Nazari, Fatemeh | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41812 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Shamsaei, Abolfazl
  7. Abstract:
  8. Entrance of air to close water conduits occurs in many ways. This phenomenon makes displeasing effects on water transport structures. Two-phase flows in closed conduits are studied experimentally, numerically and theoretically. Even after decades, due to the complexity of the subject, these studies still require development and reformation. Numerical and theoretical two-phase models are often limited to a special regime of flow."Volume Of Fluid"(VOF) is a model for non-mixing two-phase flows. "Fluent" software uses this model in this field of flows. Volume of fluid is used successfully in some problems like dam break or rising bubbles. Main disadvantage of this model is distribution of the fluid properties in interface area, this subject is still under correction.
    Entrance of big air pockets can have undesirable effects on performance of the conduits. It is observed in experiments that big air bubbles in inclined conduits may move against water stream and cause some damage.At first in this thesis, Fluent results are validated with Taylor bubble results. Then motion of the air bubbles in long low-gradient conduit is simulated. According to the large geometry of long tunnels and limited processing power available, the conduit dimensions in the numerical model have been reduced. Reducing of dimensions is done by dimensional analysis and determining the main forces of phenomenon. Simulation results show that air blow-back or terrible reduction of flow section does not occur. Finally, defects in the Fluent's Volume of fluid model is investigated. It can be seen that distribution of properties in interface area is the main weakness of this numerical model
  9. Keywords:
  10. Two Phase Flow ; Fluent Software ; Volume of Fluid ; Lang Low-Gradient Conduit

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