Showing papers in "Journal of Aircraft in 2002"

High-Fidelity Aerostructural Design Optimization of a Supersonic Business Jet

Abstract: This paper focuses on the demonstration of an integrated aerostructural method for the design of aerospace vehicles. Both aerodynamics and structures are represented using high-fidelity models such as the Euler equations for the aerodynamics and a detailed finite element model for the primary structure. The aerodynamic outer-mold line and a structure of fixed topology are parameterized using a large number of design variables. The aerostructural sensitivities of aerodynamic and structural cost functions with respect to both outer-mold line shape and structural variables are computed using an accurate and efficient coupled-adjoint procedure. Kreisselmeier‐ Steinhauser functions are used to reduce the number of structural constraints in the problem. Results of the aerodynamic shape and structural optimization of a natural laminar-flow supersonic business jet are presented together with an assessment of the accuracy of the sensitivity information obtained using the coupled-adjoint procedure.

Free-Vortex Filament Methods for the Analysis of Helicopter Rotor Wakes

Abstract: The theoretical basis and the numerical implementation of free-vortex filament methods are reviewed for application to the prediction and analysis of helicopter rotor wakes. The governing equations for the problem are described, with a discussion of finite difference approximations to these equations and various numerical solution techniques. Both relaxation and time-marching wake solution techniques are reviewed. It is emphasized how the careful consideration of stability and convergence (grid-independent behavior) are important to ensure a physically correct wake solution. The implementation of viscous diffusion and filament straining effects are also discussed. The need for boundary condition corrections to compensate for the inevitable wake truncation are described. Algorithms to accelerate the wake solution using velocity field interpolation are shown to reduce computational costs without a loss of accuracy. Several challenging examples of the application of free-vortex filament methods to helicopter rotor problems are shown, including multirotor configurations, flight near the ground, maneuvering flight conditions, and descending flight through the vortex ring state

Comparison of wing characteristics at an ultralow Reynolds number

Abstract: The hydrodynamic characteristics of 20 wings of different airfoil shape were measured at Re = 4 X 103. Each wing had an aspect ratio At of 7.25. Comparison of the measured wing characteristics showed that hydrodynamic characteristics of a wing with a rectangular airfoil can be improved by either a camber of 5%, a sharp leading edge, or proper corrugation

Separation Control in Duct Flows

Abstract: Active control of separation in a duct flow is achieved using an array of fluidic actuators based on synthetic-jet technology. A two-dimensional serpentine duct model is designed to produce controlled separated flow in two configurations, in which the flow is either completely separated or has a separation bubble. An array of synthetic-jet actuators is placed within the separated flow domain in the diffuser section downstream of the onset of separation. Actuation leads to complete flow attachment up to U in =75 m/s (M≃0.2) and to partial reattachment up to U in = 105 m/s (M≃0.3)

Navier-Stokes Optimization of Supersonic Wings with Four Objectives Using Evolutionary Algorithm

Abstract: The design optimization of wings for supersonic transport by means of Multiobjective Evolutionary Algorithms is presented. Three objective functions are first considered to minimize the drag for transonic cruise, the drag for supersonic cruise and the bending moment at the wing root at the supersonic condition. The wing shape is defined by planform, thickness distributions and warp shapes in total of 66 design variables. A Navier-Stokes code is used to evaluate the aerodynamic performance at both cruise conditions. Based on the results, the optimization problem is further revised. The definition of the thickness distributions is given more precisely by adding control points. In total 72 design variables are used. The fourth objective function to minimize the pitching moment is added. The results of the revised optimization are compared with the three-objective optimization results as well as NAL’s design. Two Pareto solutions are found superior to NAL’s design for all four objective functions. The planform shapes of those solutions are “Arrow wing” type.

