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  • 1.
    Eller, David
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    An Efficient Boundary Element Method for Unsteady Subsonic Aerodynamics in the Time Domain: Theory and Application Exemples2003Report (Other academic)
  • 2.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    An efficient method for time-domain low-speed aerodynamics: Theory and examples2005Report (Other academic)
  • 3.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efficient flight mechanics simulation of elastic aircraft configurations2005Conference paper (Other academic)
  • 4.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Fast, Unstructured-Mesh Finite-Element Method for Nonlinear Subsonic Flow2012In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 49, no 5, p. 1471-1479Article in journal (Refereed)
    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.

  • 5.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Flutter Equation as a Piecewise Quadratic Eigenvalue Problem2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 3, p. 1068-1070Article in journal (Refereed)
  • 6.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Friction, Freeplay and Flutter of Manually Controlled Aircraft2007In: IFASD 2007: International Forum on Aeroelasticity and Structural Dynamics, 2007Conference paper (Other academic)
    Abstract [en]

    The effect of nonlinear friction and freeplay in the control system on flut- ter is investigated for the case of light aircraft with manually operated control surfaces. A standard linear modal subspace model of the aeroelastic system is extended with nonlinear terms, so that time-domain simulations can be per- formed. Furthermore, the harmonic balance method is employed to obtain a frequency-domain formulation, which allows a convenient, though approxi- mate, computation of the stability boundary. Comparison with time-domain analyses for the case of a full aircraft configuration show that typical magni- tudes of hinge friction can stabilize oscillations with small displacement am- plitudes, while large amplitude motion remains unstable. Harmonic balance methods can be used to determine if such a behavior is present, but time- domain computations are necessary to evaluate the response of the system to a given excitation.

  • 7.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Non-iterative solution of the flutter eigenvalue problem using Laplace-domain aerodynamic loads.2009In: IFASD 2009, 2009Conference paper (Other academic)
    Abstract [en]

    An efficient method for the non-iterative solution of the nonlinear flutter eigenvalue problem is presented. The properties of the piecewise quadratic decomposition employed make it particularly suitable for the parallel solution of aeroelastic stability problems where interaction of rigid-body and elastic motion is of interest or where the flutter damping must be obtained with accuracy, e.g. when comparison to flutter flight testing is intended. Ad- ditionally, the method allows the use of Laplace-domain aerodynamics if available. The paper presents a realistically complex test case which exposes some of the advantages and current shortcoming of the proposed solution procedure.

  • 8.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    On an Efficient Method fo Time-Domain Computational Aeroelasticity2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The present thesis summarizes work on developing a method for unsteady aerodynamic analysis primarily for aeroelastic simulations. In contrast to widely used prediction tools based on frequency-domain representations, the current approach aims to provide a time-domain simulation capability which can be readily integrated with possibly nonlinear structural and control system models. Further, due to the potential flow model underlying the computational method, and the solution algorithm based on an efficient boundary element formulation, the computational effort for the solution is moderate, allowing time-dependent simulations of complex configurations. The computational method is applied to simulate a number of wind-tunnel experiments involving highly flexible models. Two of the experiments are utilized to verify the method and to ascertain the validity of the unsteady flow model. In the third study, simulations are used for the numerical optimization of a configuration with multiple control surfaces. Here, the flexibility of the model is exploited in order to achieve a reduction of induced drag. Comparison with experimental results shows that the numerical method attains adequate accuracy within the inherent limits of the potential flow model. Finally, rather extensive aeroelastic simulations are performed for the ASK 21 sailplane. Time-domain simulations of a pull-up maneuver and comparisons with flight test data demonstrate that, considering modeling and computational effort, excellent agreement is obtained. Furthermore, a flutter analysis is performed for the same aircraft using identified frequency-domain loads. Results are found to deviate only slightly from critical speed and frequency obtained using an industry-standard aeroelastic analysis code. Nevertheless, erratic results for control surface hinge moments indicate that the accuracy of the present method would benefit from improved control surface modeling and coupled boundary layer analysis.

