air dam and vortec generators

[Hateful]

I found a few extra magnetic labels, so I attached some fuzzy material to them and placed them before my over sized fins. I'm sure they are the wrong size and placed in the wrong place too, according to someone.

[SL8Brick]

Originally Posted by Hateful

I'm sure they are the wrong size and placed in the wrong place too, according to someone.

I was just tryin' to be helpful.

[sonyhome]

Originally Posted by civic_matic_00

they seem to work just fine judging from the reaction of water dorplets when it was raining a couple of days ago. the water droplets were zipping down the window a lot faster during the time. I could see the difference between the water droplets reaction on the area where airtabs are installed to areas where no VGs are present. the middle of the window had water dropplets that were zipping down fast, the outer part of the windows (both sides) water droplets were moving down slower.

My understanding is that the airtabs should create a pocket of stagnant air in the back, with the air-flow forming a (virtual) teardrop shape behind the car.
Therefore, the water droplets should NOT move there, or at worst move upwards if there's turbulences comming from under the car and disturbing the stagnant air.

Am I mistaken?

[Hateful]

I don't mind the input and do like looking at what others have done. I just tend to follow my own line of thinking and don't try to make an exact copy of what I see. There are several things to consider; such as how fast can I go before these things go flying off. Smaller ones would stay on better at speeds I do not drive. I've been at 65mph and they seem okay. A car company would have to be sure at much higher speeds.

My thoughts on the fuzzy stuff is that it will cause smaller swirls before the fin and help the air move around the fin more easily;a pretreatment of sort.

By all means feel free to comment; with my off the wall mods I expect it.

[dosco]

Originally Posted by sonyhome

My understanding is that the airtabs should create a pocket of stagnant air in the back, with the air-flow forming a (virtual) teardrop shape behind the car.
Therefore, the water droplets should NOT move there, or at worst move upwards if there's turbulences comming from under the car and disturbing the stagnant air.

Am I mistaken?

Yes, you are mistaken. The airtabs are supposed to create vortices behind then that reattach the airflow to the vehicle. "Stagnant air" is not necessarily attached air depending on the location on the vehicle. (Technically, there are stagnation points at every inside and outside corner of the car with "stagnant air")

Civic's comments make sense and are to be expected for vortex generators placed on that location of a car.

[sonyhome]

Ah maybe I see: Since the incline of the rear window is low angle, the vortices are pressed back onto the rear window into a laminar flow floating above a small turbulent layer...
There should however still be a stagnant pocket just behind the airtabs, between the car body and the vortices, before the vortices get pushed down and the air reattaches to the window...

[civic_matic_00]

not really sure how they are working and I can't really say I have a full understanding of the theory of VGs. from what I have read is that the stagnant air is somewhat energized causing a better flow of air on the surface (don't know how accurate that is) and therefore reduce drag and reduce the mechanical effort in moving the car.

before I had the airtabs the water droplets on my rear window swirls instead of simply moving from top to bottom. with the airtabs, water droplets go straight down. I take that as an indication that the airflow now has less drag on the rear of the car which may result in FE gains. at any rate, it is an interesting experiment.

all of this remindes me of shark scales which looks a lot like miniature VGs on the shark's skin. this is said to be the secret in their ability to swim fast and before has baffled scientists since they thought that the scales design would actually result in more drag.

[dosco]

Originally Posted by sonyhome

Ah maybe I see: Since the incline of the rear window is low angle, the vortices are pressed back onto the rear window into a laminar flow floating above a small turbulent layer...

Sort of. The vortices add energy to the airflow to reestablish the boundary layer, thus resticking the airflow to the windscreen.

There should however still be a stagnant pocket just behind the airtabs, between the car body and the vortices, before the vortices get pushed down and the air reattaches to the window...

Perhaps, depends on the thicknes of the boundary layer, energy in the freestream, etc. Odds are there are probably very small "bubbles" behind the airtabs, but I would speculate they are very very small. Like 1" long or smaller.

[sonyhome]

So for a 2-box design, I wonder if airtabs would be better or if a spoiler would, or if both kinda achieve the same in that case.

I suspect it would not be good to have the air go straight down the vertical rear window of an SUV.

Would civic matic benefit from adding more airtabs, but this time at the end of his trunk? After all, he too will have a vertical bumper...

[dosco]

Originally Posted by sonyhome

So for a 2-box design, I wonder if airtabs would be better or if a spoiler would, or if both kinda achieve the same in that case.

I suspect it would not be good to have the air go straight down the vertical rear window of an SUV.

Would civic matic benefit from adding more airtabs, but this time at the end of his trunk? After all, he too will have a vertical bumper...

I'm not sure what a "2-box" is, but I can tell you that a spoiler and a vortex generator are not the same thing. A spoiler - on a car - is either merely a decoration or a device to create downforce.

In other news, I built a "knock off" Airtab with meat tray foam. It sits next to a "chevron" type vortex generator on the aft end of the roof of my '99 Camry.

I suppose I should have done some wool tuft testing to characterize the airflow back there, but I do know from looking at the rain and snow on the back there that there is a large separation bubble that is huge at ~30 mph and is sizeable (but smaller) at ~60 mph.



A vortex generator is a way to add energy to airflow for one of two reasons, to reattach separated airflow, or to "clean up" turbulent airflow.