Vortex Flaps Research Articles

Analysis of a Wing–Fuselage Biplane with Trailing-Edge Flaps in Low-Speed Flow

In this paper, the low-speed aerodynamic characteristics of a basic wing–fuselage supersonic biplane incorporating trailing-edge flaps are assessed using both wake and balance measurements. The effects of the flap attachment location, flap deflection, and flap length are evaluated. These experiments employed a flow velocity of and a Reynolds number of , along with a model having a simple three-dimensional wing–fuselage supersonic biplane configuration; and wake data were obtained with a five-hole probe. Installing the flap near the wingtip was found to produce strong interactions between the wingtip and the flap vortices in the wake, leading to significant induced drag at the wingtip. The local lift increases not only at the flap attachment location but also over the entire wingspan. Positioning the flaps near the body is determined to be more effective, and it gives rise to higher lift and smaller drag than in the case of installing the flap near the wingtip, due to the effects of the tapered wing configuration. The effects of the flap length and flap deflection are also confirmed, with longer flaps and larger flap deflection giving higher lift and more drag.

Evolution of vortices in the wake of an ARJ21 airplane: Application of the lift-drag model

Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency. The near-ground evolution characteristics of wake vortices form the foundation of the wake separation system design. In this study, we analysed the near-ground evolution of vortices in the wake of a domestic aircraft ARJ21 initialised by the lift-drag model using large eddy simulations based on an adaptive mesh. Evolution of wake vortices formed by the main wing, flap and horizontal tail was discussed in detail. The horizontal tail vortices are the weakest and dissipate rapidly, whereas the flap vortices are the strongest and induce the tip vortex to merge with them. The horizontal tail and flap of an ARJ21 do not significantly influence the circulation evolution, height change and movement trajectory of the wake vortices. The far-field evolution of wake vortices can therefore be analysed using the conventional wake vortex model.

Numerical Study on Aerodynamic Characteristics of Slender-bodied Reusable Rockets Using Fins and Vortex Flaps at Very High Angles of Attack

Numerical Study on Aerodynamic Characteristics of Slender-bodied Reusable Rockets Using Fins and Vortex Flaps at Very High Angles of Attack

Numerical and experimental investigations of a nonslender delta wing with leading-edge vortex flap

The aim of this paper is to numerically and experimentally evaluate the control efficiency of a series of leading-edge vortex flaps for a nonslender delta wing at a moderate Reynolds number. Both downward and upward deflected leading-edge vortex flaps are examined by experimental measurements and numerical simulations. It has been found in the wind tunnel experiments that the upward deflected vortex flap increases the vortex lift at low angles of attack due to the enhancement of the vortex strength while at high angles of attack the aerodynamic performances are significantly deteriorated due to a premature flow stall. Meanwhile the flap deflected downward has an excellent performance at high angles of attack, especially with a flap deflection angle of −70°. Consequently, numerical simulations of this optimal configuration are conducted to explore the mechanism of aerodynamic performance improvement and the vortical structures. A recently modified turbulence model has been demonstrated to be suitable to capture the complex vortex structures in this type of flow. In addition, the numerical results are in good agreement with those of the PIV data. Obviously the lift enhancement is due to the fact that the stall phenomenon of the baseline wing is significantly delayed by the vortex flap. This has been proved by the comparisons of vortical topologies, mean pressure coefficients and the limiting streamlines between the experimental measurements and the numerical simulations. Besides, the drag coefficient is reduced by an additional vortex system generated at the leeside of the flap. Furthermore, our simulations are capable of discerning the classical dominant frequencies of helical mode instability, Kelvin–Helmholtz instability and vortex wandering. Correspondingly some unsteady phenomena encountered in the two cases are investigated by the distributions of high levels of turbulent kinetic energy.

Wind Tunnel Testing of Passive High-Lift Systems

This paper presents experimental results obtained with passive high lift systems using a combination of smart flap kinematics and vortex generators. A mid-scale 2.5D wind tunnel model based on DLR-F15 is tested in INCAS Subsonic Wind Tunnel, swept at 30 deg, incorporating the slat, 54 flap/VG/chord extension configurations and test matrix, developed by Dassault-Aviation. INCAS designed, manufactured and instrumented components to be added to the existing INCAS-F15 2D wind tunnel model. The test campaign was completed and results are presented.

