Large-eddy simulation of oscillating boundary layers: Model comparison and validation

Abstract

Large-eddy simulations of oscillating boundary layers over smooth and rough walls in the fully turbulent regime have been carried out. Several models for the unresolved subgrid-scale (SGS) stresses are compared, as well as different approximate treatments of the wall layer, where none of the momentum-transporting eddies is resolved. The simulations show that the use of advanced SGS models coupled with approximate boundary conditions can predict the flow successfully. Dynamic SGS eddy-viscosity models yield more accurate results than the fixed-coefficient one, which yields an excessively large SGS eddy viscosity, damping the wall-normal fluctuations. The shifted logarithmic-law approximate boundary condition, which accounts for the inclination of the near-wall eddies, results in prediction of the wall stress within 3% of the experimental data throughout the cycle. The standard logarithmic law also gives adequate results, with a maximum error of 6%. A modification of the rough-wall logarithmic law that accounts for transitional roughness effects was also tested; at this Reynolds number, however, this correction made little difference in the numerical results. Copyright 2008 by the American Geophysical Union.