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Publications (10 of 27) Show all publications
Silva, W. A., Chwalowski, P., Wieseman, C. D., Keller, D. F., Eller, D. & Ringertz, U. (2017). Computational and experimental results for the KTH-NASA wind-tunnel model used for acquisition of transonic nonlinear aeroelastic data. In: 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017: . Paper presented at 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, 25 June 2017 through 28 June 2017. International Forum on Aeroelasticity and Structural Dynamics (IFASD)
Open this publication in new window or tab >>Computational and experimental results for the KTH-NASA wind-tunnel model used for acquisition of transonic nonlinear aeroelastic data
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2017 (English)In: 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, International Forum on Aeroelasticity and Structural Dynamics (IFASD) , 2017Conference paper, Published paper (Refereed)
Abstract [en]

A status report is provided on the collaboration between the Royal Institute of Technology in Sweden and the NASA Langley Research Center regarding the aeroelastic analyses of a full-span fighter configuration wind-tunnel model. This wind-tunnel model was tested in the Transonic Dynamics Tunnel in the summer of 2016. Large amounts of data were acquired including steady/unsteady pressures, accelerations, strains, and measured dynamic deformations. The aeroelastic analyses presented include linear aeroelastic analyses, CFD steady analyses, and analyses using CFD-based reduced-order models. The reduced-order model results also include a comparison of the aeroelastic response of the model in free air and in a computational mesh of the Transonic Dynamics Tunnel in order to determine, computationally, the effects of the wind tunnel on the aeroelastic response. 

Place, publisher, year, edition, pages
International Forum on Aeroelasticity and Structural Dynamics (IFASD), 2017
Keywords
Aeroelasticity, Aircraft models, Data reduction, Elastic waves, NASA, Structural analysis, Structural dynamics, Supersonic aircraft, Transonic aerodynamics, Aeroelastic response, Fighter configuration, Large amounts of data, NASA Langley Research Center, Reduced order models, Royal Institute of Technology, Transonic dynamics tunnels, Wind tunnel modeling, Wind tunnels
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-236828 (URN)2-s2.0-85048631056 (Scopus ID)9788897576280 (ISBN)
Conference
17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, 25 June 2017 through 28 June 2017
Note

QC 20181221

Available from: 2018-12-21 Created: 2018-12-21 Last updated: 2018-12-21Bibliographically approved
Silva, W. A., Chwalowski, P., Wieseman, C. D., Eller, D. & Ringertz, U. (2017). Computational results for the KTH-NASA wind-tunnel model used for acquisition of transonic nonlinear aeroelastic data. In: 58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017: . Paper presented at 58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017, 9 January 2017 through 13 January 2017. American Institute of Aeronautics and Astronautics Inc, AIAA
Open this publication in new window or tab >>Computational results for the KTH-NASA wind-tunnel model used for acquisition of transonic nonlinear aeroelastic data
Show others...
2017 (English)In: 58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017, American Institute of Aeronautics and Astronautics Inc, AIAA , 2017Conference paper, Published paper (Refereed)
Abstract [en]

A status report is provided on the collaboration between the Royal Institute of Tech- nology (KTH) in Sweden and the NASA Langley Research Center regarding the aeroelastic analyses of a full-span fighter configuration wind-tunnel model. This wind-tunnel model was tested in the Transonic Dynamics Tunnel (TDT) in the summer of 2016. Large amounts of data were acquired including steady/unsteady pressures, accelerations, strains, and measured dynamic deformations. The aeroelastic analyses presented include linear aeroelastic analyses, CFD steady analyses, and analyses using CFD-based reduced-order models (ROMs).

