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flowType extensional flow and obtaining extensional stress

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Old   July 26, 2021, 13:06
Default flowType extensional flow and obtaining extensional stress
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Sourav Mandal
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I can easily visualise the flowType in a nozzle geometry like in the attached figure 3. When I searched on this topic (extensional flow or extensional stress), there are important practical implications like in -
There is a functionObject called flowType that comes with both OpenFOAM-v2012 & OpenFOAM-8. The v8 provides the description:

PHP Code:
foamInfo flowType
File
    
/opt/OpenFOAM/OpenFOAM-8/src/functionObjects/field/flowType/flowType.H

Description
    Calculates 
and writes the flowType of a velocity field.

    
The flow type parameter is obtained according to the following equation:
    \
verbatim
                 
|D| - |Omega|
        
lambda = -------------
                 |
D| + |Omega|

        -
rotational flow
         0 
simple shear flow
         1 
planar extensional flow
    
\endverbatim

Examples
cannot find any tutorials using "flowType" 
On this topic there are a few threads, but nothing very illuminating.
The polymer mixing example used a software called BEMflow that provides the "particle flow number" in the range 0 to 1 (rotational, shear, elongation), through (probably) a particle tracking method. In contrast, OPenFOAM provides the flowType that ranges between -1 to +1 (rotational, simple shear, planar extensional). For my application (3D bio-printing i.e. flowing hydrogel with living cells through nozzles), it would be very nice to know what portion of the fluid is experiencing how much of stress (shear & extension).

Now, my question is
Is there a way to decouple extensional stress and shear stress & quantify these two parameters individually in OpenFOAM?


I'm not sure if this is the correct forum (maybe in programming & development?) but any kind of input would be very welcome
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elongation, extension, flowtype, shear stress, shearstress

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