High Resolution Modeling of Turbulence in Wave Boundary Layers

Marcelo Garcia, University of Illinois at Urbana-Champaign

Usage Details

Wave boundary-layer flows play an important role on coastal engineering and coastal sediment transport. However, current state-of-the-art models fail to accurately predict the complex mechanics of the turbulence and momentum exchange between seabed and free-stream velocity under oceanic flow conditions. Recent experimental and numerical studies in our laboratory suggest the presence of a phase lag between the time instance when the maximum bed shear stress occurs with respect to the maximum free-stream velocity in transitional, oscillatory, boundary-layer flows. However, the validity of the aforementioned phase-lag findings for the case of real seabed where different levels of roughness and porosity may exist remains unknown. It is likely that the turbulent spots, which are arrowhead-shaped turbulent flow structures associated with local bed shear stress peaks and strong turbulent bursting, cause a phase lag to exist for the case of rough seabed, too. The proposed work is the first computational effort to simulate the effect of bed roughness height and bed porosity on the maximum bed shear stress phase difference compared to the maximum free-stream velocity value. Also, it will be the first numerical study that will quantify the effect of roughness regime on the turbulent characteristics and quadrant analysis under oscillatory flow conditions. It will also be the first study of the turbulent flow over various porosity porous bed for the case of oscillatory flow and among the first studies that will study the mixing layer and momentum exchange between the free-stream oscillatory flow and the pore-scale flow under oscillatory conditions. Such an analysis pushes the limits of the existing literature of turbulence-resolving numerical studies in terms of the computational resources and the high performance computing facilities it requires, and thus, it can be materialized only in a petascale supercomputer such as Blue Waters. The proposed work combines the expertise of Prof. Marcelo García's group from Ven Te Chow Hydrosystems Laboratory of the CEE Department and Prof. Paul Fischer's group from the CS and MechSE Departments with the leading-edge petascale computing resources of Blue Waters available at Illinois and aims to become one of the most comprehensive studies on the effect of turbulent structures on the oscillatory boundary layer.