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fluid flow but temperature raises from nowhere?

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Old   September 10, 2014, 15:19
Default fluid flow but temperature raises from nowhere?
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I have following physics defined for one fluid and one solid:
Code:
  | +-3 Physics 1	Regions	[all_inside]
  | | | 	Interfaces	[Interface 1]
  | | +-1 Models	 	 
  | | | +-1 Constant Density	 	 
  | | | +-2 Gas	 	 
  | | | | `-1 Air	Database Material	Air (Air) [Standard/Gases]
  | | | |   `-1 Material Properties	 	 
  | | | |     +-1 Density	Method	Constant
  | | | |     | `-1 Constant	Value	1.18415 kg/m^3
  | | | |     +-2 Dynamic Viscosity	Method	Constant
  | | | |     | `-1 Constant	Value	1.85508E-5 Pa-s
  | | | |     +-3 Specific Heat	Method	Constant
  | | | |     | `-1 Constant	Value	1003.62 J/kg-K
  | | | |     +-4 Thermal Conductivity	Method	Constant
  | | | |     | `-1 Constant	Value	0.0260305 W/m-K
  | | | |     `-5 Turbulent Prandtl Number	Method	Constant
  | | | |       `-1 Constant	Value	0.9
  | | | +-3 Gradients	Gradient Method	Hybrid Gauss-LSQ
  | | | | 	Limiter Method	Venkatakrishnan
  | | | | 	Custom Accuracy Level Selector	2.0
  | | | | 	Verbose	false
  | | | | 	Least-Squares Quality Criterion	true
  | | | | 	Flat Cells Curvature Criterion	true
  | | | | 	Cell Skewness Criterion	true
  | | | | 	Chevron-Cell Criterion	true
  | | | | 	Least-Squares Tensor Minimum Eigenvalues Ratio	0.1
  | | | | 	Normalized Flat Cells Curvature Factor	1.0
  | | | | 	Maximum Safe (Positive) Skewness Angle (deg)	75.0
  | | | | 	Minimum Unsafe (Positive) Skewness Angle (deg)	88.0
  | | | | 	Use TVB Gradient Limiting	false
  | | | | 	Acceptable Field Variation (Factor)	0.05
  | | | +-4 Gravity	 	 
  | | | +-5 K-Epsilon Turbulence	 	 
  | | | +-6 Realizable K-Epsilon Two-Layer	Buoyancy Production of Dissipation	Boundary Layer Orientation
  | | | | 	Cmu	0.09
  | | | | 	C1e	1.44
  | | | | 	C2e	1.9
  | | | | 	Ct	1.0
  | | | | 	Sigma_k	1.0
  | | | | 	Sigma_e	1.2
  | | | | 	Sarkar	2.0
  | | | | 	Tke Minimum	1.0E-10
  | | | | 	Tdr Minimum	1.0E-10
  | | | | 	Secondary Gradients	On
  | | | | 	Convection	2nd-order
  | | | | 	Normal Stress Term	false
  | | | | 	Curvature Correction Option	Off
  | | | | 	Two-Layer Type	Shear Driven (Wolfstein)
  | | | | 	Two-Layer ReY*	60.0
  | | | | 	Two-Layer Delta ReY	10.0
  | | | +-7 Reynolds-Averaged Navier-Stokes	 	 
  | | | +-8 Segregated Flow	Minimum Absolute Pressure	1000.0 Pa
  | | | | 	Flow Boundary Diffusion	true
  | | | | 	Unsteady Flux Dissipation Corrections	false
  | | | | 	Limit Acoustic-CFL Option	Per-Model
  | | | | 	Secondary Gradients	On
  | | | | 	Convection	2nd-order
  | | | | 	Delta-V Dissipation	Off
  | | | +-9 Segregated Fluid Temperature	Secondary Gradients	On
