Elliptical oil drops

[Jennifer Donlea]

On Fri, 12 Sep 2003 00:08:51 GMT, [email protected] wrote:

>
>So the question is: What causes them?
>

I've seen these things and never thought about them. I'm usually fixing a flat or eating summer
sausage when I see them. And in general, I try not to think. Here's my try:

A car starts to overheat on its way up a hill and the coolant starts to overfill the radiator
overflow tank. The car surges forward, and a
1/8 cup of hot water with antifreeze comes out of the overflow tank. This water, on its way to
earth, passes over the engine or other oily stuff in the engine compartment of the car, and makes
a bolus of oil/water mixture. Then it hits the road in a glob, forming the ellipse, with the oil
pushed away from the center by the water. Water dries up, oil stays.

Jennifer D

 

[Stu]

Is it, a single large drop halfway through breaking into two smaller drops, as it hits the road?

 

[Stu]

damn to late

 

[Benjamin Weiner]

[email protected] wrote:
> Dave Salovesh writes:

> > http://www.mindspring.com/~darsal/droplets/ell1-close.jpg (63kb JPEG)

> Eureka! These are the ones and they are, in fact, everywhere where there is slow traffic and
> automobile engines are stressed (hot) so that they drip.

Interesting, I never noticed these, although I tried to look for them while riding today.

> I find them mostly on narrow mountain roads where engines get hot and all sorts of residual oil
> drops off, ...

> Why are rain drops no more than about 3mm in diameter (unless in a strong downdraft)? How are they
> limited to this size? If you can visualize this process with a more viscous fluid (oil, paint or
> hot roofing tar), then you should come upon it. The three mentioned substances produce these rings
> as well.

This, at least, I think I understand: raindrops are limited in size by an instability of the
underside (heavy fluid overlying lighter fluid.) Surface tension can stabilize the short length
scales but not longer, so there is a maximum size dependent on the surface tension of the fluid.

I had to do a little research to find the mode of breakup, but here is a link with a picture:

http://www.ems.psu.edu/~fraser/Bad/BadRain.html

I was surprised that an oil ring could be as big as the one Dave Salovesh photographed. The
characteristic size must depend on the surface tension of the fluid and quite possibly on the
relative timescales for drop breakup and freefall from car to road surface.

 

[Jobst Brandt]

Benjamin Weiner writes:

>>> http://www.mindspring.com/~darsal/droplets/ell1-close.jpg

>> Eureka! These are the ones and they are, in fact, everywhere where there is slow traffic and
>> automobile engines are stressed (hot) so that they drip.

> Interesting, I never noticed these, although I tried to look for them while riding today.

>> I find them mostly on narrow mountain roads where engines get hot and all sorts of residual oil
>> drops off, ...

>> Why are rain drops no more than about 3mm in diameter (unless in a strong downdraft)? How are
>> they limited to this size? If you can visualize this process with a more viscous fluid (oil,
>> paint or hot roofing tar), then you should come upon it. The three mentioned substances produce
>> these rings as well.

> This, at least, I think I understand: raindrops are limited in size by an instability of the
> underside (heavy fluid overlying lighter fluid.) Surface tension can stabilize the short length
> scales but not longer, so there is a maximum size dependent on the surface tension of the fluid.

It is also evident from the pressure profile of a sphere in an airflow, that the highest pressure is
at the stagnation point head-on, and the lowest pressure is at about the 1/4 points. This will cause
the development shown in the raindrop URL below.

> I had to do a little research to find the mode of breakup, but here is a link with a picture:

> http://www.ems.psu.edu/~fraser/Bad/BadRain.html

Eureka again. We now have the source, cause and pictures of elliptical oil drop rings on roads.

> I was surprised that an oil ring could be as big as the one Dave Salovesh photographed. The
> characteristic size must depend on the surface tension of the fluid and quite possibly on the
> relative timescale for drop breakup and freefall from car to road surface.

With higher viscosity and surface tension than water, the last stage of the raindrop-blowup, the
thick collar closes to make a "soap bubble." Those who observed soap bubble landings probably
noticed that soap bubbles burst leaving a wet ring.

