Resolution of Void-Fraction Errors and Ringing in the Edwards Solver

Resolve the incomplete void-fraction validation and significant numerical ringing in the HybridAllMach solver, determining whether improved homogeneous-equilibrium, drift-flux, or six-equation formulations can provide reliable void-fraction predictions.

Background

The final HybridAllMach implementation extends the pressure-based solver with Kurganov–Noelle–Petrova-type shock capturing and a rarefied-tail blending treatment. Although it remains stable through the 600 ms Edwards blowdown and improves the pressure root-mean-square error, substantial ringing remains.

The authors specifically identify void-fraction prediction as unresolved and leave open whether the problem should be addressed through an improved HEM formulation or by adopting drift-flux or six-equation models. This is a concrete validation and model-development problem rather than a general aspiration.

References

Moreover, the void fraction validation is not yet complete as there is significant ringing even with the HybridAllMach Solver. Complete resolution of this problem is reserved for future work, whether using an improved HEM solver, or driftFlux or 6 equation model.

— Agentic Porting, Construction and Initial Verification and Validation of Libraries within the Open Source Unified TRAnsient Multi-Phase Advanced Reactor simulation Kit (Outram Park) Part I: Thermal Hydraulics  (2608.17504 - Ong et al., 18 Aug 2026) in Section 6, Future Work, subsection “Verification and Validation”