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Three Dimensional Large Eddy Simimulation of Lock-Exchange Density Currents

Mahdinia, Mani | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41022 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozabadi, Bahar; Farshchi, Mohammad
  7. Abstract:
  8. In this thesis, lock-exchange density currents are investigated using the dynamic large eddy simulation (LES) method. These are flows that occur under the influence of gravity and density gradient. In the lock-exchange type currents, a bulk of heavy fluid is released under an ambient lighter fluid. One charachteristic of such flows is the presence of turbulence at different scales across flow and Kelvin-Helmholtz and lobe and cleft instabilities at the interface, which additionally act to complicate the matter. Although lots of efforts have been devoted to simulate density currents, much of the previous simulations have used Reynolds Average Navier-Stockes (RANS) methods. Practically, these methods are not able to capture fine details of the flow like the interface vortices, time evolution of current fluctuations, creation of turbulence on the channel bed and the like. So regarding the high cost of Direct Numerical Simulation (DNS), the dynamic large eddy simulation has been used in this project. The number of the previous studies which use this method for density currents is very limited and this renders the LES mthod a new developing method for density currents. The current research is conducted for the density current flows in plain channel, forward-facing and backward facing steps and curved channel geometries. All of the previous studies except one target the plain channel geometry and so the present study includes also the first high-resoultion simulations in complex geometries. The results include physical phenomena like current front time evolution, energy changes with time, evolution of turbulence streaky structures on the channel bed, secondary flow in various sections of the channel, current height changes with time, density contours and surfaces and flow streamlines
  9. Keywords:
  10. Kelvin-Helmholtz Instability ; Lock-Exchange Flow ; Density Current ; Turbulence ; Large Eddy Simulation (LES) ; Cleft Instability ; Lobe Instability

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