Hi Sanjeet
 

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.

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

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

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

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

question
 

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:confused:, so i did the same for it, but then it said there was divergence in temperature:confused:, 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)

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:confused:

any idea?
help me plz :(

maryam

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

maryam

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:(

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

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:

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.

Hey Depan

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

Divergence in AMG Solver
 

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.