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  • 1. Boelens, O. J.
    et al.
    Badcock, K. J.
    Görtz, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Morton, S.
    Fritz, W.
    Karman, S. L., Jr.
    Michal, T.
    Lamar, J. E.
    F-16XL Geometry and Computational Grids Used in Cranked-Arrow Wing Aerodynamics Project International2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 2, p. 369-376Article in journal (Refereed)
    Abstract [en]

    The objective of the Cranked-Arrow Wing Aerodynamics Project International was to allow a comprehensive validation of computational fluid dynamics methods against the Cranked-Arrow Wing Aerodynamics Project flight database. A major part of this work involved the generation of high-quality computational grids. Before the grid generation, an airtight geometry of the F-16XL, aircraft was generated by a cooperation of the Cranked-Arrow Wing Aerodynamics Project International partners. Based on this geometry description, both structured and unstructured grids have been generated. The baseline structured (multiblock) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory. Although the algorithms used by the National Aerospace Laboratory had become available just before the Cranked-Arrow Wing Aerodynamics Project International and thus only a limited experience with their application to such a complex configuration had been gained, a grid of good quality was generated well within four weeks. This time compared favorably with that required to produce the unstructured grids in the Cranked-Arrow Wing Aerodynamics Project International. The baseline all-tetrahedral and hybrid unstructured grids have been generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, trimmed unstructured grids have been generated at the European Aeronautic Defence and Space Company's Military Air Systems, University of Tennessee at Chattanooga SimCenter, Boeing Phantom Works, Royal Institute of Technology, and the Swedish Defence Research Agency. All grids generated within the framework of the Cranked-Arrow Wing Aerodynamics Project International will be discussed in the paper. Both results obtained on the structured grids and the unstructured grids showed a significant improvement in agreement with flight-test data in comparison with those obtained on the structured multiblock grid used during the Cranked-Arrow Wing Aerodynamics Project.

  • 2.
    Borglund, Dan
    KTH, Superseded Departments, Aeronautical Engineering.
    Aeroservoelastic design optimization with experimental verification2001In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 38, no 5, p. 958-961Article in journal (Refereed)
    Abstract [en]

    A demonstration of integrated design optimization of an aeroservoelastic system was presented. It was shown that the simultaneous design of structural and control system required a two-step procedure to result in a minimum weight design and a control law that is well-designed for all operating conditions. The essential dynamics was predicted using a aeroservoelastic model, and final design with 42% less weight penalty was obtained using the integrated approach.

  • 3.
    Borglund, Dan
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Robust aeroelastic stability analysis considering frequency-domain aerodynamic uncertainty2003In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 40, no 1, p. 189-193Article in journal (Refereed)
    Abstract [en]

    The problem of modeling frequency-domain aerodynamic uncertainty for a slender wing structure is investigated. Based on an unsteady lifting-line theory used for the generalized aerodynamic forces, a quite versatile uncertainty description with a clear physical interpretation is proposed. The uncertainty description is easily put in a form suitable for application of the mu framework in robust linear control. Because only frequency response matrices are required for the mu computations, the proposed uncertainty description can be used for robust stability and performance analysis without rational function approximations of the aerodynamic transfer function matrices. The usefulness of the uncertainty description and the methods available for robust aeroelastic stability analysis is demonstrated by performing aeroelastic wind-tunnel experiments.

  • 4.
    Borglund, Dan
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    The mu-k method for robust flutter solutions2004In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, no 5, p. 1209-1216Article in journal (Refereed)
    Abstract [en]

    A straightforward frequency-domain method for robust flutter analysis is presented. First, a versatile uncertainty description for the unsteady aerodynamic forces is derived by assigning uncertainty to the frequency-domain pressure coefficients. The uncertainty description applies to any frequency-domain aerodynamic method, benefits from the same level of geometric detail as the underlying aerodynamic model, exploits the modal formulation of the flutter equation, and is computed by simple postprocessing of standard aerodynamic data. Next, structured singular value analysis is applied to derive an explicit criterion for robust flutter stability based on the flutter equation and a parametric uncertainty description. The resulting procedure for computation of a worst-case flutter boundary resembles a p-k or g-method flutter analysis, produces match-point flutter solutions and allows for detailed aerodynamic uncertainty descriptions. Finally, the proposed method is successfully applied to a wind-tunnel model in low-speed airflow.

