Transitional flow in intracranial aneurysms – A space and time refinement study below the Kolmogorov scales using Lattice Boltzmann Method

•Simulations on aneurysms with up to one billion cells.•Quantification of Kolmogorov micro-scales.•A systematic assessment of laminar and transitional flow in aneurysms.•Recommendations on the choice of resolutions for CFD simulations.•Exploration of critical Re at which flow transitions in aneurysms.

Most Computational Fluid Dynamics (CFD) studies of hemodynamics in intracranial aneurysms are based on the assumption of laminar flow due to a relatively low (below 500) parent artery Reynolds number. A few studies have recently demonstrated the occurrence of transitional flow in aneurysms, but these studies employed special finite element schemes tailored to capture transitional nature of flow. In this study we investigate the occurrence of transition using a standard Lattice Boltzmann Method (LBM). The LBM is used because of its computational efficiency, which in the present study allowed us to perform simulations at a higher resolution than has been done in the context of aneurysms before. The high space-time resolutions of 8 µm and 0.11 µs resulted in nearly 1 × 109 cells and 9 × 106 time steps per second and allowed us to quantify the turbulent kinetic energy at resolutions that are of the order of the Kolmogorov scales. We perform an in-depth space and time refinement study on 2 aneurysms; one was previously reported laminar, while the other was reported transitional. Furthermore, we investigate the critical Reynolds number at which the flow transitions in aneurysms under time constant inflow conditions.