Leading-edge Extension Research Articles

Beyond conventional: An integrated aerostructural optimization approach for innovative tailplane configurations

This research paper presents a comprehensive study focused on optimizing innovative tailplane configurations for transport jet aircraft. This study aims to enhance the aerodynamics of the aircraft's rear end by introducing a novel tail arrangement. The ultimate goal is to reduce the size of the horizontal empennage, which will have a positive impact on aircraft fuel efficiency. To fulfill its objectives, this work develops a systematic approach, integrating advanced methodologies such as the Design of Experiments and Response Surface Models for both aerodynamics and structural disciplines. By levering response surfaces methodology, the aerostructural optimization has been performed towards a size reduction of the horizontal tail. Results indicate a potential 9% reduction in the tailplane reference area, which could result in enhanced aerodynamic performance and weight saving. This target would only be achievable if the innovative design includes a Leading Edge Extension device to maintain the stability and handling characteristics of a conventional reference aircraft. The impact of the innovative optimized tail arrangement developed in this study at the aircraft level resulted in a 1% reduction in block fuel for a mission range of approximately 3,400 nautical miles for a 180-seat capacity jet aircraft (similar to A320neo). Furthermore, from an industrial perspective, this paper also demonstrates how an automated workflow assists with CAD modeling, mesh creation, simulation execution, and surrogate models to accelerate complex multidisciplinary optimization processes, thereby reducing the time and costs associated with the development of a new aircraft configuration.

Study of the Impact of Aerodynamic Model Fidelity on the Flight Characteristics of Unconventional Aircraft

The article presents a study on the influence of aerodynamic model fidelity on dynamic characteristics. The Simulation and Dynamic Stability Analysis (SDSA) package was used to calculate the dynamic characteristics, using both eigenvalues (linearized model) and a time history approach (nonlinear model). The tests were carried out for a rocket aircraft designed in a tailless configuration with a leading edge extension and rotating side plates. Due to these features, the rocket plane can be classified as an unconventional configuration, which requires special attention. Aerodynamic characteristics of the rocket plane were measured in a subsonic wind tunnel and calculated using Euler model equations-based software (MGAERO) and low-order potential-flow code (PANUKL). The paper presents the results of dynamic analysis in the form of standard modes of motion characteristics. A comparison of dynamic characteristics calculated using a set of aerodynamic data with different fidelity is shown and discussed. Both longitudinal and lateral cases were included. The presented results show that the potential methods, considered old-fashioned and despite many simplifications, are still an attractive tool and can be used to analyze even complex, unconventional configurations.

An investigation into directional characteristics of the rocket plane in a tailless configuration

This paper embraces result of wind tunnel tests of a rocket plane designed to space tourism application. The rocket plane is designed in a tailless configuration with a leading edge extension (LEX) and side plates on the wing’s tip which work as all moving tail. Usually for such a concept of control, movable surfaces are position in a horizontal direction while in the considered concept there is no classical rudder, and the movable surfaces are mounted with a significant dihedral angle. The research was carried out in the subsonic closed circuit wind tunnel with an open test section. Moreover, MGAERO and PANUKL package were used for numerical computations. The first research question is to investigate how the configuration of the side plate affects the directional stability of the rocket plane. The second aim is to study the efficiency of the side plates deflected like an all moving tail for both low and high angles of attack. As a result of this investigation, the directional stability derivatives and the control derivatives were obtained. Finally, the experimental results were compared with numerical outcomes to establish does software with no full flow model can be applicable for design an aircraft with all moving tail in case of low of angles of attack.

