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CFX 2019 R2

- June 14, 2026 at 7:28 am
  
  1805611570
  Subscriber
  
  I have a question about ANSYS CFX 2019 R2.
  How can I define the initial volume fraction of two components in a single fluid domain? The two phases have different densities and tend to form a clear stratification due to buoyancy effects.
  In addition, external forces act on the flow field, causing the interface between the two phases to evolve gradually over time.
  What is the correct way to set up the initial volume fraction distribution for both phases in CFX 2019 R2 to properly capture this stratified initial condition and its subsequent interface evolution?
- June 15, 2026 at 7:11 am
  
  NickFL
  Subscriber
  
  You can set up expressions to define the situation. Say for example you have the inital interface at x=3 [m]. Create an expression for the volume fraction, you could write: if(x < 3[m], 1.0, 0). You can then use this in the initialization tab. Open the Domain, then move to the Initilization tab. Near the bottom will be the initial values, you can use the expression you have created.

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