Showing papers on "Lift-induced drag published in 2010"

Drag and lift reduction of a 3D bluff-body using active vortex generators

Abstract: In this study, a passive flow control experiment on a 3D bluff-body using vortex generators (VGs) is presented. The bluff-body is a modified Ahmed body (Ahmed in J Fluids Eng 105:429–434 1983) with a curved rear part, instead of a slanted one, so that the location of the flow separation is no longer forced by the geometry. The influence of a line of non-conventional trapezoidal VGs on the aerodynamic forces (drag and lift) induced on the bluff-body is investigated. The high sensitivity to many geometric (angle between the trapezoidal element and the wall, spanwise spacing between the VGs, longitudinal location on the curved surface) and physical (freestream velocity) parameters is clearly demonstrated. The maximum drag reduction is −12%, while the maximum global lift reduction can reach more than −60%, with a strong dependency on the freestream velocity. For some configurations, the lift on the rear axle of the model can be inverted (−104%). It is also shown that the VGs are still efficient even downstream of the natural separation line. Finally, a dynamic parameter is chosen and a new set-up with motorized vortex generators is proposed. Thanks to this active device. The optimal configurations depending on two parameters are found more easily, and a significant drag and lift reduction (up to −14% drag reduction) can be reached for different freestream velocities. These results are then analyzed through wall pressure and velocity measurements in the near-wake of the bluff-body with and without control. It appears that the largest drag and lift reduction is clearly associated to a strong increase of the size of the recirculation bubble over the rear slant. Investigation of the velocity field in a cross-section downstream the model reveals that, in the same time, the intensity of the longitudinal trailing vortices is strongly reduced, suggesting that the drag reduction is due to the breakdown of the balance between the separation bubble and the longitudinal vortices. It demonstrates that for low aspect ratio 3D bluff-bodies, like road vehicles, the flow control strategy is much different from the one used on airfoils: an early separation of the boundary layer can lead to a significant drag reduction if the circulation of the trailing vortices is reduced.

Span Efficiencies of Wings at Low Reynolds Numbers

Abstract: Elegant and inviscid analytical theory can predict the induced drag on lifting wings of finite span. The theoretical prediction is then often modified by multiplication with a dimensionless coefficient for which the departure from a value of 1 is used as a way to incorporate realistic and necessary departures from the idealized model. Unfortunately, there are conflicting definitions of these dimensionless coefficients, often known as span efficiencies, so that even if numerical values are assigned in a clear and transparent fashion, their application and validity remain unclear. Here, the differences between two commonly used definitions of span efficiency are identified and it is shown that for the case of airfoil sections and finite wings at chordwise Reynolds numbers less than 10 5 , neither one has values close to those commonly assumed in the aeronautics literature. The cause of these significant viscous modifications to inviscid theory is traced to the movement of separation points from the trailing edge of real airfoils. A modified nomenclature is suggested to reduce the likelihood of confusion, and appropriate formulations for the drag of streamlined bodies in viscous flows at moderate Reynolds number are considered, with application to small-scale flying devices, both natural and engineered.

Modeling Strategy and Numerical Validation for a Darrieus Vertical Axis Micro-Wind Turbine

Abstract: This paper presents a model for the evaluation of optimal spatial grid node distribution in the CFD analysis of a Darrieus vertical axis micro wind turbine, by analyzing the trends over a 360° rotation of some indicators of near-blade mesh quality. To this purpose, a complete validation campaign has been conducted through a systematic comparison of numerical simulations with wind tunnel experimental data. Both two-dimensional and three-dimensional grids, characterized by average y+ values of 30 and 1, have been tested by applying some statistical techniques as a guidance in selecting the appropriate grid configuration and corresponding turbulence model. Finally, the tip downstream recirculation zone due to the finite blade extension and the influence of spokes have been analyzed, achieving a numerical quantification of the influence of induced drag and spokes drag on overall rotor performance.Copyright © 2010 by ASME

