Unique Phenomenon

1engineer

1engineer

Moderator
I use RainX windshield washer fluid (the orange color) during winter months. With this fluid I can drive on the interstate at 70 mph in a steady rain without using the wipers. The fluid causes the drops to "run" off and give me a pretty clear view without any wipers. I drove 300 miles in the rain and snow yesterday and noticed something unique to the 4Runner: The aerodynamic shape of the vehicle causes some strange water flow across the windshield. I drew a quick sketch of this action and you will see what I mean. The "dots" are where a water drop will start and the "line" is the direction of flow from start. The view is from the driver's seat. As you can see, all fluid (and airflow naturally) starting in the middle (top to bottom)will flow towards the side of the windshield. Once you get to the middle and above (top to bottom) the air flow goes over the windshield. Probably not much interest but I found it unique.
 

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1engineer said:
I use RainX windshield washer fluid (the orange color) during winter months. With this fluid I can drive on the interstate at 70 mph in a steady rain without using the wipers. The fluid causes the drops to "run" off and give me a pretty clear view without any wipers. I drove 300 miles in the rain and snow yesterday and noticed something unique to the 4Runner: The aerodynamic shape of the vehicle causes some strange water flow across the windshield. I drew a quick sketch of this action and you will see what I mean. The "dots" are where a water drop will start and the "line" is the direction of flow from start. The view is from the driver's seat. As you can see, all fluid (and airflow naturally) starting in the middle (top to bottom)will flow towards the side of the windshield. Once you get to the middle and above (top to bottom) the air flow goes over the windshield. Probably not much interest but I found it unique.
Click to expand...

interesting.. looks like the nose creates a wave of air that hits the middle (height) of the windshield. that would explain why the bottom part follows the side curvature of the windshield and keeps the drops from moving all the way to the top of the windshield. Do you have a bug deflector on your truck?

Okki
 
Unique, yes........ But very, very sad.

You have the Appalachians outside your doorstep. I'd kill for that. Go enjoy them.

You're an important contributor here and I don't want to see you lose it..... But you're getting close.
 
Hey...This is the type of stuff us engineering types notice...what seems boring and pointless to others, we see as entertaining and beneficial.
 
JohnnyT said:
Unique, yes........ But very, very sad.

You have the Appalachians outside your doorstep. I'd kill for that. Go enjoy them.

You're an important contributor here and I don't want to see you lose it..... But you're getting close.
Click to expand...

I do not have a bugshield.

@JohnnyT -
I rode 1500 miles of singletrack on my Mtn bike last season before in late August I cracked some ribs after the front tire slid out in a high speed turn. I drove 15 minutes from my home to ski Friday night. I still play basketball 2X/wk and started Crossfit 2X/wk in January. I travel to watch my children play soccer. I remembered to take my wife out for a nice dinner for Valentine's Day. I even got her a card. I'm ok. I just thought a few people might find this interesting. I see things a bit differently than others.

@clockwork -
Some people look PAST the raindrops on a windshield thinking of something that can make them seem relevant. A few people look AT the raindrops on a windshield thinking what they can do to improve things and help those people.
 
1engineer said:
I do not have a bugshield.

@JohnnyT -
I rode 1500 miles of singletrack on my Mtn bike last season before in late August I cracked some ribs after the front tire slid out in a high speed turn. I drove 15 minutes from my home to ski Friday night. I still play basketball 2X/wk and started Crossfit 2X/wk in January. I travel to watch my children play soccer. I remembered to take my wife out for a nice dinner for Valentine's Day. I even got her a card. I'm ok. I just thought a few people might find this interesting. I see things a bit differently than others.

@clockwork -
Some people look PAST the raindrops on a windshield thinking of something that can make them seem relevant. A few people look AT the raindrops on a windshield thinking what they can do to improve things and help those people.
Click to expand...

Not only an engineer, but a philosopher! :)
 
As a fellow engineer I will test this to see if living just pass the foot hills of this same mountain causes the same reaction while driving east 1 hour and then back west the same distance...

This is life...
 
The rain-x uses a surface tension modifier (some are Si based and practically impossible to remove from glass) to make the water like itself more that the windshield. So the droplets (rivulets) 'roll' along the surface instead of wetting it and sliding. The streamline velocity (relative velocity as truck is moving more than air) increases with distance away from the hood. One might expect the lowest points on the windshield nearer the hood surface to have much lower momentum transfer (maybe not enough to push them up the windshield, so they roll off to the side). The rivulets higher up should have higher momentum transfer so they might be lift upward and may be moving faster too. Depending on how well the glass is Rain-X coated (underneath the wiper vs. not underneath) the propagation rates might be different in different regions. It might be interesting to video tape the phenomenon and see if there is a critical droplet size that is created for various velocities. Larger drop might be sheared into or detach completely. One might be inclined to propose a shear induced detachment model that could be used to predict the mean free rivulet size as a function of speed limit. Or possibly optimize concentrate of said surface tension modifier.

... or you could turn your wipers on and think about something else ...

it is pretty interesting
 
Last edited:
tlflow said:
The rain-x uses a surface tension modifier (some are Si based and practically impossible to remove from glass) to make the water like itself more that the windshield. So the droplets (rivulets) 'roll' along the surface instead of wetting it and sliding. The streamline velocity (relative velocity as truck is moving more than air) increases with distance away from the hood. One might expect the lowest points on the windshield nearer the hood surface to have much lower momentum transfer (maybe not enough to push them up the windshield, so they roll off to the side). The rivulets higher up should have higher momentum transfer so they might be lift upward and may be moving faster too. Depending on how well the glass is Rain-X coated (underneath the wiper vs. not underneath) the propagation rates might be different in different regions. It might be interesting to video tape the phenomenon and see if there is a critical droplet size that is created for various velocities. Larger drop might be sheared into or detach completely. One might be inclined to propose a shear induced detachment model that could be used to predict the mean free rivulet size as a function of speed limit. Or possibly optimize concentrate of said surface tension modifier.

... or you could turn your wipers on and think about something else ...

it is pretty interesting
Click to expand...

My head hurts.

I'm glad I'm not as booksmart as some of you guys- life must be exhausting for ya!

Seriously though, great detailed explanation!
 
Antman said:
My head hurts.

I'm glad I'm not as booksmart as some of you guys- life must be exhausting for ya!

Seriously though, great detailed explanation!
Click to expand...

Oddly enough, engineering is form of ADD ... therefore it's incurable. I was first diagnosed in 1987, I got treatment but relapsed in 1993.

I hope my engineer buddy got a kick out of it ... I find myself doing the same thing way too often. (my baby girl - 15 - is like "seriously? ... you are sooo weird")
 
Soooooo it happen to rain this morning so I thought I'd perform a control on Engineer1's outlandish observations. :lmao:

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Seems to me he did not put enough emphasis on the speed variable as well as the "preceding car spray" attribute to the experiment.
BAZINGA!


Okki :driving:
 
Glad to see there are others on here who sometimes look at things and go "hmmmmmm" instead of complaining about all the smalll things.

@okki
(knock knock) penny - (knock knock) penny - (knock knock) penny
 
The only thing I understood from this thread is that there is another Crossfitter amongst us...thats awesome! I know you've only done it since January but you'll love it. I wonder who else does CrossFit on the forum?
 
1engineer said:
Some people look PAST the raindrops on a windshield thinking of something that can make them seem relevant. A few people look AT the raindrops on a windshield thinking what they can do to improve things and help those people.
Click to expand...

That's just good.

It was probably wasted on the target but the exceptional quality didn't go unnoticed.
 
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