Using source terms

jsm · August 20, 2009, 06:05

Hi,

I am currently doing one project in Fluent. In this I am giving mass (Kg) and energy (J/Kg) as input through source terms (UDF) to develop the flow inside the closed domain.

In source terms, i have one issue. In Fluent, generally source terms are given per unit volume. I calculated mass and energy source terms for my domain volume (where I am going to hook the source UDF) and ran the simulation. But temperature is going to very high value (4000K). However mass source is coming correctly in to the domain. I am sure that temperature can not go to this high value with given mass and energy source. I cross checked the energy value given through UDF. It is correct.

I consulted with technical support experts. But I did not get any proper way to solve this issue. Is Fluent can handle source terms correctly? Anybody faced similiar kind of issues in Fluent and other CFD softwares?

I appreciate your help and suggestions.

SKK · August 20, 2009, 06:50

I have used STAR CD before where I used user subroutine in order to model some scalars. To justify the ability of any software in such situation is to model something very simple and check the solution against analytial values. In your case I would suggest modeling something like heat conduction through a rod to check the source terms are implemented/working how they should be.

It might just be the formulation you used. Generally these source terms are given per unit volume (in finite volume method). Google for some examples or look in the book by Versteeg & Malalasekera to see some example of how to formulate such equations.

jsm · August 20, 2009, 07:18

Hi SKK,

Yes. You are correct. Currently I am doing such kind of simple simulation to justify. However, my actual simulation is combustion phenomenon. Instead of simulating the combustion, I am giving source terms as input to develop the flow field. Is your simulation also similar kind?

SKK · August 20, 2009, 07:28

Unfortunately nope, my simulation, which I did a few years back was modeling k-w SST turbulence equation and transition modeling. I just had a look at the above mentioned book and there is a bit on combustion modelling on chapter 10. Have a look in there, it might be of some help. Sorry for not being able to help much. Hopefully someone else with combustion modelling experience will be able to help you. Goodluck.

jsm · August 20, 2009, 07:44

Hi SKK,

Thanks for your suggestions. I will check that CFD book.

August 20, 2009, 06:05	Using source terms	#1
jsm Senior Member JSM Join Date: Mar 2009 Location: India Posts: 192 Rep Power: 20	Hi, I am currently doing one project in Fluent. In this I am giving mass (Kg) and energy (J/Kg) as input through source terms (UDF) to develop the flow inside the closed domain. In source terms, i have one issue. In Fluent, generally source terms are given per unit volume. I calculated mass and energy source terms for my domain volume (where I am going to hook the source UDF) and ran the simulation. But temperature is going to very high value (4000K). However mass source is coming correctly in to the domain. I am sure that temperature can not go to this high value with given mass and energy source. I cross checked the energy value given through UDF. It is correct. I consulted with technical support experts. But I did not get any proper way to solve this issue. Is Fluent can handle source terms correctly? Anybody faced similiar kind of issues in Fluent and other CFD softwares? I appreciate your help and suggestions. __________________ With regards, JSM

August 20, 2009, 07:18		#3
jsm Senior Member JSM Join Date: Mar 2009 Location: India Posts: 192 Rep Power: 20	Hi SKK, Yes. You are correct. Currently I am doing such kind of simple simulation to justify. However, my actual simulation is combustion phenomenon. Instead of simulating the combustion, I am giving source terms as input to develop the flow field. Is your simulation also similar kind? __________________ With regards, JSM

August 20, 2009, 07:44		#5
jsm Senior Member JSM Join Date: Mar 2009 Location: India Posts: 192 Rep Power: 20	Hi SKK, Thanks for your suggestions. I will check that CFD book. __________________ With regards, JSM

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August 20, 2009, 06:50		#2
SKK Member Join Date: Mar 2009 Posts: 55 Rep Power: 17	I have used STAR CD before where I used user subroutine in order to model some scalars. To justify the ability of any software in such situation is to model something very simple and check the solution against analytial values. In your case I would suggest modeling something like heat conduction through a rod to check the source terms are implemented/working how they should be. It might just be the formulation you used. Generally these source terms are given per unit volume (in finite volume method). Google for some examples or look in the book by Versteeg & Malalasekera to see some example of how to formulate such equations.

August 20, 2009, 07:28		#4
SKK Member Join Date: Mar 2009 Posts: 55 Rep Power: 17	Unfortunately nope, my simulation, which I did a few years back was modeling k-w SST turbulence equation and transition modeling. I just had a look at the above mentioned book and there is a bit on combustion modelling on chapter 10. Have a look in there, it might be of some help. Sorry for not being able to help much. Hopefully someone else with combustion modelling experience will be able to help you. Goodluck.