The variation of turbulent eddy viscosity during a wave cycle.

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Nelly Oldekop, Toomas Liiv

Monday 29 june 2015

14:05 - 14:20h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 2C. Coastal engineering

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One of the most problematic issues that have to be dealt with in connection with the surf zone hydrodynamics is the accurate determination of turbulent eddy viscosity under breaking waves. Most hydrodynamic and sediment transport models tend to neglect the unsteady character of this term. This means, that turbulent eddy viscosity on the seabed changes both in time and space. This paper focuses on the results obtained during experimental runs in the wave flume of Laboratory of Fluid Mechanics in Tallinn University of Technology. Experiments were performed on the beach model with an inclination of 1 to 17. Velocities were measured using 2D LDA apparatus in various profiles around the breaking point. Measurements were performed extremely close to bed allowing the calculation of bottom shear stresses under wave. The paper presents results of the study of turbulent eddy viscosity in the surf zone on the bottom of the hydraulically smooth beach model. It was found that turbulent viscosity varies both in time and space as the wave propagates and is at least an order of magnitude larger than the corresponding dynamic viscosity.