Numerical simulations of the transition from laminar to turbulent regimes of planar viscous flows past airfoils

The turbulent transition of the planar flow past the NACA0015 (National Advisory Committee for Aeronautics) profile is investigated at Reynolds number 180 000. Different angles of attack α from 0° to 23° are considered. The boundary layer instabilities and vortex formation in the wake are discussed in detail. Direct numerical simulations are performed at high spatial resolutions using an in-house Lagrangian vortex particle method called diffused vortex hydrodynamics. Lift and drag force coefficients are compared against experimental data, showing a good agreement up to the stall inception where turbulent three-dimensional effects are more important. Shedding and merging of near field eddies are also discussed. Time-frequency spectral maps of wall vorticity fluctuations are investigated in order to evaluate in-depth the observed flow characteristics and the identification of different transients. Using high time-space resolutions, this analysis represents one of the first approaches in literature for describing the two-dimensional turbulence generated by the flow past a body in terms of vorticity dynamics. All the numerical simulations are carried out for a long term in order to achieve statistically consistent regimes.