Divergence in AMG solver!
Hi everyone!
I'm trying to simulate in Fluent a 2D compressible flow around the NACA 0012, in order to study the velocity profiles in the boundary layer. Reynolds=500000 and M=0.22 Boundary conditions:  inlet: pressureinlet (direction x)  outlet: pressureoutlet  top & bottom: symmetry Turbulence: KEpsilon. Intensity of turbulence: 3.1% and Lenght scale: 0.0976m Solution method: Pressurevelocity coupling, scheme: coupled. Second order After 15 iterations, three errors appear: # Divergence detected in AMG solver: pressure coupled > Decreasing coarsening group size! # Divergence detected in AMG solver: pressure coupled > Increasing relaxation sweeps! # Divergence detected in AMG solver: pressure coupled > Changing to Wcycle! It also gives me some messages saying: turbulent viscosity limited to viscosity ratio of 10^5 in 1325 cells I don't know what it means and how to solve it... I'm really desperated! :S Any ideas?? Thanks in advance! 
Have you used the FMG initializer at all to get a good approximate starting solution for your case? The FLUENT documentation describes how to use it.
Also, try reducing your Courant number. The default is 200, try lowering that to between 50100. 
I've already solve it!! I ran it in transient and it converged very well, then I changed to steady.
Anyway, thank you for your advice ;) 
Glad to hear you solved the problem! Your solution does work but I imagine it took a while for you to wait until the solution settled out. I would suggest trying the solutions I've mentioned above. They should help you get a converged steady state solution much quicker than performing a transient analysis.

Quote:
Thanks in advance! 
2 Attachment(s)
Hello everyone,
Hope everyone is doing fine. I am modeling a 3D model of underdrain pipe flow. Details about the model is : Inlet: pressure inlet with hydrostatic pressure outlet: pressure outlet wall and symmetry Solver: Pressure based Model: Standard ke model Solution Method: coupled Least square cell based gradient and 2nd order upwind momentum Time : transient URF was all 1 except k and e. Those were 0.8 I started with 0.0015 time step. After running 5 second ( almost 35000 iteration) it gave the error " divergence detected in AMG solver: k" so I reduced all URF to 0.7 . Then it gave the error " divergence detected in AMG solver: epsilon ". I reduced the URF to 0.5~0.6. Then it gave several error after 2.7 sec run time. # Divergence detected in AMG solver: pressure coupled > Decreasing coarsening group size! # Divergence detected in AMG solver: pressure coupled > Increasing relaxation sweeps! # Divergence detected in AMG solver: pressure coupled > Changing to Wcycle! turbulent viscosity limited to viscosity ratio of 10^5 in 93000 cells. Please find the following image for error and residuals. I tried with Flow courant number 100, but no improvement. Before showing error it gives same mass flow rate in outlet for long time, which I assume as converged. I am not an expert in CFD field. Trying to learn these things for my thesis. Hope someone can help me how can I get rid of these error. Thanks in advance Regards, Tanjina 
Hey Tanjina!
Did you manage to find solution to you problem? I have similar problem right now. Quote:

That's the solution for # Divergence detected in AMG solver
Hi Guys!
It may come too late but it could help someone else in the future: When you get the following error message: :rolleyes: # Divergence detected in AMG solver: pressure coupled > Decreasing coarsening group size! # Divergence detected in AMG solver: pressure coupled > Increasing relaxation sweeps! # Divergence detected in AMG solver: pressure coupled > Changing to Wcycle! It actually means that your interfaces are not well configured; please check them on “Mesh Interfaces” and select “coupled wall” on “interface option” Please let us know if it works Thanks Loffy 
# Divergence detected in AMG solver: temperature > Increasing relaxation sweeps! #
Hi,
I am modelling 2 hydropneumatic tanks in transient 2 phase condition. My model is planar. I have a ball valve in my model. I made the geometry by distinct faces. It works when I use coarse mesh size, but when I make my mesh finer, or change it to tri mesh even when I add inflation this error appears during first iteration! "# Divergence detected in AMG solver: temperature > Increasing relaxation sweeps!" I tried hybrid initialization and defining my interfaces in ball valve as matching but no success. I think maybe my mesh is not joining well in fine mesh case at interfaces. But I do not know how to solve it. It is very urgent. Can anybody kindly help me to find the problem? 
