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Old 01-20-2014, 06:24 PM   #3 (permalink)
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how can?

Originally Posted by CFECO View Post
Looks like Attached flow, on a shape "Much" steeper than "the Template". How can it be?
I do not have an answer which is as good as your question.Some thoughts:
*In Hucho's 2nd-Edition he shows a single image of a body of revolution which is optimized for low drag.It's like a 'laminar' profile which has it's maximum cross-section well aft on the body.It has a 'fast' rear contour.There's no further mention of it.
*It may behave as the NACA/Morelli shape,which has really low drag with high ground clearance,and then it's Cd falls apart when lowered into 'normal' ground clearance.(Cd 0.17 became Cd 0.35 in Morelli's case)
*Orion's high ground clearance may allow for the 'jet pumping action' which truncated boat-tailed bodies experience in free flight,a condition where the flow is more axially symmetrical,and the under flow it highly energetic,with equal pressure/velocity.
*Hucho says (for road vehicles) that beyond 23-degrees,we'll have separation and a transition to a squareback wake as you can see in the #14 drag table of the aft-body rear inclination thread.Between 28,to 32-degrees,the wake would dance back and forth between fastback type and squareback wake,with pulsations,booming,and maximum drag.
*W.A.Mair shows full separation beyond 22-degrees.Pretty close agreement.
*It could be that Orion's shape only works for Orion-like vehicles.I'm hoping that Neil Blanchard will have something from Goro Tamai's book which will help.I've ordered the book,but it is sold out on Amazon and I'll just have to wait it out for delivery.
*I compared Kach22i's VW Volkhart Sagitta aft-body wind tunnel smoke flow photo with a protractor and am seeing separation beyond 22-degrees.
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Last edited by aerohead; 01-20-2014 at 07:03 PM.. Reason: spelling
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