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Old 07-31-2012, 07:36 PM   #1 (permalink)
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An interesting presentation

A useful presentation. It gives dimensions (all but one) to models and gives their CD from tests. This can be used to check your simulations.

They also do some other experiments. One they play with a boat tail. Another they play with vortex generators ( they found airtabs to reduce drag by about 3% on one of the models).


http://www2.warwick.ac.uk/fac/sci/wm...ntation_rc.pdf

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Old 07-31-2012, 08:51 PM   #2 (permalink)
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...wonder if all those %-improvements are linearly additive, or do they have interactions that 'might' negate or diminish each other along the way?
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Old 07-31-2012, 09:00 PM   #3 (permalink)
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Interesting paper.

And sure enough: their results show the Airtabs helping. (Smacks forehead.)
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Old 08-02-2012, 10:30 AM   #4 (permalink)
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Interesting.

My old rubber apparition aerocap (17 degree slope no boat-tail) was not far from their optimum. (25 degree slope, 10 degree boat-tail).

The diffuser did not appear to be that big a deal.

Some of this echoes aerohead's practical experience with his boat-tail pickup.
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Old 08-02-2012, 01:54 PM   #5 (permalink)
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I was under the impression that you started to get separtaion when you started getting in the ~+15 deg range. What am I missing?
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Old 08-02-2012, 01:57 PM   #6 (permalink)
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You can exceed 15 degrees, and approach the low 20's, and still retain attachment with the right shape (curve).
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Old 08-02-2012, 02:20 PM   #7 (permalink)
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Cool, thanks for posting it.
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Old 08-02-2012, 02:31 PM   #8 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
You can exceed 15 degrees, and approach the low 20's, and still retain attachment with the right shape (curve).
But it looks, like thier model was straight--not curved.
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Old 08-02-2012, 02:34 PM   #9 (permalink)
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Quote:
Originally Posted by Diesel_Dave View Post
I was under the impression that you started to get separtaion when you started getting in the ~+15 deg range. What am I missing?
Quote:
Originally Posted by Diesel_Dave View Post
But it looks, like their model was straight--not curved.
...with a "straight" sloping roofline, there's a 'sudden' breakpoint the airflow has to traverse over, which isn't there with a smoothly tapering (curving) roofline, and it's that 'suddeness' of change that creates airflow problems.
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Old 08-02-2012, 06:02 PM   #10 (permalink)
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models

Quote:
Originally Posted by Diesel_Dave View Post
But it looks, like thier model was straight--not curved.
At the beginning of the piece they mention that the models are from the 1970s,a time when Hucho,Jannsen,and Emmelmann were doing 'optimization' work on Giorgio's body styles commissioned by Volkswagen.
Hucho mentions the 'high cost' of curved glass in his book(s) and at the time,automakers were nursing nickels,searching for ways to control production costs.
No one builds shapes like those today.They've gone the way of the Easter Island Lumber Co..

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