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  • 51.
    Mengmeng, Zhang
    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.
    Transonic airfoil and wing design using inverse and direct methods2015In: 53rd AIAA Aerospace Sciences Meeting, Kissimmee, Florida: American Institute of Aeronautics and Astronautics, 2015Conference paper (Refereed)
    Abstract [en]

    A hybrid inverse/direct-optimization method for subsonic/transonic airfoil and wing shape design is presentedwith application to a range of airfoil and wing cases, in preparation for the test cases defined for the Special Sessionof SciTech 2015. The method is hybrid in the sense that it combines the traditional inverse design technique witha gradient-based procedure to approach the optimum aerodynamic surface. This paper emphasizes the first part, thedevelopment of SCID, the Surface Curvature Inverse Design method, the theory upon which it is based, includingmany of the details involved with shocks, smoothing and cross flow. The application of SCID to wing design posesmany challenges, and how they are met is discussed in the context of a number of inverse design test cases for airfoilsand wings. But it also includes results from the adjoint optimization and compares them. The procedure workswell for airfoils and the twist optimization for wings. The real benchmarks for our hybrid approach are the threeOptimization Discussion Group design problems. Solutions are presented for the drag minimization of the airfoil testcases along with the wing twist optimization problem, and conclusions are drawn from the results obtained. A swept-back transonic wing is designed by SCID with encouraging results, showing that SCID works fine with wings. Workhas started on the drag minimization of the CRM wing in transonic flight, and final results will be presented in a futurepaper.

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  • 52.
    Mengmeng, Zhang
    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.
    Raymer, D.
    Enhancement of CEASIOM with Rapid-Meshing Tool for Aircraft Conceptual Design2012In: Aerotecnica Missili & Spazio, The journal of Aerospace Science, Technology and Systems, E-ISSN 2524-6968, Vol. 91, no 3/4, p. 79-85Article in journal (Refereed)
    Abstract [en]

    This paper details the development and application of the RDS-SUMO-CEASIOM-EDGE rapid-CFD tool. It uses theRDS CAD model as geometry for automated meshing and CFD analysis to produce an aero-data base for control andstability analysis. It is applied to two non-conventional design proposals, an asymmetric twin-prop aircraft and anairliner with rear Open Rotor propulsion, retractable canard, and a “chin-rudder” instead of vertical tail. For bothconfigurations,yaw control is problematic, and the stability and control analysis is used to assess control surface sizing and stabilityaugmentation system.

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  • 53.
    Merino Martínez, Roberto
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Design and Analysis of the Controland Stability of a Blended WingBody Aircraft2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Future aircraft generations are required to have higher performance and capacities.

    This achievement should be fulfilled with the minimum cost and environmental

    impact. This calls for the design of new unconventional configurations, such as the

    Blended Wing Body (BWB), a tailless aircraft which integrates the wing and the

    fuselage into a single lifting surface. It has been proven in previously published

    works that this concept is feasible, has an efficient economical performance and

    is a promising candidate for solving the current air traffic problems, despite its

    challenging control and stability features. Moreover, the size of the vertical surfaces,

    such as the winglets, condition the radar detectability of the BWB model,

    especially for military missions. The goal of the department of Aeronautical and

    Vehicle Engineering at the Royal Institute of Technology (KTH) and of the department

    of Air Transport Systems of the German Aerospace Centre (DLR) is to

    investigate new ways to improve the conceptual design process of the aircrafts in

    a multidisciplinary environment. In order to design future unconventional aircraft

    configurations (such as the Blended Wing Body), the CEASIOM (Computerised

    Environment for Aircraft Synthesis and Integrated Optimisation Methods) geometry

    module, AcBuilder, is replaced and enhanced by implementing the Common

    Parametric Aircraft Configuration Scheme (CPACS), developed by the DLR as

    a basis technology. CPACS is meant to become a unified software framework to

    allow the sharing of the work and information, making it accessible for every person.

    It requires an implementation of the software modules in a framework using

    a common language for all the tools, in order to make later alterations of this

    framework easier. A detailed research of the latest developments and advances

    in the BWB concept was performed in order to identify the main principles and

    best design options. Afterwards, by using the implemented improved tool CPACSCreator

    (CC) based on CPACS, instead of Acbuilder, a BWB aircraft baseline

    was designed. The aerodynamic behaviour and performance of this model were

    then analyzed with the aid of the improved CEASIOM platform, with an special

    emphasis on its control and stability features. This analysis enables to improve

    the baseline design and the allocation and size of the control surfaces was studied

    and optimized. The minimum winglet required for a target flight performance was

    identified, due to its importance for reducing the drag and the radar detectability

    of the aircraft.

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  • 54. Mialon, Bruno
    et al.
    Khrabrov, Alex
    Ben Khelil, Saloua
    Huebner, Andreas
    Da Ronch, Andrea
    Badcock, Ken
    Cavagna, Luca
    Eliasson, Peter
    Zhang, Mengmeng
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Ricci, Sergio
    Jouhaud, Jean-Christophe
    Roge, Gilbert
    Hitzel, Stephan
    Lahuta, Martin
    Validation of numerical prediction of dynamic derivatives: The DLR-F12 and the Transcruiser test cases2011In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 47, no 8, p. 674-694Article, review/survey (Refereed)
    Abstract [en]

