Showing papers on "Lift-induced drag published in 2012"

A numerical study of microparticle acoustophoresis driven by acoustic radiation forces and streaming-induced drag forces

Abstract: We present a numerical study of the transient acoustophoretic motion of microparticles suspended in a liquid-filled microchannel and driven by the acoustic forces arising from an imposed standing ultrasound wave: the acoustic radiation force from the scattering of sound waves on the particles and the Stokes drag force from the induced acoustic streaming flow. These forces are calculated numerically in two steps. First, the thermoacoustic equations are solved to first order in the imposed ultrasound field taking into account the micrometer-thin but crucial thermoviscous boundary layer near the rigid walls. Second, the products of the resulting first-order fields are used as source terms in the time-averaged second-order equations, from which the net acoustic forces acting on the particles are determined. The resulting acoustophoretic particle velocities are quantified for experimentally relevant parameters using a numerical particle-tracking scheme. The model shows the transition in the acoustophoretic particle motion from being dominated by streaming-induced drag to being dominated by radiation forces as a function of particle size, channel geometry, and material properties.

Aeroelastic Modeling of Elastically Shaped Aircraft Concept via Wing Shaping Control for Drag Reduction

Abstract: Lightweight aircraft design has received a considerable attention in recent years as a means for improving cruise efficiency. Reducing aircraft weight results in lower lift requirements which directly translate into lower drag, hence reduced engine thrust requirements during cruise. The use of lightweight materials such as advanced composite materials has been adopted by airframe manufacturers in current and future aircraft. Modern lightweight materials can provide less structural rigidity while maintaining load-carrying capacity. As structural flexibility increases, aeroelastic interactions with aerodynamic forces and moments become an increasingly important consideration in aircraft design and aerodynamic performance. Furthermore, aeroelastic interactions with flight dynamics can result in issues with vehicle stability and control. Abstract This paper describes a recent aeroelastic modeling effort for an elastically shaped aircraft concept (ESAC). The aircraft model is based on the rigid-body generic transport model (GTM) originally developed at NASA Langley Research Center. The ESAC distinguishes itself from the GTM in that it is equipped with highly flexible wing structures as a weight reduction design feature. More significantly, the wings are outfitted with a novel control effector concept called variable camber continuous trailing edge (VCCTE) flap system for active control of wing aeroelastic deflections to optimize the local angle of attack of wing sections for improved aerodynamic efficiency through cruise drag reduction and lift enhancement during take-off and landing. The VCCTE flap is a multi-functional and aerodynamically efficient device capable of achieving high lift-to-drag ratios. The flap system is comprised of three chordwise segments that form the variable camber feature of the flap and multiple spanwise segments that form a piecewise continuous trailing edge. By configuring the flap camber and trailing edge shape, drag reduction could be achieved. Moreover, some parts of the flap system can be made to have a high frequency response for roll control, gust load alleviation, and aeroservoelastic (ASE) modal suppression control. Abstract The aeroelastic model of the ESAC is based on one-dimensional structural dynamic theory that captures the aeroelastic deformation of a wing structure in a combined motion that involves flapwise bending, chordwise bending, and torsion. The model includes the effect of aircraft propulsion due to wing flexibility which causes the propulsive forces and moments to couple with the wing elastic motion. Engine mass is also accounted in the model. A fuel management model is developed to describe the wing mass change due to fuel usage in the main tank and wing tanks during cruise. Abstract The model computes both static and dynamic responses of the wing structures. The static aeroelastic deflections are used to estimate the effect of wing flexibility on induced drag and the potential drag reduction by the VCCTE flap system. A flutter analysis is conducted to estimate the flutter speed boundary. Gust load alleviation via adaptive control has been recently investigated to address flexibility of aircraft structures. A multi-objective flight control approach is presented for drag reduction control. The approach is based on an optimal control framework using a multi-objective cost function. Future studies will demonstrate the potential benefits of the approach.

Aerodynamic drag reducing apparatus

Abstract: An aerodynamic drag reducing apparatus for use with vehicles having downstream surfaces that are not streamlined. The apparatus includes folding panels that extend rearward for use in a drag reducing configuration and collapse for use in a space saving configuration.

