<div dir="ltr">Swarandeep,<div><br></div><div>Another issue that can arise in RBC simulations is poor numerical conditioning due to the non-dimensionalization. The non-dimensional form of the equations used in the Nek5000 examples is based off the conduction scales which result in a very small time-step and large velocities at larger Ra. I don't think you're case is high enough for it to be a problem, but you might try using the "freefall" scales if you aren't already. </div><div><br></div><div>I suggest consulting the Scheel, Emran and Schumacher paper for some details on running an RBC simulation with Nek5000.</div><div><br></div><div><span style="font-family:Arial,sans-serif;font-size:13px">Scheel, Janet D., Mohammad S. Emran, and Jörg Schumacher. "Resolving the fine-scale structure in turbulent Rayleigh–Bénard convection." </span><i style="font-family:Arial,sans-serif;font-size:13px">New Journal of Physics</i><span style="font-family:Arial,sans-serif;font-size:13px"> 15.11 (2013): 113063.</span></div><div><font face="Arial, sans-serif"><br></font></div><div><font face="Arial, sans-serif">Kind Regards,</font></div><div><font face="Arial, sans-serif"><br></font></div><div><font face="Arial, sans-serif">Phil S.<br></font><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Jun 5, 2017 at 10:00 AM, <span dir="ltr"><<a href="mailto:nek5000-users-request@lists.mcs.anl.gov" target="_blank">nek5000-users-request@lists.mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Send Nek5000-users mailing list submissions to<br>
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Today's Topics:<br>
<br>
1. Re: Corner elements giving large values<br>
(<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>)<br>
2. Re: Corner elements giving large values<br>
(<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>)<br>
<br>
<br>
------------------------------<wbr>------------------------------<wbr>----------<br>
<br>
Message: 1<br>
Date: Mon, 5 Jun 2017 01:12:39 +0530<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
Subject: Re: [Nek5000-users] Corner elements giving large values<br>
Message-ID:<br>
<<a href="mailto:mailman.7988.1496605362.2967.nek5000-users@lists.mcs.anl.gov">mailman.7988.1496605362.2967.<wbr>nek5000-users@lists.mcs.anl.<wbr>gov</a>><br>
Content-Type: text/plain; charset="UTF-8"<br>
<br>
Hi Nek Forum, Paul<br>
<br>
Thanks for the suggestions. I implemented them. Waiting for the<br>
simulation to be over.<br>
<br>
Another issue I have is that the BC for T at the inner cylinder wall<br>
does not stay at 0 as I have given in userbc. It becomes 0.2 over some<br>
time.<br>
<br>
Thank you<br>
Swarandeep<br>
<br>
<br>
<br>
<br>
<br>
On Fri, Jun 2, 2017 at 10:28 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
><br>
> Hi Swarandeep,<br>
><br>
> Set p26 in the .rea file to be 0.1 and make certain IFCHAR is F (a few lines below);<br>
><br>
> Make certain your dt is positive (param 12)<br>
><br>
> Paul<br>
><br>
> ______________________________<wbr>__________<br>
> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
> Sent: Friday, June 02, 2017 10:31 AM<br>
> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
><br>
> Dear Nek Forum, Paul<br>
><br>
> Yes, I have user defined grid such that the locations of the<br>
> elements are distributed to lie on the chebyshev grid at the top and<br>
> bottom and near the side walls.<br>
> Also please tell which param sets the CFL.<br>
><br>
> Thank you<br>
> Swarandeep<br>
><br>
><br>
> On Fri, Jun 2, 2017 at 8:00 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>><br>
>> Dear Swarandeep,<br>
>><br>
>> Did you refine your element size at the top and bottom and near the side walls?<br>
>><br>
>> Please set your CFL to 0.05 in order to get the flow started.<br>
>><br>
>> Best,<br>
>><br>
>><br>
>> Paul<br>
>><br>
>> ______________________________<wbr>__________<br>
>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>> Sent: Friday, June 02, 2017 1:04 AM<br>
>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
>><br>
>> Hi Nek Forum, Paul<br>
>><br>
>> The top and bottom BC are zero heat flux. Please let me n=know<br>
>> how to control the CFL. It is 0.5 in the logfile. I am having no<br>
>> particular difficulty except these corner elements at the junction of<br>
>> inner cylinder and the top/bottom planes. Is there a better way to<br>
>> treat edge boundary elements. Also is it possible to have different<br>
>> order of elements at different locations.<br>
>><br>
>> Thank you<br>
>> Swarandeep<br>
>><br>
>> On Fri, Jun 2, 2017 at 12:50 AM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>>><br>
