Leading-edge Extension Vortex Research Articles

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.

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.

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.

중앙동체가 LEX-삼각날개 형상의 와류에 미치는 영향

An experimental study of the vortical flow over a yawed delta wing with leading edge extension(LEX) was conducted to investigate the effects of the existence of a centerbody configuration on the flow characteristics of the wing and LEX vortices using off-surface visualization and PIV measurements. The qualitative investigation using these two techniques indicated that the effect of the centerbody existence on the vortex formation was minimal at somewhat low range of angles of attack and sideslip angles. However, the quantitative analysis of the surface pressure measurements revealed the effect of centerbody existence to be prominently increased for the cases with higher angles of attack and sideslip angles. It was also found that the centerbody effect was not significant compared to the effect of sideslip for the present LEX-delta wing configuration.⠌蘀؀㘴〮㔻᠀䡯浥…⁦慭楬礠浡湡来浥湴

Computational Study of F/A-18 E/F Abrupt Wing Stall in the Approach Configuration

This computational study evaluated lateral instabilities observed during developmental testing of the preproduction F/A-18E/F in the power-approach configuration. These instabilities, described here as abrupt wing stall (AWS), occurred whenever the airplane exceeded 12-deg angle of attack. The AWS was quickly corrected in flight test by the closure of a vent at the wing root, without understanding its physical cause or cure. Computational solutions with both the vent open and closed provide insight into the likely cause of the instability, revealing two distinctive flow topologies. Specifically, all F/A-18 Hornet models depend upon strong vortex flows from the leading-edge extension (LEX) to provide lift at elevated angle of attack. Flow through the open vent displaces the LEX vortex core inboard and up off the wing's upper surface. This displacement dramatically weakens the flow stability over the wing's entire upper surface. Wind-tunnel studies performed in parallel by another researcher provide quantitative corroboration of the computational solutions. Finally, computational-fluid-dynamics metrics developed within the NASA/Navy/Industry AWS program are applied to determine their validity at this low-speed flight condition and modified to enhance their viability as predictive tools for AWS prone configurations.

Vortex Flow Visualization of a Yawed Delta Wing with Leading Edge Extension

The development and interaction of vortices over a yawed delta wing with leading-edge extension (LEX) was investigated through off-surface flow visualization using micro water droplets and a laser beam sheet. Angles of attack of 12, 16, 20, and 24 deg were tested at sideslip angles of 0, -5, and -10 deg. The flow Reynolds number based on the main-wing chord was 1.82 × 10 5 . The wing vortex and the LEX vortex coiled around each other while maintaining comparable strength and identity at a zero sideslip. The increase of angle of attack intensified the coiling and shifted the cores of the wing and LEX vortices inboard and upward. By sideslip, the coiling, the merging and, the diffusion of the wing and LEX vortices increased on the windward side, whereas they became delayed significantly on the leeward side. Also the migration behavior of vortices on the windward and leeward sides of the wing changed considerably

The vortical flow field of delta wing with leading edge extension

The interaction and breakdown of vortices over the Leading Edge Extension (LEX)- Delta wing configuration has been investigated through wing-surface pressure measurements, the off-surface flow visualization, and 5-hole probe measurements of the wing wake section. The description focused on analyzing the interaction and the breakdown of vortices depending on the angle of attack and the sideslip angle. The Effect of angle of attack and sideslip angle on the aerodynamic load characteristics of the model is also presented. The sideslip angle was found to be a very influential parameter of the vortex flow over the LEX-delta wing configuration. The introduction of LEX vortex stabilized the vortex flow, and delayed the vortex breakdown up to a higher angle of attack. The vortex interaction and breakdown was promoted on the windward side, whereas it was suppressed on the leeward side.

