Quote:
Originally Posted by winkosmosis
But my point is that the template is meaningless in this context. People are overlaying it arbitrarily on their cars and then thinking that where the lines fall happen to describe some kind of ideal shape. The shape of the template is only ideal for the whole shape described by it.
It's completely backward reasoning.
You're right, it's not just attached flow that matters. It's attached flow that allows the car to leave as small and clean a hole as possible in the atmosphere once air is done flowing around it.
You can do better with common sense. Start with a horizontal surface (most roofs), increase the curve gradually, and don't exceed 20°, or 15°, or 10°, or whatever (depending on airspeed). Trying to align a template arbitrarily with a whole front end that has zero relevance to a normal car is a waste of time and energy.
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*Hucho's point is that once the front end has attached flow,you go after the aft-body.
*Hucho lays out the rulebook for doing the aft-body,and the 'Template' is the embodiment of all the 'critical thinking' requirements to pull that off, with a minimum of material(mass,cost,inertia,momentum,tooling,invest ment,etc.).
*The 'Template' cannot precipitate separation,so for as long as you dare follow it,you're guaranteed attached flow.
*When you do decide to do the Fachsenfeld/Kamm/Breer 'chop',the wake will have the highest base pressure,i.e. the lowest pressure drag which is what streamlining is all about.
*The gradual curve that you speak of is the scientific premise of the 'Template'
* There is no 'arbitrary' alignment allowed with the 'Template.'
* As far as 'ideal',if that means the biggest bang for the buck,then yes it's ideal.
* if you're steeper you lose.
* if your less steep you lose.
* The 'front' of the 'Template' is ideal for sub-transonic flow.The emphasis for the 'Template' is on the aft-body.This is where all fluid mechanics text will emphasize that we focus our attention,including road vehicle aerodynamics which is only a branch of fluid mechanics.
*The 'small and clean hole' you mention is the wake area.If you use the 'Template' there is no effective wake at all.Pressure drag is completely elliminated.
*If you're going to debate with an anecdotal brief such as 'common sense' your going to lose the debate every time.There is no such thing as common sense.It doesn't stand as prima facie evidence.