CFX 2019 R2

[1805611570]

CFX Multiphase Flow: Why is the volume of each phase not conserved during a transient simulation without mass transfer?

I am performing a transient multiphase flow simulation in ANSYS CFX using two immiscible phases. Mass transfer between the phases is disabled, so no phase change occurs. The two phases separate only because of their density difference.

I found that the total volume of the computational domain is conserved, but the volume of each individual phase changes over time. Since there is no mass transfer between the phases, I expected the volume of each phase to remain constant throughout the simulation.

Is this behavior normal in CFX? What could cause the volume of each phase to change even though mass transfer is turned off? Could it be related to numerical diffusion, interface compression, compressibility settings, or another aspect of the multiphase model?

Any suggestions or explanations would be greatly appreciated.