Strongly-Coupled Multigrid Method for 3-D Incompressible Flows Using Near-Wall Turbulence Closures

An efficient artificial compressibility algorithm is developed for solving the three-dimensional Reynolds-averaged Navier-Stokes equations in conjunction with the low-Reynolds number k-ω turbulence model (Wilcox, 1994). Two second-order accurate central-differencing schemes, with scalar and matrix-valued artificial dissipation, respectively, and a third-order accurate flux-difference splitting upwind scheme are implemented for discretizing the convective terms. The discrete equations are integrated in time using a Runge-Kutta algorithm enhanced with local time stepping, implicit residual smoothing, and V-cycle multigrid acceleration with full- and semi-coarsening capabilities. Both loosely and strongly-coupled strategies for solving the turbulence closure equations are developed and their relative efficiency is evaluated. Calculations are carried out for turbulent flow through a strongly-curved 180 deg pipe bend discretized with fine, highly-stretched and skewed meshes. It is shown that the strongly-coupled multigrid algorithm, with semi-coarsening in the transverse plane, is an efficient approach for simulating flows of practical interest with advanced near-wall turbulence closures.