Visualization and Flowfield Measurements of the Vortical Flow over a Double-Delta Wing

The vortical flow of a 65-deg flat plate delta wing with a leading edge extension(LEX) was examined through off-surface visualization, 5-hole probe and hot-film measurements. The off-surface flow visualization technique used micro water droplets generated by a home-style ultrasonic humidifier and a laser beam sheet. The angles of attack ranged from 10 to 30 degrees, and the sideslip angles ranged from 0 to -15 degrees. The Reynolds number was <TEX>$1.82{\times}10^5$</TEX> for the flow visualization, and <TEX>$1.76{\times}10^6$</TEX> for the 5-hole probe and hot-film measurements. The comparison of the visualization photos and the flow field measurement showed that the two results were in a good agreement for the relative position and the structure of the wing and LEX vortices, even though the flow Reynolds numbers of the two results were much different. The wing vortex and the LEX vortex coil each other while maintaining a comparable strength and identity at zero sideslip. Neither a looping of the wing vortex around the strake vortex, nor the lopsided coiling of the stronger strake and the weaker wing vortices was observed. At non-zero sideslip, the downward movement of the LEX vortex when going downstream was enhanced on the windward side, and the downward and inboard movement of the LEX vortex when going downstream was suppressed on the leeward side. The counterclockwise coiling of the wing and LEX vortices was decreased significantly on the leeward side.

옆미끄럼을 갖는 LEX/삼각 날개 형상에 대한 높은 받음각 와유동의 가시화 연구

An off-surface flow visualization experiments have been performed to investigate the flow field over a delta wing with the leading edge extension(LEX). The model is a flat wing with sweepback angle. The free stream velocity is 6.2 m/s, which corresponds to Reynolds number of based on the wing root chord. The angle of attack and sideslip angle range from and , respectively. The visualization technique of using the micro water-droplet and the laser beam sheet enabled to observe the vortical flow structures, which can not be obtained by 5-hole probe measurements. With sideslip angle, the interaction and breakdown of the LEX and wing vortices was promoted in the windward side, whereas, it was suppressed in the leeward side.

Load Measurements on the Leading-Edge Extension, Wing, and Body of an F/A-18

The pressure difference across the wing and leading-edge extension (LEX) of a rigid 6% scale model of an F/A-18 was measured, and the integrated static and rms loads were computed. The total loads on the aircraft were obtained using a sting-mounted balance from which the body loads can be deduced by subtracting the LEX and wing loads. The effects of Mach number and angle of attack were analyzed and results for M = 0.25, 0.6, and 0.8 at a = 20‐35 deg are presented. The effectiveness of the LEX as a highlift device is demonstrated by comparing the individual lift contributions from the wing and LEX at different angles of attack and Mach numbers. It is shown that the LEX vortex can generate large nonlinear static lift while inducing high unsteady lift on the aircraft.

LATERAL OSCILLATIONS OF AN AIRCRAFT MODEL AT HIGH ANGLES OF ATTACK

Lateral oscillations occurring on the aircraft model of NASA TP 1803 at angles of attack ranging from 25° to 60° have been investigated in a low-speed wind tunnel for configurations including fuselage with wing or with a combination of wing and leading-edge extension (LEX). The wind tunnel experiment was conducted in the range of Mach number from 0·1 to 0·2, and the range of the Reynolds number based on the body diameter from 2·8×10 5to 5·6×10 5. The time-varying side force coefficients, which may represent the displacements of oscillation in the lateral direction, were measured to obtain the root-mean-square values and the power spectra. Flow visualization of the vortices generated from the forebody, wing and LEX of the model has also been performed in a water tunnel. It was found that the entire system of the flow and the sting-supported model locks-in at the resonant oscillation frequency as the lateral oscillation occurs. The presence of LEX significantly enhances the oscillation amplitude especially at high enough angles of attack, i.e., α>40 °.The enhancement of the lateral oscillation, as suggested by the water tunnel visualization, seems closely related to the breakdown of the LEX vortices in general and the location of breakdown in particular. The power spectra of the test model with wind and LEX exhibit a transition from weakly nonlinear to broad band oscillations as αis increased from 45° to 60°. The appearance of a broad range of frequencies around or below the dominant frequency, that can be indicative of possible chaotic oscillation, corresponds to a sharp drop of the lateral oscillation amplitude. The effect of Reynolds number is notable only at α>50°.Variation of the sideslip angle between 0 and 10° appears to have no discernible effects on the amplitude of lateral oscillation for the test model with wing and LEX.

