Showing papers on "Lift-induced drag published in 2006"

Influence of rheological parameters on polymer induced turbulent drag reduction

Abstract: Direct numerical simulations (DNS) of polymer induced drag reduction in turbulent channel flows up to the maximum drag reduction (MDR) limit have been performed using a fully spectral method in conjunction with kinetic theory based elastic dumbbell models for the description of polymer chain dynamics. It is shown that to obtain significant levels of drag reduction large polymer chain extensibility and high Weissenberg numbers are required. In addition, it is demonstrated that to capture flow dynamics in the high drag reduction (HDR) and MDR regimes, very long computational domain lengths of the order of 10 4 wall units are required. The simulation results in turn have been used to develop a scaling that describes the interplay between rheological parameters (i.e., maximum chain extension and relaxation time) and the extent of drag reduction as a function of Reynolds number. In addition, turbulence statistics are analyzed and correlations between the polymer body force and velocity fluctuations have been developed with particular emphasis on the HDR and MDR regimes. These observations have been used to decipher the effect of polymer additives on the dynamics of the flow and drag reduction.

Drag reduction of a bluff body using adaptive control methods

Abstract: A classical actuator is used to control the drag exerted on a bluff body at large Reynolds number (Re=20000). The geometry is similar to a backward-facing step whose separation point is modified using a rotating cylinder at the edge. The slow fluctuations of the total drag are directly measured by means of strain gauges. As shown by visualizations, the actuator delays the separation point. The size of the low-pressure region behind the body is decreased and the drag reduced. It is found that the faster the rotation of the cylinder, the lower the drag. In a first study, the goal of the control is for the system to reach a drag consign predetermined by the experimentalist. The control loop is closed with a proportional integral correction. This adaptive method is shown to be efficient and robust in spite of the large fluctuations of the drag. In the second method, the system finds itself its optimal set point. It is defined as the lowest cost of global energy consumption of the system (drag reduction versus energy used by the actuator). For this purpose, an extremum seeking control method is applied in order to deal with the large background noise due to turbulence. It consists in a synchronous detection of the response measured in the drag measurements to a modulation of the actuator. The phase shift and amplitude of the modulation estimate the local gradient of the total energy function. With this gradient estimation, the system goes to the minimum of global power consumption by itself. The system is found to be also robust and reacts successfully to changes of the external mean flow. This experiment attests to the real efficiency of local active control in reducing autonomously the global energy consumption of a system under turbulent flow.

Ground Effect Aerodynamics of Race Cars

Abstract: We review the progress made during the last thirty years on ground effect aerodynamics associated with race cars, in particular open wheel race cars. Ground effect aerodynamics of race cars is concerned with generating downforce, principally via low pressure on the surfaces nearest to the ground. The “ground effected” parts of an open wheeled car's aerodynamics are the most aerodynamically efficient and contribute less drag than that associated with, for example, an upper rear wing. Whilst drag reduction is an important part of the research, downforce generation plays a greater role in lap time reduction. Aerodynamics plays a vital role in determining speed and acceleration (including longitudinal acceleration but principally cornering acceleration), thus performance. Attention is paid to wings and diffusers in ground effect and wheel aerodynamics. For the wings and diffusers in ground effect, major physical features are identified and force regimes classified, including the phenomena of downforce enhancement, maximum downforce and downforce reduction. In particular the role played by force enhancement edge vortices is demonstrated. Apart from model tests, advances and problems in numerical modeling of ground effect aerodynamics are also reviewed and discussed.

