Investigation of the Sweep Independence Principle for transitional regime of the flow past an aerofoil*

Highly resolved incompressible Large Eddy Simulations of the flow past a NACA-4412 aerofoil have been carried out for a chord-based Reynolds number of 50.000 at 5 degrees incidence considering both straight and 30 degrees swept-back infinite wings. Furthermore, two different sets of incoming flow conditions have been studied: one with an incoming laminar flow that naturally transitions to turbulence on the profile, the other with grid generated turbulence superimposed on the incoming flow. The main objective of the study is the verification of the so-called ''independence sweep principle''. This principle suggests that the boundary layer on a swept wing can be analysed using a linear superposition of the straight wing flow with the one generated by the mean spanwise velocity. Detailed results from the transitional laminar case and the one carrying upstream induced turbulence have allowed to establish the validity range of the principle in these two regimes. In particular, the flow with incoming turbulence delivers results on separation, reattachment, mean profiles and Reynolds stresses that can be extrapolated to higher Reynolds number flows.