Turbulence Kinetic Energy inside Suspended Vegetation Domain under Periodic Water Waves

Abstract

A series of laboratory experiments for wave interacting with suspended vegetation was conducted. The vegetation was modeled by a group of rigid vertical cylinders with three different configurations. The aim was to study the characteristics of turbulence kinetic energy (TKE) inside the suspended vegetation domain. The velocities at different elevations inside and outside the vegetation domain were measured by acoustic Doppler velocimeter. The forces acting on cylinders were also directly measured using a force transducer. The drag force coefficients were then calculated using the velocity and force data in the Morrison's formula. A clear negative current was found near the bottom of the suspended vegetation domain. The strength of the current grew with the increase of vegetation volume density and incident wave height and the decrease of relative water depth kh. The time-averaged TKE followed the same trend. Two peaks were found in the phase-averaged TKE. The variations of measured force with incident wave height, relative water depth, and vegetation volume density were also studied. A model previously proposed in the literature was modified to predict the TKE under water waves by introducing the Keulegan-Carpenter (KC) number to quantify the oscillatory motions. The drag force coefficient in the model was also replaced by a new empirical formula in terms of KC number. The results of the new model showed better agreement with the experimental data obtained in this paper. The new model was further validated using other published experimental data, showing reasonable agreement as well.