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics Inc, AIAA, 2017
Keywords
Aeroelasticity, Aircraft models, Data reduction, Dynamics, NASA, Structural dynamics, Supersonic aircraft, Transonic aerodynamics, Aeroelastic analysis, Computational results, Fighter configuration, Large amounts of data, NASA Langley Research Center, Reduced order models, Transonic dynamics tunnels, Wind tunnel modeling, Wind tunnels
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-207425 (URN)2-s2.0-85017344489 (Scopus ID)9781624104534 (ISBN)
Conference
58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017, 9 January 2017 through 13 January 2017
Note

QC 20170524

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-05-24Bibliographically approved
Ringertz, U., Eller, D., Keller, D. F. & Silva, W. A. (2017). Design and testing of a full span aeroelastic wind tunnel model. In: 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017: . Paper presented at 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, 25 June 2017 through 28 June 2017. International Forum on Aeroelasticity and Structural Dynamics (IFASD)
Open this publication in new window or tab >>Design and testing of a full span aeroelastic wind tunnel model
2017 (English)In: 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, International Forum on Aeroelasticity and Structural Dynamics (IFASD) , 2017Conference paper, Published paper (Refereed)
Abstract [en]

An aeroelastic wind tunnel model has been designed and built for testing in the Transonic Dynamics Tunnel. The aircraft configuration represents a modern light weight fighter with a swept wing and canards. The model is designed using composite materials for all lifting surfaces and the fuselage shell. The lifting surfaces are attached to an internal backbone structure using aluminum spars and bulkheads to transfer the aerodynamic loads to the sting. The wing design is also made with a strong internal frame to provide strong support for external stores without giving too stiff overall wing properties. External stores interfaces in the form of pylons, sway braces and pre-tension arrangements are modeled with additional detail to provide realistic kinematics. The model is heavily instrumented with accelerometers, strain gauges, and pressure taps. A unique feature of the test set-up was the use of an optical motion tracking system that made it possible to accurately measure model deformations during wind tunnel testing. A new system for unsteady pressure measurements was also used for the test providing accurate unsteady pressure data from almost 200 pressure taps on the wing surfaces. Wind tunnel testing was performed both in air and heavy gas with the model tested in three different configurations. A large amount of unique data was obtained for both static and dynamic aeroelasticty with simultaneous measurements of model deformation and wing surface pressures. 

Place, publisher, year, edition, pages
International Forum on Aeroelasticity and Structural Dynamics (IFASD), 2017
Keywords
Aeroelasticity, Flutter, Transonic, Wind tunnel, Deformation, Elastic waves, Fighter aircraft, Flutter (aerodynamics), Lift, Pressure measurement, Structural dynamics, Supersonic aircraft, Swept wings, Transonic aerodynamics, Tunnels, Wind stress, Aircraft configurations, Optical motion tracking, Simultaneous measurement, Transonic dynamics tunnels, Unsteady pressure measurements, Wind tunnel modeling, Wind-tunnel testing, Wind tunnels
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-236792 (URN)2-s2.0-85048602227 (Scopus ID)9788897576280 (ISBN)
Conference
17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, 25 June 2017 through 28 June 2017
Note

QC 20181221

Available from: 2018-12-21 Created: 2018-12-21 Last updated: 2018-12-21Bibliographically approved
Lokatt, M. & Eller, D. (2016). Finite-volume scheme for the solution of integral boundary layer equations. Computers & Fluids, 132, 62-71
Open this publication in new window or tab >>Finite-volume scheme for the solution of integral boundary layer equations
2016 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 132, p. 62-71Article in journal (Refereed) Published
Abstract [en]

An unstructured-mesh finite-volume formulation for the solution of systems of steady conservation laws on embedded surfaces is presented. The formulation is invariant to the choice of local tangential coordinate systems and is stabilized by a novel up-winding scheme applicable also to mixed-hyperbolic systems. The formulation results in a system of non-linear equations which is solved by a quasi-Newton method. While the finite volume scheme is applicable to a range of conservation laws, it is here implemented for the solution of the integral boundary layer equations, as a first step in developing a fully coupled viscous-inviscid interaction method. For validation purposes, integral boundary layer quantities computed using a minimal set of three-dimensional turbulent integral boundary layer equations are compared to experimental data and an established computer code for two-dimensional problems. The validation shows that the proposed formulation is stable, yields a well-conditioned global Jacobian, is conservative on curved surfaces and invariant to rotation as well as convergent with regard to mesh refinement.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Embedded surfaces, Finite-volume method, Integral boundary layer equations, Steady conservation laws, Unstructured meshes, Up-wind scheme
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-186926 (URN)10.1016/j.compfluid.2016.04.002 (DOI)000375814700007 ()2-s2.0-84962911736 (Scopus ID)
Note

