| 1. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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A dual-lattice hydrodynamic-thermal MRT-LBM model implemented on GPU for DNS calculations of turbulent thermal flows
- 2022
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Ingår i: International journal of numerical methods for heat & fluid flow. - : Emerald Group Publishing Limited. - 0961-5539 .- 1758-6585. ; 35:5, s. 1703-1725
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Tidskriftsartikel (refereegranskat)abstract
- PurposeThe purpose of this paper is to present a fast and bare bones implementation of a numerical method for quickly simulating turbulent thermal flows on GPUs. The work also validates earlier research showing that the lattice Boltzmann method (LBM) method is suitable for complex thermal flows.Design/methodology/approachA dual lattice hydrodynamic (D3Q27) thermal (D3Q7) multiple-relaxation time LBM model capable of thermal DNS calculations is implemented in CUDA.FindingsThe model has the same computational performance compared to earlier publications of similar LBM solvers. The solver is validated against three benchmark cases for turbulent thermal flow with available data and is shown to be in excellent agreement.Originality/valueThe combination of a D3Q27 and D3Q7 stencil for a multiple relaxation time -LBM has, to the authors’ knowledge, not been used for simulations of thermal flows. The code is made available in a public repository under a free license.
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| 2. |
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| 3. |
- Forslund, Tobias O.M. 1992-
(författare)
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MRT Lattice Boltzmann Method on multiple Graphics Processing Units with halo sharing over PCI-e for non-contiguous memory
- 2022
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Ingår i: Proceedings of the Eleventh International Conference on Engineering Computational Technology. - : Civil-Comp Press.
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Konferensbidrag (refereegranskat)abstract
- The Lattice Boltzmann Method (LBM) has been shown to be well suited for implementation on Graphics Processing Units (GPUs). The benefit of GPU implementations compared to CPU is in the reduction of computational time, by as much as 2 orders of magnitude. This staggering difference is due to how computations for LBM are both explicit and local, meaning that it can make full use of the GPUs capabilities, like most other cellular automata methods. Although GPUs have a significantly larger performance in terms of floating-point operations per second (FLOPS) compared to a CPU it has two significant drawbacks; First, the complexity of the calculations is limited due to the relative simplicity of the GPU core design compared to a CPU, secondly, the memory of a GPU is usually limited in comparison, ranging from a few GB up to ???? 100 GB for high-end enterprise cards. Because the LBM method is suitable for execution on GPUs the first point is not necessary to consider. But the second point becomes a limitation as larger, or more highly resolved computational domains are of interest. This can be remedied by distributing the computations across several GPUs executing in parallel. The GPUs share values in overlapping regions called halo-values that need to be transferred each time step. If the memory is contiguous then each transfer can be executed as a single efficient memory transfer call that utilizes the PCI-e lanes efficiently. If this is not the case then support exists for copying of so-called strided memory which has a constant offset between values for either single strided (2D) or double strided (3D). These functions practically result in bad PCI-e lane utilization and to remedy this a method is proposed, the halo-values are calculated and packed into a contiguous memory buffer that is then communicated between the GPUs via the PCI-e lanes. It is shown that the method introduces some additional overhead compared to single GPU execution but maintains a reasonable 70% performance compared to the single GPU case.
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| 4. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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Non-Stokesian flow through ordered thin porous media imaged by tomographic-PIV
- 2021
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Ingår i: Experiments in Fluids. - : Springer. - 0723-4864 .- 1432-1114. ; 62:3
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Tidskriftsartikel (refereegranskat)abstract
- The 3D flow-fields in a staggered and cubic arrangement of mono-radii cylinders are investigated using tomographic-PIV. The cylinder Reynolds-number is in the range of ≈10 to ≈800 giving an almost complete overview of the transition region. Two pore-scale effects are discovered. The first, visible in the cubic packing, is a spatially alternating lateral velocity field, which has a significant impact on the pressure drop and transversal dispersion. The second effect, present in the staggered array, is an example of a disturbance propagation effect that takes place in the laminar steady region; this manifests as a peculiar and complex flow-pattern. In accordance with other studies, it is shown that Darcy’s law can, from an engineering point of view be valid far beyond the limit for Stokesian flow.
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| 5. |
- Forslund, Tobias O.M. 1992-, et al.
(författare)
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Steady-State Transitions in Ordered Porous Media
- 2023
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Ingår i: Transport in Porous Media. - : Springer Nature. - 0169-3913 .- 1573-1634. ; 149:2, s. 551-577
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Tidskriftsartikel (refereegranskat)abstract
- Previously performed experiments on flow through an ordered porous media cell with tomographic particle image velocimetry reveal a complex three-dimensional steady-state flow pattern. This flow pattern emerge in the region where inertial structures have been previously reported for a wide range of packings. The onset of these steady-state inertial flow structures is here scrutinized for three different types of packing using a finite difference method. It is concluded that the onset of the flow structure coincides with a symmetry break in the flow field and discontinuities in the pressure drop, volume averaged body forces and heat transfer. A quantity for identifying the transition is proposed, namely the pressure integral across the solid surfaces. It is also shown that the transition can both increase and decrease the heat transfer dependent on the actual geometry of the porous medium.
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| 6. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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The Effects of Periodicity Assumptions in Porous Media Modelling
- 2021
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Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 137:3, s. 769-797
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Tidskriftsartikel (refereegranskat)abstract
- The effects of periodicity assumptions on the macroscopic properties of packed porous beds are evaluated using a cascaded Lattice-Boltzmann method model. The porous bed is modelled as cubic and staggered packings of mono-radii circular obstructions where the bed porosity is varied by altering the circle radii. The results for the macroscopic properties are validated using previously published results. For unsteady flows, it is found that one unit cell is not enough to represent all structures of the fluid flow which substantially impacts the permeability and dispersive properties of the porous bed. In the steady region, a single unit cell is shown to accurately represent the fluid flow across all cases studied
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