Abstract

Present dissertation describes the turbulent convection in horizontal layers of air and water separated by an evaporative shear-free water surface during natural convection. A detailed analysis of the hydrodynamic turbulent structure on water and air sides is presented in this study. The major portion of the research comprised of experimental investigation in addition to simulation of simultaneous airside and waterside velocity fields. The experimental measurements were made using non-intrusive state-of-the-art techniques, namely particle image velocimetry (PIV) and laser induced fluorescence (LIF) for instantaneous measurements of velocity and temperature fields, respectively. The numerical study shows organized bulk vortical motions on air and water sides. The results also show that for unstable thermal stratification the magnitude of the airside velocities is an order of magnitude higher than the waterside velocities. The experimental results show that the water and air flow fields undergo three-dimensional flow interactions which form complex flow patterns. A detailed spectral analysis has been performed to investigate the temporal and spatial scales of turbulent motions induced during natural convection. The wavenumber and frequency spectra showed the existence of two distinct power law regimes. In low wavenumber (100 rad/m < k < 800 rad/m) and low frequency (0.06 Hz < f < 0.8 Hz) ranges, the spectra exhibit -3 slopes providing the first evidence of the existence of the buoyancy subrange in the waterside flow field during natural convection, where the energy loss is due to the work against buoyancy. At higher wavenumbers and frequencies, the inertial subrange with the classical slope of -5/3 is observed. The results also show that the scaling parameters proposed for wall-bounded natural convection are also suitable for natural convection across evaporative air-water interface. The average temperature profiles show a characteristic boundary layer distribution in the near surface region with an extensive core of constant temperature in the bulk. The temperature profiles within the conduction layer are found to be in good agreement with previous theoretical and experimental results. The present results show z -1 dependency in the thermal source layer and z -1/3 dependency in the bulk region away from the interface which are in good agreement with the past theoretical analysis.