The DLR project LEISA combines and focuses activities in the research areas of high lift system design, flow control and aero-acoustic design methods, which have been carried out rather independently up to now. Furthermore, the competence in the fields of aerodynamics, aero-acoustics, structures and flight systems will be integrated to provide an interdisciplinary assessment of high lift system design for transport aircraft configurations. The project LEISA started at the beginning of 2005, so up to now only few results are available. This paper addresses the integrated design approach and first results for a noise reduced slat device and combined wind tunnel testing results for aerodynamics and aeroacoustics.

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Experimental investigations have been carried out with the two-dimensional DLR-F15 high-lift wing section model in DNW-KKK cryogenic wind tunnel in order to differentiate between the influence of Mach-and Reynolds number on the stall behavior. Due to the cryogenic environment Mach-and Reynolds number have been varied independently between M = 0.1-0.25 and Re = 1.4 x 10 6-15.6 x 10 6. The investigation covers 2-element and 3-element configurations at various slat and flap settings and two different slat shapes. Focus of the investigation is to identify conditions of turbulent leading edge stall, shock related lift limitations and flap separations and their influence on achievable maximum lift coefficient.

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The high lift system noise of current transport aircraft is dominated by slat noise under certain operating conditions. Suitable means to reduce the noise impact in the vicinity of airports are (i) to increase the distance between the source and the observer and (ii) to reduce source noise levels. Both objectives can only be achieved by means of a multidisciplinary aerodynamic and acoustic development since the slat is at the same time a very important element to achieve the necessary high lift performance and the dominant noise source of a high lift system 1 . First attempts to reduce slat noise by means of a slat setting optimization were conducted at DLR in the mainframe of the project Leiser Flugverkehr 2 . This purely acoustically driven study revealed that a slat gap reduction results in a local flow speed decrease at the slat trailing edge and thus to remarkable noise reductions of up to 10 dB, the latter of course depending on the magnitude of the slat gap reduction. The drawback of this approach was that at the same time the aerodynamic performance of the high lift system was degraded by a non-acceptable level. However, this study was the starting point of the DLR project LEISA (Low noise exposing integrated design for start and approach) that combined activities in the research areas of high lift system design and aero-acoustic design, which were carried out rather independently up to this point in time. In the project LEISA different types of high lift configurations were addressed and investigated in a 2-dimensional approach. The first one is a long chord slat that provided a source noise reduction of about 6 dB while maintaining the aerodynamic performance of the reference slat system. The second, and more radical concept was to omit the slat and apply a droop nose system in order to reduce the aerodynamic losses as much as possible. The finally achieved source noise reduction with the droop nose system was about 8 dB while from the aerodynamic point of view about 50% of the losses were recovered. Based on these promising results the transposition of these high lift systems to a real 3-dimensional wing was carried out in the follow-up project SLED (Silent Leading Edge Devices). The final outcome of the project SLED can be summarized as follows. From the aerodynamic point of view the performance of the 3-dimensional long chord slat compares very well to the reference slat system. The final droop nose design was capable to recover about 40% of the lift loss due the omitted slat. The final acoustic results in terms of source noise levels are an overall 4 dB noise reduction for the long chord slat and about 6 dB noise reduction in case of the droop nose. The obtained aerodynamic and acoustic characteristics were finally transposed to flight in order to assess the effect on community noise which can be expressed in terms of noise isocontour areas. Regarding the 60 dB(A) and the 65 dB(A) noise iso contour areas the achieved benefit is a reduction of up to 40% of the respective area's size. 1 Research Eng.,...

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