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Large Eddy Simulation of Continuous Density Current Impinging on Obstacles

Abbaszadeh, Shahabaddin | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45269 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozabadi , Bahar; Afshin, Hossein
  7. Abstract:
  8. Density currents as a particular form of stratified fluid motion in nature have attracted the interest of many researchers in the past decades. These flows are formed whenever a fluid with specific density begins to move through another fluid with different density called ambient fluid. Prediction of propagation of turbulent density currents, especially because of their remarkable influence on the environment, is one of the researcher’s interests in geophysics and engineering. Density currents have a lot of applications in industry and nature. Sand storm in deserts, turbidity currents in oceans and avalanches are natural examples and leakage of dense gas into the atmosphere due to reservoir fracture, ventilation in buildings, and spread of waste water and cooling water into sea are some industrial examples of these currents. In the nature, when density current is moving on a loose bed, usually the surface of the bed is not smooth. Existence of natural and man-made obstacles has many influences on the physical behavior and structure of density current. In this study, the propagation of continuous density current impinging on the obstacles is modeled using Large Eddy Simulation. LES method has lower computational cost comparing Direct Numerical Simulation method, though; it has more accuracy than RANS methods.
    In present study, a three dimensional rectangular channel and some presumed cylindrical obstacles with the cross section of square, triangle and dune are used. Heights of all the obstacles are equal to 0.86 of the height of channel inlet. In this study, the influence of the number of the obstacles and change in their geometry on the fundamental parameters of the flow is investigated. Change of the location of flow front, contours and iso-surfaces of concentration, pressure contours, turbulent kinetic energy and vorticity, profiles of vertical structures of the flow including velocity profiles, concentration and turbulent kinetic energy and change of the location of backward flow (Bore) are a part of the results presented in this study. Results of this study generally show that in case of having more than one obstacles, the first obstacle will determine the condition of upstream flow and it will make the flow less turbulent in this region while, turbulence condition of the downstream of the obstacles is intensely dependent on the last obstacle and the phenomena around it. In the case of using obstacles with different geometries and equal height, it can be mentioned that the change in geometry is only influential in downstream and on the obstacles themselves, but in upstream of the obstacle the only effective parameter is the height of the current and the obstacle. Besides, the change of flow geometry can cause differences in flow passage over the obstacles and the structure of the flow around the obstacles
  9. Keywords:
  10. Large Eddy Simulation (LES) ; Turbulence ; Obstruction ; Continuous Density Current

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