[Tobi]

Hi all,


I am solving the specific humidity in my humidity thermodynamic library. Since a few weeks, I added the functionality to add source/sinks using the fvOptions capabilities. However, I do have some problem here. Consider the equation:





which I implemented as:

    fvScalarMatrix specHumEqn                                                   
    (                                                                           
        fvm::ddt(rho, specHum)                                                  
      + fvm::div(phi, specHum)                                                  
     ==                                                                         
        fvm::laplacian(muEff, specHum)                                          
      + fvOptions(rho, specHum)                                                 
    );                                                                          
                                                                                
    specHumEqn.relax();                                                         
    fvOptions.constrain(specHumEqn);                                            
    specHumEqn.solve();                                                         
    fvOptions.correct(specHum);

Now, I want to add a humidity source using the fvOption functionality. This is working fine but something is wrong here. Imagine the following snippet

sourceHumidity                                                                  
{                                                                               
    type            scalarSemiImplicitSource;                                   
                                                                                
    timeStart       0;                                                        
    duration        5.0;                                                        
    selectionMode   all;                                                        
    cellZone        zone;                                                       
                                                                                
                                                                                
    volumeMode      absolute;                                                   
    injectionRateSuSp                                                           
    {                                                                           
        thermo:specificHumidity   (1 0);
    }                                                                           
}

I would expect to increase the quantity inside the volume (1 cubic meter) to a value of 5 after 5 s (for each second increase the value by 1). However, in my case it is 4.21693 and I cannot get the reason why. Any hints?

If I program it like that, it works:

    fvScalarMatrix specHumEqn                                                   
    (                                                                           
        fvm::ddt(rho, specHum)                                                  
      + fvm::div(phi, specHum)                                                  
     ==                                                                         
        fvm::laplacian(muEff, specHum)                                          
        + rho*dimensionedScalar("non", dimensionSet(0,0,-1,0,0,0,0), 1)                                                 
    );                                                                          
                                                                                
    specHumEqn.relax();                                                         
    fvOptions.constrain(specHumEqn);                                            
    specHumEqn.solve();                                                         
    fvOptions.correct(specHum);

[Tobi]

Ah I found the problem but now I am a bit lost:


The explicit source is added to the equation but without the density information

    eqn += Su + fvm::SuSp(Sp, psi);

I guess here we do have a bug.
Tobi

[Tobi]

Yes we do have the bug here and I asked a similar question a few weeks ago while we pointed out that there is a problem. Using density based solvers, we do neglect the density in this function (addSup). I am checking it with the people from the Foundation and will report / provide a patch.

[Tobi]

Hi all,


I already discussed a few thing here. As some quantities do not need the multiplication by the density it is not a bug per se. However, one should keep this in his mind. Maybe a workaround will be started to explicitly activate the density multiplication. Well, I keep you up to date. Alternatively, one can use the coded... fvOptions functionality and do the multiplication manually.

[rocco96]

Hi,
I am also trying to add the humidity equation to interCondensatingEvaporatingFoam to study an open flat channel formed by water and air. My problem is that I cannot make the specific humidity dependent on the saturation temperature. Do you have any advice?
Best regards,
Rocco