Induced Drag Reduction Using Aeroelastic Tailoring with Adaptive Control Surfaces

Abstract: This paper describes the use of full-span deforming control surfaces (including controlled chordwise cambering of the wing) to provide effective subsonic induced drag control with precise control of the spanwise lift distribution. Examples of these proposed controllers are smart, adaptive actuators for advanced unmanned air vehicle concepts. Reshaping the wing spanwise lift distribution with aeroelastic tailoring concepts is shown to reduce induced drag at high airspeeds. Active controllers such as conventional ailerons or leading-edge devices also reduce induced drag if they have a tailored spanwise deflection pattern; the required deflections of these surfaces depend on wing deformation and can be so large that they are not practical. Combining wing aeroelastic stiffness tailoring with active control surface design to create a control-friendly structure reduces induced drag and requires only small controller inputs. An exact solution for the actuator deflections to generate an elliptical lift distribution for the aeroelastic wing, for minimum induced drag, is discussed. A formal optimization problem is posed for cases in which multiple surfaces are used to control drag. This controller optimization solution is complicated because aeroelastic phenomena, such as control reversal, limit the effectiveness of some actuators at high speed.

Minimizing induced drag with wing twist, computational-fluid-dynamics 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 computational-fluid-dynamics (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.

Peak-Seeking Control for Drag Reduction in Formation Flight

Abstract: Formation flight is a known method of improving the overall aerodynamic efficiency of a pair of aircraft. In particular, one craft flying in the correct position in the vortex wake of another can realize substantial reductions in drag, with the amount of the reduction dependent on the relative positions of the two craft. This paper looks at such a pair, with one craft flying behind and to the side of the lead plane. The precise position of the second craft relative to the first to maximize the drag reduction is to be determined online, leading to a peak-seeking control problem. A new method of speak-seeking control, using a Kalman filter to estimate the characteristics of the drag reduction, is derived and discussed. A simple model of the two-plane formation using horseshoe vortices is defined, and the peakseeking controller is applied to this model. The method is demonstrated in simulation using this simplified model. S an airplane flies, it causes an upwash ahead of the wing and leaves a wake behind. This wake is characterized by the downwash behind the wing and by an accompanying upwash in the area on either side of the downwash region. By flying in the area of upwash, a second aircraft can gain a substantial efficiency boost because of the reduction in induced drag it will experience. This leads to the well-known fact that two aircraft flying in an appropriate formation can achieve overall efficiency much greater than were they flying separately. 1 This effect is analyzed using inviscid aerodynamic assumptions and lifting-line theory in Ref. 2, where it is noted that the effects were considered by Munk as early as 1919. The theory was put to test in actual aircraft by Hummel, 3 who established a fifteen per cent reduction on the second of a pair of civilian aircraft. Because of the gains in efficiency, formation flight has been investigated as a way of increasing the range and duration of autonomous aerial vehicles. In Refs. 4 and 5, formations of several aircraft are considered, with the object of creating a solar-powered formation that could cruise at high altitude for arbitrarily long times. In Ref. 4, decentralized controllers are derived for a formation of five highaspect-ratio craft and are shown to be capable of maintaining a prescribed formation despite the nonlinear, destabilizing moments induced on each plane by the aircraft ahead of it in the formation. The formation maintenance problem for a pair of F-16 class aircraft is considered in Ref. 6, though that paper relegates the rolling moments on the trailing craft to an inner-loop controller and considers only the lift and side force in designing an autopilot for the trailing plane. In this paper, only a pair of aircraft is considered. The two craft can be thought of as a leader and a follower. The leader flies straight

Drag Reduction on Gurney Flaps by Three-Dimensional Modifications

Abstract: Miniflaps at the trailing edge of airfoils, that is, Gurney flaps, change the Kutta condition and thereby produce higher lift. Unfortunately, because of the flow separation downstream of such trailing edges, the drag also increases. Investigations are described with the aim to stabilize the wake flow to achieve drag reduction. When hot-wire anemometry is used, a tonal component in the spectrum of the velocity fluctuations downstream of the Gurney flap is shown. This points to the existence of a von Karman vortex street. Modifications of the Gurney flap can reduce this flow instability, which results in a drag reduction. Trailing-edge modifications, such as slits or holes in Gurney flaps and vortex generators, were tested in experiments. The experiments were carried out using straight wings and a swept wing at a Re = 1 × 10 6 At lower angles of attack of the airfoils with geometrical modifications a drag reduction was observed. This drag reduction was determined through force measurements. The flowfield behind the Gurney flaps was also investigated numerically, using methods based on Reynolds averaged Navier-Stokes and detached eddy simulation

