Truncation Errors,Exact and Heuristic Stability Analysis of Two-Relaxation-Times Lattice Boltzmann Schemes for Anisotropic Advection-Diffusion Equation |
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Authors: | Irina Ginzburg |
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Abstract: | This paper establishes relations between the stability and the high-order
truncated corrections for modeling of the mass conservation equation with the two-relaxation-times (TRT) collision operator. First we propose a simple method to derive
the truncation errors from the exact, central-difference type, recurrence equations of
the TRT scheme. They also supply its equivalent three-time-level discretization form.
Two different relationships of the two relaxation rates nullify the third (advection) and
fourth (pure diffusion) truncation errors, for any linear equilibrium and any velocity set. However, the two relaxation times alone cannot remove the leading-order
advection-diffusion error, because of the intrinsic fourth-order numerical diffusion.
The truncation analysis is carefully verified for the evolution of concentration waves
with the anisotropic diffusion tensors. The anisotropic equilibrium functions are presented in a simple but general form, suitable for the minimal velocity sets and the
d2Q9, d3Q13, d3Q15 and d3Q19 velocity sets. All anisotropic schemes are complemented by their exact necessary von Neumann stability conditions and equivalent
finite-difference stencils. The sufficient stability conditions are proposed for the most
stable (OTRT) family, which enables modeling at any Peclet numbers with the same
velocity amplitude. The heuristic stability analysis of the fourth-order truncated corrections extends the optimal stability to larger relationships of the two relaxation rates,
in agreement with the exact (one-dimensional) and numerical (multi-dimensional) stability analysis. A special attention is put on the choice of the equilibrium weights. By
combining accuracy and stability predictions, several strategies for selecting the relaxation and free-tunable equilibrium parameters are suggested and applied to the
evolution of the Gaussian hill. |
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