A pencil distributed finite difference code for strongly turbulent wall-bounded flows

We present a numerical scheme geared for high performance computation of wall-bounded turbulentflows. The number of all-to-all communications is decreased to only six instances by using a two-dimensional (pencil) domain decomposition and utilizing the favourable scaling of the CFL time-stepconstraint as compared to the diffusive time-step constraint. As the CFL condition is more restrictiveat high driving, implicit time integration of the viscous terms in the wall-parallel directions is no longerrequired. This avoids the communication of non-local information to a process for the computation ofimplicit derivatives in these directions. We explain in detail the numerical scheme used for the integra-tion of the equations, and the underlying parallelization. The code is shown to have very good strong andweak scaling to at least 64 K cores.