Effect of wave-current flow on double-averaged turbulence properties over rough bed of hemispherical obstacles

Abstract

ABSTRACT Combined wave-current turbulent characteristics are investigated over a rough bed comprising of hemispheres positioned at different spacings (p/r = 4, 6, and 8; p is the patch distance and r is the height of the hemisphere) in terms of time-space averaged (double-averaged) flow components. An Acoustic Doppler Velocimetry was used to measure the instantaneous velocity components for all background flow cases that comprised current-only flow and wave superimposed on current (wave frequency 0 Hz, 1 Hz, and 2 Hz). This study attempts to characterize the double-averaged velocity, relative and formed induced turbulence intensity, and Reynolds shear stress for the specific flow layers due to the interaction of wave-current flow over the hemispherical rough bed. The study further explores how these parameters are modulated with the change in spacing between the roughness elements. The relative contribution of the different turbulent busting events is analyzed for the different positions with respect to the hemispherical elements. Results show that sweep and ejection are the major contributors to all flow conditions and roughness cases explored herein. Furthermore, the anisotropic structure of turbulence due to the superposition of waves for different rough bed conditions is explored in the double-averaged perspective.