The rest is left as an exercise for the student.

Good work. "Cigars" all around for the researchers.

Jobst Brandt [email protected]

 

[Dave Salovesh]

In <[email protected]>, [email protected] opined:

> An example is here:
>
> http://www.mindspring.com/~darsal/droplets/half-ellipse.jpg

That probably should be:

http://www.mindspring.com/~darsal/droplets/ell1-close.jpg

or

http://www.mindspring.com/~darsal/droplets/family.jpg

half-ellipse.jpg illustrates another type of oil mark I frequently found but hadn't really
noticed before.

--
Dave Salovesh [email protected]

 

[Dave Salovesh]

In <[email protected]>, [email protected] opined:

(...)

> bicyclists do not see what they are looking at, as with getting flats.

I'm sure it's been done before, but what is it that cyclists don't see about flats?

--
[email protected] | depending, of course, | moc.gnirpsdnim@lasrad Dave Salovesh | on your
perspective | hsevolaS evaD

 

[Jobst Brandt]

Dave Salovesh writes:

> (...)

>> bicyclists do not see what they are looking at, as with getting flats.

> I'm sure it's been done before, but what is it that cyclists don't see about flats?

They don't see road hazards that causes the flats, glass, thorns, pot holes, metal debris or rocks.
I'm sure there are more. I sense there is a correlation between riders who never find tools and
money on roads, and riders with a high incidence of flat tires.

Jobst Brandt [email protected]

 

[David Damerell]

Dave Salovesh <[email protected]> wrote:
>[email protected] opined: (...)
>>bicyclists do not see what they are looking at, as with getting flats.
>I'm sure it's been done before, but what is it that cyclists don't see about flats?

Allegedly, debris in the road.

Certainly I see other riders ride blithely over glass that I then maneuver to avoid.
--
David Damerell <[email protected]> Kill the tomato!

 

[Tim McNamara]

In article <[email protected]>, [email protected] wrote:

> Chris Zacho writes:
>
> > I guess I failed. What's an "oil ring"?
>
> You must have missed the start of this thread or certain responses thereafter, but there is hope.
> Dave Salovesh, being a good researcher, went on the road and photographed a few of the many he
> found. An example is here:
>
> http://www.mindspring.com/~darsal/droplets/half-ellipse.jpg
>
> So the question is: What causes them?

I'll admit to being pretty stumped, as the feature I expected to see in the photographs was absent.
That feature was a center drop mark surrounded by the ellipse.

My theory was this: the rings are the result of oil dripping from hot engines, when the oil is hot
and at its lowest viscosity. The shape of the rings is the consequence of the speed of the car, the
long axis being oriented to direction of travel. My further permutation of the theory was that the
upper part of the oil drop travels further than the lower part, but that would just leave a stripe
not a ring.

So then I thought about high-speed photos of drops hitting a surface, and noticed that there tends
to be a splash ring propogating outward from the impact point of the main body of the drop. I was
then expecting to see a drop near the center rear of the ring, surrounded by an elliptical shaped
ring caused by the oil splashing- but there is no center drop in most of the rings in the photos. I
guess it's possible that the rear of the splash ring lands on top of the initial impact and the rest
of the ring forms an ellipse due to forward momentum. That's my best guess anyway.

 

[Jobst Brandt]

Tim McNamara writes:

>>> I guess I failed. What's an "oil ring"?

>> You must have missed the start of this thread or certain responses thereafter, but there is hope.
>> Dave Salovesh, being a good researcher, went on the road and photographed a few of the many he
>> found. An example is here:

>> http://www.mindspring.com/~darsal/droplets/half-ellipse.jpg

>> So the question is: What causes them?

> I'll admit to being pretty stumped, as the feature I expected to see in the photographs was
> absent. That feature was a center drop mark surrounded by the ellipse.