Hydrofoil Drag Reduction by Partial Cavitation

Abstract: Partial cavitation reduces hydrofoil friction, but a drag penalty associated with unsteadycavity dynamics usually occurs. With the aid of inviscid theory a design procedure isdeveloped to suppress cavity oscillations. It is demonstrated that it is possible to suppressthese oscillations in some range of lift coefficient and cavitation number. A candidatehydrofoil, denoted as OK-2003, was designed by modification of the suction side of aconventional NACA-0015 hydrofoil to provide stable drag reduction by partial cavitation.Validation of the design concept with water tunnel experiments has shown that the partialcavitation on the suction side of the hydrofoil OK-2003 does lead to drag reduction anda significant increase in the lift to drag ratio within a certain range of cavitation numberand within a three-degree range of angle of attack. Within this operating regime, fluc-tuations of lift and drag decrease down to levels inherent to cavitation-free flow. Thefavorable characteristics of the OK-2003 are compared with the characteristics of theNACA-0015 under cavitating conditions.

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

Abstract: Skin-friction drag reduction in turbulent boundary layer flow of inhomogeneous polymer solutions is investigated using direct numerical simulations. A continuum constitutive model (FENE-P) accounting for the effects of polymer microstructure and concentration is used to describe the effect of viscoelasticity. The evolution of wall friction along the streamwise direction is a function of the dynamics of the polymer distribution in the boundary layer. It is observed that polymer transport decreases drag reduction downstream compared to the homogeneous case. The fluctuations of polymer concentration are anti-correlated with those of the streamwise velocity. Concentration is largest in the low-speed streaks. The physical process creating this effect is primarily that of dilution of the high-speed streaks, where due to the local turbulence structure the dispersion of polymer is strongest. Thus, the polymer-induced drag reduction phenomenon is sustained primarily in the vicinity of the low-speed streaks where the injected polymer additive is most effective.

Comparative Scaling of Flapping- and Fixed-Wing Flyers

Abstract: The scaling laws in the geometry, velocity, and power for flapping flyers, for example, birds, and fixed-wing aircraft are discussed from a comparative point of view, and the aerodynamic implications of the scaling, particularly on the lift-to-drag ratio, flapping span efficiency, induced drag, parasite drag, and propulsive efficiency are explored. The results shed insights into flapping flight and provide a useful guideline for the preliminary design of a flapping-flight vehicle.

Optimal scheduling of control surfaces on flexible wings to reduce induced drag

Abstract: An aircraft wing structure is a complex assemblage of interconnected elements composed of both metallic and composite materials. To capture the physics of the structural response at an appropriate level of accuracy the finite element method is employed to model the aircraft structure. The external aerodynamic loads distribution in both the chord and span direction are predicted using the USSAERO paneling method. The Automated StRuctural Optimization System[1] (ASTROS) is used for modeling the structure, the steady aerodynamic loads, and carrying out the trim analysis of a free flying flexible air vehicle. Two wing models are selected for this investigation. The first model, referred to as the Goland Wing[2], has a “beam-rod” structural model. The second model considered is a built-up model typical of a fighter type aircraft[3] and is shown in Figure 7 with the corresponding aerodynamic panel model. Both models have 20 discrete control surfaces along the trailing edge of each aerodynamic model. The aerodynamic effects of gaps between each of the discrete surfaces are ignored to simulate a “so-called” conformal control surface[4]. R.T. Jones[5] has demonstrated that wings having an elliptical spanwise lift distribution ensures minimum induced drag. Therefore, in the present study, the control surfaces are scheduled to obtain an elliptical spanwise load distribution. It is worth noting that the methodology developed in this work is general and can be used to obtain any desired distribution, not just elliptical. In addition, as demonstrated by Munk[7], induced drag is independent of the distribution of lift in the chordwise direction. For the current study induced drag calculations are carried out considering the “Trefftz-plane”[6] downstream from the trailing edge. The wing is held at a trimmed level flight condition using the angle of attack while the control surfaces are used only to obtain the desired elliptical spanwise pressure distribution.

