Quote:
Originally Posted by cyclopathic
I agree with you that VGs are not a magic item which gives you higher MPG by just having them, and use of them should be looked in context. What I specifically refer to is that VGs when used properly can help to increase efficiency of properly designed spoilers by increasing speed of flow and decreasing spoiler stall speed.
If not used properly they will do nothing or hurt, but this can be said of any aero mod.
Edit: not sure which vehicle they used. There are more production cars/SUVs use them now. I followed hybrid Avalon last night it had OEM VGs on rear underpan.
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I think it's time for images.
Are we talking 'wings' or 'spoilers'?
If VGs allow the inviscid flow to more closely follow the aft-body contour of a car,it won't really alter the local air velocity.
A wing will already be above the separated flow in 'clean' air and little affected by VG modification.
If a spoiler is in separated flow,VGs can help with reattachment onto the boot/spoiler,a clear advantage.
A spoiler doesn't have a stall speed.It's just a reattachment apparatus on a car with designed-in separation.
And with a wing,the VGs would have to be on the wing itself to be able to alter its stall characteristics,something well researched since 1920.
The other thing,is that there are about six different types of VGs in use.Each has a specific advantage.All six types would want to be investigated.And their performance depends on the local boundary layer thickness,along with orientation,location,and spacing.
They require a wind tunnel for investigation.If you're going to do a moving-floor tunnel as is available in North Carolina,you're looking at $4,000/hour for testing.And you'll be there for days.
I agree that VGs have their place,but we may be forced to leave it up the the Mitsubishi's of the world to figure out how to best use them.