Aerodynamic Design of Active Flow Control on the Vertical Tail

Kurzfassung

t In this work the application of active flow control with tangential blowing is investigated to delay flow separation on the vertical tailplane (VTP) of a modern passenger transport aircraft. While tangential blowing is known to be effective on wing geometries, the aim of this work is to design the aerodynamic part of a blowing system in order to show two things: That tangential blowing can be effective on a VTP as well and that its efficiency can be increased when deviating from a full span slot. The design is done using numerical methods based on the Reynolds-averaged Navier-Stokes equations. The sizing case for the area of the VTP is a one-sided engine failure at low speed accompanied by small-to-medium sideslip angles. To compensate the asymmetric thrust, a large rudder deflection is needed to achieve the high side force required. The objective here is to increase the side force by delaying the flow separation to allow reducing the VTP area to cruise flight requirements, saving drag and weight. The design case mentioned leads to non-linear aerodynamic characteristics caused by partial flow separation. These differ from a typical passenger aircraft wing geometry due to the VTP’s low-aspect ratio, highly-swept planform. Therefore, understanding the complex three-dimensional baseline flow over the VTP is the basis of this work. Building on this, the tangential blowing slot is developed in three steps. First, a 2D section is used to analyze the effects of geometry changes in the vicinity of the slot. In a next step this geometry is extended to 2.5D where a constant chord geometry with extension in spanwise direction is used. This allows accounting for the large sweep angle of the VTP and opens the possibility to examine apart from a continuous full span slot also discrete slots. Introducing the discrete slots leads to the creation of a vortex system over the rudder which helps to attach the flow not only in the path of the jet but also in between the jets in spanwise direction. The slot width and the gap between the slots are varied to optimize this vortex system. The findings were in a last step transferred to the 3D vertical tailplane. Due to the reduction of the slot extension over the span a considerable mass flow reduction of around 50% could be achieved for the same increase in side force coefficient. Thus it could be shown that the side force coefficient can be significantly increased using tangential blowing which is more efficient when using discrete slots.