In this paper, which can be regarded as a companion of that by Corvaro et al. (2010), experimental results on the internal flow kinematics of waves which propagate on different types of beds, focusing on the nearbed dynamics induced by a porous bed, are illustrated and analyzed. The porous bed induces a major attenuation in the upstream-to-downstream direction of both wave height (≈ 30%) and internal flow velocity (≈ 50% for the maximum and minimum phases). The relationship between the wave height and the internal flow attenuation has been analyzed by means of wave energy arguments. We also found that the averaged reduction of mean flow between the smooth and porous-bed cases is approximately of 45% and 55%, respectively, for the horizontal and vertical velocity components. The stronger reduction of the vertical velocity is due to a significant variation of this velocity profile with respect to what occurs on an impermeable bed. An optical technique is used to extract the flow velocity from suitable video images; the wave dynamics on the porous medium is analyzed by evaluating the mean wave flow, the turbulence and the vorticity fields over the layer. The turbulence, indirectly characterized in terms of instantaneous velocity spectra, is found to be largely confined within the bottom boundary layer, located at a position deeper than the peaks of the mean flow. From the analyses of the instantaneous velocity spectra a clear anisotropy and inhomogeneity are found for the nearbed turbulence. This is confirmed by the presence, in the bottom boundary layer, of elongated coherent vortical structures whose intensity is the maximum during the wave crest and trough phases.

Flow dynamics on a porous medium / Corvaro, Sara; E., Seta; Mancinelli, Alessandro; Brocchini, Maurizio. - In: COASTAL ENGINEERING. - ISSN 0378-3839. - 91:(2014), pp. 280-298. [10.1016/j.coastaleng.2014.06.001]

Flow dynamics on a porous medium

CORVARO, SARA;MANCINELLI, ALESSANDRO;BROCCHINI, MAURIZIO
2014-01-01

Abstract

In this paper, which can be regarded as a companion of that by Corvaro et al. (2010), experimental results on the internal flow kinematics of waves which propagate on different types of beds, focusing on the nearbed dynamics induced by a porous bed, are illustrated and analyzed. The porous bed induces a major attenuation in the upstream-to-downstream direction of both wave height (≈ 30%) and internal flow velocity (≈ 50% for the maximum and minimum phases). The relationship between the wave height and the internal flow attenuation has been analyzed by means of wave energy arguments. We also found that the averaged reduction of mean flow between the smooth and porous-bed cases is approximately of 45% and 55%, respectively, for the horizontal and vertical velocity components. The stronger reduction of the vertical velocity is due to a significant variation of this velocity profile with respect to what occurs on an impermeable bed. An optical technique is used to extract the flow velocity from suitable video images; the wave dynamics on the porous medium is analyzed by evaluating the mean wave flow, the turbulence and the vorticity fields over the layer. The turbulence, indirectly characterized in terms of instantaneous velocity spectra, is found to be largely confined within the bottom boundary layer, located at a position deeper than the peaks of the mean flow. From the analyses of the instantaneous velocity spectra a clear anisotropy and inhomogeneity are found for the nearbed turbulence. This is confirmed by the presence, in the bottom boundary layer, of elongated coherent vortical structures whose intensity is the maximum during the wave crest and trough phases.
2014
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11566/184304
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