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Old 01-30-2010, 04:15 PM   #35 (permalink)
aerohead
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template

Quote:
Originally Posted by ChazInMT View Post


More questions, (really pretty much an assertion) and graphics as promised earlier.

Aerohed, I post this image yet again to question your application of the template. It sure seems like the flow is following down the back of this Audi. I also know that this particular Audi has a pretty incredible Cd at 2.5. Based on this, I'd find it hard to believe that the Green Template has any relevance whatsoever. It also seems as though the Red Template is relevant due to the apparent attached flow and the incredible engineering involved on this particular car. So it seems to me that scaling the Red Template so that the Arching section matches the aft shape we're analyzing, makes it relevant. If the shape ends up falling off the back end, it's done. Separation occurs at that point. If the analyzed shape stays within the template, it's aero baby.

Clearly, no car design which stands taller that 3 feet could make effective use of making the bottom chord of this template as the ground plane under the bottom of the tires. Of course if you do this, the flow separation would never occur, but the roof line would be very long. I challenge this use of the template.

Below are 2 other template overlay examples to further prove what seems to me the logical application of this template.



Above we see attached flow on the back of this BMW, the upper arch of the template follows the roofline at the back, the template runs out into the car, so the flow remains attached all the way back.



On this Benz, the Upper arch of the template matches the roofline again, it needs to be scaled quite small to fit, and as you can see, the rear window goes beyond our template and low & behold, flow separation occurs at this point.

Again, If I'm misunderstanding this, and somehow my logic is not really being supported by real life examples, please let me know. Otherwise, we must look to not apply this template by placing the bottom chord under the tires and scaling the size of it up to match the high point of the roof.

I can, and will, load as many images as it takes showing how my application of the template makes sense. I challenge you to find a real world example of how your use of the template has been violated, while my use of it has not, and flow separation is evident.
The clock-face template is a thought exercise which might find application if a person had no other resources to work with.Using the aft portion would provide a separation-free aftbody for a vehicle,albeit,very long.
I'd like you to do a search for "Aerodynamic Streamlining Template:Part-C ,and look at the 2nd image.
This is the template that I advocate members use as a go-no-go minimum for attached flow.I believe the smoke flow traces over the two cars you have shown will be in better agreement with this template.
I repeat,I do not advocate that any member or lurker actually use the clock-face template.I presented it as a way to illustrate the evolution of streamlining.And as your intuitive instincts are rebelling against it you are correct in assessing that we can do better.Which is the whole point of the 2.5:1 teardrop template.
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