The XV-JP Needs Help, Please, from a Jeep Aerodynamicist. (Really)

NH Moto Expo

Adventurer
I'm wondering if a brush style door sweep might be the best idea? A semi stiff brush will deflect the air without actuall touching anything. Kind of like the brushes found on the side of UPS trailers to deflect spray. You can either attach it to the cap or the roof of the jeep.

Different than rubber and IMHO will look better.
 

4xdog

Explorer
I've spent lots of time in rheology, the flow of materials, but that's usually fluids not gases...

It must be just hitting a resonant frequency under certain conditions, like blowing across a beer bottle opening. You are probably on the right track to just "change something". You may just need something to disrupt the airflow enough to prevent that resonating.

I kinda like this thinking. If one looks at most recent fixed radio antennas, they're non-uniform in cross section with sort of an spiral pattern. Most current sunroof deflectors have a toothed or stepped front edge to reduce the noise over the older smooth-edged style. Both of these seem to work pretty well.

Rather than fill the gap, it might be a worthwhile experiment to double-stick tape something to the outside edges so the flow isn't laminar going into the gap. I was looking online for pix of the black rubber strips with a sawtooth ribbed pattern on them that are often sold as corner protectors for car bumpers. Here's an image that gives an idea:
bumper-guard-801.jpg



It might be interesting to see what happens if a ribbed section
were stuck to the Jeep roof at various places along the gap to break up the uniform cross section. Might make the noise worse, or better, but almost certain to be interesting...

Don

 
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mhiscox

Exp. Leader Emeritus
Jay: Thanks for the warning about the paint. I probably would have failed to think about it.

Everybody else: Good ideas. Seems like doing something is the important first step. I'll see what I can find that won't look too fugly, and report back.
 

mhiscox

Exp. Leader Emeritus
Here some that maybe wouldn't look too hokey ...when compared to a swimming pool noodle.
That's the ticket, I think. Gets around the disruptive looks of something homemade, and it's actually made for the purpose, unlike pool noodles and gutter screens. They're the right size, come ready to attach, and are certainly good enough to test the idea that just making the air flow do something different will get rid of the howl.

Plus they seem to imply they're for Corvettes and tractor-trailer rigs, and the XV-JP is about halfway in-between . . . ;)

So I just ordered them up and will report back as soon as they arrive. And thanks for the help; I really appreciate the advice.
 

Recce01

Adventurer
a very quick and inexpensive test you can do would be a mountain bike inner tube or two? Just slide them up there and add air. We used to do this between cab and bed of trucks with stereo boxes that pass through. It worked well as an insulator. It may have an effect on wind noise?
 

GR8ADV

Explorer
Ok, maybe it is the engineer in me that would want to limit the variables. My thoughts are that we still have not determined if that gap is in fact your problem. Possibly it is the roofline, the lights, or some other surface, etc. While you wait for that special brown truck that always brings good things, I would try to re create the problem, pull over to the shoulder and then shove anything I could in there from a towel to a pool noodle, to see if it affects the problem. Ok it will be ugly but likely only for a few miles.:) If it changes the situation then at least you know for sure what the problem is. I am not sure anyone knows the impact of the vortex thingies; maybe nothing, maybe better maybe worse.
 

mhiscox

Exp. Leader Emeritus
Well, we've got some Airtabs. A whole bunch, in fact, of which we'll start with two.

Airtabs--when not painter yellow to match a Corvette--look like this:

P1010592.jpg

P1010593.jpg


If you want them to improve aerodynamics or reduce spray off the back of your trailer, you use lots of them an inch apart. But all I want to do is to do something different to the airflow, so I just put a couple of them in a likely location.

It's a peel-and-stick application, and after cleaning the area well and prepping with some alcohol, I stuck them down and they seem to hold pretty well:

P1010589.jpg


I've got two of them set about three inches back from the windscreen and a bit less than a foot from each side. I bought the paint I'd need to make them a matching silver, but am not going to bother since you can barely see them; the truck is too tall, and it's pretty dark in that area.

P1010591.jpg


You can see them a bit it this photo I took from the front standing on a stool.

P1010594.jpg.


So far, so good. Nothing to do now but drive around. The wind howl was not routine, so I'll need to have the right conditions before I can even guess whether it I've made things better or worse. I'll let you know what I learn just as soon as I learn something.
 

reece146

Automotive Artist
If you still are having issues you may want to add some on the vertical face above the front door windows and/or on the roof. The idea is to change the flow dynamic. If you can keep laminar flow over the body longer then the noise making turbulence may be out of the range of the panel that is fluttering and making noise (if I am recalling the original issue correctly).

Try it like you've got done first though... I'm wondering if the air in that gap will be close to stagnant already so the air tab will not really do much to change flow... but it might be enough to change the pressure profile even if not how they are intended to be used.

 

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