Mechanism for Warp-Controlled Twist of a Morphing Wing

Abstract: A new concept for actively controlling wing twist is described. The concept relied on introducing warping deformation of the wing skin, which was split at the trailing edge to create an open-section airfoil. An internal screw mechanism was introduced near the trailing edge, so that the load-carrying capability of the wing was maintained while allowing the introduction of warping displacement between the lower and upper wing skins at the trailing edge. Simple structural modeling of the warping wing based on generalized thin-walled beam theory was performed. A demonstration wing was built based on a NACA 23012 airfoil section with a span of 0.68 m and a chord length of 0.235 m. A maximum peak-to-peak twist of 27 deg was demonstrated, with excellent correlation between theory and experiment. Wind-tunnel tests showed that warping could change the lift coefficient by as much as 0.7 at maximum peak-to-peak twist. Analytical and vortex-lattice models were demonstrated to give accurate predictions of the lift coefficient at smaller absolute twist angles. Furthermore, analytic modeling of the wing drag was shown to be in close correspondence with the drag measurements and showed that wing warping could be used to influence the lift induced drag. In general, it was demonstrated that at lower angles of attack, a more positive twist resulted in a higher lift-to-drag ratio. This study proved that a twist-active wing can have sufficient gain to control the rolling motion of an aircraft and to ensure that the lift-to-drag ratio is maximized at various flight conditions.

Induced-Drag Minimization of Nonplanar Geometries Based on the Euler Equations

Abstract: The induced drag of several nonplanar configurations is minimized using an aerodynamic shape optimization algorithm based on the Euler equations. The algorithm is first validated using twist optimization to recover an elliptical lift distribution. Planform optimization reveals that an elliptical planform is not optimal when side-edge separation is present. Optimized winglet and box-wing geometries are found to have span efficiencies that agree well with lifting-line analysis, provided the bound constraints on the entire geometry are accounted for in the linear analyses. For the same spanwise and vertical bound constraints, a nonplanar split-tip geometry outperforms both the winglet and box-wing geometries, because it can more easily maximize the vertical extent at the tip. The performance of all the optimized geometries is verified using refined grids consisting of 88-152 million nodes.

Effect of Blade Inclination Angle on a Darrieus Wind Turbine

Abstract: This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0 deg, 30 deg, 60 deg, 90 deg, and 120 deg for a rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall rotor torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.

Aerodynamic characteristics of flying fish in gliding flight

Abstract: The flying fish (family Exocoetidae) is an exceptional marine flying vertebrate, utilizing the advantages of moving in two different media, i.e. swimming in water and flying in air. Despite some physical limitations by moving in both water and air, the flying fish has evolved to have good aerodynamic designs (such as the hypertrophied fins and cylindrical body with a ventrally flattened surface) for proficient gliding flight. Hence, the morphological and behavioral adaptations of flying fish to aerial locomotion have attracted great interest from various fields including biology and aerodynamics. Several aspects of the flight of flying fish have been determined or conjectured from previous field observations and measurements of morphometric parameters. However, the detailed measurement of wing performance associated with its morphometry for identifying the characteristics of flight in flying fish has not been performed yet. Therefore, in the present study, we directly measure the aerodynamic forces and moment on darkedged-wing flying fish (Cypselurus hiraii) models and correlated them with morphological characteristics of wing (fin). The model configurations considered are: (1) both the pectoral and pelvic fins spread out, (2) only the pectoral fins spread with the pelvic fins folded, and (3) both fins folded. The role of the pelvic fins was found to increase the lift force and lift-to-drag ratio, which is confirmed by the jet-like flow structure existing between the pectoral and pelvic fins. With both the pectoral and pelvic fins spread, the longitudinal static stability is also more enhanced than that with the pelvic fins folded. For cases 1 and 2, the lift-to-drag ratio was maximum at attack angles of around 0 deg, where the attack angle is the angle between the longitudinal body axis and the flying direction. The lift coefficient is largest at attack angles around 30∼35 deg, at which the flying fish is observed to emerge from the sea surface. From glide polar, we find that the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck. However, the induced drag by strong wing-tip vortices is one of the dominant drag components. Finally, we examine ground effect on the aerodynamic forces of the gliding flying fish and find that the flying fish achieves the reduction of drag and increase of lift-to-drag ratio by flying close to the sea surface.

