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Implementing Appropriate Numerical Filters in the Lattice Boltzmann Method for Solving Multiphase Incompressible Flows with Large Density Ratio

Bidi, Saeed | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49831 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Hejranfar, Kazem
  7. Abstract:
  8. In this study, two finite-difference lattice Boltzmann methods (FDLBM) are applied and assessed for the simulation of two-phase liquid-vapor flows with high density ratios. For this aim, the He-Shan-Doolen type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting system of equations are discretized by using the second-order central difference and modified Lax-Wendroff schemes. Suitable numerical dissipation terms and filters are applied to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions and at the same time to remove the numerical oscillations in the interface region of the two phases.Three discontinuity-detecting sensors for properly switching between a second-order and a higher-order filter are applied and examined in the solution algorithm of the second-order FDLBM. It is indicated that the filtering procedure applied can reasonably reduce the spurious oscillations and improve the numerical stability of the second-order FDLBM. The accuracy and efficiency of the solution procedure adopted here based on the solution of the LB equation using the second-order central difference and modified Lax-Wendroff schemes are examined by simulating different two-phase systems. The test cases simulated herein for validating the results of the two-phase flows are an equilibrium state of a planar interface in a liquid-vapor system, a droplet suspended in the gaseous phase, the coalescence of two droplets, and the phase transition in a liquid-vapor system. Results obtained are in good agreement with the analytical solutions and also the numerical results reported in the literature. It is shown that the second-order central difference scheme applied to solve the LB equation is more accurate and robust than the modified Lax-Wendroff scheme in simulating the two-phase flows with high density ratios
  9. Keywords:
  10. Lattice Boltzmann Method ; Multiphase Flow ; Incompressible Flow ; Large Density Ratio ; Liquid-Vapor Two Phase Flow ; Finite Difference Lattice Boltzmann Method ; Numerical Filters

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