Continuity equation in VOF

- December 30, 2019 at 9:39 pm
  
  soumitra2102
  Subscriber
  
  Hi,
  
  Which are the equations solved by the VOF model for primary and secondary phases? More specifically, I want to know if the VOF model ever directly touches the primary phase for solving continuity equation?
  
  Also, what does the continuity equation residuals seen in the convergence plot of a vof model solving process indicate? Is the equation solved for a mixture?
  
  I went through the theory manual for knowing exactly which and how many equations are solved in it. However, it's pretty confusing as just after introduction, limitations of the VOF model, the next topic on equations starts with Vapor-fraction equation which is nothing but a continuity equation for secondary phase. Then comes momentum and energy equations. It is not understood from the manual is continuity equation is ever solved for primary phase or not.
  
  Thank You.
- January 2, 2020 at 2:50 pm
  
  Rob
  Forum Moderator
  
  What are you trying to work out? The continuity equation is used to track mass through every cell, VOF then interacts with that to work out where the free surface is.
- January 15, 2020 at 2:04 am
  
  soumitra2102
  Subscriber
  
  In the VOF model, Fluent solves vapor fraction equation for secondary phase to get its volume fraction.
  
  This volume fraction that is just obtained is then used to find out volume fraction of the primary phase using the volume fraction summation constraint.
  
  Now, my question is, with these two volume fractions, does Fluent solve two continuity equations for the two alphas or just one continuity equation with the mixture properties?
- January 15, 2020 at 6:14 am
  
  DrAmine
  Ansys Employee
  
  It solves one co continuity equation and one volume fraction equation.
- January 15, 2020 at 6:28 am
  
  soumitra2102
  Subscriber
  
  For which phase the continuity equation is solved?- the mixture (mixture properties) or the primary phase or the secondary phase?
  
  Also, does that continuity equation contain interphase mass transfer term on right hand side just like in the vapor fraction equation or is it zero?
- January 15, 2020 at 7:07 am
  
  DrAmine
  Ansys Employee
  
  for the bulk (mixture).
  
  The continuity equation does not contain mass source terms due to phase change as the sum of phase change terms is zero. Only VOF equation contains these terms +energy equation. So it is zero.
- January 15, 2020 at 3:36 pm
  
  soumitra2102
  Subscriber
  
  Thank You So much Mr. Adenhadj.
  From theory guide, it wasn’t that clear until now.
  
  Thanks.