>>> Hi Swarandeep,<br>
>>><br>
>>> Sorry - I misunderstood. I guess my question was more about the<br>
>>> temperature bcs at the bottom and top of the domain?<br>
>>><br>
>>> In general, however, there should be no difficulty. What happens<br>
>>> when you reduce your dt ?<br>
>>><br>
>>> You need to keep the CFL < ~0.5 in general. CFL is printed in the logfile,<br>
>>><br>
>>> grep tep logfile<br>
>>><br>
>>> and you'll see it "C= ....."<br>
>>><br>
>>> Paul<br>
>>><br>
>>><br>
>>><br>
>>><br>
>>> ______________________________<wbr>__________<br>
>>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>>> Sent: Thursday, June 01, 2017 1:57 PM<br>
>>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
>>><br>
>>> Hi NekForum, Paul<br>
>>><br>
>>> I intent to have isothermal conditions at the inner and outer<br>
>>> cylinders. The differential heating is achieved by imposing a<br>
>>> temperature difference across the two cylinders. I have used T = 1 and<br>
>>> 0 values for non-dimensional temperature. I think it should be fine.<br>
>>> Do you see any problem here.<br>
>>><br>
>>> Thank you<br>
>>> Swarandeep<br>
>>><br>
>>> On Thu, Jun 1, 2017 at 11:28 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>>>><br>
>>>> Hi Swarandeep,<br>
>>>><br>
>>>> Is 0/1 a realistic BC for T ?<br>
>>>><br>
>>>> Best,<br>
>>>><br>
>>>> Paul<br>
>>>><br>
>>>> ______________________________<wbr>__________<br>
>>>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>>>> Sent: Thursday, June 01, 2017 12:53 PM<br>
>>>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>>> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
>>>><br>
>>>> Hi Nek Forum, Paul<br>
>>>><br>
>>>> I am having temp = 1 and temp = 0 at the inner and outer<br>
>>>> boundaries. Gravity is pointing in the -ve z-direction along the axis<br>
>>>> of the<br>
>>>> annulus. The top and bottom planes have zero heat flux conditions.<br>
>>>> I have Coriolis force added as a body force.<br>
>>>> The Rayleigh number is around 10000. The resolution is 8, 25,<br>
>>>> 24 elements in the r, phi and z directions respectively with order 9.<br>
>>>> My initial condition is very low arbitrary velocity<br>
>>>> perturbation (~10^(-8)). The time resolution is set to 10^(-5) for<br>
>>>> param12. The CFL is<br>
>>>> set to 0.5. Please indicate how to control it.<br>
>>>><br>
>>>> As you have rightly mentioned, I start the simulation with a<br>
>>>> very low value of the Rayleigh number and gradually increase it. Yet,<br>
>>>> the corner values only get large. Other regions of the domain are<br>
>>>> fine.<br>
>>>><br>
>>>> Thank you<br>
>>>> Swarandeep<br>
>>>><br>
>>>> On Thu, Jun 1, 2017 at 7:38 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>>>>><br>
>>>>> Hi Swarandeep,<br>
>>>>><br>
>>>>> How large is your Rayleigh number and what is your resolution?<br>
>>>>> What are your thermal bcs? What are your ICs?<br>
>>>>><br>
>>>>> There should be no particular issue with your configuration - but you do need to<br>
>>>>> control spatial and temporal resolution.<br>
>>>>><br>
>>>>><br>
>>>>> For RB, you often have to start at low Ra and/or small dt because the nonlinear<br>
>>>>> response can often drive the velocities to be quite high very rapidly before the<br>
>>>>> CFL constraint kicks in. RB flows are one of the rare instances where I use<br>
>>>>> variable time step size (param 12 > 0), but even then you have to keep the target<br>
>>>>> CFL quite small until the flow is established.<br>
>>>>><br>
>>>>> hth,<br>
>>>>><br>
>>>>> Paul<br>
>>>>><br>
>>>>> ______________________________<wbr>__________<br>
>>>>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>>>>> Sent: Thursday, June 01, 2017 7:27 AM<br>
>>>>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>>>> Subject: [Nek5000-users] Corner elements giving large values<br>
>>>>><br>
>>>>> Dear Nek forum,<br>
>>>>><br>
>>>>> I am simulating Rayleigh Benard flow in a 3D finite cylindrical annulus.<br>
>>>>> I am getting spurious large values of velocity at the corner regions<br>
>>>>> of the annulus i.e. the edges where the inner cylinder joins the<br>
>>>>> top and bottom<br>
>>>>> planes. The boundary condition is no-slip and no penetration for velocity<br>
>>>>> at these edges. Can someone point out a plausible reason.<br>
>>>>><br>
>>>>> Thank you<br>
>>>>> Swarandeep<br>
>>>>> ______________________________<wbr>_________________<br>
>>>>> Nek5000-users mailing list<br>
