[eegala]

Try these two methods,

1. First run the cold flow without energy equation, and then start the energy and species transport equations. Than give a high temperature by patching above 1400 K near the fuel + air mixing zone.

2. Reduce the time step to a very low value (around 10^-6 s) and run for some iterations and then increase the time step.

The errors in combustion simulations occurs due to very high local gradients due to ignition.

[sanjeetlimbu]

Thanks for help!

actually i was doing patch with 766K for whole body (my case is autoignition for a closed system vessel, so not inlet point to patch).. doing the same cold flow step calculation to initialise. but could not get ignition

If I do with 1400K as you adviced... Will it show the low temperature two stage ignition which that fuel mixture show at 766K.

Anyway I will try with 1400 and see...

thanks again

[sanjeetlimbu]

Dear Sir


I tried using the cold flow+ patch at 1400K the body -part in mesh , but no combustion observed , only the temp raised....

I tried then 900K but no raise observed in products _ CO2 or H20 in mole fraction...

In both cases the temperature just climbs to the patch value and there is no temp /pressure raise after than

[sanjeetlimbu]

Dear sir...

Can i get autoignition using chemical equilibrium- in partially premixed

As I tried the flamelet , but getting some error about the scaler mixture fraction limit grater than domain largest mixture fraction.

Since I used the equilibrium, and can you guide me how to achieve autoignition by any method... I am facing huge problem

[sanjeetlimbu]

Pl reply I think that due to some setting the reaction not happening - its seem suppressed chemistry case

[Maryam-A]

Hello everybody
I used uds for adding transport equation of particles to investigate Brownian motion and thermophoresis ,but see divergence detected for x-momentum .
I reduced all URF and tried different solving method but no help
after that I did try what you said with the f-cycle and bcgstab method, but it then said there was divergence in Y-Momentum, so i did the same for it, but then it said there was divergence in temperature, so i did the same for it, and the same for uds.

when i did that it just gave out this error:

Error: > (greater-than): invalid argument [2]: wrong type [not a number]
Error Object: 1.#qnan


Any ideas?
Please help me it took me much time to define source term,convection flux and boundary flux according to manual (no help from my supervisor )

Thanks

[Abhya]

Originally Posted by Maryam-A

Hello everybody
I used uds for adding transport equation of particles to investigate Brownian motion and thermophoresis ,but see divergence detected for x-momentum .
I reduced all URF and tried different solving method but no help
after that I did try what you said with the f-cycle and bcgstab method, but it then said there was divergence in Y-Momentum, so i did the same for it, but then it said there was divergence in temperature, so i did the same for it, and the same for uds.

when i did that it just gave out this error:

Error: > (greater-than): invalid argument [2]: wrong type [not a number]
Error Object: 1.#qnan


Any ideas?
Please help me it took me much time to define source term,convection flux and boundary flux according to manual (no help from my supervisor )

Thanks

Try getting a flow field close to the physical field without the source terms first, after sufficient convergence switch on the source terms (keep all solver parameters to the default values)

[Maryam-A]

Thankyou for your advice
I tried it before, but no change

when I used default mass flow rate(as convection flux of uds equation), it ran without problem but as you know I wanted to investigate effect of Brownian and Thermophresis of particle,so I should use udf for convection flux of equation by particle's density and I think this causes all the problems about divergence

any idea?
help me plz

maryam

[Maryam-A]

I still cant solve divergence detected problem in -x momentum
I really dont know why and what part of my code causes this problem
please help me

maryam

[Maryam-A]

maybe mu-uds-flux-function leads to divergence, because I see problem as soon as active this part in uds panel.

this is:

DEFINE_UDS_FLUX(my_uds_flux,f,t,i)
{
cell_t c0, c1 = -1;
Thread *t0, *t1 = NULL;

real NV_VEC(psi_vec), NV_VEC(A), flux = 0.0;

c0 = F_C0(f,t);
t0 = F_C0_THREAD(f,t);
F_AREA(A, f, t);