Design and manufacturing of aerospace composite structures, state-of-the-art assessment

Abstract: The results ofan assessment ofthe state of theartin the design and manufacturing of largecompositestructures are described. The focus of the assessment is on the use of polymeric matrix composite materials for large airframe structural components, such as thosein commercial and military aircraft and spacetransportation vehicles. Applications of composite materials for large commercial transport aircraft, general aviation aircraft, rotorcraft, military aircraft, and uninhabited rocket launch vehicles are reviewed. The results of the assessment of the state of the art include a summary of lessons learned, examples of current practice, and an assessment of advanced technologies under development. The results of the assessment conclude with an evaluation of the future technology challenges and advancements associated with applications of composite materials to the primary structures of commercial transport aircraft and advanced space transportation vehicles. These future technologies include breakthroughs in materials and process methods, next generation design tools, and nondestructive examination methods. I. Introduction A N assessment of the design and manufacturing practices for large composite structures has been conducted to determine the current state of the art for these technologies. The background that motivated the assessment was a series of unexpected manufacturing and design problems with the composite structures of several NASA experimental vehicles currently under development. The focus of the assessment is on the use of polymeric matrix composite materials for large airframe structural components such as those in commercial and military aircraft and space transportation vehicles. The baseline for the assessment is the historical evolution of the use of composite materials in actual aerospace vehicles. The assessment emphasizes the application of composite structures in moderately to heavily loaded aerospace vehicles. Applications of composite materials are reviewed for large commercial transport aircraft,generalaviation aircraft,rotorcraft, military e ghteraircraft, and military transport aircraft. The baseline also includes the application of composite materials for uninhabited rockets and space transportation vehicles. The assessment of the state of the art includes a summary of lessons learned, examples of current practice, and an assessment of advanced technologies under development. The assessment concludes with an evaluation of the future technology challenges associated with applications of composite materials to the primary structure of commercial aircraft and advanced space transportation vehicles. As a preamble to assessing the state of the art in the design and manufacturing of composite structures, the design requirements for aerospace vehicles are briee y reviewed. Because of the universal design requirement to minimize the gross takeoff weight of all aerospace vehicles, aerospace structural components are designed at or near zero margin of safety. Whereas the margin of safety is not

Computational and Experimental Investigation of Limit Cycle Oscillations of Nonlinear Aeroelastic Systems

Abstract: A wide variety of pathologies, such as store-induced limit-cycle oscillations, have been observed on high-performance aircraft and have been attributed to transient nonlinear aeroelastic effects. Ignoring the nonlinearity of the structure or the aerodynamics will lead to inaccurate prediction of these nonlinear aeroelastic phenomena. The current paper presents the development and representative results of a high-fidelity multidisciplinary analysis tool that accurately predicts limit-cycle oscillations (LCOs) of an aeroelastic system with combined structural and aerodynamic nonlinearities. Wind-tunnel measurements have been carried out to validate the findings of the investigation. The current investigation concentrates on the prediction of the critical physical terms that dominate the mechanism of LCO. The aeroelastic computations predict LCO amplitudes and frequencies in very close agreement with the experimental data. The results emphasize the importance of modeling the nonlinearities of both the fluid and structure for the accurate prediction of LCO for nonlinear aeroelastic systems.

Computational Modeling of Hovering Rotor and Wake Aerodynamics

Abstract: Steady-state Reynolds-averaged Navier ‐Stokes computations are presented for a range of UH-60A model-rotor testcasesinhover. Thecomputationsaredesignedto assessgrid-related effectson thenumericalresultsandemploy 1)structuredoversetgridswithhighresolution ontherotorblades,2 )asystematicvariationofgridresolutioninthe rotor wake, and 3 ) a systematic variation of outer-boundary locations. Computed rotor performance values agree very well with experimental measurements and show little sensitivity to either grid resolution or outer-boundary locations. However, the computations uniformly overpredict the blade sectional thrust near the rotor tip. This overprediction of blade tip thrust is explained by an analysis of the circulation distribution in the computed rotor wake system.

Review of Active Techniques for Aerospace Vibro-Acoustic Control

Abstract: This paper presents a review of active techniques for aerospace vibro-acoustic control. First, the mechanisms of airborne or structure-borne sound generation and transmission in aerospace vehicles are briefly reviewed. The main approaches of passive and active noise/vibration control are then summarised, and three examples of active systems that have already been developed into practical aerospace applications are briefly described. Finally the actuator, sensor, and control system requirements for aerospace applications are discussed.

