Question about LES-PaSR combustion model with reactingFoam

liuxy · November 7, 2019, 08:43

I am new to Openfoam. I am simulating a simple jet (CH4) and coflow (air) problem (SandiaD in tutorial case) with PaSR turbulence combustion model. When I am using RAS model, jet is spreading and mixing well but when i tried to use LES model, jet is not spreading. Jet is going straight. no mixing is taking place and it is not looking LES from any angle. what would be the problem? what changes should be done to implement LES model in reactingFoam??

zkth · November 7, 2019, 12:13

Quote:

Originally Posted by liuxy

I am new to Openfoam. I am simulating a simple jet (CH4) and coflow (air) problem (SandiaD in tutorial case) with PaSR turbulence combustion model. When I am using RAS model, jet is spreading and mixing well but when i tried to use LES model, jet is not spreading. Jet is going straight. no mixing is taking place and it is not looking LES from any angle. what would be the problem? what changes should be done to implement LES model in reactingFoam??

Hi,
Post your setting of combustionProperties and turbulenceProperties to get help pls.
Kai.

liuxy · November 8, 2019, 00:41

The attached zip file is the "combustionProperties", "turbulenceProperties" and the wrong distribution of CO2

zkth · November 8, 2019, 10:30

Quote:

Originally Posted by liuxy

The attached zip file is the "combustionProperties", "turbulenceProperties" and the wrong distribution of CO2

Hi,
Not sure which version you are using. I use OF5,6,7. The PaSRCoeffs in combustionProperties is:
PaSRCoeffs
{
Cmix 0.03;
turbulentReaction true;//on;//yes;
//useReactionRate true;
}
Without turbulentReaction true, you assume laminar flame.

For turbulenceProperties, I have:

cubeRootVolCoeffs
{
deltaCoeff 1;
}

Hope this helps.
Kai.

zkth · November 8, 2019, 10:32

Btw, you are free to choose your own Cmix based on your requirement.
Kai.

Southuno · January 27, 2021, 06:09

Hi Liuxy, do you solve this problem?
The same situation I am that the LES model can't obtain reasonable results of Sandia D flame from RAS model.

random_ran · January 29, 2021, 18:02

> i tried to use LES model, jet is not spreading

LES is cost. Usually required more denser grid. Have you tried finer mesh?

Southuno · January 30, 2021, 21:04

Same problem.
The methane jet does't spead, but i dont know if it is the problem of mesh resolution.
I will try this.

random_ran · February 1, 2021, 00:11

Okay, I will play with `SandiaD_LTS` at the same time.

Southuno · February 4, 2021, 06:37

Hi Ran,

The problem that methane doesn't spread is caused by lower SGS viscosity nut and lower turbulent thermal diffusion coefficient alphat. I compare these two values between RANS model case and LES case, and find that they are different by several orders of magnitude.

Hence, if you increase these two values by 10 times on EEqn.H and YEqn.H of reactingFoam, you would get similar results by LES model. But I dont know if it is a reasonable way to solve this problem, it just can get a better result.

Best

November 7, 2019, 08:43	Question about LES-PaSR combustion model with reactingFoam	#1
liuxy New Member XiangYang Liu Join Date: Jun 2019 Posts: 2 Rep Power: 0	I am new to Openfoam. I am simulating a simple jet (CH4) and coflow (air) problem (SandiaD in tutorial case) with PaSR turbulence combustion model. When I am using RAS model, jet is spreading and mixing well but when i tried to use LES model, jet is not spreading. Jet is going straight. no mixing is taking place and it is not looking LES from any angle. what would be the problem? what changes should be done to implement LES model in reactingFoam??

January 29, 2021, 18:02		#7
random_ran Member Ran Join Date: Aug 2016 Posts: 69 Rep Power: 10	> i tried to use LES model, jet is not spreading LES is cost. Usually required more denser grid. Have you tried finer mesh? __________________ Yours in CFD, Ran

February 1, 2021, 00:11		#9
random_ran Member Ran Join Date: Aug 2016 Posts: 69 Rep Power: 10	Okay, I will play with `SandiaD_LTS` at the same time. __________________ Yours in CFD, Ran

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November 8, 2019, 10:32		#5
zkth New Member kai Join Date: Nov 2019 Posts: 6 Rep Power: 7	Btw, you are free to choose your own Cmix based on your requirement. Kai.

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January 30, 2021, 21:04		#8
Southuno New Member Jiannan Liu Join Date: Jun 2020 Posts: 4 Rep Power: 6	Same problem. The methane jet does't spead, but i dont know if it is the problem of mesh resolution. I will try this.

February 4, 2021, 06:37		#10
Southuno New Member Jiannan Liu Join Date: Jun 2020 Posts: 4 Rep Power: 6	Hi Ran, The problem that methane doesn't spread is caused by lower SGS viscosity nut and lower turbulent thermal diffusion coefficient alphat. I compare these two values between RANS model case and LES case, and find that they are different by several orders of magnitude. Hence, if you increase these two values by 10 times on EEqn.H and YEqn.H of reactingFoam, you would get similar results by LES model. But I dont know if it is a reasonable way to solve this problem, it just can get a better result. Best