  • 5.
    Borglund, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Upper-bound flutter speed estimation using the mu-k method2005In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 42, no 2, p. 555-557Article in journal (Refereed)
    Abstract [en]

    The use of upper-bound μ-k estimation method in the development of robust flutter analysis and flutter testing, was described. Since only the frequency-domain aerodynamic forces are required to compute μ(k), established aerodynamic methods can be used for the robust flutter analysis. A robust flutter analysis considering wing-tip aerodynamic uncertainty was developed in MATLAB® for a wind-tunnel model in low-speed airflow. The results show that the extended procedure for robust flutter analysis was successfully applied to a wind-tunnel model in low-speed airflow.

  • 6.
    Borglund, Dan
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Kroo, I. M.
    Aeroelastic design optimization of a two-spar flexible wind-tunnel model2002In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 39, no 6, p. 1074-1076Article in journal (Refereed)
  • 7.
    Borglund, Dan
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Nilsson, Ulrik
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Robust wing flutter suppression considering aerodynamic uncertainty2004In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, no 2, p. 331-334Article in journal (Refereed)
    Abstract [en]

    A robust aeroservoelastic stability analysis considering frequency-domain aerodynamic uncertainty is utilized for robust control law design for flutter suppression of a flexible wing. The problem of stabilizing the wing in flutter using a minimum amount of control power is posed. For this purpose, numerical optimization is used to minimize the norm of a simple low-order controller subject to constraints on robust closed-loop stability. Robust stability is enforced in the optimization problem by posing constraints on the upper bounds on structured singular values and eigenvalues obtained from a linear stability analysis. The resulting controller is synthesized using gain scheduling, and robust wing flutter suppression is demonstrated in wind-tunnel testing.

  • 8.
    Borglund, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Efficient computation of robust flutter boundaries using the mu-k method2006In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 43, no 6, p. 1763-1769Article in journal (Refereed)
    Abstract [en]

    A simple and efficient algorithm for robust flutter analysis is presented. First, a general linear fractional transformation formulation of the mu-k method is provided, making it straightforward to pose the uncertain flutter equation in a form suitable for structured singular value analysis. The new formulation establishes a close connection between mu-k flutter analysis and traditional frequency-domain flutter analysis, which is used to formulate an efficient algorithm for computation of robust flutter boundaries. The proposed method is successfully applied to an F-16 sample test case with uncertain external stores aerodynamics, showing that standard tools for structural dynamics and unsteady aerodynamics can be used to perform robust flutter analysis with only modest additional modeling.

  • 9.
    Borglund, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Solution of the Flutter Eigenvalue Problem with Mixed Structural/Aerodynamic Uncertainty2011In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 48, no 1, p. 343-348Article in journal (Refereed)
    Abstract [en]

    The solution of the flutter eigenvalue problem with mixed structural/aerodynamic uncertainty was examined. A delta-wing wind-tunnel model was used as a test case. The model had a simple structural design and was made of glass-fiber and carbon-fiber composite materials. It had a semispan of 0.88 m and mean chord of 0.70m and was mounted vertically in the low-speed wind tunnel L2000. The numerical analysis was based on a NASTRAN model with shell elements for the wing, mass elements for the missile, and aerodynamic panels for doublet-lattice aerodynamic loads. The relatively stiff missile was modeled as a rigid body attached to the wing tip. The nominal eigenvalue was always an interior point of the corresponding eigenvalue set. A parameter sweep taking only aerodynamic uncertainty into account was performed by solving the eigenvalue problem for a set of parameter values. The eigenvalue sets based on one patch and seven patches, respectively, showed only slight difference.