Active Control of Separation on a Wing with Oscillating Camber

Abstract: Introduction L OW-REYNOLDS-NUMBER effects are signiŽ cant in the aerodynamics of low-speed airfoils, aircraft intended to operate in low-density environments, and small-scale lifting surfaces such as insect and bird wings. Current aerodynamic applications includemicro-aerialvehicles and unmannedaerial vehicles, as well as aircraft operating at high altitudes or low-density atmospheres other than Earth’s. The primary difŽ culty with the operation of a wing at low Reynolds number is that the  ow over the suction surface encounters an adverse pressure gradient at a point at which the boundary layer is quite likely to still be laminar. Because a laminar boundary layer is incapable of negotiating any but the slightest adverse pressure gradient, the  ow will inevitably separate. The separated  ow then transitions to turbulence, entrains  uid, and reattaches to form a turbulent boundary layer. The resulting structure is the laminar separation bubble, which has been described by Lissaman.1 A number of different  ow-control approaches have been investigated to reduce separationand improve efŽ ciency at lowReynolds numbers. Continuous blowing and sucking have long been shown to havepronouncedeffects.More recently, intermittentblowing and sucking in the form of synthetic jets have shown their effectiveness and suggest the presence of optimum values in the range of frequency inputs, which can translate to other oscillatory inputs.3i5 Mechanical momentum transfer and acoustic excitation have also been explored. The approach presented herein employs an adaptive wing.6 Naturally, all practical wings are adaptive in the sense that they use actuators to alter lift coefŽ cient by changing effectiveproŽ le with a subsequentloss in efŽ ciency.A truly adaptivewing, however, refers to an airfoil, which can change its proŽ le to adapt optimally to  ow conditions. Similar concepts have been explored in the past, such as the snap-through airfoil, which changes local airfoil camber by moving a  exible portion of the pressure surface or the Defense AdvancedResearch Projects Agency “smart wing,” which uses torsional elements to twist the wing. Modern smart materials such as piezoelectricactuators offer great promise in the area of future stall

Navier-Stokes Analysis of Helicopter Rotor Aerodynamics in Hover and Forward Flight

Abstract: Reynolds-averaged compressible Navier ‐Stokes computations are presented for the hovering 7A model rotor and a low aspect ratio NACA0012 rotor in nonlifting forward e ight. For enhanced hover performance prediction, aeroelastic effects are taken into account by tightly coupling the e ow solver with a e nite element model of the blade based on Timoshenko beam theory. Good agreement between computed and measured rotor performance is achieved for three collective pitch settings on structured periodic grids featuring noncongruent cell faces along the periodicity planes. Results of a hybrid Navier ‐Stokes/Euler chimera hover computation are presented, in addition to the periodic grid analysis demonstrating the superiority of the overset grid approach with respect to tip vortex conservation. The unsteady Navier ‐Stokes computations for the nonlifting forward e ight test case show more sensitivity relative to time step size than comparable Euler analyses. Overall correlation of computed and experimental near-tip pressure distributions over blade azimuth is considered to be fair, and the strong transonic effects on the advancing blade are adequately captured by the numerical analysis.

Apparent Mass of Parafoils with Spanwise Camber

Abstract: For an arbitrarily shaped body, there may be more than one center of apparent mass The apparent mass of a parafoil shape for motions along various axes is computed using potential flow analysis From this, the 6 x 6 apparent mass matrix about some reference point is computed Parametric forms for estimating the terms are given The existence of multiple mass centers results in off-diagonal terms in this matrix that couple the translational and rotational motions It is shown how the nondiagonal 6 x 6 apparent inertia matrix about a certain reference point can be used to compute the corresponding apparent mass matrix at any other reference point Dynamic equations including nonlinear terms are presented

Match-Point Solutions for Robust Flutter Analysis

Abstract: The computation of robust e utter speeds presents a signie cant advancement over traditional types of e utter analysis. In particular, π-method analysis is able to generate robust e utter speeds that represent worst-case e ight conditions with respect to potential modeling errors. Robust e utter speeds may be computed using a model formulation that has been previously presented; however, that formulation has limitations in its ability to generate a match-point solution. A model formulation is introduced for which π-method analysis is guaranteed to compute a match-point solution. The match-point solution is immediately realized by analyzing a single model so the computation time is reduced from the previous approach that required iterations. Also, the solution is able to consider parametric uncertainty in any element, whereas the previous formulation did not consider mass uncertainty. The match-point formulation is derived by properly treating the nonlinear perturbations and uncertainties that affect theequation of motion. TheAerostructures Test Wing isused to demonstrate thatthe π-method analysis computes match-point e utter speeds using this new formulation.

