Showing papers on "Lift-induced drag published in 1998"

Recent progress in drag prediction and reduction for civil transport aircraft at ONERA

Abstract: The paper gives a survey of recent work at ONERA in the fields of drag prediction and drag reduction. The far-field drag analysis has been extended to Euler codes. This approach enables physical drag sources to be identified and artificial (spurious) drag to be eliminated. Progress achieved in drag prediction of inviscid flow is illustrated through appropriate examples of drag analysis on an airfoil, a wing and a wing-body configuration. A first application of the far-field analysis to Navier-Stokes codes is also reported. First results obtained for an airfoil are promising. As far as drag reduction is concerned, the main efforts are devoted to the evaluation of advanced concepts tackling the main drag sources of a civil transport aircraft which are wave drag, lift induced drag and skin friction drag. The first case presented deals with wave drag reduction of an airfoil through local wall deformation. Significant improvements predicted after design modification have been confirmed by an experimental verification. Then, the potential to reduce lift induced drag by a careful design of a particular wing tip device is discussed. Finally, progress in hybrid laminar flow investigations is demonstrated.

Drag prediction based on a wake-integral method

Abstract: This paper discusses the analytical aspects of the determination of drag acting on a model in a wind tunnel under subsonic or transonic flow conditions. The drag integral is derived from the integral form of the momentum equation in order to take the compressible flow effects into account. The drag integral can be broken down into profile drag (including wave drag) and induced drag. An analytical expression for induced drag has been developed in order to minimize the grid dependency problem, which is inherent in the numerical solution procedure. This analytical approach allows us to evaluate the effect of the wind tunnel walls on the drag. Predicted drag numbers from several different formulas are compared with experimental measurements.

Drag Forces Experienced by Two, Full-Scale Vehicles at Close Spacing

Abstract: The present study aims to document the drag reduction for a two-vehicle platoon by operating two full-scale Ford Windstar vans in tandem on a desert lakebed Drag forces are measured with the aid of a special tow bar force measuring system designed and manufactured at USC The testing procedure consists of a smooth acceleration, followed by a smooth deceleration of the platoon Data collected during acceleration allows the calculation of the drag force on the trail-vehicle, while data collected during deceleration is used to calculate the drag on the lead vehicle Results from the full-scale tests show that the drag behaviors for the two vans are in general agreement with the earlier conclusions drawn from the wind tunnel tests--namely, both vans experience substantial drag savings at spacings of a fraction of a car length

Wingtip vortex device for induced drag reduction and vortex cancellation

Abstract: The present invention is a wingtip vortex device for induced drag reduction and vortex cancellation The wingtip vortex device is an aerodynamic drag reduction system installed at the wingtips of an aircraft The wingtip vortex device comprises an impeller located ahead of the wingtip chord, a wind turbine device located behind the wingtip chord, and an intermediate gear device for coupling the impeller with the wind turbine and/or for generating power Thus, the wingtip vortex device is self-contained as the impeller is powered by the vortex-driven turbine As a result, induced drag is reduced without requiring an external power source such as the aircraft propulsion system

Base Drag Reduction Caused by Riblets on a GAW(2) Airfoil

Abstract: AMONG various methods explored for turbulent drag reduction on aerodynamic surfaces, riblets have beer the most promising.' As much as 4-8% of viscous drag reduction has been reported for simple two-dimensional configurations Plastic sheets with symmetric v-grooves (manufactured by the 3M Co.) have been employed widely in research- Assessment of viscous drag reduction on two-dimensional airfoils. both at low and transonic speeds, has been reported as well.- Excellent reviews on the subject covering aspects of drag reduction and flow structure are contained in Refs. 1 and 7. 13; There have been very few attempts exploring the fuse of giblets in separated flows, either from the point of view of drag reduction or separation control-r'xB0; Recently. Krishnan et al.' showed that riblets actually increase the base drag (about 8.7 on a long axisymmetric body with a blunt base at low speeds: the base diameter was about four times the boundary -layer thickness ahead of the base corner-They used 3M riblet sheers and systematically studied the effect of h+` on base pressure. They also speculated that, while riblets caused an increase in the base drag for a large-scale separated flow (like on the axisymmetric blunt base'), the effect could be favorable on an airfoil with a blunt trading edge, which is a case of a small-scale separated flow. 13; The present investigation was undertaken specifically to assess the effect of 3M riblets on the base pressure of an airfoil with a blunt trailing edge. Experiments were made at low speeds on a 13.6% thick GAW(2) airfoil model, which has a trailing-edge thickness ratio of 0.5%. The results show very clearly that the base drag reduction of an engineering value can be achieved for the optimized riblet geometry.

