Two computer programs were addressed in the dCSE project summarised here. The first, SWT, is designed for the direct numerical simulation of turbulent flow in an infinite plane channel. It has, in the recent past, also been used to simulate the response of such a flow to irrotational strain [3], and turbulent Couette-Poiseuille flow (a channel flow driven both by a pressure gradient as well as by moving walls, [9]). Both of these investigations aimed at clarifying the effect of pressure gradients on turbulence. The second, SS3F, has so far been predominantly used to simulate the dynamics of vortices in stratified flow [2], [1], [4].
SWT is a development of the vectoral [15] channel-flow code of Kim et al [10], parallelised and translated to modern fortran [3]. SWT uses the same Runge-Kutta scheme, and the same FFT routines, as SS3F; one coordinate direction uses Chebyshev basis functions, however, which are suitable for plane channel flows with one non-periodic direction.
The SS3F code solves the incompressible Navier-Stokes equations in the Boussinesq approximation, using a Fourier representation in all three coordinate directions. The infinite boundary condition described by Corral & Jiménez [5] is implemented in one of these directions while the other two are periodic. The viscous terms are time advanced analytically, while a low-storage 3rd order Runge-Kutta scheme is used for the advective and buoyancy terms.