Showing papers on "Lift-induced drag published in 2005"

Aerodynamic and Static Aeroelastic Characteristics of a Variable-Span Morphing Wing

Abstract: The morphing concept for unmanned aerial vehicles is a topic of current research interest in aerospace engineering. One concept of morphing is to change the wing configuration during flight to allow for multiple flight regimes. A particular approach to planform morphing is a variable-span morphing wing to increase wingspan to reduce induced drag and increase range and endurance. The wing area and the aspect ratio of the variable-span morphing wing increase as the wingspan increases. This means that the total lift increases while the induced drag is reduced, whereas the wing-root bending moment increases, thus, requiring a larger bending stiffness of the wing structure. Therefore, a study of the variable-span morphing wing requires not only aerodynamic analysis but also an investigation of the aeroelastic characteristics of the wing. The aerodynamic characteristics of the variable-span morphing wing are investigated, and a static aeroelastic analysis is performed.

Direct numerical simulation of polymer-induced drag reduction in turbulent boundary layer flow

Abstract: We describe a method for direct numerical simulation of polymer-induced friction drag reduction in turbulent boundary layers. The effect of the polymer additives that induce spatial variations of skin-friction drag is included in the momentum equation through a continuum constitutive model for the viscoelastic stress, which is based on the evolution of a parameter describing the fluid microstructure. We demonstrate that the turbulence structure and polymer microstructure evolve asynchronously as one moves in the streamwise direction. We observe an initial development length, which is followed by a quasisteady region where variations in drag reduction are weak. High drag reduction behavior can be present at short downstream distances from the inflow plane.

Spanwise Lift Distribution for Blended Wing Body Aircraft.

Abstract: A study is presented of the effects of spanwise lift distribution on aerodynamic efficiency for a blended wing body (BWB) configuration of a given baseline planform. The baseline geometry is initially assessed by a high-fidelity aerodynamic model based on a multiblock structured grid Reynolds-averaged Navier-Stokes (RANS) solution. The accuracy of the simulation is investigated by a grid sensitivity study regarding total drag and its pressure drag and skin-friction drag components. Excessive outer wing loading with associated shock wave, hence, wave drag, has been revealed to be the major factor degrading the aerodynamic performance of the baseline BWB model. To relieve the outer wing, an efficient low-fidelity panel method aerodynamic model is used for the inverse design to achieve the target lift distributions through the variation of twist distribution along the span, shifting the load inboard. For the given BWB geometry, the baseline model is retwisted to achieve an elliptic, a triangular, and an averaged elliptic/triangular spanwise loading distribution. The designs are then analyzed using the high-fidelity RANS aerodynamic model. The wave drag component of the total drag for different span loadings is extracted from the flowfield solution to gain insight into the drag reduction provided by the new twist designs

Numerical Simulations of Membrane Wing Aerodynamics for Micro Air Vehicle Applications

Abstract: To gain insight into the aerodynamics of flexible wing-based micro air vehicles (MAVs), we study the threedimensional interaction between a membrane wing and its surrounding fluid flow. A nonlinear membrane structural solver and a Navier‐Stokes flow solver are coupled through the moving boundary technique and time synchronization. Under the chord Reynolds number of 9 × × 10 4 , the membrane exhibits self-initiated vibrations in accordance with its material properties and the surrounding fluid flow. The vortical flow structure, its effect on the aerodynamic parameters, and the implications of the membrane deformation on the effective angle of attack and flow structure are discussed. Nomenclature C D = drag coefficient CL = lift coefficient c = chord length c p = pressure coefficient D = drag Fpx = form drag Fpy = lift caused by pressure force Fτ x = drag caused by friction L = lift U = freestream speed u = chordwise velocity v =v ertical velocity x = chordwise distance from the leading edge Z = half-wing span z = spanwise distance from the root α = angle of attack

Effect of Tip Vortex on Wing Aerodynamics of Micro Air Vehicles

Abstract: Tip vortex induces downwash movement, which reduces the effective angle of attack of a wing. For a low-aspect. ratio, low-Reynolds-number wing, such as that employed by the micro air vehicle (MAV), the induced drag by the tip vortex substantially affects its aerodynamic performance. In this paper we use the endplate concept to help probe the tip-vortex effects on the MAV aeredynamic characteristics. The investigation is facilitated by solving the Navier-Stokes equations around a rigid wing with a root-chord Reynolds number of 9 x 10 4

