Top-hat filter for LES

Shevin W. · March 19, 2021, 04:07

Hello, everyone!
I wanna realize a nonlinear subgrid scale model for LES utilizing UDF. However, the filter function troubles me for a long time. In some papers, the Top-hat (or box) filter is adopted to conduct the test filter.In Openfoam, this filter for variable u is conducted as follows:
test filter(u) = sum(u*cell face area)/sum(cell face area)

How can i realize this filter by UDF?
Moreover, many varibles are yet to be filtered. Is there a code which filters any inputted varible?

Thanks very much!

Shevin W. · March 21, 2021, 21:05

I have solved this problem by the following method.
The variable over the cell surface was caculated by utilizing the variable value and its gradient in the center of the cell:

Variable over the cell surface = value in the center of the cell + variable gradient * the distance between the surface and the center

And the sum operation of variable utilized the macro: c_face_loop.

March 19, 2021, 04:07	Top-hat filter for LES	#1
Shevin W. New Member Join Date: Mar 2021 Posts: 8 Rep Power: 5	Hello, everyone! I wanna realize a nonlinear subgrid scale model for LES utilizing UDF. However, the filter function troubles me for a long time. In some papers, the Top-hat (or box) filter is adopted to conduct the test filter.In Openfoam, this filter for variable u is conducted as follows: test filter(u) = sum(u*cell face area)/sum(cell face area) How can i realize this filter by UDF? Moreover, many varibles are yet to be filtered. Is there a code which filters any inputted varible? Thanks very much!

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March 21, 2021, 21:05		#2
Shevin W. New Member Join Date: Mar 2021 Posts: 8 Rep Power: 5	I have solved this problem by the following method. The variable over the cell surface was caculated by utilizing the variable value and its gradient in the center of the cell: Variable over the cell surface = value in the center of the cell + variable gradient * the distance between the surface and the center And the sum operation of variable utilized the macro: c_face_loop.