Fuel efficient dynamic air dam system

Abstract: Active, aerodynamic controller that describes a method for dynamically controlling airflow using computer controlled movable air dams and airfoils on motor vehicles. It is well known that motor vehicles generally have a great deal of aerodynamic friction also known as drag. Fuel efficiency is greatly affected by a vehicle's aerodynamic drag. Aerodynamic drag is caused by both induced drag and parasitic drag. Parasite drag is somewhat fixed by the overall design and shape of a vehicle. Parasite drag is caused primarily by the laminar flow of air over the smooth surfaces of the vehicle's hood, roof, windows, side mirrors and door panels. Induced drag is much more variable and is primarily created by the differential pressure effects of air flowing over, under and around a vehicle, as well as the relative airflow caused by both ground effect and atmospheric air density and wind. This invention serves to actively minimize the effects of induced drag thus reducing the amount of fuel used by vehicles fitted with this invention.

Application of theoretical principles to swimsuit drag reduction

Abstract: This study investigated the basic fluid mechanics associated with the hydrodynamic drag of a human. The components of drag (frictionD SF, pressureD P and waveD W) on a human swimmer were analysed by applying classical fluid dynamic fundamentals. General methods of reducing drag were considered and the most probable method identified, applied and tested on swimsuit hydrodynamic drag. This study employed turbulators, either one (upper back) or three (across the upper back, the chest and across the buttocks), that were compared to an identical full body suit with no turbulators. Male and female elite competitive swimmers (n = 7 each) were towed in an annular pool to determine passive drag at speeds from 0.4 to 2.2 m s−1. The total drag was reduced by 11–12% by one turbulator and 13–16% by three turbulators. The total drag was decomposed intoD SF, DP andD W to determine the mechanisms responsible for the reduced total drag by the turbulators. The presence of the turbulators did not significantly increase friction or wave drag; however, flow was attached to the body as there was a significant reduction in pressure drag (19–41%), with the greatest reduction being for three turbulators (chest, back, buttocks). This study demonstrated the importance of pressure drag in determining total drag at high human swimming speeds, and that drag reducing technology can significantly reduce it, in this case by appropriately sized and placed turbulators.

Induced Drag Minimization: A Variational Approach Using the Acceleration Potential

Abstract: A method of predicting the minimum induced drag conditions in conventional or innovative lifting systems is presented. The method is based on lifting-line theories and the small perturbation acceleration potential. Assuming linearity and rigid wake aligned with the freestream, the optimal conditions are formulated using the Euler‐Lagrange integral equation subject to the conditions of fixed total lifting force and wing span. The Lagrange multiplier method is applied, and equations for the design optimum are obtained and solved directly. Particular attention is paid to the Hadamard finite-part integrals involved in the solution process. Munk’s drag theorems are also applied in order to verify the quality of the solutions. In this paper, where the theoretical/computational foundation is laid for the induced drag minimization of general lifting-line configurations, the case of the biplane under optimal conditions is extensively analyzed. It is demonstrated that, under optimal conditions, the two wings (which have the same wing span) have the same circulation distribution. Cases of finite, infinite, and infinitesimal distances between the wings are analyzed as well. It is shown that the optimal distribution is, in general, not elliptical. The proposed theoretical approach is general, and it offers a valuable tool for direct prediction of minimum induced drag in both planar and nonplanar lifting systems. Results obtained by the proposed approach shed light on some of the mathematical issues involved, and they can be used for verifying results obtained by numerical math-programming-based optimization.

