LES Convergence

canopus · December 27, 2010, 15:57

Hello
I am trying to do LES of a coaxial air jet with Re around 14000 issuing out into atmosphere.
The computaional domain starts from the exit plane of the jets where I put a velocity distribution & outflow is assumed 30D downstream.
The code is an incompressible LES with dynamic SGS.
I have played with different grid sizes & I am getting some nice pictures.

But how can I check if the solution is acceptable?
I do not have experimental data.

I have googled and found some bits & pieces but I am not able to put them in a shape.

Can you please elaborate how to use the pointers that I found?

1. ratio of eddy viscosity to laminar viscosity?
2. FFT of velocity data and map it to the scales?
3. Kinetic energy distribution?
4. Statistical average?

Any other pointers please let me know..

Thanks
SM

harishg · December 27, 2010, 17:05

This test case have been commonly used in many experimental studies and you should be able to find experimental data in the literature. Another option is performing LES of some well known benchmark cases to show the robustness of code and model.

What is the purpose of this study? There are so many statistical quantities that you can present. The important thing is to present the statistics which are relevant to the goal of the study.

NewtonKF · December 28, 2010, 08:09

Look for the paper of Hussein "Velocity measurements in a high-Reynolds-number, momentum-conserving, axisymmetric, turbulent jet" there are lots of experimental data for isothermal jet analyses...

For itens 2, 3 and 4 I suggest you to read the book of Pope "Turbulent Flows"...

Good luck...

December 27, 2010, 15:57	LES Convergence	#1
canopus Member SM Join Date: Dec 2010 Posts: 97 Rep Power: 15	Hello I am trying to do LES of a coaxial air jet with Re around 14000 issuing out into atmosphere. The computaional domain starts from the exit plane of the jets where I put a velocity distribution & outflow is assumed 30D downstream. The code is an incompressible LES with dynamic SGS. I have played with different grid sizes & I am getting some nice pictures. But how can I check if the solution is acceptable? I do not have experimental data. I have googled and found some bits & pieces but I am not able to put them in a shape. Can you please elaborate how to use the pointers that I found? 1. ratio of eddy viscosity to laminar viscosity? 2. FFT of velocity data and map it to the scales? 3. Kinetic energy distribution? 4. Statistical average? Any other pointers please let me know.. Thanks SM

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December 27, 2010, 17:05		#2
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	This test case have been commonly used in many experimental studies and you should be able to find experimental data in the literature. Another option is performing LES of some well known benchmark cases to show the robustness of code and model. What is the purpose of this study? There are so many statistical quantities that you can present. The important thing is to present the statistics which are relevant to the goal of the study.

December 28, 2010, 08:09		#3
NewtonKF Member Newton KF Join Date: Mar 2009 Posts: 36 Rep Power: 17	Look for the paper of Hussein "Velocity measurements in a high-Reynolds-number, momentum-conserving, axisymmetric, turbulent jet" there are lots of experimental data for isothermal jet analyses... For itens 2, 3 and 4 I suggest you to read the book of Pope "Turbulent Flows"... Good luck...