Effects of Surface Wave on the Turbulence underneath in Langmuir Circulation

The turbulence statistics in upper oceans and lakes can be significantly influenced by the forcing of surface waves and wind-driven shear, leading to Langmuir circulation. In the present work, the role of surface waves in the distortion of turbulence is studied using wave-phase-resolved simulations, where the Navier-Stokes equations are solved on a boundary-fitted curvilinear grid that evolves with the wave surface. In the simulation setup, we consider turbulent flows driven by a steady monochromatic wave and constant shear stress. The characteristics of Langmuir circulation, such as the elongated, counter-rotating vortices and the enhanced vertical fluctuations, are captured. Meanwhile, the phase-resolved simulations enable us to analyze the distortion of turbulence by the instantaneous wave orbital motions. The alternating normal and shear straining associated with the wave orbital motions are found to result in phase-variations of turbulence statistics, including the strength of vortices and the Reynolds stress. Analyses of vorticity dynamics and Reynolds stress budget in the Lagrangian framework also reveal how the phase-varying turbulent fluctuations contribute to the cumulative distortion of turbulence and the energy transfer between the wave and turbulence.