Lower Wing Surface Research Articles

Optimization of Three-Dimensional Wings in Ground Effect Using Multiobjective Genetic Algorithm

Shape optimization with a multiobjective optimization technique and tradeoff analysis of the three-dimensional wings-in-ground effect have been performed. Unlike an airplane out-of-ground effect, a wing-in-ground vehicle has to satisfy static height stability in order to cruise steadily in ground effect. However, it is difficult to simultaneously satisfy both high aerodynamic performance and static height stability because of the strong tradeoffs between the two. Amultiobjective optimization technique can address this problem. Inmultiobjective optimization, the optimum is not unique; rather, it is a set of nondominated potential solutions called Pareto optima. In this study, after 19 evolutions of a genetic algorithm, 74 nondominated Pareto optima are obtained and four different groups can be observed from thePareto optima.Each group represents a set of the potential global solutions for a single objective or combined objectives. The analysis of the Pareto optima suggests that the lift is increased because of increased pressure on the lower wing surface, but the influence of pressure on the upper surface is not significant. The wing thickness and curvature increase the lift further, but they are not favorable for static height stability and the lift–drag ratio; a swept-forward wing can improve the static height stability.

Influence of endplate on aerodynamic characteristics of low-aspect-ratio wing in ground effect

A numerical analysis is performed to investigate the aerodynamic characteristics and static height stability of the endplate on aspect-ratio-one wing in ground effect. The investigation is carried out on angles of attack from 0° to 10° and ground clearances at a trailing edge from 5% of chord to 50%. The analysis shows that the ground effect increases the lift by high pressure on the lower surface, reduces the induced drag, increases the suction on the upper surface, and consequently considerably enhances the lift-drag ratio. The endplate, which prevents the high-pressure air escaping from the air cushion and reduces the influence of wing-tip vortex, augments lift and lift-drag ratio further. Interestingly, the drag with the endplate does not increase as much as the lift does when the airfoil is brought close to the ground. From the analysis and visualization of computation results with the endplate, it is found that two wing-tip vortices are generated from each wing surface, their strengths are stronger, diminished rapidly and the influence of the wing-tip vortices are decreased. The outward drift of wing-tip vortex, which is generated from the lower wing surface, is observed. Irodov’s criteria are also numerically evaluated to investigate the static height stability of wings with and without the endplate. The comparison of Irodov’s criteria shows that the endplate is not favorable for static height stability but reduces the deviation of the static height stability with respect to pitch angles and heights.

Controlling the near vortex wake of a swept half-wing by means of mini-flaps

The effect of mini-flaps on the flow pattern in the near vortex wake behind a model swept half-wing is investigated. The distributions of the time-average flow velocity were measured in a subsonic wind tunnel, in a section normal to the freestream velocity vector located at a distance of 3.8 wing half-spans from its trailing edge. When mini-flaps are mounted on both upper and lower wing surfaces, two vortices (tip and auxiliary) of the same sign are observable in the above-mentioned flow section; they are separated by an extended region of vorticity of the opposite sign. The model angle-of-attack effect on the intensities of the tip and auxiliary vortices is estimated.

전산유체/전산구조 연계 방법을 사용한 항공기날개의 정적 공탄성 해석

A static aeroelastic analysis for supersonic aircraft wing equipped with external store under the wing lower surface is performed using computational fluid dynamics (CFO) and computational structural technology(CST) coupling methodology. Two mapping algorithms, which are the pressure mapping algorithm and the displacement mapping algorithm, are used for CFD/CST coupling. A three-dimensional unstructured Euler code and finite element analysis program are used to calculate the flow properties and the structural displacements, respectively. The coupling procedure is repeated in an iterative manner until a specified convergence criterion is satisfied. Static aeroelastic analysis for a typical supersonic flight wing is performed and final converged wing configuration is obtained after several iterations.