    The dynamic derivatives are widely used in linear aerodynamic models in order to determine the flying qualities of an aircraft: the ability to predict them reliably, quickly and sufficiently early in the design process is vital in order to avoid late and costly component redesigns. This paper describes experimental and computational research dealing with the determination of dynamic derivatives carried out within the FP6 European project SimSAC. Numerical and experimental results are compared for two aircraft configurations: a generic civil transport aircraft, wing-fuselage-tail configuration called the DLR-F12 and a generic Transonic CRuiser, which is a canard configuration. Static and dynamic wind tunnel tests have been carried out for both configurations and are briefly described within this paper. The data generated for both the DLR-F12 and TCR configurations include force and pressure coefficients obtained during small amplitude pitch, roll and yaw oscillations while the data for the TCR configuration also include large amplitude oscillations, in order to investigate the dynamic effects on nonlinear aerodynamic characteristics. In addition, dynamic derivatives have been determined for both configurations with a large panel of tools, from linear aerodynamic (Vortex Lattice Methods) to CFD. This work confirms that an increase in fidelity level enables the dynamic derivatives to be calculated more accurately. Linear aerodynamics tools are shown to give satisfactory results but are very sensitive to the geometry/mesh input data. Although all the quasi-steady CFD approaches give comparable results (robustness) for steady dynamic derivatives, they do not allow the prediction of unsteady components for the dynamic derivatives (angular derivatives with respect to time): this can be done with either a fully unsteady approach i.e. with a time-marching scheme or with frequency domain solvers, both of which provide comparable results for the DLR-F12 test case. As far as the canard configuration is concerned, strong limitations for the linear aerodynamic tools are observed. A key aspect of this work are the acceleration techniques developed for CFD methods, which allow the computational time to be dramatically reduced while providing comparable results.

  • 55.
    Montsarrat, Christophe
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Fluid motion analysis in the cryogenic tanks of the upperstage of Ariane 5 during the ascent phase2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the frame of the improvement of the performances for Ariane 5, an analysis iscarried out to explain the pressure drop observed in the ascent phase of some flights inthe liquid hydrogen (LH2) tank of the upper stage. This stage is mainly idle until therocket is out of the atmosphere but is submitted to important excitation throughoutthe ascent phase in the atmosphere. Due to excitation, the liquid contained in thetank moves and breaks the thermodynamic equilibrium. This movement, sloshing isidentified as the most likely cause of the pressure drop observed. It is investigated inthis thesis to understand how exactly it impacts the thermodynamic equilibrium inthe tank.The pressure drop called creux PGRH can be explained by the mixing of the topof the liquid with the liquid bulk, colder than the top, when the liquid is sloshing.This movement changes the saturation conditions and yields pressure and temperatureevolutions in the ullage volume of the tank. Observations on Ariane 5 flightsshowed that the first asymmetric mode was mainly excited during this first phase ofascension. Simple models such as the pendulum model are used to simulate the dynamicbehaviour of this mode. Its stability is also investigated through lateral andlongitudinal excitations.The thermodynamics of the system in the tank can be modelled by a one-dimensionalmodel. Based on an experiment with liquid nitrogen in a cylindrical tank, the heatfluxes are calculated and plugged in the model. The pressurisation phase is first simulatedthrough self and active pressurisation to estimate the importance of the thicknessof the thermal boundary layer. Sloshing is included in the model thermodynamicallyby considering a more important conductive coefficient in the sloshing layer. The amplitudeof sloshing can be linked to the new conduction term thanks to a literaturerelation but it underestimates the actual magnitude of the pressure drop. The modelis extended to a two-dimensional model to take into account the sloshing mechanically,knowing the velocities from the pendulum model. It is found to be not accurate mostlydue to the turbulence of the sloshing layer not considered in the model.The models give in any case important results regarding the influence of some tankparameters such as the ullage volume, the importance of the pressurisation phase anda necessary distinction between chaotic and stable sloshing. From this, the data ofAriane 5 flights is analysed. The flights are divided in three families according to themagnitude of the pressure drop measured. A fault tree analysis is performed to ruleout possible influences and put forward a theory on the creux eventually.

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  • 56.
    Muld, Tomas W.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Efraimsson, Gunilla
    Henningson, Dan S.
    Herbst, Astrid H.
    Orellano, Alexander
    Detached Eddy Simulation and Validation on the Aerodynamic Train Model2009In: EUROMECH COLLOQUIUM 509: Vehicle Aerodynamics, 2009Conference paper (Other academic)
    Abstract [en]

    We present CFD-simulations of the flow around the aerodynamic train model(ATM). The turbulence modelling technique is detached eddy-simulation(DES), where the DES model is based on the k-ω SST RANS model. TheReynolds number for the simulation is 60.000 based on the hydraulic diame-ter (3m in full scale), free-stream velocity and kinematic viscosity of air. Themodel used is in 1:50 scale. The numerical results are compared to water tunnelexperimental data on the ATM available from the German Aerospace Center(DLR). The velocity field is measured using particle image velocimetry (PIV).The numerical setup is made to match the experimental setup as close as possi-ble. Focus of the analysis is on the flow in the wake of the train. Comparisonsof the averaged velocity and the velocity fluctuations in the wake shows that theoverall levels and trends are captured by the numerical simulations. However,the peak value of the velocity magnitude in the wake seems to be overestimatedby the DES technique used.

  • 57.
    Nissan, Danny
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Effects of vortex induced vibrationson cylinders in tandem configurationat critical Reynold numbers2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Vortex-induced vibrations (VIV) and wake interference on circular cylinders have

    reached a lot of research attention over the years. However, most research is done

    for relativly low Reynold numbers (sub-critical) and does not correspond to real

    world chimney situations. A real chimney in the south of Sweden has experienced

    some large vibrations and data gathered from this chimney shows a correlation

    between these motions and wind directions. Results from 2D CFD simulations used

    to simulate VIV on a circular cylinder when laying in the wake of another larger, and

    fix, cylinder at critical Reynold numbers are presented in this thesis. Simulations

    are done for three cases; one single cylinder, for comparisons, and two simluations

    for cylinders in tandem arrangement, at 35 and 70 m respectively. Results show

    that the cylinder when in tandem arrangement experience much larger vibrations

    than the single cylinder. For velocities above 10 m/s the tandem arrangement can

    lead to resonance on the cylinder, which is not occuring in the case with a single

    cylinder. This thesis shows that even at distances of 70 m, wake interference can

    have a large effect on VIV and more advanced models and simulations would be

    useful for better predictions of the behaivor of chimneys.

