Showing papers on "Lift-induced drag published in 1990"

Supersonic aircraft drag reduction

Abstract: This paper reviews aerodynamic drag reduction for friction, wave and vortex drag associated with supersonic cruise aircraft and suggests approaches and research directions. Suction laminar flow control may also enable improved low-speed, high-lift systems, improved lift-to-drag ratio for subsonic cruise, reduced parasitic viscous drag for favorable interference wave drag reduction approaches, and turbulent skin friction reduction via slot injection. Flow separation control at cruise proffers opportunities for increased leading-edge thrust, increased lift increment from upper surface, increased fuselage lift/camber for wave drag-due-to-lift reduction, improved performance of various favorable interference wave drag reduction schemes, as well as possibly better low-speed, high-lift systems and wing cruise performance.

Minimum Induced Drag for Wings with Spanwise Camber

Abstract: Linear theory is used to develop optimum circulation distributions and their associated minimum induced drag for wakes from lifting surfaces with various spanwise camber. The work is largely computational and results for cases previously investigated analytically are generally in good agreement. However, some previously published results are found to be in error, and a new solution for the induced drag of a wing with dihedral is given. New results are computed for polynomial and superelliptic camber lines. An empirical correlation is demonstrated between the induced drag factor and the inverse arc length for a variety of optimum cases.

Gas turbine engine fan duct base pressure drag reduction

Abstract: An aircraft is provided with an aircraft base pressure drag reduction apparatus including apparatus for ducting boundary layer air on board an aircraft wherein the air produces ram air drag, apparatus for using the air for work, and apparatus for ducting the used boundary layer air to a low pressure area of an aircraft which otherwise produces base pressure drag on the aircraft to reduce the base pressure drag that the low pressure area would otherwise produce. In a more particular embodiment of the invention the low pressure area of the aircraft is in a fan duct of an aircraft gas turbine engine. In the preferred embodiment the low pressure area in a fan duct of an aircraft gas turbine engine is on the pylon fairing and the means for using the air for work includes at least one means for bleeding boundary layer air from the surface of the aircraft for reducing aircraft boundary layer induced drag.

Outer-layer manipulators for turbulent drag reduction

Abstract: The last ten years have yielded intriguing research results on aerodynamic boundary outer-layer manipulators as local skin friction reduction devices at low Reynolds numbers; net drag reduction device systems for entire aerodynamic configurations are nevertheless noted to remain elusive. Evidence has emerged for dramatic alterations of the structure of a turbulent boundary layer which persist for long distances downstream and reduce wall shear as a results of any one of several theoretically possible mechanisms. Reduced effectiveness at high Reynolds numbers may, however, limit the applicability of outer-layer manipulators to practical aircraft drag reduction.

The Computation of Induced Drag with Nonplanar and Deformed Wakes

Abstract: The classical calculation of inviscid drag, based on far field flow properties, is reexamined with particular attention to the nonlinear effects of wake roll-up. Based on a detailed look at nonlinear, inviscid flow theory, it is concluded that many of the classical, linear results are more general than might have been expected. Departures from the linear theory are identified and design implications are discussed. Results include the following: Wake deformation has little effect on the induced drag of a single element wing, but introduces first order corrections to the induced drag of a multi-element lifting system. Far field Trefftz-plane analysis may be used to estimate the induced drag of lifting systems, even when wake roll-up is considered, but numerical difficulties arise. The implications of several other approximations made in lifting line theory are evaluated by comparison with more refined analyses.

Viscous drag reduction via surface mass injection

Abstract: Slot injection systems on the surfaces of aerodynamic bodies have been noted to consistently furnish substantial local skin friction reductions which are predictable on the basis of current numerical methods. Only crude systems studies, however, have been thus far completed. The most common configuration for slot ingestion in the literature involves tangential injection of air along a two-dimensional surface on which air constitutes the mainstream flow; attention is presently given to slot injection in low-speed and high-speed flows, as well as a discussion of aircraft applications and an evaluation of prospective possibilities for practical drag-reduction systems.