Numerical simulation of flow over delta wing with trailing‐edge jet at high angle of attack

AbstractThe incompressible Reynolds‐averaged Navier–Stokes equations, together with a modified mixing length algebraic turbulence model, are solved to simulate the flow over a delta wing with trailing‐edge jets at high angles of attack. An artificial compressibility method and a Beam–Warming implicit approximate factorization scheme are employed to discretize the equations. The computed results indicate that trailing‐edge jets tend to not only decrease the pressure but also increase the velocity at the cores of the streamwise primary vortices. This moves the vortex breakdown locations aft and stabilizes the vortical flow. As a result, the jets lead to a decreased pressure on the upper wing surface and an increased pressure on the lower wing surface, thereby increasing the overall lift. Computations further show that as the exit area of the trailing‐edge jets is enlarged, or, as the jets are deflected downward, the above‐mentioned effects become more pronounced. Copyright © 2004 John Wiley & Sons, Ltd.

地面効果を受けてローリング運動する高迎角デルタ翼の空力動特性

Dynamic properties of aerodynamic forces and moments acting on a delta wing were experimentally studied in a low-speed wind tunnel. The wing could make a smooth and periodic arbitrary motion, such as pitching, yawing, rolling, translation motions, and their combinations by a manipulator equipped with stepping motors controlled by a microcomputer, which had six degrees of freedom. The objective of the research is to analyze unsteady aerodynamics of the rolling delta wing with regard to the altitude from the ground. It was found that the hysteresis loops of lift, drag and rolling moment were drawn with the roll angles and amplified owing to the ground effect. The factors to determine the wing properties in the large angle of attack are the pressure on the windward side of the delta wing and the leading edge vortices which were broken down and reconstructed according to the wing motion. The pressure on the lower wing surface was also influenced by the clearance between the delta wing and the ground plate, which deduces the ventulli or stagnant effects.

Prediction of Airfoil Stall in Icing Conditions Using Wing Surface Pressures

Initialworkispresentedonanin-e ightstallmargininstrumentationsystemthatmaintainsaccuracyindependent of wing leading-edge ice formations. The system uses four surface pressures, measured aft of the ice formation, from which the aircraft’ s normalized lift coefe cient is determined. The pressure port locations are selected such that the calibration algorithm remains nearly constant as the leading-edge ice shape and thickness change. Windtunnel data are presented for three ice formations, varying in both type and thickness. The indicated normalized lift coefe cient, based on the no ice algorithm, is compared to the actual normalized lift coefe cient under icing conditions. From this comparison, the four port locations were found to be located at 22 and 41% of the chord on the upper wing surface and 41 and 68% on the lower wing surface.

On aerodynamic modelling of an insect–like flapping wing in hover for micro air vehicles

This theoretical paper discusses recent advances in the fluid dynamics of insect and micro air vehicle (MAV) flight and considers theoretical analyses necessary for their future development. The main purpose is to propose a new conceptual framework and, within this framework, two analytic approaches to aerodynamic modelling of an insect-like flapping wing in hover in the context of MAVs. The motion involved is periodic and is composed of two half-cycles (downstroke and upstroke) which, in hover, are mirror images of each other. The downstroke begins with the wing in the uppermost and rearmost position and then sweeps forward while pitching up and plunging down. At the end of the half-cycle, the wing flips, so that the leading edge points backwards and the wing's lower surface becomes its upper side. The upstroke then follows by mirroring the downstroke kinematics and executing them in the opposite direction. Phenomenologically, the interpretation of the flow dynamics involved, and adopted here, is based on recent experimental evidence obtained by biologists from insect flight and related mechanical models. It is assumed that the flow is incompressible, has low Reynolds number and is laminar, and that two factors dominate: (i) forces generated by the bound leading-edge vortex, which models flow separation; and (ii) forces due to the attached part of the flow generated by the periodic pitching, plunging and sweeping. The first of these resembles the analogous phenomenon observed on sharp-edged delta wings and is treated as such. The second contribution is similar to the unsteady aerodynamics of attached flow on helicopter rotor blades and is interpreted accordingly. Theoretically, the fluid dynamic description is based on: (i) the superposition of the unsteady contributions of wing pitching, plunging and sweeping; and (ii) adding corrections due to the bound leading-edge vortex and wake distortion. Viscosity is accounted for indirectly by imposing the Kutta condition on the trailing edge and including the influence of the vortical structure on the leading edge. Mathematically, two analytic approaches are proposed. The first derives all the quantities of interest from the notion of circulation and leads to tractable integral equations. This is an application of the von Kármán-Sears unsteady wing theory and its nonlinear extensions due to McCune and Tavares; the latter can account for the bound leading-edge vortex and wake distortion. The second approach uses the velocity potential as the central concept and leads to relatively simple ordinary differential equations. It is a combination of two techniques: (i) unsteady aerodynamic modelling of attached flow on helicopter rotor blades; and (ii) Polhamus's leading-edge suction analogy. The first of these involves both frequency-domain (Theodorsen style) and time-domain (indicial) methods, including the effects of wing sweeping and returning wake. The second is a nonlinear correction accounting for the bound leading-edge vortex. Connections of the proposed framework with control engineering and aeroelasticity are pointed out.

