intialize flow for LES simulation in CFX

raunakjung · February 21, 2017, 23:18

How to initialize flow for LES simulation in CFX ?
I am not sure how to carry out initialization for LES simulations .

https://www.sharcnet.ca/Software/Ans.../i1303019.html

Thank You

ghorrocks · February 21, 2017, 23:53

Conceptually you initialise a LES simulation the same way you initialise a normal simulation.

LES is not a topic for beginners. Unless you have taken care of near wall modelling, filter length scale and turbulence spectrum decay then you are wasting your time with LES. If you are not aware of what these issues are then I do not recommend you attempt LES until you do further background reading.

raunakjung · February 22, 2017, 01:49

Thank you for yor reply. This is my first attempt for LES. While my research is deficient I am using y+ =1 and doing my mesh according to turbulent length scale determined by previous k-e simulations.

I couldnt understand the following " The behavior of the velocity fluctuation is applied according to the following rules when you select Automatic or Automatic with Value as the Initialization option, as well as specify a velocity fluctuation:

If an initial values file is not found, the fluctuation is applied to the initial velocity field.

When an initial values file is used, it is assumed that you are restarting from a previous set of results, and the fluctuation is not applied.

If you want to apply a velocity fluctuation on a restart (for example, if the initial guess is a RANS solution), you can override this behavior by setting the expert parameter apply ic fluctuations for les to t. "

February 21, 2017, 23:18	intialize flow for LES simulation in CFX	#1
raunakjung Senior Member raunak jung pandey Join Date: Jun 2016 Posts: 102 Rep Power: 10	How to initialize flow for LES simulation in CFX ? I am not sure how to carry out initialization for LES simulations . https://www.sharcnet.ca/Software/Ans.../i1303019.html Thank You

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February 21, 2017, 23:53		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Conceptually you initialise a LES simulation the same way you initialise a normal simulation. LES is not a topic for beginners. Unless you have taken care of near wall modelling, filter length scale and turbulence spectrum decay then you are wasting your time with LES. If you are not aware of what these issues are then I do not recommend you attempt LES until you do further background reading.

February 22, 2017, 01:49		#3
raunakjung Senior Member raunak jung pandey Join Date: Jun 2016 Posts: 102 Rep Power: 10	Thank you for yor reply. This is my first attempt for LES. While my research is deficient I am using y+ =1 and doing my mesh according to turbulent length scale determined by previous k-e simulations. I couldnt understand the following " The behavior of the velocity fluctuation is applied according to the following rules when you select Automatic or Automatic with Value as the Initialization option, as well as specify a velocity fluctuation: If an initial values file is not found, the fluctuation is applied to the initial velocity field. When an initial values file is used, it is assumed that you are restarting from a previous set of results, and the fluctuation is not applied. If you want to apply a velocity fluctuation on a restart (for example, if the initial guess is a RANS solution), you can override this behavior by setting the expert parameter apply ic fluctuations for les to t. "