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  • 1. Frink, N. T.
    et al.
    Tomac, Maximillian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Collaborative study of incipient separation on 53°-swept diamond wing2016In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219Article in journal (Refereed)
    Abstract [en]

    A systematic analysis of incipient separation and subsequent vortex formation from moderately-swept blunt leading edges is presented for a 53°-swept diamond wing. This work contributes to a collective body of knowledge generated within the multinational NATO/STO AVT-183 Task Group titled "Reliable Prediction of Separated Flow Onset and Progression for Air and Sea Vehicles". Details of vortex formation are inferred from numerical solutions of two flow solvers after establishing a good correlation of the global flow field and surface pressure distributions with those from wind tunnel measurements. From this, significant and sometimes surprising insights into the nature of incipient separation and part-span vortex formation are derived from the wealth of information available in the computational solutions.

  • 2.
    Goetzendorf-Grabowski, Tomas
    et al.
    Institute of Aeronautics & Applied Mechanics, Aircraft Design Department, Warsaw University of Technology, 00-665 Warsaw, Poland.
    Vosy, J.B.
    Sanchiz, S.
    Molitor, Paul
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Tomac, Maximilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Coupling Adaptive-Fidelity CFD with S&C Analysis to Predict Flying Qualities2009In: 27th AIAA Applied Aerodynamics Conference, 2009Conference paper (Refereed)
    Abstract [en]

    CEASIOM, the Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods, is a framework tool that integrates discipline-specific tools for conceptual design. At this early stage of the design it is very useful to be able to predict the °ying and handling qualities of this design. In order to do this, the aerodynamic database needs to be computed for the configuration being studied which then has to be coupled to the stability and control tools to carry out the analysis. This paper describes how the adaptive-fidelity CFD module of CEASIOM computes the aerodynamic dataset of an air craft configuration, and how that dataset is analyzed by the SDSA module to determine the °ying qualities of the aircraft. These predicted °ying qualities are then compared with the °ight-test data of the Ranger 2000 trainer aircraft in order to verify the goodness of the overall approach.

  • 3. Mendenhall, M.R.
    et al.
    Perkins, S.C.
    Tomac, Maximilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Nangia, Raj K.
    Nangia Aero Research Associates.
    Comparing and benchmarking engineering methods for the prediction of X-31 aerodynamics2012In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 20, no 1, p. 12-20Article in journal (Refereed)
    Abstract [en]

    A number of useful engineering methods are available for fast and economic estimates of the aerodynamic characteristics of complex flight vehicles. This article investigates the application of three specific engineering methods to the X-31 fighter configuration, and CFD, wind tunnel, and flight test data are used for comparison and evaluation purposes. The emphasis is on static longitudinal stability aspects up to high angles of attack; however, selected asymmetric and unsteady effects are considered. Results from the engineering methods are in good agreement with experiment and CFD for angles of attack up to 15° for most cases and higher angles for some cases. Results for pitching moment are in good agreement with CFD, but many of the nonlinear characteristics of the airplane are not predicted by the engineering methods. The quality of the longitudinal stability results is discussed in terms of the prediction of the center of pressure on the vehicle. The results provide improved understanding of the continued usefulness of engineering methods as an analysis tool during the design phase and into the flight test diagnostic phase of a new aircraft.

  • 4.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Oppelstrup, Jesper
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis, NA.
    Zhang, Mengmeng
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Tomac, Maximillian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Coupling parametric aircraft lofting to CFD & CSM grid generation for conceptual design2011In: 49th AIAA Aerospace Sciences Meeting, 2011, 2011Conference paper (Refereed)
  • 5.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Tomac, Maximilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Nangia, Raj
    Nangia Aero Research Associates.
    Mendenhall, M.
    Engineering methods for SACCON configurationsIn: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868Article in journal (Refereed)
  • 6.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Tomac, Maxmilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirasek, Adam
    Cavagna, Luca
    Riccobene, Luca
    Ricci, Sergio
    Computation of Aeroelastic Effects on F-16XL at Flight Conditions FC70 and FC252017In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, no 2, p. 409-416Article in journal (Refereed)
    Abstract [en]

    This article presents an aeroelastic study of CAWAPI F-16XL aircraft. The structural model of this aircraft is not publicly available and is therefore replaced by a structural model estimate that is constructed based on data available in public literature. The aeroelastic solution is done using solution for two flight conditions-FC70 and FC25. The primary task is to assess the importance of the aeroelastic effects on the FC70 solution and to assess whether large discrepancies are observed at flight condition FC70 between the computational and experimental data.

