wheel/wheel arch drag

[aerohead]

Saw this.Nice!
https://www.ara.bme.hu/oktatas/tanta...larch-drag.pdf

[BabyDiesel]

I saw a -0.104 total reduction in Cd from the sealed wheels with fairings. Did I read that right?

If so, that is around the same effectiveness as a boat tail!

[skyking]

Originally Posted by BabyDiesel

I saw a -0.104 total reduction in Cd from the sealed wheels with fairings. Did I read that right?

If so, that is around the same effectiveness as a boat tail!

No, you did not read it right. The 0.102 number is wheel arches covered, without wheels. that is a key detail
0.022 is the number from the same graphic for our kind of car.
That would be a big deal for my .38 CD beetle.

[freebeard]

0.022 before adding suspension and steering, and wheel and tire details. I'd look more at the variation with different details than presume a quantifiable value.

Filling the wheelarch cavity increased drag which was not expected.
...
2. Sealed wheelarch opening
...
11.Wheel arch cavity fully filled

I wonder how they define "filled" and "sealed"

Additional investigation of...cavity volume

[BabyDiesel]

Originally Posted by skyking

No, you did not read it right. The 0.102 number is wheel arches covered, without wheels. that is a key detail
0.022 is the number from the same graphic for our kind of car.
That would be a big deal for my .38 CD beetle.

Not the chart on Page 4, but down to pages 11-13 is where I got the number in my previous post. Page 12, bottom right corner to be exact.

The front and rear wheel fairing 120mm deep lowered the total drag by 0.071. This corresponds to a 17.15% reduction in total drag. (#7, pg. 11)

Edit: the 0.104 reduction was from the best configuration of mods, per page 12

[skyking]

Those are measured on a wheel rig, not car body. I would look at the difference in base pressure that the relatively narrow wheel rig will generate vs a car body and scale the effects accordingy.

[aerohead]

Originally Posted by freebeard

0.022 before adding suspension and steering, and wheel and tire details. I'd look more at the variation with different details than presume a quantifiable value.



I wonder how they define "filled" and "sealed"

I'm interpreting their language as:
*the car,in ground proximity,with wheelhouses and wheels,etc. is Cd 0.316.
*with the wheels removed,at same ground clearance,and the wheel houses completely paneled in (as if they were never there in the first place),the Cd goes to 0.214.A 32.2% drag reduction.
By comparison,
*the addition of wheels to the VW flow body increased drag by 53%.
*Cogotti measured a 2.15X drag increase when wheels were added to his low -drag car body.
*Morelli experienced a doubling of drag when wheels were added to his 'banana' car.
*Hucho speaks of a 'doubling' of drag when wheels are added to a low drag body.
*FIAT
ditto.
*on a 1972 semi-trailer,the wheels appear to add zero drag,as they are completely embedded within the turbulence of the rolling sky scraper.
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We'd want to be careful about any generalizations.

[aerohead]

Originally Posted by BabyDiesel

Not the chart on Page 4, but down to pages 11-13 is where I got the number in my previous post. Page 12, bottom right corner to be exact.

The front and rear wheel fairing 120mm deep lowered the total drag by 0.071. This corresponds to a 17.15% reduction in total drag. (#7, pg. 11)

Edit: the 0.104 reduction was from the best configuration of mods, per page 12

Goro Tamai found that the wheel-related drag on their solar racer could be reduced by 80%.They did a test rig as did Cranfield,and then verifies by on road empirical tests.
There's some fruit to pick here,but as members have mentioned,we've got to be careful of the context in which the data is acquired/presented.

[aerohead]

I snagged this image this morning.You can see the forward bias for drag and why the front is more important according to the Cranfield study.

[freebeard]

Now I'm wondering about an air curtain for the drivers door window.