DOI: 10.1615/TSFP4
LES OF TRANSITIONAL BOUNDARY LAYER AT HIGH FREE-STREAM TURBULENCE INTENSITY, AND IMPLICATIONS FOR RANS MODELLING
摘要
Large-eddy simulations of a transitional flow over a flat plate are performed for different free-stream conditions. Interest focuses, in particular, on the mechanisms in the boundary layer before transition occurs, the practical context being flow over turbine blades. These considerations are motivated by the wish to study the realism of a RANS-type model designed to return the "laminar fluctuation energy" observed well upstream of the location at which transition sets in. The assumptions underlying the model are discussed in the light of turbulence-energy budgets deduced from the simulations. It is shown that the pre-transitional field is characterised by elongated streaky structures which, notwithstanding the very different structural properties, lead to the amplification of fluctuations by conventional shear-stress / strain interaction, rather than by pressure diffusion, the latter being the process central to the formulation of the RANS-type model.