Effect of surface coating on defrosting water drainage characteristics of vertical-fin microchannel frosting evaporator

Vertical-fin microchannel heat exchanger has better frosting and defrosting performance owing to its better water drainage along vertical fins. Effect of hydrophilic and superhydrophobic coatings on frosting and defrosting performance is experimentally compared and drainage performance is investigated by dynamic dip testing and simulation. Results show that since water has smaller adhesive force on superhydrophobic fins, defrosting water carries some frost while is separated from the evaporator in form of frost-water mixture. Hence, the superhydrophobic vertical-fin microchannel evaporator has shorter defrosting duration by 9.8%. Both hydrophilic and superhydrophobic samples have satisfactory cyclic repeatability without obvious capacity attenuation. During defrosting, most water can flow down the leading edge extension. The residual water of the superhydrophobic sample is 61 g/m2, which is 19.6% less than that of hydrophilic one.

Vortex interaction on a LEX configuration

Flow visualization experiments were conducted in a water channel and a low-speed wind tunnel at Reynolds number of 1.54 times 104 to 1.2 times 105 for a leading-edge extension model, which is referred to as a NASA TP-1803 model in this study. In addition, particle image velocimetry velocity measurements were taken in the water channel to obtain the quantitative information about the three-dimensional velocity field over the strake and wing surfaces. The results obtained at low, medium and high angles of attacks represent three distinct cases of interaction between the strake and wing vortices. Namely, at α = 5o and 10° the strake and wing vortices were developed over the wing surface without significant interaction noticed; at α = 20°, the strake vortex strongly interacted with the wing vortex in an intertwining manner, which was sensitive to Reynolds number; at α = 30°, the breakdown of the strake vortex took place close to the junction of the strake and the wing; thus, the interaction of the strake and the wing vortices appeared to be less significant than the case of α = 20°.Graphic abstract

Airside heat transfer and pressure drop of an aluminum heat exchanger having a new louver fin with leading edge extension

Conventional louver fins have an inherent problem of condensate drainage. In this study, a newly developed louver fin is introduced. The louver fin has an extension at leading edge. Dry and wet surface heat transfer and pressure drop characteristics of the heat exchanger made of the new fins were investigated, and results are compared with those having trailing edge extension fins or conventional fins. For conventional sample, significant differences between dry and wet j and f factors were observed. Dry j factors were 166% larger than wet j factors, and wet f factors were 68% larger than dry f factors. The discrepancies were significantly reduced for the samples having extensions, which suggests that extensions are effective in condensate control. The present sample having leading edge extension yielded higher dry j factors than the sample having trailing edge extension, probably due to proper allocation of louvers. Wet j factors of the two extended samples were approximately the same, which means that the condensate drainage is better for trailing edge extension than leading edge extension. Under dry condition, j/f1/3 of leading edge sample were 132 % and 59% higher than those of trailing edge extension and conventional sample respectively. However, under wet condition, j/f1/3 of leading edge extension sample were 87% and 205% higher than those of trailing edge extension and conventional sample. This confirms that the present leading edge extension sample shows better performance than trailing edge extension sample, both under dry and wet condition.

Persistent and polarized global actin flow is essential for directionality during cell migration.

Cell migration is hypothesised to involve a cycle of behaviours beginning with leading edge extension. However, recent evidence suggests that the leading edge may be dispensable for migration, raising the question of what actually controls cell directionality. Here we exploit the embryonic migration of Drosophila macrophages to bridge the different temporal scales of the behaviours controlling motility. This reveals that edge fluctuations during random motility are impersistent and weakly correlated with motion. In contrast, flow of the actin network behind the leading edge is highly persistent. Quantification of actin flow structure during migration reveals a stable organisation and asymmetry in the cell-wide flowfield that strongly correlates with cell directionality. This organisation is regulated by a gradient of actin network compression and destruction, which is controlled by myosin contraction and cofilin-mediated disassembly. It is this stable actin-flow polarity, which integrates rapid fluctuations of the leading edge that controls inherent cellular persistence.

