Thread: Air Tabs
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Old 06-01-2012, 02:58 PM   #56 (permalink)
aerohead
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Quote:
Originally Posted by ksa8907 View Post
I think im confused? Are people trying to keep attached flow over the window or reduce the low pressure zone at the rear. I think the later is where the real gain is to be made.
They go hand in hand.
*The base pressure behind the VW is dependent on where the boundary layer separates,as the entire wake will be at this pressure.
*If you can move the separation point further back the 'new' separation point will typically be in a region of higher static pressure,which will raise the base pressure a little closer to the forward stagnation pressure;which reduces the delta-P across the car,lowering the pressure drag which is the largest component of profile drag.
*VGs are supposed to create small eddies which transfer kinetic energy from the 'invisid' outer flow,down into the boundary layer,helping to maintain attachment in the presence of an adverse pressure gradient (downstream of the point of minimum pressure).
*VGs are typically for flow reattachment onto the boot of a notch back car.
*Since the Beetle has no 'boot',there's really nothing to reattach to.
*Without the 'reattachment',any pressure gain you might get from the VGs are eaten away at by the constant increase in interference drag and induced drag of the vorticity they produce.Gains could be 'negative.'
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*The Beetle needs a rear end.
*The New New Beetle has a better rear.
*The AUDI TT rear is better.
*The PORSCHE would be even better
*The 'Template' is reported to be the lowest drag.
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If you can find the thread for the aero-modded Chrysler Airflow,you can see what Carl Breer would have done to your car.It was actually the world's first K-form car.
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