passively variable angle VG; fixes crosswinds

[gregersonke]

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.

[California98Civic]

Originally Posted by 4drviper

I tried quoting but it won't accept more than 3 so I tried to just lay them out. I don't think any of them were replying to you tho... not too sure what I was exactly thinking but yeah.

Not trying to attack you. Just responding to your idea with some feedback.

Originally Posted by 4drviper

And yes. Gosh I'm going to suck at writing thesis..es...

You'll do fine with your thesis. You'll write drafts. You'll get feedback. Your next draft will improve. Write lots of drafts. Is this project part of the thesis?

Originally Posted by gregersonke

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.

How did you do your testing? There are lots of variables, not just placement of VGs, that could contribute to changes in FE. I am not saying I think the VGs did not work for you.

[4drviper]

Originally Posted by gregersonke

Also I installed them with the high side of the vg facing forward to center of the car rather than backwards away from center.

https://www.youtube.com/watch?v=VDmqxGxvSL0

https://www.youtube.com/watch?v=g-Tkpwr5v-0

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".

[JulianEdgar]

Ok, with this approach:

Fit fin-type vortex generators on the hood in front of the windscreen to change A-pillar separation and so reduce susceptibility to crosswinds.

I don't think they will work.

1. Car stability is most determined by the lateral centre of pressure location. If the car turns away from wind gusts (most common), you need to move the centre of pressure rearwards. Rear fins are the easiest way of doing this, and in my testing on a Gen 1 Insight, have worked extremely well.

2. Separated flow on the downwind side of the car will, however also cause instability (as you earlier indicated). The yaw angle at which downwind side separation occurs depends on:

- the shape of the front corner of the car
- the shape of the A pillar
- the surface roughness of the side of the car

The only thing that your vortex generators could impact on this list is the behaviour of the A pillar - and the hood location is a long way from the A pillar.

I'd try the VGs on the A pillars and the front corners of the car.

[gregersonke]

Originally Posted by California98Civic

How did you do your testing? There are lots of variables, not just placement of VGs, that could contribute to changes in FE. I am not saying I think the VGs did not work for you.

Truthfully, I did it for the crosswinds not fuel economy. The fuel economy was the 20k miles before and thus far the 4k after. But an observation afterwards of a sudden spike in fuel economy immediately following was a bonus on my part and it's been pretty consistent, i've not seen a single decrease in fuel mileages. I've even beaten previously set fuel economy highs on trips with higher average speeds no less. Where I used to get 44 to no more than 47mpg covering a large part of a 72 mile each way journey at 80-82mph now I'm getting 51-56mpg (no battery) and up to 78 mpg (previously 72-75) mpg when I daily charge each way. Which would require me driving 70-75mph before to achieve and now doing at higher speeds. With the Covid 19 traffic, I've had to speed up to avoid basically being run over on the I5 interstate route I take every day. It's pretty crazy that such a simple modification would make so much difference.

[gregersonke]

All I can say, is try it the way I have it. See where it goes for you. If you have a way to wind tunnel test it, I'd be curious as to the results on that.

[4drviper]

I wish I was studying this.. it would be more fun. It's just a hobby.

Originally Posted by JulianEdgar

...
1. Car stability is most determined by the lateral centre of pressure location. If the car turns away from wind gusts (most common), you need to move the centre of pressure rearwards. Rear fins are the easiest way of doing this, and in my testing on a Gen 1 Insight, have worked extremely well.

2. Separated flow on the downwind side of the car will, however also cause instability (as you earlier indicated). The yaw angle at which downwind side separation occurs depends on:

- the shape of the front corner of the car
- the shape of the A pillar
- the surface roughness of the side of the car

The only thing that your vortex generators could impact on this list is the behaviour of the A pillar - and the hood location is a long way from the A pillar.

I'd try the VGs on the A pillars and the front corners of the car.

So, from #1 I understand that VGs will "attract" the center of pressure toward their downstream area.
And from #2 I understand that what I was going to do could easily (when overdone) worsen the crosswind instability by keeping the center of pressure even more off.

I was also considering directly placing them on the A-pillar which would also deal with the buffeting with open window at medium to high speeds. So I start at the bottom of A-pillar and where should I stop? For some reason I feel putting them on the roof between the top of B and C-pillars would be effective.

