Making a "Kammback" with the Sunroof and Rear Window

[jeff88]

Cd- Thanks for those CFDs. Can you help me decipher them, I don't know what it all means. Is rear window and rear passenger windows all open a good thing? Or is my idea going to work?

Can you do one with the sunroof, rear window and rear passenger windows open, I would like to see what happens then.

Also, the video you posted doesn't seem to work, at least for me.

[Cd]

I ran some quick and sloppy tests of the Cd ( or cD ) and in both cases the drag went way up. More so with both windows down versus just the sunroof ( around 21% with both windows open )

I would guess that the airflow is creating some major turbulence in the area right before it enters the low pressure zone ( the open windows ) as well .

Look at the ( virtual ) increased frontal area that the airflow is causing. This test only took into account the drag coefficient and not the total drag including the frontal area.

So, no apparently this test will not show any benefits in drag reduction.

If you have the free time, and are willing to buy a battery powered carbon monoxide alarm, I say go for it ! A real world test is always nice to have in the archive here, even just to prove that it doesn't work.
It can be referenced to when the question gets asked again.

http://www.hardwareworld.com/Carbon-...d-pYB7HRK.aspx

If I did such a test, I would make sure that the air had as smooth a passage as possible to the back. If the seats in the rear fold down, this would be a good time to do it. Also i would add tufts at the rear of the vehicle ( inside the vehicle ) to show the direction of the airflow.

As far as deciphering the images, I'm clueless and would have to point you to Aerohead.

I can tell that there is a major disturbance in the force ...er of the air entering the open windows / sunroof but that's all i can decipher. I'm puzzled at the change in pressure at the front of the vehicle once the windows are opened.
I suspect this software has some bugginess. ( But hey its FREE ! so no complaints here ! )

If i have time i will try the open window as well as sunroof idea as well. Perhaps tomorrow.

[jeff88]

Originally Posted by Cd

As far as deciphering the images, I'm clueless and would have to point you to Aerohead.

Aerohead (or anybody), can you help me with what the images mean, I have never tried breaking down a cD image before.

I just happened to have bought a CO alarm for my new house (laundry closet is in hallway directly across from my bedroom and there is a gas dryer) and I haven't installed it on the wall yet, so I may put it in the truck while not doing laundry/in the house.

Now I just need to get this rear window fixed, so I can try this mod out!

[aerohead]

Originally Posted by jeff88

Aerohead (or anybody), can you help me with what the images mean, I have never tried breaking down a cD image before.

I just happened to have bought a CO alarm for my new house (laundry closet is in hallway directly across from my bedroom and there is a gas dryer) and I haven't installed it on the wall yet, so I may put it in the truck while not doing laundry/in the house.

Now I just need to get this rear window fixed, so I can try this mod out!

I'm struggling to 'believe' the software's isobaric interpretation.
The image does not appear to do a proper accounting of velocity pressure vs body location.
The thing to bear in mind is that around the side-view mirrors,the air has achieved its maximum velocity and lowest pressure.
With a squareback,these velocities pretty much remain constant until the trailing edges of the body where it breaks away.
*with the window down you destroy the flow support surface and the air must flow into the void.
*This destroys the flow behind the window.
*The lowest pressure is at the side mirrors.
*The pressure behind the vehicle is higher than at the side-
view mirrors.
*If you open the window and backlight,air will flow from back to front.It's got to,based upon the pressure differential.
*This counter-flow triggers shearing forces which generate vortices which rob power.
*Attempting to use the cabin as a duct forces air to flow within an extremely
high-drag inner wall boundary of tremendous surface roughness,not to mention everything within the 'duct.'(seats,headrests,shoulder belts,etc.)
*The interior flow steals kinetic energy from the exterior flow,giving it no chance for any pressure recovery in the wake region.
* In an aircraft,the only reason you'd use a duct,is to channel air to the embedded engine,who's tailpipe and or fans develop a net thrust propulsion.