Vortex Roll-up Research Articles

Computational Study of Shocked V-Shaped N2/SF6 Interface across Varying Mach Numbers

The Mach number effect on the Richtmyer–Meshkov instability (RMI) evolution of the shocked V-shaped N2/SF6 interface is numerically studied in this research. Four distinct Mach numbers are taken into consideration for this purpose: Ms=1.12,1.22,1.42, and 1.62. A two-dimensional space of compressible two-component Euler equations is simulated using a high-order modal discontinuous Galerkin approach to computational simulations. The numerical results show good consistency when compared to the available experimental data. The computational results show that the RMI evolution in the shocked V-shaped N2/SF6 interface is critically dependent on the Mach number. The flow field, interface deformation, intricate wave patterns, inward jet development, and vorticity generation are all strongly impacted by the shock Mach number. As the Mach number increases, the V-shaped interface deforms differently, and the distance between the Mach stem and the triple points varies depending on the Mach number. Compared to lower Mach numbers, higher ones produce larger rolled-up vortex chains. A thorough analysis of the Mach number effect identifies the factors that propel the creation of vorticity during the interaction phase. Moreover, kinetic energy and enstrophy both dramatically rise with increasing Mach number. Lastly, a detailed analysis is carried out to determine how the Mach number affects the temporal variations in the V-shaped interface’s features.

Wake flow behind a transversely rotating sphere confined in a pipe at low Reynolds numbers

Direct numerical simulations are performed to investigate the flow past a transversely rotating sphere confined in a pipe. Three sphere diameters of d=0.2D, 0.5D, and 0.8D (D is the pipe diameter) and sphere Reynolds numbers (based on the sphere cross-sectional mean velocity and d) of Res=250–500 are considered. The simulation results highlight the combined effects of the blockage ratio (BR=d/D) and the nondimensionalized rotation rate Ω in the range of 0.2–1.2 on the wake flow. For each BR, with increasing Res and Ω, the wake flow undergoes a transition of the flow pattern from steady symmetry and unsteady symmetry to unsteady asymmetry. For BR=0.2, the variation in flow behaviors with Ω is similar to those reported in the previous studies on a transversely rotating sphere subjected to a uniform flow. With increasing BR from 0.2 to 0.5, the unsteady asymmetric wake flow is characterized by distorted near-wake vortex rings and a series of staggered inward rolled-up vortex arcs on the double streamwise vortex threads, which results in a low-frequency modulation of the unsteady wake flow. These rolled-up vortex arcs are connected with downstream quasi-streamwise vortices and form hairpin-like vortices. Dynamic Mode Decomposition (DMD) analysis shows that the distorted near-wake vortex rings are associated with the antisymmetric DMD mode at the adjacent frequency around the symmetric primary DMD mode. With BR=0.8, there is a drastic increase in the sphere's force coefficients. A more complex wake flow behavior is found due to a strong interaction between the wake flow and the near-pipe-wall flow. At Ω=1.2, dominant asymmetric flow structures are characterized by impingement of the vortex filaments. The low-frequency modulation of these wake structures is also analyzed using the DMD analysis.

Aerodynamic and acoustic investigations of rotor-rotor wake interaction

The paper presents part of the experimental activities carried out in the GARTEUR Action Group RC/AG-26 to study the acoustic and aerodynamic characteristics of small rotor configurations, including the influence of the rotor-rotor interactions. Two rotors, equipped with two-bladed propellers of a diameter of D=330.2 mm, were operated at two rotating speeds of 8025 RPM and 10120 RPM and arranged in different configurations. Isolated rotor and two different coaxial configurations in hover conditions were assessed. The aerodynamic loads and the rotor slipstream characterisation, in terms of flow field velocity, tip vortex characterization as well as acoustics emissions, were performed using a six-component load cell, Particle Image Velocimetry and microphone measurements. The isolated pusher rotor presented better aerodynamic performance with respect to the puller one. The coaxial configurations result in a loss of thrust and an increase in torque compared to the isolated rotors. The upper rotor is barely affected by the presence of the lower one, while the lower rotor experiences a thrust loss ranging from 17 to 19%. The configuration with the larger rotor distance experiences greater performance loss. The mean velocity fields of the isolated rotors are measured and compared with the coaxial configurations for assessing the roto-rotor interaction, the results support the aerodynamic behaviour. The isolated rotor slipstream characterisation was carried out by phase-locked measurements covering the full rotor azimuth angle range from 0° to 350° with an increment of 30°. Tip vortex paths are followed up to a vortex age of 3.5 rotor revolutions. The 3D reconstruction of the tip vortices is conducted to gain insight into the slipstream behaviour and enhance the occurring vortex roll-up during the second revolution. The tip vortex jitter is investigated and the anisotropic distribution is confirmed along the slipstream. Furthermore, the noise emission intensifies in magnitude for the coaxial configuration with increasing relative gap between the rotors. The turbulent kinetic energy and the meandering of the blade tip vortices support the findings of the acoustics results.

