large "dirty" vehicle seemed to have less on an "impulse wake" then a smaller more aero vehicle. Again this did not seem to be intuitive or logical, but I also need to clearly state, it was far from anything from scientific observation. That puzzlement was my motivation for sharing.

[aerohead]

Originally Posted by j-c-c

I think the sitting still and observing a passing vehicles interaction is lot different then different two cars passing head on at speed. I suspect the increase in complexity, and understanding is nearly insurmountable when only in an observation mode.

There are some SAE Papers which address the phenomena. It wasn't of interest, as, like with gravity, I just live with it.
I've never had a problem 'driving' a vehicle, and buffeting,winds,and storms just add interest to the experience.

[aerohead]

Originally Posted by freebeard

Really? The car rocks in roll instead of yaw, the Δ in closing speed halves. Fineness ratio and Reynolds number work the same.

A big dirty vehicle moving at high speed in a high crosswind might throw a lightweight vehicle into the ditch. I extrapolate from strings of boxcars blown off railroad trestles in high winds.

1) waiting in a left turn lane, at a red light, other than for under-inflated tires, a car doesn't have any degree of freedom for yaw in its suspension.
2) in closing, the velocities are additive. In my case, we were both closing at 75-mph ( 150-mph relative motion ).
3) for standard SAE 'air', Reynolds number has only to do with vehicle length and velocity.
4) I've no personal knowledge of light vehicles sent into ditches in response to a commercial vehicle. Hucho devoted an entire chapter to concerns about this sort of thing. In 1990, the first time I went to Bonneville, about 10-miles east of the raceway, a triple-trailer rig was laying on it's side, west-bound on I-80. There's a price for load floors 48-inches off the ground and square-edged trailer sides. ( stupid American manufacturers )
5) empty boxcars would succumb the same way as an 18-wheeler. ( stupid American boxcar manufacturers )

[aerohead]

Originally Posted by j-c-c

My opening post, as an observer sitting still, I suspect there was a yaw component, and if observed at double speed in head on passing, yaw interaction would be likely twice as fast and not humanly discernible. Also, in my opening comment, to restate, a large "dirty" vehicle seemed to have less on an "impulse wake" then a smaller more aero vehicle. Again this did not seem to be intuitive or logical, but I also need to clearly state, it was far from anything from scientific observation. That puzzlement was my motivation for sharing.

It certainly could be true. We'd have to consider it on a case-specific basis. No generalities exist.
The lower the drag for a vehicle, the less affected by some of these conditions.

[j-c-c]

So I share something in common regarding observations and as useful as with Newton and his apple regarding gravity?

I get your point, in the big scheme of things, this topic is likely not of them,