Forebody tangential slot blowing on an aircraft geometry

The effect of forebody tangential slot blowing on the flowfield about an F/A-18 aircraft is investigated numerically using solutions of the Navier-Stokes equations. Computed solutions are obtained for an aircraft geometry which includes the fuselage, a wing with deflected leading-edge flap, empennage, and a faired-over engine inlet. The computational slot geometry corresponds to that used in full-scale wind-tunnel tests. Solutions are computed using flight test conditions and jet mass flow ratios equivalent to wind-tunnel test conditions. The effect of slot location is analyzed by computing two nontime-accurate solutions with a 16-in. slot located 3 in. and 11 in. aft of the nose of the aircraft. These computations resolve the trends observed in the full-scale wind-tunnel test data. The flow aft of the leading-edge extension vortex burst is unsteady. A time-accurate solution is obtained to investigate the flow characteristics aft of the vortex burst, including the effect of blowing on tail buffet.

Installed F/A-18 inlet flow calculations at a high angle of attack

One of the goals of the high alpha technology program (HATP) is to accurately predict the inlet performance for aircraft operating at extreme attitudes (a = 60 deg, /8 = 10 deg). In this article, the numerical results for three cases are presented. The cases studied are full scale, 19.78% model scale at design mass flow, and model scale at a reduced mass flow. The effects of Reynolds number on the predicted flowfleld is demonstrated with the model and full scale calculations. The inlet mass flow is reduced 25% to investigate the effect mass flow rate has on the flow entering the inlet and on the inlet duct performance. All cases are at 30-deg angle of attack and 0-deg yaw. Surface static pressures along the forebody and under the leading edge extension (LEX) agreed well with the data for all three cases. The predicted inlet recoveries obtained for full scale and model scale Reynolds numbers were very similar. The predicted inlet recoveries were lower than data. This discrepancy may be partly due to poor inlet lip definition and grid resolution. The predicted inlet recovery for the reduced mass flow rate case was significantly higher than the design mass flow case. The reduction of inlet mass flow rate had a small effect on the external flowfleld. The choice of the turbulence model length scale has a significant impact on the position of the windward side LEX vortex.

Pitch rate/sideslip effects on leading-edge extension vortices of anF/A-18 aircraft model

Pitch rate/sideslip effects on leading-edge extension vortices of anF/A-18 aircraft model

Navier-Stokes predictions for the F-18 wing and fuselage at large incidence

Navier-Stokes solutions have been obtained using the Chimera overset grid scheme for flow over the wing, fuselage, and wing leading-edge extension (LEX) of the F-18 aircraft at high incidence. Solutions are also presented for flow over the fuselage forebody at high angles of attack. The solutions are for turbulent flows at high-Reynolds-number flight-test conditions, and are compared with available qualitative and quantitative experimental data. Comparisons of predicted surface flow patterns, off-surface flow visualizations, and surface- pressure distributions are in good agreement with flight-test data. The ability of the numerical method to predict the bursting of the LEX vortex as it encounters the adverse pressure gradient field of the wing is demonstrated. HIGH angle-of-attack technology program is currently underway Vvithin NASA. The objectives of the program include the development of flight-valida ted design methods that accurately predict the aerodynamics and flight dynamics of aircraft maneuvering in the high-angle-of-attack regime. Toward meeting these objectives, the program integrates ground-based experimental and computational investigations with flight-test investigations conducted on an F-18 at the NASA Ames-D den Flight Research Facility. The flight tests include surface 1 off-surface flow visualizations, as well as quantitative m irements of the flow surrounding the air- craft at large i ence. This database provides a unique op- portunity for C '•-).) code validation at actual high-alpha flight conditions. This paper presents results of Navier-Stokes com- putations of the flow about the wing, fuselage, and wing lead- ing-edge extension (LEX) of the F-18 at conditions matching those of the flight tests. Previous numerical predictions for the isolated F-18 fuselage forebody were reported in Refs. 1-3. Numerical prediction of the flow over aircraft flying at large angles of attack is a difficult aerodynamic problem. High- angle-of-attack flows contain large regions of three-dimen- sional separated flow, where the boundary layers leave the surface of the body along surfaces of separation, and roll up on the leeward side of the body to form strong, concentrated vortical flows. Separated flows historically have been treated by a wide variety of computational methods, ranging from simple potential flow methods to time-marching Navier-Stokes techniques. However, the close coupling that exists between the strength and location of the leeward vortical flow and the location of the viscous layer separation lines has precluded