Drag reducing system

Abstract: Systems and methods for reducing drag in vehicles, typically trucks (20), such as tractor- trailers, have moveable moving drag reducing apparatus (22). This movable drag reducing apparatus is for movement into and out of various positions, in accordance with the location of the vehicle with respect to its distance (D) from an obstacle (26).

Aerodynamic and Aeroacoustic Three-Dimensional Design for a "Silent" Aircraft

Abstract: This paper presents a three-dimensional airframe design methodology for low noise emission and high fuel efficiency, based on a blended-wing-body type aircraft. The design methodology uses a combination of high and low fidelity tools to assess the performance and acoustics of the aircraft. The goal set by the Silent ** Aircraft Initiative is a viable, commercial aircraft design with noise levels imperceptible outside the airport perimeter in a well-populated urban environment. To be viable, the aircraft requires a fuel burn comparable to modern conventional aircraft. The detailed airframe design incorporates leading edge camber of the centerbody to provide pitch trim without penalties in induced drag, wave drag, and trim drag. A low noise approach is achieved with reduced approach velocity and increased distance between the airframe and the observer. This slow and steep approach profile is enabled through a combination of thrust vectoring, quiet drag generation, and leading edge high-lift devices. The blended-wing-body type airframe design presented in this paper is both quiet with an OASPL of approximately 65 dBA and highly efficient with a cruise ML/D of 18.5. The paper concludes with ideas to further reduce noise to meet the aggressive SAI goal with minimal cruise performance penalty.

Aerodynamic Comparison of Hyper-Elliptic Cambered Span (HECS) Wings with Conventional Configurations

Abstract: An experimental study was conducted to examine the aerodynamic and flow field characteristics of hyper-elliptic cambered span (HECS) wings and compare results with more conventional configurations used for induced drag reduction. Previous preliminary studies, indicating improved L/D characteristics when compared to an elliptical planform prompted this more detailed experimental investigation. Balance data were acquired on a series of swept and un-swept HECS wings, a baseline elliptic planform, two winglet designs and a raked tip configuration. Seven-hole probe wake surveys were also conducted downstream of a number of the configurations. Wind tunnel results indicated aerodynamic performance levels of all but one of the HECS wings exceeded that of the other configurations. The flow field data surveys indicate the HECS configurations displaced the tip vortex farther outboard of the wing than the Baseline configuration. Minimum drag was observed on the raked tip configuration and it was noted that the winglet wake lacked the cohesive vortex structure present in the wakes of the other configurations.

Low Speed Design and Analysis of Wing/Winglet Combinations Including Viscous Effects

Abstract: The design and analysis of winglets is presented from an aerodynamic point of view. The winglets considered are small fences placed upward at the tip of the wing to improve the wing efficiency by decreasing the induced drag for a given lift. Viscous corrections are accounted for by using a two-dimensional viscous polar, with the assumption that at design conditions the flow is fully attached. The comparison of the inviscid and viscous designs indicates that viscosity has little effect on the optimum geometry. In the presence of viscous drag, the winglets produce a small thrust; due to viscosity, the overall efficiency gain is decreased. The effect of a small yaw angle on a wing equipped with such optimal winglets indicates that, even in the presence of viscous effects, they provide weathercock stability.

Method of Reducing Drag and Increasing Lift Due to Flow of a Fluid Over Solid Objects

