Is plane-channel flow a friendly case for the testing of large-eddy simulation subgrid-scale models?

We present the grid-convergence behavior of channel-flow direct numerical simulations (DNS) at coarse resolutions typically encountered in large-eddy simulation subgrid-model testing. An energy-conservative discretization method is used to systematically vary the streamwise (N-x) and spanwise (N-z) resolution. We observe that the skin friction does not converge monotonously, and at coarse resolutions, a line of N-x-N-z combinations is found where the error on the skinfriction is zero. Along this line, mean profiles are evaluated and found to fit surprisingly well fully resolved DNS results. The location of this line is shown to depend on the Reynolds number and the wall-normal resolution.