QC 20160523

Available from: 2016-05-23 Created: 2016-05-16 Last updated: 2017-08-16Bibliographically approved
Eller, D. & Tomac, M. (2015). Implementation and evaluation of automated tetrahedral-prismatic mesh generation software. Computer-Aided Design
Open this publication in new window or tab >>Implementation and evaluation of automated tetrahedral-prismatic mesh generation software
2015 (English)In: Computer-Aided Design, ISSN 0010-4485, E-ISSN 1879-2685Article in journal (Refereed) Published
Abstract [en]

An open-source implementation of an efficient mesh generation procedure for hybrid prismatic-tetrahedral meshes intended for use in Reynolds-averaged Navier-Stokes solutions is presented. The method employed combines the established, and very fast, Delaunay-based tetrahedral mesh generator TetGen with a novel technique for the creation of a prismatic layer, where constrained global optimization of the envelope is employed. Once a well-shaped envelope is thus obtained, a semi-structured layer of pentahedral elements is extruded between wall and envelope surface. Satisfactory mesh quality is demonstrated by comparing solutions obtained using the new meshes with reference data computed on high-quality advancing-front grids. Mesh generation time is shown to be substantially smaller than with many other methods. Overall, the presented implementation is deemed a valuable tool for cases where many meshes need to be generated for routine analyses and turnaround time is critical. 

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Automatic Mesh Generation, Boundary Layer, Tetrahedral-Prismatic Mesh
National Category
Mechanical Engineering
Research subject
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-171086 (URN)10.1016/j.cad.2015.06.010 (DOI)000368951500010 ()2-s2.0-84954364489 (Scopus ID)
Note

QC 20150811

Available from: 2015-07-17 Created: 2015-07-17 Last updated: 2017-12-04Bibliographically approved
Tomac, M. & Eller, D. (2014). Towards automated hybrid-prismatic mesh generation. In: Procedia Engineering: . Paper presented at International Meshing Roundtable, IMR23 2014, 12 October 2014 through 15 October 2014 (pp. 377-389). (C)
Open this publication in new window or tab >>Towards automated hybrid-prismatic mesh generation
2014 (English)In: Procedia Engineering, 2014, no C, p. 377-389Conference paper, Published paper (Refereed)
Abstract [en]

An open-source implementation of an efficient mesh generation procedure for hybrid prismatic-tetrahedral meshes intended for use in Reynolds-averaged Navier-Stokes solutions is presented. The method employed combines the established, and very fast, Delaunay-based tetrahedral mesh generator TetGen with a novel technique for the creation of a prismatic layer. Satisfactory mesh quality is demonstrated by comparing solutions obtained using the new meshes with reference data computed on advancing-front grids. Mesh generation time is shown to be substantially less than with some other methods. Overall, the presented implementation is deemed a valuable tool for cases where many meshes need to be generated for routine analyses and turnaround time is critical. © 2014 The Authors.

Keywords
Automatic mesh generation, Boundary layers, Computational fluid dynamics, Hybrid mesh, Navier Stokes equations, Turnaround time, Hybrid meshes, Novel techniques, Open source implementation, Prismatic layers, Reynolds - Averaged Navier-Stokes, Routine analysis, Tetrahedral meshes, Mesh generation
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-168855 (URN)10.1016/j.proeng.2014.10.398 (DOI)000358739700030 ()2-s2.0-84949134695 (Scopus ID)
Conference
International Meshing Roundtable, IMR23 2014, 12 October 2014 through 15 October 2014
Note

QC 20150611

Available from: 2015-06-11 Created: 2015-06-09 Last updated: 2015-09-07Bibliographically approved
Eller, D. & Jansson, N. (2013). Efficient Laplace-Domain Aerodynamics for Load Analyses. In: : . Paper presented at International Forum on Aeroelasticity and Structural Dynamics,24-26 June 2013, Bristol. Bristol
Open this publication in new window or tab >>Efficient Laplace-Domain Aerodynamics for Load Analyses
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

