Abstract
Abstract
Highlights
Oscillatory boundary layer (OBL) flows have received great attention in the past owing to their large range of applications in both nature and engineered systems
Despite of all these advances, most of the state-of-the-art simplified models fail to accurately predict the underlying physics related to the turbulent flow–bed interaction; this is especially true when it comes to the prediction of friction coefficients, which are of high importance for the estimation of sediment transport (Fredsøe & Deigaard 1992; Nielsen 1992; Liu, García & Muscari 2007; García 2008) as well as the phase difference of the maximum bed shear stress with respect to the maximum free stream velocity
Flow regimes Akhavan et al (1991a) and Ramaprian & Tu (1983) used dimensional analysis and examined the similarity laws of oscillatory and pulsatile pipe flows, respectively. They considered that the OBL flows can be categorized into four regimes based on three length scales: a geometrical length scale based on the diameter of the pipe R, an inertia length scale δt = u∗/ω and a viscous length scale δv = ν/u∗
Summary
Oscillatory boundary layer (OBL) flows have received great attention in the past owing to their large range of applications in both nature and engineered systems. Despite of all these advances, most of the state-of-the-art simplified models fail to accurately predict the underlying physics related to the turbulent flow–bed interaction (e.g. see Guizien, Dohmen-Janssen & Vittori 2003; Blondeaux, Vittori & Porcile 2018); this is especially true when it comes to the prediction of friction coefficients (defined later in the text), which are of high importance for the estimation of sediment transport (Fredsøe & Deigaard 1992; Nielsen 1992; Liu, García & Muscari 2007; García 2008) as well as the phase difference of the maximum bed shear stress with respect to the maximum free stream velocity This fact highlights the need for the development of better numerical models for non-equilibrium and transitional flows and may be a sign of an incomplete understanding of the OBL behaviour, especially in the transitional regime as will be shown . Special effort is placed in examining the flow structures and resistance through the transitional/intermittent turbulent regime
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