Aerodynamic noise reducing structure for aircraft wing slats

Details Aerodynamic noise reducing structure for aircraft wing slats Aerodynamic noise reducing structure for aircraft wing slats

2001-04-17

2002-05-28

Carone, Michael J. (Department: 3641)

Aeronautics and astronautics

Aircraft sustentation

Sustaining airfoils

C244S00100R, C244S199100, C244S201000

Reexamination Certificate

active

06394396

ABSTRACT:

PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 100 19 185.1, filed on Apr. 17, 2000, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a structural arrangement for aerodynamic noise reduction in connection with leading edge slats on the wings of commercial transport aircraft. Particularly, the structure provides an aerodynamic effect on a wing slat in order to reduce the noise generated by air flowing around the slat, and through the air gap between the slat and the leading edge of the wing, especially during take-off and landing phases of flight of an aircraft.
BACKGROUND INFORMATION
Various noise sources contribute to the total noise generated during the flight of a modern commercial transport aircraft.
Among the various noise sources, aero-acoustically generated noise that results from the flow pattern of air around the aircraft structure is becoming an evermore significant portion of the total flight noise. This is because the noise generated by other sources such as the engines has been reduced in recent years by technical advances of those components. In present day commercial transport aircraft, it is roughly estimated that approximately 50% of the total flight noise during a landing approach is generated by the flow of air around the aircraft structure, while the other half of the total noise is generated by the engines.
Further improvements, i.e. reductions, in the noise generated by the engines are only practically and economically efficacious if similar technical advances for reducing the aerodynamic flow noise around the aircraft fuselage can be simultaneously achieved. It is becoming especially important to reduce the aerodynamic flow noise in view of ever stricter noise level limits, especially around airports with a high aircraft traffic volume. A major factor contributing to the total aerodynamic flow noise during landing and take-off of a modern commercial transport aircraft, is the noise generated by the airflow around high-lift slats deployed from the leading edges of the wings during the landing and take-off phases.
To facilitate an understanding of the aerodynamic noise generated in connection with the leading edge slats,
FIG. 4
of the present application shows representative streamlines of the air A flowing around a generally conventional wing, which is schematically shown in section. The wing arrangement includes a main wing
2
, a leading edge slat
1
that is extended or deployed forward of the leading edge of the main wing
2
, and a landing flap
11
that is extended or deployed rearward from the trailing edge of the main wing
2
. Throughout this specification, the term “forward” and the like refers to the normal forward flight direction of the aircraft, for example the direction in which the aircraft nose and the wing leading edges are oriented. As is generally known, the extended slat
1
and landing flap
11
change the effective camber and angle of attack of the airfoil profile of the wing structure, and also influence the airflow over the surfaces of the wing, so as to increase the lift, e.g. for landing and takeoff. In this extended configuration, the slat
1
is deployed forwardly and downwardly from the leading edge nose
2
A of the main wing
2
so as to form a slat air gap
13
between a rearwardly facing concave curved surface
3
of the slat
1
and the convexly profiled leading edge nose
2
A of the main wing
2
.
On the other hand, during cruise flight, the slat
1
is retracted into a retracted position (not shown) directly on the leading edge nose
2
A of the main wing
2
so as to reduce the aerodynamic drag and avoid unnecessary increased lift. In this context, the leading edge slat
1
must be retracted smoothly and flushly against the leading edge nose
2
A of the main wing
2
, so as to form a substantially continuous aerodynamic contour. Namely, the slat
1
is adjacent to the leading edge nose
2
A, with at most only a small, aerodynamically insignificant, gap or space therebetween. Therefore, the rear concavely curved surface
3
of the leading edge slat
1
has a profile curvature substantially matching that of the leading edge nose
2
A of the main wing
2
, so that the slat
1
smoothly matches or mates onto the leading edge nose
2
A of the main wing
2
without a resistance-causing gap or discontinuity therebetween.
Unfortunately, the profile curvature of the rear concave surface
3
of the slat
1
may be optimal for mating onto the leading edge nose
2
A of the main wing
2
in the retracted position, but it is not optimal for the airflow through the slat air gap
13
between the leading edge nose
2
A and the slat
1
in its deployed position as shown in FIG.
4
. As a result, the airflow A forms an eddy or vortex
15
that extends lengthwise along the length of the slat
1
(i.e. in the wing span direction). This vortex
15
involves the turbulent eddy recirculation of air in the hollow space defined and bounded by the rear concave curvature
3
of the slat
1
, whereby this space generally has a tapered concave shape or tear-drop shape. This vortex
15
further exhibits or generates a fluctuating fluid pressure field of the affected airflow, which is believed to be the cause of the aerodynamic noise generated in this area. Noise measurements in an aero-acoustic wind tunnel have confirmed that a significant reduction of the noise generated by the extended slat can be achieved by arranging a rigid fairing or filler member in the space along the rear concave curvature
3
of the slat
1
, which would otherwise be occupied by the vortex
15
.
Attempts have been made in the prior art to reduce the aerodynamically generated noise, especially in connection with the slats and the mounting thereof. For example, a study in this regard was published by Werner Dobrzynski and Burkhard Gehlhar entitled “Airframe Noise Studies on Wings with Deployed High-Lift Devices”, from the Deutsches Zentrum fuer Luft und Raumfahrt e.V. (DLR), Institut fuer Entwurfsaerodynamik, Abteilung Technische Akustic, Forschungszentrum Braunschweig, Germany, at the Fourth American Institute of Aeronautics and Astronautics AIAA/CEAS Aeroacoustics Conference on Jun. 2 to 4, 1998 in Toulouse, France.
Among other things, this study disclosed a proposed noise reducing arrangement in which a sheet metal guide member is pivotally connected to the slat in the area of the concavely curved rear or inner surface of the slat facing toward the leading edge nose of the main wing. This sheet metal air guide can be pivoted relative to the slat. Particularly, the air guide member can be extended or deployed relative to the slat during take-off and landing when the slat is deployed relative to the wing. On the other hand, the sheet metal air guide member will be pivoted against the slat during cruise flight when the slat is to be retracted relative to the wing. While such a proposed solution may have achieved a reduction of aerodynamically generated noise in wind tunnel tests, it is considered that such a solution could never be practically carried out in an actual aircraft construction, for practical reasons.
For example, in the previously proposed arrangement, when the slat is retracted against the leading edge nose of the main wing for cruise flight, the gap between these two components is not sufficiently large for accommodating a rigid air guide member tilted or pivoted inwardly against the rear surface of the slat. On the other hand, if the gap is made larger to accommodate the air guide member, then a disadvantageous aerodynamic gap or discontinuity would be formed along the aerodynamic contour provided by the slat and the wing in combination. Moreover, if a flexible air guide component is provided, which is to be adapted against the inner contour of the slat in the retracted position, then such a component would not have sufficient strength and stiffness in order to withstand the aerodynamic forces in the deployed condition.
M

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