Effects of Sideslip on the Aerodynamics of Low-Aspect-Ratio Low-Reynolds-Number Wings

Abstract: The growing interest in micro aerial vehicles has brought attention to the need for an improved understanding of the aerodynamics of low-aspect-ratio wings at lowReynolds numbers. In this study, flat plate wings with rectangular and tapered planforms were fabricated with aspect ratios of 0.75, 1, 1.5, and 3, and the aerodynamic loading was measured at Reynolds numbers between 5 10 and 1 10. Surface tuft visualization was used to observe the interactions between the tip vortices and the leading-edge vortex. The tests were initially conducted at a sideslip angle of 0 and were then repeated for 10, 20, and 35 with and without winglets. Measurements made with a sixcomponent force balance showed that a decrease in aspect ratio caused an increase in stall and CLmax due to the nonlinear lift induced by the interacting flow on the upper wing surface. In addition, the detachment of tip vortices after stall leads to a sudden decrease in drag coefficient as the magnitude of the induced drag drops significantly. At increasing sideslip angles, the effects of the crossflow still contribute to an increase in lift but significantly reduce the pitching moment about the quarter-chord, thus decreasing the wing’s ability to recover from angle-of-attack perturbations. These results show that, while the effects of tip vortices and the leading-edge vortex complicate the flowfield around a low-aspect-ratio wing, particularly at increased sideslip angles, their impact tends to improve the aerodynamic performance.

Span Morphing: A Conceptual Design Study

Abstract: The use of variable wing span to enhance flight performance and control authority of high endurance, medium altitude UAV is investigated. Asymmetric span extension is used to replace ailerons and maintain roll control over the entire flight envelope of the vehicle. The span extension required to generate a rolling moment equal to that produced by ailerons is estimated at four flight points. The study is performed using Tornado Vortex Lattice Method (VLM). 36% increase in wing semi-span is required to maintain roll authority. On the other hand, symmetric span morphing is used to reduce induced drag and enhance the endurance capability of the vehicle. 20% symmetric span morphing was found to be the optimum to reduce the overall drag of the wing by 10% at the start of cruise and 2.5% at the end of cruise. The morphing wing structure is to be designed using Zero Poisson’s ratio Accordion honeycomb with elastomeric skins. The geometry of the honeycomb will be optimised using the Genetic Algorithm (GA) optimiser to minimise the structural weight of the wing while meeting various design constraints.

Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil

Abstract: A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 × 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12° to almost 20°, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60°. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30° and 45°. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8° and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions.

Dynamics of a microchain of superparamagnetic beads in an oscillating field

Abstract: The dynamics of microchains containing superparamagnetic particles in an oscillating field are studied experimentally. The chains are first formed by a static directional field, and then manipulated by an additional dynamical perpendicular field. The present methodology represents a simple reversible chaining process, whose particles can be re-dispersed after removal of the field. The motion of superparamagnetic chains is dominated by magnetic torque and induced hydrodynamic drag. The effects of key parameters, such as field strengths and the lengths of particle chains, are thoroughly analyzed. Distinct behaviors, from rigid body oscillations and bending distortions to rupture failures, are observed by increasing the amplitudes of oscillating fields or chains’ lengths. Because of lower induced drag, a shorter chain follows the field trajectory closely and oscillates more synchronically with the external field. On the other hand, the influences of field strengths are not consistent. Even the overall oscillating phase trajectory in a stronger external field deviates less significantly from the corresponding field trajectory, a stronger dynamical component of the external field results in larger phase angle lags at certain points. The experimental results confirm the criterion of ruptures can be effectively determined by the value of (N*Mn1/2), where Mn is the Mason number defined as the ratio of induced drag to dipolar attraction, and N represents the number of particles contained in a chain.

Wingtip vortex control via the use of a reverse half-delta wing

Abstract: The effect of a 65° sweep reverse half-delta wing (RHDW), mounted at the squared tip of a rectangular NACA 0012 wing, on the tip vortex was investigated experimentally at Re = 2.45 × 105. The RHDW was found to produce a weaker tip vortex with a lower vorticity level and, more importantly, a reduced lift-induced drag compared to the baseline wing. In addition to the lift increment, the RHDW also produced a large separated wake flow and subsequently an increased profile drag. The reduction in lift-induced drag, however, outperformed the increase in profile drag and resulted in a virtually unchanged total drag in comparison with the baseline wing. Physical mechanisms responsible for the RHDW-induced appealing aerodynamics and vortex flow modifications were discussed.

