[Gfs-users] Doubt on Equilibrium of a droplet suspended in an electric field (Different densities and simulation)

[Mobin Malik]

Dear Gerris users,

I am trying to replicate the axisymmetric Gerris Test case "Equilibrium of a droplet suspended in an electric field". 

Case: http://gfs.sourceforge.net/tests/tests/electro.html  
Publication:  http://gfs.sourceforge.net/tests/tests/electro.html  

I am new to Gerris and have read other posts related to this topic. 

1 - I would like to know how do I include "dimensionless density" of two different fluids, for instance, castor oil (958kg/m**3) and silicone oil (1023 kg/m**3) in the equation.

2- I am trying to create a simulation .ppm or .gfs (gfsview) to visualise the droplet deformation.

• I edited the reference case and ran using gerris2D electroDD.gfs but received an error message. 
  gerris: file 'electroDD.gfs' is not a valid simulation file
  electroDD.gfs:1:5: unknown class 'GfsElectroHydroAxi'
• Do I need other required files for this? 
• Please find attached, my test case file.

I would be grateful if someone could point me in the right direction.

Thanks in advance,
Newbie Gerris User
Mobin

[Manash Pratim Borthakur]

Hi,

  For point 1, you can specify the density in the "alpha" value in the "PhysicalParams" section. For eg, 

   

   These two lines in the define section -

       Define VAR(T,min,max) (min+CLAMP(T,0,1)*(max-min))

       Define RHO(T) VAR(T,RHOR,1.0)

   where, RHOR is the density ratio between the fluids and T is the VOF tracer.

  and inside the main body,

       PhysicalParams { 

      alpha = 1.0/RHO(T) 

       }

  For point 2, write "GModule electrohydro" in the top section.

  Hope this helps.

Regards,

Manash 

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[Mobin Malik]

Dear Manash,

Thank you for your reply. For the time being, I put point 1 on hold (assuming similar density ratio).

In regards to point 2, I added GModule electrohydro to initialize the Electrohydro module as you suggested:
1 0 GModule electrohydro GfsElectroHydroAxi GfsBox GfsGEdge {} {

but now I get a new error.  

gerris: file `electroDD.gfs' is not a valid simulation file

electroDD.gfs:1:5: unknown class `GModule'

I tried including GfsSimulation but still did not work.
Hope to hear from you or anyone soon.

Cheers,
Mobin

[Manash Pratim Borthakur]

Hi,

You misunderstood me. The ""GModule electrohydro" should be in a separate line above the  "1 0 GfsElectroHydroAxi GfsBox GfsGEdge {}" line, something like :

#Define ....

GModule electrohydro

1 0 GfsElectroHydroAxi GfsBox GfsGEdge {} {

  ......

}

Regards,

Manash

[Mobin Malik]

Dear Manash,

Thank you for pointing that out. 

I managed to get .mpg file for Rhoe and passive tracer T but my question is how do I get a simulation which illustrates the droplet deformation (oblate/prolate)?
Attached is my coding so far.

Hope to hear from you or anyone soon.

Cheers,
Mobin

[Mobin Yunus Malik]

Hello,

Could someone point out why did the authors use sin(theta) in electro.gfs instead of cos(theta) which is used in Equation 43 and 44 of the paper?
http://gfs.sourceforge.net/tests/tests/electro.html 
 
Secondly, the else term has A*x**(-2)*(x**(-2)... which according to the paper should be x**(-4)-(x**(-2)...

function vtr(x)
{
   if (x < 1.)
return A*x*(1.-x**2)*(3.*sin(theta)**2-1.);
   else
return A*x**(-2)*(x**(-2)-1.)*(3.*sin(theta)**2-1.);
}

Any answer would be appreciated.

Kind regards,
Mobin