Autonomous Slat-Cove Filler Device
Aerospace
Autonomous Slat-Cove Filler Device (LAR-TOPS-87)
Reduction of aeroacoustic noise associated with the leading edge of aircraft wings
Overview
NASA's Langley Research Center developed a deployable and stowable mechanical design for filling the cavity behind the leading-edge slat (i.e., slat cove), when it is extended upon landing approach of an aircraft. Aerodynamic flow over an unfilled cavity typically exhibits strongly unsteady behavior that is a source of aeroacoustic noise. Conventional leading-edge slat devices for high lift are a good example of such geometric and flow conditions and are a prominent source of airframe noise. Experimental and computational results have shown that a slat-cove filler device could significantly reduce the noise produced by slat structures without aerodynamic penalty. The proposed structural concept will enable autonomous achievement of the desired deployed shape. The design will facilitate a clean cruise configuration with minimal weight addition to the aircraft. NASA is seeking development partners and potential licensees.
The Technology
NASA Langley designed the shape memory alloy slat-cove filler to provide significant broad-band noise reduction to any aircraft wing structure that has a leading-edge, high-lift device and that is distinct from the main-wing element. The design can be retrofitted to existing aircraft structures and can be easily incorporated into the existing or future designs for aircraft wing structures. The concept involves very few components, requires no additional mechanical support from pneumatic or hydraulic systems, and makes use of existing slat-actuation systems for retraction. The design is autonomous, simple, and constitutes low-weight addition. The concept is also considered fail-safe because the lift would not be diminished in the event that the slat cove filler failed to deploy.
Several advancements have been devised to accommodate complex features encountered in application to practical airframe structures. Graphics from a computational model of a 2D physical demonstration system show the configuration and strain in the slat-cove filler in the deployed and stowed conditions. Features enabling stowage of a large curvilinear length (sliding hinge) and maintenance of the optimized outer mold line (auxiliary component) are highlighted. Other advancements for application to 3D, flight airframes are visible in the image from a model for one entire section of a slat-cove-filler treatment for a wide-body, transport-class aircraft.
NASA Langley also offers a design for a deformable structure that is deployed from the leading edge of the main-wing element, termed the slat-gap filler. It closes and covers the gap between the slat and the main-wing element, but can be readily and autonomously opened in emergency to regain the baseline high-lift configuration and its corresponding lift performance at high angles of attack. This approach has similar benefits as the slat-cove filler device.
Benefits
- Provides significant broadband noise reduction: ~4 effective perceived noise decibels (EPNdB) reduction
- Incorporates easily into existing aircraft structure or future designs of aircraft wing structures
- Requires no additional mechanical support from pneumatic or hydraulic systems
- Constitutes low-weight addition
Applications
- Commercial Aerospace - Aircraft that incorporate a leading-edge, high-lift device that is distinct from the main-wing element
- Launch vehicle or rockets
- Automobiles
Similar Results
Low, Drag, Variable-Depth Acoustic Liner
The drag penalty incurred by a conventional acoustic liner is dependent, to a large extent, on the perforate open area ratio (porosity) of the perforated facesheet. As the open area ratio is decreased, the facesheet behaves more like a solid surface and the drag is reduced. However, if the open area ratio is too small, the external acoustic field will be isolated from the resonators (in the liner), and the system will not provide noise reduction.
The technology is a new type of variable-depth acoustic engine liner, which will reduce the drag and potentially manufacturing cost of this class of engine liner. Individual resonators within a conventional variable-depth liner are effective near resonance, but provide less acoustic benefit at other frequencies. In fact, at anti-resonance, a resonator behaves similar to a hard wall (i.e., the normal component of the particle velocity at the inlet is zero). Therefore, the proposed innovation couples neighboring resonators (tuned for different frequencies) together within the core of the liner. In other words, multiple resonators share a single inlet/port. Sharing inlets reduces the overall number of openings needed to maintain the acoustic performance of the liner by a factor of two or more. Reducing the open area ratio will in turn reduce the liner drag, and will reduce the number of holes that have to be machined into the facesheet, potentially reducing manufacturing cost.
