Is there an Aerodynamicist in the house?

[rtcosic]

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.

Ah! Nip up the fold that forms the 'hinge'.
That has promise.
Thank you.

Putters off to calibrate the pliers.

 

[Screwdriver]

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.

All I know about aerodynamics and especially turbulence is that the subject is fantastically complicated, right up there with rocket science. We can all see what's going on with these lightweight aerofoil sections and that damping will help reduce it but it is important also to define what "the problem" is and exactly what "it" you want to eliminate.

From my perspective the OP wants to stop the excessive beating where there appears to be some positive feedback leading to {lit.} chaotic behaviour. Mass and damping will certainly reduce the effect but will it merely move it to a different frequency? OTOH I suggest linking say the middle two will prevent them from creating a feedback loop where one "wing" goes bonkers and amplifies the effect to the others.

The other thing to remember is that the sheer power of a fan acting on such a relatively small surface area is enormous. Does make me wonder if there's something we're not being told regarding the installation and whether or not the vent volume and cross sectional area is compatible with the fan unit.

Either way a fascinating problem and an hilarious video though to be honest, I am not entirely sure why I find it so funny. It just is!

 

[voipio]

Funny 'cause it's a bit like watching the cancan?

 

[Munkul]

I'm no expert, but:
It'll all be mixed/turbulent flow at any speed, as the airflow is balanced against the shutter opening weight.

It's definitely resonance at the fan setting 3, and you've two realistic options: Damp the movement (read: jam the flaps a bit) or add mass.

 

[jenki]

I think Munkul is correct some sort of resonance, is the extract pipe well supported could it be a pulsed flow in the pipework remember the pictures of early gas turbine engines and the exhaust flow.

 

[Dilkris]

Ah! Nip up the fold that forms the 'hinge'.
That has promise.
Thank you.

Putters off to calibrate the pliers.

I'm on this guys team....

 

[Gareth J]

You can ones that actively open/shut, all linked together via an actuator. Much better in windy spots where they'll flap anyway. Not sure if available as a separate unit or always built into a fan.

 

[skotl]

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

That's quite satisfying to watch

Spoiler: (but)

I'd hate it if it was on my house!

 

[rtcosic]

That's quite satisfying to watch

Spoiler: (but)

I'd hate it if it was on my house!

70 other viewers seem to agree with you so far.