Divergence detected
Quote:

Divergence detected in AMGsolver: pressure coupled
Hi guys,
being relatively new to CFD, I'm trying to analyse a model of a 3Dwing in FLUENT 14.5. I've put a link below where you can find my mesh, a little over 1,6*10^6 cells octree mesh from ICEM. Inviscid flow, Energy equations ON, all models turned off. I've chosen for the simplest options available to simply analyse lift on the wing. Materials: Fluid is air, ideal gas, default settings Boundary conditions Inlet: pressurefarfield, M=0.15, Gauge pressure=101325 Pa Farfield: pressurefarfield, M=0.15, Gauge pressure=101325 Pa Outlet: pressurefarfield, M=0.15, Gauge pressure=101325 Pa Symmetry: symmetry Wing: wall Flap: wall Solution methods Coupled scheme, default settings, Pseudo Transient Further more I've run a FMGinitialization with default settings, except for: Number of cycles on level 1: 100 Eventually my simulation will not start due to the error: Divergence detected in AMGsolver: pressure coupled I've tried using a SIMPLE scheme for the solution methods which let again to Divergence detected in AMGsolver: xmomentum. Also I've changed the combination of Boundary conditions (inlet  farfield  outlet):  pressure inlet  farfield  pressure outlet  velocity inlet  farfield  outflow  pressure inlet  wall  pressure outlet Below I've added links to my case and data as well. Mesh: https://www.dropbox.com/s/qdt066dkij...ACA230124.msh Case: https://www.dropbox.com/s/5tn6zyr2mp...ACA230124.cas Data: https://www.dropbox.com/s/dao5536kpc...ACA230124.dat My questions are: 1. Is my combination of Boundary Conditions feasible? 2. What do I have to change to get this going? 
I have some additional information concerning my error in the previous post:
In the command window the following was displayed: Divergence detected in AMG solver: pressure coupled > Decreasing coarsening group size! Divergence detected in AMG solver: pressure coupled > Increasing relaxation sweeps! Divergence detected in AMG solver: pressure coupled > Changing to Wcycle! Do I have to dig deeper into the AMGsolver or is there something wrong with my general settings? In the meantime  I have tried a different Mach number with the Boundary Conditions, being M=0.6.  Also I have changed the Relaxation Factor for Density from 1.0 to 0.5.  Furthermore I have changed the Convergence Criterion of the Residuals Monitors from 'absolute' to 'none'.  Finally I've changed the FMG Courant Number from 0.75 to 0.1 The latter two were attempts to solve the problem that I've read elsewhere here on the forum. However none of the above measures have solved the issue. Is there anyone who knows how to solve this and share his or her wisdom? 
Using Multiphase
Hi, I am analysis injector in multiphase, during the analysis I am getting error as" Divergence detected in AMG solver: pressure coupled "
Please help me Models  Model Settings  Space Axisymmetric Time Unsteady, 2ndOrder Implicit Viscous Standard kepsilon turbulence model Wall Treatment Standard Wall Functions Multiphase kepsilon Models Dispersed Approach Heat Transfer Enabled Solidification and Melting Disabled Radiation None Species Disabled Coupled Dispersed Phase Disabled NOx Pollutants Disabled SOx Pollutants Disabled Soot Disabled Mercury Pollutants Disabled Models  Model Settings  Space Axisymmetric Time Unsteady, 2ndOrder Implicit Viscous Standard kepsilon turbulence model Wall Treatment Standard Wall Functions Multiphase kepsilon Models Dispersed Approach Heat Transfer Enabled Solidification and Melting Disabled Radiation None Species Disabled Coupled Dispersed Phase Disabled NOx Pollutants Disabled SOx Pollutants Disabled Soot Disabled Mercury Pollutants Disabled Boundary Conditions  Zones name id type  fuel_inlet 5 velocityinlet oxidizer_inlet 6 velocityinlet wall_ 7 wall pressure_outlet 8 pressureoutlet axis 9 axis wallsurface_body 10 wall Setup Conditions fuel_inlet Condition Value  Supersonic/Initial Gauge Pressure (pascal) 0 is zone used in mixingplane model? no oxidizer_inlet Condition Value  Supersonic/Initial Gauge Pressure (pascal) 0 is zone used in mixingplane model? no wall_ Condition Value  Wall Thickness (mm) 0 Heat Generation Rate (w/m3) 0 Material Name aluminum Thermal BC Type 1 Temperature (k) 300 Heat Flux (w/m2) 0 Convective Heat Transfer Coefficient (w/m2k) 0 Free Stream Temperature (k) 300 Wall Motion 0 Shear Boundary Condition 0 Define wall motion relative to adjacent cell zone? yes Apply a rotational velocity to this wall? no Velocity Magnitude (m/s) 0 XComponent of Wall Translation 1 YComponent of Wall Translation 0 Define wall velocity components? no XComponent of Wall Translation (m/s) 0 YComponent of Wall Translation (m/s) 0 External Emissivity 1 External Radiation Temperature (k) 300 Wall Roughness Height (mm) 0 Wall Roughness Constant 0.5 Rotation Speed (rad/s) 0 Xcomponent of shear stress (pascal) 0 Ycomponent of shear stress (pascal) 0 Fslip constant 0 Eslip constant 0 Surface tension gradient (n/mk) 0 Specularity Coefficient 0 Convective Augmentation Factor 1 pressure_outlet Condition Value  Gauge Pressure (pascal) 0 Backflow Direction Specification Method 1 is zone used in mixingplane model? no axis Condition Value  wallsurface_body Condition Value  Wall Thickness (mm) 0 Heat Generation Rate (w/m3) 0 Material Name aluminum Thermal BC Type 1 Temperature (k) 300 Heat Flux (w/m2) 0 Convective Heat Transfer Coefficient (w/m2k) 0 Free Stream Temperature (k) 300 Wall Motion 0 Shear Boundary Condition 0 Define wall motion relative to adjacent cell zone? yes Apply a rotational velocity to this wall? no Velocity Magnitude (m/s) 0 XComponent of Wall Translation 1 YComponent of Wall Translation 0 Define wall velocity components? no XComponent of Wall Translation (m/s) 0 YComponent of Wall Translation (m/s) 0 External Emissivity 1 External Radiation Temperature (k) 300 Wall Roughness Height (mm) 0 Wall Roughness Constant 0.5 Rotation Speed (rad/s) 0 Xcomponent of shear stress (pascal) 0 Ycomponent of shear stress (pascal) 0 Fslip constant 0 Eslip constant 0 Surface tension gradient (n/mk) 0 Specularity Coefficient 0 Convective Augmentation Factor 1 Solver Settings  Equations Equation Solved  Flow yes Volume Fraction yes Turbulence yes Energy yes Numerics Numeric Enabled  Absolute Velocity Formulation yes Unsteady Calculation Parameters  Time Step (s) 1e06 Max. Iterations Per Time Step 20 Relaxation Variable Relaxation Factor  Density 1 Body Forces 1 Volume Fraction 1 Granular Temperature 1 Turbulent Kinetic Energy 1 Turbulent Dissipation Rate 1 Turbulent Viscosity 1 Energy 1 Linear Solver Solver Termination Residual Reduction Variable Type Criterion Tolerance  Flow FCycle 0.1 Turbulent Kinetic Energy Flexible 0.1 0.7 Turbulent Dissipation Rate Flexible 0.1 0.7 Energy Flexible 0.1 0.7 PressureVelocity Coupling Parameter Value  Type Coupled Pseudo Transient no Flow Courant Number 1 Explicit momentum underrelaxation 1 Explicit pressure underrelaxation 1 Discretization Scheme Variable Scheme  Density Second Order Upwind Momentum Second Order Upwind Volume Fraction Modified HRIC Turbulent Kinetic Energy Second Order Upwind Turbulent Dissipation Rate Second Order Upwind Energy Second Order Upwind Solution Limits Quantity Limit  Minimum Absolute Pressure 1 Maximum Absolute Pressure 5e+10 Minimum Temperature 1 Maximum Temperature 5000 Minimum Turb. Kinetic Energy 1e14 Minimum Turb. Dissipation Rate 1e20 Maximum Turb. Viscosity Ratio 100000 Mesh Quality: Orthogonal Quality ranges from 0 to 1, where values close to 0 correspond to low quality. Minimum Orthogonal Quality = 1.51819e01 Maximum Aspect Ratio = 2.58088e+01 Mesh Size Level Cells Faces Nodes Partitions 0 29209 59553 30345 1 1 cell zone, 7 face zones. 
Hi Kanmaniraja,
Could please provide some additional information about your case? What is the size of your mesh, what does the quality report say, which 'Boundary Conditions' and 'Solution Controls' do you use? Your error can be caused by various issues, so the more information the better. 
Hi,
Guys I am trying to simulate the fulfilling of a bottle with compressed air in Fluent. I set as boundary conditions Inlet_pressure  is a constant value, and mass flow inlet also a constant value. Models: viscouslaminar, energy on Now when I run the simulation I receive the following errors iter continuity xvelocity yvelocity energy time/iter # Divergence detected in AMG solver: temperature > Increasing relaxation sweeps! Error: Divergence detected in AMG solver: temperature Error: Divergence detected in AMG solver: temperature Error Object: #f Any suggestions? 10x 
All times are GMT 4. The time now is 00:39. 