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-   -   Solution Diverging with Trimmer Mesh (http://www.cfd-online.com/Forums/star-ccm/113504-solution-diverging-trimmer-mesh.html)

rietuk February 20, 2013 16:34

Solution Diverging with Trimmer Mesh
 
Hi,

I am simulating nozzle flow.
Initially I used a polyhedral mesh and the solution converged but the mesh was not aligned with the flow. I then used a trimmer mesh, firstly with volumetric control to increase the resolution along the jet centreline but the solution diverged. This is with the same boundary conditions and initial solution based on the polyhedral mesh and a further simulation starting from no solution.
I thought it was an issue with the volumetric control therefore started again, used a trimmer mesh, refined by field function. The mesh looked good but again the solution diverged.
Are there any obvious reasons why a refinement of trimmer mesh would cause the solution to diverge? Is there another way to refine my mesh along the jet centreline?
Thanks for your help

siara817 February 20, 2013 17:15

Have you tried using 1st order for your solvers? If you go to continua/physics/models and click on each model to change them to first order.

rietuk February 20, 2013 17:36

Hi,

Just changed the solvers to 1st order and the solution still diverges after about 200 iterations

Is there anything else I can try?
Thanks fory your suggestion

arjun February 23, 2013 07:06

Quote:

Originally Posted by rietuk (Post 409169)
Hi,

Just changed the solvers to 1st order and the solution still diverges after about 200 iterations

Is there anything else I can try?
Thanks fory your suggestion


try green gauss grads.

rietuk February 23, 2013 07:56

Hi,

How do I enable green gauss grads?
Thanks

arjun February 23, 2013 08:50

Quote:

Originally Posted by rietuk (Post 409668)
Hi,

How do I enable green gauss grads?
Thanks


in the gradient model.

rietuk February 25, 2013 18:22

Hi,

The green gauss grads didn't stop the solution diverging. Is there anything else I can try?
The solution with refinment of a polyhedral mesh converges. Is there something wrong with the refinement of a trimmer mesh?
Thanks again

siara817 February 26, 2013 04:34

The other way is to reduce the under-relaxation factors for the solvers.
However it seems that your problem is meshing problem.
check the quality of your mesh. under Representation button, right click on the volume mesh and click repair. Then check some parameters to see how is the quality. Also you can go to the mesh button at the toolbar and click on the Diagnostics. See how is the quality of your mesh.

rietuk February 27, 2013 05:50

I have run the diagnostics but do not really understand the result. Please could you help me decipher the results? Are there any problems with the mesh?

Thanks very much


Boundaries of region Region 1:
Boundary Supersonic.NozzleEnd: 4990 faces (725 triangular, 3931 quadrilateral, 334 polygonal)
Extents:
x: [-1.7199441265e-002, 1.7199414698e-002] m
y: [4.7600000000e-002, 4.7600000000e-002] m
z: [-1.7199994832e-002, 1.7199489998e-002] m
surface area: 2.5046555675e-004 m^2
maximum boundary skewness angle = 4.4404441833e+001 deg in cell with pro-STAR Cell ID 1462007
Boundary Supersonic.BackWall: 10335 faces (146 triangular, 9641 quadrilateral, 548 polygonal)
Extents:
x: [-2.2472767801e-001, 2.2499997918e-001] m
y: [-1.8503454204e-017, 1.7347234760e-018] m
z: [-2.2492098468e-001, 2.2496523856e-001] m
surface area: 1.5728729963e-001 m^2
maximum boundary skewness angle = 1.6066276550e+001 deg in cell with pro-STAR Cell ID 1262014
Boundary Supersonic.Wall: 1858 faces (713 triangular, 1003 quadrilateral, 142 polygonal)
Extents:
x: [-6.6533111398e-001, 6.7499995615e-001] m
y: [-1.8503454204e-017, 1.5000000000e+000] m
z: [-6.6627009729e-001, 6.6488350765e-001] m
surface area: 4.3908433914e+000 m^2
maximum boundary skewness angle = 7.3802474976e+001 deg in cell with pro-STAR Cell ID 1282845
Boundary Supersonic.Outlet: 1244 faces (14 triangular, 1092 quadrilateral, 138 polygonal)
Extents:
x: [-6.6533111398e-001, 6.7499995615e-001] m
y: [1.5000000000e+000, 1.5000000000e+000] m
z: [-6.6627009729e-001, 6.6488350765e-001] m
surface area: 1.3925027847e+000 m^2
maximum boundary skewness angle = 6.8445991516e+001 deg in cell with pro-STAR Cell ID 1246219
Boundary Supersonic.Inlet: 8023 faces (178 triangular, 7483 quadrilateral, 362 polygonal)
Extents:
x: [-1.7199999419e-002, 1.7199614628e-002] m
y: [-2.1684043450e-019, 1.6927399783e-018] m
z: [-1.7199998728e-002, 1.7199553642e-002] m
surface area: 9.2931446852e-004 m^2
maximum boundary skewness angle = 2.8490482330e+001 deg in cell with pro-STAR Cell ID 2254323
Boundary Supersonic.NozzleInner: 93587 faces (7212 triangular, 83537 quadrilateral, 2838 polygonal)
Extents:
x: [-1.7199999419e-002, 1.7199993944e-002] m
y: [4.1204656301e-021, 4.7600000000e-002] m
z: [-1.7199999943e-002, 1.7199974894e-002] m
surface area: 4.9826093018e-003 m^2
maximum boundary skewness angle = 4.2953495026e+001 deg in cell with pro-STAR Cell ID 1467600
Boundary Supersonic.NozzleOuter: 40232 faces (3034 triangular, 36895 quadrilateral, 303 polygonal)
Extents:
x: [-1.9199974328e-002, 1.9199978807e-002] m
y: [2.5393132223e-021, 4.7600000000e-002] m
z: [-1.9199999803e-002, 1.9199985455e-002] m
surface area: 5.7216174901e-003 m^2
maximum boundary skewness angle = 3.9444232941e+001 deg in cell with pro-STAR Cell ID 2211770
Region Region 1:
5782 tetrahedral cells
1994876 hexahedral cells
122792 wedge cells
84 pyramid cells
131026 polyhedral cells
2254560 cells total
6760402 interior faces (142158 triangular, 6438996 quadrilateral, 179248 polygonal)
2408370 vertices

