4 research outputs found
Lattice Boltzmann method for computational aeroacoustics on non-uniform meshes: a direct grid coupling approach
The present study proposes a highly accurate lattice Boltzmann direct
coupling cell-vertex algorithm, well suited for industrial purposes, making it
highly valuable for aeroacoustic applications. It is indeed known that the
convection of vortical structures across a grid refinement interface, where
cell size is abruptly doubled, is likely to generate spurious noise that may
corrupt the solution over the whole computational domain. This issue becomes
critical in the case of aeroacoustic simulations, where accurate pressure
estimations are of paramount importance. Consequently, any interfering noise
that may pollute the acoustic predictions must be reduced.
The proposed grid refinement algorithm differs from conventionally used ones,
in which an overlapping mesh layer is considered. Instead, it provides a direct
connection allowing a tighter link between fine and coarse grids, especially
with the use of a coherent equilibrium function shared by both grids. Moreover,
the direct coupling makes the algorithm more local and prevents the duplication
of points, which might be detrimental for massive parallelization. This work
follows our first study (Astoul~\textit{et al. 2020}) on the deleterious effect
of non-hydrodynamic modes crossing mesh transitions, which can be addressed
using an appropriate collision model. The Hybrid Recursive Regularized model is
then used for this study. The grid coupling algorithm is assessed and compared
to a widely-used cell-vertex algorithm on an acoustic pulse test case, a
convected vortex and a turbulent circular cylinder wake flow at high Reynolds
number.Comment: also submitted to Journal of Computational Physic
Analysis and reduction of spurious noise generated at grid refinement interfaces with the lattice Boltzmann method
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.Comment: Submitted to Journal of Computational Physics May201