Abstract
Physical phenomena at an air–water interface are of interest in a variety of flows with both industrial and natural/environmental applications. In this paper, we present novel experimental techniques incorporating a multi-camera multi-laser instrumentation in a combined particle image velocimetry and laser-induced fluorescence system. The system yields accurate surface detection thus enabling velocity measurements to be performed very close to the interface. In the application presented here, we show results from a laboratory study of the turbulent airflow over wind driven surface waves. Accurate detection of the wavy air–water interface further yields a curvilinear coordinate system that grants practical and easy implementation of ensemble and phase averaging routines. In turn, these averaging techniques allow for the separation of mean, surface wave coherent, and turbulent velocity fields. In this paper, we describe the instrumentation and techniques and show several data products obtained on the air-side of a wavy air–water interface.
Highlights
The physical processes at a gas–liquid interface are important for many industrial applications as well as natural environmental problems
The surface waves significantly modify the boundary layers on both sides of the interface and it is well established that it is through waverelated dynamical processes that the air and water boundary layers are coupled (see Sullivan and McWilliams (2010) for a review on the topic)
To locate the interface in the Laser-induced fluorescence (LIF) images (PIVSD), we developed a surface detection algorithm based on local variations of image intensity gradients, computed by kernel convolution
Summary
The physical processes at a gas–liquid interface are important for many industrial applications as well as natural environmental problems. In the geophysical sphere, which largely motivates this study, fluxes of momentum and scalars across the wavy air–sea interface provide boundary conditions for both the atmosphere and the oceans and are pivotal in controlling the evolution of weather and climate. These fluxes are affected by fine-scale, coupled dynamics above and below the wavy ocean surface. The surface waves significantly modify the boundary layers on both sides of the interface and it is well established that it is through waverelated dynamical processes that the air and water boundary layers are coupled (see Sullivan and McWilliams (2010) for a review on the topic). The turbulence injected into the water column significantly enhances surface mixing (Drennan et al 1996; Melville et al 1998; Veron and Melville 1999; Melville et al 2002; Thorpe et al 2003; Gemmrich and Farmer 2004) and leads to substantial deviations from the classical theories (Agrawal et al 1992; Thorpe 1993; Melville 1994; Anis and Moum 1995; Melville 1996; Terray et al 1996; Veron and Melville 2001) and causes significant energy dissipation (Banner et al 2014; Thomson et al 2016; Schwendeman et al 2014; Zappa et al 2016; Sutherland and Melville 2013, 2015)
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