Abstract: A method for reducing drag, increasing lift and heat transfer using a de-turbulating device is disclosed, with the preferred form of the deturbulator being a flexible composite sheet. The flexible composite sheet comprising a membrane, a substrate coupled to the membrane, and a plurality of ridges coupled between the membrane and the substrate, wherein a vibratory motion is induced from the flow to at least one segment of a membrane spanning a distances, wherein the vibratory motion is reflected from at least one segment of the membrane to the flow, and; wherein a reduction in fluctuations is caused in the flow pressure gradient and freestream velocity U at all frequencies except around f, where f » U/s. hi one embodiment, the flexible composite sheet can be wrapped around a blunt leading edge of a plate facing an incoming flow of fluid, hi another embodiment, the flexible composite sheet can also be wrapped around one or more regions of an aerodynamic surface where a flow pressure gradient changes from favorable to adverse, hi another embodiment, the flexible composite sheet is replaced with a plurality of plates coupled to a substrate, wherein the plurality of plates has edges that interact with a fluid flow similar to a compliant surface. A method of adding a system of small viscous sublayer scale (around 30-80 micron height) backward and /or forward facing steps on the surface of an airfoil or other 2-D or 3-D streamlined aerodynamic body is disclosed, where the backward facing step is in a favorable pressure gradient and forward facing step is in an adverse pressure gradient, so as to speed up the freestream flow over the front portion of the airfoil or body and reduce skin friction drag by creating a marginally separated thin (0.1 to 10 microns) slip layer next to the wall behind the backward facing step and extending a significant distance behind said step. This method reduces the drag and increases lift if the body is a wing. Also the same method can be applied to a bluff body, such as an automobile to reduce flow separation induced drag by stabilizing the wake flow and making it appear to the flow as a solid streamiling extension of the original body. The gas mileage of a vehicle improves when treated in this manner.

Drag of Spheroid-Cone Shaped Airship

Abstract: Drag coefficients of streamlined bodies and complete airships are compared to confirm some general trends. Data obtained from flight testing an electrically powered, helium-filled, dirigible balloon with a spheroid-cone hull form are analyzed. Wind-tunnel tests indicate that placing a cone behind a sphere reduces its drag coefficient by about 50%, but flight-test data suggest the drag coefficient of the spheroid-cone airship is relatively high. The influence of atmospheric turbulence and nonsteady flow effects are discussed.

Active Control of Flow Separation on a Swept Constant Chord Half Model in a High-Lift Configuration

Abstract: The purpose of this manuscript is to address the impact of active separation control by means of pulsed blowing in a three-dimensional and complex flow environment. Experimental investigations are undertaken in order to enhance the performance of a three-element high-lift configuration by preventing the flow separation on the single-slotted flap. The configuration includes some less investigated aspects as the wing has a constant sweep angle of 30 and a finite wing span. An eort is made to implement an actuator system inside the small flap in order to excite the flow locally with the desired frequency and amplitude. The results show that, despite the strong three-dimensionality due to sweep and finite wing span, periodic excitation is able to delay separation on the flap or to reattach an already separated flow. Lift is improved by 10% to 12% over a wide range of angle of attack and flap settings. The influence on drag by periodic excitation seems to be ambiguous because in some cases the higher induced drag due to the attached flow compensates the drag benefit resulting from the elimination of the recirculation region. However, preliminary tests show that high amplitude forcing in the wing tip area is able to reduce the drag by as much as 10%.

Active Multiple Winglets for Improved Unmanned-Aerial-Vehicle Performance

Abstract: The addition of a winglet to a flight vehicle is known to enhance cruise performance. The addition of multiple, active winglets to an existing unmanned aerial vehicle (UAV) is studied to determine the potential of these devices to augment both cruise and maneuvering performance. Passive and active multiple winglets are shown to increase range and endurance, providing the potential for increased payload. Active multiple winglets are shown to be a viable replacement for ailerons and to provide gust alleviation for improved handling qualities and sensor performance. Two methods of predicting winglet performance enhancements are applied and compared to the U.S. Marine Corps Dragon Eye UAV configuration. Nomenclature az = normal acceleration C = specific fuel consumption CDi = induced drag coefficient CL = lift coefficient D = drag E = endurance e = efficiency factor g = gust K = induced drag constant K1, K2 = proportionality constant L = lift R = range S = wing area W = weight � = propeller efficiency

