Abstract
Boundary layer dynamics are investigated using a 2-D numerical model that solves the Volume-Averaged Reynolds-Averaged Navier-Stokes equations, with a VOF-tracking scheme and a k - ϵ turbulence closure. The model is validated with highly resolved data of dam break driven swash flows over gravel impermeable and permeable beds. The spatial gradients of the velocity, bed shear stress, and turbulence intensity terms are investigated with reference to bottom boundary layer (BL) dynamics. Numerical results show that the mean vorticity responds to flow divergence/convergence at the surface that result from accelerating/decelerating portions of the flow, bed shear stress, and sinking/injection of turbulence due to infiltration/exfiltration. Hence, the zero up-crossing of the vorticity is employed as a proxy of the BL thickness inside the shallow swash zone flows. During the uprush phase, the BL develops almost instantaneously with bore arrival and fluctuates below the surface due to flow instabilities and related horizontal straining. In contrast, during the backwash phase, the BL grows quasi-linearly with less influence of surface-induced forces. However, the infiltration produces a reduction of the maximum excursion and duration of the swash event. These effects have important implications for the BL development. The numerical results suggest that the BL growth rate deviates rapidly from a quasi-linear trend if the infiltration is dominant during the initial backwash phase and the flat plate boundary layer theory may no longer be applicable under these conditions.
Original language | English |
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Pages (from-to) | 6329-6350 |
Number of pages | 22 |
Journal | Journal of Geophysical Research: Oceans |
Volume | 120 |
Issue number | 9 |
Early online date | 19 Sept 2015 |
DOIs | |
Publication status | Published - Sept 2015 |
Bibliographical note
Funded byMexican National Council of Science and Technology (CoNACyT) . Grant Number: 490080
Fulbright-Garcia Robles grant
Instituto de Ingeniería UNAM
International Collaborative Research project
University of Delaware
DGAPA UNAM
National Science Foundation . Grant Numbers: OCE-0845004 , OCE-1332703
University of Delaware
UK Engineering and Physical Sciences Research Council
‘Flood MEMORY: Multi-Event Modelling Of Risk & recoverY’ . Grant Number: EP EP/K013513/1
Keywords
- swash zone
- hydrodynamics
- boundary layer