# Courant no%23 and sharp corner in 3D

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 January 28, 2008, 16:56 Is there a way to improve the #1 Member   Alain Martin Join Date: Mar 2009 Posts: 40 Rep Power: 8 Is there a way to improve the value of the Courant number automatically while running the solver? I am having problems when the fields reached the location of some sharp corner in my domain. The Courant number exponentially grows and the solver stops. It seems that I need a very small delta_t or a very fine mesh to improve the solution. Should I get rid of the sharp corner altogether or is there a better solution? Thanks -Alain

 April 15, 2008, 03:28 Dear friends, I have the s #2 Senior Member   ZHOU Bin Join Date: Mar 2009 Location: Nanjing/Shanghai/Torino, Nanjing/Shanghai/Piemente, China/Italy Posts: 164 Rep Power: 8 Dear friends, I have the same problem. My case is a rectangle with the size 430*75 micrometers, inside there are many circles, this is a steady state flow around those many circles. 1. the stop time setting The inlet velocity is 0.0617m/s, so I set the stop time to be 430*10^(-6)/0.0617*10=0.07; 2. Courant number consideration Co=deltaT*U/deltax, which should be smaller than 1, in my case the deltaT for the mesh should be deltax=75*10^(-6)/14=5.36*10^(-6)m, deltaT

 April 15, 2008, 12:56 Dear friends, I spend a who #3 Senior Member   ZHOU Bin Join Date: Mar 2009 Location: Nanjing/Shanghai/Torino, Nanjing/Shanghai/Piemente, China/Italy Posts: 164 Rep Power: 8 Dear friends, I spend a whole day to simulate this "simple" problem, but the Courant number increases exponently with time goes by. Here I use icoFoam, because I have calculated the Re is very small. I have tried simpleFoam, and shut down the turbulent. I do not know why I have this problem. I will report in the forum when I solve this problem. Best regards, Zhou Bin

 April 15, 2008, 23:00 I haven't checked recently, bu #4 Senior Member   Sandeep Menon Join Date: Mar 2009 Location: Amherst, MA Posts: 386 Rep Power: 15 I haven't checked recently, but I'm pretty certain that icoFoam doesn't have adaptive time-stepping based on the Courant number put in. That's easy enough to fix. Use: # include "setDeltaT.H" after you evaluate the Courant number, and increment runTime after that within the loop. Take a cue from icoDyMFoam. Hope this helps. __________________ Sandeep Menon University of Massachusetts Amherst https://github.com/smenon

 April 16, 2008, 12:16 I had a similar problem in a v #5 New Member   T K Join Date: Mar 2009 Posts: 1 Rep Power: 0 I had a similar problem in a very simple Poiseuille flow cell. Turns out my Inlets and Outlets were defined as Patches in the blockMeshDict. Double-check your boundary conditions, there may be some simple error.

 October 23, 2008, 15:30 I think this is a very common #6 Member   Cem Albukrek Join Date: Mar 2009 Posts: 50 Rep Power: 8 I think this is a very common problem. I am dealing with the exact same issue; Courant number suddenly growing after a few time steps and the case blowing up. It becomes a challenge to figure out whether the phenomena is physical, wrong boundary conditions or bad mesh quality related. To summarize, I am trying to simulate a coarse windsurfer case, for which I am using icoFOAM to keep things simple and making sure I do not violate laminar and incompressibility constraints. The vehicle is inside a rectangular tunnel with blockage of 1%. My boundary conditions are: INLET: atmospheric velocity profile and zero pressure (normal) gradient OUTLET: constant atmospheric pressure and zero velocity (normal) gradient SIDEWALLS: Slip (zero (normal) gradient on velocity and pressure) CEILING: Slip FLOOR: No-Slip (0 velocity, zero pressure (normal) gradient) I am able to pass the CheckMesh with less than 0.1% non-orthogonal triangles with maximum angle at 82 degrees: Create polyMesh for time = constant Time = constant Mesh stats points: 295150 edges: 1832591 faces: 2971710 internal faces: 2765446 cells: 1434289 boundary patches: 29 point zones: 0 face zones: 20 cell zones: 5 Number of cells of each type: hexahedra: 0 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 1434289 polyhedra: 0 Checking topology... Boundary definition OK. Point usage OK. Upper triangular ordering OK. Topological cell zip-up check OK. Face vertices OK. Face-face connectivity OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces ... Patch Faces Points Surface Board 19792 10152 ok (not multiply connected) Boom 12668 6356 ok (not multiply connected) Footstrap-FL 759 397 ok (not multiply connected) Footstrap-FR 693 382 ok (not multiply connected) Footstrap-RL 761 399 ok (not multiply connected) Footstrap-RR 727 397 ok (not multiply connected) Mast 30082 15551 ok (not multiply connected) MastBase 316 182 ok (not multiply connected) Sail-Luff 4964 3220 ok (not multiply connected) Sail-Panel1 6560 3393 ok (not multiply connected) Sail-Panel2 21116 10776 ok (not multiply connected) Sail-Panel3 23751 12118 ok (not multiply connected) Sail-Panel4 18337 9371 ok (not multiply connected) Sail-Panel5 13876 7109 ok (not multiply connected) Sail-Panel6 1084 607 ok (not multiply connected) Sailor 19026 9713 ok (not multiply connected) Shorts 9593 4873 ok (not multiply connected) TendonJoint 230 134 ok (not multiply connected) VR0-Bottom 2552 1408 ok (not multiply connected) VR1-Bottom 3014 1657 ok (not multiply connected) VR2-Bottom 2516 1381 ok (not multiply connected) VR3-Bottom 1306 728 ok (not multiply connected) VR4-Bottom 4016 2128 ok (not multiply connected) WT-BasePlate 2839 1610 ok (not multiply connected) WT-Ceiling 2074 1101 ok (not multiply connected) WT-Inlet 576 322 ok (not multiply connected) WT-Outlet 622 345 ok (not multiply connected) WT-SideWall1 1218 664 ok (not multiply connected) WT-SideWall2 1196 653 ok (not multiply connected) Checking geometry... Domain bounding box: (-46.1548 -73.0691 -3.42362) (68.8019 46.4194 37.9327) Boundary openness (1.55306e-16 6.01054e-17 1.85018e-15) OK. Max cell openness = 1.74667e-16 OK. Max aspect ratio = 22.515 OK. Minumum face area = 9.07881e-07. Maximum face area = 24.1368. Face area magnitudes OK. Min volume = 4.31759e-10. Max volume = 31.4018. Total volume = 198531. Cell volumes OK. Mesh non-orthogonality Max: 82.6972 average: 17.0984 *Number of severely non-orthogonal faces: 577. Non-orthogonality check OK. <

 November 18, 2008, 09:21 Dear Alain, change your ico #7 Senior Member   Wolfgang Heydlauff Join Date: Mar 2009 Location: Germany Posts: 136 Rep Power: 8 Dear Alain, change your icoFoam.C like I did with my turbFoam.C and the adjustable timestepControl will be working. See http://www.cfd-online.com/OpenFOAM_D...tml?1227012935 With ongoing calculation the Co-Number will decrease/timestep will increase.

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