Characteristics of the Dissimilar Turbulent Transport Processes of Heat and Momentum During Wind-Wave Dynamical Interactions

Heat and momentum transport processes are studied through direct numerical simulations of air-water two-phase flows with surface waves under wave-wind couplings. Three wave age cases, sea state changing from wind sea to swell, are analyzed to investigate the roles of surface waves in the turbulent transport of heat and momentum, which are examined by decomposing the statistics into the plane-averaged, wave-coherent, and turbulent-induced components. Under wind sea conditions, a dissimilarity in turbulent transfer between heat and momentum is observed in the near-surface region. This discrepancy arises from the enhanced countergradient heat transport on the leeward side, which is caused by wave-coherent structures. The surface waves induce phase-dependent variations in the temperature and flow structures, reducing the scale of temperature structure. This reduction further results in a weaker contribution of ejections and sweeps to heat transfer. In contrast, momentum transport is predominantly downgradient on the leeward side due to the large-scale flow structure. This difference in coherent structures leads to the dissimilar transport between heat and momentum. Under lower-frequency swell conditions, surface waves induce an upward momentum that enhances the vortical structures near the wave surface. The transfer efficiency of turbulent momentum and heat gradually reaches equilibrium, after which both transport processes become more analogous.