Particle diameter larger than channel width still passes through in Particle Tracing – how to enforce size exclusion?

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Particle diameter larger than channel width still passes through in Particle Tracing – how to enforce size exclusion?

I am using Particle Tracing for Fluid Flow in COMSOL (v5.6 and 6.3) to model transport of finite-size particles in narrow channels / porous-media-like geometries.

I have specified a particle diameter of 1 mm, while the channel (or pore throat) width is smaller than 1 mm. However, during the simulation the particle still passes through the constriction. Even when a Wall condition with Freeze is applied, the particle appears to slide through the narrow region instead of being geometrically excluded.

From what I can tell, COMSOL seems to track the particle as a point mass and does not automatically enforce hard-sphere size exclusion based on the specified diameter. I suspect the diameter is being used only for drag/forces and not for collision detection with walls.

My questions are:

Is there a built-in way in COMSOL to enforce particle–wall contact based on the particle radius, so that particles cannot pass through openings smaller than their diameter?

If not, what is the recommended approach to model size exclusion reliably (e.g. wall offsetting, modified geometry, near-wall capture forces, or other workarounds)?

Are there solver or time-stepping settings that can prevent particles from numerically “jumping” through narrow gaps?

Any guidance on best practice for modeling finite-size particle transport and exclusion in narrow channels or porous geometries would be greatly appreciated.

Thank you in advance.


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