Gravity currents over topography in a two-layer ambient

  • Author / Creator
    Nicholson, Mitchell G. D.
  • A total of 95 full- and partial-depth lock release experiments were conducted to investigate the qualitative and quantitative properties of gravity current flow over sinusoidal topography in a two-layer ambient. Density differences between fluids are limited to a Boussinesq regime and are described by the density ratio, S≡(ρ1−ρ2)/(ρ0−ρ2) where ρ0 is the gravity current fluid density, ρ1 is the lower ambient layer density, and ρ2 is the upper ambient layer density. Bottom boundary topographic profiles are characterized by the ratio of amplitude to the average channel depth, A/H, and one-quarter the mean absolute slope, A/λ, where λ is the topographic wave length. Initial fluid depths are described by the fractional lock-fluid height, D/H, and the fractional lower layer height, h1/H. Particular emphasis is placed on analyzing the average slumping speed resulting from initial conditions, for which trends with S, D/H, h1/H, A/λ are described along with the relative unimportance of A/H for 0.1 < A/H < 0.4. Despite large A/H, the instantaneous front speed of the gravity current typically stays relatively constant as a result of the counterbalancing influences from the contracting/expanding channel and along-slope variations in the buoyancy force. Qualitative properties such as interfacial motions up- and downstream of the front and large Kelvin-Helmholtz vortices downstream of topographic peaks leading to sloshing motions are identified and described. Also identified is the early-time critical density ratio, Scrit, for which the interfacial disturbance created by the collapse and propagation of the lock-fluid transitions from travelling faster (subcritical gravity current) to slower (supercritical gravity current) than the average gravity current front speed. Finally, a model is presented that predicts the minimum number of topographic peaks the gravity current will overcome in the long time limit.

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • 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.