February 2018 - Nek5000-users - mailman3.cels.anl.gov

Re: [Nek5000-users] Nek5000-users Digest, Vol 108, Issue 2
by nek5000-users＠lists.mcs.anl.gov 02 Feb '18

02 Feb '18

Thank you Paul and Phillip for such a quick reply. I will run the jet case attached. So why was there no such problem when the first vortex from the wake of a circular cylinder was leaving the domain? On Sat, Feb 3, 2018 at 1:49 AM, <nek5000-users-request(a)lists.mcs.anl.gov> wrote: > Send Nek5000-users mailing list submissions to > nek5000-users(a)lists.mcs.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > or, via email, send a message with subject or body 'help' to > nek5000-users-request(a)lists.mcs.anl.gov > > You can reach the person managing the list at > nek5000-users-owner(a)lists.mcs.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Nek5000-users digest..." > > > Today's Topics: > > 1. Outflow Boundary Condition Clarification > (nek5000-users(a)lists.mcs.anl.gov) > 2. Re: Outflow Boundary Condition Clarification > (nek5000-users(a)lists.mcs.anl.gov) > 3. Re: Outflow Boundary Condition Clarification > (nek5000-users(a)lists.mcs.anl.gov) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sat, 3 Feb 2018 00:40:32 +0530 > From: nek5000-users(a)lists.mcs.anl.gov > To: nek5000-users(a)lists.mcs.anl.gov > Subject: [Nek5000-users] Outflow Boundary Condition Clarification > Message-ID: > <mailman.7741.1517598636.19102.nek5000-users(a)lists.mcs.anl.gov> > Content-Type: text/plain; charset="utf-8" > > Im trying to simulate the formation of shear layer when a jet exits a > nozzle and enters the flow domain. As the FIRST vortex leaves the outlet ( > at which I have provided 'O' boundary condition using genbox) the solution > diverges. I tried to implement the 'turbulent outflow' subroutine as > suggested in the forum but now the vortex affects the upstream flow. But > when I run the flow past circular cylinder example, the vortices leave the > domain without any issue even though only 'O' boundary condition is used'. > What is the difference between the two cases and what can i do to prevent > the issue? > > -- > Nitish Kovalam > Aerospace Engineering > Indian Institute of Space Science and Technology >

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Outflow Boundary Condition Clarification
by nek5000-users＠lists.mcs.anl.gov 02 Feb '18

02 Feb '18

Im trying to simulate the formation of shear layer when a jet exits a nozzle and enters the flow domain. As the FIRST vortex leaves the outlet ( at which I have provided 'O' boundary condition using genbox) the solution diverges. I tried to implement the 'turbulent outflow' subroutine as suggested in the forum but now the vortex affects the upstream flow. But when I run the flow past circular cylinder example, the vortices leave the domain without any issue even though only 'O' boundary condition is used'. What is the difference between the two cases and what can i do to prevent the issue? -- Nitish Kovalam Aerospace Engineering Indian Institute of Space Science and Technology

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shear stress and auto_averager
by nek5000-users＠lists.mcs.anl.gov 02 Feb '18

02 Feb '18

Hi all, Further my last request, since rm2 files contain the cross product running averages, how I can know the time-averaged <uv>, <vw>, and <uw> exactly? I know there is a way by calling auto_averager subroutine, but it doesn't have a good performance. To get the shear stress, what I did for the averaging is, 1. call averaging avg0f.0000*** files to get mean of u, v and w; 2. call averaging rm20f,0000** files to get mean of <uv>, <vw>, and <uw> (but I don't know exactly what they are since I dont know the order of results. 3. sqrt(mean<uw>-mean<u>*mean<w>) Do you think the process is correct? Kind regards, Jian

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(no subject)
by nek5000-users＠lists.mcs.anl.gov 02 Feb '18

02 Feb '18

Hi all, Further my last request, since rm2 files contain the cross product running averages, how I can know the time-averaged <uv>, <vw>, and <uw> exactly? I know there is a way by calling auto_averager subroutine, but it doesn't have a good performance. To get the shear stress, what I did for the averaging is, 1. call averaging avg0f.0000*** files to get mean of u, v and w; 2. call averaging rm20f,0000** files to get mean of <uv>, <vw>, and <uw> (but I don't know exactly what they are since I dont know the order of results. 3. sqrt(mean<uw>-mean<u>*mean<w>) Do you think the process is correct? Kind regards, Jian

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Clarification on PN-PN formulation with IFCHAR=T
by nek5000-users＠lists.mcs.anl.gov 01 Feb '18

01 Feb '18

Dear all, I am doing DNS of an incompressible flow using the PN-PN formulation with IFCHAR=T. We chose the PN-PN formulation because we wanted to ensure continuous pressure field. We chose the characteristics based time-stepping for stability. More than a question, I would like to see if I am understanding the solution process correctly. I've read the "NEK_doc.pdf" file dated from July 2015 which contains information on the PN-PN formulation, and Dr. Fischer's notes on implementation of the OIFS/characteristics approach. I've also looked at the code. >From what I can tell, the main difference when using PN-PN with IFCHAR=T vs. IFCHAR=F is that instead of having the non-linear terms on the RHS (IFCHAR=F) (see Eq. 7.7 from NEK_doc.pdf), we have the \tilde{u}^n-q (q=1,...,k) terms from the material derivative which act as an explicit forcing term. Then, the pressure field is solved, decoupled from velocity, using Eq. 7.13 from NEK_doc.pdf. The computed pressure is then used to solve the Helmholtz system for the velocity field. Does this seem correct? Specially the part of the pressure solve being decoupled from velocity. From the code, it definitely seems that way. Also, if the flow is incompressible, that means Q_T in eq 7.13 is zero, but shouldn't grad(Q_T) be zero as well? Thanks for your attention, Juan Diego

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