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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. 2] 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.

Figure 3: Implementation of overset mesh
(Click to enlarge)

SC/Tetra CFD Software Powerful Meshing Capabilities Accommodate Slat Articulation

When the M2AESTRO team was selecting the CFD software to perform the FSI analysis, the ability to handle both the complex deformation of the SCF and the use of nonlinear materials were determining factors. The overset mesh feature in SC/Tetra overlapped movable and deformable slave meshes onto a master mesh. The meshes could accommodate the significant deformation associated with slat articulation. In this work, the research team set the slat/SCF and flap as slave meshes while the tunnel test section and main wing were part of the master mesh (Figure 3).

 

Coupling SC/Tetra to the structural solver (Abaqus) for the FSI analysis was straight forward because SC/Tetra has a built-in connection to the Abaqus Co-simulation Engine. This was another significant reason for choosing SC/Tetra. In addition, both the fluid and structural solvers were weakly coupled, allowing for the implementation of the SMA constitutive model.

Figure 4: CFD model for Boeing-NASA CRM airfoil
(Click to enlarge)

First FSI Analysis of SCF Retraction and Deployment

CFD models of a scaled, 2D section of a high-lift wing, known as the Boeing-NASA Common Research Model (CRM), were developed for retracted, untreated deployed, and SCF-modified deployed configurations at multiple angles of attack. Boundary conditions included walls representing the test section floor and ceiling, surface of the airfoil, zero static pressure at the outlet, and uniform freestream velocity at the inlet (Figure 4). A CFD analysis was performed for each model under the same inflow conditions to investigate how the lift, drag and pressure changed based on the angle and configuration.

 

Using the overset mesh feature and the SC/Tetra native link to Abaqus, the FSI analysis was conducted for the CRM wing with an SMA-based SCF. Of particular interest was the SCF response to two loading conditions with flow: 1) fixed, fully deployed configuration and 2) slat retraction/deployment. For both load cases, an initial CFD analysis was used to initialize the flow. Based on the FSI analysis the SCF demonstrated under flow, that it could maintain its shape when fully deployed (and thus its noise reducing capability), SCF was compliant to articulation of the slat, and autonomously redeployed during slat deployment.

 

Early in the FSI analysis, when the slat was subject to significant amounts of articulation (and thus fluid volume deformation), portions of the fluid volume mesh associated with the slat/SCF would be essentially eliminated, or greatly reduced in size, leading to zero volume elements. This could cause problems for the analysis. Dr. Hartl talks about how the team solved this problem. “The solution to this problem was to create a remeshing scheme for the slave mesh (essentially local remeshing of the fluid model). At specified times, as the slat articulated, the FSI analysis was stopped and the deformed slave mesh was remeshed. Flow results from the previous analysis were used as initial conditions for the new FSI analysis.” The results mapping feature in SC/Tetra greatly facilitated this operation. Using both the overset mesh and local remeshing, full slat retraction and deployment was possible.

Figure 5: Velocity contours from FSI retraction/deployment analysis
(Click to enlarge)

Figure 5 shows the velocity contour of the flow from the FSI analysis at various stages of slat retraction and deployment. The M2AESTRO team believes this is the first FSI analysis of a morphing SMA-based structure attached to a moving rigid body (the slat) relative to a fixed rigid body (the main wing).

 

Concurrent to the computational work, an experimental model of the CRM wing was developed, constructed, and tested under the same conditions as the computational CFD and FSI models. Both the computational and experimental model results compared well for lift, drag and pressure. This provided an initial means of validating the computational work, and the results have been promising so far.

 

Currently, techniques for measuring the SCF displacement are being developed. Once implemented, these measures will provide additional data to validate the computational models.

 

The CFD and FSI analyses permitted assessment of the SCF without the need to build several different experimental test models. The matrix of computational test points was also used to identify safe conditions for future experimental tests. Once validated with experimental data at the safe conditions, the computational analysis can be performed for conditions that may not be possible to attain experimentally. In addition, another virtue of the computational analyses is that significantly more data can be extracted from the computational analysis compared to experimental tests. This is due to geometric constraints and limited (and potentially expensive) metrologies.

 

Process Turn-Around Time Still a Challenge

While CFD is known to be widely used in the aerospace industry, the time required to generate the computer model and perform the computational analysis can still be an issue. As a result, CFD is often used in the later stages of the aerospace system design process. Dr. Hartl expounds: “During the earlier stages of the design process, engineers typically rely on fast, low-fidelity solutions, such as the panel-method or lifting-line theory. Morphing structures are also becoming more popular in the aerospace industry. Proper analysis of system behaviors when using these complex materials requires multiple CFD analyses for the different configurations that the structure can exhibit. If an FSI analysis is needed for the morphing application, the CFD software must be capable of being coupled with a structural analysis software to facilitate the analysis process.”

 

Future Computational Needs

The M2AESTRO team will continue to use CFD as a high fidelity method to help grow their understanding about how morphing structures behave in flow. Experimental tests are limited by the number of configurations and conditions that can be tested. CFD can be used to examine many more cases. The pressure distributions from the CFD analysis can also be applied to structural models of a physical prototype to determine how the complex non-linear structures behave under flow. The opportunities are endless, and the M2AESTRO team hopes to continue working with Software Cradle and its products. As Software Cradle continues to enhance FSI capabilities, this will help the M2AESTRO team achieve its goals.

*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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