Manual DES blending function

jonasa97 · May 25, 2020, 11:54

Hi,

Is it possible to manually specify the DES blending function in parts of the domain whilst also having it calculated according to the normal expression in the rest of the domain?

Many thanks for any input on this

!

Gert-Jan · May 25, 2020, 14:00

Not sure if the parameters can be a expression. If so, then you can make them depend on a coordinate using functions like step, max or min. And as such switch them on or off in a certain range of the coordinate....

jonasa97 · May 25, 2020, 14:26

Hi Gert-Jan,

Thanks for your answer. I'm not quite sure I understand what you mean with 'parameters'? I assume you are referring to the expert parameters? I'm afraid I haven't found anything relating to the DES blending function there.

Gert-Jan · May 25, 2020, 16:12

If you select the DES model in CFX-Pre, you can open the advanced settings tab. There you can change e.g. the BF1 and BF2 values. I thought you mentioned these blend factors that allow you to control the DES simulation......

jonasa97 · May 25, 2020, 18:12

I wanted to control the blending function directly (not through the SST shielding functionality). Though I must admit that your suggestion is very insightful and inventive, it will only allow me to switch to the very 'safe' F2 shielding functions, given a certain conditional expression is satisfied. Unfortunately, this will not allow me to set the DES blending function - only enable me to control the regions in which an SST blending function is used for shielding. If the solver clips the DES blending function at 1, then this could be bypassed by multiplying the conditional expression for the blending function factor by a large scalar. Thanks for your suggestion.

Gert-Jan · May 26, 2020, 02:34

If you want more control, then you'd better program it yourself or switch to OpenFOAM.

May 25, 2020, 11:54	Manual DES blending function	#1
jonasa97 New Member Jonas Join Date: Dec 2019 Posts: 15 Rep Power: 6	Hi, Is it possible to manually specify the DES blending function in parts of the domain whilst also having it calculated according to the normal expression in the rest of the domain? Many thanks for any input on this !

May 25, 2020, 14:00		#2
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,823 Rep Power: 27	Not sure if the parameters can be a expression. If so, then you can make them depend on a coordinate using functions like step, max or min. And as such switch them on or off in a certain range of the coordinate.... jonasa97 likes this.

May 25, 2020, 16:12		#4
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,823 Rep Power: 27	If you select the DES model in CFX-Pre, you can open the advanced settings tab. There you can change e.g. the BF1 and BF2 values. I thought you mentioned these blend factors that allow you to control the DES simulation...... jonasa97 likes this.

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May 25, 2020, 14:26		#3
jonasa97 New Member Jonas Join Date: Dec 2019 Posts: 15 Rep Power: 6	Hi Gert-Jan, Thanks for your answer. I'm not quite sure I understand what you mean with 'parameters'? I assume you are referring to the expert parameters? I'm afraid I haven't found anything relating to the DES blending function there.

May 25, 2020, 18:12		#5
jonasa97 New Member Jonas Join Date: Dec 2019 Posts: 15 Rep Power: 6	I wanted to control the blending function directly (not through the SST shielding functionality). Though I must admit that your suggestion is very insightful and inventive, it will only allow me to switch to the very 'safe' F2 shielding functions, given a certain conditional expression is satisfied. Unfortunately, this will not allow me to set the DES blending function - only enable me to control the regions in which an SST blending function is used for shielding. If the solver clips the DES blending function at 1, then this could be bypassed by multiplying the conditional expression for the blending function factor by a large scalar. Thanks for your suggestion.

May 26, 2020, 02:34		#6
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,823 Rep Power: 27	If you want more control, then you'd better program it yourself or switch to OpenFOAM.