# Cascaded Lattice Boltzmann Modeling and Simulations of Three-Dimensional Non-Newtonian Fluid Flows

## TL;DR

This paper introduces a robust 3D cascaded lattice Boltzmann method based on central moments for simulating complex non-Newtonian fluid flows, demonstrating improved stability and accuracy over existing models.

## Contribution

A novel 3D cascaded LBM using central moments and multiple relaxation times tailored for generalized Newtonian fluids, with enhanced stability and accuracy.

## Key findings

- Demonstrated second-order grid convergence.
- Achieved stable simulations of shear thinning and thickening fluids.
- Showed improvements over SRT and MRT collision models.

## Abstract

Non-Newtonian fluid flows, especially in three dimensions (3D), arise in numerous settings of interest to physics. Prior studies using the lattice Boltzmann method (LBM) of such flows have so far been limited to mainly to two dimensions and used less robust collision models. In this paper, we develop a new 3D cascaded LBM based on central moments and multiple relaxation times on a three-dimensional, nineteen velocity (D3Q19) lattice for simulation of generalized Newtonian (power law) fluid flows. The relaxation times of the second order moments are varied locally based on the local shear rate and parameterized by the consistency coefficient and the power law index of the nonlinear constitutive relation of the power law fluid. Numerical validation study of the 3D cascaded LBM for various benchmark problems, including the complex 3D non-Newtonian flow in a cubic cavity at different Reynolds numbers and power law index magnitudes encompassing shear thinning and shear thickening fluids, are presented. Furthermore, numerical stability comparisons of the proposed advanced LBM scheme against the LBM based on other collision models, such as the SRT model and MRT model based on raw moments, are made. Numerical results demonstrate the accuracy, second order grid convergence and significant improvements in stability of the 3D cascaded LBM for simulation of 3D non-Newtonian flows of power law fluids.