Finite element appoximation and augmented Lagrangian preconditioning for anisothermal implicitly-constituted non-Newtonian flow

TL;DR

This paper develops finite element methods and a specialized preconditioner for simulating steady anisothermal non-Newtonian flows with implicit rheology, proving convergence and demonstrating robust computational performance.

Contribution

It introduces new finite element approximations and a block preconditioner tailored for complex non-Newtonian flow models with temperature effects.

Findings

Proved convergence of the numerical approximations to weak solutions.

Designed a multigrid-based preconditioner with robust convergence.

Validated the approach on Navier-Stokes and power-law systems.

Abstract

We devise 3-field and 4-field finite element approximations of a system describing the steady state of an incompressible heat-conducting fluid with implicit non-Newtonian rheology. We prove that the sequence of numerical approximations converges to a weak solution of the problem. We develop a block preconditioner based on augmented Lagrangian stabilisation for a discretisation based on the Scott-Vogelius finite element pair for the velocity and pressure. The preconditioner involves a specialised multigrid algorithm that makes use of a space-decomposition that captures the kernel of the divergence and non-standard intergrid transfer operators. The preconditioner exhibits robust convergence behaviour when applied to the Navier-Stokes and power-law systems, including temperature-dependent viscosity, heat conductivity and viscous dissipation.