next up previous
Next: About this document ...

Badr Alkahtani
Iterative Method (GMRES) vs Direct Solver for Solving Navier-Stokes Equations

P O BOX 1142
RUWAIDAH
RIYADH 11989
alhaghog@gmail.com

We consider the steady Navier-Stokes problem in two dimensions to be solved using numerical iterative methods. Firstly, we consider a test problem with a known solution and therefore the results of the numerical solutions can be compared with the exact solution. Secondly, we solve the lid-driven cavity problem at high Reynolds number, and the results can be compared with previous results. We discretize the problem using Chebyshev discretization in the $ x$ and $ y$ directions. Because of the non-linearity of the Navier-Stokes equations, Newton linearization is used to work in terms of correction terms. Here, we combine the use of iterative Newton linearization with a direct solver to solve the vorticity-streamfunction formulation. The direct solver employs the back substitution Gauss elimination method with piovting for solving the linear system. We solve the Navier-Stokes problem exploiting the accuracy of the use of Chebyshev discretization to obtain the numerical solution at high Reynolds number and to recognize the type of resulting matrix. The resulting matrix which arise from the discretization is usually full and the linear system is solved by a direct solver. In the second half of the work, we try to solve the linear system araised from the discretization using the iterative method (GMRES) at high Reynolds number and compare it with the direct solver. If the time help, a preconditioner will be used to improve the ierations. At high Reynolds number, GMRES diverges while the direct solver can do higher than the GMRES for the same discretisation grid. To conclude, a relation between the direct solver and the GMRES can be drawn. Also, a relation between the Reynolds number and convergence of GMRES can be observed.




next up previous
Next: About this document ...
Copper Mountain 2014-02-23