Measuring Aerodynamic Interference Drag Between a Bird Body and the Mounting Strut of a drag Balance

Abstract: 1.The drag of a bird body mounted on the strut of a drag balance in a wind tunnel is more than the sum of the drags of the isolated strut and the isolated body. The strut changes the air flow around the body and generates additional drag, known as interference drag. This paper describes practical methods for measuring the drag of bird bodies: a strain-gauge drag balance, dimensions for struts made with machine or hand tools, and a procedure for correcting drag measurements for interference drag. 2.Interference drag can be measured by extrapolating a relationship between the drag of isolated struts with different crosssectional sizes and shapes and the drag of a body mounted on those struts. The interference length the length of an isolated strut that produces drag equal to the interference drag is a usefulquantity for predicting interference drag. 3.The relationship mentioned above is a straight line for a model peregrine falcon (Falco peregrinus L.) body mounted on smooth struts struts with convex cross-sectional shapes ranging from streamlined to circular. This finding simplifies the determination of interference drag in three ways: (i) the line can be found from measurements with just two struts a standard strut with low drag and a calibration strut with high drag; (ii) the two struts need not have the same shape for example, the standard strut can be changed to a calibration strut by attaching a spoiler without disturbing the body mounted on the strut and (iii) a single value of interference length (33.1mm) describes smooth struts with a range of shapes and sizes. These struts had drag coefficients between 0.33 and 0.91 at Reynolds numbers between 2100 and 10800. 4.The interference length of a strut supporting the actual falcon body with a feathered surface is not significantly different from that of the strut supporting the model body with a rigid surface. 5.As a hypothesis, interference length (hI, in metres) of a smooth strut varieswith the size of the body mounted on it: hI=0.0365m0.333 where m is the body mass (in kg) of the intact bird.

Effects of nonplanar outboard wing forms on a wing

Abstract: It is possible for a constant span to obtain better aerodynamic performance from a wing with a nonplanar outboard wing form than from a wing with a planar outboard form, despite the added drag from the increased wetted area. Furthermore, the semispan rolling-moment characteristics indicate the lower wing-root bending moment for some nonplanar configurations. These conclusions are based on an experimental and computational investigation of the aerodynamic characteristics of planar and nonplanar outboard wing forms. Seven different configurations - planar rectangular, nonplanar rising arc, nonplanar drooping arc, planar sheared, sheared with dihedral, sheared with anhedral, and planar elliptical - were investigated for two different spans. Flow-visualization photographs indicate that there are three vortex systems associated with the sheared forms. The lower induced drag coefficients of nonplanar wings are believed to accrue from the movement of vorticity away from the center-of-span line, resulting, in some instances, in induced efficiencies higher than that of a planar elliptical wing. Flow surveys indicate that the effective span, as determined by the location of the tip vortex, might not be a sufficient yardstick of the induced performance of a nonplanar wing.

Wingtip Vortex Turbine Investigation for Vortex Energy Recovery

Abstract: A flight test investigation has been conducted to determine the performance of wingtip vortex turbines and their effect on aircraft performance. The turbines were designed to recover part of the large energy loss (induced drag) caused by the wingtip vortex. The turbine, driven by the vortex flow, reduces the strength of the vortex, resulting in an associated induced drag reduction. A four-blade turbine was mounted on each wingtip of a single-engine, T-tail, general aviation airplane. Two sets of turbine blades were tested, one with a 15' twist (washin) and one with no twist. Th power recovered by the turbine and the installed drag increment were measured. A trade-off between turbine power and induced drag reduction was found to be a function of turbine blade incidence angle. This test has demonstrated that the wingtip vortex turbine is an attractive alternate, as well as an emergency, power source.

Convex curvature concept of viscous drag reduction

Abstract: Experiments have indicated that for certain convex aerodynamic surface curvature ratios, wall-shear stresses remain low over considerable streamwide distances even after curvature is removed The research whose progress is presently evaluated was first suggested by Bushnell (1983), who proposed that the convex-surface curvature be used in axisymmetric bodies to ascertain whether the viscous component of total drag is reduced Attention is given to the evolution of the concept's implementation in an axisymmetric nose-body combination for passive viscous drag reduction

A closer look at the induced drag of crescent-shaped wings

Abstract: Recent interest in the induced drag characteristics of crescent-shaped wings has led to a closer look at the methods used for determination of induced drag from computational aerodynamic methods. Induced drag may be computed by integration of surface pressure, or by evaluation of a contour integral in the Trefftz plane. A high-order panel method was used to study the induced drag of crescent and elliptical wings using both techniques. Induced drag computations using surface-pressure integration were strongly affected by panel density and angle of attack. Accurate drag computations for the crescent wing were obtained only when the spanwise as well as chordwise panel density was extremely high. Trefftz-plane results for the two wing planforms do not show this sensitivity to panel density or angle of attack. Span efficiencies of 0.994 for the crescent wing and 0.987 for the elliptical wing were computed by the Trefftz-plane technique. Substitution of a force-free, rolled-up wake geometry on the crescent wing did not change the pressure-integrated drag significantly. The slightly higher span efficiency of the crescent wing is attributed to a more nearly elliptical spanwise lift distribution. The chord distribution of the elliptical wing was modified to produce an elliptical span-loading on a wing with an unswept quarter-chord line. This wing demonstrated a span efficiency equal to that of the crescent wing.

