Irabike
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Joined: Mon Apr 02, 2018 8:35 am
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Leaf Number: 311153

Airflow design flaw?

Mon Apr 02, 2018 9:01 am

I decided to look for a forum after this experience with my 2017 Leaf. I was hearing this thumping noise that sounded like the right rear tire was flat or the fender was flapping. Didn’t see anything when I looked. It started again when I reached 30 mph. I looked backwards and saw my back right window was all the way down. It stopped when I put it up. Anyone else experience this? Is it a design flaw?

WetEV
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Re: Airflow design flaw?

Mon Apr 02, 2018 9:35 am

Irabike wrote:I decided to look for a forum after this experience with my 2017 Leaf. I was hearing this thumping noise that sounded like the right rear tire was flat or the fender was flapping. Didn’t see anything when I looked. It started again when I reached 30 mph. I looked backwards and saw my back right window was all the way down. It stopped when I put it up. Anyone else experience this? Is it a design flaw?


Most cars do this. One window open creates a resonance at low audio frequencies. Open a second window or close the open window.
WetEV
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IssacZachary
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Re: Airflow design flaw?

Mon Apr 02, 2018 1:11 pm

This is what I love about my 1972 VW Beetle. It's called a wing window. You can adjust it so you don't get that turbulent sound wave at the window when is opened.

I think all modern cars are basically designed to be driven with the windows up. By opening any window you essentially mess up the aerodynamic shape of the vehicle and cause turbulence that causes that sound.

I'm sure we're not going to see a convertible Leaf any time soon either.
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TheLostPetrol
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Leaf Number: 307105
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Re: Airflow design flaw?

Mon Apr 02, 2018 1:14 pm

WetEV wrote:
Irabike wrote:I decided to look for a forum after this experience with my 2017 Leaf. I was hearing this thumping noise that sounded like the right rear tire was flat or the fender was flapping. Didn’t see anything when I looked. It started again when I reached 30 mph. I looked backwards and saw my back right window was all the way down. It stopped when I put it up. Anyone else experience this? Is it a design flaw?


Most cars do this. One window open creates a resonance at low audio frequencies. Open a second window or close the open window.


Yes. My empirical observation is that a one-inch opening of a window on the opposite side of the cabin is enough to suppress the resonance.
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Nubo
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Re: Airflow design flaw?

Mon Apr 02, 2018 3:00 pm

Irabike wrote:I decided to look for a forum after this experience with my 2017 Leaf. I was hearing this thumping noise that sounded like the right rear tire was flat or the fender was flapping. Didn’t see anything when I looked. It started again when I reached 30 mph. I looked backwards and saw my back right window was all the way down. It stopped when I put it up. Anyone else experience this? Is it a design flaw?



https://blogs.unimelb.edu.au/sciencecom ... -you-nuts/
I noticed you're still working with polymers.

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Nubo
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Re: Airflow design flaw?

Mon Apr 02, 2018 3:01 pm

Nubo wrote:
Irabike wrote:I decided to look for a forum after this experience with my 2017 Leaf. I was hearing this thumping noise that sounded like the right rear tire was flat or the fender was flapping. Didn’t see anything when I looked. It started again when I reached 30 mph. I looked backwards and saw my back right window was all the way down. It stopped when I put it up. Anyone else experience this? Is it a design flaw?


Helmholtz resonance -- the same effect as blowing over the top of a bottle. It tends to be more pronounced the more aerodynamic the vehicle is.

https://blogs.unimelb.edu.au/sciencecom ... -you-nuts/
I noticed you're still working with polymers.

NeilBlanchard
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Re: Airflow design flaw?

Wed Apr 04, 2018 12:51 pm

I have found that cracking the front windows is both effective air flow, and quieter than cracking the rear windows. Open the dash vents, and then crack the front windows just enough to get the noise to a minimum - and usually you then get much better air flow from the vents. I think it is then possible to slightly improve the car's drag.

If you open both front and back windows, then you can also avoid the booming resonance.

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