Hybrid Optimal Control Approach to Commercial Aircraft Trajectory Planning

Abstract: CD = coefficient of drag CD0 = coefficient of parasite drag CL = coefficient of lift CLmax = maximum coefficient of lift CTc;4 = first thrust temperature coefficient CVmin = minimum speed coefficient D = drag force, 0:5 VSCD Gt = temperature gradient on maximum altitude GW = mass gradient on maximum altitude g = acceleration due to gravity h = altitude hM0 = maximum operating altitude hmax = maximum altitude at maximum takeoff weight under Instrument Society of America conditions hu = maximum dynamic altitude K = coefficient of induced drag L = lift force, 0:5 VSCL M = Mach number MM0 = maximum operating Mach number m = mass _ m = fuel flow mmax = maximum mass (maximum takeoff weight) mmin = minimum mass (operating empty weight) _ mmin = minimum fuel flow S = reference wing surface area T = thrust Tmax = maximum thrust V = true airspeed VCAS = calibrated airspeed VM0 = maximum operating calibrated airspeed Vstall = stall speed x = distance = angle of attack TISA = temperature deviation from International Standard Atmosphere = thrust specific fuel flow = flight-path angle = atmospheric density

Drag Reduction for Spike Attached to Blunt-Nosed Body at Mach 6

Abstract: A HIGH-SPEED flow over a blunt body generates a bow shock wave in front of it, which causes a rather high surface pressure and, as a result, high aerodynamic drag. The surface pressure on the blunt body can be substantially reduced if a conical shock wave is generated by attaching a forward-facing spike. Thus, the introduction of the spike decreases the drag and increases the lift coefficient. The spike produces a region of recirculating separated flow that shields the blunt-nosed body from the incoming flow. The applicability of the spike is limited due to the possible appearance offlowoscillations in the separation region, which may reduce its positive effects and may cause aerodynamic disturbances during the flight [1]. Many experimental studies focused their attention on the influence of the spike’s length on the aerodynamic characteristics of blunt bodies for various angles of attack at some transonic [2], supersonic [3–5], or even hypersonic [6–8] speeds. This Note contributes to the experimental study of the fluid flow structure and aerodynamic characteristics of a spike attached to blunt body atMach 6. This Note analyzes the aerodynamic effects of the spike attached to the blunt body by using schlieren flow visualization and measured aerodynamic forces and moments. This Note briefly describes the experimental results of the research on a hemispherical blunt nose body with and without spike at L=D ratio of 1.5 and 2 (where L is the spike length and D is cylinder diameter), and angle of attack from 0 to 8 deg, with a 1 deg step. An in-depth description of the experiment conditions and results may be found in [9].

Aeroelastic tailoring using lamination parameters: drag reduction of a Formula One rear wing

Abstract: The aim of the present work is to passively reduce the induced drag of the rear wing of a Formula One car at high velocity through aeroelastic tailoring. The angle-of-attack of the rear wing is fixed and is determined by the required downforce needed to get around a turn. As a result, at higher velocity, the amount of downforce and related induced drag increases. The maximum speed on a straight part is thus reduced due to the increase in induced drag. A fibre reinforced composite torsion box with extension-shear coupled upper and lower skins is used leading to bending-torsion coupling. Three-dimensional static aeroelastic analysis is performed loosely coupling the Finite Element code Nastran and the Computational Fluid Dynamics panel code VSAERO using ModelCenter. A wing representative of Formula One rear wings is optimised for minimum induced drag using a response surface methodology. Results indicate that a substantial induced drag reduction is achievable while maintaining the desired downforce during low speed turns.

Winglet Design and Optimization for UAVs

Abstract: Winglets are known improve the efficiency of large aircraft at high subsonic speeds, but winglet designs for smaller aircraft such as UAVs are largely unproven. Winglets improve efficiency by diffusing the shed wingtip vortex, which in turn reduces the drag due to lift and improves the wing’s lift over drag ratio. This research investigates methods for designing and optimizing winglet geometry for UAVs that operate at Reynolds numbers near 10. The design methodology is based on the vortex lattice method. Optimized designs are tested and compared with base designs for validation and include both Whitcomb and blended winglets. Designs are validated using wind tunnel tests. The resulting methodology is then applied to existing UAV platforms for specific performance improvements.

