Coherent structures in wave boundary layers. Part 2. Solitary motion

Abstract

This study continues the investigation of wave boundary layers reported by Carstensen, Sumer & Fredsøe (J. Fluid Mech., 2010, part 1 of this paper). The present paper summarizes the results of an experimental investigation of turbulent solitary wave boundary layers, simulated by solitary motion in an oscillating water tunnel. Two kinds of measurements were made: bed shear stress measurements and velocity measurements. The experiments show that the solitary-motion boundary layer experiences three kinds of flow regimes as the Reynolds number is increased: (i) laminar regime; (ii) laminar regime where the boundary-layer flow experiences a regular array of vortex tubes near the bed over a short period of time during the deceleration stage; and (iii) transitional regime characterized with turbulent spots, revealed by single/multiple, or, sometimes, quite dense spikes in the bed shear stress traces. Supplementary synchronized flow visualization tests confirmed the presence of the previously mentioned flow features. Information related to flow resistance are also given in the paper.

Numerical simulation of tsunami-scale wave boundary layers

“…For example, Suntoyo and Tanaka (2009), who used the closure of Menter (1994), found results that were, at least, qualitatively consistent with the experimental work of Sumer et al (2010). More recently used the closure of Saffman (1970) to directly simulate experimental cases of Sumer et al (2010). The computed boundary layer flow compared favourably with the experimental measurements, with the model adequately detailing the transition from laminar to turbulent conditions.…”

“…Blondeaux, 1987;, have recently been applied to the study boundary layer dynamics beneath solitary waves. For example, Suntoyo and Tanaka (2009), who used the closure of Menter (1994), found results that were, at least, qualitatively consistent with the experimental work of Sumer et al (2010). More recently used the closure of Saffman (1970) to directly simulate experimental cases of Sumer et al (2010).…”

“…We will first validate the numerical model against experimental measurements of Sumer et al (2010) who, using an oscillating tunnel, considered boundary layers generated by transient waves having free stream velocity signals of the form:…”

“…Most commonly studies have focused on the boundary layer developing beneath idealised solitary waves. Theoretical solutions for laminar boundary layer flow have been derived by Liu et al (2007), whilst the experimental work of Sumer et al (2010Sumer et al ( , 2011 has provided a quantitative insight into the boundary layer dynamics across the transition from laminar to fully turbulent conditions. Though direct numerical simulations have proved capable of providing a detailed description of the experimentally observed flow field across these scales Blondeaux, 2008, 2011), they are computationally intensive and thus unsuitable for practical engineering applications.…”

“…In Section 3 the model will then be validated, largely for transient solitary-type waves based on the experimental measurements of Sumer et al (2010). In Section 4 the model will be utilised for the simulation of tsunami-scale wave boundary layers based on three idealised synthetic wave forms, characterised as: (1) single (i.e.…”