An existing finite-element solver for steady, non-linear subsonic flow is extended in order to treat unsteady potential flow problems in the Laplace domain. The numerical formulation makes use of unstructured meshes including explicitly modelled, triangulated wake surfaces. Meshes can contain both linear and quadratic volume and surface elements, thus allowing to favor either very fast solution times or high spatial resolution. Aeroelastic problems are dealt with by modelling moving or deforming bodies by means of transpiration boundary conditions. Deformations of the aerodynamic mesh are computed either by projection of aerodynamic mesh nodes onto the finite elements of a structural shell model, or by radial basis function interpolation suitable for beam-type structural models. In addition to simple validation cases, an application of the solver for the evaluation of gust loads on a commuter aircraft is presented. In order to evaluate the use of the method in the context of a relevant, industrial-scale load analysis, typical geometrical and structural models for a twin-turboprop aircraft in the 15t-class (e.g. Saab 340, CN-235, Dash 8, Do 328) are employed.

Place, publisher, year, edition, pages
Bristol: , 2013
Keywords
Aeroelasticity, Flight Loads, Unsteady Aerodynamics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-124309 (URN)2-s2.0-84907301240 (Scopus ID)
Conference
International Forum on Aeroelasticity and Structural Dynamics,24-26 June 2013, Bristol
Funder
Vinnova, DNr 2009-01340
Note

QC 20130719

Available from: 2013-06-28 Created: 2013-06-28 Last updated: 2013-07-19Bibliographically approved
Tomac, M. & Eller, D. (2013). Steps Towards Automated Robust RANS Meshing. In: Proceedings of the 4:th CEAS Conference in Linkoping, 2013: . Paper presented at 4th CEAS Air & Space Conference, 16-19 September 2013, Linköping, Sweden (pp. 114-123). Linköping University Electronic Press
Open this publication in new window or tab >>Steps Towards Automated Robust RANS Meshing
2013 (English)In: Proceedings of the 4:th CEAS Conference in Linkoping, 2013, Linköping University Electronic Press, 2013, p. 114-123Conference paper, Published paper (Other academic)
Abstract [en]

The creation of high-quality discretizations for use in viscous flow simulations remains a challenging task. Even with modern software tools and substantial human effort, the application of state-of-the-art mesh generation algorithms in the presence of geometric features such as concave corners may still result in inadequate local mesh configurations, which can severely affect the resolution of important flow features. To address such issues, mesh generation tools for hybrid unstructured grids often expose a considerable number of algorithm configuration parameter. The resulting flexibility does indeed enable the creation of sufficiently resolved hybrid meshes, although the process often requires a very considerable amount of time even for an experienced user. In a production environment where a large number of detailed simulations of single aircraft configuration are performed, the cost in terms of man-hours may be acceptable. For other applications with requirements for short turn-around time, a more automated approach is desirable. Since an automatic mesh generation procedure cannot rely on user intervention for the resolution of geometric complications or edge cases, a robust strategy for the handling of the surface geometry en- countered in realistic aircraft configurations must be implemented.

The approach presented here is based on a segregated prismatic/tetrahedral mesh generation procedure, and aims to achieve robustness by means of local geometric modifications. Criteria chosen and algorithmic modifications make use of similar principles as in earlier work, but are adapted for the specific requirements of mesh generation for aircraft configura- tions. An existing set of open-source tools is exploited for mesh data structures, file format support, surface mesh generation and tetrahedral volume meshes.

The mesh generation strategy presented is based on four phases, starting with the creation of a sufficiently resolved surface mesh. In a second step, the envelope mesh of the prismatic boundary layer mesh is determined; the robustness of this stage is the primary contribution of the present work. Thirdly, tetrahedral elements are generated to fill the volume between the envelope of the prismatic layer and the farfield boundaries, and finally, pentahedral elements are grown between adapted wall and envelope mesh.

