ESR7 | Matthias Plath

Because of global warming, the demand in environmental footprint reduction for civil aircraft is rising significantly. One direct consequence of this demand is to lower the aerodynamic drag of civil aircraft. The aerodynamic drag can be roughly divided into two different parts: the drag due to the pressure distribution and the drag due to viscous forces. The viscous drag is mostly determined by the physical state of the so-called boundary layer, which is the flow directly at the surface. While a turbulent boundary layer is characterized by a chaotic, high mixing flow field with eddies of different sizes, shows a laminar boundary layer a smooth, non-chaotic path.

When a flow runs along a surface it will be laminar and depending on different complex conditions it will turn turbulent after a certain distance traveled along the surface. This phenomenon is called transition and the location where it is happening is called transition point. One of the most important differences between these two physical states is that a turbulent boundary layer delivers higher viscous drag, due to stronger friction of the flow on the airfoil, than its laminar counterpart. A promising technique, which directly follows from the explained knowledge, is to reduce the viscous drag at aircraft airfoils by keeping the boundary layer laminar as long as possible. Such an airfoil is than called a laminar airfoil.

Nevertheless of the large benefits of laminar airfoil do they also bring some difficulties. Because the transition locations can be very sensitive and can change significantly along the surface, laminar airfoils are much more prone to a phenomenon called flutter. The flutter phenomenon occurs when the surrounding flow field is inducing rapidly increasing amplitude vibrations to the airfoil structure, which can in the worst case scenario lead to the destruction of an aircraft. Therefore the goal of this thesis is to predict the onset of flutter on laminar airfoil in transonic flow by using high order numerical simulation methods. The work is focused on developing and implementing a robust and efficient Fluid-Structure interaction algorithm based on solutions of the compressible RANS (Reynolds averaged Navier Stokes) equations with transition model approximated with an accurate disretization method. The approach of global linear stability analysis is used to determine the onset and occurrence of the flutter phenomenon.