Session: 12-01-01 Wave theories I

Paper Number: 126690

126690 - Estimate of Shear Velocity at Wind-Wave Interface Using Flow Measurements in Both Air and Water 

We present flow measurements in both air and water sides and various methods to estimate shear velocity at the air-water interface in laboratory wind-wave conditions. Experiments were conducted in a wind-wave-current flume at Texas A&M University at  a fetch of 6.2 m with three freestream wind speeds of 6, 8, and 10 m s^-1, corresponding wave age (the ratio of phase speed to the friction velocity) of 1.1, 0.9, and 0.8, respectively. Instantaneous velocities above and beneath the waves were separately obtained using the particle image velocimetry (PIV) technique. The instantaneous velocity fields were decomposed into the mean, wave-induced, and turbulent velocity components. The shear velocities were estimated from both air- and water- side measurements with the mean velocity profile and the eddy-correlation methods. The results show that the turbulent wind stress determined from the profile method is consistently higher than those from the eddy-correlation methods. With the assumption that the stress at the surface is in local equilibrium, the eddy-correlation method was most reliable for shear velocity measurements. The result from the comparison of different methods is useful in determining the scaling of water side turbulence such as dissipation rate of turbulence kinetic energy with the air side velocity measurements, or vice versa.

Presenting Author: Kuang-An Chang Texas A&M University

Presenting Author Biography: Kuang-An Chang is a Professor in the Zachry Department of Civil & Environmental Engineering at Texas A&M University, with a joint appointment in the Department of Ocean Engineering.

Authors:

Jitae Do Texas A&M University
Binbin Wang University of Missouri
Kuang-An Chang Texas A&M University