[forAurora]

Dear foamers：
I am trying to simulate the jet in crossflow with reactingFoam, but when the crossflow inlet temperature is set to high temperature (~1500K or ~2000K), there is a problem.

My computational domain is shown in the figure.I use timeVaryingMappedFixedValue to set the temperature distribution at the inlet. If the temperature distribution is between 900-2600K (or 500-1500K after scaling), the calculation will diverge, like this.

--> FOAM FATAL ERROR: (openfoam-2012)
 Maximum number of iterations exceeded: 100 when starting from T0:300.28 old T:3500 new T:1904.52 f:1.63724e+07 p:101617 tol:0.030028

   From Foam::scalar Foam::species::thermo<Thermo, Type>::T(Foam::scalar, Foam::scalar, Foam::scalar, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar, Foam::scalar)const, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar, Foam::scalar)const, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar)const) const [with Thermo = Foam::janafThermo<Foam::perfectGas<Foam::specie> >; Type = Foam::sensibleEnthalpy; Foam::scalar = double; Foam::species::thermo<Thermo, Type> = Foam::species::thermo<Foam::janafThermo<Foam::perfectGas<Foam::specie> >, Foam::sensibleEnthalpy>]
   in file /public1/soft/openfoam/2012/OpenFOAM-v2012/src/thermophysicalModels/specie/lnInclude/thermoI.H at line 76.

If the inlet temperature is set to a uniform 300K, there will be no problem.

Because I set a variable time step, sometimes after a period of time the time step becomes very small (like 1e-12s), which makes the calculation meaningless (this is usually accompanied by the lowest temperature in the flow field becoming the set minimum (200K)), and sometimes the calculation will just diverge.

I have read in other postings that the time step becomes very small probably because the final flow field is so different from the initial case that it takes some crazy time step to reach the correct flow field (I forget the exact posting, thanks to that responder), but I found it to be of little use when I tried it, or maybe I tried to initialize the flow field incorrectly.

The same fluid is entering at inlet (40m/s) and jetIn (160m/s), just marking them as two components at constant/reactions to study mixing, and not setting up the chemical reactions to occur.

I tried to solve this problem by changing the janaf coefficients in constant/thermo, but it did not work well. I also tried to modify the maximum number of iterations, but this proved to be useless, as I don't think it should be a problem of insufficient number of iterations. After making the choice, I changed the ddtScheme from backsward to Euler to continue the calculation, but this would result in a significant decrease in the accuracy of the calculation.

I also noticed that the results of calculations performed for the same setup could be different. Sometimes the problem occurs in the first few steps at the beginning of the calculation, and sometimes it occurs after thousands/tens of thousands of time steps, which simply makes me think that it is a matter of luck anymore.

The computational mesh I use is a simple geometric mesh generated by blockMesh, after first generating a homogeneous mesh and then a simple refineMesh locally. so there is not much problem in the mesh quality?

After trying various boundary conditions, I still can't solve this problem, if I still want to get finer results with the same mesh size (e.g. set ddeScheme to backward, maybe I should try other discrete formats?) What should I do? In particular, what can be the reason for the phenomenon that the temperature becomes the minimum value set?

I am new to CFD and OpenFOAM and would really really appreciate any advice you may have. Thanks in advance!!