  • 10.
    Bérard, Adrien
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Isikveren, Askin
    University of Bristol.
    Conceptual Design Prediction of the Buffet Envelope of Transport Aircraft2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 5, p. 1593-1606Article in journal (Refereed)
    Abstract [en]

    This paper describes a methodology that inexpensively predicts the buffet envelope of new transport airplane wing geometries at the conceptual design stage. The parameters that demonstrate a strong functional sensitivity to buffet onset were identified and their relative effect was quantified. To estimate the buffet envelope of any target aircraft geometry, the method uses fractional change transformations in consort with a generic reference buffet onset curve provided by the authors or the buffet onset of a known seed airplane. The explicit design variables required to perform buffet onset prediction are those describing the wing planform and the wingtip section. The mutually exclusive nature of the method's analytical construct provides considerable freedom in deciding the scope of free-design-variable complexity. The method has been shown to be adequately robust and flexible enough to deal with a wide variety of transport airplane designs. For the example transport airplanes considered, irrespective of aircraft morphology and en route flight phase, the relative error in prediction was found to be mostly within +/-5.0%, with occasional excursions not exceeding a +/-9.0% bandwidth. The standard error of estimate for the lift coefficient at 1.0 g buffet onset at a given Mach number was calculated to be 0.0262.

  • 11. Carlsson, M.
    et al.
    Kuttenkeuler, Jakob
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Design and testing of a blended wing body aeroelastic wind-tunnel model2003In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 40, no 1, p. 211-213Article in journal (Refereed)
  • 12.
    Carlsson, Martin
    KTH, Superseded Departments, Vehicle Engineering.
    Aeroelastic model design using an integrated optimization approach2004In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, no 6, p. 1523-1526Article in journal (Refereed)
    Abstract [en]

    An elastic wind-tunnel model was designed with an internal carbon fiber/epoxy composite beam as primary structure and with prescribed static and dynamic behavior. The sequential stiffness and mass design approach was used in order to find a design with resonably representative properties. The integrated stiffness and mass design optimization was shown to improve the quality of the model significantly. It was found that the stiffness and frequency objectives did not cause any significant problem, but the mode shape matching was more involved.

  • 13.
    Carlsson, Martin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Control surface response of a blended wing body aeroelastic wind-tunnel model2005In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 42, no 3, p. 738-742Article in journal (Refereed)
    Abstract [en]

    The aeroelastic behavior of a blended wing body- (BWB-) type wind-tunnel model is investigated. The design concept, numerical modeling, and experimental procedures are described together with comparisons of numerical and experimental results. The main focus is on aeroelastic response due to static and dynamic control surface deflections. The numerical analysis is performed using a finite element structural model and doublet lattice aerodynamics. The agreement between the predicted and experimental aerodynamic loads and aeroelastic deformations are good overall. However, the investigation shows that the loads due to control surface deflections are slightly overpredicted by the numerical analysis. The results indicate that available numerical methods are capable of predicting aeroelastic behavior of the BWB-type aircraft with reasonable accuracy.

  • 14.
    de Try, Fredrik
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Estimation of flight load history using global positioning system data2004In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, no 2, p. 418-420Article in journal (Refereed)
    Abstract [en]

    The Global Positioning System (GPS) and velocity data were used to estimate flight load history. For the study, a SK60:072 aircraft equipped with and inertial measurement unit (IMU) and GPS receiver was used. It was suggested that the method of superimposing filtered IMU data from a reference aircraft shows promising results. It was also suggested that the number of occurrences using GPS data with superimposed higher frequency IMU data agrees well with the number of occurrences obtained using only the IMU data.

  • 15.
    de Try, Fredrik
    KTH, Superseded Departments, Aeronautical Engineering.
    Flight-path reconstruction using numerical optimization2004In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, no 4, p. 959-962Article in journal (Refereed)
  • 16.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Fast, Unstructured-Mesh Finite-Element Method for Nonlinear Subsonic Flow2012In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 49, no 5, p. 1471-1479Article in journal (Refereed)
    Abstract [en]

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

  • 17.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Flutter Equation as a Piecewise Quadratic Eigenvalue Problem2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 3, p. 1068-1070Article in journal (Refereed)
  • 18.
    Eller, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Heinze, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Approach to Induced Drag Reduction with Experimental Evaluation2005In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 42, no 6, p. 1478-1485Article in journal (Refereed)
    Abstract [en]

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

  • 19.
    Görtz, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirasek, A.
    Morton, Scott. A.
    McDaniel, David R.
    Cummings, Russell M.
    Lamar, John E.
    Abdol-Hamid, Khaled S.
    Standard Unstructured Grid Solutions for Cranked Arrow Wing Aerodynamics Project International F-16XL2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 2, p. 385-408Article in journal (Refereed)
    Abstract [en]

