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Old 07-06-2020, 03:29 PM   #56 (permalink)
aerohead
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turbulence

Quote:
Originally Posted by 4drviper View Post
I asked if they would be generating vortices in crosswind, not "reduce drag" under any and all circumstances. And please stop repeating "it cannot work in turbulence". I understand that they don't work BEST but that doesn't mean zero. Gortex generating devices can be completely submerged in turbulent air (ideally just below freestream for least drag) and still be functional. Although not as strong as freestream type, it is usually found to be more drag-efficient and stronger vortices are easier to break up so I guess I could see why someone would want a "submerged" VG not freestream VG(like airplane).


Now you think they reduce drag? Make up your mind. CAFE is mostly if not entirely longitudinal drag. I even made a separate reply I don't care about longitudinal drag.

Tesla is irrelevant here because my car's bottom will never become like Model Y. Your answer sounds like an answer that says "Sell it and buy a Porsche" when people ask how to make my Honda Civic a little more fun.



And you keep misunderstanding what I'm referring to. I am very well aware that I don't need someone to repeatedly remind me that these are design features. I hope my post count doesn't make me look THAT stupid.

Even Kias have them.

Can we only talk about the red part?? It's the 3rd time you bring up the yellow part which makes me believe you think I'm a 17 year old thinking his mustang is an aerodynamic marvel because the brochure said so.



Please stay focused or just don't.
1) I believe that you've confused turbulent boundary layer with turbulence. They don't have anything to do with one another.
2) It is true that there exist sub-boundary layer VGs, but not turbulence-immersed VGs.
3) If a strake is already buried in 'turbulence' there's nothing that it can produce.
4) And strakes are basically there to help isolate a diffuser from wheel-induced, turbulent transverse flow contamination.
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As to your comment on diffusers:
* All working diffusers are exposed to a turbulent boundary layer.
* No working diffuser is exposed to turbulence. They are not the same animal.
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As to aircraft 'freestream' VGs:
* They do not exist on Planet Earth or in the known universe.
* Not even on 'laminar' airfoils.
* I don't follow your logic about stronger vortices being easier to break up. Can you help us out with that?
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As to CAFE,
* all turbulence is entropy.None of the kinetic energy of turbulence can be converted to pressure recovery.
* it is the pressure recovery which is responsible for drag reduction, via reduced pressure drag.
* pressure drag is a function of separation.
* the belly pan is there to prevent any separation upstream of the diffuser.
* the diffuser cannot function without the belly pan. By definition. It's an observed scientific fact, corroborated by multiple investigators under peer-review.
* CAFE standards drive higher fuel economy, and the cheapest way to higher fuel economy is lower drag.
* Hucho wrote his book for automotive designers.
* auto designers use Hucho's data for CAFE compliance. Track racers use it to win races. Econoracers use it for mpg or distance records. Bonneville racers for speed records.
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For sub-sonic, incompressible flow, the red and yellow portions of a diffuser do not act independently. They react to one another, in both directions, simultaneously. They cannot be examined independently, as on an aircraft, where attached flow is assumed. Automobiles are bluff bodies and their drag is ruled by flow separation.
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Last edited by aerohead; 07-06-2020 at 03:35 PM.. Reason: add data
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