This research presents the results of two interrelated
sets of experiments examining the dynamics of plumes and fountains
in two-layer and continuously stratified environments.
The first study examines the evolution of an axisymmetric turbulent
fountain in a two-layer stratified environment. Interacting with the
interface, the fountain is observed to exhibit three regimes of
flow. It may penetrate the interface but nonetheless return to the
source where it spreads as a radially propagating gravity current;
the return flow may be trapped at the interface where it spreads as
a radially propagating intrusion or it may do both. These regimes
have been classified using empirically determined regime parameters
which govern the relative initial momentum of the fountain and the
relative density difference of the fountain and the ambient fluid.
The maximum vertical distance travelled by the fountain in a
two-layer fluid has been theoretically determined by extending the
theory developed for fountains in a homogeneous environment. The
theory compares favourably with experimental measurements. We have
also developed a theory to analyse the initial speeds of the
resulting radial currents. We found that the currents exhibited two
different regimes of flow.
The second study presents experimental results of the generation of
internal gravity waves by a turbulent buoyant plume impinging upon
the interface between a uniform density layer of fluid and a
linearly stratified layer. The wave field is observed and its
properties measured non-intrusively using axisymmetric Schlieren. In
particular, we determine the fraction of the energy flux associated
with the plume at the neutral buoyancy level that is extracted by
the waves. On average, this was found to be approximately 4 per
cent. Within the limits of the experimental parameters, the maximum
vertical displacement amplitude of waves were found to depend
linearly upon the maximum penetration height of the plume beyond the
neutral level. The frequency of the waves was found to lie in a
narrow range relative to the buoyancy frequency. The results are
used to interpret the generation of waves in the atmosphere by
convective storms impinging upon the tropopause via the mechanical
oscillator effect. / Applied Mathematics
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.10048/673 |
| Date | 11 1900 |
| Creators | Ansong, Joseph Kojo |
| Contributors | Sutherland, Bruce R. (Physics and of Earth and Atmospheric Sciences), Moodie, Bryant (Mathematical and Statistical Sciences), Reuter, Gerhard (Earth and Atmospheric Sciences), Myers, Paul (Earth and Atmospheric Sciences), Craster, Richard (Mathematical and Statistical Sciences), Caulfield, Colm-Cille P. (Mathematics, University of Cambridge) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 4911567 bytes, application/pdf |
| Relation | Ansong, J.K. et. al. (2008), Journal of Fluid Mechanics, Vol. 595, 115-139 |
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