LONG TERM GOAL
To develop a framework for basic understanding of the sea-floor dynamics by coupling direct numerical simulations (DNS) for turbulent flow with multi-phase sediment transport capabilities to provide basis for advancing our current knowledge of sea-floor dynamics.
The objectives of this project are:
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Understand the hydrodynamics of flow over 2D and 3D ripple.
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Understand wave-current interactions over bedforms for canonical cases, and obtain improved parameterization for overall energy dissipation. The implications of bottom-stress on sediment transport will also be explored.
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Couple the existing DNS code for turbulent flows with classic dilute passive-scalar sediment transport formulation and dilute two-phase formulation to study the uncertainties introduced by sediment bottom boundary conditions.
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Explore the potential possibilities to undertake a long-term development of a multi-phase sediment transport model for concentrated flow suitable to integrate with DNS for turbulent flow.
Direct Numerical Simulation (DNS) for Steady Flow over Sand Ripple:
DNS has been performed for a steady flow over sand ripple. The physical domain is a channel with half-height of 2cm, streamwise and spanwise length of 10cm. The domain has two sinusoidal ripples on the bottom with height from crest to trough of 0.5cm, and wavelength of 5 cm. The domain is discretized with a resolution of (194*193*192) grid points. Fig.4 shows part of the computational domain of the problem (domain from lower-wall y=0 to y=1cm in the wall-normal direction is shown). A periodic ripple is imposed close to the lower-wall of the channel on the virtual no-slip surface. A spline method was used to interpolate the ripple on to the computational mesh. In the wall-normal direction, non-uniform mesh was used. The grid spacing varied from 0.94 wall-units (corresponding to real length of 0.003cm) adjacent to the virtual no-slip surface to 6.5 wall-units (corresponding to real length of 0.02cm) at the centerline. In the horizontal directions, the streamwise and spanwise grid spacing was approximately 15 and 8 wall-units respectively.