Airplane design: Past, present, and future

Abstract: The state of the aerospace industry in general, and specifically the aeronautics and aircraft design portion of it, is examined in a long-term historical context. The current crisis in aeronautics is shown to be both a unique development and a continuation of our cyclical past, for reasons to be discussed in the text of the article. The evolution of the methods and techniques that have been available to synthesize and develop a new airplane configuration are also examined. Although much will change in terms of tools and techniques, much will remain remarkably invariant in basic overall design strategies and the attributes of those skilled in their execution. Finally, some positive steps are suggested that we individually (in our respective companies, agencies, and institutions), and collectively as an aeronautics community, can take to ensure the development of a future generation of airplane designers who are as skilled as those who have created our heritage

Limit-Cycle Hysteresis Response for a High-Aspect-Ratio Wing Model

Abstract: An experimental high-aspect-ratio wing aeroelastic model with a slender body at the tip has been constructed, and the response due to flutter and limit-cycle oscillations (LCOs) has been measured in a wind-tunnel test. A theoretical model has been developed and calculations made to correlate with the experimental data. Structural equations of motion based on nonlinear beam theory are combined with the ONERA aerodynamic stall model to study the LCO hysteresis phenomenon of a high-aspect-ratio wing model. Time simulation and a harmonic balance approach are each used to compute the LCO hysteretic response.The results between the theory and experiment are in good agreement.

Recent results on two-dimensional airfoils using a lattice Boltzmann-based algorithm

Abstract: There have been significant advancements made in the lattice Boltzmann-based software PowerFLOW during the last couple of years for computational fluid dynamics. Recently, the newest version, PowerFLOW 3.2, was used to simulate two NACA airfoil benchmark cases. The results are compared with available experimental data as well as other numerical results

Evolution of U.S. military aircraft structures technology

Abstract: A survey of the major structures technology developments that have ineuenced modern aircraft design is presented. The authors’ perspectives on the key materials and design concepts that are presently driving U.S. Air Force and Navy military airframes are presented. The current focus of research and development (R&D) structuraldevelopmentresourcesandthereasonsforthisfocusareaddressed.Somethoughtsonhowtoapproachfuture designs are provided, and the structures technologies that are expected to be the focus of future R&D efforts are identieed.

Linear and Nonlinear Aeroelastic Analysis of Fighter-Type Wing with Control Surface

Abstract: Linear and nonlinear aeroelastic analyses of a fighter-type wing with a control surface have been performed by using frequency-domain and time-domain analyses. Modes from free vibration analysis and a doublet-hybrid method are used for the computation of subsonic unsteady aerodynamic forces. The fictitious mass modal approach is used to reduce the problem size and the computation time in the linear and nonlinear flutter analyses. For the nonlinear flutter analysis, the control surface hinge is represented by a free-play spring and is linearized by using the describing function method. The linear and nonlinear flutter analyses indicate that the flapping mode of the control surface and the hinge stiffness have significant effects on the flutter characteristics. From the nonlinear flutter analysis, limit-cycle oscillation and chaotic motion are observed in a wide range of air speed below the linear flutter boundary, and a jump of limit-cycle oscillation amplitude is observed.

Recent Improvements to a Hybrid Method for Rotors in Forward Flight

Abstract: Ahybrid Navier ‐Stokes/full potential solver has been developed for the efe cient prediction of three-dimensional unsteady viscous e ow phenomena that occur over helicopter rotors in forward e ight. The method combines a Navier‐Stokes analysis near the blade, modeling the viscous e ow and near wake with a potential e ow analysis in the far e eld, modeling inviscid isentropic e ow. A grid motion module has been developed to account for the blade motion and elastic deformations. Free and prescribed wake models have been developed to account for the tip vortex effects once the vortex leaves the viscous e ow region and enters the potential e ow region. Sample results are presented for a two-bladed AH-1G rotor in descent and for a UH-60A rotor in high-speed forward e ight. Comparisons with experiments, e ight test data, and other numerical simulations are given.

