Modeling inviscid compressible flows with shocks and vortex-dominated dynamics remains challenging for particle–grid methods due to moving discontinuities, cell-crossing noise, and quadrature degradation under strong deformation. Building on a FLIP–APIC framework with vorticity-aware tensor artificial viscosity, we identify a long-time RTI failure mode: particle depletion at spike heads degrades quadrature and particle–grid coupling, producing nonphysical, void-like dents. Standard mitigations (CPDI-lite and subcell-jittered seeding) reduce but do not eliminate this artifact. We therefore add two sampling-aware controls: (i) conservative split resampling that replenishes depleted cells while exactly conserving mass, momentum, and internal energy; and (ii) a soft-switch that attenuates only the APIC affine term when local support is insufficient. Tests on the Sod shock tube and single-/multi-mode RTI show that the method removes spike-head voids in long-time RTI while preserving vortex roll-up, and matches reference Euler growth metrics.
Yao et al. (Fri,) studied this question.