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Wind vibration/noise/resonance reduction.

Wind vibration/noise/resonance reduction.

Wind vibration/noise/resonance reduction.

(OP)
It has been a long time since I have studied aerodynamics.  Maybe someone here can easily suggest an answer to me.  And, thank you in advance for your input on a question that is so basic as mine.

I just installed a new Kargomaster Congo Cage (Rack) on my 2004 Jeep Wrangler.  The Cage is built from 1.625" round, hollow, smooth, steel bars.  I plan to alternate between a Surco Safari Basket and Kargomaster Utility Bars that attach to the Cage in order to haul stuff (camping equipment, kayak, etc.).

Here is the problem--very loud, annoying wind noise/humming because of the wind turbulence around the top front round bar at speeds above 40-60 mph.  It is almost like the sound of an aluminum baseball bat when it is swung through the air at a high speed.

Some solutions I have seen suggested include:

Install a front wind deflector/fairing to the front edge of the Cage and my windshield--similar to those you see on Yakima racks/baskets.  These are designed to deflect the wind up and over the Cage/bar/rack/utility basket.

The problem with the Yakima fairings/deflectors is that they are rounded to adapt to a cartop that is not flat like a Jeep Wrangler.  As a result, it would not only look bad, but may not be as effective.  If this solution would be preferable to the others, I could purchase a piece of black plexiglass and fabricate a fairing.  If I do this, how much will the angle at which I install the fairing affect its effectiveness?

The next alternative is that Yakima has deflectors that attach to the back side of the front bars and kind of look like a wing or spoiler.  So, the wind hits the front of the round bar, and as it flows to the back of the bar, the "spoilers" interrupt and supposedly reduce the vibration/humming.

Lastly, I have read that one fellow Jeep Wrangler owner with the Kargomaster Congo Cage, wrapped his front and rear top crossbars in pipe insulation (using some black duct tape to secure it).  He suggests that it disrupts the airflow around the front and rear crossbars when compared to the smooth metal surface of the hollow steel bars enough to almost entirely dampen the vibration/humming noise.

So, my science/turbulence/aerodynamics question for the day is, "Which approach will most effectively dampen the vibration of that 1.625" round, hollow, steel, top front bar of my Cage and reduce the humming/turbulance/wind noise?"

Thanks again.

RE: Wind vibration/noise/resonance reduction.

Yep, drag a round tube through the air fast and you get a vortex street behind it.  You'd think Kargomaster would fix it for free, given the price they charge.  Yeah, right.  

First thing I'd try is a rope wrapped tight around the tube in a fast- helix spiral, like the spiral fins they put on car radio antennas (and smokestacks).  If it helps at all, keep it in mind for the a-pillar tubes.  For the straight cross-tubes, I'd try to splice on a trailing edge, first mocking it up in cardboard or cheap plastic to see how small it could be and still be effective.



Mike Halloran
Pembroke Pines, FL, USA

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