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

Rotating computational domain
by nek5000-users＠lists.mcs.anl.gov 13 Oct '18

13 Oct '18

Hello Neks, I am an undergraduate student new to Nek and I am working on a simulation studying dynamic stall in a dynamically pitching airfoil. I want to do a pitch and hold simulation at low Reynold's number (Re = 12000) where I rotate the entire computational domain up to about 50 degrees AOA and then hold at 50 degrees, with steady inflow ux = 1. I would like to rotate the domain about the z axis, which passes through the quarter chord location of the airfoil profile (modified NACA 0012). Because of the steep AOA, I would like to stay away from pitching the airfoil within the stationary domain with ALE to avoid too much mesh deformation. To this end, I have been scouring documentation to try and find a method of applying a rotational mesh velocity to the entire domain about the z axis while keeping the flow within the domain at ux = 1. I am feeling very stuck. Others have suggested applying a Coriolis force to the flow, but I don't really see how this would simulate rotation of the entire domain. It seems to me that simulation of a Coriolis force would be acceptable to correct the flow field to always be ux = 1 inside a rotating domain, but I don't see how that would apply a mesh velocity anywhere. Are there any examples where an entire computational domain is rotated that I can look at, or has anybody done similar work who can point me in the right direction? Regards, -Harry

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Parameter settings on filterWeight and filterCutoffRatio
by nek5000-users＠lists.mcs.anl.gov 31 Aug '18

31 Aug '18

Hi neks, Recently I am working on an LES simulation in an annular pipe to see how transverse velocity goes with Re increasing. But I am quite wondering how I should set filterWeight and filterCutoffRatio in my example while in the turbChannel demo they are selected to 10 an 0.9 respectively as proposed value. They should be sensitive parameters in LES simulation, don't they? Is there any references concerned about them to help me see them more clearly? If it is convenient for you could you please reply me a url to the reference? Thank you so much for your assistence. best regard -- JU Haoran Department of Nuclear Science and Technology, School of Energy and Power Engineering, Xi'an Jiaotong University, 710049. No.28 Xianning West Road, Xi'an, Shanxi Province, China. Email: juhaoran012(a)163.com

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Re: [Nek5000-users] Statistics toolbox for Nek5000
by nek5000-users＠lists.mcs.anl.gov 30 Aug '18

30 Aug '18

Dear Philipp, Thanks for the reply. Do you have the older version of the statistics toolbox? I'm using the old version of Nek anyways. In the repository that I found, there is only the 'compile' and 'run' directories, but there is not 'post2d' directory, which according to the manual that you sent is where the subroutines for computing budget terms are located. As I mentioned before, what I would like to do is to compare the code against mine to make sure there are no bugs. Thank you, Juan Diego

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The number of adjacent element
by nek5000-users＠lists.mcs.anl.gov 30 Aug '18

30 Aug '18

Hi, Neks! Could I easy identify the number of adjacent element? For example, if I know, that now I am in the "e=25" element, could I know "e" neighbors? I know, that the mesh is globaly unstructured, but anyway? Best regards, Valdemar

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Exodus II to Nek
by nek5000-users＠lists.mcs.anl.gov 30 Aug '18

30 Aug '18

Sorry for asking again, but I need to check that the boundary conditions are all satisfied. I have checked the velocities, the only axial velocity is exactly same. That is may be, I am applying the periodic boundary conditions in the axial direction only, or the way I calculated the azimuthal and radial velocities is not sufficient, is that right? Hint, I drive the flow using a force like the way of turbChannel example. Also,I am using VisIt to calculate and plot the velocity components. My pipe length is 5D, which I think it is sufficient to capture all turbulence scales. Ali Embry-Riddle Aeronautical University

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Freestream BC: Dirichlet/Neumann BC
by nek5000-users＠lists.mcs.anl.gov 29 Aug '18

29 Aug '18

Dear Nek users, I am wondering is there a way to assign the freestream BC as “U = expression and dv/dy = expression” , instead of assigning U and V directly? Could anyone please help me on this? Thanks in advance

