Dynamics of an oscillatory boundary layer over a sediment bed in Euler-Lagrange simulations
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arXiv
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| Format: | Preprint |
| Publié: |
2024
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| _version_ | 1866914072786632704 |
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| author | Van Doren, Jonathan S. Kasbaoui, M. Houssem |
| author_facet | Van Doren, Jonathan S. Kasbaoui, M. Houssem |
| contents | We investigate the dynamics of an oscillatory boundary layer developing over a bed of collisional and freely evolving sediment grains. We perform Euler-Lagrange simulations at Reynolds numbers $\mathrm{Re}_δ= 200$, 400, and 800, density ratio $ρ_p/ρ_f = 2.65$, Galileo number $\mathrm{Ga} = 51.9$, maximum Shields numbers from $5.60 \times 10^{-2}$ to $2.43 \times 10^{-1}$, based on smooth wall configuration, and Keulegan-Carpenter number from $134.5$ to $538.0$. We show that the dynamics of the oscillatory boundary layer and sediment bed are strongly coupled due to two mechanisms: (I) bed permeability, which leads to flow penetration deep inside the sediment layer, a slip velocity at the bed-fluid interface, and the expansion of the boundary layer, and (II) particle motion, which leads to rolling-grain ripples at $\mathrm{Re}_δ= 400$ and $\mathrm{Re}_δ= 800$. While at $\mathrm{Re}_δ= 200$ the sediment bed remains static during the entire cycle, the permeability of the bed-fluid interface causes a thickening of the boundary layer. With increasing $\mathrm{Re}_δ$, the particles become mobile, which leads to rolling-grain ripples at $\mathrm{Re}_δ= 400$ and suspended sediment at $\mathrm{Re}_δ= 800$. Due to their feedback force on the fluid, the mobile sediment particles cause greater velocity fluctuations in the fluid. Flow penetration causes a progressive alteration of the fluid velocity gradient near the bed interface, which reduces the Shields number based upon bed shear stress. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_10945 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Dynamics of an oscillatory boundary layer over a sediment bed in Euler-Lagrange simulations Van Doren, Jonathan S. Kasbaoui, M. Houssem Fluid Dynamics We investigate the dynamics of an oscillatory boundary layer developing over a bed of collisional and freely evolving sediment grains. We perform Euler-Lagrange simulations at Reynolds numbers $\mathrm{Re}_δ= 200$, 400, and 800, density ratio $ρ_p/ρ_f = 2.65$, Galileo number $\mathrm{Ga} = 51.9$, maximum Shields numbers from $5.60 \times 10^{-2}$ to $2.43 \times 10^{-1}$, based on smooth wall configuration, and Keulegan-Carpenter number from $134.5$ to $538.0$. We show that the dynamics of the oscillatory boundary layer and sediment bed are strongly coupled due to two mechanisms: (I) bed permeability, which leads to flow penetration deep inside the sediment layer, a slip velocity at the bed-fluid interface, and the expansion of the boundary layer, and (II) particle motion, which leads to rolling-grain ripples at $\mathrm{Re}_δ= 400$ and $\mathrm{Re}_δ= 800$. While at $\mathrm{Re}_δ= 200$ the sediment bed remains static during the entire cycle, the permeability of the bed-fluid interface causes a thickening of the boundary layer. With increasing $\mathrm{Re}_δ$, the particles become mobile, which leads to rolling-grain ripples at $\mathrm{Re}_δ= 400$ and suspended sediment at $\mathrm{Re}_δ= 800$. Due to their feedback force on the fluid, the mobile sediment particles cause greater velocity fluctuations in the fluid. Flow penetration causes a progressive alteration of the fluid velocity gradient near the bed interface, which reduces the Shields number based upon bed shear stress. |
| title | Dynamics of an oscillatory boundary layer over a sediment bed in Euler-Lagrange simulations |
| topic | Fluid Dynamics |
| url | https://arxiv.org/abs/2404.10945 |