Hybrid RANS-LES modelling with an energy backscatter function incorporated in the LES mode

In conjunction with the conventional SGS viscosity model, the additional Leonard term, stemmed from a Taylor expansion of the subgrid stress tensor, is incorporated in the LES mode of hybrid RANS-LES modelling. The energy backscatter function implied by this term is exploited to enhance the turbulence-resolving capability in hybrid RANS-LES computations when dealing with free shear layer emanating from a RANS-modelled upstream boundary layer. Using an existing algebraic hybrid model as the testing platform, the Leonard term is combined with the Smagorinsky model and forming a mixed-type SGS model that is further hybridized with a mixing-length RANS model in the near-wall region. The resulting model is examined in simulations of a turbulent channel flow, a periodic hill flow and a backward-facing step flow. It is shown that the model is able to enhance resolved turbulence level in free shear layer and producing mean flows and resolved turbulent statistics in reasonable agreement with available experimental, DNS or full LES data.