EFFECT OF THE HORIZONTAL CANARD OF THE SHARP-EDGED FOREBODY OF THE MANEUVERABLE AIRCRAFT MODEL ON THE VORTEX FLOW STRUCTURE

This paper presents the results of numerical studies of the effect of horizontal canard installation in a maneuverable aircraft model with a sharp-edged forebody, which smoothly turns into the leading edge extension, on the longitudinal aerodynamic characteristics at low subsonic speeds (M = 0.15) within the range of angles of attack α = 0°–35° using the two-parameter k-ω shear stress transport turbulence model with empirical correction for the streamline curvature. The results of the numerical calculations are in satisfactory agreement with the experimental data obtained in the T-102 wind tunnel at TsAGI within the entire range of the angles of attack. Based on the numerical and experimental studies, it is shown that installation of a horizontal canard has a positive effect on the aerodynamic characteristics of the maneuverable aircraft model at rather high angles of attack (α > 19°). The positive effect of the horizontal canard installation is mainly due to the influence of the vortex structures generated from the sharp-edged forebody on the trajectory, which yields favorable interference of the forebody and wing vortices.

LEX and wing tip plates’ interaction on the Rocket Plane in tailless configuration

ABSTRACTThe article includes study on the influence of a LEX (leading-edge extension) and wing tip plates on aerodynamic characteristics of the Rocket Plane in tailless configuration for manned suborbital flights. The research was conducted only for the low speed regime in the wind tunnel at the Warsaw University of Technology. Tests were carried out for a few configurations of the Rocket Plane. Moreover, two shapes of LEX were investigated. Analysis of results was focused on the aerodynamic synergism effect only. The influence of LEX and the wing tip plates of the Rocket Plane on the aerodynamic coefficients was identified.

The Role of Stress Fibers in the Shape Determination Mechanism of Fish Keratocytes

Crawling cells have characteristic shapes that are a function of their cell types. How their different shapes are determined is an interesting question. Fish epithelial keratocytes are an ideal material for investigating cell shape determination, because they maintain a nearly constant fan shape during their crawling locomotion. We compared the shape and related molecular mechanisms in keratocytes from different fish species to elucidate the key mechanisms that determine cell shape. Wide keratocytes from cichlids applied large traction forces at the rear due to large focal adhesions, and showed a spatially loose gradient associated with actin retrograde flow rate, whereas round keratocytes from black tetra applied low traction forces at the rear small focal adhesions and showed a spatially steep gradient of actin retrograde flow rate. Laser ablation of stress fibers (contractile fibers connected to rear focal adhesions) in wide keratocytes from cichlids increased the actin retrograde flow rate and led to slowed leading-edge extension near the ablated region. Thus, stress fibers might play an important role in the mechanism of maintaining cell shape by regulating the actin retrograde flow rate.

Simulation validation of static and forced motion flow physics of a canard configured TransCruiser

The basic objective of this work is to validate CFD simulations performed on a transonic cruiser configuration called the TCR. The low speed aerodynamic characteristics of the TCR have previously been investigated at the Russian TsAGI T-103 wind tunnel as part of the European Framework 6 SimSAC project. The experimental results showed that static and dynamic pitch moment curves are very nonlinear. These experimental data are used in this work to validate CFD predictions using the Cobalt flow solver with an overset grid approach. Two types of wind tunnel tests were conducted: static tests for angle-of-attack sweeps at zero degrees sideslip and angle-of-sideslip sweeps at different angles of attack. The dynamic tests include forced sinusoidal oscillations in one of three modes of pitch, yaw, and roll. Both static and dynamic tests were conducted with/without a vertical tail and at different canard deflections. Dynamic tests are small- and large-amplitude motions with frequencies of 0.5, 1.0, and 1.5 Hz. CFD results were obtained with different turbulence models and using a single mesh or an overset grid approach, and then compared with the experimental data. The effects of the canard downwash flow on the wing aerodynamic performance are also investigated. The comparison between the experimental and CFD simulations show that the results match well. The overset mesh that includes a gap between the canard and fuselage leads to the same predictions as the single mesh that has no gaps. The CFD solutions show that vortices are formed over the canard, fuselage, leading-edge extension (LEX), wing, and the vertical tail (at sideslip angles). Each vortex appears to have a primary vortex accompanied by a smaller counter-rotating secondary vortex. These vortices are influenced by the canard presence and deflection. At high angles of attack, the canard vortex has two favorable effects in terms of increasing the maximum lift and delaying the wing vortex breakdown. In the range of angles of attack between 18° and 24°, the canard vortex core moves upward off the canard surface and the LEX and wing vortices interact and then merge; both effects lead to a sudden change in the slopes of the force and moment curves. Finally, the CFD data show that increasing the canard deflection produces a stronger vortex over the canard, but leads to smaller fuselage and LEX vortices.