Study of three dimensional separated flows, relation between induced drag and vortex drag

Abstract: This is achieved by experimentation on a finite aspect ratio wing where these two types of drag can be more easily separated and quantified. Finally, an experimental method based on the lifting line theory is proposed for the measurement of the induced drag of an aerofoil through downstream velocity surveys

Wind-tunnel investigation on the effect of a crescent planform on drag

Abstract: Lift and drag forces were compared for elliptic and crescent wing models at cruise and climb conditions in the NASA/Langley 14 x 22-ft subsonic tunnel. The force measurements were obtained for an angle-of-attack range from -3 to 10 deg at a Reynolds number of about 1.7 million. The results indicate that for attached flow conditions, the crescent wing with its highly swept tips generates less lift-dependent drag than the elliptic wing for given lift force, wing span, and freestream conditions. The drag reduction is thought to be the result of the favorable influence of trailing wake deformations on the pressure distribution of the highly swept outboard region of the crescent wing.

Method and arrangement for reducing the induced drag of a wing

Abstract: In order to reduce the induced drag of a wing over which flow passes it is provided that an element (3') of the lateral flow (3) is deflected at the end (2) of the wing through a gap on the underneath of the wing (1) into a guide duct (6). In this guide duct (6), the element of the lateral flow (3) is diverted at its outlet (8) on the underneath of the wing (1) such that it is directed downwards, so that a rotational impulse is produced which opposes the normal vortex.

Analysis of vessels' wind forces through the utilisation of a physical-mathematical model-ii

Abstract: A physical-mathematical model consisting of six elementary fluid dynamic forces and stall effects acting on a ship is proposed by the authors. They then examine specific fluid forces in the model, such as induced drag, cross flow drag and stall effects. This examination generated a new mathematical model. In this paper, data presented in previous papers concerning wind forces on various types of ships was analysed using this new mathematical model. It was found that these formulae could describe measured forces and give reasonable physical representations of the formulae in terms of fluid dynamics. For the estimation of fluid dynamic forces, correlation between the coefficients of wind forces and six nondiemnsional hull parameters (aspect ratio, B/L, B/H, T/L, X/L and Ax/Ay), and the correlation between wind force coefficients were examined. The coefficients of correlations between some parameters or fluid dynamic coefficients had significant levels in these cases. Therefore, each fluid dynamic coefficient of wind forces could be estimated from nondimensional hull parameters and the correlation between fluid dynamic coefficients.

Blockage Corrections at High Angles of Attack in a Wind Tunnel

Abstract: Recent developments have increased the need to investigate flight conditions at high angles of attack. Because these conditions have to be studied in wind tunnels, it is obvious that the blockage corrections must be assessed as accurately as possible. With this in mind, we thought of comparing the results obtained from the same model in two different wind tunnels: the Aeritalia wind tunnel and the Emmen F + W 32.4 m2. The size of the Emmen makes the wall and blockage corrections negligible. Therefore, in practice, with any differences in the results coming from tests conducted in the two wind tunnels, it is only necessary to make corrections to those coming from the Aeritalia wind tunnel. Since the Emmen wind tunnel provided us with the exact results, our work consisted of establishing a method of correction whose validity could be verified. Initially we tried to use Maskell's formula introducing constant coefficients according to test conditions but the results were not satisfactory. We then developed Maskell's formula and decided to use the flat-plate pressure coefficient as a base pressure coefficient—which is needed in Maskell's formula—when no such coefficient can be deduced from the model. In all these cases, the induced drag coefficient was expressed as a function of the lift coefficient. Final corrections for lift and moment coefficients were very satisfactory, though the drag coefficient was slightly overcorrected.

