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Old 06-11-2020, 01:17 AM   #31 (permalink)
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Originally Posted by aerohead View Post
I've no knowledge of anyone actually optimizing VG type, number, and location placement outside a laboratory environment.
Pages 146 -150 of my book.

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Old 06-14-2020, 05:08 AM   #32 (permalink)
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Well, don't leave us in suspense - what were the results?!
It was nothing more than driving around with tufts to see if I can get any serious crosswind, so the results may not sound like worthy of 8 hours.

I thought the V arrangement (opening facing either forward or backward) was not taking advantage of the full number of VGs since in crosswind, one side of the V will be overlapping too much.

From Mr. Edgar's testing, I think that would be sufficient for my purpose to reduce the sideways forces in crosswind since I already tamed it down with some airtabs behind the rear axle, for the time being.

Now I'm looking at my car how I can firmly attach rooftop strake, and tryign to find some information on low speed characteristics of MiG-15/17.

Also about to buy the book.. the lack of scientific knowledge on my part while trying to have some fun with this is too painful.

And about "anyone actually optimizing VG type, number, and location placement outside a laboratory environment", I see too many toyotas with tiny nubs around the mirror, tail light, and D-pillars. But most importantly the plastic cover under where spare tire would/used to be.. if they are not VGs I don't know what else they are so a point in the right direction would be very helpful, thank you.
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Old 06-14-2020, 11:51 AM   #33 (permalink)
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Originally Posted by 4drviper View Post
... Also about to buy the book.. the lack of scientific knowledge on my part while trying to have some fun with this is too painful. ...
That is good thinking. Hours of frustrating testing or a mod that doesn't seem to work as expected... more information needed... report back what you learn. Would love to see updayes.
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Old 06-15-2020, 06:38 PM   #34 (permalink)
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Yeah I just would like to reiterate, I dont care about improving MPG as far as this thread goes.
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Old 06-24-2020, 01:36 PM   #35 (permalink)
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Originally Posted by JulianEdgar View Post
Pages 146 -150 of my book.
Like I said, I've no knowledge of anyone succeeding in the optimization of VGs. The metrics by which 'success' would be quantified doesn't even have the surface scratched between pages 146-150.
'It's not what you know. It's what you think you know that just ain't so.' Samuel Clements.
Any reading of a 'real' scientific investigation will 'explain' the situation.
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Old 06-24-2020, 01:43 PM   #36 (permalink)
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tiny nubs

Quote:
Originally Posted by 4drviper View Post
It was nothing more than driving around with tufts to see if I can get any serious crosswind, so the results may not sound like worthy of 8 hours.

I thought the V arrangement (opening facing either forward or backward) was not taking advantage of the full number of VGs since in crosswind, one side of the V will be overlapping too much.

From Mr. Edgar's testing, I think that would be sufficient for my purpose to reduce the sideways forces in crosswind since I already tamed it down with some airtabs behind the rear axle, for the time being.

Now I'm looking at my car how I can firmly attach rooftop strake, and tryign to find some information on low speed characteristics of MiG-15/17.

Also about to buy the book.. the lack of scientific knowledge on my part while trying to have some fun with this is too painful.

And about "anyone actually optimizing VG type, number, and location placement outside a laboratory environment", I see too many toyotas with tiny nubs around the mirror, tail light, and D-pillars. But most importantly the plastic cover under where spare tire would/used to be.. if they are not VGs I don't know what else they are so a point in the right direction would be very helpful, thank you.
Those tiny nubs are the outcome of acoustic wind tunnel testing, and simply 'tune' the natural harmonic frequency ( wind noise ) of that surface, and it's octaves, beyond the reach of the human ear.
Noise pollution is an issue which all automakers must address. Tire noise especially.
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Old 06-24-2020, 01:51 PM   #37 (permalink)
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design

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Originally Posted by California98Civic View Post
I was not vouching for the study. The OP mentioned it. I was curious. I am not willing to assume it means they work, either. Anyway, my understanding it that the Evo design's airtab placement took a lot of windtunnel time. I imagine micro adjustments matter a lot.
One reason there was a lack of widespread adoption had to do with commercial car washes and the damage rotating brushes could inflict on the VGs. Rooftop, satellite antennae must be very robust to survive the rigors of a modern car wash.
The difficulty of hand washing would be a turnoff as well. Class-action lawsuits from those snagging wedding rings on the damned things.
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Old 06-24-2020, 02:00 PM   #38 (permalink)
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Toyota excrescences

