Author(s): Mosedul Sarkar; Sankar Sarkar

Linked Author(s):

Keywords: Degraded bed; Open channel flow; structure functions; Scaling laws; turbulent flow; TKE budget

Abstract: This present study focuses on the laws of turbulence and estimation of the turbulent kinetic energy (TKE) budget for flow over a bimodal degraded bed under equilibrium conditions. The analyses of turbulence were performed based on the three-dimensional velocity data captured by using a Vectrino velocimeter. The streamwise velocity and Reynolds shear stress profiles show an excellent agreement with the existing literature. In view of the advancement in the direction of bed degradation, the measured velocity data captured at different streamwise locations (before, on and after the maximum equilibrium depth of degradation) were further processed to explore the scaling laws of turbulence and TKE budget based on structure functions data. To this end, the second-, third-, and mixed third-order velocity structure functions were estimated. The structure functions data indicated the existence of inertial subrange within lower ranges of the time-lags and confirmed their agreement with the Kolmororov’s 2/3-, and 4/5-, and Monin–Yaglom’s 4/3-laws. However, the TKE dissipation rates estimated by Kolmororov’s 4/5- and Monin–Yaglom’s 4/3-laws of turbulence show significant differences in their values. The TKE budget results show that in the vicinity of the degraded bed, TKE dissipation rate is more than that of TKE production and turbulent diffusion rates. On the other hand, the pressure diffusion has larger negative values in the near-bed. However, all the turbulence parameters show no significant differences at as one moves from the initial bed-level (bed-level measured before the detachment started) to the free-surface.

DOI: https://doi.org/10.26077/bd87-97c0

Year: 2022