# An improved non-reflecting outlet boundary condition for weakly-compressible SPH

## TL;DR

This paper introduces a hybrid outlet boundary condition for weakly-compressible SPH that improves accuracy and efficiency, validated through flow simulations and new test problems.

## Contribution

A novel hybrid boundary condition combining characteristics-based and frozen-particle methods for weakly-compressible SPH.

## Key findings

- Accurate flow simulations with fewer particles.
- Effective boundary condition for wind-tunnel-like flows.
- Open source implementation provided.

## Abstract

Implementation of an outlet boundary condition is challenging in the context of the weakly-compressible Smoothed Particle Hydrodynamics method. We perform a systematic numerical study of several of the available techniques for the outlet boundary condition. We propose a new hybrid approach that combines a characteristics-based method with a simpler frozen-particle (do-nothing) technique to accurately satisfy the outlet boundary condition in the context of wind-tunnel-like simulations. In addition, we suggest some improvements to the do-nothing approach. We introduce a new suite of test problems that make it possible to compare these techniques carefully. We then simulate the flow past a backward-facing step and circular cylinder. The proposed method allows us to obtain accurate results with an order of magnitude less particles than those presented in recent research. We provide a completely open source implementation and a reproducible manuscript.

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Source: https://tomesphere.com/paper/1907.04034