Set up FGM model for hydrogen/air flame combustion

Kinder · July 24, 2022, 05:20

Hello,

I am having trouble setting up the FGM model for the combustion of hydrogen coming out of a tube into still air. I believe there is a problem with hybrid initialization. I have tried patching reaction progress to c=1 everywhere at first, but the result is H2 mole fraction is 1 everywhere and temperature is 400K everywhere (these are actually my tube inlet boundary conditions... it's as if they propagate to the entire domain). I do not have an air inlet, I would just like to set still air for the whole domain except the fuel inlet initially but I could not find how to do that (when I try that; I cannot patch reaction progress anymore because the fluid is only air). So the domain is just made of the pdf-mixture. I tried patching c=1 in the tube and c=0 elsewhere using cell registers but that gave the exact same result (H2 everywhere and constant 400K everywhere). Is anyone able to explain how to initialize?

LuckyTran · July 24, 2022, 13:58

Why are you patching progress variable and not mixture fraction?

Use standard initialization and not hybrid initialization if you already know what you want your fields to look like.

Kinder · July 26, 2022, 13:26

I have now tried with standard initialization, progress variable kept at default setting value which is 1 and patched mixture fraction = 0 in the full domain since at the start there is only oxidizer in it. I was running transient with FGM model and premixed flamelets, it's not giving me any flame which is weird. I thought about creating a hot point thanks to cells registers to ignite the mixture. Is this a reasonable idea or is it my setup that is still not fine?

July 24, 2022, 05:20	Set up FGM model for hydrogen/air flame combustion	#1
Kinder New Member Kennie Join Date: Jul 2022 Posts: 3 Rep Power: 3	Hello, I am having trouble setting up the FGM model for the combustion of hydrogen coming out of a tube into still air. I believe there is a problem with hybrid initialization. I have tried patching reaction progress to c=1 everywhere at first, but the result is H2 mole fraction is 1 everywhere and temperature is 400K everywhere (these are actually my tube inlet boundary conditions... it's as if they propagate to the entire domain). I do not have an air inlet, I would just like to set still air for the whole domain except the fuel inlet initially but I could not find how to do that (when I try that; I cannot patch reaction progress anymore because the fluid is only air). So the domain is just made of the pdf-mixture. I tried patching c=1 in the tube and c=0 elsewhere using cell registers but that gave the exact same result (H2 everywhere and constant 400K everywhere). Is anyone able to explain how to initialize?

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July 24, 2022, 13:58		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	Why are you patching progress variable and not mixture fraction? Use standard initialization and not hybrid initialization if you already know what you want your fields to look like.

July 26, 2022, 13:26		#3
Kinder New Member Kennie Join Date: Jul 2022 Posts: 3 Rep Power: 3	I have now tried with standard initialization, progress variable kept at default setting value which is 1 and patched mixture fraction = 0 in the full domain since at the start there is only oxidizer in it. I was running transient with FGM model and premixed flamelets, it's not giving me any flame which is weird. I thought about creating a hot point thanks to cells registers to ignite the mixture. Is this a reasonable idea or is it my setup that is still not fine?