Characterization of turbulent airflow over evolving water‐waves in a wind‐wave tank

Abstract

[1] Results of an experimental investigation of the turbulent boundary layer in airflow over evolving young wind-waves are presented. The experiments were conducted in a laboratory wind-wave flume consisting of a closed-loop wind tunnel capable of generating wind speed that may exceed 15 m/s, atop of a 5 m long wave tank. Simultaneous measurements of mean wind velocity and of instantaneous fluctuations of the horizontal and vertical air velocity components were carried out along the test section at different airflow rates and at numerous heights above the highest wave. Instantaneous surface elevation at the air sensors' location was simultaneously recorded. The friction velocities at all locations and for all airflow rates were determined by two independent methods: by fitting the logarithmic velocity profiles and by extrapolating the measured Reynolds shear stresses to mean water surface level. The variation with height and along the test section of the fluctuations of two velocity components, in the mean flow and in the vertical directions, was also studied and the results compared with flow behavior over rough and smooth plates. Wave-induced airflow parameters were then investigated by application of cross-spectral analysis. Results on the vertical extent of wave-induced boundary layer, on the phase relation between the wave-induced velocity fluctuations and the surface elevation, as well as on the wave-induced Reynolds shear stress are reported.Citation: Zavadsky, A., and L. Shemer (2012), Characterization of turbulent airflow over evolving water-waves in a wind-wave tank,

Dynamic Balances in a Wavy Boundary Layer

“…The said property is that the value of the momentum flux stays constant t(z 0 , x 0 ) between the surface and the critical height, it is discontinuous at z c , and is equal to zero above the critical height (Lin 1955;Zavadsky and Shemer 2012), that is, A useful property of the momentum flux t(z; x 0 ) involves the critical height z c , where the mean wind speed matches the wave's phase speed, that is, U(z c ) 5 c, and thus x 0 5 2log(z c /z 0 ).…”

Water waves excited by near-impulsive wind forcing

“…Kawai (1979), van Gastel et al (1985), Janssen (1986), Caulliez, Makin & Kudryavtsev (2008), Liberzon & Shemer (2011) stressed that the water shear current also modifies the short-wave gravity-capillary dispersion relation due to the Doppler shift effect. Zavadsky & Shemer (2012) performed high-resolution measurements of turbulent velocity profiles in the air above wind waves. The existence of a logarithmic velocity profile at all operational conditions was demonstrated.…”

Surface waves and wave‐coupled effects in lower atmosphere and upper ocean

“… Druzhinin et al [2012]suggest a numerical algorithm to conduct direct numerical simulations of the wind flow over steep waves. They demonstrate the flow separation and over features known from observations, and provide comparisons with an analytical quasi‐linear model of wind‐wave interactions Zavadsky and Shemer [2012]…”

“…They demonstrate the flow separation and over features known from observations, and provide comparisons with an analytical quasi-linear model of wind-wave interactions. Zavadsky and Shemer [2012] took a detailed look at very young waves in a laboratory tank. Their fine measurements produce results on the vertical extent of wave-induced boundary layer in the air, on the phase relation between the wave-induced velocity fluctuations and the surface elevation, on the wave-induced Reynolds shear stress at very early stages of wave development.…”