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Old   March 17, 2015, 05:41
Default Simple Flow Problem
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hey guys need help in solving this question. I did attach a pic to see overview of question.

Here's the detail i put while solving this question:
SOLVER TYPE : Pressure Based
Velocity Formulation : Absolute
Time : Steady

MODEL : Laminar

MATERIAL : Water<Liquid>

BOUNDARY CONDITION : INLET- velocity magnitude = 1 m/s
gauge pressure = 100000 Pa

OUTLET - gauge pressure = 100100 Pa

**Rest are walls with default setting.

REFERENCE VALUE : COMPUTE from Inlet

SOLUTION CONTROL : pressure = 0.2
momentum = 0.6

***HYBRID INITIALIZATION

And Here's the result i am getting :

- After Initialization :

Setting Post Processing and Surfaces information ... Done.
/solve/initialize/hyb-initialization
Initialize using the hybrid initialization method.

Checking case topology...
-this case has inlets & outlets both
-pressure information is not available at the boundaries,
so it will be initialized with constant pressure

iter scalar-0

1 1.000000e+00
2 6.955973e-05
3 1.515677e-05
4 1.302184e-05
5 1.477042e-05
6 7.976428e-06
7 8.482481e-06
8 9.215501e-06
9 6.680556e-06
10 8.885878e-06
hybrid initialization is done.
Warning: convergence tolerance of 1.000000e-06 not reached
during Hybrid Initialization.


-Divergence detected in AMG solver: pressure correction
-# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
-# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
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File Type: jpg ehl-QUESTION.jpg (34.0 KB, 137 views)
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Old   March 17, 2015, 06:31
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Is ur gauge pressure is atmospheric pressure
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Old   March 17, 2015, 06:35
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yes it is atmospheric pressure..
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Old   March 17, 2015, 06:36
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Then set ur gauge pressure to zero.
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Old   March 17, 2015, 06:38
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Both inlet and outlet
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Old   March 17, 2015, 06:50
Default Inlet and Outlet gauge pressure = 0 Pa
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Initialize using the hybrid initialization method.

Checking case topology...
-this case has inlets & outlets both
-pressure information is not available at the boundaries,
so it will be initialized with constant pressure

iter scalar-0

1 1.000000e+00
2 6.945340e-05
3 1.450468e-05
4 1.625007e-05
5 1.728765e-05
6 1.128941e-05
7 8.551013e-06
8 8.563514e-06
9 1.146841e-05
10 7.437878e-06
hybrid initialization is done.
Warning: convergence tolerance of 1.000000e-06 not reached
during Hybrid Initialization.
Writing Settings file...
writing rp variables ... Done.
writing domain variables ... Done.
writing fluid (type fluid) (mixture) ... Done.
writing l-outlet (type pressure-outlet) (mixture) ... Done.
writing l-inlet (type velocity-inlet) (mixture) ... Done.
writing int_fluid (type interior) (mixture) ... Done.
writing l-back (type wall) (mixture) ... Done.
writing l-bottom (type wall) (mixture) ... Done.
writing l-front (type wall) (mixture) ... Done.
writing l-top (type wall) (mixture) ... Done.
writing s1-bottom (type wall) (mixture) ... Done.
writing s2-top (type wall) (mixture) ... Done.
writing zones map name-id ... Done

iter continuity x-velocity y-velocity z-velocity time/iter
1 1.0000e+00 6.4548e-03 2.8059e-01 1.2227e-03 0:33:18 999
2 1.0000e+00 3.6747e-01 1.6220e+01 6.2894e-03 0:33:16 998
3 1.2984e-01 3.3730e-03 5.3236e-01 3.7364e-03 0:36:33 997
# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
4 1.0000e+00 2.0753e-01 2.4740e+01 2.8992e-03 0:39:11 996
5 2.8992e-01 2.1585e-02 6.4564e-01 2.2856e-02 0:41:16 995
6 2.6850e+00 7.2350e-02 5.5865e-01 6.9776e-02 0:42:55 994
# Divergence detected in AMG solver: pressure correction -> Increasing relaxation sweeps!

Error: Divergence detected in AMG solver: pressure correction
Error Object: #f
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Old   March 17, 2015, 07:29
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Is ur simulation is 3D or 2D
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Old   March 17, 2015, 07:42
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Its 3D , With thickness of 1mm
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Old   March 17, 2015, 07:46
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Whats ur solution method details??
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Old   March 17, 2015, 08:19
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Solution method is SIMPLC with default setting of other parameter under that.
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Old   March 17, 2015, 08:30
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use SIMPLE as pressure velocity coupling
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Old   March 17, 2015, 11:12
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What turbulence model u have been using
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Old   March 18, 2015, 00:18
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Turbulence model is Laminar.
And still i am not getting converge solution with any of the solver.

Btw i have one more doubt :
Why is it when we bring a mesh file from ICEM to FLUENT its quality degraded???
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Old   March 18, 2015, 01:18
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Due to fluent accepts only unstructured mesh. Use k- epsilon model for ur flow
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Old   March 18, 2015, 01:22
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I have used k-epsilion model as well. It didn't work.

Btw then what is the solution for my mesh. How can i call my structured mesh to fluent without affecting its quality.

Btw does high aspect ratio effect the solution in my case.
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Old   March 18, 2015, 01:44
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Select ur output solver as fluent. Before that convert ur premesh to unstructured mesh.


Aspect ratio must be close to 1 shows high quality. 0 shows low quality.
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Old   March 18, 2015, 05:15
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I am sorry but how aspect ratio can be less than 1. Its maximum side/minimum side.
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Old   March 18, 2015, 10:41
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Simple flow? I think no...
You have an inlet velocity of 1 m/s with a cross area of 10,001mm x 1mm.
Then the fluid should pass in a restriction of about 0,001mm x 1mm: approximately your fluid will reach a velocity of 10000 m/s!!!!

Are you sure of your boundary conditions?

Even with low inlet velocity you should expect also cavitation.
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Last edited by ghost82; March 18, 2015 at 12:09.
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Old   March 18, 2015, 11:56
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I know cavitation is suppose to happen there. But still how can solve this situation???

What changes should i bring to my boundary condition or any other conditions to get the final results.

Btw can you also explain me how cavitation is affecting my result???(if you think it is)
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Old   March 18, 2015, 12:05
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The problem here is not cavitation.
How did you set your inlet velocity? From experimental or..?
It's non physical to have 10000 m/s velocity in the restriction..Try to solve for Bernoulli and you will notice that you need to have a non physical pressure inlet...
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