vortex generators in front of rear wheels

[Julian Edgar]

Originally Posted by ChazInMT

As I keep trying to point out when I see VG Gimmicks discussed, Skin drag is not the enemy of fuel efficiency with vehicles, it is pressure/form drag that we must address.

By messing with air only an inch or so away from the skin of the car, air which is already decidedly non-laminar...meaning it is already vortexing...these devices accomplish nothing.

If you want to improve your cars aerodynamics, you need to make changes in the shape of the car, this will affect the pressure, hopefully reducing drag.

Buffeting the buffeted air 1" from the skin of a car which is creating effects on the air many feet out from the skin in every direction is like wondering why the flow of a 6 foot deep river isn't changed by more than a tiny fraction if there is a stony bottom or a smooth one.

When you look at VG's in the big picture, they're a joke. You will never gain a discernible change in fuel efficiency with VG's alone.

But vortex generators aren't about changing skin drag, are they? They're about energising the boundary layer to make the airflow better follow changes in shape and so, yes, reduce pressure drag.

[aerohead]

Originally Posted by JeffD

Another VG data point to throw into the mix....
I tried Vortex Generators in front of my rear wheels and attempted my first ABA testing (Actually BABA). Found a flat stretch of road, 54 mph using cruise control (never shut the car off so it was the same each time), no AC, relatively calm but humid out. Couldn't help but have a few cars passing me going the other way. I don't know where other folks live, but it's hard to find a good testing spot around here.
Anyhow, these are the numbers:

With VG's
North: 29.8, 30.9, 29.4, 29.6
South: 31, 30.4, 29.9

W/o VG's
North: 30, 29.6
South: 30.7, 30.5, 30

I don't see much difference.
Has anyone got data for VG's in front of rear wheels?

If you can get a chase car to video the truck during a rain,you'll discover a jet of air emanating from the open wheel cavity.
The most simple solution would be the skirt as it is an inpenetratable barrier to the air.
The VG would be directing vortical kinetic energy into a void which cannot support air flow.

[justme1969]

Vg must be sized and shaped for mass of air so speed will be factor.
Vg must be positioned where they get high pressure and good flow or they are just more stuff creating turbulance.
There is more to this than gluing a gull winged shape to your door pillar etc.
You really need a smoke generator to test them and an educated guess to position them.