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  • 58.
    Oprea, Alexandra
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    3D Fuel Tank Models for System Simulation2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of the present master thesis is to optimize the current fuel tank simulations procedure for the next generation of JAS 39 Gripen ghters developed by SAAB AB. The current simulation process involves three dierent steps performed in three dierent computer environments. While the procedure works reasonably well on the fuel tank models of the previous version of the aircraft, it is too slow for the new Gripen tank models and their high level of detail. An optimized version of the procedure is put forward, which allows for tank analysis and fuel system simulation within reasonable time frames. Suggestions are made for future improvements.

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  • 59.
    Opwonya Nokrach, Basil
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Maintaining optimal measures of effectiveness by scenario requirements optimization2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis proposes a solution on how to manage support resources in such a way that optimized Measures of Effectiveness (MOE), such as Availability and Number of Backorders, are kept within a specified range without incurring the full scale re-optimizations in OPUS10 with every change in operative scenario. This has previously been experienced by FMV.

    The hypothesis in this study is that the different risks inherent in the different scenarios are the causes of the changes in the MOE. Therefore by capturing the risks involved and treating those risks, it is possible to preempt the risks developing into problems. A solution to this end has been crafted based on the methodologies of Technical Measurement and Quality Function Deployment (QFD).

    QFD methodology recommends going to the intended operational environment of the system, to capture the requirements. This study proposes using the norms of the Swedish Armed Forces (SWAF) as stipulated in the regulations regarding transports within the army," Transportreglemente", augmented with the methods of System Architecture to catch the stated and unstated user requirements.

    The methods of Technical Measurement are then used to turn the requirements into Measures of Effectiveness, Key Performance Parameters (KPP), Measures of Performance (MOP) and Technical Performance Measures (TPM).

    This study shows how to use the QFD House of Quality (HOQ) in the design of optimal support infrastructure, by prioritizing the MOP in order of criticality to support system performance. The MOP are then subjected to a sensitivity analysis ,before being used to design experiments which are tested to see which designs are satisfactory in relation to target performance within a tolerance band.

    A design tradeoff of the design of different support infrastructure is performed in case of unsatisfactory performance or as new data is acquired as a result of an Estimation, Feasibility or Performance analysis.

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  • 60.
    Oriol, Nicolas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Enhancement of Current Attitude and Orbit Control Systems / Guidance, Navigation and Control Simulation Tools2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this master project is to enhance current Attitude and Orbit Control Systems / Guidance, Navigation and Control simulation tools that are used in the Guidance, Navigation and Control section (TEC-ECN), at the European Space Agency.

    Two tools are improved. First, elements are added in a Matlab/Simulink toolbox used to perform quick AOCS/GNC simulations. These elements are related to low-thrust orbital manoeuvres. A simulation template is also created to simulate manoeuvres that independently change each of the orbital elements.

    The second tool developed is a Workbook used during Concurrent Engineering sessions by AOCS/GNC specialists. It allows them to size the di_erent actuators for attitude and orbit control, and realise pointing error budgets helping making trade-o_'s between di_erent pieces of hardware.

  • 61.
    Otero, Evelyn
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Acceleration of Compressible Flow Simulations with Edge Using  Implicit Time Stepping2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computational fluid dynamics (CFD) is a significant tool routinely used indesign and optimization in aerospace industry. Often cases with unsteadyflows must be computed, and the long compute times of standard methods hasmotivated the present work on new implicit methods to replace the standardexplicit schemes. The implementation and numerical experiments were donewith the Swedish national flow solver Edge, developed by FOI,universities, and collaboration partners.The work is concentrated on a Lower-Upper Symmetric Gauss-Seidel (LU-SGS)type of time stepping. For the very anisotropic grids needed forReynolds-Averaged Navier-Stokes (RANS) computations of turbulent boundary layers,LU-SGS is combined with a line-implicit technique.  The inviscid flux Jacobians which contribute to the diagonalblocks of the system matrix are based on a flux splitting method with upwind type dissipation giving  control over diagonal dominance and artificial dissipation.The method is  controlled by several parameters, and comprehensivenumerical experiments were carried out to identify their influence andinteraction so that close to optimal values can be suggested. As an example,the optimal number of iterations carried out in a time-step increases with increased resolution of the computational grid.The numbering of the unknowns is important, and the numberings produced by mesh generators of Delaunay- and advancing front-type wereamong the best.The solver has been parallelized with the Message Passing Interface (MPI) for runs on multi-processor hardware,and its performance scales with the number of processors at least asefficiently as the explicit methods. The new method saves typicallybetween 50 and 80 percent of the runtime, depending on the case, andthe largest computations have reached 110M grid nodes. Theclassical multigrid acceleration for 3D RANS simulations was foundineffective in the cases tested in combination with the LU-SGS solverusing optimal parameters. Finally, preliminary time-accurate simulations for unsteady flows have shown promising results.

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    Thesis
  • 62.
    Otero, Evelyn
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Acceleration of Compressible Flow Simulations with Edge using Implicit Time Stepping2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computational fluid dynamics (CFD) has become a significant tool routinely used in design and optimization in aerospace industry. Typical flows may be characterized by high-speed and compressible flow features and, in many cases, by massive flow separation and unsteadiness. Accurate and efficient numerical solution of time-dependent problems is hence required, and the efficiency of standard dual-time stepping methods used for unsteady flows in many CFD codes has been found inadequate for large-scale industrial problems. This has motivated the present work, in which major effort is made to replace the explicit relaxation methods with implicit time integration schemes. The CFD flow solver considered in this work is Edge, a node-based solver for unstructured grids based on a dual, edge-based formulation. Edge is the Swedish national CFD tool for computing compressible flow, used at the Swedish aircraft manufacturer SAAB, and developed at FOI, lately in collaboration with external national and international partners. The work is initially devoted to the implementation of an implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) type of relaxation in Edge with the purpose to speed up the convergence to steady state. The convergence of LU-SGS has been firstly accelerated by basing the implicit operator on a flux splitting method of matrix dissipation type. An increase of the diagonal dominance of the system matrix was the principal motivation. Then the code has been optimized by means of performance tools Intel Vtune and CrayPAT, improving the run time. It was found that the ordering of the unknowns significantly influences the convergence. Thus, different ordering techniques have been investigated. Finding the optimal ordering method is a very hard problem and the results obtained are mostly illustrative. Finally, to improve convergence speed on the stretched computational grids used for boundary layers LU-SGS has been combined with the line-implicit method.