  • 7.
    Tomac, Maximilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Adaptive-fidelity CFD for predicting flying qualities in preliminary aircraft design2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    To reduce development cost and to avoid late design fixes in aircraft design, methods that are fast and economic in estimating the aerodynamic characteristics of complex flight vehicles at the preliminary design stage are desired. This work and thesis focus on the adaptive-fidelity CFD approach, with emphasis on the high end of the CFD tools available today.

    The core idea of the method is to use computationally cheap modeling in the part of the flight envelope where it is applicable. When the complexity in the flow field increases more details and realism is included in the mathematical model, at a computationally higher cost. A typical case where this would be required could be at the border of the flight envelope, where flow phenomena such as shocks, flow separation, and interacting vortex systems could occur.

    Since the number of cases needed to resolve the flight envelope could be in the order of ten thousands automation is required. The bottlenecks are the discretization of the fluid volume and evaluation of raw CFD data and post processing of the data. These issues are also discussed in this work.

    The method has been tested on two real flying aircraft, the X-31 delta-winged aircraft with vector thrust, and the Ranger 2000 Jet trainer, as well as on the SACCON preliminary wing-body UCAV design. The results provide improved understanding of the usefulness of this method as an analysis tool during the preliminary design phase all the way into the flight test diagnostic phase of a new aircraft.

     

  • 8.
    Tomac, Maximilian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Towards Automated CFD for Engineering Methods in Aircraft Design2014Doctoral thesis, comprehensive summary (Other academic)
  • 9.
    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.

  • 10.
    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)
  • 11.
    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.

  • 12.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirasek, Adam
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulations of F-16XL in Low-Speed High-Alpha Flight2017In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, no 6, p. 2070-2076Article in journal (Refereed)
    Abstract [en]

    This paper reports on the computational fluid dynamics study of flow around the F-16XL aircraft in low-speed high-alpha flight. Previous work established that the computed pressure for this case compared less favorably with those measured in flight tests than did similar comparisons for cases at lower angles of attack. One reason suggested for the discrepancy was that the flow over the outer-wing panel was unsteady. This paper presents time-accurate computations with physical modeling that can capture such unsteady flow phenomena, namely, so-called hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation modeling. The simulations obtained are compared with those measured during flight testing of the vehicle as well as with results computed with more conventional steady physical modeling. Over the outer wing panel, the unsteady simulations compare substantially better than the steady results with the flight-test data, confirming unsteady aerodynamic effects are at play. At the inner-wing locations, the correlations among the simulations (unsteady and steady) and with the flight test are good, confirming the suspicion that the flow is mostly steady there. Although differences are found among all the results compared, they are not exceedingly large; but, the conclusion that unsteady aerodynamic effects are at play over the outer-wing panel are undeniable.

  • 13.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    CFD study of vortex separation phenomena on blunt diamond wing2015In: 53rd AIAA Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics, 2015Conference paper (Refereed)
    Abstract [en]

    The details of how a vortex lifts off a blunt swept leading edge are not so well understood, and this paper undertakes a comprehensive CFD study of the phenomena. Current day experience shows that the location for the start of the vortex depends on the grid resolution of the numerical solution and the physical modeling used to account for the turbulence in the flow. In this work multiple levels of grid refinement, together with ap- propriate adaptation of the grids, are carried out to the extent that stabilizes the location of the separation. Various turbulence models are also used in combination with the grid sequencing showing a strong effect on vortex separation position due to chosen turbulence model.

  • 14.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Creation of aerodynamic database for the X-312010In: 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010, p. 2010-0501-Conference paper (Refereed)
    Abstract [en]

    Adaptive fidelity computional fluid dynamics (CFD) uses CFD tools spanning from vortexlattice methods codes to more advanced inviscid Euler solvers and finally URANS (Unsteady Reynolds Averaged Navier Stokes) CFD solvers. At the high end the automatization process is no longer a simple straight forward task, for this purpose a script-driven tool has been developed for integration into the multi-fidelity framework CEASIOM developed in the SimSAC project. The scripting technologies to prepare, conduct, post-process and collect aerodynamic forces & moments into the aero-dataset. The tool together with the CEASIOM framework has been applied to the X-31 to create an aerodynamic dataset that is then analyzed by the stability & control tool SDSA to assess the modes of motion inherent in the dataset.

