Learning Forum

[Milhm]

Hi,nnI am working on spray cooling.I want to spray water in a compressible flow.The stagnation pressure is 4Mpa and static pressure is 0.696Mpa.I set operating pressure to zero and i enter 4Mpa and 0.696Mpa in pressure inlet boundary conditions.I enabled species transport.In materials for mixture template, i select ideal gas for density, mixing law for Cp and Sutherland Law for viscosity.I use pressure swirl atomizer.nnAt the beginning of injection i recieve this error:# Divergence detected in AMG for pressure coupled: protective actions enabled!nn# Divergence detected in AMG for pressure coupled, temporarily solve with BCGSTAB!nnError: Divergence detected in AMG solver: pressure couplednnWhat should I do?what is wrong?.nnRegardsnnMiladn

[Rob]

Please answer the questions posted in n

Hi,I am working on spray cooling.I want to spray water in a compressible flow.The stagnation pressure is 4Mpa and static pressure is 0.696Mpa.I set operating pressure to zero and i enter 4Mpa and 0.696Mpa in pressure inlet boundary conditions.I enabled species transport.In materials for mixture template, i select ideal gas for density, mixing law for Cp and Sutherland Law for viscosity.I use pressure swirl atomizer.At the beginning of injection i recieve this error:# Divergence detected in AMG for pressure coupled: protective actions enabled!# Divergence detected in AMG for pressure coupled, temporarily solve with BCGSTAB!Error: Divergence detected in AMG solver: pressure coupledWhat should I do?what is wrong?RegardsMilad/forum/discussion/comment/97471#Comment_97471

in THIS thread. Creating more threads/posts on this subject is highly not recommended. n

[Milhm]

Excuse me.I did not know where and how should i ask my question.nWould you please answer my question?What should i do to simulate DPM in compressible flow?n

[Amine Ben Hadj Ali]

Excuse me.I did not know where and how should i ask my question.Would you please answer my question?What should i do to simulate DPM in compressible flow?/forum/discussion/comment/97691#Comment_97691

Can you try without particles first?n

[Milhm]

At first i run the simulation with compressible air.Air is ideal gas and sutherland law is used for viscosity.here operating pressure is zero and i enter 4Mpa and 0.696Mpa in pressure inlet boundary conditions.Fluent solves this problem without any error.Then i turn on species transport but i do not turn on Discrete phase model.I change my material from air to mixture template and i run the simulation again.Fluent solves this too without any error.nThen i turn on Discrete phanse.I want to use pressure-swirl-atomizer.At the beginning of injection i recieve this error:# Divergence detected in AMG for pressure coupled: protective actions enabled!n# Divergence detected in AMG for pressure coupled, temporarily solve with BCGSTAB!nError: Divergence detected in AMG solver: pressure couplednnnI attached the paper that i want to simulate.nnBest regardsn

[Amine Ben Hadj Ali]

As Ansys staff I do not look into attached documents. You might post the title of the paper and doi, instead. Are you able to inject using surface injection? Can you post your injection settings.n

[Milhm]

paper: Numerical investigation of droplets-gas mixing performance in depth adjustable underwater launcher cooling chamber -  https://doi.org/10.1108/EC-09-2017-0343nNo i am not able to inject using surface injection.nI should say after that error i get another error:nError: Invalid cp (0.000000e+00 J/kgK) for oxygen at temperature 1.#QNAN0 Kn I set Cp in material as mixing law.what is wrong with cp?.I have four pressure swirl atomizer like this.n

[Rob]

If air is an ideal gas, where is the oxygen coming into the model? How many particle streams have you got? n

[Milhm]

My particles are droplet .I think to enable the droplet in injection settings, i should enable species transport. Is it correct?nI assumed 200 particle streams for any injection.n

[Rob]

If they're evaporating, yes, you need species. If they're not evaporating you don't. That still doesn't explain why you have air and oxygen in the mixture. n

[Milhm]

yes they are evaporating.nwhen i turn on species transport, the material of the domain changes from air to mixture-template. Mixture-template includes oxygen,nitrogen and water.n

[Rob]

I'd suggest changing it back to air, it's more efficient than solving for two inert gases. n

[Milhm]

if i change it to air, i can not define water as an evaporating species. And i can not simulate evaporationn

[Rob]

You need to add water to the mixture too. n

[Amine Ben Hadj Ali]

And check the tutorial Evaporating Spray. n

[Milhm]

You need to add water to the mixture too./forum/discussion/comment/97838#Comment_97838

when i turn on species transport, the default material is named mixture template and it already includes water,oxygen and nitrogen.nwhat should i do?Should i delete oxygen and nitrogen from the mixture?.nI should say another thing.If i set the operating pressure to a value which is not equal to zero,Fluent solve problem without error.Fluent simulate evaporation without error.But the calculated values of pressure and velocity for example mach number anb absolute pressure for compressible flow... are not correct.nWhat should i do?n

[Amine Ben Hadj Ali]

Remove oxygen from mixture material. I assume default equation of state is incompressible ideal gas. Fir low mach number flows provide an operating pressure no matter what you choose as EOS and adjust openings accordingly.

[Milhm]

I removed oxygen and nitrogen from material. i run the simulation and injection was done. but it is almost unable to cool the compressible crossflow. Droplets can not penetrate in the domin.what is the problem?I have a doubt if i had simulate the compressible crossflow correctly or not.nstagnation pressure:4MPa - static pressure:0.696MPa - stagnation temperature:500k - static temperature:303.5k - Mach number:1.8nI set the operating pressure to zero.My boundary conditions are pressure inlet and pressure outlet.nI send contours of the domain.Are they correct and meaningful?nThe values of turbulent kinetic energy and turbulent intensity are very high.Are they correct?nBest regrdsnn

[Amine Ben Hadj Ali]

Hi, can you first try injecting one single particle or along the inlet surface? Moreover I cannot tell if the field are reasonable as you are not sharing an update about the used BC'sn