  • 9.
    Eller, David
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    On an efficient method for time-domain unsteady aerodynamics2003Licentiate thesis, comprehensive summary (Other scientific)
  • 10.
    Eller, David
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Carlsson, Martin
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    An efficient aerodynamic boundary element method for aeroelastic simulations and its experimental validation2003In: Aerospace Science & Technology, ISSN 1270-9638, Vol. 7, no 7, p. 532-539Article in journal (Refereed)
  • 11.
    Eller, David
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Heinze, Sebastian
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    A computational study on the use of redundant control surfaces to improve the induced drag of aeroelastic configurations2003Report (Other academic)
  • 12.
    Eller, David
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Heinze, Sebastian
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    An approach to induced drag reduction and its experimental evaluation2004Conference paper (Refereed)
    Abstract [en]

    An approach to minimize the induced drag of an aeroelastic configuration by means of multiple leading and trailing edge control surfaces is investigated. A computational boundary-element model is constructed and flap settings which reduce the induced drag predicted by the model are found by means of numerical optimization. Further, experiments with an elastic wind tunnel model are performed, showing both the potential for drag reduction and weaknesses of the simulation method employed.

  • 13.
    Eller, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Heinze, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Approach to Induced Drag Reduction with Experimental Evaluation2005In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 42, no 6, p. 1478-1485Article in journal (Refereed)
    Abstract [en]

    An approach to minimize the induced drag of an aeroelastic configuration by means of multiple leading- and trailing-edge control surfaces is investigated. A computational model based on a boundary-element method is constructed and drag-reducing flap settings are found by means of numerical optimization. Further, experiments with an elastic wind-tunnel model are performed in order to evaluate the numerically obtained results. Induced-drag results are obtained by analyzing lift distributions computed from optically measured local angles of attack because standard techniques proved insufficient. Results show that significant reductions of induced drag of flexible wings can be achieved by using optimal control surface settings.

  • 14.
    Eller, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Jansson, Natascha
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Efficient Laplace-Domain Aerodynamics for Load Analyses2013Conference 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.

  • 15.
    Eller, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Aeroelastic Simulations of a Sailplane2005Report (Other academic)
  • 16.
    Eller, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Tomac, Maximilian
    FS Dynamics Sweden AB.
    Implementation and evaluation of automated tetrahedral-prismatic mesh generation software2015In: Computer-Aided Design, ISSN 0010-4485, E-ISSN 1879-2685Article in journal (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, 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. 

  • 17.
    Jansson, Natascha
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Robust Turbulence Load Alleviation2011In: IFASD 2011: International Forum on Aeroelasticity and Structural Dynamics, 2011Conference paper (Other academic)
    Abstract [en]

    Using a comparatively detailed aeroelastic model for a generic commuter aircraft, a turbulence load alleviation system is designed with the objective of reducing structural fatigue. An H-optimal controller for the nominal model is found to be highly sensitive to small disturbances in the control system dynamics, so that a slightly perturbed closed-loop model is destabilized. Robust control methods are exploited to construct an alternative controller which improves robustness to disturbances at a small cost in nominal performance. Finally, fatigue loads experienced by the (open-loop and controlled) model are evaluated by means of two different load reconstruction methods, showing that the simpler modal displacement approach may introduce significant errors in wing bending moments.

  • 18.
    Lokatt, Mikaela
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    A study of unsteady aerodynamic loads on a natural laminar flow wing model2017Manuscript (preprint) (Other academic)
  • 19.
    Lokatt, Mikaela
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Experimental validation of a viscous-inviscid interaction model2017Manuscript (preprint) (Other academic)
  • 20.
    Lokatt, Mikaela
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Finite-Volume Scheme for the Solution of Integral Boundary Layer EquationsManuscript (preprint) (Other academic)
  • 21.
    Lokatt, Mikaela
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Finite-volume scheme for the solution of integral boundary layer equations2016In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 132, p. 62-71Article in journal (Refereed)
    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.

