| Popis: |
One of the key problems in the research on fluvial hydraulics is to correctly reproduce the flow dynamics over a riverbed in laboratory experiments. Generally, while performing experiments, attention is paid to specific hydraulic conditions related to the flow regime, sediment transport, and bed erosion. In this context, the sediment size of the riverbed to be analysed plays an important role. It is a common practice to create the bed manually using a screeded mixture of sediments with random orientation that could be very different from that observed in natural riverbeds. To overcome this issue, a manually created gravel bed is required to be water worked before performing the experiments to get a bed surface, which resembles to that of a natural gravel bed river. Such a bed is termed as water-worked gravel bed (WGB). In recent past, even though the bed topography of WGB has been intensively studied, its effects on the flow features, which govern the near-bed flow field, are still to be explored under varying flow rates. In this study, the double averaged (DA) turbulence characteristics such as velocity, Reynolds shear, and normal stresses, and form induced shear and normal stresses, are analysed for three different flow rates. A comparative study infers that with an increase in flow rate the magnitude of all flow features increases, especially in the near-bed flow zone. The reason for such occurrence is attributed to a higher flow rate that enhances the near-bed turbulence, and in turn the velocity fluctuations. |
