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Old 01-31-2011, 06:58 PM   #186 (permalink)
aerohead
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some knowns

Quote:
Originally Posted by KamperBob View Post
Thanks for chiming in, Phil. My goal was to validate the simulation against a problem with known result. Flow should hug the template until very late. (It must separate eventually which is probably why late tail chopping does little harm IMHO.)

I first ran a cylinder, hoping to see some regime change as a function of Re but no dice. That's when I switched to foils before giving up. (To its credit a pure white image produced a clean flow field.)

Unless parameters can be tuned by someone more talented than yours truly, I'm inclined agree with Chernyshenko that these (finite difference) simulations are a toy for art not a tool.
Bob,her are some hard data that may shed some light on the CFD model:

*the original Jaray/Klemperer 'pumpkin seed' wind tunnel model of 1922 registered Cd 0.13.The model is virtually the template out to 65.5 % aft-body,then it takes a dive below 22-degrees,ending at 75 % aft-body.
* Kamm tested a simplistic version of Jaray's pumpkin seed in 1935.This model had zero tumblehome and zero body radiusing at edges.This model had Cd 0.21.
* Kamm's K-form model is the same length as the Jaray but his roofline departs the template at around 17 % of aft-body,arcing down to 25 degrees at rear terminus.This model also scores Cd 0.21.
*Walter Lay's model of 1933 follows the template to 88 % aft-body.This model,while having no tumblehome,does have plan taper beginning at the max camber point.The plan taper boat tail angle is a constant 12.5 degrees all the way to the tip.This model scores Cd 0.12.
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I'm not sure about all the parameters Flow Illustrator will accept,but if there was a way to include any of these features,then we'd have hard numbers with which to compare the results.
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