  | | | | 	Convection	2nd-order
  | | | | 	Flow Boundary Diffusion	true
  | | | +-10 Steady	 	 
  | | | +-11 Three Dimensional	 	 
  | | | +-12 Turbulent	 	 
  | | | `-13 Two-Layer All y+ Wall Treatment	Iterative Ustar	false
  | | +-2 Reference Values	 	 
  | | | +-1 Gravity	Value	[0.0, -9.81, 0.0] m/s^2
  | | | +-2 Reference Altitude	Value	[0.0, 0.0, 0.0] m
  | | | +-3 Minimum Allowable Temperature	Value	0.0 C
  | | | +-4 Reference Pressure	Value	1.0 atm
  | | | +-5 Minimum Allowable Wall Distance	Value	1.0E-6 m
  | | | `-6 Maximum Allowable Temperature	Value	4726.85 C
  | | `-3 Initial Conditions	 	 
  | |   +-1 Pressure	Method	Constant
  | |   | `-1 Constant	Value	1.0 atm
  | |   +-2 Static Temperature	Method	Constant
  | |   | `-1 Constant	Value	25.0 C
  | |   +-3 Turbulence Specification	Method	K + Epsilon
  | |   +-4 Turbulent Dissipation Rate	Method	Constant
  | |   | `-1 Constant	Value	0.1 m^2/s^3
  | |   +-5 Turbulent Kinetic Energy	Method	Constant
  | |   | `-1 Constant	Value	0.001 J/kg
  | |   `-6 Velocity	Method	Constant
  | |     | 	Coordinate System	Laboratory
  | |     `-1 Constant	Value	[0.0, 0.0, 0.0] m/s
  | `-4 Physics 2	Regions	[mesh]
  |   | 	Interfaces	[Interface 1]
  |   +-1 Models	 	 
  |   | +-1 Circumferential Heat Flux Averaging	 	 
  |   | +-2 Constant Density	 	 
  |   | +-3 Gradients	Gradient Method	Hybrid Gauss-LSQ
  |   | | 	Limiter Method	Venkatakrishnan
  |   | | 	Custom Accuracy Level Selector	2.0
  |   | | 	Verbose	false
  |   | | 	Least-Squares Quality Criterion	true
  |   | | 	Flat Cells Curvature Criterion	true
  |   | | 	Cell Skewness Criterion	true
  |   | | 	Chevron-Cell Criterion	true
  |   | | 	Least-Squares Tensor Minimum Eigenvalues Ratio	0.1
  |   | | 	Normalized Flat Cells Curvature Factor	1.0
  |   | | 	Maximum Safe (Positive) Skewness Angle (deg)	75.0
  |   | | 	Minimum Unsafe (Positive) Skewness Angle (deg)	88.0
  |   | | 	Use TVB Gradient Limiting	false
  |   | | 	Acceptable Field Variation (Factor)	0.05
  |   | +-4 Segregated Solid Energy	Secondary Gradients	On
  |   | +-5 Solid	 	 
  |   | | `-1 Al	Database Material	Al (Aluminum (pure)) [Standard/Solids]
  |   | |   `-1 Material Properties	 	 
  |   | |     +-1 Density	Method	Constant
  |   | |     | `-1 Constant	Value	2702.0 kg/m^3
  |   | |     +-2 Specific Heat	Method	Constant
  |   | |     | `-1 Constant	Value	903.0 J/kg-K
  |   | |     `-3 Thermal Conductivity	Method	Constant
  |   | |       `-1 Constant	Value	237.0 W/m-K
  |   | +-6 Steady	 	 
  |   | `-7 Three Dimensional	 	 
  |   +-2 Reference Values	 	 
  |   | +-1 Minimum Allowable Temperature	Value	100.0 K
  |   | `-2 Maximum Allowable Temperature	Value	5000.0 K
  |   `-3 Initial Conditions	 	 
  |     `-1 Static Temperature	Method	Constant
  |       `-1 Constant	Value	25.0 C
with one inlet( 1 atm pressure ) and outlet ( Mass Flow Inlet , -0.0083333 kg/s)

