| 1. |
- Luckring, J. M., et al.
(författare)
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Toward improved CFD predictions of slender airframe aerodynamics using the F-16XL aircraft (CAWAPI-2)
- 2017
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics Inc.. - 0021-8669 .- 1533-3868. - 9781624102561 ; 54:2, s. 378-387
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Tidskriftsartikel (refereegranskat)abstract
- A coordinated project has been underway to improve CFD predictions of slender airframe aerodynamics. The work is focused on two flow conditions and leverages a unique flight data set obtained with an F-16XL aircraft. These conditions, a low-speed high angle-of-attack case and a transonic low angle-of-attack case, were selected from a prior prediction campaign wherein the CFD failed to provide acceptable results. In this paper the background, objectives and approach to the current project are presented. The work embodies predictions from multiple numerical formulations that are contributed from multiple organizations, and the context of this campaign to other multi-code, multi-organizational efforts is included. The relevance of this body of work toward future supersonic commercial transport concepts is also briefly addressed.
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| 2. |
- Bérard, Adrien, et al.
(författare)
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Conceptual Design Prediction of the Buffet Envelope of Transport Aircraft
- 2009
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 46:5, s. 1593-1606
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a methodology that inexpensively predicts the buffet envelope of new transport airplane wing geometries at the conceptual design stage. The parameters that demonstrate a strong functional sensitivity to buffet onset were identified and their relative effect was quantified. To estimate the buffet envelope of any target aircraft geometry, the method uses fractional change transformations in consort with a generic reference buffet onset curve provided by the authors or the buffet onset of a known seed airplane. The explicit design variables required to perform buffet onset prediction are those describing the wing planform and the wingtip section. The mutually exclusive nature of the method's analytical construct provides considerable freedom in deciding the scope of free-design-variable complexity. The method has been shown to be adequately robust and flexible enough to deal with a wide variety of transport airplane designs. For the example transport airplanes considered, irrespective of aircraft morphology and en route flight phase, the relative error in prediction was found to be mostly within +/-5.0%, with occasional excursions not exceeding a +/-9.0% bandwidth. The standard error of estimate for the lift coefficient at 1.0 g buffet onset at a given Mach number was calculated to be 0.0262.
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| 3. |
- Boelens, O. J., et al.
(författare)
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F-16XL Geometry and Computational Grids Used in Cranked-Arrow Wing Aerodynamics Project International
- 2009
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 46:2, s. 369-376
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Tidskriftsartikel (refereegranskat)abstract
- The objective of the Cranked-Arrow Wing Aerodynamics Project International was to allow a comprehensive validation of computational fluid dynamics methods against the Cranked-Arrow Wing Aerodynamics Project flight database. A major part of this work involved the generation of high-quality computational grids. Before the grid generation, an airtight geometry of the F-16XL, aircraft was generated by a cooperation of the Cranked-Arrow Wing Aerodynamics Project International partners. Based on this geometry description, both structured and unstructured grids have been generated. The baseline structured (multiblock) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory. Although the algorithms used by the National Aerospace Laboratory had become available just before the Cranked-Arrow Wing Aerodynamics Project International and thus only a limited experience with their application to such a complex configuration had been gained, a grid of good quality was generated well within four weeks. This time compared favorably with that required to produce the unstructured grids in the Cranked-Arrow Wing Aerodynamics Project International. The baseline all-tetrahedral and hybrid unstructured grids have been generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, trimmed unstructured grids have been generated at the European Aeronautic Defence and Space Company's Military Air Systems, University of Tennessee at Chattanooga SimCenter, Boeing Phantom Works, Royal Institute of Technology, and the Swedish Defence Research Agency. All grids generated within the framework of the Cranked-Arrow Wing Aerodynamics Project International will be discussed in the paper. Both results obtained on the structured grids and the unstructured grids showed a significant improvement in agreement with flight-test data in comparison with those obtained on the structured multiblock grid used during the Cranked-Arrow Wing Aerodynamics Project.
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| 4. |
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| 5. |
- Borglund, Dan
(författare)
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Aeroservoelastic design optimization with experimental verification
- 2001
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 38:5, s. 958-961
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Tidskriftsartikel (refereegranskat)abstract
- A demonstration of integrated design optimization of an aeroservoelastic system was presented. It was shown that the simultaneous design of structural and control system required a two-step procedure to result in a minimum weight design and a control law that is well-designed for all operating conditions. The essential dynamics was predicted using a aeroservoelastic model, and final design with 42% less weight penalty was obtained using the integrated approach.
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| 6. |
- Borglund, Dan, et al.