/* If face lies at domain boundary, use face values; */
/* If face lies IN the domain, use average of adjacent cells. */

if (BOUNDARY_FACE_THREAD_P(t)) /*Most face values will be available*/
{

NV_DS(psi_vec, =, F_U(f,t), F_V(f,t),F_W(f,t), *, ro_p);

flux = NV_DOT(psi_vec, A); /* flux through Face */
}
else
{
c1 = F_C1(f,t); /* Get cell on other side of face */
t1 = F_C1_THREAD(f,t);

NV_DS(psi_vec, =, C_U(c0,t0),C_V(c0,t0),C_W(c0,t0),*,ro_p);
NV_DS(psi_vec, +=, C_U(c1,t1),C_V(c1,t1),C_W(c1,t1),*,ro_p);

flux = NV_DOT(psi_vec, A)/2.0; /* Average flux through face */

}

/* Fluent will multiply the returned value by phi_f (the scalar's
value at the face) to get the "complete'' advective term. */

return flux;
}

***********************************************
help me plz

[Farzaneh*]

Hi everybody
I'm modeling the plume of an industrial stack with fluent, to find the concentration of SO2 in a special distance of stack, and there are 9 components that coming out from the stack.
the temperature of stack is 141 degree of centigrade and the ambient temperature is 15 degree.
when I define just SO2 for the outlet of stack, the solution will be converge. but when I inter all of components, at final it's diverged and I see these messages:
divergence of temperature
divergence of species-1
divergence of species-2

could you help me please? I think I make a mistake in the definition of mixture that comes out from the stack.

Farzaneh

[bo_5042]

Thanks, everyone. This thread really helped me. I'll describe my case for future readers.

I'm using ANSYS FLUENT 18.2 to develop a transient model for a reactive packed bed. The model diverges in the middle of the simulation without obvious fluctuation in any of the observed parameters. The error messages are:

# Divergence detected in AMG for mp-x-momentum: protective actions enabled!
# Divergence detected in AMG for mp-x-momentum, temporarily solve with BCGSTAB!
# Divergence detected in AMG for mp-y-momentum: protective actions enabled!
# Divergence detected in AMG for mp-y-momentum, temporarily solve with BCGSTAB!
# Divergence detected in AMG for mp-z-momentum: protective actions enabled!
# Divergence detected in AMG for mp-z-momentum, temporarily solve with BCGSTAB!

Divergence detected in AMG solver: pressure correction# Divergence detected in AMG for gas-species-0: protective actions enabled!
# Divergence detected in AMG for gas-species-0, temporarily solve with BCGSTAB!

I changed the cycle type of all species from the default "Flexible" to "F-cycle" in Advanced Solution Control. The BCGSTAB is used. The problem is solved.

[mz_uon]

Hey Depan

For how long did you run your simulation? Does anyone have any suggestions?
(Although this is quite an old post)

Originally Posted by whtrs

hi

I have ever meet this kind of problem。
At begining, I stop the calculation of all specie equations and energy euqation， after some iterations，turn on those equations。And no divergence detected anymore. good luck to you!

depan

[Amanpreet]

Hello
i am facing the issue while simulating a model in icepak.
what i do to resolve this issue
1. Refine the mesh
2. Change the under relaxation setting.

Every time solution diverges and error shows "divergence detected in AMG solver: species-0 "
Please help to resolve this
Thanks

[mz_uon]

Originally Posted by Amanpreet

Hello
i am facing the issue while simulating a model in icepak.
what i do to resolve this issue
1. Refine the mesh
2. Change the under relaxation setting.

Every time solution diverges and error shows "divergence detected in AMG solver: species-0 "
Please help to resolve this
Thanks

Hello Amanpreet

See my earlier post. How I resolved this was by solving only a few equations and after some amount of simulation initiating other equations.