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Texas A&M University
CFD and FSI Analyses of an Aircraft Wing Leading Edge Slat with Superelastic Shape Memory Alloy Cove Filler

[Vol. 1] Researchers at Texas A&M University are conducting CFD (Computational Fluid Dynamics) and FSI (Fluid-Structure Interaction) analyses of an aircraft wing leading edge slat that uses a Slat Cove Filler (SCF), made from a superelastic shape memory alloy, to reduce aeroacoustic noise when the slat is deployed. Grid management challenges were encountered because the compression of the filler can cause mesh elements to go to zero volume. The CFD software needs to handle complex mesh deformations, nonlinear materials, and facilitate the FSI analysis. Initial results show the computational and experimental results compare well.

 

Minimizing Aircraft Aeroacoustic Noise Near Airports

Texas A&M University is using sophisticated computational methods to investigate material driven solutions that can reduce aeroacoustic noise produced by aircraft airframes.

 

High noise levels near airports have been linked to human health issues. While many airports were originally located far from high population areas, urban sprawl has caused significant growth near airports. In addition, increasing passenger demand for air travel means more air traffic. These have led to increased concerns about noise produced by aircraft, which can affect health, disrupt communities, and negatively impact the overall environment.

Picture 1: M2AESTRO Research Team

Dr. Darren Hartl, Assistant Professor, Department of Aerospace Engineering at Texas A&M University, leads the Multifunctional Materials and Aerospace Structures Optimization (M2AESTRO) Lab research team that is focused on developing novel structural and material concepts for aerospace applications (Picture 1). The team is comprised of two post-docs, seven graduate students, and a dozen undergraduate researchers. William Scholten, a PhD student and National Science Foundation (NSF) Graduate Fellow, has been performing SCF research since he was an undergraduate researcher.

Figure 1: Flow in vicinity of leading–edge slat (Click to enlarge)

Dr. Hartl provides background for one of his team’s projects. “Aeroacoustic noise created by flow passing over an aircraft’s body and wings is one of the major sources of aircraft noise. Traditionally, the airframe is designed to be very streamlined so it is very efficient and produces low noise during cruise conditions (high speed and altitude). Leading-edge devices, such as the leading-edge slat, are flush against the surface of the main wing, significantly reducing drag and noise while allowing for sufficient lift to maintain steady, level flight. However, during approach and landing (low speed and low altitude maneuvers at airports), the slats are deployed to alter the lift and stall characteristics of the aircraft. When deployed, the slats introduce geometric discontinuities to the airflow, which generate airframe noise.” Dr. Hartl notes that a significant source of airframe noise, during approach and landing, is the leading-edge slat due to the circulation region inside the slat-cove (Figure 1a).

Morphing Aerostructure and Large Recoverable Inelastic Deformation

A high potential solution to mitigate the noise produced by the leading-edge slat is the slat-cove filler (SCF) which fills the cove aft of the slat and guides the airflow along a desired path (Figure 1b). The SCF has two main configurations: deployed and retracted (Figure 2). When deployed, the SCF is passively modifying the airflow while maintaining its shape to the aerodynamic loading. When the slat is retracted during cruise conditions, the SCF undergoes significant deformation that would exceed what typical aerospace materials (aluminum, steel, titanium) can sustain before yielding.

Figure 2: Leading-edge slat configurations
(Click to enlarge)

The significant deformation, along with requirements to provide stiffness against the aerodynamic loading and compliance to slat retraction (for reduced actuation force), led National Aeronautics and Space Administration (NASA) engineers to consider superelastic shape memory alloys (SMAs) for the SCF design. Superelastic SMAs are special types of active materials that can undergo a solid-phase transformation under sufficiently applied stress, which enables the material to achieve large amounts of recoverable inelastic deformation.

 

Dr. Hartl explains the situation when analyzing the aerodynamics of deforming structures. “This thin morphing aerostructure can significantly affect the surrounding flow field. In turn, the flow field can affect the structural response of the SCF. “ The purpose of the research at M2AESTRO is to understand the response of the SMA-based SCF when subjected to flow using a computational Fluid-Structure Interaction (FSI) analysis with Computational Fluid Dynamics (CFD), and experimental wind tunnel tests, to assess its effects on wing performance. This work has been funded by the NSF and the NASA Langley Research Center.

 

CFD and FSI Make it Possible to Analytically Evaluate the Performance of the SCF at Many Flight Conditions

Using FSI analysis, two-way coupling between the aerodynamic flow field and the SCF structure demonstrated how the SCF behaved when subjected to aerodynamic loads and correspondingly, how these behaviors affected the flow field.

 

To perform an accurate FSI analysis of the SMA-based SCF, subjected to aerodynamic loading, the M2AESTRO team needed to use a CFD software capable of simulating complex phenomena including significant complex deformation (significant translation and rotation, body-to-body contact, and volume elimination) and nonlinear materials.

 

Dr. Hartl explains the meshing challenge in this way. “During slat retraction, the SCF undergoes a significant amount of deformation between its deployed and retracted states due to contact with the main wing and the slat. In addition, the SCF is undergoing deformation while connected to a rotating rigid body that is moving relative to a fixed rigid body. The complex deformation of the SCF can quickly lead to the creation of zero volume elements in a typical CFD model.“ Modeling slat/SCF articulation in CFD software is not possible without a feature that can account for complex deformation and near elimination of fluid volumes.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of January 30, 2018 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors in this brochure.

Company Details

 

Texas A&M University
Established 1876
Type Land-grant, sea-grant, space-grant university
Location College Station, Texas, USA
Academic Staff 4,900
Students 68,825 (as of Fall 2017)
Graduate Students 15,135 (as of Fall 2017)
URL www.tamu.edu

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