Extents:
x: [-6.6533111398e-001, 6.7499995615e-001] m
y: [-1.8503454204e-017, 1.5000000000e+000] m
z: [-6.6627009729e-001, 6.6488350765e-001] m
Maximum interior cell index delta: 1637064, average: 5.4672870859e+002
Maximum cell face index delta: 4977273, average: 1.2919498470e+003
Volume range: [6.4683247501e-015, 1.1530551128e-003] m^3
Minimum volume in cell with pro-STAR Cell ID 1469238
Minimum distance between centroids of neighbor cells = 1.3194574657e-005
between cells with pro-STAR Cell ID 1967702 and 1967701
Maximum skewness angle = 7.4639190674e+001 deg in cell with pro-STAR Cell ID 1282859
Face validity:
Minimum Face Validity: 1.0000000000e+000
Maximum Face Validity: 1.0000000000e+000
Face Validity < 0.50 0 0.000%
0.50 <= Face Validity < 0.60 0 0.000%
0.60 <= Face Validity < 0.70 0 0.000%
0.70 <= Face Validity < 0.80 0 0.000%
0.80 <= Face Validity < 0.90 0 0.000%
0.90 <= Face Validity < 0.95 0 0.000%
0.95 <= Face Validity < 1.00 0 0.000%
1.00 <= Face Validity 2254560 100.000%
Volume Change:
Minimum Volume Change: 2.432260e-003
Maximum Volume Change: 1.000000e+000
Volume Change < 0.000000e+000 0 0.000%
0.000000e+000 <= Volume Change < 1.000000e-006 0 0.000%
1.000000e-006 <= Volume Change < 1.000000e-005 0 0.000%
1.000000e-005 <= Volume Change < 1.000000e-004 0 0.000%
1.000000e-004 <= Volume Change < 1.000000e-003 0 0.000%
1.000000e-003 <= Volume Change < 1.000000e-002 249 0.011%
1.000000e-002 <= Volume Change < 1.000000e-001 16796 0.745%
1.000000e-001 <= Volume Change <= 1.000000e+000 2237515 99.244%
Maximum boundary skewness angle in region = 7.380247e+001 deg
Overall Face Validity:
Minimum Face Validity: 1.000000e+000
Maximum Face Validity: 1.000000e+000
Face Validity < 0.50 0 0.000%
0.50 <= Face Validity < 0.60 0 0.000%
0.60 <= Face Validity < 0.70 0 0.000%
0.70 <= Face Validity < 0.80 0 0.000%
0.80 <= Face Validity < 0.90 0 0.000%
0.90 <= Face Validity < 0.95 0 0.000%
0.95 <= Face Validity < 1.00 0 0.000%
1.00 <= Face Validity 2254560 100.000%
Overall Volume Change:
Minimum Volume Change: 2.432260e-003
Maximum Volume Change: 1.000000e+000
Volume Change < 0.000000e+000 0 0.000%
0.000000e+000 <= Volume Change < 1.000000e-006 0 0.000%
1.000000e-006 <= Volume Change < 1.000000e-005 0 0.000%
1.000000e-005 <= Volume Change < 1.000000e-004 0 0.000%
1.000000e-004 <= Volume Change < 1.000000e-003 0 0.000%
1.000000e-003 <= Volume Change < 1.000000e-002 249 0.011%
1.000000e-002 <= Volume Change < 1.000000e-001 16796 0.745%
1.000000e-001 <= Volume Change <= 1.000000e+000 2237515 99.244%


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