# Solving the Volume Fraction Equation in a Multiphase M.

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 August 2, 2011, 14:18 Solving the Volume Fraction Equation in a Multiphase M. #1 New Member   Massimiliano Join Date: Aug 2011 Posts: 1 Rep Power: 0 Hi there, I need to solve two simple scalar transport equations (two scalars UDS0, UDS1 introduced, no diffusion, no source), along the Fluent continuity, momentum and Volume Fraction Equations, for a Eulerian Multiphase Model. At this initial stage, the two scalar transport equations have been defined to easily replace the Volume Fraction Equation of Fluent. In other words, we want them to give us the same evolution for the scalars UDS0 and UDS1 in time and space, as the Fluent volume fractions equation does for the C_VOF. The problem turns out to be more difficult than it seems though! Initially, I tried to disable the volume fraction equation from the Controls panel, since the scalar equations were supposed to give us the same results. The simulation slows terribly down, and diverges after a while. Then, I decided to leave all the equations enabled, overwriting in the UDF the C_VOF with the scalars. The evolution seems to be well predicted, but the simulation crashed down inexplicably after 500-600 timesteps. The last attempt, I left all the equations to go, without the overwriting, but even if their dynamic are very similar, the scalars tend to wrong values, since their sum is sensibly bigger than one!!!!! How can I overcome this problem??Please help me!!!!! Thank you Max somy1 likes this.

March 20, 2012, 08:49
#2
Member

chenxizhong
Join Date: Feb 2012
Posts: 30
Rep Power: 5
Hi Massimiliano, have you solved the promble? rencently I encounted the same problems, can you give me some suggestion? thanks.
Quote:
 Originally Posted by Max585 Hi there, I need to solve two simple scalar transport equations (two scalars UDS0, UDS1 introduced, no diffusion, no source), along the Fluent continuity, momentum and Volume Fraction Equations, for a Eulerian Multiphase Model. At this initial stage, the two scalar transport equations have been defined to easily replace the Volume Fraction Equation of Fluent. In other words, we want them to give us the same evolution for the scalars UDS0 and UDS1 in time and space, as the Fluent volume fractions equation does for the C_VOF. The problem turns out to be more difficult than it seems though! Initially, I tried to disable the volume fraction equation from the Controls panel, since the scalar equations were supposed to give us the same results. The simulation slows terribly down, and diverges after a while. Then, I decided to leave all the equations enabled, overwriting in the UDF the C_VOF with the scalars. The evolution seems to be well predicted, but the simulation crashed down inexplicably after 500-600 timesteps. The last attempt, I left all the equations to go, without the overwriting, but even if their dynamic are very similar, the scalars tend to wrong values, since their sum is sensibly bigger than one!!!!! How can I overcome this problem??Please help me!!!!! Thank you Max

 Tags fraction, multiphase model, scalar, uds, volume

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