Drag Prediction for the NASA CRM Wing-Body-Tail Using CFL3D and OVERFLOW on an Overset Mesh

Abstract: In response to the fourth AIAA CFD Drag Prediction Workshop (DPW-IV), the NASA Common Research Model (CRM) wing-body and wing-body-tail configurations are analyzed using the Reynolds-averaged Navier-Stokes (RANS) flow solvers CFL3D and OVERFLOW. Two families of structured, overset grids are built for DPW-IV. Grid Family 1 (GF1) consists of a coarse (7.2 million), medium (16.9 million), fine (56.5 million), and extra-fine (189.4 million) mesh. Grid Family 2 (GF2) is an extension of the first and includes a superfine (714.2 million) and an ultra-fine (2.4 billion) mesh. The medium grid anchors both families with an established build process for accurate cruise drag prediction studies. This base mesh is coarsened and enhanced to form a set of parametrically equivalent grids that increase in size by a factor of roughly 3.4 from one level to the next denser level. Both CFL3D and OVERFLOW are run on GF1 using a consistent numerical approach. Additional OVERFLOW runs are made to study effects of differencing scheme and turbulence model on GF1 and to obtain results for GF2. All CFD results are post-processed using Richardson extrapolation, and approximate grid-converged values of drag are compared. The medium grid is also used to compute a trimmed drag polar for both codes.

Aerodynamic characteristics of wind turbine blade airfoils at high angles-of-attack

Abstract: Airfoil characteristics at deep stall angles were investigated. It appeared that the maximum drag coefficient as a function of the airfoil upwind y/c ordinate at x/c=0.0125 can be approximated by a straight line. The lift-drag ratios in deep stall of a number of airfoils with moderate lower surface thickness coincide. It was found that the lift-drag ratio of airfoils with leading edge separation is independent of aspect ratio. The lift-drag ratios of the various sections of a non-rotating and a rotating blade in deep stall coincide with the two-dimensional curve.

Simulation of Active Drag Reduction for a Square-Back Vehicle

Abstract: An active flow control approach was investigated in order to reduce the aerodynamic drag of a generic square-back vehicle. Using Large Eddy Simulations, it could be shown that steady blowing along the rear edges of the vehicle can reduce the drag by more than 10%. The blowing angle was varied, and a most effective angle of 45°. was found. The control method leads to a delay of shear layer vortex generation and to changes in the wake structure that cause a pressure increase on the rear surface of the vehicle. A simple estimation of the energy balance showed that the energy input needed for the active control is relatively large. Only for one case investigated in this study a small net power gain was found.

Aerodynamic Influence of a Half-Span Model Installation for High-Lift Configuration Experiment

Abstract: Lowspeed wind tunnel experiment of a high-lift configuration aircraft model JSM (Jaxa high-lift configuration Standard Model) is implemented at 6.5m by 5.5m low-speed wind tunnel in JAXA (JAXA-LWT1). The aerodynamic influence of a half-span model installation is assessed with changing a height of a spacer, which locates between a fuselage and wind tunnel wall. Variation of the aerodynamic characteristics depending on the spacer height in the experiment agrees well with computational results which is assumed wind tunnel wall boundary layer. Aerodynamic coefficients obtained in the experiment become closer to the result of a free-flight computation when the spacer height becomes lower. Local lift distribution estimated by the pressure distribution around the wing cross section changes continuously along spanwise direction when the spacer height increases or decreases. On the other hand, the local drag changes mainly in the inboard area. The variation of the induced drag evaluated by the relation between CD and square of CL shows that an effect of the spacer installation mainly appears as an increment of the effective aspect ratio and resultant changes in slope of the lift curve and reduction of the induced drag. However, an influence of the flow interaction near wind tunnel wall is not negligible. An estimation of desirable height of the spacer for the half-span model experiment is performed by comparing the computational result for the full-span model in free-flight condition and the half-span model installed on non-slip wall condition. Based on the effective aspect ratio of free-flight condition, the spacer height approximately 2 ~ 3 times of the displacement thickness of the floor boundary layer is a best candidate for the spacer height.