  • 15.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirásek, A.
    Factors influencing accurate shock vortex interaction prediction on F-16XL aircraft2014In: 52nd Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics Inc , 2014Conference paper (Refereed)
    Abstract [en]

    Computational Fluid Dynamics methods continues to play an increasingly important role in design and validation. Some examples are conditions that cannot be tested prior to fight test. In order to rely on these methods it is essential that these methods are validated and evaluated to state-of-the-art wind tunnel test and/or in-fight data. In a previous project “Cranked-Arrow Wing Aerodynamics Project International” (CAWAPI)it was clear that all CFD methods failed to some degree in the transonic regime where shock vortex interaction phenomena was present. Detailed analysis of surface pressure distribution showed that CFD where not able replicate the correct flow field and produce acceptable results. This paper aim to map out the fight conditions for which CFD is likely to fail, and try to answer or shed light in the question why? This with the main focus on the factors that influence shock vortex interaction in the flow field.

  • 16.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Jirásek, A.
    Swedish Defernce Research Agency, FOI, Stockholm, Sweden .
    Low speed high alpha prediction on F-16XL aircraft2014In: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014, American Institute of Aeronautics and Astronautics, 2014Conference paper (Refereed)
    Abstract [en]

    This article presents the comparisons of the results of the CFD study around the F- 16XL CAWAPI configuration. The progress since the original CAWAPI has been made on the solver side by implementing several numerical techniques improving convergence of the numerical process as well as lowering numerical viscosity needed to stabilize the calculations. In addition, innovative hybrid RANS-LES model (HYB0) has been tested and a new much denser grid has been generated.

  • 17.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Nangia, R. K.
    Mendenhall, M. R.
    Perkins Jr., S. C.
    Comparing & benchmarking engineering methods on the prediction of X-31 aerodynamics2010In: 28th AIAA Applied Aerodynamics Conference, 2010, p. 2010-4694-Conference paper (Refereed)
    Abstract [en]

    NATO RTO-AVT-161 is an assessment of Stability and Control Prediction Methods for NATO Air and Sea Vehicles. Though the assessment includes the use of advanced CFD methods, a number of useful engineering methods are available for fast and economic estimates of the aerodynamic characteristics of complex flight vehicles. The objective of this paper is to investigate the use of three specific engineering methods on the X-31 fighter configuration for which CFD, wind tunnel, and flight test data are available for comparison and evaluation purposes. The emphasis is on static longitudinal stability aspects up to high angles of attack; however, selected asymmetric and unsteady effects are considered. Results from the engineering methods are in good agreement with experiment and CFD for angles of attack up to 15 degrees for most cases and higher angles for some cases. Results for pitching moment are in good agreement with CFD, but many of the nonlinear characteristics of the airplane are not predicted by the engineering methods. The quality of the longitudinal stability results is discussed in terms of the prediction of the center of pressure on the vehicle. The results provide improved understanding of the continued usefulness of engineering methods as an analysis tool during the design phase and into the flight test diagnostic phase of a new aircraft.

  • 18.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Nangia, R. K.
    Mendenhall, M. R.
    Perkins Jr., S. C.
    Engineering methods on the SACCON configuration - Some design considerations2010In: 28th AIAA applied aerodynamics conference 2010, American Institute of Aeronautics and Astronautics, 2010, p. 2010-4398-Conference paper (Refereed)
  • 19.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Nangia, Raj K.
    Consulting Engineering Nangia Aero Research Associates, Clifton, Bristol, UK.
    Mendenhall, Michael R.
    Nielsen Engineering & Research, Inc. Santa Clara, USA.
    Perkins, Stanley C.
    Nielsen Engineering & Research, Inc. Santa Clara, USA.
    Engineering methods applied to a UCAV configuration: some aerodynamic design considerationsIn: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868Article in journal (Other academic)
  • 20.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzit, A
    Charbonnier, D.
    Vos, J. B.
    Jirásek, A.
    Peng, S. -H
    Winkler, A.
    Allen, A.
    Wissocq, G.
    Puigt, G.
    Dandois, J.
    Abarca-Lopez, R.
    Unsteady aero-loads from vortices shed on A320 landing gear door: CFD compared to flight tests2016In: 54th AIAA Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics, 2016Conference paper (Refereed)
    Abstract [en]

