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Tuesday, July 9 • 10:30 - 13:00
INVESTIGATION OF A NEW LBM STABILIZATION STRATEGY: MRT AND SELECTIVE FILTERING

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At high Reynolds numbers and low viscosity flows, the Lattice Boltzmann Method Method (LBM), with single relaxation time (LBM-SRT or LBM-BGK), is characterized by numerical instabilities, due to the interaction between hydrodynamic and acoustic modes. A kinetic-based alternative to traditional, Navier-Stokes based solvers for jet noise simulations, it is easily implemented, parallelised, and it can deal with complex geometries, making the inclusion of the nozzle in the computational domain possible. The method tracks the time evolution of a certain distribution function f on a lattice with fictious particles. Taking various orders of cell-centered moments of f, macroscopic variables can be recovered. At each lattice cell, particles can move in a set number of directions. The algorithm is implemented two steps: 1) Streaming: particles move to neighboring nodes and 2) Collision: particles collide with each other. The first stabilization method emerges by noticing that different moments should be relaxed towards equilibrium at different rates, thus introducing the Multi-Relaxation Time (MRT) LBM. Collision are then performed in moment space while streaming is still accomplished on the distribution functions. Another method consists in the spatial selective filtering of the Lattice Boltzmann Equation (LBE), using an appropriate stencil. Three strategies exist: full filtering of the LBE, filtering of the collision operator or filtering of the macroscopic variables. The use of selective filtering in conjunction with LBM-BGK has been shown to successfully remove non-physical effects in 2D Double Shear Layer benchmarking tests. For the first time, the present work investigates the applicability of selective filtering in conjunction with the MRT method. The filter is implemented in Palabos; an open source, LBM-based numerical solver written in C++. The time-evolution of enstrophy and energy are tracked and compared with other existing LBM methods (BGK, MRT, Selective Filter – BGK).


Tuesday July 9, 2019 10:30 - 13:00 EDT
St-Laurent 3, Board 13-B
  T03 Aero… aircrft noise & vibr., SS02 Computational Aeroac

Attendees (4)