Rapidly convertible hybrid aircraft and manufacturing method

Abstract: A hybrid fixed wing aircraft converts into a roadworthy vehicle in a matter of seconds therefore operating efficiently in both air and ground transportation systems. The single piece wing is mounted on a skewed pivot that is on the lower portion of the fuselage and is operated by a pushbutton operating system. The aircraft includes telescopic twin boom tail design that when extended allows good pitch stability and damping. The aircraft's wing area may be increased with additional telescopic wing tip segments. This allows an increase in aspect ratio, hence improving efficiency at high loads. This feature will also creates a reduction in induced drag at cruise speed by simply retracting the tips in flight. The vehicle has a unique synchronized control system that switches from flight to ground mode without input from the operator, thereby providing a natural interface for the operator.

Influence of Wing Configurations on Aerodynamic Characteristics of Wings in Ground Effect

Abstract: A numerical analysis is performed to investigate the aerodynamic characteristics and the static height stability of the endplate and the anhedral angle on an aspect-ratio-one wing-in-ground effect. The analysis shows that the ground effect increases the lift by the high pressure on the lower surface, reduces the drag, increases the suction on the upper surface, and considerably enhances the lift-drag ratio. The endplate, which prevents the high-pressure air from escaping out of the lower surface and reduces the influence of the wing-tip vortex, further augments the lift and the lift-drag ratio. Irodov's criteria are also numerically evaluated in order to investigate the static height stability. The comparison of Irodov's criteria shows that the endplate is not favorable for the static height stability. However, the anhedral angle improves the lift as well as Irodov's criteria at various angles of attack and heights. Interestingly, the stagnation point for the anhedral angle moves forward with decreasing height at the low angles of attack and leads an increase in the pressure drag at the leading edge. This increase nullifies the advantages of the induced drag and the pressure drag. Thus, the lift-drag ratio of a wing is not improved as much with an anhedral angle as it is with an endplate.

Drag reduction in Stokes flows over spheres with nanostructured superhydrophilic surfaces

Abstract: Nanostructured surfaces offer opportunities to modify flow induced drag on solid objects. Measurements of the terminal velocity reveal that the drag associated with laminar Stokes flows can be reduced for spheres with nanostructured superhydrophilic as well as superhydrophobic surfaces. Numerical simulations suggest that the formation of recirculating or nearly stagnant flow zones leads to significant reduction in the friction drag. Such reduction, however, is offset by an increase in the form drag that arises from nonuniform pressure distributions. Our work motivates further studies to optimally balance the friction and form drag and control resistance to laminar flows over objects with nanostructured surfaces.

Aerodynamic Performance of a Gliding Swallowtail Butterfly Wing Model

Abstract: In the present study, we perform a wind-tunnel experiment to investigate the aerodynamic performance of a gliding swallowtail-butterfly wing model having a low aspect ratio. The drag, lift and pitching moment are directly measured using a 6-axis force/torque sensor. The lift coefficient increases rapidly at attack angles less than 10° and then slowly at larger attack angles. The lift coefficient does not fall off rapidly even at quite high angles of attack, showing the characteristics of low-aspect-ratio wings. On the other hand, the drag coefficient increases more rapidly at higher angles of attack due to the increase in the effective area responsible for the drag. The maximum lift-to-drag ratio of the present modeled swallowtail butterfly wing is larger than those of wings of fruitfly and bumblebee, and even comparable to those of wings of birds such as the petrel and starling. From the measurement of pitching moment, we show that the modeled swallowtail butterfly wing has a longitudinal static stability. Flow visualization shows that the flow separated from the leading edge reattaches on the wing surface at α < 15°, forming a small separation bubble, and full separation occurs at α ≥ 15°. On the other hand, strong wing-tip vortices are observed in the wake at α ≥ 5° and they are an important source of the lift as well as the main reason for broad stall. Finally, in the absence of long hind-wing tails, the lift and longitudinal static stability are reduced, indicating that the hind-wing tails play an important role in enhancing the aerodynamic performance.

