Is there an Aerodynamicist in the house?

[rtcosic]

Hmmm… seeing the video, it’s more like vortex shedding/flutter at higher flow rate. Add the Blutack and see if you can dampen it.

As to your temptingly exotic suggestion of adding spoilers or strakes… the agricultural approach would be to take the snips to the trailing edges and cut/twist loads of wee distorted serrations. But might spoil the look!

Exactly what I had in mind. It's nearly half a century since I did any Fluid Dynamics, I was hoping a nice young chap such as yourself would have access to JPL standard CFD programs and would design a precise solution! As precise as can be implemented with aero grade snips, needle-nose pliers and a carefully calibrated twist of the wrist that is.

I'll play about tomorrow and let you know the outcome.

 

[redlig]

Starts at Fan setting 3 then up to max of 5 and back to 3. No issues at 1 and 2 of course

Now everyone will want that. Could it be a resonance / pulse caused by the flaps being too heavy and forming a high pressure that eventually overcomes the weight of the flaps and so on . Just a guess. try holding one flap open and see what happens then hold one flap shut and again see the result. Don't know if it will help but it will while away a few minutes.

 

[Screwdriver]

It’s definitely flutter caused by positive feedback and chaotic airflow. Weight would help but might just change the frequency of the beating. If they are linked, you remove the feedback and they won’t flutter.

 

[brightspark]

If I can't solve it I'll stick the 150mm plastic version of this back on.

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there a pain in the a,,rse and flap in the wind. the inline dont

 

[rtcosic]

It’s definitely flutter caused by positive feedback and chaotic airflow. Weight would help but might just change the frequency of the beating. If they are linked, you remove the feedback and they won’t flutter.

Super Glue and fishing line seem to be in my future.

Deep Joy.

 

[angellonewolf]

Yes

Flow too high for these louvres

Louvres too light rather than too heavy.

Youtube upload in progress.

add a bit of blu tac to ajust the weight of the loovers get the right weight and stick a weight to it

 

[MichaelV]

Exactly what I had in mind. It's nearly half a century since I did any Fluid Dynamics, I was hoping a nice young chap such as yourself would have access to JPL standard CFD programs and would design precise solution!

I’m a humble solid mechanics wrangler, but have worked for years with those very clever fluids gurus, grappling with flow problems. Does look like classic aeroelastic flutter, so your instincts were absolutely correct.

JPL… indeed. This class of problem is really compute intensive.

Another wee tweak would be to “gum up” the hinges, thus changing frequency content and adding damping.

 

[angellonewolf]

there a pain in the a,,rse and flap in the wind. the inline dont

yes they do i put an inline in my bathroom and on a night when the winds where high the noise was pritty bad

 

[rtcosic]

there a pain in the a,,rse and flap in the wind. the inline dont

Too true. I had the cowl and single flap type in Pembrokeshire and they did that. They also flapped when there was no flow. Bernoulli and all that.
I solved that by supergluing a little circle of steel to the bottom of the flap and a tiny circular magnet into the fixed part.

So far in Warwickshire, I haven't experienced any wind at all!

 

[rtcosic]

...

Another wee tweak would be to “gum up” the hinges, thus changing frequency content and adding damping.

Is that a posh way of saying experiment with Blu Tack?

 

[MichaelV]

Is that a posh way of saying experiment with Blu Tack?

Aye; or to use my native idiom, clary a taste of glar in round them hinges!

 

[Screwdriver]

Super Glue and fishing line seem to be in my future.

Deep Joy.

I was thinking a bit of TiG welding wire to form a makeshift connecting rod. If there’s any overhang at the back, could hide it behind the shutter and if you’re really lucky, enough overhang just to drill a tiny hole to form the eye.

 

[dobbslc]

I wonder if you weighted the top flap with blue tac it would stop? It looks like a procession lead by that top flap.

 

[Screwdriver]

I wonder if you weighted the top flap with blue tac it would stop? It looks like a procession lead by that top flap.

if I was going to go that route I’d solder on some lead weight. Not something you want to be maintaining for the rest of your life.

 

[brightspark]

if I was going to go that route I’d solder on some lead weight. Not something you want to be maintaining for the rest of your life.

use the stick on ones of ally wheels

 

[dobbslc]

If it works you could weight the Blutac and then epoxy the same onto the inside, that won't bugger the finish.

 

[Member 32799]

Send it back to china

 

[mtt.tr]

Whats the problem, they are just applauding your cooking

 

[voipio]

A drop of viscous fluid (think Rocol Kilopoise) on each of the hinges, to make them work like damped toilet seats. The flaps move all too easily, since they are new, resulting in the observed unstable airflow.

 

[Robert Weaver]

1 and 2 probably laminar flow, the others in turbulent flow because of interaction and beating, as mentioned earlier. Linking them together might reduce the problem, but not eliminate it. More mass if you can, to make the individual flaps less responsive to pressure fluctuations.