    Steady and unsteady viscous flow simulations of a full-scale, semispan, and full-span model of the F-16XL-1 aircraft are performed with three different computational fluid dynamics codes using a common unstructured grid. Six different flight conditions are considered. They represent Reynolds and Mach number combinations at subsonic speeds, with and without sideslip. The steady computations of the flow at these flight conditions are made with several Reynolds-averaged Navier-Stokes turbulence models of different complexity. Detached-eddy simulation, delayed detached-eddy simulation, and an algebraic hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation model are used to quantify unsteady effects at the same flight conditions. The computed results are compared with flight-test data in the form of surface pressures, skin friction, and boundary-layer velocity profiles. The focus of the comparison is on turbulence modeling effects and effects of unsteadiness. The overall agreement with flight data is good, with no clear trend as to which physical modeling approach is superior for this class of flow. The Reynolds-averaged Navier-Stokes turbulence models perform well in predicting the flow in an average sense. However, some of the flow conditions involve locally unsteady flow over the aircraft, which are held responsible for the scatter between the different turbulence modeling approaches. The detached-eddy simulations are able to quantify the unsteady effects, although they are not consistently better than the Reynolds-averaged Navier-Stokes turbulence models in predicting the flow in an average sense in these flow regions. Detached-eddy simulation fails to predict boundary-layer profiles consistently over a range of flow regimes, with delayed detached-eddy simulation and hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation models offering a remedy to recover some of the predictive capabilities of the underlying Reynolds-averaged Navier-Stokes turbulence model. Nonetheless, the confidence in the predictive capabilities of the computational fluid dynamics codes with regard to complex vortical flowfields around high-performance aircraft of this planform increased significantly during this study.

  • 20.
    Heinze, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Assessment of Critical Fuel Configurations Using Robust Flutter Analysis2007In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 44, no 6, p. 2034-2039Article in journal (Refereed)
    Abstract [en]

    An approach to assess critical fuel configurations using robust flutter analysis is presented. A realistic aircraft model is considered to demonstrate how an available finite element model can be adapted to easily apply robust flutter analysis with respect to structural variations such as fuel-level variations. The study shows that standard analysis tools can be used to efficiently generate the system data that are required to perform robust flutter analysis. The μ-k method is used to compute the worst-case flutter speed, and the corresponding worst-case fuel configuration is found. The main advantage of the proposed approach is that μ. analysis guarantees robustness with respect to all possible fuel configurations represented by the tank model.

  • 21.
    Heinze, Sebastian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Borglund, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Robust Flutter Analysis Considering Mode Shape Variations2008In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 45, no 3, p. 1070-1074Article in journal (Refereed)
    Abstract [en]

    A study was conducted to perform robust flutter analysis, considering mode shape variation problems. The study demonstrated that the assumption of a fixed modal base can lead to incorrect flutter results. It was demonstrated the nominal model can act as the basis for performing robust flutter analysis. The study assumed that the critical flutter mode shape can be represented by a linear combination of eigenmodes. The study also demonstrated that the modal base method can be used, to solve the problem of mode shape variations. It was also demonstrated that results of mode shape variation problems can be improved significantly, by adding structural eigenvectors.

  • 22.
    Heinze, Sebastian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Karpel, Moti
    Technion - Israel Institute of Technology.
    Analysis and Wind Tunnel Testing of a Piezoelectric Tab for Aeroelastic Control Applications2006In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 43, no 6, p. 1799-1804Article in journal (Refereed)
    Abstract [en]

    A concept for exploitation of a piezoelectric actuator by using aeroelastic amplification is presented. The approach is to use the actuator for excitation of a tab that occupies the rear 25 % of a free-floating trailing edge flap. A flexible high aspect ratio wing wind tunnel model is used as a test case. Wind tunnel experiments were performed to determine frequency response functions for validation of the numerical model used for the control law design. The aeroservoelastic model is based on state-space equations of motion that accept piezoelectric voltage commands. Control laws are derived for gust alleviation with flutter and control authority constraints, and numerical results that demonstrate a significant reduction in the structural response are presented. Possible applications and feasibility of the concept are discussed.

