Inflow conditions for large-eddy simulations of mixing layers

A method to generate inflow boundary conditions for large-eddy simulations (LES) of turbulent free shear layers is presented. A time series of instantaneous velocity planes, with duration approximately equal to the integral time scale of the flow, is extracted from a periodic simulation and saved on disk. This signal is transformed into a periodic one, by using a conventional windowing technique, and is re-used in the actual simulation as many times as required to obtain converged statistics. The method is applied in a LES of a spatially developing turbulent mixing layer. It is shown that the periodicity induced by the inflow signal decays rapidly in about 25% of the domain, and that the length of the period has small effect on the statistics, which agree well with the reference experimental data. The method appears to be a cost-effective strategy in the generation of inflow data in a large variety of flows.