A Finite Element Approach to Modal Parameter Estimation of Vertical Tail Fin

The vertical stabilizers or fin of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip and provide direction stability. Vertical tails designed for aircrafts suffer from reduced stability and control effectiveness at high dynamic pressures due to aeroelastic effects. Adequate tail performance requires a detailed study on dynamic performance before investigating aeroelastic effects. Experimental modal analysis is a very extensive, time consuming and expensive process while finite element analysis is quick, accurate, fast and economical. Hence, in the present work it is purposed to carry out a detailed finite element simulation of vertical tail fin for a UAV to evaluate modal parameters such as natural frequencies and its corresponding modal shapes. CAD modeling of the vertical tail fin was done in UG NX using spline and swept commands. The vertical fin is sandwiched with polyurethene foam of density 70kg/m 3 bonded with thin Aluminum sheet of 1mm thickness as face sheets. Similarly, biwoven e-glass fiber was considered as face sheets along with PU foam as core. The meshing of model was carried out using a 10 noded solid tetrahedral element. Boundary conditions were simulated and dynamic analysis was performed to evaluate natural frequencies and corresponding modal shapes. Keywords: Modal Analysis, Natural Frequencies, Mode Shapes, Vertical Tail, FEM I. Introduction For modern UAV's, the ability to fly and maneuver at high angles of attack and at high loading conditions gives tactical advantages. For UAV's the maneuverability at very high angles of attack is achieved through a combination of the wing root leading edge extensions (LEXs) and the placement of vertical tails. A pair of large vortices generated by highly swept wing root LEXs contribute to enhanced vortex lift by developing high suction areas over the wings. The UAVs are designed to utilize unique characteristics of these vortex structures which are prime contributors to the aerodynamics of an aircraft during high angle of attack flight. The vertical tails of the UAV's are placed in closer proximity to the LEX vortex flow field to take full advantage of the concentrated energy contained in the LEX vortices to provide the directional stability and control necessary for high angle of attack maneuverability. Large buffet loads and associated fatigue damage have been observed on the tails of such aircrafts during certain flight conditions, including rapid maneuvering at subsonic Mach numbers and dynamic pressures considerably less than the maximum allowable values (1, 2).The interactions of a flexible structure with the aerodynamic forces acting on it are severe enough to influence the structural and aerodynamic design. The dynamic and aeroelastic analysis of an aircraft with main reference to its lifting and control surfaces is an essential aspect for finalization of the design cycle and is also required for obtaining flight clearance and certification of the aircraft. Correlation of the dynamic characteristics of the aircraft obtained from analysis with the Ground Vibration Test results of the aircraft was studied (3). The airframes of high performance aircraft, have suffered from an aeroelastic tail buffet problem for many years. This problem is inherent to vertical flows used to generate lift at high angles of attack as they tend to break down causing severe empennage dynamic loading and premature fatigue failures. Better understanding of the empennage buffeting problem is required for development of reliable fatigue usage monitoring systems and for the fleet management of aircraft. The challenges associated with computational simulation of empennage buffet vary from prediction of the nonlinear separated vortical flows about complex configurations to the coupled interaction between the flow and the dynamic response of the tail structure (4).Vibration analysis of an aircraft component can characterize the structural dynamics, determine the fundamental frequencies and define the complete modal data of the component. From this data, engineers can objectively evaluate their concerns about the impact of vibrations on adjacent aircraft components. These concerns have very real consequences since excessive vibrations can lead to premature component fatigue and failure (5, 6). Vertical tail fin is a critical component that must meet very high quality standards. Vertical tails designed for aircrafts suffer from reduced stability and control effectiveness at high dynamic pressures due to aeroelastic effects. Therefore, adequate tail performance requires a detailed study of dynamic performance before investigating aeroelastic effects (7, 8). Also, modal analysis is not only useful in its own right, but it also provides the basis for a number of further dynamics analyses. To this end, modal test plays an important role in the certification process of any new or

