Plumes in stratified environments

• Author / Creator

  Ansong, Joseph Kojo

• 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.

• Subjects / Keywords

  • Stratified
  • Internal
  • Gravity
  • Turbulent
  • Plumes
  • Fountains
  • Waves

• Graduation date

  Fall 2009

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R32C7X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.