The influence of mid-chord battle damage on the aerodynamic characterstics of two-dimensional wings

AbstractThis paper briefly considers the method of simulating gunfire damage to a wing and outlines the key basic assumptions used in modelling. The results of qualitative and quantitative investigations into the aerodynamic characteristics of a wing damaged at quarter chord are then presented. The results are discussed in terms of flow mechanisms, changes to surface pressure distributions and increments in lift, drag and pitching moment coefficients. For the damaged wing, the influence on force and moment coefficients was attributed to flow through the damage. This through flow was driven by the pressure differential between the upper and lower wing surfaces, and took one of two forms. The first form was a ‘weak-jet’ which formed an attached wake and resulted in small changes in force and moment coefficients. The second form resulted from either increased incidence, or damage size. This was the ‘strong-jet’, where through flow penetrated into the freestream flow, resulting in separation of the oncoming surface flow, and the development of a larger separated wake with reverse flow. The effect on force and moment coefficients was significant. The paper also compares the structure of the damage through flow with previously published results for jets in crossflows. Many similarities in the flow features were identified, although there were significant differences in the surface pressure distributions for the two cases.

Effect of underwing frost on a transport aircraft airfoil at flight Reynolds number

The effect of underwing frost on a transport aircraft airfoil in a takeoff configuration was studied. Underwing frost can occur when the lower surface of the wing is cooled by fuel cold-soaked in the wing tanks during cruise. Frost may accrete on the wing lower surface while the aircraft is awaiting takeoff. A two-dimensional test was performed in the NASA Langley Low-Turbulence Pressure Tunnel on a representative high-lift airfoil with a leading-edge slat and trailing-edge flap. Frost was simulated on the lower surface using distributed roughness particles. The test was conducted at M - 0.2 and Re = 5 x 106 to 1.6 x 10 7. The effects of the frost on performance were generally small, with the largest effects occurring for the open-slat case with the frost starting at 12% chord. In this situation, it was found that the frost contaminated the upper surface boundary layer at high angles of attack, increasing drag and reducing maximum lift.

Vortex-wing interaction of a close-coupled canard configuration

The thin-layer Navier-Stokes equations are solved numerically to investigate the effects of canard vertical position on a close-coupled, canard-wing-body configuration at a transonic Mach number of 0.90 and angles of attack ranging from — 2 to 12 deg. Canard-wing interactions are investigated for the canard positioned above, coplanar with, and below the wing (high-, mid- and low-canard positions, respectively). The computational results show favorable canard-wing interactions for the high- and midcanard configurations. The unfavorable lift and drag characteristics for the low-canard configuration are examined by analyses of the low-canard flowfield structure and found to be directly attributed to the interaction between the canard vortex and the wing surface. At relatively low angles of attack, the low-canard vortex passes under the wing surface and induces low pressures on the wing lower surface. As angle of attack is increased, the low-canard vortex impacts the wing surface and is split into two distinct vortices.