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    Licentiate_E-Otero
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  • 63.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, P
    FOI, SWEDEN.
    Improving the performance of the CFD code Edge using LU-SGS and line-implicit methods2013In: Proceedings: of the 4:th CEAS Conference in Linköping, 2013 / [ed] Tomas Melin, Petter Krus, Emil Vinterhav, Knut Övrebö, Linköping, Sweden: Linköping University Electronic Press, 2013, p. 124-134Conference paper (Refereed)
    Abstract [en]

    The implicit LU-SGS solver has been implemented in the code Edge to accelerate the convergence to steady state. Edge is a ow solver for unstructured grids based on a dual grid and edgebased formulation. LU-SGS has been combined with the line-implicit technique to improve convergence on the very anisotropic grids necessary for the boundary layers. LU-SGS works in parallel and gives better linear scaling with respect to the number of processors, than the explicit scheme. The ordering techniques investigated have shown that node numbering does inuence the convergence and that the native orderings from Delaunay and advancing front generation were among the best tested. LU-SGS for 2D Eu-ler and line-implicit LU-SGS for 2D RANS are two to three times faster than the explicit and line-implicit Runge-Kutta respectively. 3D cases show less acceleration and need a deeper study.

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    ImprovingEdge_CEAS2013
  • 64.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, P.
    Parameter investigation for computing time reduction with Lower-Upper Symmetric Gauss-Seidel and line-implicit methods2014In: AIAA AVIATION 2014 -7th AIAA Theoretical Fluid Mechanics Conference, 2014Conference paper (Refereed)
    Abstract [en]

    An implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) solver has been implemented as a multigrid (MG) smoother combined with a line-implicit method as an acceleration technique for Reynolds-Averaged Navier-Stokes (RANS) simulation on stretched meshes. The Computational Fluid Dynamics (CFD) code concerned is Edge, an edge- based finite volume Navier-Stokes flow solver for structured and unstructured grids. The paper focuses on the investigation of the parameters related to the novel line-implicit LU- SGS solver for convergence acceleration on 3D RANS meshes. The influence on the overall convergence of the Courant-Friedrichs-Lewy (CFL) number, the Left Hand Side (LHS) dissipation, and the convergence of iterative solution of the linear problem is presented and default values are defined for maximum convergence acceleration. These optimized set- tings are applied to 3D RANS computations for comparison with explicit and line-implicit Runge-Kutta (RK) smoothing. For most of the cases, a computing time acceleration of the order of 2 is found depending on the mesh type, namely the boundary layer and the magnitude of residual reduction.

  • 65.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Acceleration on stretched meshes with line-implicit LU-SGS in parallel implementation2015In: International journal of computational fluid dynamics (Print), ISSN 1061-8562, E-ISSN 1029-0257, Vol. 29, no 2, p. 133-149Article in journal (Refereed)
    Abstract [en]

    The implicit lower-upper symmetric Gauss-Seidel (LU-SGS) solver is combined with the line-implicit technique to improve convergence on the very anisotropic grids necessary for resolving the boundary layers. The computational fluid dynamics code used is Edge, a Navier-Stokes flow solver for unstructured grids based on a dual grid and edge-based formulation. Multigrid acceleration is applied with the intention to accelerate the convergence to steady state. LU-SGS works in parallel and gives better linear scaling with respect to the number of processors, than the explicit scheme. The ordering techniques investigated have shown that node numbering does influence the convergence and that the orderings from Delaunay and advancing front generation were among the best tested. 2D Reynolds-averaged Navier-Stokes computations have clearly shown the strong efficiency of our novel approach line-implicit LU-SGS which is four times faster than implicit LU-SGS and line-implicit Runge-Kutta. Implicit LU-SGS for Euler and line-implicit LU-SGS for Reynolds-averaged Navier-Stokes are at least twice faster than explicit and line-implicit Runge-Kutta, respectively, for 2D and 3D cases. For 3D Reynolds-averaged Navier-Stokes, multigrid did not accelerate the convergence and therefore may not be needed.

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  • 66.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Convergence Acceleration of the CFD Code Edge by LU-SGS2011In: 3rd CEAS European Air & Space Conference, Venice, 24-28 October 2011, CEAS/AIDAA , 2011, p. 606-611Conference paper (Refereed)
    Abstract [en]

    Edge is a flow solver for unstructured grids based on a dual grid and edge-based formulation. The standard dual-time stepping methods for compressible unsteady flows are inadequate for large-scale industrial problems. This has motivated the present work, in which an implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) type of relaxation has been implemented in the code Edge with multigrid acceleration. Two different types of dissipation, a scalar and a matrix model, have been constructed which increase the diagonal dominance of the system matrix but not the numerical viscosity of the computed solution. A parametric study demonstrates convergence accelerations by a factor of three for inviscid transonic flows compared to explicit Runge-Kutta smoothing for multigrid acceleration.

