Simulation of wave boundary layers with spatially varying bottom roughness
David R. Fuhrman
DTU Mechanical Engineering
Abstract:
Numerical results involving turbulent oscillatory wave boundary layers on spatially varying bottom roughness will be presented. This is a problem of coastal engineering interest e.g. in the scour protection of coastal structures, as well as geophysical relevance e.g. in coastal flows over naturally sorted sediments. The numerical model utilized solves Reynolds-averaged Navier-Stokes equations, coupled with a two-equation (k-omega) turbulence closure, and a discussion of boundary conditions for hydraulically rough beds will be also presented. Model results will be compared against earlier experimental measurements on beds with sudden spatial roughness changes. These demonstrate a number of interesting features, including significantly amplified bed shear stresses, asymmetric turbulence levels in subsequent half-cycles, as well as period-averaged streaming in the direction of larger roughness. Results from a subsequent parametric study will also be presented, including the effects of gradual (rather than sudden) roughness changes.