Sorry. As Dave pointed out, I should have cited these URL's:

http://www.mindspring.com/~darsal/droplets/ell1-close.jpg
http://www.mindspring.com/~darsal/droplets/family.jpg

The "Bad Rain Drops" URL shows the mechanism:

http://www.ems.psu.edu/~fraser/Bad/BadRain.html

Unfortunately the last drawing in this URL, the drop should have a line across the bottom, showing
that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a wet ring on
the surface where they land. If that surface is moving relative to the bubble, the ring will be
elliptical.

The unanswered question that I have is, why they all have nearly the same aspect ratio of major to
minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all have
the same velocity to the road when they burst, but why?

Jobst Brandt [email protected]

 

[Paul Kopit]

On Fri, 12 Sep 2003 16:00:24 GMT, [email protected] wrote:

>They don't see road hazards that causes the flats, glass, thorns, pot holes, metal debris or rocks.
>I'm sure there are more. I sense there is a correlation between riders who never find tools and
>money on roads, and riders with a high incidence of flat tires.
>
>Jobst Brandt [email protected]

When asked how to get fewer flats, the first thing I recommend is a new prescription for eyeglasses.

You don't see what you don't have in your area. Here in the Los Angeles area I can see glass and
holes but am blind to thorns.

 

[Jobst Brandt]

Paul Kopit writes:

>> They don't see road hazards that causes the flats, glass, thorns, pot holes, metal debris or
>> rocks. I'm sure there are more. I sense there is a correlation between riders who never find
>> tools and money on roads, and riders with a high incidence of flat tires.

> When asked how to get fewer flats, the first thing I recommend is a new prescription for
> eyeglasses.

> You don't see what you don't have in your area. Here in the Los Angeles area I can see glass and
> holes but am blind to thorns.

You jest! Puncture vine abounds here, as it does in most of the USA according to biologists. You can
recognize the plant and its light tan seed pods that lie close to the source. When I see puncture
vine along roadsides, I make sure to avoid any tan "pebbles" nearby.

http://elib.cs.berkeley.edu/cgi/img_query?enlarge=0000+0000+0801+0392 http://tinyurl.com/d0xo
http://www.barbwired.com/andy/PunctureVine/

Jobst Brandt [email protected]

 

[A Muzi]

> "KBH" <[email protected]> wrote in message news:[email protected]...
> > My theory:
> >
> > Imagine a sphere, sliced up into a very large number (you can take the
limit
> > to infinity if you want) of horizontal slices. Now set this on the
ground
> > and smear it in one direction - what shape do you have? An ellipse! Therefore, a drop of oil,
> > dropped from a moving car, would tend to make
this
> > shape. But perhaps on a normal flat road, the velocity of the drop
would
> > typically be too high, and its angle of collision with the road too
large,
> > to make a nice ellipse. This is why you would be more likely to see
them on
> > an uphill - the vehicle is traveling slower, and the upward angle of the road serves to lessen
> > the angle of collision between drop trajectory and road, allowing the creation of a recognizable
> > ellipse.

"Peter Cole" <[email protected]> wrote in message
news:aa38b.418513$Ho3.66306@sccrnsc03...
> My theory is identical, except to explain the ring, rather than just an elliptical smear, I'd say
> that as the drop hits the road, its forward
velocity
> would cause it to trap air, essentially blowing a bubble, the "projection"
of
> which on the road would be an outline, or ring.

I don't know either but a ring is more likely formed by evaporation than by a bubble.

I can't wait to see the asnwer

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

 

[Dan]

> Unfortunately the last drawing in this URL, the drop should have a line across the bottom, showing
> that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a wet ring on
> the surface where they land. If that surface is moving relative to the bubble, the ring will be
> elliptical.
>
> The unanswered question that I have is, why they all have nearly the same aspect ratio of major to
> minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all have
> the same velocity to the road when they burst, but why?
>

It does seem that the rings might be due to the detritus of bubbles that had burst in the air
instead of on impact. (If this is what you meant all along, then color me slow.) Seeing as that a
ring of oil trailing a bubble parachute would be a very unstable thing, it is very possible that
these bubbles always burst upon attaining about the same velocity. A splatter of small spherical
droplets then form the ring patterns seen.

