The present study focuses on the unphysical effects induced by the use of non-uniform grids in the lattice Boltzmann method. In particular, the convection of vortical structures across a grid refinement interface is likely to generate spurious noise that may impact the whole computation domain. This issue becomes critical in the case of aeroacoustic simulations, where accurate pressure estimations are of paramount importance. The purpose of this article is to identify the issues occurring at the interface and to propose possible solutions yielding significant improvements for aeroacoustic simulations. More specifically, this study highlights the critical involvement of non-physical modes in the generation of spurious vorticity and acoustics. The identification of these modes is made possible thanks to linear stability analyses performed in the fluid core, and non-hydrodynamic sensors specifically developed to systematically emphasize them during a simulation. Investigations seeking pure acoustic waves and sheared flows allow for isolating the contribution of each mode. An important result is that spurious wave generation is intrinsically due to the change in the grid resolution (i.e. aliasing) independently of the details of the grid transition algorithm. Finally, the solution proposed to minimize spurious wave amplitude consists of choosing an appropriate collision model in the fluid core so as to cancel the non-hydrodynamic mode contribution regardless the grid coupling algorithm. Results are validated on a convected vortex and on a turbulent flow around a cylinder where a huge reduction of both spurious noise and vorticity are obtained.

本研究的重点是在格子Boltzmann方法中使用非均匀网格引起的非物理效应。特别是，穿过网格细化界面的涡旋结构的对流可能会产生杂散噪声，这些杂散噪声可能会影响整个计算域。在航空声学仿真的情况下，此问题变得至关重要，在航空声学仿真中，准确的压力估算至关重要。本文的目的是确定在接口处出现的问题，并提出可能的解决方案，从而对航空声学仿真产生重大的改进。更具体地说，本研究强调了非物理模式在伪涡旋和声学产生中的关键作用。由于在流体核心中执行了线性稳定性分析，并且专门开发了非流体动力传感器以在仿真过程中系统地强调它们，因此可以识别这些模式。寻找纯声波和剪切流的研究可以隔离每种模式的影响。一个重要的结果是，杂散波的产生本质上是由于网格分辨率（即混叠）的变化而引起的，而与网格过渡算法的细节无关。最后，提出的最小化杂散波幅度的解决方案包括在流体核心中选择适当的碰撞模型，以消除非流体动力模式的影响，而不考虑网格耦合算法。