A Stabilized Finite Element Dynamic Overset Method for the Navier-Stokes Equations
A Dissertation Presented for the Doctor of Philosophy in Computational Engineering, The University of Tennessee at Chattanooga
Chao Liu, May 2016
In terms of mesh resolution requirements, higher-order finite element discretization methods offer a more economic means of obtaining accurate simulations and/or to resolve physics at scales not possible with lower-order schemes. For simulations that may have large relative motion between multiple bodies, overset grid methods have demonstrated distinct advantages over mesh movement strategies. Combining these approaches offers the ability to accurately resolve the flow phenomena and interaction that may occur during unsteady moving boundary simulations. Additionally, overset grid techniques when utilized within a finite element setting mitigate many of the difficulties encountered in finite volume implementations. This research presents the development of an overset grid methodology for use within a streamline/upwind Petrov-Galerkin formulation for unsteady, viscous, moving boundary simulations. A novel hole cutting procedure based on solutions to Poisson equation is introduced and compared to existing techniques. A MPI-based parallel three-dimensional overset grid assembly framework is developed. Order of accuracy is examined via the method of manufactured solutions. The potential benefits of using Adaptive Mesh Refinement (AMR) in overset grid simulations are explored by combining the overset method with an AMR approach. The importance of considering linearization due to the overset boundaries within the preconditioning is studied. Numerical experiments are performed comparing an ILU(k) preconditioner with two proposed modifications referred to as “triangular inter-grid ILU(k)” and “Jacobi inter-grid ILU(k)”. The efficiency gains observed from the proposed modifications are also applicable to general parallel simulations on distributed memory machines, regardless of whether an overset grid approach is used. Overset grid results are presented for several inviscid and viscous, steady-state and time-dependent moving boundary simulations with linear, quadratic, and cubic elements.
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