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Old 03-25-2008, 03:34 PM   #1 (permalink)
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tigra AERO PROJECT rear end question

I am estimating of modify my car like in the first photo, but I have some doubts.

In middle pic, you can see the upper vision of my car.
The rear window and the back end of car they have a particular shape and, I assume an air flow like red and blue, that I have marked.









Differents angles of two flow in the rear end Is it a possible source of drag?
Can I resolve this problem?

Similar rear end one has it the Bristol Fighter :



but in this car, the two flow : from the flanks and from the rear windows has a minor angle difference .
On original tigra, the uper flanks has angled up by 6°, and roof-spoiler angle is 15°, but the real airflow from central car line minor of 15° because, the rear spoliler deviate upper the flow, consequently, I do not have a total by 21° (6°+15°), of angled flow (cause of cross vortex), but a minor value.
If I create new shape like the first photo, I can put the central flow at 15°, optimum for lowest drag, I go to increase the actuale cross vortex and I create more drag (I think).

have you, of the councils give to me?

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Old 03-25-2008, 07:03 PM   #2 (permalink)
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Ah, the Jaray shape, I really like those designs from an aesthetic standpoint.

Honestly, I would not worry about the vortices, you're always gonna have two trailling vortices unless you have something close to a round boattail. Plus, you car is pretty well designed when you look at the c pillars and the slope of the back light.

One thing your car could probably benefit from is a lip spoiler that would otherwise be a decklid extension on a notchback as the B angle in your illustration is borderline. You should first check if you have an occurence of that arch vortex on you car or if the flow simply detach somewhere on the back light. One very easy way to ckeck would be to do some wool tuft tests at the bottom of the back light. You can even just apply wool tufts on one side, but do the test in to directions to account for sidewinds.
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Old 03-25-2008, 07:40 PM   #3 (permalink)
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Hi tasdrouille.

my car has an Cd of 0.31, no bad, but also no good.
The opel has spold a lot hours in wind tunnel and the effects of this one they can are visible in some elements of car.
Rounded rear wheel arc (the profile), fill gapping in the front car, mirriors ect...
Although this one, the drag coefficient is "high".
So, I think that high drag contribution source is the rear end of car.

months ago I have applyed the wool tufts to look the rear flow in the rear windows.
Only detachments present is located between the rear windows and the decklid in a small bubble.
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Old 03-25-2008, 07:45 PM   #4 (permalink)
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the bubble

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Old 03-25-2008, 07:51 PM   #5 (permalink)
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I think you are on the right track with a center ridge. The diagram shows a vehicle having more or less the same cross section along the longitudinal axis.

As seen in an earlier posted about a pickup truck bed canopy, the optimal shape has a ridge.

Vortices have weight. A center ridge will tend to guide the "A" pillar vortices outboard where they can simply fall off the vehicle before they interact with the roof vortex. The other option would be a fence to seapate the "A" pillar and roof vortices, but a fence will aggravate and already compromised rear visibility sitation.

Can you extend your roof ridge out to the end of the "bubble?"
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Old 03-25-2008, 07:58 PM   #6 (permalink)
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Quote:
Originally Posted by Big Dave View Post
I think you are on the right track with a center ridge. The diagram shows a vehicle having more or less the same cross section along the longitudinal axis.

As seen in an earlier posted about a pickup truck bed canopy, the optimal shape has a ridge.

Vortices have weight. A center ridge will tend to guide the "A" pillar vortices outboard where they can simply fall off the vehicle before they interact with the roof vortex. The other option would be a fence to seapate the "A" pillar and roof vortices, but a fence will aggravate and already compromised rear visibility sitation.

Can you extend your roof ridge out to the end of the "bubble?"
wow,it is an complex answer

I you would be pleasing if you made one outline me
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Old 03-25-2008, 11:11 PM   #7 (permalink)
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H4MM3R -

Quote:
Originally Posted by H4MM3R View Post
That '96 tigra looks magnificenza!
Yeah, and it looks like an Opel-Insight in Fabrio's mockups!

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Old 03-25-2008, 11:43 PM   #8 (permalink)
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Old 03-26-2008, 03:14 PM   #9 (permalink)
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Quote:
Originally Posted by Big Dave View Post
I think you are on the right track with a center ridge. The diagram shows a vehicle having more or less the same cross section along the longitudinal axis.

As seen in an earlier posted about a pickup truck bed canopy, the optimal shape has a ridge.

Vortices have weight. A center ridge will tend to guide the "A" pillar vortices outboard where they can simply fall off the vehicle before they interact with the roof vortex. The other option would be a fence to seapate the "A" pillar and roof vortices, but a fence will aggravate and already compromised rear visibility sitation.

Can you extend your roof ridge out to the end of the "bubble?"
Ok, I finlly understand

A center ridge is an idea, and I wanted to discus with you only for undertand news.
If I build the bridge, do more 'small, that, from the cover the bubble.
Possible material is the transparent plexiglass, but the problem arises of how to anchor.
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Old 03-26-2008, 05:22 PM   #10 (permalink)
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I like the original design. You will always have vortices. With your design they will be lessened.

Anchoring it depends on how detailed you want to get. Ideally, building a new lightweight fiberglass/polycarbonate hatch that mounts in the factory location but is "oversized" to fit the dimensions you laid out would be best.

Ofcourse, this method is not easy . I still think the best anchoring method will be to attach it to the hatch lid somehow. By doing so, you can make the mod reversible.

To decrease interference drag/vortices, be sure to apply large radii to all edges (if it's practical to do so...).

I really like the look, by the way.

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