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

Abstract

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. © 2012 American Geophysical Union. All Rights Reserved.