Airfoil Aerodynamic Performance Modification using Hybrid Surface Actuators

Abstract: Global modifications of the aerodynamic characteristics of a commercial transport swept airfoil at cruise (low) angles of attack (when the baseline flow is fully attached) are achieved without moving control surfaces using hybrid actuators that are surface mounted on the pressure side of the airfoil 0.21c downstream of its leading edge. Control is effected by the manipulation of trapped vorticity concentrations that are induced by leveraging the presence of a miniature, O(0.01c) obstruction integrated with a synthetic jet actuator. At Rec = 1.3·10 6 , the operation of the hybrid actuators with maximum Cµ = 0.5 10 -3 results in continuous variation of the pressure drag from 15% greater to 50% less than the pressure drag of the baseline airfoil with minimal lift penalty and consequently an increase of the lift to pressure drag ratio in excess of a factor of two. High-resolution particle image velocimetry measurements at Rec = 6.7·10 5 are used to characterize the evolution of the boundary layer on the surface of the airfoil and estimate the total drag coefficient. It is shown that the overall drag is reduced by 29% and yields an increase in L/D of 27%.

Ideal aerodynamics of ground effect and formation flight

Abstract: The theoretical induced-drag benefits are presented for ideally loaded wings flying in formation and ground effect. An optimum-downwash approach using a vortex-lattice implementation was used to study formations of wings loaded optimally for minimum induced drag with roll trim. An exact approach was also developed to examine the drag of elliptically loaded wings in formation. The exact approach allows for decomposition of the benefits by considering the mutual-interference contributions from different pairs of wings in a formation

Aerodynamic effect of roof-fairing system on a heavy-duty truck

Abstract: Aim of this study is to investigate an aerodynamic effect of a drag-reducing device on a heavy-duty truck. The vehicle experiences two different kinds of aerodynamic forces such as drag and uplifting force (or downward force) as it is traveling straight forward at constant speed. The drag force on a vehicle may cause an increase of the rate of fuel consumption and driving instability. The rolling resistance of the vehicle may be increased as result of the negative uplifting or downward force on the vehicle. A device named roof-fairing system has been applied to examine the reduction of aerodynamic drag force on a heavy-duty truck. As for a engineering design information, the drag-reducing system should be studied theoretically and experimentally for the best efficiency of the device. Four different types of roof-fairing model were considered in this study to investigate the aerodynamic effect on a model truck. The drag and downward force generated by vehicle has been obtained from numerical calculation conducted in this study. The forces produced on four fairing models considered in this study has been compared each other to evaluate the best fairing model in terms of aerodynamic performance. The result shows that the roof-fairing mounted truck has bigger negative uplifting or downward force than that of non-mounted truck in all speed ranges, and drag force on roof-fairing mounted truck has smaller than that of non-mounted truck. The drag coefficient (C_D) of the roof-fairing mounted truck (Model-3) is reduced up to 41.3% than that of non-mounted trucks (Model-1). A downward force generated by a roof-fairing mounted on a truck is linearly proportional to the rolling resistance force. Therefore, the negative lifting force on a heavy-duty truck is another important factor in aerodynamic design parameter and should be considered in the design of a drag-reducing device of a tractor-trailer. According to the numerical result obtained from present study, the drag force produced by the model-3 has the smallest of all in all speed ranges and has reasonable downward force. The smaller drag force on model-3 with 2/3h in height may results of smallest thickness of boundary layer generated on the topside of the container and the lowest intensity of turbulent kinetic energy occurs at the rear side of the container.