Analysis of coherent structures over interacting barchan dunes based on tomographic particle image velocimetry

The influence of barchan dune interaction upon unsteady flow separation and wake dynamics around the fixed-bed downstream barchan dune (DBD) model are experimentally investigated at a Reynolds number of 2640 based on the tomographic particle image velocimetry (PIV) system. The time-averaged statistics including the mean velocities, recirculation area, vortex spatial topology, Reynolds stress, and turbulent kinetic energy were used to characterize the flow field and large-scale anisotropy. It was found that arch-shaped vortex “chains” with strong spanwise coherence shedding from isolated barchan crestline populate the whole wake region, while elongated rod-shaped vortex structures with strong streamwise coherence induced by the up-downwash flow around the DBD were found to fill the whole measurement range, which is closely related to “sheltering” effect on the incoming flow acting at DBD due to the presence of upstream barchan dune (UBD). Additionally, in order to study the complex dynamic features of these predominated vortex structure transformations, time-resolved planar particle image velocimetry was applied. This technique allows for providing complementary insights into the temporal behavior of the unsteady coherent flow structures populating the wake field in different experimental configurations. It was found that the basic unsteady flapping motion, vortex roll-up, and complex vortex interactions including vortex pairing, merging, and breaking up can all be analyzed by dividing into certain scales with ease in a combination wavelet and Lagrangian framework.

Integrated Three-Dimensional Airloads and Stresses on Lift-Offset Coaxial Rotors at Extreme Speeds

This paper investigates the three-dimensional (3-D) dynamic stresses on a modern four-bladed hingeless coaxial rotor—inspired by the gross dimensions of the Sikorsky S-97 Raider at extreme flight speeds. The stresses are obtained using integrated 3-D (I3D) aeromechanical analysis—defined as the coupling of 3-D finite element-based structural dynamics with 3-D Reynolds-averaged Navier–Stokes–based fluid dynamics. The coupling was carried out with the University of Maryland/U.S. Army structural dynamic solver X3D and the U.S. Army CREATETM–AV Helios suite of fluid dynamic solvers. The new structural analysis is both enabled and driven by advanced high-performance computing, parallel and scalable solvers, high-order 3-D brick finite elements unified with multibody dynamics, integrated aeromechanics, and a special 3D-to-1D fluid–structure interface that refines the power of the delta-coupling procedure while retaining the advantages of existing computational fluid dynamics mesh motion schemes. The analysis is carried out at 220 knots (μ=0.5)—the cruise speed of the S-97 Raider without reduced tip speed—in order to study the stresses in extreme conditions. At such high speeds, the blade lift is dominated by the complex tip vortex roll-up, and the pitching moments and drag are dominated by the unsteady transonic shocks at the tip. Interesting 3-D dynamic stress patterns are revealed all across the blade that have remained invisible until now since they could neither be predicted nor measured in flight. The key conclusion is that such high-fidelity analysis is now indeed possible and, in fact, necessary to get deeper insights into the dynamics of coaxial rotors at extreme speeds.

Frequency response of separated flows on a plunging finite wing with spoilers

The effectiveness of lift and bending moment reduction on a plunging wing was investigated in an experimental study to understand the effects of unsteady wing motion. The frequency response of the lift/moment reduction was studied for finite-span mini-spoilers placed on a finite wing. Single, multiple, and spanwise periodic mini-spoilers located at various spanwise locations all exhibit a decaying frequency response of the effectiveness of lift/moment reduction with increasing frequency and amplitude of the oscillations. This happens for pre-stall angles of attack as the mini-spoilers induce shear layer separation, roll-up of vorticity, and recirculation regions, generating additional lift. For the post-stall angles of attack, stronger leading-edge vortices are already shed from the clean wing at high frequencies, and the spoilers are not able to influence the development of the vortices, resulting in a decaying frequency response. The cut-off frequency for all spoiler configurations is similar and scales with the reduced frequency at pre-stall angles of attack, whereas the Strouhal number based on the peak-to-peak amplitude of the plunge oscillations becomes the scaling parameter at post-stall angle of attack. The spoilers exhibit similar cut-off frequency to their two-dimensional counterparts. The finite-spoilers delay or displace the shear layer away from the wing surface, similar to the two-dimensional mechanisms.

