Assessment of implicit LES modelling for bypass transition of a boundary layer

The implicit LES model recently introduced by Dairay et al. (2017), which is based on numerical dissipation introduced via the discretisation of the viscous term, is assessed for the case of a flat plate boundary layer submitted to external turbulence and undergoing bypass transition. The free stream turbulent fluctuations are generated using a recently proposed linear forcing method adapted to control their intensity and length scale. Two configurations are considered, one with the leading edge of the plate taken into account and one without. LES results for the configuration without leading edge are compared with a DNS, and results for the configuration with leading edge are compared with available experimental and numerical reference data from the literature. Global parameters, unconditional and conditional statistics, as well as Reynolds stress budgets are analysed, and good agreements are obtained with reference data, hence confirming the ability of the model to predict accurately transitional flows. In particular, it is shown that, thanks to its action limited to the smallest resolved scales, the model is only active in the transitional and turbulent regions and therefore does not alter the development of the streaks in the laminar region of the boundary layer.