Induced Drag of Ground Vehicles and Its Interaction with Ground Simulation

Abstract: For the aerodynamic development of an aircraft the induced drag is an important quantity and it has a significant impact on the design of the wing The induced drag corresponds to the power requirement of the wing to generate the necessary lift In many cases this is the dominant source of drag for aircraft In ground vehicle aerodynamics the concept of induced drag up to now has attracted much less attention This is partly due to the fact, that vehicle aerodynamicists usually optimize the vehicles to generate little or no lift The second reason is that it is much more difficult for a ground vehicle to separate the total drag into the different contributions During wind tunnel tests of vehicles with and without ground simulation some astonishing results were found, especially when comparing results for different rear end shapes Notchback vehicles typically displayed lower drag results when measured with ground simulation, whereas wagon backs showed higher drag figures compared with the case without ground simulation To explain these surprising results, the contribution of induced drag to the total drag was analyzed in detail The proportion of induced drag was determined from measured polar diagrams Different lift levels of the vehicles were created using an adjustable rear spoiler, whereas the trim level of the vehicle was kept constant Notchbacks typically generate rear lift and wagon backs rear downforce The two rear end types therefore are b-cated on different branches of the parabola describing the induced drag By improvement of the ground simulation typically the lift is reduced and thus the induced drag is modified Due to the difference in the basic lift level the drag is reduced for the notchback and increased for the wagon back Induced drag can of course describe only a part of the complex influence of improved ground simulation Notchback vehicles do not generally show lower drag results when using ground simulation Nevertheless induced drag can explain some significant influences found in recent test results

Wing tip devices

Abstract: A tip device (10) to act as an outboard continuation of an aircraft wing (2) or other aerodynamic lifting surface has a downward cant angle, a leading edge (3, 8, 11) swept back in relation to the leading edge of the inboard lifting surface, and a chord reducing in the outboard direction of the device. A favourable balance between induced drag reduction and increased wing root bending moment can thereby be achieved. Preferably the device also has an upwardly canted portion at its root end so that the downward cant commences from a relatively elevated spanwise location, thereby alleviating any ground clearance problems.

Drag reduction in aircraft model using elliptical winglet

Abstract: Aerodynamic characteristics for the aircraft model with NACA (National Advisory Committee for Aeronautics) wing No. 653-218 have been studied using subsonic wind tunnel of 1000 mm x 1000 mm rectangular test section and 2500 mm long of Aerodynamics Laboratory Faculty of Engineering (Universiti Putra Malaysia). Six components wind tunnel balance is used for measuring lift, drag and pitching moment. Tests are conducted on the aircraft model with and without winglet of two configurations at Reynolds numbers 1.7 x 10 5 , 2.1 x 10 5 , and 2.5 x 10 5 . Lift curve slope increases more with the addition of the elliptical winglet and at the same time the drag decreases more for the aircraft model with elliptical shaped winglet giving an edge over the aircraft model without winglet as far as Lift/Drag ratio for the elliptical winglet is considered. Elliptical winglet of configuration 2 (Winglet inclination 60 0 ) has, overall, the best performance, giving about 6% increase in lift curve

Approach to induced drag reduction with experimental evaluation

Abstract: An approach to minimize the induced drag of an aeroelastic configuration by means of multiple leading- and trailing-edge control surfaces is investigated. A computational model based on a boundar ...

Aerodynamic Forces on an Airdrop Platform

Abstract: attack over the range -10o to 178o and with the plate undergoing dynamic pitching which was scaled from full-size platform motion. The results showed that the dynamic pitching of the plate significantly increased the lift and drag coefficients of the plate when compared against the plate at static angles of attack. The peak lift coefficient was increased by 72% and the maximum drag coefficient was increased by 350%. Although the peak lift coefficient occurred at the same angle of attack in both cases, the peak drag coefficient was delayed by ~42o with the dynamically pitching plate.

Conceptual Design of an Adaptive Wing for a Three-Surfaces Airplane

Abstract: The article describes the activities developed by Politecnico di Milano, as partner of Active Aeroelastic Aircraft Structures (3AS) EU project, focused on the preliminary investigations on the Active Adaptive Wing Camber (AAWC) concept, based on a device able to continuously change the camber angle of a wing. After a short description of the device, a preliminary investigation on the possible advantages of that device on the performances of a reference aircraft is reported. The investigation is formulated solving an optimization problem where the induced drag is minimized.

