The Dreaded VG's again...

[kach22i]

Originally Posted by freebeard

What works to replace a front wheel skirt is an air curtain. They are used by BMW and Ford.

Good response but we are told that air-curtains take a great deal of engineering and testing to get right.

It would be nice if someone in the forum slapped some of these VG's in front of their front wheels and gave us some real life feedback.

At least I think it would be nice.

We can talk about it all day, but if we have a willing Guinea pig, I say we encourage them.

[freebeard]

Maybe they need to be pushed forward to toward the stagnation point because the air is moving sideways at that location.

[aerohead]

Originally Posted by pugmanic

I have a question over vortex generators. I understand that they have very specific uses, and come with their own drag penalties, but I was wondering if they can be used to reduce certain problem areas of auto aerodynamics.

Looking at their use in Aircraft, they are predominantly used to keep flow attached to a wing with a high angle of attack, to lower stall speed of the wing.

Would it not make sense to install them in front of the front wheel arch/well? By installing one or more VG on the front bumper/wing, would this smooth airflow around the front wheels?

I have no means of testing or simulating this.

Goro Tamai,in his book on solar racers mentioned 'taco' fairings,which did resemble hard taco shells,which were put the belly at the leading opening of the hourglass-shaped openings of steering wheels.
The fairings were to cause the air to 'jump' the void,then re-attach the flow once past the openings.Tesla uses a form of these underneath their Model S.
I suppose one could attach them vertically in hopes of jumping the body-side's wheel openings,however,historically,a flush wheel skirt would offer better performance.

[Shepherd777]

Modern funny cars travel almost 340 MPH in 1000 feet from a standing start.

This Napa car, and many others, have little diverters or aero fences on the leading edge of their steering tire wheel wheels. Presumably to make the air jump across the wheel well opening.

Also notice the very large radii at the trailing edge of the wheel well opening.

I'm curious as to how a similar leading edge fence would do on my big truck, only doing 55-70 MPH. I always planned on trying VGs in this location.

[freebeard]

...have little diverters or aero fences...

It appears to be a wickerbill, or Gurney flap.

[Shepherd777]

Originally Posted by freebeard

It appears to be a wickerbill, or Gurney flap.

Thanks for the tech info.

[aerohead]

Originally Posted by pugmanic

Are there any general rules of thumb for the size of VGs?

I have also seen on Air craft VG's, they are often angled in a Zig-Zag pattern along the wings, rather than perpendicular to the leading edge. Does anyone know the thinking behind this?

*There are at least six different types of VGs.
*Some are co-rotating,some counter-rotating.
*Some are sub-boundary later height.
*Some are super-boundary layer-height.
*An aerodynamicist would specify a particular type for an aircraft,calculate the boundary layer thickness at the proposed attachment location,calculate the spacing and orientation.Or experiment with models to sneek up on the optimized setup through trial and error measurements in a wind tunnel.
*Without full-scale wind tunnel testing,or full-scale CFD it's impossible to accurately design for VGs.

[aerohead]

Originally Posted by Shepherd777

Modern funny cars travel almost 340 MPH in 1000 feet from a standing start.

This Napa car, and many others, have little diverters or aero fences on the leading edge of their steering tire wheel wheels. Presumably to make the air jump across the wheel well opening.

Also notice the very large radii at the trailing edge of the wheel well opening.

I'm curious as to how a similar leading edge fence would do on my big truck, only doing 55-70 MPH. I always planned on trying VGs in this location.

Bob,if you can locate a Tesla S take a gander at what they've done under the nose with the leading edge of the front wheel hour-glass openings.
They've got angled fairings to create this 'jump' and re-attachment beyond the rearward termination of the opening.
The scale of the fairing,with respect to the size of the opening may suggest something about 'sizing' and angles.
This is 'underbody' flow,and it's complicated with the ground plane,but it would be a beginning point perhaps.

[Vman455]

Originally Posted by gumby79

15° off the direction of flow (not travel) this will require testing before installing.
The top/tip must reach up above the boundary lair into free flow to be able to pull it were you want.
you tube link. Velox Motorsports FRS / BRZ Diffuser Flow Visualization Testing
This will be better than oil , easyer to clean up . They used" China Wight clay "and water.

Zig zag ... my theory is that they are trying to cause counter-rotating vortices. Instead of co-rotating vortices. I dont know witch is better , this may be application specific.

As for use look at the Mitsubishi Evo, top of the back window VG's were used to reduce instability caused from separated air (due to the back glass angle and a trunk too short to allow for reattached boundary lair)
buffetting the back end reducing the safe top speed

Mitsubishi's paper indicated the VGs on the Evo were used to reduce the Cd of the car overall and improve the effectiveness of the rear wing. The new Civic Type-R does the same:



Compare to the base Civic hatch, which uses a slotted spoiler to keep flow attached to the (too-steep) rear glass:

[freebeard]

I'd like to know the logic behind the jumbo hinge covers. If it involves vortices, it would seem it would most likely be located at the edge between the roof top and side.