The aim of this project was to investigate the different porous media flow regimes and to clarify the mechanisms of stream-subsurface exchange at the pore scale. The Ultrasonic Velocity Profiler (UVP) system was used to measure the velocity distribution when the porous media was housed in a closed conduit, i.e. no stream flow could develop. It was found that the time-averaged velocity profiles have a wavy variation due to the flow decelerating and accelerating in the widest and narrowest sections of the pore-space. The spatially averaged higher order moments of velocity showed that a transition of flow properties occurred twice. There is a clear distinction between low, medium and high Reynolds number tests. These relate to three (micro-scale) porous media flow regimes: (1) the unsteady laminar regime, (2) the transitional regime and (3) the turbulent regime. Experiments were then performed in a tilting laboratory flume, which housed the same porous media (i.e. nine layers of spheres). This time there was a turbulent free-surface flow (of depth H) above the porous layer, which acted like a rough permeable wall. A set of reference measurements were also taken at a flow depth of <i>H </i>= 0mm. Particle Image Velocimetry (PIV) was used to measure the velocity distribution of both the stream flow, and the perturbed subsurface flow. From the stream flow experiments a distinct band of high turbulence was found just above the porous media. It is caused by intense shearing just above the roughness elements and is enhanced to some extent, by stream-subsurface interaction. The stream flow velocity statistics resemble those of a plane mixing layer.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:499688 |
| Date | January 2008 |
| Creators | Horton, Nial |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=25938 |
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