Yaw Angle Effect on Flow Structure over the Nonslender Diamond Wing

Yaw Angle Effect on Flow Structure over the Nonslender Diamond Wing

Effect of a centerbody on the vortex flow of a double-delta wing with leading edge extension

The effect of the presence of a centerbody on the vortex flow of a uniquely-shaped double-delta wing was experimentally investigated through simultaneous off-surface flow visualization and wing-surface pressure measurements. The uniquely-shape double-delta wing was formed by attaching a leading edge extension (LEX) to the apex portion of a 65-deg sweep delta wing with sharp edges. The flow Reynolds number was 1.82 × 10 5 for the off-surface flow visualization, 1.76 × 10 6 for the wing-surface pressure measurement. Visualization results show that the presence of a centerbody under the lower surface of the double-delta wing model slightly advanced coiling interaction of the wing and LEX vortices at the downstream chord positions, at least for the selected angle of attack of 24-deg. Quantitative analysis of wing-surface pressure measurements revealed the effects of the presence of a centerbody to be prominent for the cases with higher angles of attack and sideslip angles. Up to angle of attack α = 24 -deg , the presence of the centerbody had a small influence on the suction pressure distribution on the wing upper surface, even at the large sideslip angle of −20-deg. However, at higher angles of attack of 28-deg and 32-deg, the presence of the centerbody caused a decrease in the magnitude of suction pressure distributions on the wing's upper surface, and the difference of the suction pressure distribution between the two configurations was not negligible at non-zero sideslip angles.

Dye Visualization of the Flow Structure over a Yawed Nonslender Delta Wing

S TUDIES of aerodynamic structures and behaviors of the nonslender delta wings are invariably essential to develop a method to control the development of the vortex breakdown as well as the development of vortices. Unsteady aerodynamics of nonslender delta wings, consisting of shear layer instabilities, the structure of vortices, the occurrence of breakdown, and fluid/structure interactions were extensively reviewed by Gursul et al. [1]. They emphasized the sensitivity of the vortical flow structures varying the angle of attack of the deltawing.Yavuz et al. [2] studied thevortical flow structure on a plane immediately adjacent to the surface of nonslender delta wing, 38:7 deg. Yaniktepe and Rockwell [3] performed experimental investigations on the flow structures at trailing-edge regions of diamondand lambda-type wings. In both wings, vortical flow structures in the crossflowplanes of trailing edge vary rapidly with the angles of attack . Sohn et al. [4] visually investigated the development and interaction of vortices in crossflow planes at various locations on the delta wing with leading edge extension (LEX) using micro water droplets and a laser beam sheet. The range of angle of attack was taken as 12 24 deg at yaw angles of 0, 5, and 10 deg. It was indicated that, by introducing yaw angle , the coiling, merging, and diffusion of thewing and LEX vortices increased on the windward side, whereas they became delayed significantly on the leeward side. Their study confirmed that the yaw angle had a profound effect on the vortex structures. Taylor and Gursul [5] visualized leading-edge vortices of a 50 deg sweep angle, having angles of attack as low as 2:5 deg. Gursul et al. [6] report that combat air vehicles (UCAVs) and micro air vehicles have particularly dominant vortical flows having low sweep angles (25–55 deg), and future UCAVs are expected to be highly maneuverable and highly flexible. Yaniktepe and Rockwell [7] aimed at investigating the unresolved concepts, which included averaged structure of shear layer from the leading edge of the wing, unsteady features of separated layer adjacent to the surface of the wing, and control of flow structure by leading-edge perturbations. Elkhoury and Rockwell [8] have investigated to provide various measurements of the visualized dye patterns, including the degree of interaction of vortices, the onset of vortex breakdown, and effective sweep angle of the wing root vortex, as a function of both Reynolds number and angle of attack . Elkhoury et al. [9] had investigated the Reynolds number dependence of the near-surface flow structure and topology on a representative UCAV planform. The present investigation focuses on the formation and development of leading-edge vortices, vortex breakdown, and threedimensional separationandstallof thecomplexanddisorganizedflow structure over the delta wing. The leading-edge sweep angle was 40 deg. The angle of attack was varied within the range of 7 17 deg and the yaw angle was varied within the range of 0 15 deg.