Drag Reduction by Controlling Flow Separation Using Stepped Afterbodies

Abstract: A method has been proposed of controlling separated base flows as a means of reducing aerodynamic drag. A series of steps attached to the base of the body of interest is used to control flow separation by forming a system of captive vortices on the steps. Kentfield's wind tunnel experiments seemed to confirm this concept for axisymmetric bodies at low subsonic Mach numbers and low Reynolds numbers. He reported drag reductions of as much as 56% using stepped afterbodies as compared to identical bodies with flat bases. The paper presents results obtained from further investigations of this stepped base concept in conjunction with both fin- and spin-stabilised configurations at high subsonic,

Aerodynamic drag of a pair of bodies in transonic and supersonic flow

Abstract: The aerodynamic characteristics of models of pairs of bodies on the flow acceleration and deceleration intervals are investigated experimentally at transonic and supersonic flow velocities. The dependence of the drag coefficient of the pair model on the relative drag of the leading body is determined for supersonic velocities.

Induced Drag Based on Leading Edge Suction for a Helicopter in Forward Flight

Abstract: Estimating induced drag for a helicopter in forward flight is a three-dimensional, unsteady aerodynamic problem complicated by fluid compressibility and wake geometry. Based on an acceleration potential approach, the chordwise velocity and the derivative d$/dt of the velocity potential at the leading edge of a thin rotor blade in subsonic flow were re-examined in this paper to assess unsteady and compressibility effects on the induced drag using a leading-edge suction model. The chordwise velocity was shown to have a singular and a continuous component. The d$/dt was shown to be continuous and hence does not contribute to induced drag. The induced drag calculated from the leading-edge suction model and the more traditional model to be referred to as the induced angle model were compared to quantify the differences in the two approaches. The results show that variations can be significant. While these variations cannot substantiate the validity of either approach, it is clear that the leading edge suction model is simpler to apply with fewer assumptions. b A A d

Design of a three-component wall-mounted balance

Abstract: The design and evaluation of a three-component, wall-mounted pyramidal balance for a small wind tunnel is discussed. The balance was designed to measure lift, drag, pitching moment, and angle of attack. The specific design of each component and mathematical models used to design the balance are covered. Balance evaluation consisted of calibration, tare, and interaction analysis.

チップベーンによる水平軸風車の増出力に関する研究 : 続報,可視化による増出力効果の解明

Abstract: This paper presents the experimental analysis of power augmentation effects of horizontal axis wind turbine using a tip vane The flow visualization method is used to analyze the augmentation phenomenon The flow around a tip vane, tip vortex and flow patterns on the blade surface are visualized The following results are described (1) Strength of tip vortex, induced drag and turbulence on the blade tip can be diminished by the tip vane (2) A tip vane can generate the diffuser effect

An aerodynamic tradeoff study of the scissor wing configuration

Abstract: A scissor wing configuration, consisting of two independently sweeping wings was numerically studied. This configuration was also compared with an equivalent fixed wing baseline. Aerodynamic and stability and control characteristics of these geometries were investigated over a wide range of flight Mach numbers. It is demonstrated that in the purely subsonic flight regime, the scissor wing can achieve higher aerodynamic efficiency as the result of slightly higher aspect ratio. In the transonic regime, the lift to drag ratio of the scissor wing is shown to be higher than that of the baseline, for higer values of the lift coefficient. This tends to make the scissor wing more efficient during transonic cruise at high altitudes as well as during air combat at all altitudes. In supersonic flight, where the wings are maintained at maximum sweep angle, the scissor wing is shown to have a decided advantage in terms of reduced wave drag. From the view point of stability and control, the scissor wing is shown to have distinct advantages. It is shown that this geometry can maintain a constant static margin in supersonic as well as subsonic flight, by proper sweep scheduling. Furthermore, it is demonstrated that addition of wing mounted elevons can greatly enhance control authority in pitch and roll.

Parametric analysis of swept-wing geometry with sheared wing tips

Abstract: A computational parameter study is presented of potential reductions in induced drag and increases in lateral-directional stability due to sheared wing tips attached to an untwisted wing of moderate sweep and aspect ratio. Sheared tips are swept and tapered wing-tip devices mounted in the plane of the wing. The induced-drag results are obtained using an inviscid, incompressible surface-panel method that models the nonlinear effects due to the deflected and rolled-up wake behind the lifting surface. The induced-drag results with planar sheared tips are compared to straight-tapered tip extensions and nonplanar winglet geometries. The lateral-directional static-stability characteristics of the wing with sheared tips are estimated using a quasi-vortex-lattice method. For certain combinations of sheared-tip sweep and taper, both the induced efficiency of the wing and the relevant static-stability derivatives are predicted to increase compared to the wing with a straight-tapered tip modification.