Heat transfer correlation for anti-icing systems

Abstract: Nomenclature Aimp = total area of jet impingement a;b;c = constants C = constant Cp = specie c heat capacity of air Cx = distance between the holes d = hole diameter G = mass e ow per unit area of impingement h = heat transfer coefe cient N = average heat transfer coefe cient, q=Aimp.Tpiccolo i N Tlipskin) L = length of nozzle N = number of holes Nu = local Nusselt number Nu = average Nusselt number Pr = Prandtl number q = heat transfer from impinging air, w £Cp £.Tpiccolo i N Texhaust/£3600 Re = Reynolds number based on hole diameter, .w=Nholes/£.d=Aholeπ/ ReG = Reynolds number based on impingement area, 4Gd=oπ T = temperature N T = average temperature w = mass e ow rate Zn = perpendicular distance from hole to lipskin µ = jet impingement angle π = dynamic Viscosity

Experimental Investigation of Self-Actuating, Upper-Surface, High-Lift-Enhancing Effectors

Abstract: The increase in the maximum lift of an airfoil caused by small, movable tabs mounted on its upper surface has been explored in low-speed, wind-tunnel experiments at a chord Reynolds number of 1 :0 ££ 10 6 . These devices, herein called lift-enhancing effectors, have a chord that is 9% that of the airfoil and deploy passively at angles of attack approaching stall.Compared to theclean airfoil, themaximum lift coefe cientis increased by approximately 20%withthesesimpledevices.Theliftincreaseismainlycausedbytheeffectorsactingas“ pressuredams,” allowing lower pressures upstream of their location than would occur otherwise. At an effector the pressure recovers in a stepwise manner and continues downstream toward a trailing-edge value that is higher than that of the clean airfoil. This higher trailing-edge pressure also contributes to the increase in lift by allowing higher pressures over much of thelowersurface. It has been shown that, in the absence of separation, properly installed effectors will lay e ush on the surface and allow the airfoil to have the same performance in the low-drag range as the clean airfoil.

Structural Optimization of a Hat-Stiffened Panel Using Response Surfaces

Abstract: A design study for structural optimization of a hat-stiffened laminated composite panel concept for an upper cover panel of a typical passenger bay of a blended wing-body transport airplane configuration is described. The feasibility of a hat-stiffened composite panel concept for an upper cover panel is investigated and is compared on the basis of weight to a thick sandwich panel concept that has been selected by designers as the baseline concept for the upper cover panel. The upper cover panel is designed for two load cases: internal pressure only and combined internal pressure and spanwise compression due to wing bending. The structural optimization problem is formulated using the panel weight as the objective function, with constraints on stress and buckling. The spacing of the hat stiffeners, the thickness of the skin, and the thickness of the components of the hat stiffener are used as design variables. The initial geometry of the hat-stiffened panel design is determined using the PANDA2 program by restricting the design to have uniform cross section in the spanwise direction. Because of the pressure loading, a more efficient design has variable cross section. Such designs are obtained by combining the STAGS finite element program with the optimization program in the Microsoft EXCEL spreadsheet program using response surfaces. Buckling and stress response surfaces are constructed from multiple STAGS analyses and are used as constraints in the optimization. The optimization conducted with the response surfaces results in considerable weight savings compared to the uniform cross section design, albeit a more complex design. Initial optimization cycles identify a design space where simple approximate analyses, such as Euler-Bernoulli beam theory and Kirchhoff plate theory applied to laminated composites, can be used to predict the behavior of the structure.

Velocity Field Above a Rotor Disk by a New Dynamic Inflow Model

Abstract: The potential e ow equations are converted to ordinary differential equations through a Galerkin approach in which velocity and pressure potential functions are expanded in terms of closed-form solutions to Laplace’ s equation. Because the method gives differential equations for the e ow in terms of a relatively few generalized coordinates that represent modes of the e owe eld, the resultant equations can be used effectively in preliminary design, real-time simulations, and dynamic eigenvalue analysis for aeroelasticity. This new theory is more general than the Peters ‐He dynamic wake model because it has a more rigorous derivation and includes ine ow modes previously neglected in the Peters ‐He model. Results are presented in the frequency domain for simple harmonic motion. Thecompletevelocity e eld above the disk is obtained by this new methodology, foraxial and skewed e ows, for various skew angles, and for different pressure distributions and are compared with the Peters ‐He model and with an exact solution obtained by a convolution integral.