I can imagine two failure modes of the bubble structure. One is the approximately radially
symmetric failure of the bubble parachute. This produces a cylindrically symmetric spray of
droplets. The other is an instability in the ring that results in thinning of one side of the ring.
This leads to a rupture of the ring and most of the mass ending up in one side of the ring.
(results in a half elipse?)

 

[John Albergo]

[email protected] wrote:

>
>
>Unfortunately the last drawing in this URL, the drop should have a line across the bottom, showing
>that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a wet ring on
>the surface where they land. If that surface is moving relative to the bubble, the ring will be
>elliptical.
>
>The unanswered question that I have is, why they all have nearly the same aspect ratio of major to
>minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all have
>the same velocity to the road when they burst, but why?
>
Assuming that most oils have the same surface tension, then I'd guess that most oil drips would be
about the same size, and "pop" at about the same airspeed (relative wind). Perhaps the size of the
resulting road ring is due to the "altitude" of the burst?

>
>

 

[Tim McNamara]

In article <[email protected]>, [email protected] wrote:

> Tim McNamara writes:
>
> > I'll admit to being pretty stumped, as the feature I expected to see in the photographs was
> > absent. That feature was a center drop mark surrounded by the ellipse.
>
> Sorry. As Dave pointed out, I should have cited these URL's:
>
> http://www.mindspring.com/~darsal/droplets/ell1-close.jpg
> http://www.mindspring.com/~darsal/droplets/family.jpg

Yup, I saw those and they immediately disproved my splash theory.

> The "Bad Rain Drops" URL shows the mechanism:
>
> http://www.ems.psu.edu/~fraser/Bad/BadRain.html

I had briefly thought about the oil droplet being hollowed out but that seemed unlikely due to the
viscosity of oil, and I further dismissed the idea because I didn't think the hollow shape would
leave a ring. I didn't think about soap bubbles...

> The unanswered question that I have is, why they all have nearly the same aspect ratio of major to
> minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all have
> the same velocity to the road when they burst, but why?

Terminal velocity of an oil droplet? If the car is going too fast, the oil atomizes and if going too
slow, it leaves a blob rather than a ring?

 

[Sergio Servadio]

Don't blame it on me. Because of problems with our local connection I was able to read the beginning
of this 'story'and a few posts of the thread, but not all by all means. For me surely, and I would
assume for the benefit of others too, how about having someone make a resume and play the moderator?
Why not you, Jobst?

Sergio Pisa

 

[Ryan Cousineau]

In article <[email protected]>, [email protected] wrote:

> Tim McNamara writes:
>
> >>> I guess I failed. What's an "oil ring"?

> http://www.ems.psu.edu/~fraser/Bad/BadRain.html
>
> Unfortunately the last drawing in this URL, the drop should have a line across the bottom, showing
> that it is the cross section of a nearly a complete "soap bubble". Soap bubble leave a wet ring on
> the surface where they land. If that surface is moving relative to the bubble, the ring will be
> elliptical.
>
> The unanswered question that I have is, why they all have nearly the same aspect ratio of major to
> minor axis, regardless of size. They range from 20 to 200mm in length. It means that they all have
> the same velocity to the road when they burst, but why?

Because only a drop moving at a given velocity (and above a certain size) will be moving at the
right speed to form a bubble in the distance between vehicle and road. Slow moving oil drops stay
together, faster ones burst before landing.

--
Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

[Paul Kopit]

On Fri, 12 Sep 2003 18:55:33 GMT, [email protected] wrote:

>You jest! Puncture vine abounds here, as it does in most of the USA according to biologists. You
>can recognize the plant and its light tan seed pods that lie close to the source. When I see
>puncture vine along roadsides, I make sure to avoid any tan "pebbles" nearby.

Yes, it exists but I don't see it. I was running a worn rear tire and went over some. When I was
patching the tube, I found the 4 tiny holes... one at a time. I normally look for one hole, unless
it's a pinch.