Prius Aerodynamics tuft test vids (no rain on rear glass = flow separation?)

[kennybobby]

Originally Posted by F8L

I'm really curious to see how all of this pans out, particularly anything related to the wheels and the high offset (sunken in) effect. So many Prius owners opt for wider wheels with a lower offset. I am concerned about the effect the increased width and decreased offset will have on aerodynamics. If you push the wheel out so it is flush with the body line is this going to increase turbulence?

i think it will increase turbulence, but even if it could somehow decrease turbulence slightly, what would be the payback time of additional fuel savings to offset the cost of the new wheels? Seems like a wheel skirt would have more aero benefit and cost less...

[kennybobby]

Hey Ryan, have you looked at comparing the aero template to your car--what is the angle of the rear glass with respect to the horizontal of the vehicle and the distance back from the roof apex?

[Daox]

Originally Posted by ryannoe

No testing with video or yarn was completed today. I did drive the Prius in the rain and during stop lights, rain gathered on the back glass. After accelerating to 60 mph (power mode because I didn't want them to collect into jumbo drops and let gravity do all of the work) the droplets were unscathed and BARELY pushing their way to the rear. After my 6 mile run, there were still roughly half of the droplets attached to the window. I shouldn't say this, but I was pretty much watching those droplets the entire drive

You guys had me doubting my initial thoughts of the separated flow, but now I'm more confident that the flow has separated. Hope to have something for you soon.

-Ryan

It would be interesting to see what happens to the tuffs if they were raised say 1/4" or so. I wonder how thick your boundry layer is.

[ryannoe]

Originally Posted by kennybobby

Hey Ryan, have you looked at comparing the aero template to your car--what is the angle of the rear glass with respect to the horizontal of the vehicle and the distance back from the roof apex?

KennyBobby - What aero template?

It would be interesting to see what happens to the tuffs if they were raised say 1/4" or so. I wonder how thick your boundry layer is.

Daox - I had a similar idea. More coming soon on it.

[F8L]

Originally Posted by kennybobby

i think it will increase turbulence, but even if it could somehow decrease turbulence slightly, what would be the payback time of additional fuel savings to offset the cost of the new wheels? Seems like a wheel skirt would have more aero benefit and cost less...

I should have stated the new wheels are not for fuel economy. They are added for looks and or handling. I'm interested in the negative impact of offset and width if all other factors are kept constant.

[kennybobby]

hey Ryan,

http://ecomodder.com/forum/showthrea...ion-21952.html

and

http://ecomodder.com/forum/showthrea...rt-c-9287.html

[MetroMPG]

Originally Posted by F8L

I should have stated the new wheels are not for fuel economy. They are added for looks and or handling. I'm interested in the negative impact of offset and width if all other factors are kept constant.

Maybe of interest:


Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

[F8L]

Originally Posted by MetroMPG

Maybe of interest:


Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

Thanks. I've been testing the effects of 17" wheels/tires on mpg since I bought my first Prius in 2005. There is ALWAYS a negative hit associated with upsizing. My question on the aero effects of such a change or that of decreased offset was an effort to try and figure out all of the variables that go into this fuel economy loss so we can try to reduce it.

[kennybobby]

Hey Metro,

Would you please explain the meaning of the presence or absence of snow patches on the probe?

[ryannoe]

Hey all,

No fun tuft videos to watch today but I ran some drag test coast downs today.

I want to slowly swing everyone's opinion over to flat plate drag so I'm going to give you guys that value as much as possible to get you familiar with it

2012 Toyota Prius (no mods) FPD: 0.6885 m^2

Rolling Resistance with factory tires: 0.0116

or if you're stubborn --- Cd: 0.28 with a frontal area of 2.39 m^2

(remember FPD is the same as CdA)

The frontal area was measured by finding a picture from the web and using GIMP to color it in and using histogram to count the pixels. I used the manufacturer's height to determine pixel size per square inch of area.

Since FPD doesn't care what the frontal area is, it's my preferred method.

Have a great night!

-Ryan