Intrusive measurement evaluation for sediment-laden flows interacting with an obstacle

Richard Wilson, Heide Friedrich, Craig Stevens

Wednesday 1 july 2015

9:30 - 9:45h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 8F. Engineering - Instrumentation

The interaction of sediment-laden flows with obstacles is a growing area of research. Sediment-laden flows are also commonly known as turbidity currents, Due to practical limitations, there are minimal experimental data available on the spatio-temporal distribution of velocity and sediment concentration fields of currents passing an obstacle. For this study, an instrumental rack consisting of an array of UVP transducers and siphons is used to measure velocity and density characteristics of turbidity currents and their interaction with a rectangular obstacle. Tests are conducted for a range of different transducer rack arrangements to determine whether their intrusive components have a significant influence on fluid flow. Lock-exchange initiated gravity currents comprised of kaolinite and glass microspheres are released in a 400 mm wide, 5000 mm long Perspex flume, filled with ambient water to an upstream depth of 300 mm. Detailed velocity contours plots surrounding the obstacle and instrument racks are obtained for each testing condition. Results show that immediately after colliding with the obstacle, the current varied in velocity distribution for all tests. It was concluded that this was likely due to the locally unpredictable nature of unsteady structures formed, rather than rack instrumental influence. Differences in velocity distributions converged to a point where all tests showed nearly identical distributions once the current head had passed the obstacle. It is therefore recommended that in future tests a recording time window of at least 20 s from collision of the current with the obstacle should be implemented. The proposed instrument arrangement is suitable for studying the effect of obstacles for passing currents, and ensures the obstacle effect dominates the signal.