POD analysis of regular waves interacting with large scale flow structures in the water column

• PIV velocity measurements in a high Reynolds number turbulent shear flow, conducted in a flume tank. • Implementation of a new POD-based method for wave-turbulence separation. • Characterization of the turbulent flow gaussianity as a function of the wave propagation direction. • Increase of the TKE across the water column due to waves, especially when propagating against the current. • Quadrant analysis of the flow structures distortion under the wave action. To accurately characterize prospective tidal energy sites where vortices and wavy environment coexist, it is essential to gain a deeper understanding of wave-vortex interactions. Given the complexity and multi-scale nature of these coupling processes, we focus on the interaction between regular surface waves and vortices developing in the water column. Based on Particle Image Velocimetry measurements conducted in a flume tank, two flow configurations are studied: monochromatic waves propagating either with or against the current, each interacting with large-scale flow structures in a high Reynolds number turbulent shear flow. These flow configurations are characterised by a negative mean velocity vertical gradient. In this work, the Proper Orthogonal Decomposition is implemented to extract the wave velocity field from raw velocity measurements. After validating this wave-turbulence decomposition, the results show that the wave propagation modifies the integral time scale of the free flow, the vertical mixing and its associated energy transfer. The energetic vertical exchanges are primarily governed by the free surface proximity, the kinetic energy levels in the free flow without waves and the wave propagation direction. Waves lead to limit the vertical mixing by reducing the production of the kinetic energy. A quadrant analysis also reveals the instantaneous flow distortion under the wave action, especially when waves propagate against the current.