Primary breakup of liquid jet—Effect of jet velocity profile

The present work examines the effect of the velocity profile on primary breakup of liquid jets emanating from fuel injectors. Direct numerical simulation is used to simulate liquid jet breakup. Different velocity profiles are imposed on the liquid and their effect on breakup is examined. It is a common practice in the literature to use flat or uniform velocity profiles in such studies. The validity of this assumption is assessed and its implications are highlighted. Droplet sizes and degree of atomization are compared for all the cases. Further, a detailed comparison of jet breakup structure is made for two cases—parabolic and power-law velocity profiles. The liquid surface is observed to show two-dimensional waves initially, which subsequently transform into three-dimensional waves and give rise to ligament formation and surface breakup. Tip vortex rollup and its role in jet breakup is discussed. The distinction between different velocity profiles is examined in detail in terms of surface waves, degree of atomization, and jet structure.

Aerodynamic Characterization of a Generic High-Speed Projectile Configuration

A combined experimental and numerical study was conducted on a generic projectile configuration with low-aspect-ratio fins. The main objectives of this study were to characterize the aerodynamic behavior and validate numerical simulations for a range of Mach numbers (0.4–4) to facilitate an understanding of major flow features such as forebody and fin-generated shock waves, crossflow shear layer vortex, and fin vortex interactions. Measurements included forces and moments, surface oil flow visualization, and high-speed shadowgraph imaging. Numerical simulations were performed using the CFD++ solver. The results showed an excellent match between the experimental and numerical force and moment data. Pressure contours obtained using numerical simulations were integrated to obtain the contributions of individual components toward the total normal force on the body. Flow visualization results show a few complex and interesting flow features, such as shear layer roll-up, crossflow and fin tip vortex interactions, and shock-wave–boundary-layer interactions. The effects of vortex strength and location were analyzed to determine their contributions to the overall forces on the model. The database generated will be very useful for further validation of the numerical tool and a better understanding of vortex-dominated supersonic flows.

Effect of moving end wall on tip leakage flow in a compressor cascade with different clearance heights

Numerical simulations have been carried out to investigate the effect of the moving end wall on the tip leakage flow structure in a compressor cascade with four different tip clearance heights. A detailed comparison of the leakage flow’s loss; mass flow rate; and the tip leakage vortex and its roll-up, trajectory, size, and interaction with the passage flow was made. The results show that the performance of the cascade changes more severely as the tip clearance height increases with the moving end wall than with the stationary end wall. The roll-up of the tip leakage vortex has been studied by analyzing the pathline structure and vorticity distribution. An alternative explanation is proposed for the initial roll-up mechanism of the tip leakage vortex. The vorticity transport is responsible for the initial roll-up of the vortex, whereas the leakage jet/passage flow shearing is responsible for the vortex development. The smaller the clearance height is, the easier it is for the moving end wall to alter the vorticity transport from the gap to the tip leakage vortex.

Investigation of flow characteristics and velocity fields of excited two parallel plane jets

An experimental investigation was conducted to study the flow characteristics and velocity fields of excited two parallel plane jets. The experiments were carried out at a jet Reynolds number of 200. A loudspeaker system was used to create the jets pulsation and to vary the intensity of jet pulsations at a constant excitation frequency of 40 Hz. A hot-wire anemometer was used to measure the velocities of the jets as they exited. The flow patterns were visualized using a laser-light sheet technique combined with smoke flow visualization. The jet spread widths were determined from images taken with a long-exposure method using binary edge detection. A particle image velocimetry measurement technique was used to render the flow field behaviors of the parallel jets. The introduction of jet pulsation by the speaker led to the roll-up of coherent vortices along the shear layers of the jets. These vortices became more prominent as the intensity of jet pulsations increased. These coherent vortices broke apart into turbulent eddies, resulting in wider jet spread with higher pulsation intensities. Two counter-rotating vortices were detected at the jet exit. These vortices moved closer to the jet exits as the jet pulsation intensity was increased. The intensity of turbulence and the presence of vortices were both influenced by the magnitude of the jet pulsation. Greater jet pulsation led to higher turbulence levels, a more pronounced vorticity field, and a more efficient transfer of momentum, consequently enhancing the mixing process.

