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Water on the side windows

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Marc View Drop Down
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    Posted: January/12/13 at 12:31am
Is there something for the Mini to prevent the water from sloshing all over the side windows?  There are only a few things I don't like about my Clubman... and this is one.  Sometimes it gets so bad I can't see out the side windows at all.  I've never owned a car that pools water on the windows like this:



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Post Options Post Options   Thanks (0) Thanks(0)   Quote shasti212 Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 8:21am
Unfortunately I dont think there is a way around it. Try rainex on the side windows? It comes from the wipers...

I hate when there is mud in the water and then I can't see anything. .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CINIMIN Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 9:13am
Jack -

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marc Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 9:54am
Yeah, I wish it was that simple.  The rain guards all require a full door frame.

I was thinking that maybe there's a strip of plastic that could be glued to the post, in front of the window.

The reason the side windows pool water is because there are low pressure zones to the sides of the car. The windshield is so tall that air flows to the sides.  Wind hits the windshield, and unlike many cars, the wind is deflected to the sides as well as above the car.  Moving air is lower pressure than still air, pulling the water along with it.

Based on the slow flow of water, I don't believe the pressure is too different than the surrounding air.  It's just enough of a difference to allow the water to hang at the top of the window.  I don't think it would take much of a change in the airflow to cause the air pressure increase to a point where the water would travel over the roof or off the car, rather than creep along the sides.

Maybe all it needs is a leading-edge spoiler that disrupts the laminar flow, and allows the water to break free of the surface.  ;-)

... yes, I'm a pilot.  :-)


Edited by Marc - January/12/13 at 10:02am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CINIMIN Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 10:38am
Vortex generators on the A pillar?

Edited by CINIMIN - January/12/13 at 10:41am
Jack -

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marc Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 10:55am
Not sure where to position vortex generators on the pillar, but they could work.  Maybe I'll buy a few and experiment with positions.

Or, maybe a small/sharp lip along the length of the pillar might be enough to get the water to loose adhesion.  My only fear about a long lip is that I'd probably get opposite the desired effect, as there will be a low pressure zone behind the lip.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marc Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 11:05am
... actually, if vortex generators were installed above the windshield (near the leading edge of the roof) - it could stabilize the flow above the car, and change the relative pressure of the side windows.

hmmm....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CINIMIN Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 1:33pm
I think it may have more to do with a flow pattern around the rear view mirror than a pressure gradient. At the speeds you are dealing with any brunelli effect is going to be very very minor...
Jack -

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marc Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 10:43pm
It's all related.  Lift is caused by the difference in pressure between the upper and lower half of the wings, along the direction of travel.  Brunelli's principle says that there is a direct relationship between the speed of the air/fluid and the pressure change. Brunelli's principle doesn't explain how to build a wing, but does help explain why wings have lift.

That said... When I got back from my trip my car was filthy (dirty snow/water).  I could see exactly where the water flowed over the car and the side windows.  The water evenly spilled over the A pillar, and once it got to the side window, the water slowly rose up, and traveled along the top of the window. 

I've also noticed that at slower speeds the water is a thin sheen across the entire side window surface.

So, I put 2 and 2 together and realized that the higher speeds causes a greater pressure difference, causing the flow of water to travel where the pressure is lowest - in this case, at the top of the window.  I mean, examining the photo, it's clear that the lower part of the window barely has any wind on it at all, as there are stationary droplets.

Anyway, I don't know the solution, but I do think it's solvable.  At the moment I'm thinking that I'd rather try to solve it by changing the flow of the water, rather than try to change the aerodynamics of the car.  As I said before, maybe a small/sharp lip along the trailing edge of the A pillar would allow the water to break free of the car.

... I don't know. Pinch 


Edited by Marc - January/12/13 at 10:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CORNERS Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 11:23pm
Those side window deflectors were really popular when I was in Japan. I think it was so people could smoke but still have the window cracked in the rain. (Almost everyone smokes in Japan it seems and their cigarettes make really thick smoke)


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Post Options Post Options   Thanks (0) Thanks(0)   Quote CINIMIN Quote  Post ReplyReply Direct Link To This Post Posted: January/12/13 at 11:56pm
Marc - Brunelli's Principal has been discredited as the reason for areodynamic lift for a very long time.  One of the better explinations of lift can be found at http://www.allstar.fiu.edu/aero/airflylvl3.htm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marc Quote  Post ReplyReply Direct Link To This Post Posted: January/13/13 at 2:18am
You said Brunelli, not me, and he wasn't completely wrong, it's just not the complete story.... Which, is what I also said above when you mentioned him (I said specifically "help explain lift"). All I've ever been talking about is air pressure. The water is at the top of the window, defying gravity because this is where the air pressure is lowest. So, why? It's due to the relative speed of the air traveling around the car. It's in balance between drag/friction, gravity, and air pressure.

Now, I know you'd want to say, "No, no. It's the flow of air around the wing, not the speed of the air." Well, they're one in the same. Is the massive amounts of air that flow downward over the wing the lift (Brunelli completely neglected this), or is it the difference of pressure between the upper and lower wing? It's certainly the pressure difference that's "lift". What's the cause of that difference? The changes in direction (flow) of faster moving air relative to the air under the wing. The reason the speed is so different isn't because the air must travel and meet at the same point at the back of the wing. He was totally wrong in that respect. It's because the air above the wing is dragged downward by the faster moving air moving over the wing. All this air, moving from above the wing leaves a low pressure zone above the wing. The speed of the air is part of the reaction which causes the pressure difference, and the speed of the air is a result of the flow of air around the wing. Larger changes to airflow have greater speed. You can't have one without the other.

So, it's not wrong to say that faster moving air has less pressure than the relative slower moving air. Most of Brunelli’s obsevations were good, however using Brunelli to explain the whole story... would be wrong. Blow across the top of a piece of paper, as you did as a kid. The faster moving air is a cause of decrease of pressure from above the paper. The piece Brunelli missed was that it's not that faster moving air itself has lower pressure, but that the displacement of air the faster moving air causes - makes for lower pressure.

Edited by Marc - January/13/13 at 1:58pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ipeverywhere Quote  Post ReplyReply Direct Link To This Post Posted: January/13/13 at 4:50pm
To my surprise, this is not a problem on the roadster. No water hits the side window.

You can always roll the windown down about an inch.

Yeah, I got nothing.
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