(författare)
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Efficient computation of robust flutter boundaries using the mu-k method
- 2006
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 43:6, s. 1763-1769
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Tidskriftsartikel (refereegranskat)abstract
- A simple and efficient algorithm for robust flutter analysis is presented. First, a general linear fractional transformation formulation of the mu-k method is provided, making it straightforward to pose the uncertain flutter equation in a form suitable for structured singular value analysis. The new formulation establishes a close connection between mu-k flutter analysis and traditional frequency-domain flutter analysis, which is used to formulate an efficient algorithm for computation of robust flutter boundaries. The proposed method is successfully applied to an F-16 sample test case with uncertain external stores aerodynamics, showing that standard tools for structural dynamics and unsteady aerodynamics can be used to perform robust flutter analysis with only modest additional modeling.
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| 7. |
- Borglund, Dan
(författare)
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Robust aeroelastic stability analysis considering frequency-domain aerodynamic uncertainty
- 2003
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 40:1, s. 189-193
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Tidskriftsartikel (refereegranskat)abstract
- The problem of modeling frequency-domain aerodynamic uncertainty for a slender wing structure is investigated. Based on an unsteady lifting-line theory used for the generalized aerodynamic forces, a quite versatile uncertainty description with a clear physical interpretation is proposed. The uncertainty description is easily put in a form suitable for application of the mu framework in robust linear control. Because only frequency response matrices are required for the mu computations, the proposed uncertainty description can be used for robust stability and performance analysis without rational function approximations of the aerodynamic transfer function matrices. The usefulness of the uncertainty description and the methods available for robust aeroelastic stability analysis is demonstrated by performing aeroelastic wind-tunnel experiments.
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| 8. |
- Borglund, Dan, et al.
(författare)
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Robust wing flutter suppression considering aerodynamic uncertainty
- 2004
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 41:2, s. 331-334
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Tidskriftsartikel (refereegranskat)abstract
- A robust aeroservoelastic stability analysis considering frequency-domain aerodynamic uncertainty is utilized for robust control law design for flutter suppression of a flexible wing. The problem of stabilizing the wing in flutter using a minimum amount of control power is posed. For this purpose, numerical optimization is used to minimize the norm of a simple low-order controller subject to constraints on robust closed-loop stability. Robust stability is enforced in the optimization problem by posing constraints on the upper bounds on structured singular values and eigenvalues obtained from a linear stability analysis. The resulting controller is synthesized using gain scheduling, and robust wing flutter suppression is demonstrated in wind-tunnel testing.
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| 9. |
- Borglund, Dan, et al.
(författare)
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Solution of the Flutter Eigenvalue Problem with Mixed Structural/Aerodynamic Uncertainty
- 2011
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Ingår i: Journal of Aircraft. - 0021-8669 .- 1533-3868. ; 48:1, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- The solution of the flutter eigenvalue problem with mixed structural/aerodynamic uncertainty was examined. A delta-wing wind-tunnel model was used as a test case. The model had a simple structural design and was made of glass-fiber and carbon-fiber composite materials. It had a semispan of 0.88 m and mean chord of 0.70m and was mounted vertically in the low-speed wind tunnel L2000. The numerical analysis was based on a NASTRAN model with shell elements for the wing, mass elements for the missile, and aerodynamic panels for doublet-lattice aerodynamic loads. The relatively stiff missile was modeled as a rigid body attached to the wing tip. The nominal eigenvalue was always an interior point of the corresponding eigenvalue set. A parameter sweep taking only aerodynamic uncertainty into account was performed by solving the eigenvalue problem for a set of parameter values. The eigenvalue sets based on one patch and seven patches, respectively, showed only slight difference.
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| 10. |
- Borglund, Dan
(författare)
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The mu-k method for robust flutter solutions
- 2004
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Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 41:5, s. 1209-1216
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Tidskriftsartikel (refereegranskat)abstract
- A straightforward frequency-domain method for robust flutter analysis is presented. First, a versatile uncertainty description for the unsteady aerodynamic forces is derived by assigning uncertainty to the frequency-domain pressure coefficients. The uncertainty description applies to any frequency-domain aerodynamic method, benefits from the same level of geometric detail as the underlying aerodynamic model, exploits the modal formulation of the flutter equation, and is computed by simple postprocessing of standard aerodynamic data. Next, structured singular value analysis is applied to derive an explicit criterion for robust flutter stability based on the flutter equation and a parametric uncertainty description. The resulting procedure for computation of a worst-case flutter boundary resembles a p-k or g-method flutter analysis, produces match-point flutter solutions and allows for detailed aerodynamic uncertainty descriptions. Finally, the proposed method is successfully applied to a wind-tunnel model in low-speed airflow.
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