Quote:
Originally Posted by Madact
Apologies for the annoyed tone and partial off-topic-ness, but
More like a handy approximation of "the shape the air molecules want to follow for optimum return to the place where they were before you tried to ram them with your vehicle" given air flow that:
* is attached flow along the upper surface
* has a given amount of initial turbulence before you 'ram it with your vehicle'
* transitions to turbulent at a particular point (about 30% length I think, just looking at it?)
And the vehicle
* is close to a particular cross sectional shape
* is travelling within a particular speed range
* has a non ideal - but reasonably smooth - surface finish
In order to
* prevent premature flow separation (i.e. before a 'kamm' style cut-off) and
* reduce drag by achieving decent pressure recovery (given all the other assumptions and conditions)
Assuming
* form (pressure) drag is dominant over skin (friction) drag
* flow hasn't been tripped to turbulent too early
* flow can't be kept laminar much more than typical
* probably a bunch of other stuff I've missed here...
Sorry if I sound frustrated there, it just irks me a little that it keeps getting applied to everything, when the reality is a whole lot more complex. It's a great tool for vehicle modding which I wouldn't be surprised if it gets you within near-as-makes-no-difference of optimal when adding a kammback to your sedan, and a decent approximation of what you want the air to be doing in a general sense, but the "grand unified theory of fluid dynamics" it ain't.
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*The 'Template' is a composite of 'solutions' recommended for road vehicle aerodynamic drag reduction,which by definition is pressure drag reduction achieved through elimination of flow separation,and is applicable to any passenger car manufactured after 1985,although it will work for 1975 Volkswagens.
*Attached flow on the roof is presumed.
*Ambient air is turbulent.
*Transition to full turbulent boundary layer occurs within the first 2-inches.
*The cross-sectional profile of any post-1984 automobile body will suffice.
*Operational velocities up to 250-mph under standard atmospheric conditions would be applicable.
*Any automobile manufactured in the last hundred years has an 'ideal' surface finish.
*If the 'Template' contour is applied as specified,separation is impossible.
*The premise of the 'Template' is to provide the proper rate of flow deceleration which enables pressure recovery.
*Pressure drag is always the dominant component of profile drag and,again,it's reduction or elimination is the premise of aerodynamic streamlining.
*The flow always trips itself to a TBL within the first 2-inches of body length.
If there is separation,then the TBL lifts away from the body's surface, inducing turbulence.If the flow does not reattach,then this will be the beginning of the wake.
*The laminar inviscid flow remains intact unless separation occurs.The variety of body styles might preclude the use of 'typical' when addressing flow.
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*If you'd like to see the full scientific derivation of the Aerodynamic Streamlining Templates,I invite you to read the thread.
*And while reality IS complex,the AST respects the complexities of reality as expressed in empirical scientific examinations for 92-years.