The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

In article , Harry
Bloomfield scribeth thus
The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.



Yes quite correct, as can be seen by some spirals here on the top of the
Emley mast in Yorkshire..


http://tx.mb21.co.uk/gallery/gallery...=336&pageid=32
--
Tony Sayer

On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.



--

Graham.

%Profound_observation%

On Tue, 02 Jun 2015 22:42:43 +0100, Graham. wrote:

On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.

Does it depend which hemisphere you're in?

That is what I was thinking, as correolis would suggest it should be the
other way darn sarf.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bob Eager" wrote in message
...
On Tue, 02 Jun 2015 22:42:43 +0100, Graham. wrote:

On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.

Does it depend which hemisphere you're in?

On 03/06/2015 08:30, Brian-Gaff wrote:
That is what I was thinking, as correolis would suggest it should be the
other way darn sarf.
Brian

But its far to localized for Coriolis to have any effect.



-- From the Sofa of Brian Gaff Reply address is active "Bob Eager"
wrote in message
...
On Tue, 02 Jun 2015 22:42:43 +0100, Graham. wrote:

On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.

Does it depend which hemisphere you're in?



--
CB

"CB" wrote in message ...
On 03/06/2015 08:30, Brian-Gaff wrote:
That is what I was thinking, as correolis would suggest it should be the
other way darn sarf.
Brian

But its far to localized for Coriolis to have any effect.

Must explain why it's seen with plug holes.

-- From the Sofa of Brian Gaff Reply address is active "Bob Eager"
wrote in message
...
On Tue, 02 Jun 2015 22:42:43 +0100, Graham. wrote:

On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it
about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.

Does it depend which hemisphere you're in?



--
CB

CB wrote:
On 03/06/2015 08:30, Brian-Gaff wrote:
That is what I was thinking, as correolis would suggest it should be the
other way darn sarf.
Brian

But its far to localized for Coriolis to have any effect.

Whoosh!

Tim

Bob Eager wrote:
On Tue, 02 Jun 2015 22:42:43 +0100, Graham. wrote:

On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.

Does it depend which hemisphere you're in?

https://www.dropbox.com/s/8ii3xyg2os...ncer.jpeg?dl=0

Tim

"Graham." wrote in message
...
On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.

Not true.
http://en.wikipedia.org/wiki/K%C3%A1...ing_problem s

On 02/06/2015 22:42, Graham. wrote:
On Tue, 02 Jun 2015 21:49:43 +0100, Harry Bloomfield
wrote:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Yes, I knew about that 30 years ago, but what I couldn't get my head
around (if it's true) is that it only works when the spiral is in one
particular direction, not the other.



Urban myth. It works because it suppresses vortex shedding by disrupting
the axial symmetry.

The problem with vortex shedding is resonance when the natural frequency
of the chimney, tower, or whatever coincides with the vortex shedding
frequency.

On 03/06/2015 13:34, newshound wrote:

The problem with vortex shedding is resonance when the natural frequency
of the chimney, tower, or whatever coincides with the vortex shedding
frequency.

Witness the Tacoma narrows bridge.
https://www.youtube.com/watch?v=nFzu6CNtqec

Usually described as forced resonance the full story is of aeroelastic
flutter but for the purposes of a Usenet post it can be thought of as
forced resonance.

On 03/06/2015 13:34, newshound wrote:

Urban myth. It works because it suppresses vortex shedding by disrupting
the axial symmetry.

It's because the ridge acts as a vortex generator, but you get a small
controlled continuous one. Without you can get the chimney moving to the
side one way, which tends to increase the attachment of the airflow on
that side, so you get lift (in this case laterally) so the chimney keeps
moving. Until finally the force is too big for the aerodynamics to
overcome, it stops moving sideways, the lift collapses, the force goes
and then the chimney goes back to the middle. On the way of course the
process reverses, and you get lift going the other way - hence the
oscillation.

Vertical ridges would do just as well - except they have to be on the
side as the wind sees it. So much easier to put a spiral.

Andy

Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about having
the wind help draw gases out of the chimney. In fact it about preventing
wind eddies shaking the chimney to destruction.


Yep. Vortex shedding.

Tim

On Tuesday, 2 June 2015 23:07:30 UTC+1, Tim+ wrote:
Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about having
the wind help draw gases out of the chimney. In fact it about preventing
wind eddies shaking the chimney to destruction.


Yep. Vortex shedding.

Tim

To bring this closer to DIY - wrapping a spiral of cable around the
top rung of a stepladder being transported on the roof rack of my car
results in a much quieter journey. (If the top rung is at the front.)

John

On 03/06/2015 07:12, wrote:
On Tuesday, 2 June 2015 23:07:30 UTC+1, Tim+ wrote:
Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about having
the wind help draw gases out of the chimney. In fact it about preventing
wind eddies shaking the chimney to destruction.


Yep. Vortex shedding.

Tim

To bring this closer to DIY - wrapping a spiral of cable around the
top rung of a stepladder being transported on the roof rack of my car
results in a much quieter journey. (If the top rung is at the front.)

John



Yes as well as industrial chimneys the effect can be seen at the other
end of the scale on some car antennae, to stop them resonating at
certain speeds

https://fgtaerodynamics.wordpress.co...karman-vortex/

http://www.conrad-electronic.co.uk/c...CEN30?ref=list



--
CB

On Tuesday, 2 June 2015 23:07:30 UTC+1, Tim+ wrote:
Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about having
the wind help draw gases out of the chimney. In fact it about preventing
wind eddies shaking the chimney to destruction.


Yep. Vortex shedding.

There is a bit of a difference between science and fiction. Please explain which latitudes this only works on:
http://wxweb.meteostar.com/models/no...lite/NHC/COMP/

Weatherlawyer wrote:
On Tuesday, 2 June 2015 23:07:30 UTC+1, Tim+ wrote:
Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about having
the wind help draw gases out of the chimney. In fact it about preventing
wind eddies shaking the chimney to destruction.


Yep. Vortex shedding.

There is a bit of a difference between science and fiction. Please
explain which latitudes this only works on:
http://wxweb.meteostar.com/models/no...lite/NHC/COMP/

?

Are you on drugs?

Tim

On 05/06/2015 21:14, Weatherlawyer wrote:
There is a bit of a difference between science and fiction. Please explain which latitudes this only works on:
http://wxweb.meteostar.com/models/no...lite/NHC/COMP/

There's a scale difference.

Water trundling 10cm across a basin at 5cm/sec is affected a lot less
than air trundling 100km across the planet at 50m/second.

Andy

Harry Bloomfield put finger to keyboard:

The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Greek bridge prog last night by any chance?
I was impressed by the video of the dampers in the earthquake.

On 02/06/2015 21:49, Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Where you watching "Impossible Engineering" on Discovery science?

on 03/06/2015, soup supposed :
On 02/06/2015 21:49, Harry Bloomfield wrote:
The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.

Where you watching "Impossible Engineering" on Discovery science?

Yes!

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

In article , Harry
Bloomfield scribeth thus
The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.



Found this totally by accident!..

Amusing lampposts;!..


https://www.youtube.com/watch?v=ptYrbQGk6DQ
--
Tony Sayer