    AFLoNext is a project of four years duration, funded by the European Commission within the Seventh Framework Programme. The project’s main objectives are proving and maturing highly promising flow control and noise reduction technologies for novel aircraft configurations, to achieve a big step forward towards improved aircraft performance and thus reducing the environmental footprint. The project consortium is composed by 40 European partners from 15 countries. One of the six technology streams, which are forming the scientific concept of AFLoNext, is concerned with the mitigation and control of vibrations in the undercarriage area during take-off and landing. Structural components in the vicinity of the landing gears, e.g. undercarriage housing walls, struts or landing gear doors, are often subject to significant dynamic loading. These loads originate from fluctuating aerodynamic pressures and resulting structural vibrations. Unsteady pressures on structural parts are caused by highly fluctuating and complex aerodynamic flow behavior under the fuselage. The paper describes the CFD approach employed to predict such dynamic loads and presents some preliminary results that have been computed with hybrid RANS-LES models and the Lattice Bolzmann method. Several vibration control devices have been proposed and are discussed in the paper. Some of these devices will be installed in the near future on the DLR Airbus 320 ATRA (Advanced Technology Research Aircraft) to perform flight tests to and to measure dynamic loads.

  • 21.
    Tomac, Maximilian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Stenfelt, Gloria
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Predictions of stability and control for a flying wing2014In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 39, p. 179-186Article in journal (Refereed)
    Abstract [en]

    The numerical simulation of a generic reduced radar signature tailless aircraft is considered. Investigation compares simulated data to low-speed wind tunnel experiments. Focus is on numerical predictions of steady longitudinal and lateral aerodynamics and influence of control surfaces on aerodynamic forces. Fully turbulent and transitional Reynolds Averaged Navier-Stokes (RANS) simulations predicted in agreement with experiment unstable pitch characteristics for low angles of attack (alpha), this was not the case for inviscid or laminar simulations. However, all simulations captured a sudden rapid increase in nose up pitch moment at higher angles of attack compared to experiments. Time accurate computations (URANS) captured non-linearity and unsteadiness in yaw moment with respect to differential split flap deflections for the studied angles of attack.

  • 22. Tomac, Maximilian
    et al.
    Tormalm, M.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stability and control assessment of a generic UCAV design using the edge flow solver2014In: 32nd AIAA Applied Aerodynamics Conference, 2014Conference paper (Refereed)
    Abstract [en]

    Accurate estimations of control effectiveness are crucial for flight mechanical model development to assess controllability. Any deficiency in the design should be corrected at an early stage. An increased interest in Unmanned Combat Aerial Vehicles (UCAV) has put focus on the controllability of low observable platforms with highly sweep delta wings without the traditional fin. The NATO STO task group AVT-201 was formed to meet this stability and control challenge and build on previous knowledge gained on complex vortical flow of rounded leading-edge delta wings. This paper presents the numerical results, using the FOI developed flow solver Edge, of the common cases for the DLR-F19 model. The effect of trailing-edge ap deections was investigated using steady RANS or time-accurate hybrid RANS-LES methods. Both static and dynamic pitch cases at low speed and high angle of attack were evaluated and compared to experimental data.

  • 23.
    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.

  • 24.
    Tomac, Maximillian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Pettersson, Karl
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Calibration and verification of a γ - Reθt transition prediction method for airfoil computations2013In: 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013, 2013Conference paper (Refereed)
    Abstract [en]

    This paper deals with the implementation and verification of a γ - Reθt correlation based transition prediction method previously presented by Langtry et al. The two additional transport equations used for predicting transition and a novel set of equations for the production terms are implemented into the Computational Fluid Dynamics code Edge. The model predicts two-dimensional transition phenomena such as transition due to Tollmein-Schlichting instabilities, bypass transition and separation induced transition. The transition prediction model is calibrated to the well-known Ercoftac wind tunnel tests using an optimization program based on a direct search method available in Matlab. The model is tested with several non-calibrated cases comparable with industry standard airfoils (low speed, transonic) and wind tunnel experiments as well as the MSES code that uses a en method. The main part of this work was performed as part of the research project Aerodynamic Loads Estimation at Extremes of the Flight Envelope (ALEF) (Grant Agreement no: 211785), 7th EU framework program.

