Three-dimensional transient Navier-Stokes solvers in cylindrical coordinate system based on a spectral collocation method using explicit treatment of the pressure

摘要

A spectral collocation method is developed for solving the three-dimensional transient Navier-Stokes equations in cylindrical coordinate system. The Chebyshev-Fourier spectral collocation method is used for spatial approximation. A second-order semi-implicit scheme with explicit treatment of the pressure and implicit treatment of the viscous term is used for the time discretization. The pressure Poisson equation enforces the incompressibility constraint for the velocity field, and the pressure is solved through the pressure Poisson equation with a Neumann boundary condition. We demonstrate by numerical results that this scheme is stable under the standard Courant-Friedrichs-Lewy (CFL) condition, and is second-order accurate in time for the velocity, pressure, and divergence. Further, we develop three accurate, stable, and efficient solvers based on this algorithm by selecting different collocation points in r-, φ-, and z-directions. Additionally, we compare two sets of collocation points used to avoid the axis, and the numerical results indicate that using the Chebyshev Gauss-Radau points in radial direction to avoid the axis is more practical for solving our problem, and its main advantage is to save the CPU time compared with using the Chebyshev Gauss-Lobatto points in radial direction to avoid the axis.