Effect of canard deflection on close-coupled canard-wing-body aerodynamics

The thin-layer Navier-Stokes equations are solved for the flow about a canard-wing-body configuration at transonic Mach numbers of 0.85 and 0.90, angles of attack from -4 to 10 degrees and canard deflection angles from -10 to +10 degrees. Effects of canard deflection on aerodynamic performance, including canard-wing vortex interaction, are investigated. Comparisons with experimental measurements of surface pressures, lift, drag and pitching moments are made to verify the accuracy of the computations. The results of the study show that the deflected canard downwash not only influences the formation of the wing leading-edge vortex, but can cause the formation of an unfavorable vortex on the wing lower surface as well.

Kinematics of take‐off and climbing flight in butterflies

High speed flash photography (flash duration 0.1 ms) was used to analyse wing movements in over 30 species of butterfly. With few exceptions, the insects showed a clap and peel mechanism of lift production at the start of the downstroke. Early in the upstroke the wings showed pronounced ventral flexure which, combined with inertial lag in the posterior parts of both wing pairs and delayed supination in the hind wing, led to the formation of a funnel‐like space between the wings. These movements, and the resultant airflow patterns, appear to be an axi‐symmetric equivalent of the ‘near’ clap and peel (here referred to as the funnel). Hind wing movements throughout the stroke are hinged upon the claval furrow. The expanded anal lobes of the hind wing lying medially to the claval furrow help to provide an air‐tight seal around the abdomen between the upper and lower wing surfaces, which increases the efficiency of the peel and funnel mechanisms. The role of the intercalary flexion lines in controlling changes in wing surface corrugation during the cycle is also investigated.

Experimental flowfield visualization of a high alpha wing at Mach 1.62

Experimental oil-flow and tuft patterns and vapor-screen flow-visualization data were obtained on a cambered wing model at Mach = 1.62 for an angle-of attack range of 0-14 deg. These data were used as flow diagnostic tools along with surface-pressure and force data and full-potential theory calculations. A large separation bubble was found on the lower wing surface at low angle of attack. The high-angle-of-attack flowfield was characterized by a large attached-flow leading-edge expansion followed by a crossflow shock. At alpha = 14 deg the crossflow shock apparently induced discrete regions of streamwise separated flow, which were clearly indicated in the vapor-screen and oil-flow photographs.

Wing microsculpturing in the termite genusAmitermes (Termitidae, Amitermitinae)

Wing microsculpturing has been described in the genusAmitermes. It occurs on the upper and lower wing surfaces and is composed of a single row of small (3–5 μm long), thorny papillae at the anterior margin and numerous micrasters all over the wing membrane (size 6–8 μm×5–7 μm; density 9200–9600/mm2). The micrasters are with 5–8 arms and of the complex type (types V–X). No arrowheads are present. The position ofAmitermes is discussed in the general scheme of termite microsculpturing. Comparison is also made with the condition in the Zoraptera, Embioptera and the Blattoidea.

Theoretical investigation of the aerodynamics of double membrane sailwing airfoil sections

The type of sailwing here investigated has a rigid leading-edge spar with a rib at each end, a wire trailing-edge, and membranes which are wrapped around this structure to form upper and lower wing-surfaces. There appears to have been no previous theoretical investigation of a sailwing of this type, although it is expected to have aerodynamic and structural advantages, including controllability by using internal pressure, and to have various applications (e.g. wind-driven generators). Previous theoretical investigations of sailwings have concerned wings with a zero-thickness single membrane. The paper presents a two-dimensional numerical analysis method for obtaining the aerodynamic characteristics of such double-membrane sailwings. Numerical examples are given which show that: i) the pressure distribution on a sailwing with a rounded leading-edge is completely different from that on a single-membrane sailwing. ii) A sailwing with a circular or oval leading-edge has sharp suction peaks in the pressure distribution that may impair performance. iii) A D-spar leading-edge sailwing shows a large improvement in respect of pressure peaks; this is in qualitative agreement with the performance improvement noted in earlier experiments elsewhere with this form of leading edge. See next Abstract.