Visualization of flow separation and control by vortex generators on an single flap in landing configuration

This paper focuses on a suppression of the flow separation, which occurs on a deflected flap, by means of vortex generators (VG's). An airfoil NACA 63A421 with a simple flap and vane-type vortex generators were used. The investigation was carried out by using experimental and numerical methods. The data from the numerical simulation of the flapped airfoil without VG's control were used for the vortex generator design. Two sizes, two different shapes and various spacing of the vortex generators were tested. The flow past the airfoil was visualized through three methods, namely tuft filaments technique, oil and thermo camera visualization. The experiments were performed in closed circuit wind tunnels with closed and open test sections. The lift curves for both cases without and with vortex generators were acquired for a lift coefficient improvement determination. The improvement was achieved for several cases by means all of the applied methods.

Experimental Investigation of Double-Hinged Vortex Flap Configurations

D ELTA wings are poor lift generators. An often-employed design approach to ameliorate the low lift production is to sharpen thewing’s leading edge. A consequence of the enforced flow separation is the formation of leading-edge vortices. The vortices induce high surface velocities over the wing and may significantly augment lift, especially as the delta becomes more slender [1]. Leading-edge flaps (formed by downward rotation of a segment of the wing’s leading edge) may be used to lessen the performance loss by recovering thrust from the vortices by positioning them over wing elements with a forward-facing area: so-called leading-edge vortex flaps (LEVFs) [2]. Studies of vortex flaps (VFs) have shown the concept to be effective [2,3]; however, their performance is constrained by the characteristics of the leading-edge vortices with incidence. The vortices expand in size and migrate inboard off the flap. As a result, the flaps lose effectiveness. A study by Rinoie and Stollery [3] showed that the maximum lift-to-drag ratio L=D for the 60 and 70 deg delta wings they tested with vortex flaps coincided with smooth flow onto the flap with no separation. As a result, increasing wing incidence requires larger flap deflections to maintain maximized L=D values. Deflecting the flap reduces lift for a given geometric angle of attack as the vortex strength is reduced, as well as to a lesser extent, the attached flow lift [4]. An additional byproduct of flap deflection is a moderate increase in the minimum-drag coefficient. As a result, the initialL=D is attenuated, butmay increase significantly beyond that of the sharp planar delta for moderate to high lift coefficients. An attempt to reduce the drag penalty as well as limit the expansion of thevortex off theflapswas documented byRao [5]. Various flap configurations were investigated, variants including constant length and segmented configurations. The segmented flaps generated two smaller distinct leading-edge vortices so as to minimize vortex spillage. Rao’s results suggested that generating multiple leading-edge vortices was effective in delaying vortex spillage and thus suction loss from the flap. Generally, experimental observation has indicated that the leading-edge vortices on a planar delta lie along a trajectory of approximately 70% of the local semispan [6]. It may be feasible to design a vortex flap that is located further inboard, such that the flap hingeline runs along a ray of approximately 65% semispan. To limit the flap size, a tab may be employed, where the outer wing surface is inclined so as to be parallel to the inner wing section (see Fig. 1). A small tab was evaluated by Hoffler and Rao [7]; some of their designs resulted in the tab having a rearward inclination such that vortex formation over the tab would contribute additional drag. Other tabbed configurations that were tested were not deemed as successful [7]. In this paper, so-called double-hinged vortex flaps (HVF) are evaluated, where the configuration consists of a planar inboard portion, a vortex flap and a planar outboard panel. HVFs may reduce vortex loss with incidence (as its hingeline orientation is closer to the natural vortex trajectory, i.e., the flap is located further inboard), the minimum-drag penalty and structural complication. The undeflected outboard panel of the HVF may also augment the strength of the primary vortex compared with a conventional LEVF, where the effective leading-edge incidence is diminished. The proposed design would mitigate against a movable flap; thewing configuration would be fixed. The basis of comparison of the flaps in this study is different from that of Hoffler and Rao [7]. In the present study the flap area is conserved for a given flap area ratio, and does not include the area of the outboard panel (or tab). The configuration and size of the outboard panels are also conceptually different from those in [7], where the tabs were approximately constant chord and were not an integral part of the wing design, but an add-on. A low-speed windtunnel investigation was conducted to evaluate the concept, characterized through force-balance, pressure measurement, surface flow visualization, and vortex burst trajectories.