now, out of nothing(?) I see temperature raises quite rapidly
but not pressure etc

any ideas why?
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Old   September 12, 2014, 18:02
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anyone to help ?

thanks
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Old   September 15, 2014, 08:54
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kris
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Hi,

You could create a threshold to see where the temperature is rising and check if the mesh is good in those locations. If the mesh is not so good, you could try and change the mesh.
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Old   September 15, 2014, 17:47
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Quote:
Originally Posted by kguntur View Post
Hi,

You could create a threshold to see where the temperature is rising and check if the mesh is good in those locations. If the mesh is not so good, you could try and change the mesh.
here are details of current mesh,

Quote:
---------------------------------------------------
--- Computing statistics in Region: all_inside
---------------------------------------------------
-> ENTITY COUNT:
# Cells: 4564916
# Faces: 31077860
# Verts: 26322593
-> EXTENTS:
x: [-8.5000e-03, 1.0900e-02 ] m
y: [0.0000e+00 , 1.6000e-02 ] m
z: [-8.5000e-03, 8.5000e-03 ] m
-> MESH VALIDITY:
Mesh is topologically valid and has no negative volume cells.
-> FACE VALIDITY STATISTICS:
Minimum Face Validity: 1.000000e+00
Maximum Face Validity: 1.000000e+00
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 4564916 100.000%
-> VOLUME CHANGE STATISTICS:
Minimum Volume Change: 7.170639e-05
Maximum Volume Change: 1.000000e+00
Volume Change < 0.000000e+00 0 0.000%
0.000000e+00 <= Volume Change < 1.000000e-06 0 0.000%
1.000000e-06 <= Volume Change < 1.000000e-05 0 0.000%
1.000000e-05 <= Volume Change < 1.000000e-04 1 0.000%
1.000000e-04 <= Volume Change < 1.000000e-03 1 0.000%
1.000000e-03 <= Volume Change < 1.000000e-02 2350 0.051%
1.000000e-02 <= Volume Change < 1.000000e-01 27658 0.606%
1.000000e-01 <= Volume Change <= 1.000000e+00 4534906 99.343%
Boundaries of region all_inside:
Boundary Default: 185218 faces (56 triangular, 549 quadrilateral, 184613 polygonal)
Face partition distribution :
-------------------------
|Worker rank |No. Faces |
-------------------------
|0 |3441 |
|1 |19246 |
|2 |9854 |
|3 |20624 |
|4 |17338 |
|5 |18368 |
|6 |19507 |
|7 |14253 |
|8 |7556 |
|9 |4355 |
|10 |16915 |
|11 |21691 |
|12 |4604 |
|13 |7466 |
-------------------------
Average number of faces : 13229 STDDEV % : 48.88 IMBALANCE % : 63.95

Extents:
x: [-8.4999506989e-03, 1.0900000000e-02] m
y: [0.0000000000e+00, 1.6000000000e-02] m
z: [-8.4999544996e-03, 8.4999523774e-03] m
surface area: 1.1837176280e-03 m^2
maximum boundary skewness angle = 8.6045150757e+01 deg in cell with pro-STAR Cell ID 4565338
Boundary outlet: 4952 faces (5 triangular, 355 quadrilateral, 4592 polygonal)
Face partition distribution :
-------------------------
|Worker rank |No. Faces |
-------------------------
|0 |0 |
|1 |0 |
|2 |0 |
|3 |0 |
|4 |4952 |
|5 |0 |
|6 |0 |
|7 |0 |
|8 |0 |
|9 |0 |
|10 |0 |
|11 |0 |
|12 |0 |
|13 |0 |
-------------------------
Average number of faces : 353 STDDEV % : 360.56 IMBALANCE % : 1300.00

Extents:
x: [-2.4996193492e-03, 2.4995032342e-03] m
y: [1.5999999788e-02, 1.6000000000e-02] m
z: [-2.4999986297e-03, 2.5000000000e-03] m
surface area: 1.9629775124e-05 m^2
maximum boundary skewness angle = 7.7250526428e+01 deg in cell with pro-STAR Cell ID 4566022
Boundary inlet: 691 faces (1 triangular, 102 quadrilateral, 588 polygonal)
Face partition distribution :
-------------------------
|Worker rank |No. Faces |
-------------------------
|0 |0 |
|1 |0 |
|2 |0 |
|3 |0 |
|4 |0 |
|5 |0 |
|6 |0 |
|7 |0 |
|8 |0 |
|9 |0 |
|10 |0 |
|11 |0 |
|12 |0 |
|13 |691 |
-------------------------
Average number of faces : 49 STDDEV % : 360.56 IMBALANCE % : 1300.00

Extents:
x: [1.0899981106e-02, 1.0900000000e-02] m
y: [1.6001000938e-03, 2.9997243352e-03] m
z: [-7.0000000000e-04, 6.9989338661e-04] m
surface area: 1.5336854631e-06 m^2
maximum boundary skewness angle = 7.2048233032e+01 deg in cell with pro-STAR Cell ID 4565926
Boundary heater_out: 56022 faces (4 triangular, 475 quadrilateral, 55543 polygonal)
Face partition distribution :
-------------------------
|Worker rank |No. Faces |
-------------------------
|0 |7170 |
|1 |0 |
|2 |6826 |
|3 |0 |
|4 |0 |
|5 |0 |
|6 |0 |
|7 |3611 |
|8 |6377 |
|9 |13782 |
|10 |0 |
|11 |0 |
|12 |6297 |
|13 |11959 |
-------------------------
Average number of faces : 4001 STDDEV % : 115.71 IMBALANCE % : 244.41