A numerical study of high-lift single element airfoils with ground effect for racing cars

Abstract: A numerical study is presented for high-lift airfoils suitable for racecar applications. The study includes the effect of ground clearance (distance between the airfoil and the ground), angle of attack and Reynolds number based on airfoil chord length. The finite volume code CFL3D, developed by NASA Langley Research Center, is used in the study. Four airfoils are used to represent different airfoil families. The study shows that Reynolds number has a very small effect on the downforce and the drag. Medium and large ground clearance are studied. For medium ground clearance the downforce and the drag increase, as airfoil gets closer to the ground. A considerable increase in the downforce can be gained by even small changes in the ground clearance. As the angle of attack increases both the drag and the downforce increase as expected. For large ground clearance the airfoil performance is close to the freestream case.

Numerical Simulation of Flow Around the Colorado Micro Aerial Vehicle

Abstract: Micro aerial vehicles (MAVs) are distinguished by their small size, low aspect ratio, and low velocity. As a result, MAVs fly at low Reynolds number flow regimes with significant drag characteristics and strong tip vortices. This investigation is focused on the aerodynamic characteristics of a recently developed MAV at the University of Colorado. The Colorado MAV has a flexible membrane wing with an aspect ratio of 1.2 and a chord of 0.27 m. Numerical simulations of the flow around the Colorado fixed wing MAV are presented using a steady state parallel compressible Navier-Stokes solver. The computational grid has 510,000 nodes and about 3 million tetrahedral elements. The maximum calculated lift coefficient is approximately 1.2. The airplane stall angle is at 30°. The high stall angle is attributed to the enhanced lift from a low pressure region above the wing caused by strong tip vortices. Minimum drag coefficient was calculated to be 0.06 at 2° angle of attack. A laminar separation bubble is formed on the upper surface of the wing at moderate angle of attack. The drag increases rapidly as the angle of attack increases. A maximum aerodynamic efficiency of L/D = 4 is observed when flying at 10 m/s.

Vortex Drag for a Simple Bluff Body at Incidence in Ground Proximity

Abstract: Aerodynamic drag is comprised of pressure drag and skin friction only. The drag component associated with lift forces is contained within these two terms. In the case of a simple wing this drag component, called induced drag, is reasonably well defined as a function of lift, but for road vehicles the relationship is more complex. In this paper the drag due to lift, which will be called vortex drag, is investigated for a simple car-like shape at incidence in proximity to the ground. The vortex drag is derived from the parabolic relationship between drag and lift. The effects of ground clearance are considered for both moving a stationary ground simulations. The results are compared with data for other simple bodies.

Measurement of the aerodynamic forces on a small particle attached to a wall

Abstract: Using operating principles similar to that applied in atomic force microscopes, we have developed a novel measuring method to study the aerodynamic forces, in particular the lift and drag force, acting on a small particle attached to a wall and immersed in a linear shear flow. Results thus far have shown that the system is capable of measuring both the minute aerodynamic lift and drag forces that a particle experiences as a result of the flow.

Unmanned aerial vehicle (UAV) deceleration system

Abstract: A system for slowing an air vehicle, including an independently supported aerodynamic drag device designed so that, after contact is made between the flying air vehicle and the aerodynamic drag device, one or more parts of the aerodynamic drag device are carried along by the air vehicle thereby decelerating the air vehicle, so that a majority of a kinetic energy dissipation of a combination of the air vehicle and the aerodynamic drag device is due to an aerodynamic drag of the aerodynamic drag device.

Wing Tip Vortex in the Near Field: An Experimental Study

Abstract: Introduction F LOW close to the wing tip is of importance for both low– and high–aspect ratio wings. Indeed, induced drag could be significantly affected by spanwise lift distribution, because there is an introduction of energy that is concentrated at the wing tip. Furthermore, even small errors in the prediction of flow close to the wing tip can significantly affect the evaluation of the structural loads acting on the wing. Knowledge of the physical behavior of the fully developed tip vortex is well established. However, experimental evidence shows, for the initial roll-up of the wing-tip vortex, complex behavior that is not adequately described by existing empirical models of the near-field flow. In fact, the tip vortex evolves from a complex threedimensional separated flow, and the resultant motion of the trailing vortices is highly unsteady. This implies that the core of the vortex fluctuates in time, and this meandering behavior causes the time-averaged Eulerian point measurement to be an average that is weighted both in time and in space. It is thus evident that the unsteadiness of the flow represents a significant challenge for both numerical and experimental analysis. Current knowledge of tip vortex flows is not adequate, and remains essentially qualitative, especially regarding the details of the mechanism of vorticity transport from the near-surface viscous layers into the trailing concentrated vortex. To achieve a better understanding of the initial phase of the tip vortex development an experimental study was performed, and its main results are described here.