An experimental investigation of a jet issuing from a wing in crossflow.

The aerodynamic interference resulting from a jet issuing normal to the chordal plane of a twodimensional wing in a crossflow has been experimentally investigated. Measurements of the interference surface pressure distribution on the wing and of the wing interference force and moment coefficients have been made for a systematic variation of jet exit location, jet exit diameter, wing angle-of-attack, and the ratio of jet exit velocity to freestream velocity, A. A comparison of the contours of constant interference surface pressure on the wing lower surface with those for an infinite flat plate reveals that they are much the same for A > 6. The dissimilarity becomes greater as X is decreased, primarily through the growth of an extensive region of positive interference surface pressure forward of the jet on the wing. Interference lift losses of approximately the same magnitude for all geometries were observed for X > 6. However, a lift augmentation occurred for X < 6 which was attenuated by increases in angle-of-attack, forward movement of the jet exit location, and decreases in jet exit size. The data indicate that the character of the interference flow is distinctly different for high and low values of the velocity ratio.

Month in the Patent Office

In an aircraft, specifically a guided missile wherein the missile shell 10 carries a stub wing 16 to which is hinged a folding wing 11 which folds about a fore‐and‐aft axis 12 on the wing lower surface and a control surface 13 is hinged to the wing part 11 about a transverse axis 14 displaced vertically from axis 12, control means for surface 13 comprises a two‐part control torque tube 15A, 15B, part 15B being mounted in bearings 17 in part 11 and fast with surface 13. The connexion between the parts of the torque tube comprises a slotted member 23 fast with part 15A and a tongue member 20 of L‐shape fast with part 15B, and of such proportions that, as shown by chain dotted lines, the two parts remain in operative engagement when the wing part 11 folds downwardly about axis 12. The wing‐folding and surface‐adjusting mechanisms are inter‐connected to ensure that the slotted member 23 is correctly oriented before wing folding commences.

Month in the Patent Office

In an arrangement for deflecting a propulsive jet forwardly for braking purposes the jet reversal is effected by moving a series of curved blades at the rear end of the jet pipe to intercept the jet stream. As shown in FIG. 1 the jet pipe 10 terminates in an opening in the upper surface 12 of a delta‐wing, the deflecting blades 17 being mounted to form a grille 14 which is normally housed forwardly of the jet discharge opening, but which is movable rearwardly by an electric motor 33 and rack‐and‐pinion gearing 27, 28 into a position where it extends across the discharge opening to reverse the jet. FIG. 2 shows a modification in which the jet is divided into two streams by a wedge shaped vane 109 to discharge through openings 107, 108 in the upper and lower wing surfaces respectively, deflexion of the streams being effected by upper and lower grilles 102, 103. In addition the vane 109 may be rotated about a pivot 140 to deflect the whole of the jet through the upper or lower wing outlet. A similar effect may be obtained without the use of a bifurcated jet pipe by modifying the arrangement according to FIG. 1 to include a downwardly directed branch of the jet pipe 10 opening in the undersurface of the wing and controlling the flow of the jet through this branch by hinged flaps at the junction of the main and branch pipes, and in the undersurface of the wing, respectively. In the case of a circular jet pipe 40, FIG 3, the rear portion of the pipe is cut off along oblique planes 41, 42, and the cut‐away portions occupied by curved vanes 43, 44 hinged about a rear transverse axis 45. The vanes 43, 44 are surrounded by curved blade grills 46, 47 which in turn are enclosed by external plates 51, 52. To effect reversal of the jet the closure plates 51, 52 are first slid forwardly clear of the grilles 46, 47, and jacks 55, 56 are then operated to move the grilles 46, 47 and the tail portion 53 of the jet pipe forwardly, thus causing the vanes 41, 42 to pivot about the axis 45 to obstruct the jet pipe and cause the jet to escape through the grilles 46, 47.