Extents:
x: [3.0003721605e-03, 6.1993200559e-03] m
y: [6.5034363930e-04, 5.4496562902e-03] m
z: [-1.5993384344e-03, 1.5993397093e-03] m
surface area: 3.2461764931e-05 m^2
maximum boundary skewness angle = 7.2869720459e+01 deg in cell with pro-STAR Cell ID 218406
Boundary i_air_mesh: 198 faces (6 triangular, 14 quadrilateral, 178 polygonal)
Face partition distribution :
-------------------------
|Worker rank |No. Faces |
-------------------------
|0 |96 |
|1 |0 |
|2 |3 |
|3 |0 |
|4 |0 |
|5 |0 |
|6 |0 |
|7 |0 |
|8 |0 |
|9 |99 |
|10 |0 |
|11 |0 |
|12 |0 |
|13 |0 |
-------------------------
Average number of faces : 14 STDDEV % : 240.71 IMBALANCE % : 600.00
(32423 original boundary faces)
Extents:
x: [3.0003721605e-03, 4.6208572326e-03] m
y: [6.5034363930e-04, 6.6666656857e-03] m
z: [-2.8619833806e-05, 1.3499997974e-03] m
surface area: 1.4178880292e-07 m^2
maximum boundary skewness angle = 7.3216674805e+01 deg in cell with pro-STAR Cell ID 187674
Boundary i_air_mesh [Interface 1]: 195380 faces (25326 triangular, 61578 quadrilateral, 108476 polygonal)
Face partition distribution :
-------------------------
|Worker rank |No. Faces |
-------------------------
|0 |21781 |
|1 |8852 |
|2 |17102 |
|3 |5501 |
|4 |401 |
|5 |4387 |
|6 |8649 |
|7 |22933 |
|8 |18014 |
|9 |25182 |
|10 |5638 |
|11 |5533 |
|12 |28196 |
|13 |23211 |
-------------------------
Average number of faces : 13955 STDDEV % : 64.20 IMBALANCE % : 102.04

Extents:
x: [3.2500000000e-03, 5.9499992837e-03] m
y: [0.0000000000e+00, 8.9000000000e-03] m
z: [-1.3500000000e-03, 1.3500000000e-03] m
surface area: 7.1679205575e-05 m^2
maximum boundary skewness angle = 8.4540542603e+01 deg in cell with pro-STAR Cell ID 185897
Region all_inside:
255 tetrahedral cells
4554 hexahedral cells
9240 wedge cells
619 pyramid cells
4550248 polyhedral cells
4564916 cells total
285294 halo cells
31077860 interior faces (1923478 triangular, 8855200 quadrilateral, 20756144 polygonal) (456962 halo faces)
26322593 vertices (828830 halo vertices)
Cell/Face partition distribution :
--------------------------------------------------------------------------------------------------------
|Worker rank |No. Non Halo Cells |No. Halo Cells |% Halo Cells |No. Total Cells |No. Faces |No. BFaces |
--------------------------------------------------------------------------------------------------------
| 0 | 339930 | 23361 | 6.87 | 363291 | 2408700 | 32488 |
| 1 | 341544 | 17595 | 5.15 | 359139 | 2358567 | 28098 |
| 2 | 338986 | 20793 | 6.13 | 359779 | 2350463 | 33785 |
| 3 | 338106 | 26539 | 7.85 | 364645 | 2331959 | 26125 |
| 4 | 291020 | 9912 | 3.41 | 300932 | 1983585 | 22691 |
| 5 | 341406 | 23885 | 7.00 | 365291 | 2376495 | 22755 |
| 6 | 341132 | 21708 | 6.36 | 362840 | 2355305 | 28156 |
| 7 | 303621 | 22366 | 7.37 | 325987 | 2065432 | 40797 |
| 8 | 340370 | 21357 | 6.27 | 361727 | 2388720 | 31947 |
| 9 | 259354 | 15508 | 5.98 | 274862 | 1717757 | 43418 |
| 10 | 309554 | 18668 | 6.03 | 328222 | 2147175 | 22553 |
| 11 | 340429 | 20214 | 5.94 | 360643 | 2335209 | 27224 |
| 12 | 340751 | 26571 | 7.80 | 367322 | 2419917 | 39097 |
| 13 | 338713 | 16817 | 4.96 | 355530 | 2295538 | 43327 |
--------------------------------------------------------------------------------------------------------
Average number of non-halo cells : 326065 STDDEV % : 7.53 IMBALANCE % : 4.75
Average number of halo cells : 20378 STDDEV % : 21.19 IMBALANCE % : 30.39
Average number of total cells : 346443 STDDEV % : 7.90 IMBALANCE % : 6.03
Average number of faces : 2252487 STDDEV % : 8.70 IMBALANCE % : 7.43
Average number of boundary faces : 31604 STDDEV % : 22.95 IMBALANCE % : 37.38
Maximum number of partition neighbours : 12

