BR-102021005700-B1 - Irregular seal for noise reduction in aircraft.

Abstract

IRREGULAR SEAL FOR NOISE REDUCTION IN AIRCRAFT. The present invention presents an irregular seal (1) for reducing aerodynamic noise in aircraft, more specifically noise generated in the wing slats (3) (18). The irregular seal (1) prevents the formation of the coherence cycle generated between the vortices (10) and the formation of acoustic waves (13) generated at the flow re-engagement point (12). This suppresses the turbulence that collides with the concave surface (9) of the slat (3) and that leads to the formation of low and medium frequency tones, preventing the formation of acoustic dipoles without significantly altering the aerodynamic characteristics of the slat (3).

Inventors

• DANIEL ACEVEDO GIRALDO
• Fernando MARTINI CATALANO
• LAURA BOTERO BOLÍVAR
• LOURENÇO TÉRCIO LIMA PEREIRA

Assignees

• UNIVERSIDADE DE SÃO PAULO - USP

Dates

Publication Date

20260317

Application Date

20210324

Claims (4)

1. 1. Irregular seal (1) for reducing aerodynamic noise in aircraft characterized by comprising a plurality of fixed elements positioned on the lower surface and close to the trailing edge (8) of the slat (3), wherein the fixed elements are arranged forming two parallel lines where the fixed elements of each line interleave.
2. 2. Irregular seal (1), according to claim 1, characterized in that the fixed elements have the shape of an elliptical, pyramidal or spherical paraboloid.
3. 3. Irregular seal (1), according to claim 1, characterized in that the fixed elements are composed of metallic, ceramic, plastic, polished or composite materials.
4. 4. Irregular seal (1), according to claim 1, characterized in that the fixed elements have dimensions of 0.03c to 0.3c height (H), 0.03c to 0.3c width (L) and 0.03c to 3c width (W), where c is the chord of the slat (3) - distance between the leading edge (4) and trailing edge (8).

Description

Field of invention: [001] The present invention falls within the field of aeronautical engineering and aerodynamics, more specifically in the treatment of aerodynamic noise reduction for high-lift devices and is applied to aircraft wing slats. Fundamentals of the invention: [002] Civil aviation has become one of the most important parts of the transportation industry worldwide in recent decades. Passenger air traffic continues to grow and shows no signs of slowing down. Furthermore, cities tend to expand near airports, and at least 21 million people are affected by aircraft noise and have developed health problems. Today, the aviation industry represents 3.6% of the global Gross Domestic Product (GDP), and the recent growth of air transport and its consequent significant environmental impacts have been identified as a socially relevant issue. Takeoff and landing procedures result in significant aircraft noise, primarily produced by engines and structures. Noise reduction has become a major concern for civil aircraft manufacturers due to noise restrictions imposed by authorities for aircraft certification and operation. Therefore, the civil aviation industry has developed ways to reduce aircraft noise by optimizing operational procedures and improving land planning and use at airports. [003] Aircraft noise refers primarily to propulsion system noise and airframe aerodynamic noise. Aircraft aerodynamic noise has become more significant following the decrease in propulsion system noise. In recent decades, the bypass ratio of turbofan engines has continuously increased, and as a result, aircraft engine noise has decreased to a level comparable to the noise originating from turbulent flow around the airframe for takeoff and landing conditions. The main components of airframe aerodynamic noise are high-lift devices and the landing gear, each with specific noise spectra. In the late 1970s, experimental studies revealed that a dominant source of aerodynamic noise was associated with fluid passing through the slat cavity, and many noise reduction modifications were investigated. [004] The amount of lift generated by a wing depends on the airfoil shape, wing area, and aircraft speed. During landing and takeoff, the aircraft speed is relatively low. To maintain high lift, aircraft designers attempt to increase wing area by altering the airfoil shape, placing movable devices on the leading and trailing edges of the wings. The device on the leading edge is called a slat, while the device on the trailing edge is called a flap. The devices are articulated and can move outward along mechanisms embedded in the main wing (slats forward and flaps backward) to increase the wing area. In addition, these devices rotate downward, increasing the effective curvature of the airfoil, which also increases lift. [005] The main body of the slat extends from the main wing, and some of the air flows along the lower surface of the main body of the slat and is separated from the lower surface. The fluid through the gap formed between the slat and the main element is accelerated due to the concave geometry of the slat and the curvature of the leading edge of the main wing element. This acceleration generates an additional increase in lift; however, it also causes the formation of vortices along the concave trailing surface of the slat due to the turbulent separation of the airflow along the lower cusp of the slat. Furthermore, the vortices are continuously supplied with more energy from the airflow of the adjacent opening. This phenomenon generates and radiates aerodynamic noise along the entire wingspan of the slat, especially when the turbulent fluid separates and flows to the upper or trailing edge of the slat. The boundary between the vortex and the gap is called the principal shear layer of the slat, and the point where the principal shear layer collides with the upper surface of the slat is called the re-engagement point. State of the art: [006] Document US2010294883 “AERODYNAMIC SEAL FOR REDUCTION OF NOISE GENERATED ON AIRCRAFT CONTROL SURFACES” refers to a noise reduction technique for aerodynamic noise, which involves a type of perforated surface placed in parts of one of the noise-generating areas. This perforated plate acts as a vortex generator, with positive vortices that reduce the high-frequency tones produced in the slat cavity. The present invention presents a different structure and aims to modify the physical phenomenon present in the slat cavity – breaking the cycle generated between the slat cusp and its trailing edge – and prevent the generation of low/mid-frequency tones and reduce broadband noise. Although the technique described in document US2010294883 reduces noise and is also applied to high-lift devices, the present invention has a different objective, attempting to reduce a type of noise that would not be possible to reduce with the perforated plate, even when located on the slat. [007] US document 6789769 “Flex