On Wednesday 11th of January 2012, Alexander Breugem defended his PHD thesis at Delft University. The The title of the work is: “Transport of suspended particles in turbulent open channel flows”
A short abstract summarizing the contents of Alexander’s PHD thesis:
Two experiments are performed in order to investigate suspended sediment transport in a turbulent open channel flow. The first experiment used particle image velocimetry (PIV) to measure the fluid velocity with a high spatial resolution, while particle tracking velocimetry (PTV) was used to measure the velocity of individual sediment particles. The sediment particles were injected in the flume close to the free surface at different distances from the measurement section. In this way, the development of a sediment plume towards an equilibrium situation could be studied. It was found that it depends on the location of the particles which flow structures they encounter. Out of equilibrium, when the particles are close to the free surface, the particles encounter mainly fast downward flow structures (sweeps), thus causing the particles to go faster than the average fluid velocity. In an equilibrium situation, the particles are close to the bed, and therefore they mainly encounter slow upward flow structures (ejections). This causes the particles to go slower than the average fluid flow velocity.
The results were compared with direct numerical simulations, in which the particle equation of motion was used to calculate the movement of individual sediment particles (performed by Marcos Cargnelutti of the Kramers laboratory). The results of the simulations compared well to the experiments, provided that a sufficiently strong resuspension mechanism was included near the bed.
The second experiment used refractive index matching, in order to make the sediment particle invisible. In this way, a PIV experiment could be performed in order to determine changes in the flow and turbulence structure due to high sediment concentrations. It was found that in the particular conditions that were studied (with a low relative density of 1.14) the changes in the flow and turbulence structure were small for volume concentrations up to 0.42%.
For information and the complete text, please follow this link.