  • 23.
    Heinze, Sebastian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Borglund, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Assessment of Uncertain External Store Aerodynamics Using mu -p Flutter Analysis2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 3, p. 1062-1068Article in journal (Refereed)
  • 24.
    Jacobsen, Marianne
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf T.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Airspace Constraints in Aircraft Emission Trajectory Optimization2010In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 47, no 4, p. 1256-1265Article in journal (Refereed)
    Abstract [en]

    This paper describes a method for handling restricted airspace in trajectory optimization problems while maintaining the full dynamics of the aircraft model. The discussion is limited to the local solution of the optimization problem. The topological problem of determining which side of the restricted regions the aircraft trajectory should take can be seen as more of a preprocessing stage that determines, for example, the shortest path. The trajectory optimization is performed with environmental objective functions describing the emissions from the aircraft engine. Results from two cases are presented. The first case is flying in the vicinity of an airport during the approach and avoiding flying directly above urban areas. The second case involves a long-distance flight with a large region of restricted airspace in the way. Both cases are performed with a model of the Swedish Air Force trainer SK60. The results show that the solution and the solution time significantly depend on the initial starting guess. With a feasible starting guess, the efficiency of the optimization algorithm is not too degraded by the nonconvex airspace constraints.

  • 25. Jirasek, A.
    et al.
    Eliasson, P.
    Wallin, Stefan
    Computational study of the high-lift a-airfoil2001In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 38, no 4, p. 769-772Article in journal (Refereed)
  • 26. Jirásek, Adam
    Vortex-generator model and its application to flow control2005In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 42, no 6, p. 1486-1491Article in journal (Refereed)
    Abstract [en]

    A new vortex-generator model is introduced, the jBAY model, which provides an efficient method for computational-fluid-dynamics (CFD) simulation of flow systems with vortex-generator arrays. The jBAY model is based on the lifting force theory of Bender, Anderson, and Yagle (Bender, E. E., Anderson, B. H., and Yagle, P. J., "Vortex Generator Modelling for Navier-Stokes Codes," American Society of Mechanical Engineers, FEDSM 996919, New York, July 1999) but uses a novel technique for defining the model control points. This greatly simplifies usage of the model as well as improving its performance and accuracy. The jBAY model is described in the context of its implementation in the CFD code Edge, an unstructured Reynolds-averaged Navier-Stokes solver. Results are presented for a single vortex generator on a flat plate and two flow control cases: an S-duct air intake and a high-lift wing configuration. The model is shown to give good agreement with both experimental results and with CFD computations where the vortex generator is fully gridded. It is demonstrated that the jBAY model is simple to apply and efficiently captures the effect of vortex generator arrays for both internal and external flows.

  • 27.
    Kaufmann, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Material Selection for a Curved C-Spar Based on Cost Optimization2011In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 48, no 3, p. 797-804Article in journal (Refereed)
    Abstract [en]

    A case study for the cost optimization of aircraft structures based on the operating cost as an objective function is presented. The proposed optimization framework contains modules for estimation of the weight, manufacturing cost, nondestructive inspection cost, and structural performance; the latter is enhanced by a kinematic draping model that allows the fiber angles to be simulated more realistically. The case study includes five material systems: aircraft-grade aluminum, two types of resin-transfer molded noncrimp fabric reinforcements, and two types of M21/T800 prepreg. The results are compared in relation to each other, and it is shown that (depending on the estimated fuel burn share of the component) a different material system is favorable when optimizing for low-operating cost.

  • 28.
    Kuttenkeuler, Jakob
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Optical measurements of flutter mode shapes2000In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 37, no 5, p. 846-849Article in journal (Refereed)
    Abstract [en]

    The usefulness of an optical motion capture system in aeroelastic wind-tunnel testing is investigated. A system consisting of four infrared charge-coupled device cameras, observing flat passive reflecting markers, is installed in a low-speed tunnel to measure Butter mode shapes. Free vibration and aeroelastic measurements are performed on four wing configurations consisting of thin flat orthotropic composite laminates with varying laminate orientation. The laminate orientations are chosen to result in dissimilar flutter mode shapes. The wings are equipped with up to 20 markers, and the motion is sampled at 240 Wt. Quantitative scalar comparisons between analysis and experiments, with respect to both amplitude and phase are done using the modal assurance criterion (MAC). Measurements of mode shapes on free vibrating wings (ground vibration tests), as well as limit-cycle Butter oscillations, show good agreement with numerical results. MAC ratings consistently exceeding 0.96 are achieved, However, it is clearly seen that the agreement is better for free vibration comparisons than for Butter This is expected considering the higher complexity of the Butter problem. Thus, the cause cannot be attributed exclusively to insufficiencies in the optical system but also to inaccuracies in the modeling. The good quality of the measurements proves the usefulness of such a noncontact positioning system in experimental wind-tunnel testing, not only in the present flutter context, but in a variety of experimental work affected by aeroelastic deformation.