The algorithm implemented into existing open source libraries was applied to two applications presented in this study, a fairly simple wing-body-stabilizer configuration typical for a tran- sonic transport aircraft (CRM) and a rather complex, detailed geometry of a delta wing fighter prototype (F-16XL). RANS solutions converged to engineering accuracy are found to yield solutions in close agreement with meshes produced by a well established grid generator for the EDGE flow solver provided that comparable resolutions are used for both the prismatic layer and the tetrahedral domain.

When comparing mesh generation timings, an interesting observation was made. For the common situation where parallel CFD solutions are performed on a compute cluster, the analyst may be evaluating post-processed results of a simulation based on a mesh created with the method presented in this paper before a serial advancing front mesh generation has even been completed.

Obviously, this does not mean that there is no need for high-quality advancing-front mesh generation tools. A substantial proportion of relevant geometries and flight conditions likely require more detailed control over mesh generation parameters than is available in a hybrid Delaunay method. However, for routine solutions where serial mesh generation time is a bottleneck, the libraries including the present method can be used to accelerate the turnaround time considerably.

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2013
Keywords
Hybrid mesh generation, Automatic mesh generation, Computational Fluid Dynamics
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-129596 (URN)978-91-7519-519-3 (ISBN)
Conference
4th CEAS Air & Space Conference, 16-19 September 2013, Linköping, Sweden
Note

QC 20131022

Available from: 2013-10-02 Created: 2013-10-02 Last updated: 2013-10-22Bibliographically approved
Eller, D. (2012). Fast, Unstructured-Mesh Finite-Element Method for Nonlinear Subsonic Flow. Journal of Aircraft, 49(5), 1471-1479
Open this publication in new window or tab >>Fast, Unstructured-Mesh Finite-Element Method for Nonlinear Subsonic Flow
2012 (English)In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 49, no 5, p. 1471-1479Article in journal (Refereed) Published
Abstract [en]

A variable-order finite-element method for the solution of the steady nonlinear potential flow equations is presented. To achieve robustness and computational efficiency, the formulation is restricted to purely subsonic flow by means of a density Modification in sonic flow regions. A test case that triggers the activation of this modification is presented to show that the method yields pressure results that are very close to those obtained with a mature Euler solver while reducing computational cost by an order of magnitude. Linear and quadratic elements are implemented, and the substantial benefit of using higher-order elements is demonstrated by means of a mesh-convergence study, showing how the convergence of induced drag and neutral point location is improved by the use or quadratic elements. For large surface meshes, the computational cost is found to be competitive with a linearized-potential boundary-element code accelerated by panel clustering.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2012
Keywords
Finite elements, potential flow, aerodynamics
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-104608 (URN)10.2514/1.C031738 (DOI)000309736200028 ()2-s2.0-84868565749 (Scopus ID)
Note

QC 20121108

Available from: 2012-11-08 Created: 2012-11-07 Last updated: 2017-12-07Bibliographically approved
Tomac, M. & Eller, D. (2011). From geometry to CFD grids-An automated approach for conceptual design. Progress in Aerospace Sciences, 47(8), 589-596
Open this publication in new window or tab >>From geometry to CFD grids-An automated approach for conceptual design
2011 (English)In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 47, no 8, p. 589-596Article, review/survey (Refereed) Published
Abstract [en]

The CEASIOM software developed in the EU-funded collaborative research project SimSAC generates stability and control data for preliminary aircraft design using different methods of varying fidelity. In order to obtain the aerodynamic derivatives by CFD, the aircraft geometry must be defined, computational meshes generated, and numerical parameters set for the flow solvers. An approach to automation of the process is discussed, involving geometry generation and mesh generation for inviscid as well as RANS flow models.

Keywords
Aircraft design, Aerodynamics, Mesh generation, Automated analysis, Computational fluid dynamics, Simulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-61001 (URN)10.1016/j.paerosci.2011.08.005 (DOI)000298126800003 ()2-s2.0-81155134851 (Scopus ID)
Note
QC 20120116Available from: 2012-01-16 Created: 2012-01-16 Last updated: 2017-12-08Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3199-8534

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