Automated Control Surface Design and Sizing for the Prandtl Plane

Abstract: This paper presents a methodology for the design of the primary flight control surfaces, in terms of size, number and location, for fixed wing aircraft (conventional or unconventional). As test case, the methodology is applied to a 300 passenger variant of the Prandtl Plane. This box wing aircraft is deemed to have low induced drag compared to conventional aircraft. The methodology is completely physics based and includes an aerodynamic analysis, followed by a control allocation algorithm and an analysis of the flight mechanics. The design has to fulfill a set of handling qualities requirements with a minimum total control surface area. An optimization algorithm is used to find the best design. Results indicate that this is possible with ailerons outboard on both wings, elevators inboard on both wings and conventional rudders in the vertical tail. The configuration allows for pure torque control and also direct lift control in the longitudinal axis. These features can potentially enhance airfield performance.

Ground effect aerodynamics

Abstract: The ‘ground effect’ is the aerodynamic phenomenon whereby the flow field around a vehicle, either an aircraft or a car, is constrained and altered by the presence of the ground. For an aircraft operating in ground effect, it is the creation of an effective air cushion between the lower surface of the wing and the ground that modifies the physics of the flow resulting in positive lift enhancement. For a car utilizing ground effect, the dominant feature is a low-pressure field between the vehicle and the ground caused by significant flow acceleration, similar to the ‘Venturi effect’, leading to downforce (negative lift) enhancement. Components such as wings and diffusers operate within this regime. The impact of ground effect is generally an increase in aerodynamic efficiency, that is, an increase in lift-to-drag ratio for aircraft or the equivalent downforce-to-drag ratio for cars. When a vehicle operates too close to the ground, the beneficial response diminishes. The ground effect can adversely affect the flight stability of an aircraft during take-off and landing as well as under cruise conditions in close proximity to the ground. This chapter provides a brief summary concerning the history of ground effect vehicles. Various methods employed to study the phenomenon are introduced; these include empirical approximations, analytical methods, numerical simulations, and wind tunnel tests. Applications of ground effect to aircraft and vehicle design are also discussed. Advantages and risks are further examined with an emphasis on control and stability. Keywords: aerodynamics; ground effect; induced drag reduction; wing-in-ground effect; diffuser-in-ground effect; wing-in-ground effect vehicles

The Dynamics of Separation Control on a Rapidly Actuated Flap

Abstract: Unsteady aerodynamic loads on a NACA 0021 airfoil during rapid flap deflections were investigated. Typical dynamic stall effects like an overshoot in lift, drag, and pitching moment have been observed. Flap deflection angle and speed were varied while the angle of attack remained constant at = 0 . To prevent stall and accompanying detrimental behavior, fluidic actuators generating discrete sweeping jets were integrated into the simple flap of the airfoil. Initial experiments at various angles of incidence but constant flap deflections proved that these actuators can prevent flow separation, increase lift, and decrease the drag of the airfoil. Dynamic tests revealed that sweeping jet actuators can also eliminate dynamic stall effects. A significant gain in lift and a substantial reduction in drag were achieved within a short period of time, even for high flap deflection angles of 30 .

Multi Objective Aerodynamic Shape Optimization of High Speed Train Nose Using Adaptive Surrogate Model

Abstract: The objective of this work is to demonstrate the possibility of using adaptive surrogate models for optimization problems which require expensive computations. A hybrid GA PSO algorithm is combined with a kriging based surrogate model. The suggested method was used to nd the optimum shape of a two dimensional nose shape of a high speed train traveling at 350 Km/hr considering both the induced aerodynamic drag and the generated aerodynamic noise. Since the prediction of aerodynamic drag and aerodynamic noise requires computational uid dynamic simulations, to limit the number of computer simulations required for optimization, a surrogate model identical to the kriging model was used. The accuracy of the surrogate model is checked using the parameter EIV there by updating the surrogate model whenever necessary. The results show that the combined shape optimization algorithm requires a small number of simulations to identify the optimum shape compared with other methods. The suggested method not only requires a small number of simulations but is also robust. This makes the study on the eect of different weights on the optimum shape feasible without the need for additional simulations. The results show that the nose shape should be slightly short and pointed to get the best aerodynamic performance in terms of induced drag and the nose shape should be slightly long and little bit blunt for the least aerodynamic noise generated. The optimum nose shapes fall between these two shapes based upon the choice of the weights. Regarding the choice of the weights for the given two dimensional test geometry the best compromise would be to choose 50% drag and 50 % noise.