  • 29.
    Kuttenkeuler, Jakob
    et al.
    KTH, Superseded Departments, Aeronautical Engineering.
    Ringertz, Ulf
    KTH, Superseded Departments, Aeronautical Engineering.
    Aeroelastic design optimization with experimental verification1998In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 35, no 3, p. 505-507Article in journal (Refereed)
  • 30. Luckring, James M.
    et al.
    Park, Michael A.
    Hitzel, Stephan M.
    Jirasek, Adam
    Lofthouse, Andrew J.
    Morton, Scott A.
    McDaniel, David R.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Univ Alabama Birmingham, USA.
    Tomac, Maximillian
    Synthesis of Hybrid Computational Fluid Dynamics Results for F-16XL Aircraft Aerodynamics2017In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, no 6, p. 2100-2114Article in journal (Refereed)
    Abstract [en]

    A synthesis is presented of recent numerical predictions for the F-16XL aircraft flowfields and aerodynamics. The computational analyses were all performed with hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation formulations, with an emphasis on unsteady flows and associated aerodynamics, and results from five computational methods are included. The work focused on one particular low-speed high angle-of-attack flight-test condition, and comparisons against flight-test data are included. This work represents the third coordinated effort using the F-16XL aircraft, and a unique flight-test dataset, to advance the knowledge of slender airframe aerodynamics as well as the capability for predicting these aerodynamics with advanced computational fluid dynamics formulations. The prior efforts were identified as the Cranked-Arrow Wing Aerodynamics Project International.

  • 31. Moens, Frédéric
    et al.
    Perraud, Jean
    Krumbein, Andreas
    Toulorge, Thomas
    Iannelli, Pierluigi
    Eliasson, Peter
    Hanifi, Ardeshir
    Totalförsvarets Forskningsinstitut, Sverige.
    Transition Prediction and Impact on a Three-Dimensional High-Lift-Wing Configuration2008In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 45, no 5, p. 1751-1766Article in journal (Refereed)
    Abstract [en]

    The evolution of the maximum-lift coefficient of a transport aircraft as a function of Reynolds number can be linked to modifications. of the laminar-turbulent transition process. In the framework of European project EUROLIFT I, a task was dedicated to the physical understanding and the numerical modeling of the transition process in high-lift configurations. Then in the follow-up project EUROLIFT II, a major step was the integration of transition-prediction tools within Reynolds-averaged Navier-Stokes solvers to estimate the impact of transition on performance. This paper presents an overview of the different activities dealing with transition in the EUROLIFT II project.

  • 32.
    Norsell, Martin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Multistage trajectory optimization with radar-range constraints2005In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 42, no 4, p. 849-857Article in journal (Refereed)
    Abstract [en]

    The problem of finding an optimal aircraft trajectory for long-distance flights in three dimensions subject to radar detection constraints is considered. A general point-mass model previously developed is not suitable because the time discretization needs to be very fine to resolve the rigid-body dynamics resulting in very large optimization problems. Different reduced mathematical models are derived and compared to the more general performance model. Finally, a long-range mission involving two subsonic jet trainers approaching a radar target is numerically simulated. The results indicate that the time a hostile radar has an approaching aircraft under surveillance can be greatly reduced by using the proposed methodology.

  • 33.
    Persson, Björn
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Radar target modeling using in-flight radar cross-section measurements2017In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, no 1, p. 284-291Article in journal (Refereed)
    Abstract [en]

    A flight experiment with the Saab 105 aircraft and the radar cross-section measurement system Arken has been performed at C and Ku bands. Two types of trajectories were flown, and the flight state was recorded using inertial and satellite navigation equipment. The data were used to recreate the flight in a simulator where the aspect angles and range to the measurement system couldbe calculated. The measured radar cross sectionas a function of time was presented and compared to various statistical fluctuation models, including the distributions used in Swerling cases. Findings showed that the generalized Pareto distribution fit the measured data best and that Swerling case 2 was a good candidate for describing the dynamics of the radar cross section at the Ku band when the aircraft approached the radar head-on. The measured radar cross-section data were analyzed using the fast Fourier transform, from which fluctuation rates for different carrier frequencies and trajectories could be estimated.

