Convergence issue for high speed combustion with radiation.

Goutham cet · July 24, 2014, 07:32

Sir,
I am currently modelling a supersonic (m=3)combustion of hydrogen injected transversely into the flow field.Using a density based solver ,k E turbulence model .p1 and do for radiation .i am using all under relaxation factor 0.1, combustion includes reaction using mechanism.To get good convergence i initiated reaction mechanism after sufficient iteration.

i am getting the value of residual for continuity is of the order of 9.0204 * 10^-3 after 20000 iteration and remains constant .On the other-hand the residual for energy still remains of the order of 1 to 10^-1 .all the values remains same for any number of iteration.

Is this correct ,or what should i do to bring the convergence of both continuity and energy further down.

Note-good grid quality has been chosen.

Thanks in advance for helpers ...please do help...

sescobar · July 25, 2014, 14:43

Hello Goutham,
Did you try to take a look at the local residual values for the energy equation?
This may allow you to elucidate if mesh quality needs to be improved locally.
A quick way to check if this is the cause is to refine your mesh in Fluent based on the local value of energy residual. Then solve for a given number of iterations. If the overall residual drops, then you may have found the cause.

Goutham cet · July 30, 2014, 08:22

Thanks a lot....i tried refining my mesh ...and the problem somewhat cleared , now both are in 1 e^-3 range ,while the mass flow rate shunting between 1333.29-1333.28 units.and its not allowing to converge further.. thinking may be there will be instability's associated flow with combustion.

July 24, 2014, 07:32	Convergence issue for high speed combustion with radiation.	#1
Goutham cet New Member Goutham S Join Date: Jul 2014 Posts: 2 Rep Power: 0	Sir, I am currently modelling a supersonic (m=3)combustion of hydrogen injected transversely into the flow field.Using a density based solver ,k E turbulence model .p1 and do for radiation .i am using all under relaxation factor 0.1, combustion includes reaction using mechanism.To get good convergence i initiated reaction mechanism after sufficient iteration. i am getting the value of residual for continuity is of the order of 9.0204 * 10^-3 after 20000 iteration and remains constant .On the other-hand the residual for energy still remains of the order of 1 to 10^-1 .all the values remains same for any number of iteration. Is this correct ,or what should i do to bring the convergence of both continuity and energy further down. Note-good grid quality has been chosen. Thanks in advance for helpers ...please do help...

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July 25, 2014, 14:43		#2
sescobar New Member Join Date: Jun 2011 Posts: 22 Rep Power: 15	Hello Goutham, Did you try to take a look at the local residual values for the energy equation? This may allow you to elucidate if mesh quality needs to be improved locally. A quick way to check if this is the cause is to refine your mesh in Fluent based on the local value of energy residual. Then solve for a given number of iterations. If the overall residual drops, then you may have found the cause.

July 30, 2014, 08:22		#3
Goutham cet New Member Goutham S Join Date: Jul 2014 Posts: 2 Rep Power: 0	Thanks a lot....i tried refining my mesh ...and the problem somewhat cleared , now both are in 1 e^-3 range ,while the mass flow rate shunting between 1333.29-1333.28 units.and its not allowing to converge further.. thinking may be there will be instability's associated flow with combustion.