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Old 12-11-2019, 02:08 PM   #8 (permalink)
aerohead
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CFD

Quote:
Originally Posted by M_a_t_t View Post
Its not technically an isometric because of the angle, but there is a different view in the google doc.

a single view in the CFD is fairly quick. less than a minute for the 2d plane. About 45 seconds for the 3d and then time to settle down I guess.

The reason I am avoiding a 3d evaluation is because my model is lacking. I created it based on pictures of the car (from a distance zoomed in), but I don't have one from above to get the taper of the tail and such. I can post one if you think it would provide more information.

I wanted to test the hood to windshield because the air appeared to be separating at the back of the roof. I was hoping that it would indirectly keep flow more attached at the back by changing how it transitioned from the front roofline.

Current car @ 25 m/s


After letting it sit and run it changed to this:


The red box is where the flow lines are originating from.







Do you mean the addition to the car or the stock bumper as modeled in my last post?

At the very end where it takes a sharp turn or where the roof ends and meets the tail?

I had to compromise on the bottom of the car.

Do you think the CFD can be used as a data point? Not necessarily accurate for numbers, but just the flow pattern around the car.
Looking at the representation,I don't believe it's worth working with it.In orthogonal view,the model is failing to represent flow separation and vorticity from the square edges which would be present in the real world.I don't have any faith that it could properly represent any aspect of flow.It could lead you down a rabbit hole if you relied on it.
The bumper would be okay if it had adequate corner radii,but as depicted in plan-view,it has none at all,and guaranteed separation.Front fenders Dittoo.A-pillars ditto.
Nothing you can do at the front can solve the issue you have at the back.The present roofline is too aggressive towards the tail,and will absolutely trigger separation.No where can you exceed 23-degrees downslope.
I understand the diffuser issue,although there's no reason an active diffuser,which could deploy downwards on the highway wouldn't solve the issue.GM did it with their 'Epcot' concept of the early 1980s.
I think you'd be better off just looking at the wind tunnel flow images of real cars here on the Aero Forum.
I'm okay with CFD,just not the 'toy' kind.If you want to get serious,you better bee a millionaire!
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Last edited by aerohead; 12-11-2019 at 02:10 PM.. Reason: add data
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