[dinesh]

Originally Posted by samir_cfd

Good day
I have a problem when I am simulate unsteady flow around a propeller, divergence detected in amg solver. x momentum, I reduce the URF but is the same problem

try to use coupled solver and also see the courant number for your case

[villager]

Some tips.
1) Use Check Case button under Run Calculation menu in modern (12+) versions of FLUENT. Maybe you have forgotten some settings, FLUENT can point some of them out.
2) Check mesh (Mesh -> Check) - skewed elements, minimal element volume (should be positive).
Check visually in your geometry utility for double faces, wrong cell zone/ boundary zone assignment.
3) Use under-relaxation factors.
4) Try to start from 1st order solver.
5) Try to use coupled p-v scheme.
6) Try change the "Advanced" options (multigrid cycle -> F-cycle with
BCGSTAB, reduce termination criteria) - find such recommendations in tutorials for your type of problem.
7) As dinesh says, for unsteady tasks Courant number should be taken into account - generally, less than 1 for explicit coupled solver, try 0.1-0.5 if you have troubles (see Changing the Courant Number in FLUENT manual).

[sarf007]

hi frns

i am doing combustion simulation of IC engine. i have used pressure based solver and under solution controls tab i hav selected PISO scheme similarly for spatial descritization i have selected "Green-Gaus node based" and PRESTO for pressure. i have even Previwed the dynamic mesh for whole 720 degress. but when i go for calculation it runs only for few degrees i.e i have started simulation from 348 deg it runs upto 871 and exactly at 871.25 it is showing error as shown below
"turbulent viscosity limited to viscosity ratio of 1.000000ee05 in 590 cells divergence detected # Divergence detected in AMG solver: x-momentum -> Increasing relaxation sweeps!

i have tried by reducing URFs but it didnt work. can anybody suggest or help me how can i overcome by this problem. it ll be great help if somebody help me out....

regards
sarf

[YANNAPOL]

Dear All,

I try "Solution Control > Explicit Relaxation Factor " reduce to 0.01, and then it works

Let's try yours

Best Regards,
Y S.

[sabin]

Hi,
I had the same divergence problem. I just made the mesh finer, now the solution is going smoothly.

All the best

Sabin Mathew

[Edison Yan]

try increasing the viscosity ratio to1e8 ' it may help, but the fine mesh is the right call!

[lucar4980]

The Under Relaxation Factors can help. Moreover, very often, this error is related to the initial solution that is too far from the final one.
If neither of these suggestions solves the problem....well, check accurately your boundary conditions.
Hope this helps.

[Maryam-A]

Hello
I'm trying simulate a micro channel heat sink (laminar flow) with temperature dependence properties that I used one UDF for all properties. after interpreted UDF, I run and see this error:
"Divergence detected in AMG solver: x-momentum"
I initialized by fmg , before this initialization I saw this error ,too.
"Divergence detected in AMG solver: temperature"
I use simple method, checked mesh and I didn't find problem.
Maybe this all problem related to my UDF?
I would appreciate if anybody help me.
sorry for grammar, I'm weak in English.

[saurabhg2014]

Originally Posted by zeybi1604

Hello. i am doing a multiphase simulation in a packed bed using the mixture model. the volume fraction used was 0.5316.i keep getting the error message "divergence detected in AMG solver: x-momentum" for all the different solvers used and i even changed the under relaxation factors. i really have no idea how to proceed with this simulation!plzz help!thank u.

you solved this problem? i am also facing same problem..any help would be great

[Alex 0122]

Hi everyone !

This may sound obvious but if you work an an unsteady flow, did you first initiate the solving of the equation with a steady flow ?

[Marya]

If your model is axisymmetric make sure that your geometry is adjusted in the first quarter of fluent coordinate system.

[sanjeetlimbu]

Dear sir

I am using 2D planer model with checmkin file to solve the model for ignitoion time.
I am unable to removef thr divergence error even after reducing the relaxation values.
I made the initialisation zero for turbulence

But unable to remove the error

[scipy]

Just ran into this divergence problem when trying to run a simple 2D natural convection problem (validation of the experiment done by P.L. Betts and I.H. Bokhari (2000), “Experiments on Turbulent Natural Convection in an Enclosed
Tall Cavity,” Int. J. Heat & Fluid Flow, Vol. 21, pp. 675‐683.).