  • 34.
    Persson, Björn
    et al.
    Swedish Defence University.
    Bull, Peter
    Swedish Defence University.
    Empirical Study of Flight-Dynamic Influences on Radar Cross-Section2016In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 53, no 2, p. 463-474Article in journal (Refereed)
    Abstract [en]

    In this work, measurements and a method for analyzing flight-dynamic effects on radar cross-section models for aircraft are presented. Flight-dynamic effects need to be considered when designing combat aircraft and creating target models for radar simulators. The work is based on flight data from three different types of aircraft: Piper PA-28 Archer II, Boeing 737, and Saab JAS 39 Gripen. Using inertial navigation and global-positioning systems, the motions of the three aircraft are recorded in flight. From the data, aspect angles toward a radar station located in the extension of the intended flight path are generated using a simulator. It is found that the major contribution to perturbations in aspect angles is due to the rotational degrees of freedom and that bivariate normal distributions are a good candidate for approximating the uncertainty in aspect angles for all three aircraft types. It is also found that each rotational degree of freedom is close to a normal distribution but that the parameter values of the distribution vary with altitude and aircraft type.

  • 35.
    Ringertz, Ulf
    KTH, Superseded Departments, Vehicle Engineering.
    Flight testing an optimal trajectory for the Saab J35 Draken2000In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 37, no 1, p. 187-189Article in journal (Refereed)
  • 36.
    Ringertz, Ulf
    KTH, Superseded Departments, Vehicle Engineering.
    Optimal trajectory for a minimum fuel turn2000In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 37, no 5, p. 932-934Article in journal (Refereed)
  • 37.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirásek, Adam
    Swedish Def Res Agcy, Div Syst Technol.
    Lamar, John
    NASA, Langley Res Ctr.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Badcock, Ken
    Univ Liverpool, Dept Engn.
    Boelens, Okko
    NLR, Natl Aerosp Lab, Dept Flight Phys & Loads, Aerosp Vehicles Div.
    Lessons learned from numerical simulations of the F-16XL at flight conditions2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 2, p. 423-441Article in journal (Refereed)
    Abstract [en]

    Nine organizations participated in the Cranked-Arrow Wing Aerodynamics Project International study and have contributed steady and unsteady viscous simulations of a full-scale semispan model of the F-16XL aircraft. Three different categories of flight Reynolds/Mach number combinations are computed and compared with flight-test measurements for the purpose of code validation and improved understanding of the flight physics. Steady-state simulations are done with several turbulence models (of different complexity, with no topology information required) that overcome Boussinesq-assumption problems in vortical flows. Detached-eddy simulation and its successor, delayed detached-eddy simulation, are used to compute the time-accurate flow development. Common structured and unstructured grids as well as individually adapted unstructured grids were used. Although discrepancies are observed in the comparisons, overall reasonable agreement is demonstrated for surface pressure distribution, local skin friction, and boundary velocity profiles at subsonic speeds. The physical modeling, be it steady or unsteady flow, and the grid resolution both contribute to the discrepancies observed in the comparisons with flight data, but at this time, how much each part contributes to the whole cannot be determined. Overall, it can be said that the technology readiness of computational fluid dynamics simulation technology for the study of vehicle performance has matured since 2001, such that it can be used today with a reasonable level of confidence for complex configurations.

  • 38.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Luckring, James M.
    What Was Learned in Predicting Slender Airframe Aerodynamics with the F-16XL Aircraft2017In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, no 2, p. 444-455Article in journal (Refereed)
    Abstract [en]

    The second Cranked-Arrow Wing Aerodynamics Project, International, coordinated project has been underway to improve high-fidelity computational-fluid-dynamics 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 validation. 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 computational fluid dynamics failed to provide acceptable results. In revisiting 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 Reynolds-averaged Navier-Stokes/unsteady Reynolds-averaged Navier-Stokes/large-eddy simulation 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, finally making the connections between the physics and aircraft features.