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Statistics toolbox for Nek5000
by nek5000-users＠lists.mcs.anl.gov 28 Aug '18

28 Aug '18

Hello everyone, I found this statistics toolbox for Nek5000 https://github.com/Mopolino8/StatsToolbox However, according to the accompanying PDF documentation, there should be some folders called cpost3d, post3d and post2d, which are not in the repository. Does anyone have access to those folders? I am trying to compute transport equation budget terms but part of my results are strange, so I want to compare how the statistics toolbox computes them to verify if there is bug in my code. Thank you! Juan Diego

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Re: [Nek5000-users] Regarding spatial resolution
by nek5000-users＠lists.mcs.anl.gov 27 Aug '18

27 Aug '18

Hi Neks, Just following up on this question. Thank you. Saikat On Thu, Aug 23, 2018 at 3:46 PM, Saikat Mukherjee <msaikat6(a)vt.edu> wrote: > Hey Neks, > > I have a very basic question about the spatial resolution of Nek5000. > Suppose my elements in the domain are squares of unit length. If my GLL > points used are 17 (or order of the polynomial used is 16), what is the > least spatial length resolved by the code? As an approximate, can one use > 1/17 units? Is there a way to calculate this least spatial length being > resolved? > > Thanks, > Saikat > > > >

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About TST_WSCAL
by nek5000-users＠lists.mcs.anl.gov 24 Aug '18

24 Aug '18

hello Neks. I am a Nek5000 user and want to test nek5000 scalability,so I try to rewirte the file. I modify the makenek file: ========================================== FFLAGS="-DTST_WSCAL" CFLAGS=" " ========================================== I added the statment in reader_par.f ========================================== param(151) = 30 param(150) = 50 ========================================== so i try to run the demo ethier,but i got the error iformation like these: ========================================== Step 42, t= 4.2000000E-03, DT= 1.0000000E-04, C= 1.002 1.8351E+01 4.4267E-01 Solving for fluid 42 PRES gmres 30 1.4718E-09 4.1884E+01 1.0000E-08 8.2129E-02 1.4073E-01 F 42 Hmholtz VELX 50 3.5103E-04 2.0863E+02 1.0000E-12 42 Hmholtz VELY 50 1.6061E-10 1.5756E+02 1.0000E-12 42 Hmholtz VELZ 50 3.0524E+02 9.4242E+01 1.0000E-12 L1/L2 DIV(V) 9.3378E-01 2.3756E+02 L1/L2 QTL 0.0000E+00 0.0000E+00 L1/L2 DIV(V)-QTL 9.3378E-01 2.3756E+02 WARNING: DIV(V)-QTL too large! 42 Fluid done 4.2000E-03 3.1138E-01 CFL, Ctarg! 84.587414707615267 0.5 43 4.2000E-03 Write checkpoint FILE:/home/export/online1/wangxm/zhouzhifeng/Nek5000demo/run/ethier/ethier0.f00001 43 4.2000E-03 done :: Write checkpoint file size = 0.44 MB avg data-throughput = 6.1MB/s io-nodes = 4 ========================================== it just runs 40 steps instead of 1000 steps , how can i deal with that? Thank you so much ~

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ICEM CFD mesh conversion in NEK5000
by nek5000-users＠lists.mcs.anl.gov 24 Aug '18

24 Aug '18

Hi Neks, I have generated a mesh in ICEM CFD software. And exported mesh in .exo format. Then I have used exo2nex to convert mesh. while running the case one error is showing. That error is shown below 0 ERROR: Vanishing Jacobian near 5th node of element 1. 1.10361832315621911E-002 -6.75425029014820044E-003 0 xyz: 2.06376E-01 3.94255E-02 0 xyz: 2.27305E-01 3.94255E-02 0 0.0000E+00 Write checkpoint 0 0.0000E+00 OPEN: xyzexodus.fld01 Jac error 1, setting p66=4, ifxyo=t an error occured: dying ... I am not able to solve this problem. Kindly help me with this. Thank you Alok Mishra Research Scholar Computational Propulsion Lab Aerospace Department IIT Kanpur

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