Aerodynamic shape optimisation of a displacement body with a discrete adjoint method

Kurzfassung

Since the introduction by Ludwig Prandtl in 1904 the boundary layer theory is an important part of aerodynamics and its research continues until the present day. In general the changes occuring within the range of flow boundary layers have a wide influence and affect the flow field far beyond. This property holds equally true for the transitional process as the shift of flow from a well ordered laminar state into full turbulence not only affects the boundary layer region itself but takes influence on the entire flow field. The transitional process is initiated by instabilities in the velocity and the pressure flow field. The occuring boundary layer instabilities then can be grouped by their way of directional propagation. Tollmien-Schlichting instabilities develop into the main flow direction while for cross flow boundary layer instabilities, propagation takes place rectangularly with respect to the main flow. The significant role of the boundary layer makes an impact on technical applications. For engineers the most important occurence of cross flow boundary instabilities can be found in the flow around aircraft wings. One characteristic aircraft design property for flight at transsonical flow is the utilisation of swept wings. For this appilication it is precisely the cross flow boundary layer instabilities which are responsibile for the initiation of transition. Typically the transition begins near the leading egde of the wing. As transition is directly related to the flow resistance the hope for future applications is to take influence on the instability development process in a way that a delay or even avoidance of flow transition could take place. If this can be achieved a significant reduction of the flow resistance could be attained and hence improve the fuel efficiency of modern aircraft. However, influence mechanisms regarding cross flow boundary layer instabilities are not well understood.