37x Speedup in Lattice Boltzmann Cylinder Flow

Resolution robustness of vortex shedding in Lattice Boltzmann cylinder flow: a scaling study for reduced-cost simulation.

Key Finding

Vortex shedding frequency in 2D cylinder flow at Re = 100 is remarkably robust under spatial coarsening. The Strouhal number is preserved within 2.5% across a 9× grid reduction (320,000 → 35,511 cells), yielding 37× wall time speedup. Mean drag coefficient remains within the literature range at all resolutions.

Method Cells Wall Time St St Error Cd Cd Error Speedup DNS (fine) 320,000 2958s 0.1333 ref 1.279 ref 1.0× Coarse 2× 80,000 296s 0.1333 0.0% 1.325 3.6% 10.0× Coarse 3× 35,511 81s 0.1300 2.5% 1.302 1.8% 36.7×

What This Means

The dominant wake physics behaves as a resolution-robust coherent mode: the vortex shedding frequency is set by global geometry and Reynolds number, not by fine-scale boundary layer resolution. This has implications for:

Reduced-order modelling : coarsened simulations preserve dominant flow physics

: coarsened simulations preserve dominant flow physics Adaptive mesh strategies : resolution can be targeted where force accuracy matters, not where frequency is already captured

: resolution can be targeted where force accuracy matters, not where frequency is already captured Sub-grid model design: models should target force amplitude recovery rather than frequency recovery, since frequency is already preserved by large-scale dynamics

Motivation

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