Application of boundary layer suction on the vertical fin of a sailplane

Abstract

High-performance aircraft have advanced so much in recent years that every part of a sailplane has to be investigated and improved separately in order to discover prospective areas for improvement. One of these areas is the vertical stabilizer of the sailplane. Sailplanes operate in the flow region where both laminar and turbulent boundary layers are present on the surfaces. In order to reduce drag, longer laminar flow regions must be established. Boundary layer control in the form of suction is a potential method to increase performance and is thus investigated. Boundary layer suction is an active boundary layer control method used to decrease the drag of a body moving through a fluid by keeping the boundary layer laminar past the point where transition occurs naturally. This is a drag reduction technique to remove the slowed bottom part of the boundary layer through slots or a poriferous material. High-performance sailplanes cannot make use of an external source of propulsion, which means that a pump cannot be used to drive the system. Therefore, a low-pressure zone on the vertical stabilizer must be identified to be used as the source of suction. In this research, computational fluid dynamics (CFD) was used to investigate the possibility to reduce drag on a glider’s vertical fin with the application of boundary layer suction. The results include the location and design of the outlet on the tail section, as well as the layout of suction holes that would result in the largest reduction in drag. It is evident from the results of this study that boundary layer suction on the JS3 vertical stabilizer is not a viable option. Although boundary layer suction reduce drag by 20 %, a necessary suction outlet port, however, increases drag. The final result is a net loss of aerodynamic performance on the vertical stabilizer.