Hydrodynamics of flow through a degraded channel bed

Abstract

This article presents experimental results of turbulent flow measured in a bimodal degraded channel bed consisting of sand-gravel mixture. Sand and gravel of uniform sizes 0.25 and 3.5 mm were mixed in the same proportions (by weight) to create a bimodal sedimentary bed. A three-dimensional Vectrino velocimeter was employed to collect three-dimensional velocities over bimodal degraded bed under equilibrium condition. The streamwise velocity, Reynolds stresses, turbulent kinetic energy (TKE), and TKE fluxes profiles were compared with the literature. However, the advancement of the existing knowledge was done by exploring the laws of turbulence. To this end, the velocity structure function method was applied. Second and third-order streamwise velocity structure functions followed by mixed third-order velocity structure functions revealed the existence of inertial subrange. The TKE dissipation rate was estimated using Kolmogorov’s and Monin–Yaglom’s scaling laws of turbulence. The anisotropy analysis indicated anisotropic turbulence in the near-bed, whereas above the initial bed-level, the anisotropy tends to follow three-dimensional isotropy. The present study notably enhances the understanding of turbulent flow through a degraded bed by demonstrating the legitimacy of laws of turbulence at different locations over the bed and providing a comprehensible acquaintance in TKE budget and Reynolds stress anisotropy.