Turbulence in thick fluid layers
Date
2011
Authors
Byrne, David John
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This thesis presents the experimental study of turbulence in fluid layers of finite depths i.e. away from the ideal quasi-2D approximation. The development and implementation of a two colour Particle Image Velocimetry/Particle Tracking hybrid is presented along with a defocused PIV diagnostic for measuring full 3D components of the velocity field. A parametric study in electromagnetically driven flows in a single and double layer configuration is presented. It is shown that as the layer depth increases there is an onset of 3D motion within the layer. Surprisingly, despite there being a substantial 3D component in the flow, the inverse energy cascade is still present. In low Reynolds number flows, a direct 3D energy cascade cannot be supported and as a result, the transition to a more 3D flow only has the effect of increasing dissipation in the system compared to that associated with quasi two-dimensional flows. The study of the vertical structure of the velocities reveals that, due to the boundary conditions of the free surface and bottom boundary, there are regions of the layer that remain 2D and that 3D motions are most prominent in the mid-layer. This leads to a difference in dissipation throughout the layer and thus the largest scale that the inverse cascade can sustain changes in the different regions of the flow. If the damping is low enough for the condensation of energy to begin, the large structure formed near the surface, may begin to affect the underlying 3D motions.
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Thesis (PhD)
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Open Access
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