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  • 67.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Implementation of Implicit LU-SGS method with Line-implicit scheme on Stretched Unstructured GridsManuscript (preprint) (Other academic)
    Abstract [en]

    A first implementation of line-implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) in Edge has been considered in this paper for convergenceacceleration on stretched meshes. The motivation comes from the lack of efficiency of the implicit LU-SGS when running in RANS meshes. Edge is a flow solver for unstructured grids based on a dual grid and edge-based formulation. The line-implicit method has been implemented in the code Edge has an acceleration method when computing explicit schemes in stretched meshes. This methods works only in regions of stretched grid where the flow equations are integrated implicitly in time along the structured lines. The combination with an implicit LU-SGS should remove the restriction of the time step for explicit schemes and accelerate the convergence to steady state. The results have shown that for highly stretched meshes, line-implicit LU-SGS could perform much faster than LU-SGS.

  • 68.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Performance Analysis of the LU-SGS Algorithm as Multigrid Smoother in a CFD Code for Unstructured GridsManuscript (preprint) (Other academic)
    Abstract [en]

    Lower-Upper Symmetric Gauss-Seidel (LU-SGS) approximate solution forlinear systems has been implemented in the CFD codeEdge, an edge-based Navier-Stokes flow solver for unstructured grids,in order to accelerate the convergence to steady state.LU-SGS has been combined with the line-implicit technique to improve convergenceon the very anisotropic grids necessary for typical High Reynolds number applications, giving theline LU-SGS.The performance of the LU-SGS algorithm is analyzed for a better comprehension ofthe solver behavior and capabilities, and to obtain maximal efficiency for2D and 3D, Euler and Reynolds-Averaged Navier-Stokes computations.The study covers code implementation using performance analysis tools, andnumerical techniques such as node ordering methods, and parallelization.The results show that by code tuning, the wall clock time was reduced by a factor of two.The node ordering influences the convergence, and orderingscoming from different types of mesh generators were close to optimal. The LU-SGS algorithm was successfully parallelized by domain decompositionand run for cases up to 110M grid points, showing linear scaling withnumber of processors. The tests indicate that 10 LU-SGS iterations is a requirementfor minimal computing time on large grids, and that multigrid acceleration may be ineffective.The computing time with line LU-SGS was about half that of theline-implicit Runge-Kutta solver for 3D Reynolds-Averaged Navier-Stokes.

  • 69.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Performance analysis of the LU-SGS algorithm in the CFD code EdgeManuscript (preprint) (Other academic)
  • 70.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gong, Jing
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    Min, Misun
    Fischer, Paul
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Laure, Erwin
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    OpenACC acceleration for the PN-PN-2 algorithm in Nek50002019In: Journal of Parallel and Distributed Computing, ISSN 0743-7315, E-ISSN 1096-0848, Vol. 132, p. 69-78Article in journal (Refereed)
    Abstract [en]

    Due to its high performance and throughput capabilities, GPU-accelerated computing is becoming a popular technology in scientific computing, in particular using programming models such as CUDA and OpenACC. The main advantage with OpenACC is that it enables to simply port codes in their "original" form to GPU systems through compiler directives, thus allowing an incremental approach. An OpenACC implementation is applied to the CFD code Nek5000 for simulation of incompressible flows, based on the spectral-element method. The work follows up previous implementations and focuses now on the P-N-PN-2 method for the spatial discretization of the Navier-Stokes equations. Performance results of the ported code show a speed-up of up to 3.1 on multi-GPU for a polynomial order N > 11.

  • 71.
    Otero, Evelyn
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Marin, Oana
    Argonne Natl Lab, MCS, Lemont, IL 60439 USA..
    Laure, Erwin
    PDC KTH, Ctr High Performance Comp, SE-10044 Stockholm, Sweden..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lossy Data Compression Effects on Wall-bounded Turbulence: Bounds on Data Reduction2018In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 101, no 2, p. 365-387Article in journal (Refereed)
    Abstract [en]

    Postprocessing and storage of large data sets represent one of the main computational bottlenecks in computational fluid dynamics. We assume that the accuracy necessary for computation is higher than needed for postprocessing. Therefore, in the current work we assess thresholds for data reduction as required by the most common data analysis tools used in the study of fluid flow phenomena, specifically wall-bounded turbulence. These thresholds are imposed a priori by the user in L (2)-norm, and we assess a set of parameters to identify the minimum accuracy requirements. The method considered in the present work is the discrete Legendre transform (DLT), which we evaluate in the computation of turbulence statistics, spectral analysis and resilience for cases highly-sensitive to the initial conditions. Maximum acceptable compression ratios of the original data have been found to be around 97%, depending on the application purpose. The new method outperforms downsampling, as well as the previously explored data truncation method based on discrete Chebyshev transform (DCT).

  • 72.
    Persson, Andreas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Detached-Eddy Simulations of Active Flow Control Systems on a Simplified Car Geometry2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The feasibility of implementing an active flow control system in ground vehicles is investigated through detached-eddy simulations of the Windsor model. This is done in the open-source CFD code OpenFOAM. Forcing is done with a zero-net-mass-flux actuator, which is modeled as a sinusoidal velocity boundary condition through slots located at the rear edge of the roof. Simulations are done in three steps: 2D, semi-3D and 3D, to give an understanding of different flow phenomena, and a parameter study is performed. Results show that drag can be reduced mainly by reducing the strength of the vortex shedding process, with a gradual decrease in effectiveness from 2D to 3D. A small drag reduction is achieved in semi-3D, and a lift reduction is achieved in 3D. DES methodology is shown to work well when simulating active flow control.