The Design of Winglets for Low-Speed Aircraft

Abstract: Although theoretical tools for the design of winglets for low-speed aircraft were initially of limited value, simple methods were used to design winglets that gradually became accepted as benefiting overall aircraft performance. As understanding was gained, improved methods were developed, which ultimately resulted a number of successful applications of winglets. The current approach incorporates a detailed component drag buildup that interpolates airfoil drag and moment data across operational lift-coefficient, Reynolds-number, and flap-deflection ranges. Induced drag is initially predicted using a relatively fast multiple 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 turning flight, yielding predicted performance that is in good agreement with flight-test results. These methods have been successfully applied to the design of winglets to improve the cross-country soaring performance of both span-limited and span-unlimited, high-performance sailplanes, as well as to improve various mission capabilities for several different categories of powered aircraft.

Flexible cross flow vortex trap device for reducing the aerodynamic drag of ground vehicles

Abstract: An improved device for the reduction of aerodynamic drag and for improved performance of multiple component vehicles by reducing the pressure on the front face of the trailing vehicle or vehicle component by controlling the flow in the gap between the leading vehicle component and the trailing vehicle component. An improved device for generating a reduction in the drag force on a bluff face object moving through air. The device consist of the application of a plurality of forward extending surfaces that are positioned adjacent to one another on the forward facing surface of a bluff face object and are aligned parallel to the object center line and perpendicular to the local flow direction. The reduction in drag force results from the summation of a plurality of local reductions in drag force generated by the interaction of vortex structures emanating from the leading edges of the plurality of forward extending surfaces with the forward facing surface of a blunt face object. The objects and advantages also extend to other applications in which an object or vehicle is moving through either a gas or fluid.

An airfoil for a helicoptor rotor blade

Abstract: An airfoil family for a helicopter rotor blade, designated SC362XX. SC362XX essentially removes the large lower surface suction peak associated with 'drag creep' at moderate lift coefficients while reducing the peak Mach number and shock strength at high lift/Mach number conditions. Another optional airfoil family for use at inboard regions of the helicopter rotor, which is designated SC3252XX airfoil family, is a relatively thicker airfoil section that includes a significant increase in thickness forward of the 30% x/c location to provide a relatively thick and rigid inboard section. The lift coefficient at which the drag divergence Mach number was optimized is the same in both families thereby readily providing application to a single rotor blade.

Experimental analysis of the aerodynamic characteristics adaptive of multi-winglets:

Abstract: The aim of this research is to study the potential use of adaptive multi-winglets for the reduction of induced drag through variations of winglet cant angles. Different studies have shown that the flow around and over the wing tip can be redirected using small aerodynamic surfaces, thereby reducing the induced drag. The model tested is composed of a rectangular wing using an NACA 653-018 profile with three winglets called ‘tip-sails,’ which are small wings without sweep along the 25 per cent chord line. The tests were made at a Reynolds number of 350 000. The results are analysed in terms of lift and drag. Results show that it is possible to find the best configuration of the three winglets to obtain the optimum aerodynamic performance for each flow regime in climb and cruise.

Drag reduction for D-shape and I-shape cylinders : (Aerodynamic Mechanism of Reduction of Drag)

Abstract: The aerodynamic mechanisms for the reduction of drag for a D-shape cylinder, wherein a front face of a circular cylinder is cut off, and an I-shape cylinder, wherein front and rear faces are cut off, are investigated. For the D-shape and I-shape cylinders with a cutting angle of 50-53° and for Reynolds number Re > 2.3 x 10 4 , the shear layer separated from the front edge reattaches on the circular arc of the cylinder, and a transition in the boundary layer as well as turbulent separation occur. As a result, the wake width decreases and the vortex formation region goes downstream. The Strouhal number increases beyond 0.28, the base pressure coefficient rises, and the drag coefficient of the cylinders decreases to half the value for a circular cylinder. The conditions of the above phenomena are clarified.