Flow Simulation of an Supersonic Transport Configuration at Low-Speed and High-Lift Conditions

The flowfield around a supersonic transport configuration with high-lift devices at a low speed and high angle of attack was investigated by solving Reynolds-averaged Navier–Stokes equations. The configuration consisted of a fuselageandacrankedarrowwingwithleading-andtrailing-edge flaps.Numericalsimulationswereconductedand validated at conditions of the wind-tunnel test. Details of the flowfield at the design condition were analyzed using computational results. The effect of the high-lift devices on aerodynamic performance was discussed. The leadingedgevorticeswerereducedbothinsizeandinstrengthbydeflectingtheleading-edge flap,andthedragwasreduced. The trailing-edge flap increased the effective camber of the wing and improved the lift force. A typical leading-edge vortex flap was confirmed. It was shown that the aerodynamic performance could be improved by deflecting the leading- and trailing-edge flaps.

Transport Aircraft Wake Influenced by a Large Winglet and Winglet Flaps

Detailed flowfields of a wind-tunnel investigation are discussed presenting the wake vortex development and evolution in the near field and extended near field behind a four-engined large transport aircraft model fitted with a large winglet. The tests use a half-model of 1:32 scale focusing on the high-lift case of a typical approach configuration at a Reynolds number of 0.5 x 10 6 based on the wing mean aerodynamic chord and at an angle of attack of 7 deg. Flowfields are carefully inspected by advanced hot-wire anemometry at seven crossflow planes up to 5.6 spans downstream of the model. Based on the measured time-dependent velocity components, the wake flowfield is analyzed by distributions of mean velocity and vorticity, turbulence intensities, and spectral densities. The near-field wing vortex sheet is dominated by seven main vortical structures, namely the winglet vortex, the wing tip vortex, the outboard flap vortex, the outboard and inboard nacelle vortices, and the vortices shed at the wing-body junction and the horizontal tail plane. In the extended near field, these vortices roll up and merge to form the remaining rolled-up vortex. The deflection of winglet flaps produce additional vortices influencing the wing tip near field and enhancing the overall merging process. Especially for the cases with asymmetrical flap deflection, the remaining rolled-up vortex shows a significant narrowband concentration of turbulent kinetic energy which may result in an amplification of inherent far-field instabilities.

Dynamics of Vortical Flows Induced by Swept-Notched Wings in Aircraft Wake Simulations

The motivation behind the present investigations is the alleviation of vortex wake hazard. The influence of wing-tip geometry modifications on the near-field wake behind swept-notched wings is investigated up to 24 span lengths, using computational fluid dynamics. Three-dimensional parallel simulations are run at a chord-based Reynolds number of 5.34 x 10 4 . The effectiveness of notched wing modifications on wake properties is assessed via comparison with conventional and original notched wings. Current results are promising: the tip and flap vortices produced by the swept-notched wings remain distinct and unmerged, unlike those associated with the conventional wing. In all cases, the wakes of the novel wings have circulations and vorticity values that are substantially lower than the original notched wing. Numerical data clearly indicate that such geometrical combinations break apart the concentrated area of streamwise vorticity shed by the wing into three or more less intense regions, significantly reducing the wake strength and induced rolling moment, and affecting the location and merging process of the overall wake system.