Drag prediction and decomposition based on CFD computations

Abstract: In this paper, advanced drag prediction methods based on the momentum conservation theorem were applied to CFD computational results. These methods can decompose total drag into drag components such as wave, viscous and induced drag as well as spurious drag attributed to numerical computations. Hence the more accurate drag prediction is possible by the elimination of the spurious drag term. The computational results showed that the advanced methods had the good capability of drag prediction and meaningful drag decomposition with accuracy. It was also found that the predicted physical drag values were weakly dependent on the mesh quality.

Passive Shock Control Concept for Drag Reduction in Transonic Flow

Abstract: The operating principle of a novel passive shock control concept for drag reduction on swept wings called D-Strips is introduced, and results of a first experimental proof of concept are presented. Wind-tunnel experiments are conducted at transonic airspeeds using an airfoil VC-Opt (9.2% relative thickness) with forced boundary-layer transition. Schlieren pictures confirm the operating principle. Wake measurements demonstrate that, locally, in the wake of D-Strips the total drag increases. However, more globally, at spanwise locations away from these positions the total drag is measurably reduced if a sufficiently strong shockwave is present above the wing-suction-side surface. In contrast to passive control by ventilation, outside of the wake of the D-Strips a wave and viscous drag reduction and observed. Furthermore, the maximum lift tends to be increased by D-Strips suggesting that the buffet-onset limit is delayed. An application of D-Strips to a swept wing at cruise conditions can yield net aircraft drag reduction because the drag rise is limited to the D-Strips and its wake, but the shock-weakening effect and the drag reduction are distributed in the wide-splayed characteristics upstream of the shock front. The effectiveness of D-Strips is less sensitive to the location of the shock wave than control concepts like two-dimensional bumps, which are only effective at the design conditions. Another application of D-Strips that can be considered is the regions with a distinct shock, for example, between engines or in the wing-root region or at the inboard engine. However, there is a need for further investigations in order to optimize D-Strips and to quantify their impact on aircraft performance. Recent experimental results indicate that airscoop-type configurations might perform better as D-Strips than Velcro-type strips. Because D-Strips are easy to apply on existing wings, an application of D-Strips for retrofit is possible.

Effect of Trailing-Edge Flap on a Tip Vortex

Abstract: The near-wake tip vortex flow structure behind a NACA 0015 airfoil with a trailing-edge flap was investigated. Lift-induced drag was computed based on vorticity and was compared with force-balance data. The vortex strength reached a maximum immediately behind the trailing edge and remained nearly constant up to two chord lengths downstream (x/c = 3). The displaced flap produced a more concentrated vortex of similar diameter and a higher induced drag compared to that of a baseline airfoil and had a larger radial gradient in circulation strength for flap angle δ < 15 deg; the vortex radius increased significantly for δ =2 0deg. For δ < ‐ 15 deg, the axial flow velocity was jetlike with the peak values increased with the flap angle. The nearly symmetric vortex was observed at x/c =2 .25 fo ra displaced flap while at x/c =1 . 5f or a baseline airfoil. The stength and interaction of the secondary and main vortices along the tip were also found to increase with the flap angle, and the vortex flow (immediately downstream of the deflected flap) was dominated by the presence of multiple vortices. The normalized circulation in the inner part of the symmetric vortex exhibited a self-similar structure, insensitive to the flap angle.

