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ONSET OF TURBULENCE ON CORIOLIS AFFECTED FLOWS??

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Old   May 4, 2007, 07:35
Default ONSET OF TURBULENCE ON CORIOLIS AFFECTED FLOWS??
  #1
Carl
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Dear all,

I appeal to your oppinions to complement mine regarding what type of flow is likely to be expected in rotating semienclosed geometries (e.g: channels).

Given the definition of turbulence as 'unpredictable disorderly mixing flow' (sorry if this not formal,... I took it from the top of my head), then I assume that 'low' Rossby numbers and 'high' shearing flows must neccesarily induce the onset of turbulence in confined rotating flows... (e.g.: due to increasingly unstable vorticity)

Unfortunately I have no means to probe it... While I see (experimentally and 'cfd-ally') that convective heat transfer increases a bit in discs with particular ventilation geometries, I can not fully assume that a properly turbulent flow is given inside of those... more even when the conditions around the rotating disc are those of irrotational flow...

Then, if the onset of turbulence for SOLID smooth disc is around Re(rotational)>2.4e5 (see Dorfman, Cobs and Saunders,and others), what can be assumed to be a safe onset of turbulence for discs having channels or funny ventilation geometries...?

My guess is that the onset of turbulence is downsized to almost half of that above... but this guess is unfortunately not yet fully trusted.

Any hint you provide will definitely help me..

Thanks.
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Old   May 6, 2007, 19:34
Default Re: ONSET OF TURBULENCE ON CORIOLIS AFFECTED FLOWS
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Glenn Horrocks
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Hi,

The usual parameter defining whether the flow is turbulent or not is the Reynolds number. For instance in fully developed pipe flow if Re is <2000 then it is laminar, if Re>3500 it is turbulent and if 2000>Re>3500 it is the transition region where the flow history and other details become important.

Glenn Horrocks
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Old   May 8, 2007, 03:32
Default Re: ONSET OF TURBULENCE ON CORIOLIS AFFECTED FLOWS
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Carl
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Thanks Glenn, I have also though about it. The thing is that this channels (or ventilation) geometries do not allow the flow to fully develop ... short L/D ratio. Then I can not fully support my assumptions on those numbers, although I can calculate them and have seen that there exist turbulence, Re(D-pipe)>2000.

What I think is that, due to misalignment of the channels with the entrance flow, there are suction and pressure sides inside the channels, which gives a changing speed profile, (changing shear profile). Or if the ventilation geometry is composed with additional geometries, then there are sudden changes of speed behind these features... I am thinking on those facts as preluder of turbulence in such channels.

...
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