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Experimental Study on Behavior of Particle-Laden Density Current over Obstacles

Yaghoubi, Sina | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45384 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Afshin, Hossein; Firoozabadi, Bahar
  7. Abstract:
  8. Density currents, caused by the intrusion of dense fluids under lighter ambient fluids, frequently occur in both natural and industrial situations. As a result of the density differences, the driving force can arise from soluble substances, temperature differences, etc. If the driving force comes from suspended particles including silt and mud, the currents are called turbidity currents. Due to the variation in concentration and the consequent driving force along the flow path, turbidity currents are significantly more complicated than saline currents. These currents play the most important role in sedimentation in lakes, seas and oceans. In addition, turbidity currents are the main factor of deposition and the reduction of storage capacity in reservoirs. This reduction in capacity is so fast that the annual mean loss of their storage capacity is more than the increase of capacity by constructing new reservoirs to supply water. Obstacles can be used to change the sedimentation pattern and prevent depositing at critical areas in reservoirs. The obstacles can postpone sediment gathering in specific locations like the bottom of outlets and power plant systems. Therefore, the sustainability of the reservoir operation can noticeably increase. The obstacles can be located in shallow regions in water reservoirs to stop the turbidity currents and cause the sediments to settle upstream and thus facilitate the elimination of sediments.
    In the present study, the structural and depositional behavior of turbidity current was investigated experimentally. Two acoustic Doppler velocimeters (ADV) were employed to measure the velocity and concentration values. Many experiments were performed with different number of obstacles, including unobstructed channel, in the present of one and two triangular-shaped obstacles. Moreover, the effects of height of the obstacles and inlet Froude number were investigated. According to the results, in the upstream of each obstacle, a region with low velocity and high concentration forms which prepares a convenient condition for deposition of suspended particles. This area become vaster, as the height of obstacles increases and inlet Froude number decreases. Additionally, due to inverse pressure gradient, a recirculation zone forms between the obstacles when the size of the obstacles grows
  9. Keywords:
  10. Density Current ; Turbidity Current ; Densimetric Froude Number ; Sedimentation ; Obstacle Presence

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