Sailplane winglet design

Abstract: Although the accuracy of methods for the design and analysis of winglets has been limited, the performance gains achieved through their use are now well established. To further these gains, an improved methodology for winglet design has been developed. This methodology incorporates a detailed component drag buildup that includes the ability to interpolate input airfoil drag and moment data across operational lift coefficient, Reynolds number, and flap-setting ranges. Induced drag is initially predicted using a relatively fast discretized, lifting-line method. In the final stages of the design process, a full panel method, including relaxed-wake modeling, is employed. The drag predictions are used to compute speed polars for both level and tuning flight. This information can then be used to obtain cross country performance over a range of thermal strengths and profiles. The performance predictions agree well with flight-test results, and are consistent with the winglet design experiences obtained thus far. Example designs for the Schempp-Hirth Discus and the Schleicher ASW-20 demonstrate that winglets can provide a small but important performance advantage over much of the operating range for both Standard and Racing Class sailplanes.

Wingtip vortex impeller device for reducing drag and vortex cancellation

Abstract: The present invention is a wingtip vortex device installed at the wingtips of an aircraft for induced drag reduction and vortex cancellation. Also, the wingtip vortex device is self-contained and is powered by the wingtip vortex. The wingtip vortex device comprises a shaft coupled between the wing and a spinner. The spinner is a streamlined body of revolution with a number of radial fins. The wingtip vortex of the aircraft induces spinner whirl, which is opposite to that of the wingtip vortex. As a result, the spinner-induced whirl produces an upwash superimposed on the downwash of the vortex. Thus, the total downwash, and hence the induced drag, are reduced.

The Paths of Soaring Flight

Abstract: Part 1 The sailplane in still air: definitions wings of finite span - downwash and induced drag the total drag of a sailplane general equations of motion of a sailplane. Part 2 Instruments for soaring flight: the measurements of vertical velocity. Part 3 The sailplane in the atmosphere: thermals - observations in flight and in the laboratory maximizing the rate of climb in thermals the practice of cross-country flying computer calculations of sailplane performance generalized optimization calculations - the calculus of variations the effect of wind the effectof CG position on performance.

An Aerodynamic Assessment of Micro-Drag Generators (MDGs)

Abstract: Commercial transports as well as fighter aircraft of the future are being designed with very low drag (friction and pressure). Concurrently, commuter airports are being built or envisioned to be built in the centers of metropolitan areas where shorter runways and/or reduced noise footprints on takeoff and landing are required. These requirements and the fact that drag is lower on new vehicles than on older aircraft have resulted in vehicles that require a large amount of braking force (from landing-gear brakes, spoilers, high-lift flaps, thrust reversers, etc.). Micro-drag generators (MDGs) were envisioned to create a uniformly distributed drag force along a vehicle by forcing the flow to separate on the aft-facing surface of a series of deployable devices, thus, generating drag. The devices are intended to work at any speed and for any type of vehicle (aircraft, ground vehicles, sea-faring vehicles). MDGs were applied to a general aviation wing and a representative fuselage shape and tested in two subsonic wind tunnels. The results showed increases in drag of 2 to 6 times that of a "clear" configuration.

Inverse optimization of transonic wing shape for mid-size regional aircraft

Abstract: Multiobjective Genetic Algorithms (MOGAs) have been applied to design a transonic wing shape. First, the wing planform is optimized by solving a multidisciplinary optimization problem based on aerodynamic, structural and fuel storing objectives and constraints. Second, three-dimensional target pressure distribution is optimized for the aerodynamic inverse design with the previously designed planform. Minimization of the profile drag and the induced drag is performed under constraints on lift and other design principles. Corresponding wing surface geometry is obtained by Takanashi's inverse method. These two multiobjective optimization problems are solved by Pareto-based MOGAs coupled with appropriate CFD solvers. Applying these two wing design procedures, Pareto surfaces can be studied for trade-offs and a good compromised solution for the wing design can be obtained.

