# A weakly compressible SPH method for violent multi-phase flows with high density ratio

## TL;DR

This paper introduces a novel weakly compressible SPH method for simulating violent multi-phase flows with high density ratios, improving efficiency and realism by using a low-dissipation Riemann solver and transport-velocity formulation.

## Contribution

It develops a multi-phase WCSPH approach that enhances computational efficiency and eliminates unnatural voids and phase separation in high-density-ratio flows.

## Key findings

- Demonstrates improved robustness in violent water-air flow simulations.
- Achieves better accuracy compared to previous methods with similar sound speed.
- Significantly increases computational efficiency for multi-phase flow modeling.

## Abstract

The weakly compressible SPH (WCSPH) method is known suffering from low computational efficiency, or unnatural voids and unrealistic phase separation when it is applied to simulate highly violent multi-phase flows with high density ratio, such as that between water and air. In this paper, to remedy these issues, we propose a multi-phase WCSPH method based on a low-dissipation Riemann solver and the transport-velocity formulation. The two-phase Riemann problem is first constructed to handle the pairwise interaction between fluid particles, then modified for the fluid-wall interaction to impose the solid wall boundary condition. Since the method uses the same artificial speed of sound for both heavy and light phases, the computational efficiency increases greatly. Furthermore, due to the transport-velocity formulation employed for the light phase and application of the two-phase Riemann problem, the unnatural voids and unrealistic phase separation are effectively eliminated. The method is validated with several 2- and 3D cases involving violent water-air flows. The results have been compared with existing experimental data, previous numerical and analytical solutions, where the proposed method demonstrates good robustness, improved or comparable accuracy, respectively, comparing to previous methods with same choice of sound speed or those with much less computational efficiency.