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I appreciate criticism but only when provided with a reasonable thought process. If one can say it won't work I can also say it will and it is not contributing to anything other than a blobby mess of opinions. All I got is "It ain't gonna work" without any hows. (That's how online forums get multiple threads claiming they get better mpg with hotter coolant but that's another story)

Let me give you an example. I think these will work in similar ways that roof extension spoilers work to reduce lift and drag in hatchback vehicles. Crosswind is never constant, which also promotes more abrupt separation on the trailing edge (in this case, A pillar and front roofline). The VGs when activated by crosswind, "...will prevent abrupt air separation at the trailing edges and therefore, contributes to lesser Wake creation, which in turn reduces the drag of the vehicle", quoted from explanation of hatchback rear spoiler.

This is why I also had an idea to just attach something to promote cleaner separation on A pillar but it already creates giant vortex as is which is out of my thinking capacity at this moment. End example.


I like to look at Toyota stuff since they seem to be going crazy with VGs for the past decade, which is my go-to item for when I can't modify the actual shape. The idea of letting the wind vary VG angle is probably not my original. If you look at any 15+ Toyota/Lexus vehicle from behind you can see the plastic cover under the trunk floor has four 1" x 6"(approx.) 2.5cm x 15cm plastic protrusions that are in line with the length of the vehicle. And I'm not going to bother posting visualizations of airflow under the car in varying crosswind because you should know it before you reply in this thread.

Toyota got the variable angle part down, and yes I'm still not certain if it wll help reduce the pull caused by crosswind and how to measure it if I could at all. Especially having seen that Airtabs do not "fill the wake" or "increase pressure on the trailing side", if I had a Camry or RX400 I'd already be testing the car with the strakes covered vs uncovered on windy interstate.


If those little pieces in line with airflow "creates more drag", I strongly believe it is smaller than margin of error in real world testing which is the only thing I could do so I won't be able to see it. But I will keep an eye out just in case I made wrong assumptions.
And, sure, airliners only have 2 of them but if they affected FE in any significant way, they wouldn't be on LH commercial airliners.

In crosswind, I actually do not know if they will help fight crosswind or not for the Airtabs did not reduce drag anywhere on my car. But like I explained in the OP I'm crossing fingers they would be efficient considering they're designed for vehicles much more sensitive to aero drag than cars.


And no those are 3/8". If one would care to read several posts above, we have been just talking about how 1" airtabs hurt MPG even on the trailing edge. It can be visualized how thin the laminar flow is on the front part of the car, put tufts on a straw perpendicular to the surface and give it some diagonal supports and go fir a drive.
What you're observing could be explained simply as a styling gimmick.
A perfect belly pan would be required for the diffuser to work in the first place. Failing that, it wouldn't matter what the diffuser looked like, it would be submerged in turbulence either way.
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Old 06-24-2020, 02:03 PM   #39 (permalink)
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4-8 %

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I don't see why it wouldn't work. Just adding two of them to my 2020 prius prime in the back on the black plasic piece behind the shark wing at an angle increased my fuel mileage about 4-8 percent in two different speed ranges 60-67 and 78+ but also drastically reduced my crosswind issues. Also I installed them with the high side of the vg facing forward to center of the car rather than backwards away from center.
Run the energy balance calculations on that data and compare to empirical data obtained in a laboratory, then see if you draw the same conclusions.
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Old 06-24-2020, 02:17 PM   #40 (permalink)
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better

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Originally Posted by 4drviper View Post


Here are two videos visualizing vortex from delta shaped VG with the pointy side facing forward and backward.

I just need to find some tests to tell me which is "better".
1) there are around six (6) different types of VGs in existence.
2) of those six, there would be applications for:
* sub-boundary layer thickness VGs
* equa- boundary layer thickness VGs
* and extra- boundary layer thickness VGs
3) 'solutions' require empirical testing, they cannot be mathematically modeled.
Each of all VGs, under at least the three height categories would need to be investigated.
4) Zero-yaw and crosswind condition testing would be mandatory.
5) optimum number of VG testing is mandatory
6) optimum placement of VG testing is mandatory
7) all the testing would require a laboratory environment, with a single variable allowed, the VGs themselves.
Only under these conditions would data have any scientific merit.

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