Extents:
x: [-8.4999506989e-03, 1.0900000000e-02] m
y: [0.0000000000e+00, 1.6000000000e-02] m
z: [-8.4999544996e-03, 8.4999523774e-03] m
Maximum interior cell index delta: 11400, average: 3.0927526227e+01
Maximum cell face index delta: 2414890, average: 5.7321716654e+02
Volume range: [5.8998222921e-18, 3.9894238087e-12] m^3
Minimum volume in cell with pro-STAR Cell ID 787931
Minimum distance between centroids of neighbor cells = 1.3502742171e-06
between cells with pro-STAR Cell ID 189285 and 220895
Maximum skewness angle = 8.9045486450e+01 deg in cell with pro-STAR Cell ID 4565385
Face validity:
Minimum Face Validity: 1.0000000000e+00
Maximum Face Validity: 1.0000000000e+00
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 4564916 100.000%
Volume Change:
Minimum Volume Change: 7.170639e-05
Maximum Volume Change: 1.000000e+00
Volume Change < 0.000000e+00 0 0.000%
0.000000e+00 <= Volume Change < 1.000000e-06 0 0.000%
1.000000e-06 <= Volume Change < 1.000000e-05 0 0.000%
1.000000e-05 <= Volume Change < 1.000000e-04 1 0.000%
1.000000e-04 <= Volume Change < 1.000000e-03 1 0.000%
1.000000e-03 <= Volume Change < 1.000000e-02 2350 0.051%
1.000000e-02 <= Volume Change < 1.000000e-01 27658 0.606%
1.000000e-01 <= Volume Change <= 1.000000e+00 4534906 99.343%
Maximum boundary skewness angle in region = 8.604515e+01 deg
Overall Face Validity:
Minimum Face Validity: 1.000000e+00
Maximum Face Validity: 1.000000e+00
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 4564916 100.000%
Overall Volume Change:
Minimum Volume Change: 7.170639e-05
Maximum Volume Change: 1.000000e+00
Volume Change < 0.000000e+00 0 0.000%
0.000000e+00 <= Volume Change < 1.000000e-06 0 0.000%
1.000000e-06 <= Volume Change < 1.000000e-05 0 0.000%
1.000000e-05 <= Volume Change < 1.000000e-04 1 0.000%
1.000000e-04 <= Volume Change < 1.000000e-03 1 0.000%
1.000000e-03 <= Volume Change < 1.000000e-02 2350 0.051%
1.000000e-02 <= Volume Change < 1.000000e-01 27658 0.606%
1.000000e-01 <= Volume Change <= 1.000000e+00 4534906 99.343%
does it look bad?

Also, what I dont know how important but there is a message:
Quote:
conjugate-gradient solver did not converge !
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Old   September 16, 2014, 06:25
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I cannot find anything wrong with your mesh statistics.
Make sure your interfaces are good.

What I was suggesting is that you create a threshold for temperature above your expected maximum. For eg. if you are expecting the max temperature would be about 400 C, create a threshold for temperature > 500 C.
As you run your simulation, look at the threshold. This will show you where the temperature is initially going high. This would give you a better idea of what is happening.
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Old   September 16, 2014, 06:46
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well, I cannot say much about interfaces , as they are not used much
also, boundary conditional etc does not contain any temperature differences..

Literally no ideas where such, immediate temp. raise is coming from

also, temperature raises pretty much on the velocity vector of the flow

any help in "debugging" is welcome !
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