Study on Hydrodynamic Characteristics of Wave Turbulent Bottom Boundary Layer Using A Large-Sized Wave Flume

Experimental studies were conducted in a super-large wave flume, aiming at uncovering the hydrodynamic characteristics involved in the turbulent wave boundary layer of full scale environment. An explicit formula of boundary layer thickness on rough turbulent flow was presented based on the measured velocity data of the present study and collected experimental data on wave boundary layer. It was found that the bottom wave-associated nominal stresses under the conditions of prototype scale tests suppress the vertical turbulence scattering upward over the boundary layer, which accounts for thickening of the boundary layer under wave condition. Such effect has yet not been reported in the literatures using oscillatory U-tube or small-sized wave flume. The phase inconsistency in the turbulent boundary layer to the free stream velocity (velocity immediately outside the boundary layer) is within 15 degrees, which is remarkably smaller than the results from oscillatory U-tubes, as well as the larger wave flume experiment presented by Xie et al. (2021), showing that the coarser bed would further reduce the phase lead. The intensity of the vertical turbulent component is approximately 1/2 of the horizontal component, which has larger ratio compared with the value of 1/5 reported by previous studies. Especially, it was also found that the vertical turbulent energy was approximately 3/4 of the turbulent energy in spanwise directions (y-direction). This means that the turbulent fluctuation has similar order in all three-directions (x, y, z) in a full scale environment and highlights that the turbulent components in all the three directions should not be neglected when calculating the total turbulent energy.