On higher order effects in marginally separated flows

If the angle of attack α of a slender airfoil reaches a critical value α s flow separation is known to occur at the upper s surface. Further increase of α initially leads to the formation of a short laminar separation bubble which has an extremely weak influence on the external flow field – a phenomenon known as marginal separation – but then rather rapidly causes a severe change of the flow behaviour, leading to leading edge stall. According to the asymptotic theory of marginal separation holding in the limit of large Reynolds numbers Re , the flow in the neighbourhood of the separation bubble is governed by an integro‐differential equation. This so‐called interaction equation contains a single controlling parameter which relates the angle of attack to the Reynolds number, with a value Γ s corresponding to α s . Some recent results concerning higher order s s corrections to this theory and their effect on the stability of steady solutions will be presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)