Supersonic Skin-Friction Drag with Tangential Wall Slot Fuel Injection and Combustion

Abstract: The large viscous drag of hypersonic vehicles is a major obstacle to the successful development of vehicles for prolonged atmospheric travel at high Mach numbers. On such vehicles, this skin-friction drag can be of similar magnitude to that of the inviscid drag on the body. To improve the vehicle’s performance, the net thrust of the propulsion system has to be enhanced, either by increasing the thrust force or by reducing the vehicle drag. Here, reductions in viscous drag can offer a large margin for improvement of the net thrust level. One of the methods for the reduction of supersonic skin friction is the injection of low-density gas into the boundary layer (film cooling). In a recent development, film cooling by slot injection of hydrogen was combined with its combustion within the boundary layer. Analysis and experiments indicated substantial reductions of supersonic skin-friction drag. This paper provides further evidence for substantial skin-friction reductions by presenting shock-tunnel data of direct drag measurements in a circular supersonic combustion chamber with and without pressure gradients and with and without combustion of hydrogen in the boundary layer. The measurements are compared with theories, and the influence of entropy layers and combustor size is investigated. Measurements show a reduction of viscous drag of up to 77%.

A new Approach to Aerodynamic Performance of Aircraft under Turbulent Atmospheric Conditions

Abstract: In the present study the influence of atmospheric turbulence on aircraft performance has been investigated and a relation between flight physics and meteorology has been established. Special attention was paid on aircraft with natural laminar flow airfoils because they exhibit an additional possibility of performance loss due to increased drag caused by a premature laminar-turbulent transition. A theoretical analysis was performed and the aerodynamic problem was extracted from the performance problem. A new wing glove for the G109b measurement aircraft as well as measurement equipment capable of detecting unsteady aerodynamic effects were developed. In-flight measurements for the validation of performance loss theories were carried out resulting in a new approach to aircraft performance under turbulent atmospheric conditions. Generally, a loss of flight performance can be the result of decreased lift, increased drag or a combination of both. The aerodynamic state and therefore the possible influencing mechanisms of atmospheric turbulence vary with the flight condition. Based on aircraft performance considerations, three principal flight conditions were determined for an in-depth study of the aerodynamic state related to these flight conditions. The flight conditions are slow flight, best glide and cruise flight. A new wing glove with favorable characteristics for aerodynamic in-flight experiments, retaining the flying qualities of the aircraft besides the asymmetric configuration, has been designed. A survey of the base flow on the glove in non-turbulent conditions by means of flight tests, wind tunnel tests and numerical simulations was conducted prior to the investigations under turbulent conditions. The results were essential as baseline data and showed that the numerous design requirements for the new wing glove were fulfilled. The flight test results show that the assumption of steady inflow conditions is incorrect for flight in atmospheric turbulence. An elevated level of micro-scale turbulence in the atmosphere is related to increased angle of attack variations. Therefore, unsteady changes in the airfoil pressure distribution are prevalent when an elevated turbulence level is encountered. Turbulence levels of 0.5% and more, which lead to different transition scenarios according to the results from flat plate experiments in transition research, do not occur in only light atmospheric turbulence, which is in turn the prerequisite for almost steady pressure distributions. The unsteady lift variations related to the angle of attack variations due to gusts are well predicted by unsteady thin-airfoil theory. A quasi-stationary approach does not cover the entire unsteady lift effects but in the case of laminar airfoils it predicts when the laminar drag bucket is left and airfoil drag increases. Especially in slow flight very close to the upper limit of the laminar drag bucket, angle of attack variations lead to increased airfoil drag. Flying at a lower angle of attack simply solves this problem. Only a slight increase in velocity is required to lower that angle of attack sufficiently.

Design of Parametric Winglets and Wing tip devices : A Conceptual Design Approach

Abstract: Winglets being a small structure play an important role in reducing the induced drag in aircraft. Many types of winglets have been designed and their significance in reducing the drag is published. ...

Methods of Reducing Vehicle Aerodynamic Drag

Abstract: A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.