Vane-airfoil combination

Abstract: A vane-airfoil combination for shifting forces associated with an airfoil. The vane-airfoil combination includes an airfoil moving through a fluid, such as air. A plurality of vanes is positioned in front of the airfoil to divert the path of the fluid to the airfoil. The change in the path of the fluid rotates the forces associated with the airfoil in relation to the original path of the fluid. Specifically, a lift force is rotated to provide a thrust component force, as well as a lift component force. In addition, a drag force is rotated to provide a lift component force, as well as a reduced drag component force. The airfoil may be any type of airfoil, such as a rotating cylinder. The vane-airfoil combination may also include a fore-body and an after-body for reducing the pressure along an upper portion of the airfoil.

Airfoil Wave-Drag Prediction Using Euler Solutions of Transonic Flows

Abstract: The objective of the present work is the evaluation of four airfoil wave-drag prediction methods based on solutions of the Euler equations. In the case of two-dimensional inviscid e ows of interest here, it is shown that the expression based on a volume integration of a positive dee nite quantity related to the artie cial viscosity systematically underestimates the wave drag. In contrast with the popular belief, it is demonstrated that no clear improvement, in terms of accuracy, results from the use of far-e eld methods with respect to body-surface pressure integration. However, drag predictions obtained with entropy-based expression applied on a surface containing only the shocks are less sensitive to high levels of false entropy production because the drag contribution associated with false entropy production is eliminated. Furthermore, in threedimensional e ows, the wave and induced drag can be distinguished. A new method is proposed to correct the body-surface pressure integration estimates that is less sensitive to the level of false entropy production.

Drag and lift

Abstract: This chapter briefly discusses the external flows. Flow around a body placed in a uniform flow develops a thin layer along the body surface with largely changing velocity, which is the boundary layer, due to the viscosity of the fluid. Furthermore, the flow separates behind the body, discharging a wave with eddies. Whenever a body is placed in a flow, the body is subject to a force from the surrounding fluid. When a flat plate is placed in the flow direction, it is only subject to a force in the downstream direction. Thereafter, a drag is produced because a streamline separates behind a body, develops vortices, and lowers its pressure. Therefore, in order to reduce the drag, it suffices to make the body into a shape from which the flow does not separate. This is called the streamline shape. Of the forces acting on a body placed in a flow, if the body is manufactured as to make the lift larger than the drag, it is called a wing, airfoil, or blade. The shape of a wing section is called an airfoil section.

The Aerodynamic Forces On Misaligned Platoons

Abstract: This report summarizes wind tunnel experimental measurementson the aerodynamic interaction between members of misaligned platoons. Experiments are conducted at the University of Southern California's Dryden Wind Tunnel Facility. All experiments are made using 1/8 scale models of 1991 Chevy Lumina minivan. Models are placed above a ground plane with a porous surface, through which slight suction is applied to remove the boundary layer. Refurbishing of the ground plane surface, and its repositioning to a 1 degree angle of attack produce significantly improved air flow through the test section. Automatization of the testing procedures allow measurements of drag, side force and yawing moment with extremely fine position resolution. The measured quantities are presented in the form of coefficient ratios by ratioing the forces and moment with the value of drag experienced by a vehicle in isolation. The results of two separate experiments are presented in this report. First, aerodynamic forces on misaligned three-vehicle platoons are presented for all possible platoon configurations resulting from a longitudinal separation range of 0 to 0.72 vehicle lengths and a lateral displacement range of 0 to 1.1 vehicle widths for the middle vehicle. Results are presented in the form of color maps of the drag, side force and yawing moment coefficient ratios for each individual vehicle in the platoon. Experimental results from a complete set of symmetric configurations and five sets of non-symmetric configurations, associated with five fixed separations between the leading vehicle and the trailing vehicle, are presented in detail. A second experiment consists of a detailed investigation of aerodynamic forces on a two-vehicle platoon in back-to-back geometry. Following previous observations, the present experiment investigates a two-fold increase in drag force occurring at specific separations between the two vehicles. Color maps for the drag, side force and yawing moment coefficient ratios document the presence of a hysteresis loop-the drag on the leading vehicle as separation increases is different from drag as separation narrows. It is argued that the resonance with hysteresis represents a matching between the wavelength of turbulent flow structure and the spacing itself. A dimensional analysis relates the drag increase phenomenon to longitudinal separations between different types of vehicles.

