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Old 12-26-2012, 09:57 AM   #1 (permalink)
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Prius Aerodynamics tuft test vids (no rain on rear glass = flow separation?)

***Can you believe I mispelled Prius in the title? LOL Sorry.***

Hey all,

I picked up a 2012 Prius two months ago. I studied aerospace engineering in college and understand the purpose of the Kamm-tail as an effective yet shorter tail for production vehicles...

However, I've been driving the vehicle and paying some attention to the rear glass and have noticed two things:

1. The flat rear glass (the vertical piece) has dust collection on it meaning there is some recirculation.

2. The kamm-tail glass remains dry when driving in the rain. I understand the angles and relative forward motion of the vehicle makes it impossible for rain to impact the rear glass but there are no streams pouring down it either indicating there is no attached flow.

I have not completed a tuft test, though I'm debating that effort.

Do we have any experts who have tackled this yet? Are there any manufacturers who tackle this? If not, I might.

Thanks guys!

Ryan


Last edited by ryannoe; 12-26-2012 at 10:10 AM..
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Old 12-26-2012, 12:44 PM   #2 (permalink)
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Fixed your title.

There is definitely attached flow on the Prius' rear glass.

Your tuft test would bear this out. Please make a video if you do - it's not much effort at all.

EG: see this tuft test of the rear glass of a 1st generation Honda Insight (showing attached flow):



From: Tuft Testing on Insight Hatch Glass (2006 Honda Insight, 1st gen.)

Perhaps the reason you're not seeing rain streaming down the rear glass is because streams on the roof can't transition to the hatchback owing to the gap (gutter) between them.
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Old 12-26-2012, 01:07 PM   #3 (permalink)
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+1 on the gap between the roof and the hatch being the culprit. Put a strip of tape over it to seal it and you should see the rain stream down the glass.
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Old 12-26-2012, 01:44 PM   #4 (permalink)
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Ok cool. Great catch! I youtube'd "Tuft Prius" and watched some short clips and the tuft on the rear wiper looks to have a nice angle to it. I think you're right.

BTW, how did you change the thread title? I couldn't find that option.
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Old 12-26-2012, 01:57 PM   #5 (permalink)
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Edit > Go Advanced (preview screen)

----

I can find 3 tuft videos for Prius on Youtube. Not your generation of Prius, and not the best view of the rear glass. Here's one:

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Old 12-26-2012, 02:16 PM   #6 (permalink)
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That's the same Prius I watched... he has a few videos similar to that one. If you look closely, he has a few tuft (tufts?) on the rear wiper, the last looks like it is pointing in the right direction without too much turbulence.
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Old 12-26-2012, 02:40 PM   #7 (permalink)
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I used rain-x on my Insight and the rear glass never had a rain drop that sat on it when I was moving at any decent speed. Not sure if you have rain-x on the glass but it could definitely make a difference.

regards
Mech
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Old 12-27-2012, 02:41 PM   #8 (permalink)
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Completed a trial tuft test yesterday in some high wind on a 2010 Honda Civic. I was astonished by the difference the crosswind makes on the vehicle. I wouldn't have thought the shear on the passenger windows would be as much as it was.

I plan on completing the "initial look" 2012 Prius tuft test this afternoon. Any recommendations from some experience before I start?

I have a GoPro cam to record from a secondary vehicle.
The yarn is bright red and nicely visible and is held by some tacky masking tape (so I don't damage the paint).

I'll make sure to post results and discussion after reviewing the video.

So... Suggestions? and anything you want to see in particular?

-Ryan
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Old 12-27-2012, 02:53 PM   #9 (permalink)
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One bit of advice: you don't necessarily have to drive fast to test airflow. The air behaves pretty much the same at 30 mph as it does at 70 mph. That may make it easier to find a suitable road to do this.

Have fun! Sounds like you're going beyond a simple examination of the rear glass (which you could have done on your own using just the Prius with the camera inside).
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Old 12-27-2012, 03:26 PM   #10 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
One bit of advice: you don't necessarily have to drive fast to test airflow. The air behaves pretty much the same at 30 mph as it does at 70 mph. That may make it easier to find a suitable road to do this.
I would suspect the separation point move closer to the roof apex the faster I go... but more than likely, I'll drive around 50 mph.

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