  • 22.
    Lokatt, Mikaela
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Robust Viscous-Inviscid Interaction Scheme for Application on Unstructured MesheManuscript (preprint) (Other academic)
  • 23.
    Lokatt, Mikaela
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Robust viscous-inviscid interaction scheme for application on unstructured meshes2017In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 145, p. 37-51Article in journal (Refereed)
    Abstract [en]

    A coupled viscous-inviscid interaction scheme combining the continuity equation for potential flow with the three-dimensional integral boundary layer equations is presented. The inviscid problem is discretized by a finite-element approach whereas an upwind-biased finite-volume scheme is employed for the boundary layer equations. The discretization is applicable to unstructured tetrahedral-triangular meshes and results in a sparse system of non-linear equations which is solved by a Newton-type method. The mathematical reasons for the singularities commonly associated with the integral boundary layer equations in separated flow regions are analyzed and the connection between the mathematical singularities and the numerical ill-conditioning is discussed. It is shown that, by a suitable choice of closure relations, it is possible to obtain a boundary layer model free from numerical ill-conditioning in separated flow regions. The accuracy of the coupled viscous-inviscid model is investigated in a number of test cases including transitional and mildly separated flow over two different natural laminar flow airfoils and three-dimensional flow over a swept wing. It is concluded that the coupled method is able to provide reasonably accurate predictions of viscous and inviscid flow field quantities for the investigated cases.

  • 24.
    Ringertz, Ulf
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Keller, D. F.
    Silva, W. A.
    Design and testing of a full span aeroelastic wind tunnel model2017In: 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, International Forum on Aeroelasticity and Structural Dynamics (IFASD) , 2017Conference 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. 

  • 25. Silva, W. A.
    et al.
    Chwalowski, P.
    Wieseman, C. D.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Computational results for the KTH-NASA wind-tunnel model used for acquisition of transonic nonlinear aeroelastic data2017In: 58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017, American Institute of Aeronautics and Astronautics Inc, AIAA , 2017Conference 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).

  • 26. Silva, W. A.
    et al.
    Chwalowski, P.
    Wieseman, C. D.
    Keller, D. F.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Computational and experimental results for the KTH-NASA wind-tunnel model used for acquisition of transonic nonlinear aeroelastic data2017In: 17th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2017, International Forum on Aeroelasticity and Structural Dynamics (IFASD) , 2017Conference 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. 

  • 27. Silva, W. A.
    et al.
    Ringertz, Ulf Torbjörn
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stenfelt, Gloria
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Keller, D. F.
    Chwalowski, P.
    Status of the KTH-NASA wind-tunnel test for acquisition of transonic nonlinear aeroelastic data2016In: 15th Dynamics Specialists Conference, American Institute of Aeronautics and Astronautics Inc , 2016Conference paper (Refereed)
    Abstract [en]

    This paper presents a status report on the collaboration between the Royal Institute of Technology (KTH) in Sweden and the NASA Langley Research Center regarding the design, fabrication, modeling, and testing of a full-span fighter configuration in the Transonic Dynamics Tunnel (TDT). The goal of the test is to acquire transonic limit-cycle- oscillation (LCO) data, including accelerations, strains, and unsteady pressures. Finite element models (FEMs) and aerodynamic models are presented and discussed along with results obtained to date.

  • 28.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    From geometry to CFD grids-An automated approach for conceptual design2011In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 47, no 8, p. 589-596Article, review/survey (Refereed)
    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.

  • 29.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    From geometry to CFD-based aerodynamic derivatives - an automated approach2010In: 27th Congress of theInternaitonal Council of the Aeronautical Sciences, 19-24 Sept 2010, Nice, France: Volume 1, 2010, p. 762-774Conference paper (Refereed)
  • 30.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Steps Towards Automated Robust RANS Meshing2013In: Proceedings of the 4:th CEAS Conference in Linkoping, 2013, Linköping University Electronic Press, 2013, p. 114-123Conference 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.

  • 31.
    Tomac, Maximillian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Towards automated hybrid-prismatic mesh generation2014In: Procedia Engineering, 2014, no C, p. 377-389Conference 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.

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