10-13-2012, 01:38 PM
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#51 (permalink)
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Master EcoModder
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S10
Quote:
Originally Posted by Smurf
I got it to work.. After you SketchUp your design, go to File, Export, 3D Model.. Save it as a .3DS file. Open Falcon, click the car, import your design.
However, according to Falcon, an S10 like mine (with ridiculous body kit, courtesy of the Warehouse model) lowered with simple cap and angled nose can achieve a 0.37.. I tried it without the nose first, and it said 0.50 CD. Intriguing to play with though, thanks for the find. |
I believe that the most recent generation of S-10s (before anything like the 'EXTREME') had Cd 0.42.
The 1st-gen S-10/GMC S-15 had Cd 0.475.
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03-07-2013, 12:37 AM
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#52 (permalink)
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Eco Sol
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Well, I have been gone for far too long busy with other things in life. Finally made a virtual kammback for the Del Sol, following the aerodynamic template. Sadly to my suprise though, it didn't seem to do anything for my aerodynamics  The high point on my car is just too far forward (right at the top of the windshield it looks like). The air separates from the car before it even makes it far enough back for the kammback to be useful.
My car is supposed to have a CD of .35 stock. The software shows .48 (with or without kammback). Maybe I am doing something wrong.
All results are at 60 MPH with the exact same settings.
Template:
Flow Lines:
Top View:
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03-07-2013, 05:04 PM
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#53 (permalink)
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Recreation Engineer
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Shortie, how does simulated drag compare to known shapes like sphere and cylinder?
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03-07-2013, 06:38 PM
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#54 (permalink)
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Eco Sol
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That is a very good question. Hadn't thought about that. Well, I tested a cylinder and this is what I came up with... I wasn't sure which way to test it, so I did both.
Cd of 1.06 on the left and 1.10 on the right.
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03-08-2013, 06:20 PM
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#55 (permalink)
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Recreation Engineer
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In 3D a cylinder is trickier due to aspect ratio depending on its dimensions. For 3D a sphere avoids that issue. For 2D a cylinder (infinite length in 3D). If your Cd and flow pattern are consistent with reference data from these well-studied standard shapes, that validates the computational method. Then simulations of unknown shapes carry more confidence to make relative drag comparisons. Ultimately, validation testing is required for absolute proof. (That's what I learned from working with professionals doing computational analysis. My role was test & measurement for validation.)
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03-09-2013, 05:51 AM
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#56 (permalink)
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Eco Sol
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Well, I tried a sphere (best one I could get anyway). It got a Cd of .62 with a Fd of .917(lbs), but I don't know what it should be.
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03-09-2013, 03:16 PM
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#57 (permalink)
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Master EcoModder
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drag coefficients
Quote:
Originally Posted by Shortie771
That is a very good question. Hadn't thought about that. Well, I tested a cylinder and this is what I came up with... I wasn't sure which way to test it, so I did both.
Cd of 1.06 on the left and 1.10 on the right.
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The circular cylinder,in free flight,away from ground proximity,and at supercritical Reynolds number would be Cd 0.82.
In ground proximity,with acceptable ground clearance,the cylinder would have Cd 0.81.
For the sphere,in free flight,the drag,below critical Reynolds number would be Cd 0.47,above critical Reynolds number the drag could be as low as Cd 0.09.Sphere drag is very much Reynolds number dependent.
The sphere,in ground proximity,with acceptable ground clearance would have Cd 0.94-0.18.
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Last edited by aerohead; 03-09-2013 at 03:18 PM..
Reason: correction
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03-10-2013, 02:52 PM
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#58 (permalink)
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Recreation Engineer
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I'd rather validate computational methods using a 2D cylinder (infinite length). It would be easier (than sphere) to get cross section of the flow pattern in its wake. I'd want to see flow agreement to confirm the proper regime. A steady separation bubble from tail eddies is the characteristic form of interest. Then fine tune simulation parameters until the Cd matches expectations. Hoerner, Hucho and others provide documentation for reference. Sorry I don't have links handy. Maybe someone else can and will share.  |
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03-10-2013, 09:23 PM
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#59 (permalink)
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Eco Sol
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This is getting far more complicated than it already is
Would results be very accurate at all, if I just used the results of the stock model I have of my car for a baseline. Then after adding changes to it just compare the difference? Or what that give me even more inaccurate results?
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Last edited by Shortie771; 03-10-2013 at 09:46 PM..
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03-11-2013, 11:27 AM
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#60 (permalink)
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Recreation Engineer
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Accuracy
Quote:
Originally Posted by Shortie771
This is getting far more complicated than it already is
Would results be very accurate at all, if I just used the results of the stock model I have of my car for a baseline. Then after adding changes to it just compare the difference? Or what that give me even more inaccurate results? |
Sorry. CFD is not simple. To determine accuracy of computer simulations requires validation. Otherwise, how does anyone know?
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