# Flow dependent forces

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 July 8, 2011, 06:05 Flow dependent forces #1 New Member   Lorenzo A. Ricciardi Join Date: Mar 2011 Posts: 27 Rep Power: 6 Hi all, I developed an incompressible turbulent single phase flow solver with a generalized actuator disk model acting as a local volume force. I can specify forces and torques as a prescribed input. However, I'd like to compute these forces as function of local flow conditions (U and other parameters)... any hint on how could I do it? Thank you

July 11, 2011, 18:13
#2
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Bernhard Gschaider
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Quote:
 Originally Posted by lichmaster Hi all, I developed an incompressible turbulent single phase flow solver with a generalized actuator disk model acting as a local volume force. I can specify forces and torques as a prescribed input. However, I'd like to compute these forces as function of local flow conditions (U and other parameters)... any hint on how could I do it? Thank you
"function of local flow conditions" is rather general. An equally general answer would be "Program it"

 July 15, 2011, 06:28 #3 New Member   Lorenzo A. Ricciardi Join Date: Mar 2011 Posts: 27 Rep Power: 6 My question was general indeed... As an OF beginner, and also an OOP beginner, I had to learn how to gain access to field data from my own additional structures and use this info ('till now I had just copy/pasted/edited some tutorials) Now I've managed to add a momentum source function of local U in a dictionary specified volume, something interesting to start playing with

July 18, 2011, 11:07
#4
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Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,912
Rep Power: 40
Quote:
 Originally Posted by lichmaster My question was general indeed... As an OF beginner, and also an OOP beginner, I had to learn how to gain access to field data from my own additional structures and use this info ('till now I had just copy/pasted/edited some tutorials) Now I've managed to add a momentum source function of local U in a dictionary specified volume, something interesting to start playing with
The question is what your primary goal is

- learning C++ in OpenFOAM (a valid goal)
- solve your problem and play around (as you said in the first post) "forces as function of local flow conditions"

In the first case the best recommendation is to do it the way everyone did: dig through the sources.

In the second case you might want to have a look at swak4foam. Instead of the vol-Field that you use as a source-term add an expressionSource-object. And for that you can specify expressions at run-time (there is a solver/case using that in the Examples). These expressions can depend on the current flow-field, but also on the state of the flow on patches, in cellSets, at the location of probes (depending on what you mean with "local flow conditions"). Once you know more concretly what it is that you want to do you can always go back and implement it yourself in C++

Bernhard

Disclaimer: as I wrote swak this might be a case of "if you've got a hammer every problem looks like a nail"

July 19, 2011, 04:48
#5
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Lorenzo A. Ricciardi
Join Date: Mar 2011
Posts: 27
Rep Power: 6
Quote:
 Originally Posted by gschaider The question is what your primary goal is - learning C++ in OpenFOAM (a valid goal) - solve your problem and play around (as you said in the first post) "forces as function of local flow conditions" In the first case the best recommendation is to do it the way everyone did: dig through the sources. In the second case you might want to have a look at swak4foam. Instead of the vol-Field that you use as a source-term add an expressionSource-object. And for that you can specify expressions at run-time (there is a solver/case using that in the Examples). These expressions can depend on the current flow-field, but also on the state of the flow on patches, in cellSets, at the location of probes (depending on what you mean with "local flow conditions"). Once you know more concretly what it is that you want to do you can always go back and implement it yourself in C++ Bernhard Disclaimer: as I wrote swak this might be a case of "if you've got a hammer every problem looks like a nail"
Actually I'm digging into part of the code and tweaking existing solvers to learn how OF works.
It's a trial and error procedure, but i think there is simply too much code for an OOP newby to simply understand it just by reading it: i'm much more used to structured Fortran code

Thanks for the pointer, anyway

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