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  • 73.
    Pettersson, Karl
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    CFD Methods for Predicting Aircraft Scaling Effects2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis deals with the problems of scaling aerodynamic data from wind tunnel to free flight  conditions. The main challenges when this scaling should be performed is how the model support, wall interference and the potentially lower Reynolds number in the windtunnel should be corrected. Computational Fluid Dynamics (CFD) simulations have been performed on a modern transonic transport aircraft in order to reveal Reynolds number effects and how these should be scaled accurately. A methodology for scaling drag and identifying scaling effects in general is presented.  This investigation also examines how the European Transonic Wind tunnel twin sting model support influences the flow over the aircraft. When the Reynolds number is differing between the wind tunnel and free flight conditions, a change in boundary layer transition position can occur. In order to estimate first order boundary layer transition effects a correlation based transition prediction method, previously presented by Menter and Langtry, is implemented in the CFD solver Edge. The transition model is further developed and a novel set of equations for the production terms is found through a CFD/optimizer coupling. The transition data, used to calibrate the CFD transition model,  have been extracted from a low Mach number wind tunnel campaign. At these low Mach numbers many compressible CFD solvers suffer of poor convergence rates and a deficiency in robustness and accuracy might appear. The low Mach number effects are investigated, and an effort to prevent these is done by implementing different preconditioning techniques in the compressible CFD solver Edge. The preconditioners are mainly based on the general Turkel preconditioner, but a novel formulation is also presented in order to make the numerical technique less problem dependent.

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  • 74.
    Pettersson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Implementation and Verification of a Correlation Based Transition Prediction Method2008In: 38th Fluid Dynamics Conference and Exhibit, American Institute of Aeronautics and Astronautics, 2008Conference paper (Refereed)
    Abstract [en]

    In many applications such as turbine and aircraft design, boundary layer transition prediction is an important topic. This paper deals with the implementation and verification of a correlation based transition prediction method previously presented by Menter and Langtry. The two additional transport equations used for predicting transition and a novel set of equations for the production terms are implemented into the CFD code Edge. The results are compared to the well-known Ercoftac wind tunnel results.

  • 75.
    Pettersson, Karl
    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.
    Aerodynamic scaling to free flight conditions: past and present2008In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 44, no 4, p. 295-313Article in journal (Refereed)
    Abstract [en]

    This report summarizes some of the problems when wind tunnel data should be scaled to free flight conditions. The main challenges in performing this extrapolation is how model support, wall interference, aeroelastic effects and a potentially lower Reynolds number in the wind tunnel should be corrected. A historical review of scale effects is presented showing wind tunnel to flight discrepancies of different types of aircraft configurations. An overview of scaling methodologies and Reynolds number effects are presented and discussed. Some modern approaches where computational fluid dynamics (CFD) are used, together with wind tunnel testing, in order to identify scaling phenomena are presented as well.

  • 76.
    Pettersson, Karl
    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.
    Comparing different CFD methods accuracy in computing local boundary layer properties2009In: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, Vol. 3, no 1, p. 98-108Article in journal (Refereed)
    Abstract [en]

    In aeronautical applications wind tunnels are often not capable of producing high Reynolds numbers which are achieved at free flight conditions. Today CFD methods are often used as a tool to estimate scale effects. CFD methods are commonly used to predict flow features at Reynolds numbers higher than what the aircraft model is subject to in the wind tunnel, and at higher Reynolds number than the turbulence model has been calibrated to. The investigation of local boundary layer properties could give useful information when the wind tunnel data is scaled to free flight conditions the question is whether the CFD methods compute these in a consistent manner when there is a large spread in Reynolds number. This work compares two different CFD solvers and two different turbulence models' accuracy in computing local boundary layer properties compared to wind tunnel measurements.

  • 77.
    Pettersson, Karl
    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.
    Implementation and Evaluation of Different Preconditioning Methods in the Compressible CFD Solver Edge2008In: 5th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008), 2008Conference paper (Refereed)
  • 78.
    Pettersson, Karl
    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.
    Reynolds number effects identified with CFD methods compared to semi-empirical methods2006In: ICAS-Secretariat - 25th Congress of the International Council of the Aeronautical Sciences 2006, Curran Associates, Inc., 2006, Vol. 3, p. 1566-1579Conference paper (Refereed)
    Abstract [en]

    In order to estimate Reynolds number effects on a transonic transport aircraft CFD calculations have been performed. The CFD calculations have been done solving the RANS equations on an unstructured grid for varying Reynolds number at transonic conditions. Low Reynolds number data have been extrapolated to a higher Reynolds number condition with different scaling methodologies in order to evaluate each methods strengths and weaknesses.

  • 79.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Modeling and simulating aircraft stability and control-The SimSAC project2011In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 47, no 8, p. 573-588Article, review/survey (Refereed)
    Abstract [en]

    This paper overviews the SimSAC Project, Simulating Aircraft Stability And Control Characteristics for Use in Conceptual Design. It reports on the three major tasks: development of design software, validating the software on benchmark tests and applying the software to design exercises. 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 flying 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. The benchmarks for validation are the F12 windtunnel model of a generic long-range airliner and the TCR windtunnel model of a sonic-cruise passenger transport concept. The design, simulate and evaluate (DSE) exercise demonstrates how the software works as a design tool. The exercise begins with a design specification and uses conventional design methods to prescribe a baseline configuration. Then CEASIOM improves upon this baseline by analyzing its flying and handling qualities. Six such exercises are presented.

  • 80.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Department of Aeronautics & Systems Technology, FOI, Swedish Defense Research Institute, Stockholm, Sweden.
    Goetzendorf-Grabowski, Tomasz
    Institute of Aeronautics & Applied Mechanics, Aircraft Design Department Warsaw University of Technology, Poland.
    Vos, Jan B.
    CFS Engineering, Lausanne, Switzerland.
    Zhang, Mengmeng
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Virtual-aircraft design & control of transcruiser: a canard configuration2011In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724Article in journal (Other academic)
  • 81.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Eliasson, Peter
    Goetzendorf-Grabowski, Tomasz
    Vos, Jan B.
    Zhang, Mengmeng
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Richardson, Thomas S.
    Design of a canard configured TransCruiser using CEASIOM2011In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 47, no 8, p. 695-705Article, review/survey (Refereed)
    Abstract [en]

    CEASIOM is a multidisciplinary software environment for aircraft design that has been developed as part of the European Framework 6 SimSAC project. It closely integrates discipline-specific tools such as those used for CAD, grid generation, CFD, stability analysis and control system design. The environment allows the user to take an initial design from geometry definition and aerodynamics generation through to full six degrees of freedom simulation and analysis. Key capabilities include variable fidelity aerodynamics tools and aeroelasticity modules. The purpose of this paper is to demonstrate the potential of CEASIOM by presenting the results of a Design, Simulate and Evaluate (DSE) exercise applied to a novel, project specific, transonic cruiser configuration called the TCR. The baseline TCR configuration is first defined using conventional methods, which is then refined and improved within the CEASIOM software environment. A wind tunnel model of this final configuration was then constructed, tested and used to verify the results generated using CEASIOM.

