# Simple Flow Problem

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March 17, 2015, 05:41
Simple Flow Problem
#1
New Member

Shailesh
Join Date: Mar 2015
Posts: 16
Rep Power: 9
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

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!
Attached Images
 ehl-QUESTION.jpg (34.0 KB, 137 views)

 March 17, 2015, 06:31 #2 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 Is ur gauge pressure is atmospheric pressure

 March 17, 2015, 06:35 #3 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 yes it is atmospheric pressure..

 March 17, 2015, 06:36 #4 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 Then set ur gauge pressure to zero.

 March 17, 2015, 06:38 #5 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 Both inlet and outlet

 March 17, 2015, 06:50 Inlet and Outlet gauge pressure = 0 Pa #6 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 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

 March 17, 2015, 07:29 #7 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 Is ur simulation is 3D or 2D

 March 17, 2015, 07:42 #8 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 Its 3D , With thickness of 1mm

 March 17, 2015, 07:46 #9 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 Whats ur solution method details??

 March 17, 2015, 08:19 #10 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 Solution method is SIMPLC with default setting of other parameter under that.

 March 17, 2015, 08:30 #11 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 use SIMPLE as pressure velocity coupling

 March 17, 2015, 11:12 #12 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 What turbulence model u have been using

 March 18, 2015, 00:18 #13 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 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???

 March 18, 2015, 01:18 #14 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 Due to fluent accepts only unstructured mesh. Use k- epsilon model for ur flow

 March 18, 2015, 01:22 #15 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 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.

 March 18, 2015, 01:44 #16 New Member   Muthu pandy Join Date: Feb 2015 Posts: 20 Rep Power: 9 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.

 March 18, 2015, 05:15 #17 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 I am sorry but how aspect ratio can be less than 1. Its maximum side/minimum side.

 March 18, 2015, 10:41 #18 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 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. __________________ Google is your friend and the same for the search button! Last edited by ghost82; March 18, 2015 at 12:09.

 March 18, 2015, 11:56 #19 New Member   Shailesh Join Date: Mar 2015 Posts: 16 Rep Power: 9 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)

 March 18, 2015, 12:05 #20 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 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... __________________ Google is your friend and the same for the search button!

 Tags ansys, ansys 14, fluent, fluent 14

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