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Old 06-28-2020, 03:05 PM   #51 (permalink)
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You lost me in your reply after you quoted me, about my question in the need for "thickness". Not a crucial point anyway on my part.

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Old 06-28-2020, 04:17 PM   #52 (permalink)
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Old 07-06-2020, 12:50 PM   #53 (permalink)
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4-strakes

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Originally Posted by 4drviper View Post
I had to bring a picture to make sure I'm not being treated like a complete idiot because I still cannot believe a manufacturer driven for profit would put this kind of "styling gimmick" at that location.




For the past 5 years I was able to spot these under many Toyota/Lexus on the road like Corolla, Camry, ES350, RX, just to name the ones I've seen a lot.

I understand manufacturers put styling diffusers on the bottom of rear bumper but not under the trunk.

And I mean the 4 "strakes" on the plastic piece covering spare tire bulge not the trailer hitch for those just looking to pick a fight.
Those structures could have something to do with DOT-regulated transverse splash and spray issues and nothing to do with drag.
That entire region is in turbulence, it couldn't possibly function as a drag-reducing diffuser. Any look at Carr's or FIAT's research would tell you that. Just saying.
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Old 07-06-2020, 01:02 PM   #54 (permalink)
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RICE?

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Originally Posted by 4drviper View Post
Are these really just RICE??
(race-inspired cosmetic enhancements)


This is corolla. I only see 2 to the very left of the picture.



This one looks like the back one is probably cosmetic but the under one??

anyone who wishes to see more can google "undercarriage + [model]" themselves.
It's CAFE standards. As corporate average fuel economy standards get more stringent, automakers are forced to clean up their vehicles to shave more and more drag. It's the lowest expense route to higher mpg.
All ICE vehicles are attempting to get as close as they can to the Tesla Model Y, which would be today's benchmark for underbodies.
The Lexus remains a 'faux diffuser' (it's fake) and remains so, even with the brand new 2021 Lexus IS sport sedan. According to the August 2020 MOTORTREND, page 12-13.
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Old 07-06-2020, 01:45 PM   #55 (permalink)
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Quote:
Originally Posted by aerohead View Post
Those structures could have something to do with DOT-regulated transverse splash and spray issues and nothing to do with drag.
That entire region is in turbulence, it couldn't possibly function as a drag-reducing diffuser. Any look at Carr's or FIAT's research would tell you that. Just saying.
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).

Quote:
Originally Posted by aerohead View Post
It's CAFE standards. As corporate average fuel economy standards get more stringent, automakers are forced to clean up their vehicles to shave more and more drag. It's the lowest expense route to higher mpg.
All ICE vehicles are attempting to get as close as they can to the Tesla Model Y, which would be today's benchmark for underbodies.
The Lexus remains a 'faux diffuser' (it's fake) and remains so, even with the brand new 2021 Lexus IS sport sedan. According to the August 2020 MOTORTREND, page 12-13.
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.
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Old 07-06-2020, 02:29 PM   #56 (permalink)
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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.
--------------------------------------------------------------------------
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.
--------------------------------------------------------------------------
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?
------------------------------------------------------------------------
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.
-------------------------------------------------------------------------
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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Old 07-08-2020, 03:15 PM   #57 (permalink)
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'the red part'

It would be for drag reduction. Subaru published wind tunnel results for fairing in this portion of their Cd 0.29,1985 XT sports coupe, in an SAE Paper which describes the entire aerodynamic development of the car.
These results are somewhere in my lectures here at EcoModder.
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Old 07-08-2020, 03:55 PM   #58 (permalink)
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Quote:
These results are somewhere in my lectures here at EcoModder.
Someone who cares could poke at Google's Advanced Search. I have indifferent results.

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