Optimum Transverse Span Loading for Subsonic Transport Category Aircraft

Abstract: This study considers the overall system impact of the design transverse aerodynamic load distribution on future subsonic, transport category aircraft. The fundamental question revisited here concerns wing design ground rules. Should the wing be designed to favor an aerodynamically optimal, “elliptical” transverse span load that minimizes induced drag? Or, should the wing be tailored to have a reduced root bending moment in order to save structural weight at some expense of increased drag? The problem is examined at three levels of technical scrutiny: from a qualitative, rational basis perspective; from a quantitative, intermediate-fidelity parametric performance perspective; and from the results of a quantitative, coupled multidisciplinary optimization trade. The quantitative tradesindicatethattailoringofthedesigntransverseloaddistributiontofavorareducedwingrootbendingmoment resultsinsomestructuralweightsavings,butattheexpenseofhigherdrag,increasedfuelconsumption,andreduced mission performance. These trades substantiate a different rational basis argument: a balancing test that will typically recommend the aerodynamically optimal design for all but the shortest-range aircraft.

Variable camber continuous aerodynamic control surfaces and methods for active wing shaping control

Abstract: An aerodynamic control apparatus for an air vehicle improves various aerodynamic performance metrics by employing multiple spanwise flap segments that jointly form a continuous or a piecewise continuous trailing edge to minimize drag induced by lift or vortices. At least one of the multiple spanwise flap segments includes a variable camber flap subsystem having multiple chordwise flap segments that may be independently actuated. Some embodiments also employ a continuous leading edge slat system that includes multiple spanwise slat segments, each of which has one or more chordwise slat segment. A method and an apparatus for implementing active control of a wing shape are also described and include the determination of desired lift distribution to determine the improved aerodynamic deflection of the wings. Flap deflections are determined and control signals are generated to actively control the wing shape to approximate the desired deflection.

Effects of strut swept angle on the drag of scramjet

Abstract: Swept angle is one of the most important geometric parameters of the strut in scramjet. The change in swept angle will make the geometric shape of the strut different and lead to distinct performances. Computational fluid dynamics method has been used in this study to obtain the cold-state flow field of scramjet model with struts of different swept angles at freestream Mach numbers 5 and 6. The results show that the effect of strut swept angle (from 0° to 60°) on the flow-field structure, total pressure losses, and drag coefficients is less. However, in the cases when strut swept angle is larger than 60°, the shock waves have been weakened significantly and so are the total pressure losses and the strut drag coefficients. In addition, the drag coefficients of all the struts are overall very small because of the small wedge angle of the leading edge. Also, the drag coefficient on the struts reduces when Mach number of freestream increases.

Modification of Flow Structure Over a Van Model by Suction Flow Control to Reduce Aerodynamics Drag

Abstract: Automobile aerodynamic studies are typically undertaken to improve safety and increase fuel efficiency as well as to find new innovation in automobile technology to deal with the problem of energy crisis and global warming. Some car companies have the objective to develop control solutions that enable to reduce the aerodynamic drag of vehicle and significant modification progress is still possible by reducing the mass, rolling friction or aerodynamic drag. Some flow control method provides the possibility to modify the flow separation to reduce the development of the swirling structures around the vehicle. In this study, a family van is modeled with a modified form of Ahmed's body by changing the orientation of the flow from its original form (modified/reversed Ahmed body). This model is equipped with a suction on the rear side to comprehensively examine the pressure field modifications that occur. The investigation combines computational and experimental work. Computational approach used a commercial software with standard k-epsilon flow turbulence model, and the objectives was to determine the characteristics of the flow field and aerodynamic drag reduction that occurred in the test model. Experimental approach used load cell in order to validate the aerodynamic drag reduction obtained by computational approach. The results show that the application of a suction in the rear part of the van model give the effect of reducing the wake and the vortex formation. Futhermore, aerodynamic drag reduction close to 13.86% for the computational approach and 16.32% for the experimental have been obtained.

Supersonic Testing of Natural Laminar Flow on Sharp Leading Edge Airfoils. Recent Experiments by Aerion Corporation.

