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The Hydraulics of Nonhydrostatic Two-Layer Flow Over an Obstacle

Homayoon, Ladan | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54158 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jamali, Mirmosadegh
  7. Abstract:
  8. Stratified flows are common in natural systems such as the oceans and the atmosphere. The hydraulics of two-layer flow over an obstacle, which helps with understanding and control of these flows, has been studied by many researchers. However, a type of two-layer flow, called the Approach-controlled flow, has not yet been fully understood, and there are ambiguities about it. Having considerable nonhydrostatic pressure in the so-called supercritical leap region, this flow type cannot be explained even qualitatively without accounting for the nonhydrostatic pressure. Also, the composite Froude number which is defined based on the hydrostatic pressure assumption for two-layer flows, is not applicable to the determination of the flow regime in the supercritical leap region. In the current study, two new mathematical models are proposed for unsteady nonhydrostatic two-layer flows, one in the Cartesian coordinates, and the other in the curvilinear coordinates, and the Approach-controlled flow is extensively studied with their aid. Both models are developed assuming ideal fluid and irrotational flow using a perturbation technique considering shallowness as the small parameter. To observe the evolution to the Approach-controlled flow, an unsteady two-layer flow experiment was conducted, and the two models were successfully applied for the simulation. Using the curvilinear model, a nonhydrostatic composite Froude number is defined for the first time, various Approach-controlled flows are simulated, and the understanding of this flow type is improved. It is shown that the critical section of the Approach-controlled flow that was thought to occur at the upstream toe of the obstacle, can take place between the upstream of the toe and the crest of the obstacle. Also, it is observed that some Approach-controlled flows can have one or two more critical sections
  9. Keywords:
  10. Two Layer Flow ; Curvilinear Coordinates ; Unsteady Flow ; Approach Controlled Flow ; Perturbation Method ; Composite Froude Number ; Non-Hydrostatic Pressure

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