SmoothDelta

r2d2 · June 14, 2005, 06:01

Hi,
I am a new user of OpenFoam and I am interested in LES, in general. Thought I should start with channelOodles and then with oodles...and a simple cold-flow "jet" with a 3D block geometry generated with blockMesh. Then, for oodles, I experienced the same problems as another member in the discussion group ( Co growing, inexplicably and then the code blows). This was until I used the "smooth" delta in "turbulenceProperites" dict with Samgorinsky. My question is regarding this soomthed delta, what does it do? (I remember seeing something about it but I just cannot find the message or the thread anymore)
Thanks,
Radu

eugene · June 14, 2005, 06:19

smoothDelta smears the SGS length scale so that larger length scales are used for small cells adjacent to larger cells. Basically you put a maximum on the ratio between SGS length scales in adjacent cells. This reduces the impact of a sudden jump in cell size on the the SGS model and by inference the resolved motion. It has no impact if all the cells are the same size or the size varies gradually.

r2d2 · June 14, 2005, 07:29

Thanks for the message. I thought of something like this, and later I remembered where I saw the brief description (in the sources for LESdeltas). So as long as my grid is "smooth" the smoothing won´t do much. Therefore I should pay more attention to the grid if I want to use the cuberootDelta.

June 14, 2005, 06:01	Hi, I am a new user of OpenF	#1
r2d2 Member Radu Mustata Join Date: Mar 2009 Location: Zaragoza, Spain Posts: 99 Rep Power: 17	Hi, I am a new user of OpenFoam and I am interested in LES, in general. Thought I should start with channelOodles and then with oodles...and a simple cold-flow "jet" with a 3D block geometry generated with blockMesh. Then, for oodles, I experienced the same problems as another member in the discussion group ( Co growing, inexplicably and then the code blows). This was until I used the "smooth" delta in "turbulenceProperites" dict with Samgorinsky. My question is regarding this soomthed delta, what does it do? (I remember seeing something about it but I just cannot find the message or the thread anymore) Thanks, Radu

June 14, 2005, 06:19	smoothDelta smears the SGS len	#2
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 21	smoothDelta smears the SGS length scale so that larger length scales are used for small cells adjacent to larger cells. Basically you put a maximum on the ratio between SGS length scales in adjacent cells. This reduces the impact of a sudden jump in cell size on the the SGS model and by inference the resolved motion. It has no impact if all the cells are the same size or the size varies gradually. sina.s likes this.

June 14, 2005, 07:29	Thanks for the message. I thou	#3
r2d2 Member Radu Mustata Join Date: Mar 2009 Location: Zaragoza, Spain Posts: 99 Rep Power: 17	Thanks for the message. I thought of something like this, and later I remembered where I saw the brief description (in the sources for LESdeltas). So as long as my grid is "smooth" the smoothing won´t do much. Therefore I should pay more attention to the grid if I want to use the cuberootDelta.