Abstract: Though inviscid drag can be the biggest component of drag on supersonic aircraft, viscous drag reduction can account for a major improvement in total drag. A significant reduction in viscous drag can be achieved by extensive laminar flow on the wings, which can be obtained by carefully designing the airfoil’s pressure gradients. This tailoring of the design is more difficult if supercritical airfoils in conjunction with high leading edge sweep are adopted. In such case the extent of laminar flow is reduced due to either adverse pressure gradient early in the boundary layer development and/or growth of cross flow instabilities. A way of avoiding these issues is to unsweep the wing and adopt biconvex-type sharp leading edge airfoils. This concept has been tested and adopted by Aerion Corporation and test results showing extensive runs of natural laminar flow (NLF), both in ground facilities and in flight, are summarized.

Aerodynamic drag reduction in a passenger vehicle using vortex generator with varying yaw angles

Abstract: Large investments are aimed at minimizing power needed for propulsion i.e., new downsized engines with new aerodynamic devices for drag reduction. For passenger vehicles the aerodynamic drag force is the dominating resistance force at higher velocity. The vehicle body is often optimized for reducing the drag resistance. Vortex generators belong to the category boundary layer manipulators. Their function is to reenergize an adverse pressure gradient boundary layer that is about to separate by transporting high momentum fluid from the outer part of the boundary layer down to the low momentum zone closer to the wall. In this experimental investigation the variation of pressure coefficient, dynamic pressure, coefficient of lift and drag with and without vortex generators (VG) on the roof of a utility vehicle have been studied at varying yaw angles of VG. The yaw angles used are 10˚, 15˚ and 20˚. To measure the effect of altering the vehicle body, wind tunnel tests have been performed with 1:15 scaled model of the utility vehicle with velocities of 2.42, 3.7, 5.42 and 7.14m/s. The experiments showed that a great improvement of the aerodynamic drag force reduction can be achieved with vortex generator.

Enhancement of Lift and Drag Characteristics of an Oscillating Airfoil in Deep Dynamic Stall Using Plasma Actuation

Abstract: The two dimensional flow past an oscillating NACA 0012 airfoil at Re = 1.35 x 10 is simulated using a large eddy simulation model and subsequently, the influence of plasma actuation on flow control over such an oscillating airfoil is theoretically predicted. Simulation results without plasma actuation were benchmarked with earlier reported experimental data. The formation, growth and separation of the vortical structures along the airfoil have been studied without and with the influence of plasma body force generated by the dielectric barrier discharge actuators. We present results for plasma actuators placed at the leading edge, mid chord and trailing edge locations in both co-flow and counter flow configurations. The force due to the actuator for a length of 1.5-2.0 cm varied in the range of 4-15 kN/m and this was predicted from a force approximation model. Our results show that depending upon the location of the actuator up to 29.2% more lift and 12.5% less drag can be obtained. Such predicted improvement in the lift and drag characteristics through the use of plasma actuation indicate a very useful application of such flow control device in enhancing the performance of oscillating airfoils.

Distribution of High-speed Train Aerodynamic Drag

Abstract: For the real configuration of CRH3 with the head + six carriages + tail train combination running at 350 km/h in the open air,the flow field was massively parallel-simulated with 160 million of computational grids.The aerodynamic drag of various components was calculated and the component drag contribution to the total train drag was analyzed.The results are helpful to local drag-reduced optimization.

Morphing aircraft wing variable-sweep:two practical methods and their aerodynamic characteristics

Abstract: In order to explore the methods of morphing aircraft variable-sweep and their aerodynamic characteristics,numerical simulation of the flow fields of a rotating variable-sweep wing-body and a shearing variable-sweep wing-body was conducted,and the aerodynamic characteristics and its mechanism were analyzed.Numerical simulation method of viscous compressible flow and hybrid grid of prism-hexahedron were used.The results demonstrate that: shearing variable-sweep has better characteristics than rotating variable-sweep in that the former has better lift-to-drag ratio and drag when flying at a speed in the range from M∞ 0.3 to M∞ 0.8,and the main reason is distinct flow field structure caused by the different variable-sweep methods.

Ship with reduced frictional drag and frictional drag reduction device for ship

Abstract: This ship with reduced frictional drag is provided with a starboard air blow-off unit, a port air blow-off unit, and a bottom air blow-off unit. The starboard air blow-off unit is disposed on the outer hull on the starboard side of the bow of a slender ship and can blow off air. The port air blow-off unit is disposed on the outer hull on the port side of the bow and can blow off air. The bottom air blow-off unit is disposed on the outer hull on the bottom of the ship and can blow off air. The bottom air blow-off unit is disposed on or near the center line of the hull.