Even though I was sure I had set everything correctly, the density of air under Boussinesqe density formulation was 0 (under materials - fluid - air), even though I've set an operating density of 1.225 kg/m3 in the operating conditions for the cell zone (an though this superseeds the setting for the material). The simulation wouldn't even start after. Initialization looked weird too (like artifacts on the screen when I tried to display the starting temperature of 320 K in the air domain).. So, if anyone runs into this problem - the fix was to set the density in the material creation after choosing Boussinesq density formulation (when you first pick it boussinesqe the density it set to zero). Now everything is fine.. URFs don't matter, SIMPLE/Coupled doesn't matter..

[Maryam-A]

Hi everybody

I am trying to investigate the effect of Brownian motion and thermophoresis in microchannel by Ansys Fluent (single phase).

I prepared UDS for transport equation include source term and diffusion term.
Finally I set boundary condition for flux of particle.
But it doesn't converge even for 1 iteration by this error:
divergence detected in Amg solver-x momentum
(I tried many ways:
different URF+different solution methods+AMG solver setting checked but no change )

Thankyou in advance for your help ,I'm stuck in my project.
what should I do?

by the way my code was correct without UDS in this case(only udfs for temperature dependent properties) and UDS was correct for 2 another 2d-article,too.

Regards

[Chethan Kodase]

I didn't receive any divergence error after I changed the time stepping method to adaptive while running calculations.

[LINDON]

Originally Posted by sudhakar
;138052

I tried from urf from .7 to .001 .but i could not get. in my problem no of cells are more than 8 lakh. my problem is shell and tube heat exchanger in 3 dimensional using seggregated solver.previous i solved same problem with out headers .but now i inserted headers now i got above problem divergence detected in AMG solver: momentum

please help me to solve this problem

Kindly check your mesh,if mesh is ok then this problem will be solved.

[deyaa.nabil]

Originally Posted by sarf007

hi frns

i am doing combustion simulation of IC engine. i have used pressure based solver and under solution controls tab i hav selected PISO scheme similarly for spatial descritization i have selected "Green-Gaus node based" and PRESTO for pressure. i have even Previwed the dynamic mesh for whole 720 degress. but when i go for calculation it runs only for few degrees i.e i have started simulation from 348 deg it runs upto 871 and exactly at 871.25 it is showing error as shown below
"turbulent viscosity limited to viscosity ratio of 1.000000ee05 in 590 cells divergence detected # Divergence detected in AMG solver: x-momentum -> Increasing relaxation sweeps!

i have tried by reducing URFs but it didnt work. can anybody suggest or help me how can i overcome by this problem. it ll be great help if somebody help me out....

regards
sarf

بسم الله الرحمن الرحيم

I answer with my simple knowledge

1) Reduce the parametres of the dynamic mesh (Spring / layering / remeshing)

2) Reduce the time step of the transient model

3) check that the density is not (incompressible) because the compression ratio is high

4) try to use coupled scheme and reduce coarant number

5) Reduce the under relaxation factor

6) reduce the stroke length or crank radius


Can you specifies clearly What is the condition of ignition you enters?

you can mailing me on (deyaa.nabil@gmail.com)


Asking Allah for helping you

Good luck

[SELENELEON]

i had the same problem, i reduced the scale of my drawing and the problem was solve

[priyanka swarnkar]

I am trying to analyze heat flow in an annulus of hollow cylinder keeping water as a medium in the annulus.

1) tried to model in 2 D axisymmetry keeping id 30mm and od 152 mm height of cylinder as 124 mm.

the boundary condition applied are: inner dia with temp 304 K and outer dia 300 K, top and bottom surface isolated means adiabatic

2) tried keeping in 2 D planar by treating it as a square of size 124 by 124 mm.

the boundary condition applied to the four sides of this square with temp 304 K from the bottom surface and 300 K to top surface, left and right walls isolated means adiabatic.

when i use air as a medium i get some kind of solution without error
but when i replace it with water, i get the error "Divergence detected in AMG for x-momentum: protective actions enabled"

can someone help me to figure out the mistake

[Saman95]

Hello Dears

I have this problem in my model. I try to simulate an 2d axisymmetric tube that a ball move along the axis boundary. in order to move this ball I enabled Dynamic mesh setting. so the mesh must be decreased/increased in number in the boundary as the picture I have attached here.

I face with error (AMG solver) as the second picture when one of the nodes on the boundary is remove.

can anyone help me how I can solve this problem?


Thanksmodel.JPG