SEA RIPPLE FORMATION - THE TURBULENT BOUNDARY-LAYER CASE

This study presents a predictive theory of ripple formation beneath se a waves. The theory is based on a linear stability analysis of a flat sandy bottom subject to an oscillatory flow. The flow regime in the bo ttom boundary layer is assumed to be turbulent; hence previous works o n the subject, which considered a laminar flow, are extended in a more relevant range of the Reynolds number. The turbulent stresses are des cribed by means of the constant eddy viscosity model proposed by Sleat h in 1991 and a two time-scale approach is used to decouple fluid moti on from bottom time development. A closed form solution is found for t he turbulent oscillatory how over a fixed wavy wall and the time devel opment of the bottom perturbation is determined by means of sediment c ontinuity equation. The conditions for ripple appearance are determine d along with their wavelength as they form. A comparison between theor etical findings and experimental data supports the validity of the pre sent approach.