The functional operation of the proposed innovation will be identical to conventional engine liners. The innovation enables a reduction of the open area ratio of the perforated facesheet (by a factor of two or more) without degrading the acoustic performance. This will decrease the liner drag, and has the potential to reduce the manufacturing cost of the liner, since fewer holes need to be machined in the facesheet.
A Method for Reducing Broadband Noise
This NASA technology is ideally suited to absorb sounds below 1000 Hz (at the low end of human auditory range), which commercially available materials have struggled to absorb effectively. NASA innovators designed the acoustic liner to mimic the geometry and the low-frequency acoustic absorption of natural reeds. To provide excellent noise absorption that endures even in a variety of challenging conditions, researchers have created and tested prototypes of acoustic filters using thin and lightweight parallel-stacked tubes one-fourth to three-eights of an inch in diameter. The assembly can feature a porous or perforated face sheet positioned on one or more sides of the acoustic absorber layer to increase noise-reduction capability as needed. These filters have demonstrated exceptional acoustic absorption coefficients in the frequency range of 400 to 3000 Hz. Results indicate that these assemblies can be additively manufactured from synthetic materials, generally plastic; however, ceramics, metals, or other materials can also be used. The reeds can be narrow or wide, hollow or solid, straight or bent, etc., giving this acoustic liner remarkable flexibility and versatility to meet the needs of virtually any application. This technology effectively demonstrates that a new class of structures can now be considered for a wide range of environments and applications that need durable, lightweight, broadband acoustic absorption that is effective at various frequencies, particularly between 400 and 3000 Hz.
Supersonic Laminar Flow Control
This technique injects precisely defined stationary transient growth disturbances into the free air slipstream over a wing that develop into streamwise elongated "streaks." These streaks are created with an alternating pattern of low and high streamwise velocity in the boundary layer flow adjacent to the aerodynamic surface of interest. Judicious selection of streak wavelength, amplitude, and profile allows the first-mode instability waves responsible for transition via oblique mode breakdown to be damped while the remaining, uncontrolled waves are kept below an amplification threshold. A similar control concept is also applicable to second mode transition at hypersonic Mach numbers.
Aerodynamically Actuated Thrust Vectoring Device
The thrust actuating device includes several innovations in the aerodynamically stable tilt actuation of propellers, propeller pylons, jets, wings, and fuselages, collectively called propulsors. The propulsors rotate between hover and forward flight mode for a tilt-wing or tilt-rotor aircraft. A vehicle designed using this technology can transition from a hovering flight condition to a wing born flight condition with no mechanical actuation and can do so without complex control systems. This results in a reduction in system weight and complexity and produces a robust and naturally stable hovering aircraft with efficient forward flight modes.
Green aviation - improved aerodynamic efficiency and less fuel burn
Currently, as fuel is burned, wing loading is reduced, thereby causing the wing shape to bend and twist. This wing-shape change causes the wings to be less aerodynamically efficient. This problem can be further exacerbated by modern high-aspect flexible wing design. Aircraft designers typically address the fuel efficiency goal by reducing aircraft weights, improving propulsion efficiency, and/or improving the aerodynamics of aircraft wings passively. In so doing, the potential drag penalty due to changes in the wing shapes still exists at off-design conditions. The unique or novel features of the new concepts are:
1. Variable camber flap provides the same lift capability for lower drag as compared to a conventional flap. The variable camber trailing edge flap (or leading edge slat) comprises multiple chord-wise segments (three or more) to form a cambered flap surface, and multiple span-wise segments to form a continuous trailing edge (or leading edge) curve with no gaps which could be prescribed by a mathematical function or the equivalent with boundary conditions enforced at the end points to minimize tip vortices
2. Continuous trailing edge flap (or leading edge slat) provides a continuously curved trailing edge (or leading edge) with no gaps to minimize vortices that can lead to an increase in drag.
3. The active wing-shaping control method utilizes the novel flap (or slat) concept described herein to change a wing shape to improve aerodynamic efficiency by optimizing span-wise aerodynamics.
4. An aeroelastic wing shaping method for analyzing wing deflection shape under aerodynamic loading is used in a wing-control algorithm to compute a desired command for the flap-actuation system to drive the present flap (or slat) system to the correct position for wing shaping.