M1703 Intestinal Permeability and Bacterial Translocation Are Modulated By the Genetic Background of the Host

G A A b st ra ct s manner with significant inhibition noted at 5.0 and 10.0 μM. 18β-GA washout restored a normal rate of cell migration. No inhibition of migration was noted between 0.625 to 2.5 μM despite reaching near complete inhibition (90-95%) of GJIC at these concentrations. The Cx-43 polypeptide exists in three isoforms under control conditions: two predominant phosphorylated forms (P2 and P1) and one minor non-phosphorylated form (P0). 18β-GA shifts the phosphorylation state of Cx-43 from nearly equal amounts of P2 and P1 to a predominantly P0 isoform at concentrations between 0.625 to 2.5 μM. Confocal microscopy revealed that Cx-43 is not present at the leading-edge lamellipodia extensions of migrating cells, but localizes primarily to the retracting edge at points of contact between cells and along lines of cortical actin filaments. Conclusions: Although a correlation exists between GJIC and Cx-43 phosphorylation state, GJIC and maintenance of the P2 isoform are not required for IEC-6 migration. Based on the specific subcellular localization of Cx-43 in migrating cells, we speculate that regulation of actin cytoskeleton dynamics may be a novel function for gap junction proteins and might regulate epithelial cell migration In Vivo along the intestinal villous. (Supported by an Intramural Research Grant for New Faculty from Michigan State University).

ClC-3 and IClswell are Required for Normal Neutrophil Chemotaxis and Shape Change

Polymorphonuclear leukocytes undergo directed movement to sites of infection, a complex process known as chemotaxis. Extension of the polymorphonuclear leukocyte (PMN) leading edge toward a chemoattractant in association with uropod retraction must involve a coordinated increase/decrease in membrane, redistribution of cell volume, or both. Deficits in PMN phagocytosis and trans-endothelial migration, both highly motile PMN functions, suggested that the anion transporters, ClC-3 and ICl(swell), are involved in cell motility and shape change ( Moreland, J. G., Davis, A. P., Bailey, G., Nauseef, W. M., and Lamb, F. S. (2006) J. Biol. Chem. 281, 12277-12288 ). We hypothesized that ClC-3 and ICl(swell) are required for normal PMN chemotaxis through regulation of cell volume and shape change. Using complementary chemotaxis assays, EZ-TAXIScantrade mark and dynamic imaging analysis software, we analyzed the directed cell movement and morphology of PMNs lacking normal anion transporter function. Murine Clcn3(-/-) PMNs and human PMNs treated with anion transporter inhibitors demonstrated impaired chemotaxis in response to formyl peptide. This included decreased cell velocity and failure to undergo normal cycles of elongation and retraction. Impaired chemotaxis was not due to a diminished number of formyl peptide receptors in either murine or human PMNs, as measured by flow cytometry. Murine Clcn3(-/-) and Clcn3(+/+) PMNs demonstrated a similar regulatory volume decrease, indicating that the ICl(swell) response to hypotonic challenge was intact in these cells. We further demonstrated that ICl(swell) is essential for shape change during human PMN chemotaxis. We speculate that ClC-3 and ICl(swell) have unique roles in regulation of PMN chemotaxis; ICl(swell) through direct effects on PMN volume and ClC-3 through regulation of ICl(swell).

