Generation of inflow data for inhomogeneous turbulence

Inflow boundary conditions for turbulent plane channel flow are generated by solving evolution equations only for the most energetic eddies. The dynamical systems are derived by Galerkin projecting the Navier-Stokes equations onto the subspaces spanned by various sets of the most energetic modes from a proper orthogonal decomposition (POD) of the same flow. Low-energy small-scale POD-modes are added randomly in order to impose some energy in the high wave number range. This is found to be crucial in order to more rapidly establish the correct level of dissipation and achieve a more realistic distribution of energy between the velocity components. The method is tested on a DNS of R*=180 and a LES of R*=400. Statistics such as mean velocity, rms-profiles, turbulent shear-stress and energy spectra become close to the fully developed state within 1500 wall units downstream the inlet.