Improvement of a Preliminary Design and Optimization Program for the Evaluation of Future Aircraft Projects

Abstract: The improvement of an integrated aircraft predesign code and its application to future aircraft concepts is reported. For the simulation of a Megaliner canard configuration as well as a supersonic commercial transport aircraft (SCT) the predesign code PrADO was extended by the higher-order panel method HISSS. The improvement of the aerodynamic model allows the simulation of interference effects between wing, tailplane and canard as well as the extension of the simulated flight regime to supersonic speeds. The application of the calibrated predesign code to a Megaliner configuration leads to differences between published and predicted design weights below 6%. Preliminary results of the simulation of a canard configuration show that a canard may not automatically increase the aerodynamic efficiency L/D. A reduction of the induced drag is overcompensated by an increase of the minimum drag due to additional friction drag of the canard. The SCT design studies also provide converged solutions, however, a redesign of the Concorde shows significant discrepancies with respect to the operational empty weight, fields for future investigations.

Experimental measurement of sideforce and induced drag on catamaran demihulls

Abstract: A catamaran comprises two demihulls and although the flow about the catamaran centre line is symmetric the flow about the centre lines of the individual demihulls is not. The asymmetric nature of the fluid crossflow around the demihulls causes sideforce and hence induced drag to be experienced on the demihulls. The sideforces generated by each demihull act in opposition and cancel whereas the induced drags of both demihulls act together to resist the forward motion of the vessel. Experimental procedures used to estimate the sideforce and induced drag are presented together with results for one hullform at two demihull separations (S/L = 0.225 and S/L = 0.329) and at several Froude Numbers. It is shown that the induced drag generated by the demihulls is negligible despite the generation of significant sideforce. The sideforce produced was found to reduce rapidly with increasing demihull separation.

Multi-member tip

Abstract: FIELD: aeronautical engineering; tips of aircraft lifting surfaces and tips of helicopter blades. SUBSTANCE: end of lifting surface is provided with multi-member tip which is mounted in horizontal plane for reduction of induced drag; it is made in form of split wing consisting of at least three small wings having their own aerodynamic profile, aerodynamic and geometric twist and mounted at optimal angles of attack relative to tip chord of lifting surface. Aerodynamic profiles, angle of attack, twist, as well as mean geometric chord are selected on the condition of prevailing intensity of tip vortex at given section of tip chord of lifting surface under optimal cruising conditions of flight. Shape in plan of small wings may be different: it is dictated by specific features of aerodynamic profile of lifting surface acting of intensity of tip vortex at definite section of tip chord. EFFECT: reduction of induced drag at subsonic and transonic speeds through change in redistribution of load over lifting surface and weakening intensity of tip vortex due to flow of air from lower to upper surface at operational angles of attack. 2 dwgp

The drag force acting on a cylinder or a flat plate exposed to a plasma flow for great Knudsen numbers

Abstract: As a continuation of previous papers, analytical expressions for the drag and/or lift forces acting on two typical non-spherical objects (a cylinder and a flat plate) exposed to a plasma flow are presented for the extreme case of great Knudsen numbers and a thin plasma sheath. Combined specular and diffuse reflection at the object's surface is included in the analysis. It is shown that the drag and/or lift coefficients are independent of the object's size and not influenced much by the plasma's temperature. The drag or lift force increases with increasing specular-reflection fraction of gas particles at the object's surface, but the rate of increase for the drag or lift force on a flat plate is appreciably greater than that for the drag force on a cylinder. Some suggestions concerning how to check the present kinetic-theory analysis and to determine the values of the specular-reflection fraction of gas particles at the object's surface through the drag or lift force measurements are proposed.

Development of Subsonic Transports With Natural Laminar Flow Wings

Abstract: The two main sources of drag that can account for more than 80 % of the total drag for current subsonic aircraft are friction and induced drag. A new Natural Laminar Flow (NLF) wing design methodology has been established to minimize these two important sources of drag. According to this method, a synthesis and sizing code, is used to estimate the benefits of NLF technology at the system level, and determine optimal wing planfonn geometry and wing area for a given mission requirement. Then, the chordwise pressure distribution and the spanwise lift distribution of the previously optimized NLF wing planform from the sizing code are parameterized carefiilly on the basis of physical insights. Inverse Aerodynamic Design Technique is then used to find the corresponding airfoil geometry for a given pressure distribution. Finally, a metamodel building method called Response Surface Methodology (RSM) is used to minimize the drag of the wing at the design cruise condition, given by the sizing code, with respect to the parameters related to the chordwise pressure distribution and the spanwise lift distribution of the NLF wing simultaneously. In this procedure, the accurate prediction of the onset of laminar-to-turbulent transition is crucial to estimate the skin friction drag. A reasonable approximation is achieved by initially computing the mean flow by means of a Navier-Stokes code, CFL3D, then a compressible linear stability analysis code, COSAL3D, to estimate transition location and, finally, CFL3D is executed again. At this time, a turbulence model is applied after the predicted transition point for a more accurate skin friction drag prediction. The paper outlines this method and applies it to the design of a subsonic transport configuration.

