Quote:
Originally Posted by aerohead
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.
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I think at the time they developed the beetle, the 1930-tees, aerodynamics was an upcoming science. And they didn't know what we now know today.
Add to this that the beetle was developed for a TOP speed of 100 km/h, aerodynamics at high speeds as we drive today wasn't interesting.
Yes, the VW beetle was one of the first cars that attempted a aerodynamic body. But if Dr. Porsche would develop the VW beetle today, with the knowledge we have now, I think he would have reconsidered the placement of the vents.
Quote:
Originally Posted by aerohead
From the smoke flow study photographs you can plainly see that the flow has completely separated from both the Golf/Rabbit and Scirocco.
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Those cars have a "sharp" edge at the end of the roof, so seperation is easier.
Look at figure 21.23 on page 143 of the book I posted earlier (
This one ).
That edge is a trick to get the airflow to seperate at the end of the roof.
The VW beetle roof is round, making it easier for the airflow to stay attached.
Quote:
Originally Posted by aerohead
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.
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Ah, I think we're talking about two different things. Those vortices are one aspect of aerodynamics, what I am talking about is what Genta calls "streamlines in the symmetry plane".
Both contribute in aerodynamic drag.
I still think the wool tuft tells a valid story and the flow is attached. If the flow wasn't attached there, the wool tufts would be going all places, and not nicely in straight lines to the bottom.
The rear of the VW beetle is not steep enough to get the flow detached, creating lift and drag. It's the same effect what caused the Audi TT to be retrofitted with a spoiler on the rear.
The effect can be seen in this picture:
Up to 30 degrees the flow stays attached, steeper then that, the flow is detached.
Maybe we should agree to disagree.
