Referent:

Neil D Sandham, Professor of Aerospace Engineering School of Engineering Sciences (Aero)

University of Southampton (Eingeladen von Prof. Dr. A. Dillmann, Gö) rsity of Southampton

Recent interest in aerofoil design for low speed applications (e.g. micro and small unmanned air vehicles) has led to renewed interest in laminar separation bubbles. This talk will review results from recent direct numerical simulations of flow over a NACA 0012 aerofoil section at a Reynolds number of 50,000. The laminar separation bubble on the aerofoil is observed to undergo a self-sustained transition to turbulence i.e. transition that persists even in the absence of upstream disturbances. The addition of forcing is found to decrease the bubble length and reduce the drag coefficient by 18%. Based on the simulation results, an unsteady viscous-inviscid interaction method, coupling integral boundary-layer methods with a potential flow solution based on panel methods, is developed to study separation bubble behaviour near stall. The method is capable of predicting large-amplitude low-Strouhal number oscillations as seen in recent experiments. Above a critical incidence the reattachment point can no longer be held and the flow develops a limit cycle behaviour in which bubble growth leads to fully stalled flow followed by a reformation of the bubble.