Abstract
Laboratory experiments on studying the structure of the turbulent air boundary layer over waves were carried out at the Wind-Wave Flume of the Large Thermostratified Tank of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS), in conditions modeling the near water boundary layer of the atmosphere under strong and hurricane winds and the equivalent wind velocities from 10 to 48 m/s at the standard height of 10 m. A modified technique of Particle Image Velocimetry (PIV) was used to obtain turbulent pulsation averaged velocity fields of the air flow over the water surface curved by a wave and average profiles of the wind velocity. The main modifications are: 1) the use of high-speed video recording (1000-10000 frames/sec) with continuous laser illumination helps to obtain ensemble of the velocity fields in all phases of the wavy surface for subsequent statistical processing; 2) the development and application of special algorithms for obtaining form of the curvilinear wavy surface of the images for the conditions of parasitic images of the particles and the droplets in the air side close to the surface; 3) adaptive cross-correlation image processing to finding the velocity fields on a curved grid, caused by wave boarder; 4) using Hilbert transform to detect the phase of the wave in which the measured velocity field for subsequent appropriate binning within procedure obtaining the average characteristics.
Highlights
The interaction between wind flow and surface waves is one of central problems of the study and parameterization of exchange processes in boundary layers of the atmosphere and ocean [1]
A modified technique of Particle Image Velocimetry (PIV) was used to obtain turbulent pulsation averaged velocity fields of the air flow over the water surface curved by a wave
We emphasize that such remote methods permit one to obtain the air flow velocity field below wave crests in wave troughs
Summary
The interaction between wind flow and surface waves is one of central problems of the study and parameterization of exchange processes in boundary layers of the atmosphere and ocean [1]. Carrying out field measurements of air flows, wave parameters for such conditions is very difficult problem The main difficulties in the experimental study of a turbulent air flow over a wavy water surface in laboratory conditions are connected with measuring wind characteristics near the water surface, especially in wave troughs, where one can expect the appearance of the most interesting features of this flow, such as shielding and separation of the flow. The technique Particle Image Velocimetry PIV is best fit for measuring the air flow in wave troughs and water flows close to the surface. In [8], the structure of average velocity fields in the air flow and their perturbations initiated by waves, as well as the structure of turbulent stresses, were successfully studied
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