Air outlet design for a passively driven hybrid laminar flow control system

Abstract

Hybrid Laminar Flow Control (HLFC) is one of various promising future aircraft applications intended to reduce aerodynamic drag and hence also fuel consumption. Airbus investigated laminar flow control technology in previous decades with active suction at the leading edge of the vertical tail plane (VTP). Recent HLFC approach concerns not only laminar flow control but also system details such as internal compartment shape and air outlet design. One possible technical solution involves passively driving the system through suction at an air outlet. The current CFD investigation is intended to aid the definition of a robust system solution that will be implemented on a flight test aircraft in upcoming years. Here, HLFC will be applied at a specified VTP section. This investigation includes variations of outlet size, shape, opening angle and location at a typical passenger aircraft VTP. A detailed analysis of typical cruise flight conditions, i.e. variations of Mach number, flight level, AoA and sideslip angle, is performed while the focus is on outlet aerodynamic performance. One of the main objectives is achieved suction pressure and hence the mass flow driven through the system. There are large differences in system efficiency depending upon the outlet location and shape. A system mass flow requirement in order to apply HLFC at a specified VTP section is fulfilled by all three investigated air outlet locations: at the VTP tip, at a middle location and at a close-to-root location. However, the aerodynamic performance of these outlets is very different. Locations at the VTP tip and mid-VTP require large outlet areas and/or large flap opening angles. This generates high aerodynamic drag. The lower VTP location is found to be the most promising compromise with respect to the achieved suction pressures and associated aerodynamic drag.