Fact or Fiction: Dimpled Underbody helps reduction in drag

i'm sure you've seen the Lexus commerical claiming that a dimpled underbody reduces overall drag on the car, is it true? and how does it do it?

would vortex generators achieve the same benefit?

Hard to say. It probably does no harm, whether it is a statistically significant effect is another matter.

BMW use dimples on their mirrors, so the dimples may work at automotive Reynolds numbers.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

Works on a golf ball!

And what is the Reynold's number of a golf ball?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

There are several makers now following BMW's lead and using dimples around the external mirror area. Most have fixed the pattern to the mirror support frame where the door window glass meets the A pillar not on the mirror itself.
I was lead to believe BMW originally used the dimples to help reduce wind noise generated by air passing between the mirror body and the A pillar.

Lexus also once ran an ad that claimed they invented headlights that turned with the steering. I remember seeing it on D series Citroen before Lexus was even imagined.

The point, don't necessarily believe everything that Toyota advertises.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

I've seen headlights that turn with the steering on a 1931 Duesenberg.

I have seen headlight that turned with steering on 1912 Harley Davidson.

Tucker had the center headlight turn with the steering.

Regarding the question.. unless there is airflow seperation downstream we're looking to minimize, dimples and vortex generators create a lot of unnecessary drag.  Compare a flat smooth panel under the car, and one with 80 vortex generators sticking out... may help in certain instances, but unless properly engineered, it will likely be a negative.  We're trying to create low pressure under the car, and the extra turbulence may not help too much if you know what I mean.

Regarding the golf ball... let's model vortex generators on a golf ball and compare it to a dimpled golf ball!