[MITgcm-support] Smagorinsky viscosity

[Kirk Bryan]

Dear Malte:
                         How are things going in the Windy City.  The MIT campus should have been good training.
I have never had any experience with non-hydrostatic flows, but why not make a test numerical calculation of an 
idealized, linear wave where you know the exact solution?
                             
                                                                                   Kirk                                                     
Kirk Bryan
Sayre Hall, AOS Program
Princeton University
Princeton, NJ 08544
tel  609-258-3688
fax 609-258-2850

________________________________________
From: Malte Jansen [mfj at uchicago.edu]
Sent: Friday, March 13, 2015 2:45 PM
To: mitgcm-support at mitgcm.org
Subject: Re: [MITgcm-support] Smagorinsky viscosity

Jody,

Are you arguing that the combination of non-hydrostatic with anisotropic grid is never desirable? It is my understanding that in the presence of stratification, turbulence (and waves) generally remain anisotropic, even for scales/processes where it might be preferable not to use the hydrostatic approximation. E.g. I thought that a hydrostatic model cannot reproduce the exact dispersion relation for internal waves, nor would it be adequate to properly represent symmetric instability - yet the aspect ratios here are still commonly much larger than one. There seem to be a range of publications which make use of non-hydrostatic models with anisotropic grids, so I don’t seem to be the only one who thinks this is reasonable, but I’m certainly not an expert on this smaller-scale stuff, so please do corrected me if I’m wrong.

Thanks,
Malte


> On Mar 13, 2015, at 6:27 PM, Jody Klymak <jklymak at uvic.ca> wrote:
>
>
>
>> Do I understand it correctly though that Smag3D uses the same viscosity coefficient for the horizontal and vertical? I’m using a 1:5 grid aspect ratio, so I don’t think I would want that.
>
> Yes, Smagorinsky uses just one viscosity for all three dimensions.
>
> I'm not sure why you would want 3-D Smagoronsky if your grid is 1:5.  Non-hydrostatic is a bit questionable as well.  What are you trying to simulate?
>
> Cheers,   Jody
>
>
>
>> Thanks,
>> Malte
>>
>>> On Mar 12, 2015, at 3:37 PM, Jody Klymak <jklymak at uvic.ca> wrote:
>>>
>>> Hi Malte,
>>>
>>> I just looked into this with Ruth Musgrave's help as well.  3-D Smagorinsky works pretty well. Your grid can be anisotropic, but probably not too anisotropic.  If you are using non-hydrostatic you probably don't want a grid that is too anisotropic anyways.   As written, it does not do any enhanced diffusivity, though I have a straight forward mod to enhance the diffusivities as well.  I guess I dont' know about any issues with the vertical advection scheme.  I'd have to take a look at it.
>>>
>>> I believe it just uses Dearborn's scheme.  So the Smagorinsky constant is just a constant.  I found to get energy to balance you had to tune this constant, so it would be great if someone moved towards a Germano type scheme.
>>>
>>> I dont' have access to my files right now, but will in a few hours, but its pretty straightforward to try.  A little less straightforward if you want your own diagnostics into the dissipation terms and matching diffusivity.
>>>
>>> I don't know anything about 2-D Smagorinsky.
>>>
>>> Cheers,   Jody
>>>
>>>> On Mar 12, 2015, at  4:03 AM, Malte Jansen <mfj at uchicago.edu> wrote:
>>>>
>>>> Hi all,
>>>>
>>>> Can anybody give me (or point me to) a brief update on the Smagorinsky viscosity implementation? The documentation seems to say that the vertical component of the Smagorinsky viscosity has not yet been implemented. Is that still true?
>>>>
>>>> I also found an old post stating that Smag does not yet work at all for the non-hydrostatic version. Is that still true?
>>>>
>>>> There now also is a Smag3D. Is there any documentation for that? Do I see it correctly that Smag3D is fully isotropic (and thus probably not recommended if the model grid is anisotropic)?
>>>>
>>>> I am running a non-hydrostatic model with non-isotropic grid. So my question is basically if there is an existing implementation of the Smagorinsky viscosity that should be adequate?
>>>>
>>>> Thanks,
>>>> Malte
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>
> --
> Jody Klymak
> http://web.uvic.ca/~jklymak/
>
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>
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