>>>>> <a href="mailto:Nek5000-users@lists.mcs.anl.gov">Nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>>>> <a href="https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users" rel="noreferrer" target="_blank">https://lists.mcs.anl.gov/<wbr>mailman/listinfo/nek5000-users</a><br>
>>>>> ______________________________<wbr>_________________<br>
>>>>> Nek5000-users mailing list<br>
>>>>> <a href="mailto:Nek5000-users@lists.mcs.anl.gov">Nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>>>> <a href="https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users" rel="noreferrer" target="_blank">https://lists.mcs.anl.gov/<wbr>mailman/listinfo/nek5000-users</a><br>
>>>> ______________________________<wbr>_________________<br>
>>>> Nek5000-users mailing list<br>
>>>> <a href="mailto:Nek5000-users@lists.mcs.anl.gov">Nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
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>>> Nek5000-users mailing list<br>
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------------------------------<br>
<br>
Message: 2<br>
Date: Mon, 5 Jun 2017 01:20:04 +0000<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
To: "<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>"<br>
<<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>><br>
Subject: Re: [Nek5000-users] Corner elements giving large values<br>
Message-ID:<br>
<<a href="mailto:mailman.7989.1496625605.2967.nek5000-users@lists.mcs.anl.gov">mailman.7989.1496625605.2967.<wbr>nek5000-users@lists.mcs.anl.<wbr>gov</a>><br>
Content-Type: text/plain; charset="us-ascii"<br>
<br>
<br>
Swarandeep,<br>
<br>
if you send me your .rea/.usr/SIZE file off-list, I'll take a look.<br>
<br>
Paul<br>
______________________________<wbr>__________<br>
From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
Sent: Sunday, June 04, 2017 2:42 PM<br>
To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
Subject: Re: [Nek5000-users] Corner elements giving large values<br>
<br>
Hi Nek Forum, Paul<br>
<br>
Thanks for the suggestions. I implemented them. Waiting for the<br>
simulation to be over.<br>
<br>
Another issue I have is that the BC for T at the inner cylinder wall<br>
does not stay at 0 as I have given in userbc. It becomes 0.2 over some<br>
time.<br>
<br>
Thank you<br>
Swarandeep<br>
<br>
<br>
<br>
<br>
<br>
On Fri, Jun 2, 2017 at 10:28 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
><br>
> Hi Swarandeep,<br>
><br>
> Set p26 in the .rea file to be 0.1 and make certain IFCHAR is F (a few lines below);<br>
><br>
> Make certain your dt is positive (param 12)<br>
><br>
> Paul<br>
><br>
> ______________________________<wbr>__________<br>
> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
> Sent: Friday, June 02, 2017 10:31 AM<br>
> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
><br>
> Dear Nek Forum, Paul<br>
><br>
> Yes, I have user defined grid such that the locations of the<br>
> elements are distributed to lie on the chebyshev grid at the top and<br>
> bottom and near the side walls.<br>
> Also please tell which param sets the CFL.<br>
><br>
> Thank you<br>
> Swarandeep<br>
><br>
><br>
> On Fri, Jun 2, 2017 at 8:00 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>><br>
>> Dear Swarandeep,<br>
>><br>
>> Did you refine your element size at the top and bottom and near the side walls?<br>
>><br>
>> Please set your CFL to 0.05 in order to get the flow started.<br>
>><br>
>> Best,<br>
>><br>
>><br>
>> Paul<br>
>><br>
>> ______________________________<wbr>__________<br>
>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>> Sent: Friday, June 02, 2017 1:04 AM<br>
>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
>><br>
>> Hi Nek Forum, Paul<br>
>><br>
>> The top and bottom BC are zero heat flux. Please let me n=know<br>
>> how to control the CFL. It is 0.5 in the logfile. I am having no<br>
>> particular difficulty except these corner elements at the junction of<br>
>> inner cylinder and the top/bottom planes. Is there a better way to<br>
>> treat edge boundary elements. Also is it possible to have different<br>
>> order of elements at different locations.<br>
>><br>
>> Thank you<br>
>> Swarandeep<br>
>><br>
>> On Fri, Jun 2, 2017 at 12:50 AM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>>><br>
>>> Hi Swarandeep,<br>
>>><br>
>>> Sorry - I misunderstood. I guess my question was more about the<br>
>>> temperature bcs at the bottom and top of the domain?<br>
>>><br>
>>> In general, however, there should be no difficulty. What happens<br>
>>> when you reduce your dt ?<br>
>>><br>
>>> You need to keep the CFL < ~0.5 in general. CFL is printed in the logfile,<br>
>>><br>
>>> grep tep logfile<br>
>>><br>
>>> and you'll see it "C= ....."<br>
>>><br>
>>> Paul<br>
>>><br>
