Quote:
Originally Posted by Gerrelt
Hi Aerohead,
Sorry, I have to disagree with you. The air does not "crash against the rear of the car".
The air normally detaches at the top of the rear decklid, creating a low-pressure area behind it. Making it hard for the engine cooling fan to get air.
Volkswagen added more and more vents in the rear decklid trying to fight this.
I don't think wool tufts give a false signal. It precisely tells what's going on. Without the spoiler the airflow is still attached to the body, with the spoiler the tufts tell that there is turbulence behind the spoiler.
Greetings,
Gerrelt.
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Is not the cooling air inlet above the top of the rear deck?
Do you think Dr.Porsche guessed that this would be an appropriate location to site the cooling/combustion air inlet.
From the smoke flow study photographs you can plainly see that the flow has completely separated from both the Golf/Rabbit and Scirocco.
In the graphic for the simplified slant back models you can also see that the only reason the air is attached along the centerline of the incline,is that the attached longitudinal vortices are holding the flow there..
Low drag cannot be achieved with attached longitudinal vortices.And they are present because the pseudo-Jaray 'fastback' is too steep to support attached flow and the violent pressure differential between the top and side flow is inducing these vortices.
This is why we are told to avoid this type of roof like the plague.
Mair's research of boat tails determined that aft-body curvature beyond a tangent angle of 22-degrees cannot support attached flow.And that is with a body of revolution which has as much body side camber as that of the boat tail 'roof.'
If you want to see a modern-day example of a proper Kamm roofline,look to today's Bugatti Veyron.Any of the three models.