Speaking of 1G Insight, are you the person who wrote Autospeed blog? That's where I read about the idea to place airtabs under the car.

Originally Posted by gregersonke

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.

Feel free to consider this fairy tale but I have experienced surprisingly good mpg as I increased crusing speed a bit which made my rpm higher so the BSFC was actually lowered more than the increased drag so I got better MPG going faster than usual.

I recognize those VGs. I considered them at one point but they were too big and thick for my taste so I passed and then they went out of business so yeah.

I tend to believe VGs near trailing edges of box shapes reducing drag (probably due to reading Airtab marketing material too much) but trying to work with a sedan I feel there are a lot more that I should consider but don't even know.

[California98Civic]

Originally Posted by gregersonke

Truthfully, I did it for the crosswinds not fuel economy. The fuel economy was the 20k miles before and thus far the 4k after. But an observation afterwards of a sudden spike in fuel economy immediately following was a bonus on my part and it's been pretty consistent, i've not seen a single decrease in fuel mileages. I've even beaten previously set fuel economy highs on trips with higher average speeds no less. Where I used to get 44 to no more than 47mpg covering a large part of a 72 mile each way journey at 80-82mph now I'm getting 51-56mpg (no battery) and up to 78 mpg (previously 72-75) mpg when I daily charge each way. Which would require me driving 70-75mph before to achieve and now doing at higher speeds. With the Covid 19 traffic, I've had to speed up to avoid basically being run over on the I5 interstate route I take every day. It's pretty crazy that such a simple modification would make so much difference.

Well longterm fuel economy returns can be hard to argue with, and I don't especially want to. It's just that there is a lot of hype about those tabs. It seems you may have happened on some very good placing of the tabs. I have read that placing matters a lot and that tiny changes can have notable effect. I think it would be really informative to see pictures of how you have placed them. Wanna post some pics and measurements?

EDIT: Ooops... missed the photo you posted. Still, what are the relative measurements to the edge of the lip, height, and details like that.

[gregersonke]

Originally Posted by 4drviper

I wish I was studying this.. it would be more fun. It's just a hobby.


So, from #1 I understand that VGs will "attract" the center of pressure toward their downstream area.
And from #2 I understand that what I was going to do could easily (when overdone) worsen the crosswind instability by keeping the center of pressure even more off.

I was also considering directly placing them on the A-pillar which would also deal with the buffeting with open window at medium to high speeds. So I start at the bottom of A-pillar and where should I stop? For some reason I feel putting them on the roof between the top of B and C-pillars would be effective.

Speaking of 1G Insight, are you the person who wrote Autospeed blog? That's where I read about the idea to place airtabs under the car.




Feel free to consider this fairy tale but I have experienced surprisingly good mpg as I increased crusing speed a bit which made my rpm higher so the BSFC was actually lowered more than the increased drag so I got better MPG going faster than usual.

I recognize those VGs. I considered them at one point but they were too big and thick for my taste so I passed and then they went out of business so yeah.

I tend to believe VGs near trailing edges of box shapes reducing drag (probably due to reading Airtab marketing material too much) but trying to work with a sedan I feel there are a lot more that I should consider but don't even know.

When I increased cruising speed before, I would get significantly worse average round trip gas mileage in the 40s, I would have to slow down to get 50s. now it's in the 50s consistently and I'm getting what Toyota says I should get in the City at highway speeds. Also, they are still selling these things on Amazon where I got a 6 pack for 11 bucks. My goal was purely for crosswinds which these actually do a pretty good job at. My theory was the curved rear window down the middle of the prius prime would benefit as the angling I used was similar to the Prius TRD setup.

[gregersonke]

Originally Posted by California98Civic

Well longterm fuel economy returns can be hard to argue with, and I don't especially want to. It's just that there is a lot of hype about those tabs. It seems you may have happened on some very good placing of the tabs. I have read that placing matters a lot and that tiny changes can have notable effect. I think it would be really informative to see pictures of how you have placed them. Wanna post some pics and measurements?

Pretty sure the spacing is 11 inches apart at the farthest point. I'd have to double check the narrow point though.