Minimizing Induced Drag with Geometric and Aerodynamic Twist, CFD Validation

Abstract: *† ‡ A more practical analytical solution for the effects of wing twist on the performance of a finite wing of arbitrary planform has recently been presented. This infinite series solution is based on Prandtl’s classical lifting-line theory and the Fourier coefficients are presented in a form that depends only on wing geometry. Except for the special case of an elliptic planform, this solution shows that, if properly chosen, wing twist can be used to reduce the induced drag for a wing producing finite lift. A relation for the optimum twist distribution on a wing of arbitrary planform was presented. If this optimum twist distribution is used, the new solution predicts that a wing of any planform can be designed for a given lift coefficient to produce induced drag at the same minimum level as an elliptic wing having the same aspect ratio and no twist. In the present paper, results predicted from this new lifting-line solution are compared with results predicted from CFD solutions. In all cases, the CFD solutions showed that the drag reduction achieved with optimum twist was equal to or greater than that predicted by lifting-line theory. Nomenclature An = coefficients in the infinite series solution to the lifting-line equation an = planform contribution to the coefficients in the infinite series solution to the lifting-line equation

Experimental Study on Drag Reduction for Bodies of Revolution Using Bionic Non-Smoothness

Abstract: In view of the idea that the bionic non-smooth surface can reduce the viscous drag of a body, the drag reduction potential was investigated for the bodies of revolution by controlling the surface boundary layer structure to form a certain non-smoothness. An orthogonal test scheme with 6 factors and 3 levels for each factor was used to evaluate the effect of 6 major influencing factors on the drag of the bodies of revolution. The non-smooth bodies of revolution with spherical convex domes, spherical dimples and riblets were tested in comparison with the original smooth body in a wind tunnel under low speed, subsonic and supersonic conditions to get the drag reduction rates of the non-smooth bodies as the test targets. The test results in-dicated that all 3 kinds of non-smooth surfaces can reduce the drag of bodies of revolution, the maximal reduction rate is about 5%. The extremum difference analysis was used to determine the influence order of the factors and their optimal levels. The impact of the different bionic surfaces on the viscous forebody drag (in-cluding the skin friction and the shock-wave drag) and the base drag of bodies of revolution were discussed.

Swimming of the semi-infinite strip revisited

Abstract: Idealized mathematical models have been devised over the years for study of the fundamentals of the swimming of fishes. The two-dimensional flexible strip propelled by execution of transverse traveling-wave undulation is one of the most well-studied of the simple models. This model is redeveloped here, with the finding that higher propulsive efficiencies are theoretically available within the undulatory swimming mode than have been previously exposed. This is by configuring the displacement wave-form for continuously zero circulation over the body length with time, and thereby avoiding the shedding of a vortex wake and its attendant induced drag. The thrust is reactive, via acceleration processes, rather than inductive via relative velocity and lift. As in most of the classical work on fish propulsion, the analysis assumes high Reynolds number and a thin boundary layer, which provides the use of ideal-flow theory. The advance speed is assumed constant and the analysis is initially linearized, but both nonlinear and linear transient analysis are provided in supporting the basic “wakeless swimming” possibility.

Influence of Drag Force on the Dynamic Performance of a Rotor-Bearing System

Abstract: In oil-film journal bearings, the fluid forces exerted on the journal consist of both the pressure force and the drag force. The drag force has been neglected in most of the existing literature that deal with rotor-bearing instability analysis, for it is argued that the drag force is of the order of the clearance over radius (C/R) ratio times the pressure force. Nevertheless, tabulated numerical solutions of performance parameters based on the finite bearing theory reveal that at small eccentricity ratios (1 0.1) with L/D40.5, the drag force in journal bearings is appreciably large in comparison with the pressure force [1]. In 1965, Mitchell et al. [2] performed an instability analysis including the drag force effects in a journal bearing with a full 3608 oil film. They derived expressions for the drag force components in radial and tangential directions and presented the modified equations of motion in infinitely short and infinitely long bearings. Akers et al. [3] included the drag force components in the equations of motion for finite journal bearings. They concluded: ‘In all cases considered the inclusion of friction in the analysis makes the bearing more stable.’ Nevertheless, another conclusion in their paper asserting that the drag force does not make an unstable bearing completely stable requires further research. The objective of the present paper is to explain how the drag force affects the stability of a rotor-bearing system. For this purpose, the Hopf bifurcation theory (HBT) is utilized to examine the dynamic behaviour of the system by directly analysing the equations of motion. The details of the application of HBT for the stability analysis of a rigid rotor symmetrically supported by two long journal bearings was presented by Myers [4] in 1984. A similar analysis, but using the short bearing theory, was published by Hollis and Taylor [5].