  • 25.
    Tomac, Maximillian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirasek, A.
    Computational Fluid Dynamics Predictions of Control-Surface Effects for F-16XL Aircraft2017In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, no 2, p. 395-408Article in journal (Refereed)
    Abstract [en]

    Computational fluid dynamics methods play an increasingly important role in aircraft design and development. Some examples are conditions that cannot be tested before a flight test. To rely on these methods, it is essential that they are assessed and evaluated with a state-of-the-art wind tunnel test and/or in-flight data. In a previous project, Cranked-Arrow Wing Aerodynamics Project International, it was reported that all computational fluid dynamics methods failed to some degree in the transonic regime where shock-vortex interaction phenomena were present. Detailed analysis of surface pressure distribution showed that computational fluid dynamics was not able replicate the correct flowfield and produce acceptable results. This paper aims to restudy those transonic flight conditions for which computational fluid dynamics underperforms and to try to determine or shed light on the extent to which surface effects contribute to the computational fluid dynamics predictions.

  • 26.
    Tomac, Maximillian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Nangia, R. K.
    Mendenhall, M. R.
    Perkins, S. C.
    Engineering methods applied to an unmanned combat air vehicle configuration2012In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 49, no 6, p. 1610-1618Article in journal (Refereed)
    Abstract [en]

    Engineering methods provide fast and economic predictions of the aerodynamic characteristics of complex flight vehicles. This paper investigates the application of three specific engineering methods to a unmanned combat air vehicle (UCAV) configuration, termed the Stability and Control Configuration (SACCON), that is still under investigation and that is the subject of an intensive computational and experimental study by the NATO Research and Technology Organization task group AVT-161 for better understanding of its stability and control characteristics. Computational fluid dynamics (CFD) data are computed for theSACCONat wind-tunnel conditions and are compared and evaluated against the measured values, especially in terms of their implications for low-speed longitudinal flight characteristics. Because of their reduced-order modeling compared with Reynolds-averaged Navier-Stokes CFD, predictions by the engineering methods are restricted to the flight-condition range governed by linear flow physics, which, for the SACCON in low speed is 0 α 10 deg. Despite the limited range in angle of attack, it was discovered that, due to the large sweep angle of theSACCONwing and its tip section of zero taper ratio, peak suction levels at the tip were so high that the boundary layer separated there instead. This viscous effect caused a discrepancy between the predicted and measured values of the pitching moment. The remedy taken was to increase the washout for theSACCONwing by modifying its twist and camber, and predictions made for this shape confirmed that linear flow physics prevailed then and that the static stability margin was increased. Furthermore, a series of predictions were made at high speed to establish the drag-divergence Mach numberMdd. The investigations carried out here demonstrate the continued usefulness of engineering methods not only as an analysis tool during the initial aircraft design phase but also as a design tool to improve the shape definition of the vehicle to achieve better performance.

  • 27.
    Tomac, Maxmillian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Oppelstrup, Jesper
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis, NA (closed 2012-06-30).
    From geometry to CFD grids - An automated approach for conceptual design2010In: AIAA Atmospheric Flight Mechanics Conference 2010, 2010Conference paper (Refereed)
  • 28.
    Zhang, Mengmeng
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Tomac, Maximillian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Wang, Cong
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Variable fidelity methods and surrogate modeling of critical loads on X-31 aircraft2013In: 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013, American Institute of Aeronautics and Astronautics, 2013Conference paper (Refereed)
    Abstract [en]

    This paper presents a method for effcient creation of the aerodynamic database for the X-31 experimental aircraft, from low fidelity (Euler) and high fidelity (RANS) CFD. The challenge is to obtain good data for extreme flight conditions. A co-Kriging interpolation model for aerodynamic moments, forces and span loads is used, with an additional decision support system (DSS) using Proper Orthogonal Decomposition for data reduction.

1 - 28 of 28
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