A multigrid technique to accelerate iteration is proposed to solve the problem of low convergence rate due to large condition number in simulating viscous flow with the least squares isogeometric method. A series of grids with different element sizes are automatically generated in analysis. The least squares isogeometric method is used to discretize the Navier-Stokes equations into a system of linear equations on the densest grid
and the system is iteratively solved using either the multigrid method as standard solver or the preconditioner of the conjugate gradient method. Numerical simulations are performed on lid driven cavity flow with Re=100
400
1 000 and 2 500. The residual of algebraic equations is reduced about 10 order of magnitude after 23 iterations
and the calculation error on characteristic parameters of the cavity flow is less than 1%. The results show that the performance of the least squares isogeometric method for viscous flow is improved when the multigrid acceleration technique is used.
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