Inverse optimization of transonic wing design using multiobjective genetic algorithms

Abstract: A Multiobjective Genetic Algorithm (MOGA) has been applied to optimize the three-dimensional target pressure distribution for the aerodynamic inverse design of transonic wing shape. The pressure distribution will be optimized to minimize the viscous drag and the induced drag under constraints on lift and other design principles. Pareto optimal solutions are. computed by MOGA based on Pareto ranking and fitness sharing. Corresponding geometry is obtained by Takanashi's inverse method. The present design procedure was successfully applied to transonic wing shape design.

Vortex Drag in Quantum Hall Effect

Abstract: A new model of momentum and electric field transfer between two adjacent 2D electron systems in the Quantum Hall Effect is proposed. The drag effect is due to momentum transfer from the vortex system of one layer to the vortex system of another layer. The remarkable result of this approach is periodical change of $sign$ of the dragged electric field with difference between the layer filling factors.

Improving the aerodynamics of top fuel dragsters

Abstract: The standard drag race is a straight ahead quarter mile race from a standing stop. As engine technology has improved, the speeds attained at the end of the quarter mile have increased. As the speed has increased, the importance of aerodynamic effects on the dragster has also increased. Lift and drag are the two primary aerodynamic effects. Lift is produced vertically downward to increase the normal force on the rear wheels, thereby increasing the ability to transmit energy from the engine through the wheels to the racetrack. Drag is an unwanted aerodynamic effect. Drag is produced by viscous interaction between the dragster and the air, by separation causing profile drag, and as a result of the lift being produced. This paper addresses the mechanisms of lift and drag production by a high speed dragster and proposes some design changes that can decrease the drag while maintaining the necessary negative lift. Preliminary wind tunnel tests on dragster models confirm that reductions in drag can be achieved. The effects of these changes on the elapsed time and final speed are estimated using a computer simulation of a quarter mile drag race. The simulation predicts a decrease in elapsed time of almost 0.1more » seconds and an increase in top speed of approximately 10 miles per hour.« less

Vortex drag in the quantum Hall effect

Abstract: A new model of momentum and electric field transfer between two adjacent 2D electron systems in the quantum Hall effect is proposed. The drag effect is due to momentum transfer from the vortex system of one layer to the vortex system of another layer. The remarkable result of this approach is a periodic change of sign of the dragged electric field as a function of the difference between the layer filling factors.

Drag Reduction of High Altitude Airships by Active Boundary Layer Control. Effect of a Cusp on the Reduction.

Abstract: The aerodynamic character of station-keeping airships at high Reynolds numbers is examined. The boundary layer developing on the surface is sucked by an axial flow fan through a slot located at the rear part of the airship and the sucked gas is blown out as a jet. To know the effect of the cusp two models with and without a cusp attached to the inlet of the suction slot were used. The flow field near the inlet, in particular the pressure on the surface, was measured as the suction discharge was varied. We obtained the form drag by integrating the pressure distribution in a wide range of Reynolds number and of suction discharge. Taking into account the jet thrust and the calculated friction drag, we finally determined the total drag and evaluated the role of the cusp. It was found that the cusp plays an efficient role in reducing the drag.

Drag and lift forces for the thin body in the supersonic flow of the non-equilibrium gas

Abstract: The classical problem of the fluid mechanics is the problem of a supersonic motion around a thin body was generalized to the case of non-equilibrium gas. The drag and lift force coefficients were founded. It is shown that the drag and lift force coefficients in the acoustically active supersonic flow are both decreased

On the Viscuous Damping Mechanisms for Vortices in Superconductors

Abstract: Vortex drag mechanisms suggested by Tinkham and by Bardeen and Stephen are considered phenomenologically and shown to be identical.