Simulation of Aircraft Landing Gears with a Nonlinear Dynamic Finite Element Code

Abstract: Recent advances in computational speed have made aircraft and spacecraft crash simulations using an explicit, nonlinear, transient-dynamic,e niteelement analysiscodemore feasible.This paperdescribes thedevelopment of a simplelanding-gearmodel, which accurately simulatestheenergy absorbed by thegearwithoutaddingsubstantial complexity to the model. For a crash model the landing gear response is approximated with a spring where the force applied to the fuselage is computed in a user-written subroutine. Helicopter crash simulations using this approach are compared with previously acquired experimental data from a full-scale crash test of a composite helicopter.

Boundary Conforming Discontinuous Galerkin Finite Element Approach for Rotorcraft Simulations

Abstract: A numerical method has been developed for predicting the complex vortex wake for a helicopter rotor in hover and in forward flight. The method is based on the solution of the three-dimensional, compressible Euler equations expressed in an arbitrary Lagrangian Eulerian reference frame. A second-order accurate discontinuous Galerkin finite element method is used to discretize the governing equations on a hexahedral mesh. Unstructured, local mesh refinement is performed to enable prediction of the structure of the vortex wake. The capabilities of this computational fluid dynamics method are demonstrated by simulations of the flow around the Caradonna-Tung helicopter rotor in hover and simulations of the flow around the Operational Loads Survey helicopter rotor in forward flight

Extension of Wake-Survey Analysis Method to Cover Compressible Flows

Abstract: We summarize the work accomplished over the last several years on wake-survey analysis method developments at Boeing. Betz and Maskell's lift-and-drag equations are extended to cover compressible flows. The small perturbation method is employed to expand the general lift-and-drag equations in the momentum integral forms, assuming downstream states that differ only slightly from the state of approach. Introducing new, simpler, and cleaner expansion procedures, it is proven that both the lift and drag of an airplane model can be predicted accurately by simply measuring flow variables inside of the model wake region. This result enables the practical application of quantitative wake surveys for accurate lift-and-drag predictions of airplane models. To demonstrate the current lift-and-drag prediction capabilities, some wake-survey analysis results from previously published data are recalculated. Because wake surveys are not needed outside of the model wake region, one complete wake survey analysis for a nonpowered engine case, including data acquisitions and reductions, can now be finished in approximately 10-15 min

Computational-Fluid-Dynamics Based Advanced Ship-Airwake Database for Helicopter Flight Simulators

Abstract: Computational e uid dynamics (CFD) is used to create an extensive aerodynamic ship-airwake database for a ship-specie c e ight simulator to train helicopter pilots for landing and takeoff from various points on a ship. The technology has been embedded into CAE’ s Merlin simulator and applied to six different ships of the Royal Navy. In achieving this, important scientie c and engineering milestones are crossed, including high geometric e delity through OEM’ s (Original Equipment Manufacturer ) CAD description of the ships, three-dimensional CFDcalculations, comparison to experimental data, and, e nally,integration, testing, and acceptance into the e ight simulator. The database is e rst built by solving the three-dimensional inviscid (Euler) e ow around the complete ship, using Finite Element Navier ‐Stokes Analysis Package, a proprietary code. And a number of wind speeds and directions, corresponding to realistic approach scenarios, are analyzed. The CFD results are then compared to a set of experiments carried out for airwakes around the Canadian Patrol Frigate and made available only after the calculations weredone. The calculationsproveto bein excellent agreement with thedata throughoutitsrange. For the purpose of integration into the simulator, the CFD solutions are interpolated onto a Cartesian grid, which is then implemented in a look-up table for the Merlin CDS, after being enhanced with turbulence models. The paper then closes with the acceptance procedure the simulator is passed through.