Experimental study of turbulent oscillatory flows over rippled beds

Rippled beds are common seabed features in coastal environments. Previous research has made much progress in understanding the flow field of wave boundary layers over rippled beds. However, relatively little has been known about the statistical properties of turbulence in the bottom boundary layers over rippled beds. To address this gap, this study presents an experimental investigation aimed at providing a thorough understanding of turbulence characteristics in wave-induced oscillatory flow over a fixed rippled bed. Experiments were performed in a wave flume, and velocities were measured using a Vectrino profiler. Typical flow features, such as ‘overshooting’ of the maximum velocities, were observed at the edge of the wave boundary layer. Periodic variations of turbulent kinetic energy were observed within one wave cycle, with values ranging from 3.2e-4 m 2 / s 2 to 1.8e-2 m 2 / s 2 . Quadrant analysis of Reynolds shear stress show that the maximum intensities of ejections were 20% larger than those of sweeps. The probability density functions of streamwise velocity fluctuations, vertical velocity fluctuations, and Reynolds shear stress all follow t location-scale distributions. Results suggest that the statistical distribution of TKE follows the exponential distribution. A logistic distribution performs well in representing the probability density function of TKE-Production. These results can provide useful insights for further developments of turbulence modelling and sediment transport incorporating higher-order turbulence statistics and intermittency.