Most turbulence studies up to the present are based on statistical modeling, however,the spatio-temporal flow structure of the turbulence is still largely unexplored. Tur-bulence has been established to have a multi-scale instantaneous streamline structurewhich influences the energy spectrum and other properties such as dissipation andmixing. In an attempt to further understand the fundamental nature of turbulence and itsconsequences for efficient mixing, a new class of flows, so called ?turbulent-like?, is in-troduced and its spatio-temporal structure of the flows characterised. These flows aregenerated in the laboratory using a shallow layer of brine and controlled by multi-scaleelectromagnetic forces resulting from a combination of electric current and a magneticfield created by a fractal permanent magnet distribution. These flows are laminar, yetturbulent-like, in that they have multi-scale streamline topology in the shape of ?cat?seyes? within ?cat?s eyes? (or 8?s within 8?s) similar to the known schematic streamlinestructure of two-dimensional turbulence. Unsteadiness is introduced to the flows bymeans of time-dependent electrical current. Particle Tracking Velocimetry (PTV) measurements are performed. The techniquedeveloped provides highly resolved Eulerian velocity fields in space and time. Theanalysis focuses on the impact of the forcing frequency, mean intensity and amplitudeon various Eulerian and Lagrangian properties of the flows e.g. energy spectrum andfluid element dispersion statistics. Other statistics such as the integral length and timescales are also extracted to characterise the unsteady multi-scale flows. The research outcome provides the analysis of laboratory generated unsteady multi-scale flows which are a tool for the controlled study of complex flow properties relatedto turbulence and mixing with potential applications as efficient mixers as well as ingeophysical, environmental and industrial fields.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:506912 |
| Date | January 2009 |
| Creators | Kewcharoenwong, Prangchira |
| Contributors | Vassilicos, John Christos ; Rossi, Stefano |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/4362 |
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