Experimental investigation of multiphase hydrodynamics of the ocean-atmosphere boundary layer within laboratory modelling

Abstract

Laboratory modelling of the processes of interaction between the atmosphere and ocean in the boundary layers is one of the most interesting from the point of view of the features of the hydrophysical experiment. The main characteristics that need to be controlled in these experiments include, first of all, the air velocity field over the rough surface waves and the underwater flow, as well as the shape of the free surface. However especial features as spray of droplets, the bubbles in the water and foam generated during the breaking of waves should also be taken into account when modelling extreme weather conditions associated with strong winds. Thus, from the point of view of experimental hydrodynamics, we are dealing with a multiphase turbulent flow with a free boundary. For purpose of experimental study on the wind-wave flume, an integrated approach is required that allows simultaneous measurements of the velocity flow fields, the sizes of droplets and bubbles, the shape of waves and parameters of foam coverage. Contact methods often do not allow for universality. This review study describes developing approaches to the use of optical methods for performing these studies. Presented results were obtained in experiments carried out on several wind-wave flumes. To study the processes of fragmentation of the water surface leading to the formation of droplets an foam, high-speed multi-angle video taking is used in combination with the shadow imaging method.