Assessment of Turbulent Kinetic Energy Balance within the Boulder Array in Gravel Bed Stream

Abstract

Influence of boulder concentration on the physical process of energy balance among the turbulent kinetic energy (TKE) budget terms in a gravel bed stream is investigated. Flow measurements were carried out in a rectangular open channel by an acoustic Doppler velocimeter (ADV) along the centre-line transects. An array of immobile boulders with large stream-wise boulder-to-boulder spacing was staggered over the gravel bed surface. Double averaging methodology (DAM) was used to analyse the measured data. The experimental results show that the TKE-budget components measured at the wake flow region differs significantly and the effect of large boulders extends up to five time of the boulder diameter in the wake flow region. The TKE production, diffusion and pressure energy diffusion rate components attains their peak values near the boulder crest level, while the TKE dissipation rate attains its peak value at the stream bed level. The results of turbulent kinetic energy budget distributions reveal to our understanding that the magnitude of the pressure energy diffusion rate at the near-bed region corroborates enhanced turbulence production which is attributed to vortex shedding and flow recirculation.