Eulerian Multiphase Model in STAR-CCM+

Start from the engineering decision, not the menu option

Use Eulerian multiphase when interpenetrating dispersed phases need separate momentum descriptions and significant phase volume fractions. In STAR-CCM+, the relevant setting only becomes meaningful when it is tied to a measurable output, a physical scale and a stated modelling assumption.

This guide deliberately avoids a release-specific click sequence. Interface names and solver options can change between releases, while the engineering checks remain stable. Use the Siemens documentation for your installed release to confirm exact menu names after the physical decision is clear.

Inputs and definitions to verify first

Before changing solver controls, confirm the quantities that actually define this problem. The most important checks for this topic are:

• phase volume fraction: confirm the value, definition, units and spatial location before using it to justify the setup.
• interphase drag: confirm the value, definition, units and spatial location before using it to justify the setup.
• bubble/drop size: confirm the value, definition, units and spatial location before using it to justify the setup.
• turbulence coupling: confirm the value, definition, units and spatial location before using it to justify the setup.

Recommended STAR-CCM+ workflow

1. Define the engineering output.

   Write down the quantity that will determine success before changing Eulerian Multiphase Model in STAR-CCM+. This prevents a software setting from becoming the objective itself.

2. Verify the physical inputs.

   Check phase volume fraction and interphase drag first. Then confirm bubble/drop size and turbulence coupling are consistent with the real operating condition.

3. Create a documented baseline.

   Run one traceable baseline with the model, mesh, boundary conditions and reference values recorded before tuning secondary options.

4. Monitor solution evidence.

   Track slip velocity, phase holdup and pressure drop. A stable residual history alone is not enough if the engineering evidence is still drifting.

5. Run one targeted sensitivity.

   Change the parameter that most directly controls the uncertainty and confirm that the engineering conclusion does not depend on one arbitrary setting.

What evidence should support the final setup?

The setup is credible when the engineering outputs are stable for the right reason—not merely because the solver stopped changing quickly. Build the evidence around:

• slip velocity: compare the baseline with at least one targeted sensitivity or independent physical expectation.
• phase holdup: compare the baseline with at least one targeted sensitivity or independent physical expectation.
• pressure drop: compare the baseline with at least one targeted sensitivity or independent physical expectation.

Where possible, compare these signals with a hand calculation, correlation, test value, conservation balance or a deliberately simplified CFD case. Independent checks are especially useful before increasing model complexity.

Common failure modes

• using a drag law outside its regime.
• missing size distribution sensitivity.
• treating a sharp free surface as dispersed flow.

If one of these appears, return to the physical definition before tuning relaxation, discretization or convergence controls. Numerical tuning should not compensate for an inconsistent model.

Turn the guide into an engineering check

Related STAR-CCM+ guides