Is it possible to make a compressible partially premixed combustion in Fluent?

tsi07 · June 14, 2017, 16:43

Hi Fluent users,

I wonder if we can simulate a compressible partially premixed combustion in Fluent?
Actually, I set a case for a partially premixed combustion with the state relation "Flamelet Generated Manifold" under chemistry.
The flamelet-mixture density is incompressible-ideal-gas. I wonder if we can work with a compressible mixture?

I also choose the "Compressibility Effects" in the PDF options.

Does that mean, the flow will be compressible?

andon6141 · February 20, 2018, 16:15

Yes

... with this option the real gas equation setup will appear in the density tab

Muneeb · November 16, 2018, 10:00

I am working on simulation of non premixed combustion of a gas turbine engine afterburner in FLUENT. when I run the simulation for ADIABATIC CASE in non premixed combustion (energy eqn 'OFF' , compressibility effects disabled) the solution is easily converged and reasonable results are obtained.

While I enable the compressibility effects in non premixed combustion window followed by recalculating the pdf table, the solution does not proceed beyond 05 iterations with error 'INCORRECT SPECIFIC HEAT VALUE' displaying for almost 100 times followed by divergence in AMG solver. (Note: I am dealing with a fuel; hydrocarbon named JP-8; chemical formula C31H48; molecular weight 420 KJ/kgmol: specific heat value 2200 J/KgK. This hydrocarbon is not available in the FLUENT database (thermodb file) therefore I am defining the fuel empirically by MANUALLY defining these values. I have also tried using various hypothetical low values of specific heat but no success. I tried with using a fuel from FLUENT database but in this case the problem of incorrect specific heat value is not encountered however convergence is still not achieved {maximum pdf table enthalpy exceeded in ------ cells}).

I tried to run the solution with species model OFF (combustion OFF), taking Air as ideal gas (compressible + energy Eqn ON), solution is converged and reasonable results are achieved. Problem is encountered only with enabling the compressibility effects while modeling non premixed combustion.

Further details are as follow:

Mesh size: 6 Million elements (hexahedral + tetrahedral)
steady state
standard k-epsilon turbulence model
radiation: OFF
periodic boundary conditions (axisymmetric 30 deg sector) with mass flow air and fuel inlets and pressure outlet
solver: Coupled (Courant number 0.3)

kindly advice how to proceed with compressibility effects enabled in modeling non premixed combustion in order to avoid the aforesaid errors. please also advice am I correctly defining the empirical fuel. Thanks in anticipation for any advice please.

June 14, 2017, 16:43	Is it possible to make a compressible partially premixed combustion in Fluent?	#1
tsi07 Member Join Date: Mar 2012 Location: USA Posts: 33 Rep Power: 14	Hi Fluent users, I wonder if we can simulate a compressible partially premixed combustion in Fluent? Actually, I set a case for a partially premixed combustion with the state relation "Flamelet Generated Manifold" under chemistry. The flamelet-mixture density is incompressible-ideal-gas. I wonder if we can work with a compressible mixture? I also choose the "Compressibility Effects" in the PDF options. Does that mean, the flow will be compressible?

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February 20, 2018, 16:15		#2
andon6141 New Member Anton Hilfer Join Date: Dec 2014 Posts: 7 Rep Power: 11	Yes ... with this option the real gas equation setup will appear in the density tab

November 16, 2018, 10:00		#3
Muneeb New Member MMSQ Join Date: Aug 2018 Posts: 14 Rep Power: 8	I am working on simulation of non premixed combustion of a gas turbine engine afterburner in FLUENT. when I run the simulation for ADIABATIC CASE in non premixed combustion (energy eqn 'OFF' , compressibility effects disabled) the solution is easily converged and reasonable results are obtained. While I enable the compressibility effects in non premixed combustion window followed by recalculating the pdf table, the solution does not proceed beyond 05 iterations with error 'INCORRECT SPECIFIC HEAT VALUE' displaying for almost 100 times followed by divergence in AMG solver. (Note: I am dealing with a fuel; hydrocarbon named JP-8; chemical formula C31H48; molecular weight 420 KJ/kgmol: specific heat value 2200 J/KgK. This hydrocarbon is not available in the FLUENT database (thermodb file) therefore I am defining the fuel empirically by MANUALLY defining these values. I have also tried using various hypothetical low values of specific heat but no success. I tried with using a fuel from FLUENT database but in this case the problem of incorrect specific heat value is not encountered however convergence is still not achieved {maximum pdf table enthalpy exceeded in ------ cells}). I tried to run the solution with species model OFF (combustion OFF), taking Air as ideal gas (compressible + energy Eqn ON), solution is converged and reasonable results are achieved. Problem is encountered only with enabling the compressibility effects while modeling non premixed combustion. Further details are as follow: Mesh size: 6 Million elements (hexahedral + tetrahedral) steady state standard k-epsilon turbulence model radiation: OFF periodic boundary conditions (axisymmetric 30 deg sector) with mass flow air and fuel inlets and pressure outlet solver: Coupled (Courant number 0.3) kindly advice how to proceed with compressibility effects enabled in modeling non premixed combustion in order to avoid the aforesaid errors. please also advice am I correctly defining the empirical fuel. Thanks in anticipation for any advice please.