와동 플랩 삼각날개를 이용한 관내 와류 발생장치 설계 및 수치해석

본 연구에서는 압력 왜곡과 유동각 왜곡을 모사하기 위하여 삼각날개를 이용한 와류 발생장치를 설계하였다. 삼각날개는 목표한 와류코어 위치와 압력왜곡율(DC90), 와류각을 만족하기 위해 후퇴각 <TEX>$65^{\circ}$</TEX>를 사용하였으며, 와류의 분포 영역을 넓히기 위해 삼각날개 전단면에 <TEX>$45^{\circ}$</TEX> 와동 플랩을 적용하였다. 제작된 와류 발생장치는 시뮬레이션 덕트를 적용한 유동 왜곡 시험에서 전압력 왜곡율의 설계 요구조건을 만족하였으며, 시험 결과로부터 검증된 전산유체해석 결과를 이용하여 와류코어 위치와 와류각의 목표 성능을 확인하였다. In this study, a swirl generator using delta wing was developed in order to simulate total pressure distortion and flow angle distortion. The delta wing was used for <TEX>$65^{\circ}$</TEX>-degree sweep back angle to satisfy the design performance for vortex core position, total pressure distortion(DC90) and swirl angle. To extend the swirling flow area, a <TEX>$45^{\circ}$</TEX>-degree vortex flap have applied to the delta wing. The swirl generator satisfied the design requirement of distortion coefficient in the flow distortion test to be applied to the simulation duct, and the performances of distortion for vortex core position and swirl angle using CFD(computational fluid dynamics) analysis results that was verified by flow distortion test results.

Managing Flap Vortices via Separation Control

A pilot study was conducted on a flapped semi-span model to investigate the concept and viability of near-wake vortex management by means of boundary layer separation control. Passive control was achieved using a simple fairing and active control was achieved via zero mass-flux blowing slots. Vortex sheet strength, estimated by integrating surface pressures, was used to predict vortex characteristics based on inviscid rollup relations and vortices trailing the flaps were mapped using a seven-hole probe. Separation control was found to have a marked effect on vortex location, strength, tangential velocity, axial velocity and size over a wide range of angles of attack and control conditions. In general, the vortex trends were well predicted by the inviscid rollup relations. Manipulation of the separated flow near the flap edges exerted significant control over either outboard or inboard edge vortices while producing small lift and moment excursions. Unsteady surface pressures indicated that dynamic separation and attachment control can be exploited to perturb vortices at wavelengths shorter than a typical wingspan. In summary, separation control has the potential for application to time-independent or time-dependent wake alleviation schemes, where the latter can be deployed to minimize adverse effects on ride-quality and dynamic structural loading.

The Vortex Merger Factor in Aircraft Wake Turbulence

AbstractVortex merger is studied within the context of two-dimensional discrete vortex sheets and demonstrated on two equally oriented circular vortices and aircraft tip and flap vortices. It is confirmed that, depending on the wing load distribution, the latter may or may not coalesce into a single counter-rotating pair. The interaction of a vortex with an equally oriented shear layer, governed by the same physical principle, suggests a possible intensification of an aircraft vortex in cross-wind shear.

Effect of counter-rotating vortices on the development of aircraft wakes

AbstractA two-dimensional vortex particle model is used for studying the development of the vortex wake generated by the wing of an aircraft in the Trefftz plane. Two-dimensional, finite-area vortex structures simulate the initial vorticity distribution at a near-field cross-section of the wing, as provided by either measurements or simulations. The code is used for studying the effect of weak or strong counter-rotating vortices on the development of an aircraft wake. Application in a three-vortex configuration, consisting of the tip and flap vortices, plus a weak negative vorticity sheet lying between them, supports the hypothesis of Graham that the merging of the tip and flap vortices is prevented, because in such an arrangement the counter-rotating vorticity sheet is wrapped around the primary vortices. The present results indicate that even in the far field the tip and flap vortices remain distinct and follow a helical trajectory with large-pitch and small-radius. The code is next applied to the two-vortex system of Savas’s triangular wing, in which the circulation of the flap vortex is comparable to that of the tip. Although a 2D analysis is inappropriate for stability analysis it is still useful for a quick qualitative investigation. Results indicate that the flap and tip vortices follow a helical trajectory with large-pitch but also very large radius. During one period, the flap vortex covers a span wise distance equal to the wing span. Such a flow has not been observed in flight or in laboratory tests. Actually, Ortega et al, who studied experimentally the triangular wing of O. Savas, found out that before concluding one full spiral, the vortices are literally destroyed (rapid spreading of their vorticity) by an instability mechanism.

