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<p>Velocity gradients are critical drivers of turbulent and scalar exchange processes within fluids. Calculating these gradients at a wavy air-water interface presents significant challenges, requiring simultaneous spatially distributed measurements of velocity fields across an undulating interface. In this study, we employ thermal marking velocimetry (TMV), an unobtrusive active velocimetry technique, to capture the surface velocity field over an unstructured grid. The surface velocity field is then used to compute the horizontal surface velocity gradient; together, these enable calculation of the wave orbital velocity, surface strain, vertical vorticity, and turbulent kinetic energy (TKE). Furthermore, a structure function-based approach is employed to estimate the TKE dissipation rate at the wavy interface. Finally, we calculate the Eulerian vortex force field at the surface, providing a quantitative experimental connection between regions of surface convergence and divergence to spanwise variation in the vertical vorticity. These measurement capabilities are important for deepening our understanding of the physical processes governing energy flux across the air-sea interface.</p>

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Thermal marking measurements of horizontal velocity gradients, turbulent kinetic energy, and its dissipation rate at an undulating wind ruffled air-water interface

  • 期刊论文

  • 发表日期：

    2026年4月6日

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  • Shantanu Soumya,
  • Nathan Laxague,
  • Ivan Savelyev,
  • Christopher Zappa

摘要

Velocity gradients are critical drivers of turbulent and scalar exchange processes within fluids. Calculating these gradients at a wavy air-water interface presents significant challenges, requiring simultaneous spatially distributed measurements of velocity fields across an undulating interface. In this study, we employ thermal marking velocimetry (TMV), an unobtrusive active velocimetry technique, to capture the surface velocity field over an unstructured grid. The surface velocity field is then used to compute the horizontal surface velocity gradient; together, these enable calculation of the wave orbital velocity, surface strain, vertical vorticity, and turbulent kinetic energy (TKE). Furthermore, a structure function-based approach is employed to estimate the TKE dissipation rate at the wavy interface. Finally, we calculate the Eulerian vortex force field at the surface, providing a quantitative experimental connection between regions of surface convergence and divergence to spanwise variation in the vertical vorticity. These measurement capabilities are important for deepening our understanding of the physical processes governing energy flux across the air-sea interface.