  • 82.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Goetzendorf-Grabowski, Tomasz
    Institute of Aeronautics & Applied Mechanics, Aircraft Design Department, Warsaw University of Technology, 00-665 Warsaw, Poland.
    Vos, Jan
    Reating Aero-Databases by Adaptive-Fidelity CFD Coupled with S&C Analysis to Predict Flying Qualities2009In: CEAS European Air & Space Conference, 2009Conference paper (Refereed)
  • 83.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Jirásek, A.
    Cavagna, L.
    Riccobene, L.
    Ricc, S.
    Aeroelastic analysis of the CAWAPI F-16XL configuration at transonic speeds2014In: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014, 2014Conference paper (Refereed)
    Abstract [en]

    This article present an aeroelastic study of CAWAPI F-16XL aircraft. The structural model for this aircraft is publicly available and is therefore replaced by a structural model estimate which is constructed based on data available in public literature. The aeroelastic solution is done using inviscid solution for two flight conditions - FC70 and FC79. The primary task is to assess importance of the aeroelastic effects on the solution and to asses weather large discrepancies observed at flight condition FC70 between the computational and experimental data.

  • 84.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Luckring, J. M.
    What was learned in predicting slender airframe aerodynamics with the F16-XL aircraft2014In: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014, American Institute of Aeronautics and Astronautics (AIAA) , 2014Conference paper (Refereed)
    Abstract [en]

    The CAWAPI-2 coordinated project has been underway to improve CFD predictions of slender airframe aerodynamics. The work is focused on two flow conditions and leverages a unique flight data set obtained with the F-16XL aircraft for comparison and verification. These conditions, a low-speed high angle-of-attack case and a transonic low angle-of-attack case, were selected from a prior prediction campaign wherein the CFD failed to provide acceptable results. In re-visiting these two cases, approaches for improved results include better, denser grids using more grid adaptation to local flow features as well as unsteady higher-fidelity physical modeling like hybrid RANS/URANS-LES methods. The work embodies predictions from multiple numerical formulations that are contributed from multiple organizations where some authors investigate other possible factors that could explain the discrepancies in agreement, e.g. effects due to deflected control surfaces during the flight tests, as well as static aeroelastic deflection of the outer wing. This paper presents the synthesis of all the results and findings and draws some conclusions that lead to an improved understanding of the underlying flow physics, and finally making the connections between the physics and aircraft features.

  • 85.
    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)
  • 86.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Puelles, Andrés
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Designing a Trans Cruiser Aircraft by Simulation: from Specification to Windtunnel Test2009Conference paper (Refereed)
  • 87.
    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)
  • 88.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Vos, Jan B.
    Preamble2011In: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 47, no 8, p. 571-572Article in journal (Refereed)
  • 89.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Zhang, Mengmeng
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Nagel, Bjorn
    Boehnke, Daniel
    Towards a Framework with Unified Geometry Management for Virtual Aircraft Design2012In: 50th AIAA Aerospace Sciences Meeting, Nashville, TN, 9-12 Jan 2012, 2012Conference paper (Refereed)
  • 90.
    Rosén, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Development of Efficient Methods used for Aft-body Assessment2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This paper presents a Master of Science thesis project, performed at SAAB Aeronautics propulsion division in 2014. A method was developed to implement performance calculations on nozzles and aircraft aft-body’s. Creating mesh for Computational Fluid Dynamics (CFD) calculations is time consuming, so efficient methods and tools are necessary to decrease time spent on meshing. Tools used to speed up the meshing and calculation process have been developed and are described in this paper. A method was developed to be used for nozzle and aft-body geometries. Efficient tools are needed because the nozzle geometry is constantly changing at different flight conditions were every new flight condition requires a new mesh and a new calculation. To validate the method a NASA wind tunnel test was used and showed reasonably good agreement with CFD. By varying the nozzle pressure ratio, shock patterns and jet plume could also be studied, which was important to estimate the performance. Two different nozzle configurations were compared with respect to aft-body drag and nozzle performance. It is shown in this paper that parametrization of geometry and good block structure in meshing are key factors to generate a mesh with high quality.

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  • 91.
    Sack, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    On Acoustic Multi-Port Characterisation Including Higher Order Modes2016In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 192, no 5, p. 834-850Article in journal (Refereed)
    Abstract [en]

    Methods to design test-procedures for acoustic multi-ports in ducts with a focus on pressure sampling positions for accurate modal decomposition are demonstrated. Acoustic fields up- and downstream of an in-duct acoustic element are excited by external sources and decomposed into transmitted and reflected aeroacoustic modal pres- sure amplitudes in order to first determine the acoustic scattering of the element. Secondly, the determination of the element source strength requires tests with no external sources, but with known terminations and scattering data. Unfavourable source and sensor positions lead to mode coupling and to ill-conditioned or even singular decomposition matrices, which results in high amplifications of uncertainties within the wave decomposition. An unoptimised but over-determined assembly is compared with a setup containing a minimum of sensors but with optimised positions. Lower uncertainty amplification, despite the usage of fewer sensors, is achieved for most frequencies, especially after the cut-on of t he higher order acoustic modes. A genetic algorithm (GA) is used to achieve this optimised setup by minimising the condition number of the decomposition matrix, which is a multi-dimensional optimisation problem with numerous local minima. To estimate the stability of the optimised configuration, a Monte-Carlo Method (MCM) is deployed to introduce normal distributed complex pressure un- certainties into the decomposition. In order to estimate the wave number, different approaches are compared - namely the classical non-dissipative wav e number estimate, an extended Kirchhoff method for viscous-thermal damping and an eigenvalue solution of the Linearised Navier Stokes Equations by Dokumaci. The presented de- composition method is not only applicable to measurement data but is equally useful to post-process results from numerical computation.