Studies on Vortex Flaps with Rounded Leading Edges for Supersonic Transport Configuration

Wind-tunnel measurements were taken on a cranked arrow wing supersonic transport configuration with leading-edge vortex flaps. Force and surface pressure measurements were made at Reynolds number based on the wing mean aerodynamic chord from 9.2 × 105 to 3.8 × 10 6 . Two different flap cross sections (the originally designed nonrounded leading edge and the rounded leading edge) were tested. The purpose of the measurements is to clarify how the differences of the Reynolds number affect the flow around the rounded leading-edge vortex flaps and the flap performance. The wing with the rounded leading-edge vortex flaps indicated some benefit of the lift/drag ratio as compared with those of the nonrounded vortex flaps at a relatively high-lift coefficient greater than 0.3

The effect of flap-end additions on aircraft trailing vortices

AbstractThe influence of flap-end geometry modifications on the near-field wake behind a generic high-lift wing/flap configuration is investigated experimentally with a single-tube yawmeter. It is found that flap-end additions tend to split the concentrated area of streamwise vorticity shed by the flap into two less intense regions, associated with the tips of the flap and the addition. For shorter additions, these regions tend to roll up together, resulting in a slightly more diffuse flap vortex of almost unchanged circulation. For larger additions, the outer region is captured by the tip vortex, which correspondingly gains in circulation at the expense of the flap vortex. In all cases, the vorticity centroid of the rolled-up wake is shifted outboard, and the overall circulation slightly increased. However, the associated lift increase implies a decrease in overall circulation at a given lift coefficient.

Benefit and Performance of Various Vortex Flap Configurations

Benefit and Performance of Various Vortex Flap Configurations

Benefit and Performance of Various Vortex Flap Configurations

Benefit and Performance of Various Vortex Flap Configurations

Experimental study of the instability of unequal-strength counter-rotating vortex pairs

A rapidly growing instability is observed to develop between unequal-strength counter- rotating vortex pairs. The vortex pairs are generated in a towing tank in the wakes of wings with outboard triangular flaps. The vortices from the wing tip and the inboard tip of the flap form the counter-rotating vortex pair on each side of the wing. The flow fields are studied using flow visualization and particle image velocimetry. Both chord- based and circulation-based Reynolds numbers are of O(105). The circulation strength ratios of the flap- to tip-vortex pairs range from −0.4 to −0.7. The initial sinuous stage of the instability of the weaker flap vortex has a wavelength of order one wing span and becomes observable in about 15 wing spans downstream of the wing. The nearly straight vortex filaments first form loops around the stronger wing-tip vortices. The loops soon detach and form rings and move in the wake under self-induction. These vortex rings can move to the other side of the wake. The subsequent development of the instability makes the nearly quasi-steady and two-dimensional wakes unsteady and three-dimensional over a distance of 50 to 100 wing spans. A rectangular wing is also used to generate the classical wake vortex pair with the circulation ratio of −1.0, which serves as a reference flow. This counter-rotating vortex pair, under similar experimental conditions, takes over 200 spans to develop visible deformations. Velocity, vorticity and enstrophy measurements in a fixed plane, in conjuction with the flow observations, are used to quantify the behaviour of the vortex pairs. The vortices in a pair initially orbit around their vorticity centroid, which takes the pair out of the path of the wing. Once the three-dimensional interactions develop, two-dimensional kinetic energy and enstrophy drop, and enstrophy dispersion radius increases sharply. This rapid transformation of the wake into a highly three-dimensional one offers a possible way of alleviating the hazard posed by the vortex wake of transport aircraft.

超音速旅客機の離陸上昇性能について―前縁ボルテックス・フラップと後縁フラップの併用―

Improvements of the take-off and climb performance of the next generation supersonic transport (SST) are one of the key features for the SST development. Take-off and climb performances have been estimated for the cranked-arrow-wing SST configuration when the leading-edge vortex flaps and the trailing-edge flaps are deflected. Results show that the take-off distance and the balanced field length are reduced when the trailing-edge flaps are deflected, as expected. The thrust required for the constant climb gradient can be reduced when the leading-edge vortex flaps and the trailing-edge flaps are deflected at the same time.