>>><br>
>>><br>
>>><br>
>>> ______________________________<wbr>__________<br>
>>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>>> Sent: Thursday, June 01, 2017 1:57 PM<br>
>>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
>>><br>
>>> Hi NekForum, Paul<br>
>>><br>
>>> I intent to have isothermal conditions at the inner and outer<br>
>>> cylinders. The differential heating is achieved by imposing a<br>
>>> temperature difference across the two cylinders. I have used T = 1 and<br>
>>> 0 values for non-dimensional temperature. I think it should be fine.<br>
>>> Do you see any problem here.<br>
>>><br>
>>> Thank you<br>
>>> Swarandeep<br>
>>><br>
>>> On Thu, Jun 1, 2017 at 11:28 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>>>><br>
>>>> Hi Swarandeep,<br>
>>>><br>
>>>> Is 0/1 a realistic BC for T ?<br>
>>>><br>
>>>> Best,<br>
>>>><br>
>>>> Paul<br>
>>>><br>
>>>> ______________________________<wbr>__________<br>
>>>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>>>> Sent: Thursday, June 01, 2017 12:53 PM<br>
>>>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>>> Subject: Re: [Nek5000-users] Corner elements giving large values<br>
>>>><br>
>>>> Hi Nek Forum, Paul<br>
>>>><br>
>>>> I am having temp = 1 and temp = 0 at the inner and outer<br>
>>>> boundaries. Gravity is pointing in the -ve z-direction along the axis<br>
>>>> of the<br>
>>>> annulus. The top and bottom planes have zero heat flux conditions.<br>
>>>> I have Coriolis force added as a body force.<br>
>>>> The Rayleigh number is around 10000. The resolution is 8, 25,<br>
>>>> 24 elements in the r, phi and z directions respectively with order 9.<br>
>>>> My initial condition is very low arbitrary velocity<br>
>>>> perturbation (~10^(-8)). The time resolution is set to 10^(-5) for<br>
>>>> param12. The CFL is<br>
>>>> set to 0.5. Please indicate how to control it.<br>
>>>><br>
>>>> As you have rightly mentioned, I start the simulation with a<br>
>>>> very low value of the Rayleigh number and gradually increase it. Yet,<br>
>>>> the corner values only get large. Other regions of the domain are<br>
>>>> fine.<br>
>>>><br>
>>>> Thank you<br>
>>>> Swarandeep<br>
>>>><br>
>>>> On Thu, Jun 1, 2017 at 7:38 PM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>> wrote:<br>
>>>>><br>
>>>>> Hi Swarandeep,<br>
>>>>><br>
>>>>> How large is your Rayleigh number and what is your resolution?<br>
>>>>> What are your thermal bcs? What are your ICs?<br>
>>>>><br>
>>>>> There should be no particular issue with your configuration - but you do need to<br>
>>>>> control spatial and temporal resolution.<br>
>>>>><br>
>>>>><br>
>>>>> For RB, you often have to start at low Ra and/or small dt because the nonlinear<br>
>>>>> response can often drive the velocities to be quite high very rapidly before the<br>
>>>>> CFL constraint kicks in. RB flows are one of the rare instances where I use<br>
>>>>> variable time step size (param 12 > 0), but even then you have to keep the target<br>
>>>>> CFL quite small until the flow is established.<br>
>>>>><br>
>>>>> hth,<br>
>>>>><br>
>>>>> Paul<br>
>>>>><br>
>>>>> ______________________________<wbr>__________<br>
>>>>> From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.<wbr>mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>]<br>
>>>>> Sent: Thursday, June 01, 2017 7:27 AM<br>
>>>>> To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
>>>>> Subject: [Nek5000-users] Corner elements giving large values<br>
>>>>><br>
>>>>> Dear Nek forum,<br>
>>>>><br>
>>>>> I am simulating Rayleigh Benard flow in a 3D finite cylindrical annulus.<br>
>>>>> I am getting spurious large values of velocity at the corner regions<br>
>>>>> of the annulus i.e. the edges where the inner cylinder joins the<br>
>>>>> top and bottom<br>
>>>>> planes. The boundary condition is no-slip and no penetration for velocity<br>
>>>>> at these edges. Can someone point out a plausible reason.<br>
>>>>><br>
>>>>> Thank you<br>
>>>>> Swarandeep<br>
>>>>> ______________________________<wbr>_________________<br>
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End of Nek5000-users Digest, Vol 100, Issue 4<br>
******************************<wbr>***************<br>
</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div>Phil Sakievich</div><div><br></div><div><div style="font-size:small">Post Doctoral Research Associate - Mechanical and Aerospace Engineering</div><div style="font-size:small">Arizona State University - Ira A. Fulton School for Engineering of Matter Transport and Energy<br>Tempe, Arizona</div></div></div></div></div></div></div>
</div></div></div>