Turbulent Kinetic Energy Budget and Turbulent Bursting in a boulder concentrated permeable gravel bed stream

Turbulent kinetic energy (TKE) budget distributions and turbulent bursting events are investigated to elucidate the physical process of energy balance among the different TKE-budget terms and turbulent bursting events within the arrays of immobile boulders placed on a gravel bed stream. In order to carry out the experimental investigations, the arrays of boulder at three different spacing were considered and an acoustic Doppler velocimetry (ADV) was employed to measure the flows along the centre-line transect of the flume. The measured data were analysed using double-averaging methodology (DAM). The experimental results reveal that the negative pressure energy diffusion rates in TKE-budget distributions at the vicinity of boulder wake flow region develops enhanced turbulence production rates corroborating the development of flow recirculation in the near-bed wake flow region. The measured TKE-fluxes in small spacing boulder arrays infers lesser magnitude in comparison to those over the medium and large spacing boulder arrays which reveal to our understanding that the collective form drag in small spacing boulder arrays caused partial reduction of TKE-fluxes by the flows. However, in the outer flow-region they are almost alike. According to the quadrant analysis, the sweep events are the prevailing events in the vicinity of the stream bed within the boulder arrays and above this a change over of the dominance from sweeps to ejections takes place for the remaining depth.