The purpose of this work is to gain insight into the problem of the bursting of a laminar separation bubble in the nose region of a slotted flap on a multi-element airfoil configuration. The interest in bubble bursting, which, especially on multi-element configurations has not been thoroughly investigated yet, was raised by the experimental results obtained while testing a computer designed flap in the low speed low Turbulence wind tunnel of the Delft University of Technology. A sudden and dangerous stall was found to occur on the flap surface due to the bursting of a bubble in its nose region.
CFD calculations, both laminar and RANS, were first performed on a single element configuration, namely the Eppler E387 airfoil (Re = 105) and then on the multi-element configuration tested in the wind tunnel (Re = 2 ·106). The results show that a strong vortex shedding can potentially originate from the separated shear layer, both on the flap and on the single element airfoil, suggesting a close connection between the two cases. The effect of transition on the structure of the bubble was investigated by imposing and then varying the transition point. The computational results suggest that the unsteady behavior of the laminar bubble has to be regarded as a major issue in order to find an effective bursting predictor method for airfoil design.