Belly pan or vortex generators?

[donee]

Hi Xringer,

I am no expert! But, the trailing edge may be too far back. Do a google of "turbulator tape" and they show the usage in sailplanes.

The problem is if the tape will add more drag than it reduces. Or a similar amount of drag then it reductes.

I doubt the same effect as a boat tail could be achieved with turbulator tape. The use in sailplanes is on already nearly perfect shapes.

I think ebdso's experience is where there are drag inducing vortices forming. These are in the areas where the top and sides of the vehicle come together, and there is a change in shape axially.

[Tango Charlie]

Turbulator strips and VG's will not smooth airflow aft of the vehicle. Their purpose is to invigorate the boundary layer and get it to 'stick'. Sorry, keep building that boat tail...

[Xringer]

Not only am I not an expert, since almost everything I know about streamlining (or think I know) comes from my experiences swimming, snorkeling, and generally messing around underwater as kid. Once, I actually took my plastic B57 model down to the lake and 'flew' it underwater. Once I had it balanced, I was amazed at it's L/D underwater, since it had none in the air (well maybe at 70 mph).
Holding a flat object (or even just my hand) outside the car window during road trips, was always very interesting to me. I was a weird kid..

To this day, I still find time to fly flat objects..
http://i46.photobucket.com/albums/f1...SPA3D/654d.jpg
http://s46.photobucket.com/albums/f1...rrent=7409.jpg
This "wing" has no washout and a super bad L/D.. But under power, it flies great.


I looked at some of those ZZ wing applications and it almost seems like the tape is introducing very tiny vortex trails off of each zigzag. Whatever it's doing, it does seem to inhibit the surface flow from separating prematurely.
Cleaner lift with less stalling? I've even never heard of ZZ tape before this week..

So, my idea of using big Zs on the TE of the CRV was to see if they would
hold the layer in place for another foot or so, before it separated.
To simulate a longer car body, to simulate a boat tail without the walls..

I guess making an actual BT is out of the question, since my wife wouldn't want to ride with me anymore..

(But wait, that could be a good thing)!

Cheers,
Rich

[Xringer]

Originally Posted by Tango Charlie

Turbulator strips and VG's will not smooth airflow aft of the vehicle. Their purpose is to invigorate the boundary layer and get it to 'stick'. Sorry, keep building that boat tail...

Haha! Well, I do have a lot of coroplas that's not doing anything right now..

[Shawn D.]

Originally Posted by Xringer

Since the tape has a much lower profile (and lower drag?) than an AirTab, the tape could hardly be seen going across the top of a CRV just before the point of separation. (1 or 2 inches back from the edge?).

It's the net effect that matters. If a device has lower additional drag itself, but results in less overall drag reduction, that's not as useful as a device that has higher additional drag, but results in more overall drag reduction.

Originally Posted by Xringer

I'm also wondering if ZigZag tape could be placed on the trailing edge of the hood? Would it help smooth the transition across the (metal-to-glass) gap? Perhaps allowing the windshield wipers to have less drag?

It would be of little use for that, for a couple of reasons:

1. The hood-to-windshield transition is a low-to-high pressure transition. Flow doesn't separate in those transitions.
2. If it did create more attachment and reduce the thickness of the boundary layer (neverminding #1 above), that would put the wipers in stronger flow, increasing drag.

[Xringer]

A good Net effect is what I'm shooting for. I guess the tape should only be used in very specif applications where it's positive effects are worth the extra drag.
One that sticks out is, the model glider being easier to control when ZZ tape was placed ahead of hinged control surfaces. IIRC, after the ZZ tape was installed the pilot no longer needed to switch to hi-rate mode on his controls.
(Maybe he was paying a price with a lower L/D or less airspeed).
----

I've seen wipers that went down out of the air stream when off. But mine are out there dragging all the time.. I guess using the smallest profile wipers I can find will be about it.
I noticed a spoiler-wing on my kid's X3 wiper. I guess it's going to provide more down pressure.. But if that pressure isn't really needed? Paying the price in drag.. Adding to the net..

[Otto]

I seem to recall a sailplane study of ZigZag tape, testing for the optimum zigzag angle. Seems like it was ~60 degrees, but I'm not sure. This stuff was on the vertical fin of a Stemme S-10 motorglider that I looked at, and was about ~0.30" thick. Got better control authority because the rudder was operating in cleaner air closer to the skin, making the rudder more effective and efficient.

Maybe the way these things work is that each zig makes its own little vortex, which rotates CW or CCW. Anyhow, the down side of the rotation of one zig flow meets the up side of rotation of the next zig flow, and they conflict and cancel each other out to some extent.

That's the theory behind why owl feathers are quiet, and why NASA et al are developing serrated trailing edges on the new generation of jet engine exhaust nozzles. Also, makes for better mixing of exhaust columns for less shear between axial flow rings, so less noise.

I hate car or other wind noise, so wanna try zigzag tape on the A pillar of my Bimmer. The inner sides of the mirrors already have little pimples as quietening turbulators, so some zigzag tape on the A pillar won't hurt.

Might put some ZZ tape just in front of the edges of the visora on my motorcycle helmets, to see of it lessens gap noise, which would be a big relief.

[Xringer]

That 'A' pillar application seems like one that can work. (Without too much of a drag cost).

After reading about this stuff and looking at the sim pics, it seems like a tape with a saw-tooth edge on the leading side would work too.

The VGs here look like little air foils placed at an off-angle to the wind. (bottom third of the page).

Each of these air foils looks to be making a CW vortex. Thinking about ZZ tape's CW & CCW vortexi stacked shoulder to shoulder.. Like compressed streams that are rotating in opposite directions.
I have to wonder why they aren't canceling each other out?

[Shawn D.]

Originally Posted by Xringer

I have to wonder why they aren't canceling each other out?

Imagine how kitchen beaters "flow" together.

[Xringer]

The blades interlace?

Whatever it's doing, it's not like EM fields being canceled out while flowing in twisted pair wire.