GPR48 Regulates Epithelial Cell Proliferation and Migration by Activating EGFR during Eyelid Development

Eyelid development is a dynamic process involving cell proliferation, differentiation, and migration regulated by a number of growth factors and cytokines. Mice deficient in the orphan G protein-coupled receptor 48 (GPR48) showed an eye open at birth (EOB) phenotype. In this study, the authors attempted to clarify the role of GPR48 in eyelid development and the molecular mechanisms leading to the EOB phenotype. Phenotypic analysis of the eyelids of Gpr48(-/-) mice was carried out using histology and scanning electron microscopy. GPR48 expression pattern was determined using X-gal staining. In vitro scratch assay was used to determine cell motility defects in Gpr48(-)(/)(-) keratinocytes. The molecular mechanism underlying GPR48-mediated eyelid closure was explored using Western blot and immunostaining analyses. Expression levels of EGFR and its phosphorylated counterpart were examined in Gpr48(-/-) and wild-type keratinocytes and in eyelids. GPR48 is highly expressed in the epithelium and apical mesenchymal cells of eyelids during embryonic development. Detailed analysis revealed that Gpr48(-/-) mice exhibited delayed leading-edge extension, reduced filopodia formation, and decreased rounded periderm cell formation around eyelid margins. Keratinocytes lacking GPR48 are defective in cell proliferation and migration with reduced F-actin staining. In addition, the phosphorylation of EGFR was dramatically decreased in cultured keratinocytes and developing eyelids in the absence of GPR48. Inactivation of GPR48 induces the EOB phenotype by reducing epithelial cell proliferation and migration, indicating that GPR48 plays an essential role in eyelid development. Furthermore, GPR48 contributes to eyelid development through the regulation of the EGFR signaling pathway.

Experimental and Computational Studies of Twin-Vertical-Tail Buffet

Characteristics and mechanism of twin-vertical-tail buffet response on airplane configuration with wing root leading edge extension (LEX) were studied by both experiment and computation. Low-speed wind tunnel experiments were carried out to measure the root bending moment and tip acceleration of vertical tail. Vortical flow patterns were visualized via laser light sheet technique. Three-dimensional computation was performed to solve the unsteady Euler equations on rigid model. The results indicate that (1) bursting of vortices emanating from LEX is the main source of twin-vertical-tail buffet; (2) the Euler equations is able to predict the general characteristics of vertical-tail buffet response reasonably.

High Resolution Turbulence Treatment of F/A-18 Tail Buffet

Unsteady tail loads of the F/A-18 are computed using various turbulence models at an angle of attack consistent with buffet induced by leading-edge extension vortex breakdown. Comparison of these industry-standard Reynolds-averaged Navier-Stokes turbulence models with the detached-eddy simulation hybrid approach reveals the inadequacies of Reynolds-averaged Navier-Stokes methods and the ability of detached-eddy simulation to reproduce the observed unsteadiness at these conditions. Computed vortex breakdown position and frequencies of the detached-eddy simulation method are shown to be accurate by comparison to flight-test and experimental results. Finally, comparison of the detached-eddy simulation unsteady tail pressures with flight-test tail pressures reveal the ability of the method to accurately reproduce F/A-18 tail buffet loads and its readiness for inclusion in a fluid-structure interaction method.