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  • 92.
    Salminen, Henry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Parametrizing tyre wear using a brush tyre model2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Studying rubber wear is important because it can save money, minimize health and environmental issues related to the particles generated from tyre wear and reduce fuel consumption. The wear of rubber is considered to be the result of energy dissipation due to friction. There are many models that describe the dynamical behaviour of vehicles and tyre, but less e ort has been dedicated to consider the tyre wear in these models.

    The purpose of the thesis was to create an easy to understand and trend-accurate tyre wear model for implementation in a complete car model. The tyre wear in the thesis is determined to be the amount of rubber volume loss due to sliding per unit length that the tyre travels. A literature study was performed with the objective of gaining knowledge of tyre models and the a ecting parameters of tyre wear. The most important parameters in determining tyre wear were identied as the forward velocity, side-slip angle, longitudinal slip, vertical load, and tyre ination pressure. The wear was chosen to be calculated with Archards wear law for these parameters both separately and combined in pairs in order to obtain a deeper understanding of the wear.

    The results show that wear is increasing exponentially for the forward velocity. Tyre wear decreases linearly as tyre ination pressure (vertical bristle sti ness) increases. The vertical load, longitudinal slip and side-slip angle yielded exponentially increasing wear. The most inuential parameters a ecting the tyre wear were the longitudinal slip and side-slip angle, these yielded wear rates up to 107 higher compared with the reference case.

    The developed tyre wear model is a good base for future work. More measurement data are needed in order to validate the model. For future work it is also recommended to implement camber angle and temperature dependency in order to study these two important parameters inuence on tyre wear.

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  • 93.
    Saquet, Pierre
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Further developments of the AcBuilder tool for constructing geometrical models of aircraft2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report, along with Laurent Gourc’s and Ben Marchant’s reports, presents the work done on the development of the new AcBuilder, realized for CEASIOM. CEASIOM is a package of different modules, developed as part of the SimSAC project, which aims to Simulate Stability And Control Characteristics for Use in Conceptual Design. First, the CEASIOM software is introduced in the context of the SimSAC project and, to know where the development of the aircraft builder tool (AcBuilder) is, an overview of the previous version is shown. Then, based on the issues noticed by the users and the programmers of CEASIOM, the goals of the project are presented in listing some modifications and improvements to bring to the software. Secondly, the document treats about the requirements for the new AcBuilder development in order to reach the goals of the project. Those requirements come from both the programming languages used (Matlab and Java) and from the technical parts of the project (geometrical

    construction of aircraft). Finally, this report presents the new AcBuilder tool, its new design interface, its new functionalities and the remaining improvements to implement in order to make the module compatible with the changes brought by the new requirements.

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  • 94.
    Sedlak, Vojtech
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics. KTH, School of Engineering Sciences (SCI), Mechanics.
    Motorcycle Cornering Improvement: An Aerodynamical Approach based on Flow Interference2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A new aerodynamic device, based on flow interference effects, is studied in order to significantly improve the cornering performance of racing motorcycles in MotoGP. After a brief overview on why standard downforce devices cannot be used on motorcycles, the new idea is introduced and a simplified mechanic analysis is provided to prove its effectiveness. The concept is based on the use of anhedral wings placed on the front fairing, with the rider acting as an interference device, aiming to reduce the lift generation of one wing. Numerical calculations, based on Reynolds-averaged Navier-Stokes equations, are performed on simplified static 2D and 3D cases, as a proof of concept of the idea and as a preparation for further analysis which may involve experimental wind-tunnel testing. The obtained results show that the flow interference has indeed a significant impact on the lift on a single wing. For some cases the lift can be reduced by 70% to over 90% - which strengthens the possibility of a realistic implementation.

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  • 95.
    Smith, Kyle
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    CFD Investigation of Fluidic Momentum Injection as Alternative to Mechanical High Lift Devices for Boundary Layer Control2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The  purpose of this computational  fluid dynamics investigation  was to consider a method for boundary  layer control using air injection  on a  modern  transonic airfoil  similar  to those found on most commercial airliners.   Common  industry  software titles  such as Pointwise  for mesh generation,  and ANSYS Fluent for the CFD computation  were implemented.   Coordinates  for  an experimental  transonic airfoil  which  had been used previously in wind tunnel  testing were acquired and used in this analysis. A full alpha sweep, from 0 degrees to stall, was performed on the standard three-element configuration at wind tunnel testing conditions.   ISA  conditions at  sea level  was assumed for  all  simulations. These simulations mirrored  previously published wind tunnel results. A series simulations  were then  performed  on the  standard  configuration with  retracted  leading edge slat and four different  injection  points.  It was  found that  although  the  flight  performance  could be matched  at lower angles of attack,  the CLmax  and lift  at the stall angle of the standard configuration could not be achieved.

     

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  • 96.
    Stensson Trigell, Annika
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Jerrelind, Jenny
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Wennhage, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
    ECO2 Vehicle Design: an initiative for a holistic perspective on future vehicle concepts2008Conference paper (Other academic)
  • 97.
    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.

     

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  • 98.
    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)
  • 99.
    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.

  • 100.
    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)
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