Use VOF when immiscible phases share a resolvable large-scale interface and design mesh/timestep around interface transport.
Start from the engineering decision, not the menu option
Use VOF when immiscible phases share a resolvable large-scale interface and design mesh/timestep around interface transport. 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.
Record the baseline value and the reason for choosing it. If the result changes materially when that assumption is varied within a defensible range, the assumption belongs in the uncertainty discussion.
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 properties: confirm the value, definition, units and spatial location before using it to justify the setup.
- initial volume fraction: confirm the value, definition, units and spatial location before using it to justify the setup.
- free-surface location: confirm the value, definition, units and spatial location before using it to justify the setup.
- gravity and pressure reference: confirm the value, definition, units and spatial location before using it to justify the setup.
Recommended STAR-CCM+ workflow
- Define the engineering output.
Write down the quantity that will determine success before changing VOF Free-Surface Setup in STAR-CCM+. This prevents a software setting from becoming the objective itself.
- Verify the physical inputs.
Check phase properties and initial volume fraction first. Then confirm free-surface location and gravity and pressure reference are consistent with the real operating condition.
- Create a documented baseline.
Run one traceable baseline with the model, mesh, boundary conditions and reference values recorded before tuning secondary options.
- Monitor solution evidence.
Track interface position, mass conservation and wave/level dynamics. A stable residual history alone is not enough if the engineering evidence is still drifting.
- 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:
- interface position: compare the baseline with at least one targeted sensitivity or independent physical expectation.
- mass conservation: compare the baseline with at least one targeted sensitivity or independent physical expectation.
- wave/level dynamics: 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 VOF for dispersed bubbles better suited to another model.
- coarse interface mesh.
- poor initialization that creates artificial mixing.
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
Calculate / structure
Use the related Abecator engineering tool or workflow to quantify the governing scale or setup assumption.
Troubleshoot
If the solved model behaves differently from the expected physics, move to the symptom-based Technical Case.
Learn the complete workflow
Follow a structured training path when the topic depends on several connected setup decisions.
Model-specific review
Use engineering support when the answer depends on your geometry, operating point, measurements or acceptance criteria.
Related STAR-CCM+ guides
Editorial and independence note
This is original Abecator CFD engineering guidance. It is written around modelling decisions, dimensional consistency, conservation and verification. STAR-CCM+ is a Siemens product name; Abecator is independent and does not reproduce Siemens documentation or third-party tutorial text. For release-specific menus and supported-model details, verify against official Siemens documentation for your installed version.