Aircraft with yaw control by differential drag

Abstract: An aircraft having an elongated fuselage and a lifting surface fastened to the fuselage. The aircraft has a device for controlling the torque around the yaw axis GZ of the aircraft in which aerodynamic forms that have devices to generate aerodynamic drag are fastened to each end of the lifting surface at non-zero distances from each side of a vertical plane of symmetry XZ of the aircraft. The drag-generating devices are commanded to produce a different aerodynamic drag at each of the two ends to generate a yaw torque on the aircraft. The aerodynamic forms, for example, have winglets improving the aerodynamics of the lifting surface, and provided with aerodynamic drag generators.

Looped airfoil wind turbine

Abstract: Looped AirFoil Wind Turbine (LAWT) (10) is a novel wind turbine with a basic system of a triangular structure (14) utilizing both lift and drag aerodynamic forces produced by wind energy. The entire triangular structure (14) could either yaw to always face the wind direction (W) or stay in a fixed position. The LAWT system (10) uses airfoil blades (12) shaped like an airplane wing, traveling linearly on travel wheels (22) riding on travel tracks (50, 52, 54). While traveling up, the wings are powered by a positive lift force and drag force while using negative lift force and drag force when traveling downward. All wings (12) are connected by a segmented chain (16) which transfers the kinetic power of wheeled wing carriages (18) directly to multiple generators (26), requiring no gears.

Incompressible Flow Over Finite Wings

Abstract: In this chapter, the aerodynamics of finite wings is analyzed using the classical lifting line model. This simple model allows a closed-form solution that captures most of the physical effects applicable to finite wings. The model is based on the horseshoe-shaped vortex that introduces the concept of a vortex wake and wing tip vortices. The downwash induced by the wake creates an induced drag that did not exist in the two-dimensional analysis. Furthermore, as wingspan is reduced, the wing lift slope decreases, and the induced drag increases, reducing overall efficiency. To complement the high aspect ratio wing case, a slender wing model is formulated so that the lift and drag can be estimated for this limiting case as well. Finally, a brief survey of panel methods is presented. These methods are capable of solving the potential flow over complex (and thick) lifting configurations. The solution, however, can be obtained by using numerical methods only. Keywords: aerodynamics; wings; slender wings; lifting line; induced drag; panel methods; aspect ratio

Redesigning the SLOCUM Glider for Torpedo Tube Launching

Abstract: Launching gliders from a submarine torpedo tube is of special interest for military operations. This is not currently possible because the wing span needed to achieve a good gliding performance is twice the standard diameter of submarine torpedo tubes. To fit lifting surfaces into small and nonconventional volumes in missiles and unmanned aerial vehicles (UAVs), retractable, compliant, and inflatable wings have been proposed by some researchers. Unfortunately, applying these solutions to underwater gliders would result in complicated wing devices or would require substantial modification to the vehicle. Lowering the wing aspect ratio while keeping constant the initial wing surface would be easier to implement, however, this would substantially degrade glider lifting performance. A possible alternative is the use of ring wings. This study investigates the hydrodynamic properties of a glider equipped with a ring wing specifically designed to fit into a torpedo tube. Specifically, a panel method is employed to compute the lift, induced drag and moment coefficient of a glider with different wing configurations. Modeled results are first compared with experimental data in the case of a glider with standard wing configuration. This study is performed on the Slocum glider due to the availability of experimental data. A numerical study is made of the Slocum glider equipped with a low aspect wing and with a ring wing. Results confirm the degradation of lifting performance of the low aspect ratio configuration. On the other hand, numerical results predict that similar gliding performance can be achieved with a Slocum glider equipped with a ring wing sized to fit the vehicle into a torpedo tube. Results encourage follow-up experimentation of these close lifting surfaces in underwater glider technology.