Supersonic Flow over Blunt Body with a Decelerator

Abstract: The work to be presented herein is a Computational Fluid Dynamics investigation of the complex fluid mechanisms that occur over blunt body with and without a decelerator, specifically with regard to the total aerodynamic drag. Drag is needed to decelerate the body. The aim of this research is to design deceleration devices for a blunt body. In this paper a qualitative analysis of the flow structure over a blunt body and blunt body with a decelerator was shown. The results will show, that the adding a deceleration device will change the flow structure behind the body especially with regard to the pressure drag and wake. Results of contour plots of Mach number for different angles of attack and different speeds will demonstrate that the aerodynamic forces and the velocity are changed when the deceleration device is integrated with the blunt body. 1 Introduction work to be presented herein is a Computational Fluid Dynamics investigation of the complex fluid mechanisms that occur over blunt body with and without a decelerator, specifically with regard to the total aerodynamic drag. Drag is needed to decelerate the body. The aim of this research is to design deceleration devices for a blunt body. In this paper a qualitative analysis of the flow structure over a blunt body and blunt body with a decelerator was shown. A drag over moving body consists of two components: pressure drag and friction drag. Drag is due to the effect of viscosity. Pressure drag is a result of the eddying motions that are generated in the fluid due to the movement of the body. Pressure drag is related to the cross-sectional area of the body and it is associated with the formation of a wake it is also important for separated flows. Frictional drag is a result of the friction between the fluid and the surfaces over which it is flowing. Frictional drag is related to the surface area exposed to the flow and it is associated with the development of boundary layers it is also important for attached flows (1-2). For a blunt body, pressure drag is the dominant source of drag, but for streamlined body friction drag is the dominant source of air resistance. In some applications of aerodynamics, a deceleration of a moving body is required therefore the prediction and controlling of the drag is essential (3). The deceleration devices such as air bag or fins can be added to the body to increase the aerodynamics drag. For a supersonic speed, a flow around blunt body is complicated due to the detached shock wave, flow separation, boundary layer and their interactions. When a decelerator is integrated with the blunt body the flow is subject to sever change of aerodynamic forces and velocity (4-5). A number of important conclusions follow from the current research. First, study of the actual flow configuration over a blunt body with a decelerator offers some insight into the complex flow phenomena. Second, adding the decelerator will increase the separation that will result in an increase of total drag.

Tip vortex behind a wing oscillated with small amplitude

Abstract: The effect of reduced frequency on the tip vortex in the near field behind a NACA 0015 wing oscillated sinusoidally within the static-stall angle (= 14 deg) was investigated at Re = 1.86 × × 10 5 . The nearly symmetric vortex was observed at 0.5 to 1.5 chords downstream of the trailing edge similar to the case of a stationary wing. The oscillating wing produced a less concentrated vortex of similar diameter and had a larger radial gradient in circulation strength, compared to that of a stationary wing, for reduced frequency less than about 0.1. The axial-flow velocity was always wake-like, with its minimum value increasing with the reduced frequency. The peak value of the vorticity and the vortex strength and the lift-induced drag were higher during pitch-down than during pitch-up. The normalized circulation in the inner part of the axisymmetric vortex also exhibited a self-similar structure, which was insensitive to the reduced frequency. The induced drag increased with the reduced frequency.

Influence of angle of attack and stabilizer deflection on T empennage flutter

Abstract: It was found using wind-tunnel tests of airplanes with T empennage that the critical speed of antisymmetric flutter (based on composition of bending and torsional oscillations of the vertical tail) has an abnormally strong dependence on stabilizer deflections and angle of attack. This specific kind of antisymmetric flutter is characterized by relatively large amplitudes of oscillations of the stabilizer in its plane. Additional work of the induced drag forces on the in-plane component of oscillations might explain the nature of this kind of flutter. The numerical method for flutter analysis is described, which takes into account the effect of angles of attack and sideslip and aerodynamic control angles on flutter critical parameters. The method is based on a modification of the vortex lattice method and allows for induced drag when computing generalized aerodynamic forces. Numerical results for the flutter critical speed compare well with test data for a dynamically similar model of the civil airplane T-shaped empennage.