  • 39.
    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)
  • 40.
    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.

  • 41.
    Schiavetta, Lucy
    et al.
    Univ Glasgow, Dept Aerosp Engn.
    Boelens, Okko
    NLR, Natl Aerosp Lab, Dept Flight Phys & Loads, Aerosp Vehicles Div.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cummings, Russel
    USAF Acad, Dept Aeronaut, Colorado Springs.
    Fritz, Willy
    EADS Mil Air Sys.
    Badcock, Ken
    Univ Liverpool, Dept Engn.
    Shock effects on delta wing vortex breakdown2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 3, p. 903-914Article in journal (Refereed)
    Abstract [en]

    It has been observed that delta wings placed in a transonic freestream can experience a sudden movement of the vortex breakdown location as the angle of incidence is increased. The current paper uses computational fluid dynamics to examine this behavior in detail. The study shows that a shock/vortex interaction is responsible. The balance of the vortex strength and axial flow and the shock strength are examined to provide an explanation of the sensitivity of the breakdown location. Limited experimental data are available to supplement the computational fluid dynamics results in certain key respects, and the ideal synergy between computational fluid dynamics and experiments for this problem is considered.

  • 42.
    Stenfelt, Gloria
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Lateral Stability and Control of a Tailless Aircraft Configuration2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 6, p. 2161-2164Article in journal (Refereed)
    Abstract [en]

    The aerodynamics of a generic aircraft configuration known as Swing was investigated. The configuration used had two trailing-edge flaps on each wing used for control around all three stability axes included pitch, roll, and yaw. Tests are done in the low-speed wind tunnel L2000 at a freestream velocity of 30 m/s corresponding to a Reynolds number of 6.9 · 105 was applied. A NACA-66009 airfoil was used for the wing, and the outer wing section was twisted up 5° around the leading-edge point of the wing. Asymmetric deflections with the same amplitude for both flaps on each wing were applied for roll control. The deflection of the flaps was recorded with a motion capture system. The infrared light was emitted from four cameras and the light was reflected back to the cameras with a scan rate of 100 Hz and the system computed the distance to the markers. The results revealed that a sudden increase in pitch moment were observed at angles of attack above 10° and the flaps deflected with the same amplitude.

  • 43.
    Stenfelt, Gloria
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Yaw control of a tailless aircraft configuration2010In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 47, no 5, p. 1807-1810Article in journal (Refereed)
    Abstract [en]

    The yaw control of a tailless aircraft configuration is investigated. The four trailing-edge control surfaces are actuated using electrical servos which are controlled using a custom designed Ethernet interface. Measurements of the yaw moment due to sideslip and due to split flap deflections have been performed using a strain gauge balance for both sting configurations in order to estimate the sting interference effects. The mass moment of inertia J is obtained from a yaw ground vibration test using the yaw sting with a torsional spring installed. Dynamic stability is estimated by performing vibration tests in yaw with the torsional spring installed. The required control surface deflections can be large due to the low dynamic pressure when landing. The configuration uses only four flaps for simultaneous control around all three axes and necessary control surface deflections for pitch, roll and yaw need to be superimposed at all times.

  • 44.
    Stenfelt, Gloria
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Ringertz, Ulf
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Yaw Departure and Recovery of a Tailless Aircraft Configuration2013In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 50, no 1, p. 311-315Article in journal (Refereed)
    Abstract [en]

    The ability to recover an aircraft from an out-of-control condition is essential both from a safety and from an economical point of view. Investigations show that a significant amount of fatal accidents occur due to loss of control outside the tested flight envelope. For passenger aircraft, safety is of greatest importance; for military aircraft, a pilot's life can be saved by an ejection seat and the remaining loss after an accident is the cost of the aircraft. The purpose of this study was to investigate departure and recovery in the yaw degree of freedom for a tailless aircraft model. In previous studies, stability and control investigations have shown that the model is not stable in yaw for low angles of attack (AOA), and a simple control model has been implemented to handle the instability at moderate sideslip angles. An increase in yaw damping due to deflected flaps is, however, observed. To accurately simulate the departure motion for the current experimental setup by using the preceding equations, a better understanding of the friction is needed.

  • 45.
    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.

  • 46.
    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)
  • 47.
    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.

  • 48.
    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.

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