A sensitivity analysis of CFD transition modelling in the context of vortex roll-up prediction

A sensitivity analysis of the transitional flow over a NACA662 − 415 foil and the elliptical Arndt wing is carried out. The SST turbulence model is complemented with the γ − ˜Reθt transition model to determine the effect of varying turbulence intensity and eddy-viscosity ratio on the integral quantities and transition locations. Local grid refinement at the transition location is used to improve convergence. The skin friction drag coeficient is found to be more sensitive to the inflow conditions for 5◦ angle of attack compared to 9◦. The movement of the transition location on the suction side is found to be responsible for this. The transition model captures a laminar separation bubble at the pressure side for both angles of attack, causing the lift coefficient to drop slightly. 3D calculations for the Arndt wing with the same foil section show that applying a transition model can decrease the boundary layer thickness by a factor of three, which is expected to influence the viscous core radius and consequently the minimum pressure in the tip vortex.