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November 14, 2014, 10:24 

#21  
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Manu Poolakkal
Join Date: Oct 2014
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Quote:
my simulation is for a double pipe counter flow heat exchanger (3d). even after 10000 iteration fluent is not displaying anything like "solution converged !" but the results seem to be not changing. what should i do? how can i check whether the solution is converged or not? 

November 18, 2014, 05:17 
Convergence in gas quenching process

#22 
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Join Date: Oct 2014
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Hi Centurion 2011,
I got a big problem in convergence criterion for my simulation through Ansys Fluent. I have almost tried all steps that you have suggested in your post about convergence. Let me expalin my problem first. Inorder to run a transient simulation, initial converged inputs are essential. So, I ran a steady state pressure based simulation. Convection and conduction processes takes place in quenching. So,obviously energy and turbulent models were switched on. I used pressure based coupled solver with pseudo transient method to speed up the convergence. The discretization schemes were (default), Pressure Standard Momentum second order upwind Energy second order upwind I have tried Higher order term relaxation with default (0.75) relaxation factor and also 0.25 (in another simulation). The simulation ran for 5000 iterations with pseudo time step of 1e05. The result was not so convincing i.e., the solution was not converged. At the end of the simulation, my conservative terms (residuals)were of the order continuity e03 momentum e05 in x direction e04 in y direction e05 in zdirection respectively energy e17 mass imbalance e+02 These residuals keeps on oscillating and I couldn't standardise the solution.I have also crosschecked the mesh. It has decent orthogonal quality and skewness. Minimum orthogonal quality is 0.20 Max. Skewness is 0.85 Max aspect ration is 45 but, these values are accepted as the geometry of the CAD model is relatively complex. And my question here is , should I try for more iterations or should I further reduce relaxation terms? If there are any other suggestions, it is always welcome. And please correct me, if the steps that I mentioned here are inappropriate. I also expect inputs from everyone. 

February 18, 2015, 15:12 

#24 
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got my problem solved long back


May 9, 2015, 09:02 

#25  
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Imran Ansari
Join Date: Jun 2014
Location: Aligarh Muslim University
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Quote:
When using NITA in the fraction Step method. As CL And CD achived to their correct value and as time advances there is no changes in these values . but continuity residual varies between 0.1 to 0.001 . Is we can say solution converged or not . is solution correct or not?? 

November 19, 2015, 04:51 
limitation of pressurebased and densitybased solvers Fluent V15

#26 
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HALOUANE Yacine
Join Date: Jun 2015
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Hello everyone,
I know that the pressure based solver is better for slow incompressible flow and the densitybased solver is recommended for supersonic flow and shock waves simulation. I'm wondering about the limitation of each solver? when or where can I use them or cannot use them? I prefer to give the reference of your answers and thank's a lot. good luck. 

November 24, 2015, 15:46 
problem

#27 
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frank
Join Date: Oct 2014
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Hi there
my case is about oilWATER two phase flow. I couldn't achieve convergence because my continuity residuals are about 10^2. what do you think about this problem? is this problem because of courant number(about 0.02) or momentum under relaxation(0.5) or multiphase flow coupled scheme that I used? 

February 7, 2016, 12:58 
continuity equation convergence

#28 
Senior Member
Join Date: Oct 2014
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Hello centurion2011.
I am simulating an open channel with some hydraulic structures inside it. Steady state, VOF for the free surface. All the variables (xvelocity, y velocity, z velocity, k, epsilon, VOF of the secondary phase) converge with residual of 10^(4), whereas the continuity equation residuals remain around 10^(1), although the flow does not change any longer during iterations (10000 iterations!). Do you know why? Thank you 

August 27, 2016, 04:08 
Convergence

#29 
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asma hosseini
Join Date: Jul 2016
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Hello
I'm working a nano channel flow with electrophorse. I'm told get a plot of EOF velocity every 2000 iterations and when 2 plots had no changes, my solution is converged. I have calculated over 51000 iterations but plots change always. What should I do? 

August 27, 2016, 04:19 

#30 
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Imran Ansari
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Location: Aligarh Muslim University
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it will depend on type of problem steady/transient >you should run more than 150 non dimensional time. and see the pattern it will be of oscillatory nature. and reduce your time step size.


October 3, 2016, 05:45 
Same convergence results  problem solved?

#31  
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Join Date: Nov 2015
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Quote:
Hi Ema40, I'm having the same results for what it seems a similar problem to yours. Did you find out the reason why continuity equation residuals remain 10^(1)? Thanks in advance! 

October 25, 2016, 05:54 

#32 
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Gujarat
Join Date: Oct 2016
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hi..i am trying to solve double pipe heat exchanger using inserts in CFD.
i used double precision, energy eqon modelturbulent(2 eq,stnd wall fun) solution method:SIMPLe(PRESSUREVELOCITY BASED)second order my energy residules are not converges during solution.so ans is not converged. boundary conditions: hot inlet:mass flow rate1.3 kg/s,inlet temp413 k hot outletpressure based cold inlet:mass flowrate1.3, temp298 k cold outlet:pressure base any one have solution?plz guide me. thanks in advance. Last edited by mahipal parmar; November 1, 2016 at 02:04. 

October 28, 2016, 19:18 

#33 
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Radwanma
Join Date: Oct 2014
Posts: 30
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Hi All,
Could you confirm that the form of ct = Turbine_Torque / (0.5*density*pi*R^3*wind_speed^2) is correct to get coefficient of torque directly from fluent, please? Thanks, 

March 13, 2017, 11:29 

#35 
Member
kaouachi anouar
Join Date: Jul 2016
Posts: 64
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hello thank you for your help please im doing simulation in fluent for study the flow overe stepped spillways but the results its stay bed please i want to send you my projet to chek can you help me please ?


March 23, 2017, 02:17 

#36  
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Grama Srivatsa
Join Date: Jun 2016
Posts: 2
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Quote:
I am working on a flow simulation values over a blunt body with a spike, after running around 5000 iterations, the residuals(continuity, Energy, Xvelocity and Yvelocity) are oscillating at E3 and E4 but the drag coefficient is constant, can I say my results have converged? 

April 20, 2017, 13:20 

#37 
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kaouachi anouar
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hello for I'm working for simulation for the flow over stepped spillways 10^3
is enough ? regards 

June 16, 2017, 21:10 

#38 
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BlackHeartInertia
Join Date: May 2017
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I check mass imbalance and it was 1e5 and I saved project. then it changes to 1e3.. why? What should i do?
Sent from my SMG570M using CFD Online Forum mobile app 

June 19, 2017, 07:30 

#39  
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June 19, 2017, 09:16 

#40  
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BlackHeartInertia
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Quote:
(In the case of residuals they are stable but dont decrease from arround 1 exp2, and convergence monitors are stable) 

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convergence, fluent, mesh 
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