A NEW MULTI-STAGE TURBINE STATOR DESIGN FOR IMPROVED PERFORMANCE RETENTION

Abstract An experimental and computational investigation into the deterioration of the first stage rotor shroud knife-edge seal clearance in a two-stage turbine which has engine representative cavity geometries. Four values of deterioration were investigated. Measurements within the first stage rotor shroud cavity show that whilst the leakage mass flow rate increases with deterioration, the angle at which the leakage flow approaches the downstream stator is essentially fixed. Because of the engine representative cavity geometry, the over-shroud leakage flow undergoes little mixing when it re-enters the mainstream and approaches the downstream stator at more than 60° negative incidence. Measurements at the exit of stator 2 identified two large positive vortices which were not consistent with the horseshoe vortex model for secondary flow. A computational investigation revealed that one originates from the rolling-up within the stator passage of the streamwise vorticity sheet associated with the first stage rotor over-shroud leakage. This roll-up vortex cannot be eliminated. The second is generated within the stator passage by the separation of the over-shroud leakage flow at the leading-edge due to the large negative incidence. This separation vortex might be eliminated by redesigning the stator. A new stator was designed, manufactured and tested. the roll-up vortex was still present but the separation vortex was eliminated. The new stator and the unchanged second stage rotor were reduced. It is estimated that the new stator would improve the lifetime average efficiency by 0.5%.

Investigations of spray breakup Rayleigh–Taylor instability via multiphase lattice Boltzmann flux solver

Poor fuel–air mixing of the diesel spray in low ambient temperature and pressure or thin air leads to intricate fuel breakup mechanism near the nozzle, which still remains worth of study. In this study, a pressure-based modified multiphase lattice Boltzmann flux solver (MLBFS) is proposed to accommodate the fuel spray breakup characteristics of multiphase, multicomponent, and large density ratio, in which the source terms of governing equation are modified emphatically for high injection pressure. Therefore, the characteristics of microscopic diesel spray breakup induced by Rayleigh–Taylor instability are investigated, including spray penetration, spray area, and spray arc length. It is revealed that the spray penetration is increased exponentially with the fuel–air density ratio Rρ. Influenced by air resistance and circulation interference, the roll-up vortex, droplet size, and spray area increase with the decreasing of Rρ (corresponding to high ambient pressure). Affected by entrainment and Rayleigh–Taylor instability, the development of the spray arc length experienced three stages: rapid growth, peak, and violent fluctuation, in which the lower Rρ facilitates development. It is concluded that Rayleigh–Taylor instability is favorable for stimulating the spray internal circulation of spray to enhance entrainment with surrounding air, while improving roll-up and breakup in the spray tail region. Such investigation is conductive to better understanding the micro-breakup mechanisms of fuel spray in the spray-induced internal combustion engine.

Optimization of Triangular Airfoils for Martian Helicopters Using Direct Numerical Simulations

Mars has a lower atmospheric density than Earth, and the speed of sound is lower due to its atmospheric composition and lower surface temperature. Consequently, Martian rotor blades operate in a low-Reynolds-number compressible regime that is atypical for terrestrial helicopters. Nonconventional airfoils with sharp edges and flat surfaces have shown improved performance under such conditions, and second-order-accurate Reynolds-averaged Navier–Stokes (RANS) and unsteady RANS (URANS) solvers have been combined with genetic algorithms to optimize them. However, flow over such airfoils is characterized by unsteady roll-up of coherent vortices that subsequently break down/transition. Accordingly, RANS/URANS solvers have limited predictive capability, especially at higher angles of attack where the aforementioned physics are more acute. To overcome this limitation, we undertake optimization using high-order direct numerical simulations (DNSs). Specifically, a triangular airfoil is optimized using DNSs. Multi-objective optimization is performed to maximize lift and minimize drag, yielding a Pareto front. Various quantities, including lift spectra and pressure distributions, are analyzed for airfoils on the Pareto front to elucidate flow physics that yield optimal performance. The optimized airfoils that form the Pareto front achieve up to a 48% increase in lift or a 28% reduction in drag compared to a reference triangular airfoil studied in the Mars Wind Tunnel at Tohoku University. The work constitutes the first use of DNSs for aerodynamic shape optimization.

Flow Structures and Aerodynamic Behavior of a Small-Scale Joined-Wing Aerial Vehicle under Subsonic Conditions

Flow behavior and aerodynamic performance of a small-scale joined-wing unmanned aerial vehicle (UAV) was studied experimentally and numerically under various pitch and yaw angle combinations in subsonic flow conditions. Selected numerical results are compared against experimental results obtained using surface oil flow visualizations and force measurements, with additional simulations expanding the range of combined pitch and yaw configurations. Under zero-yaw conditions, increasing the pitch angle leads to the formation of symmetric ogive vortex roll-ups close to the fuselage and their significant interactions with the fore-wing. Additionally, contributions to lift and drag coefficients under zero-yaw conditions by the key UAV components have been documented in detail. In contrast, when the UAV is subjected to combined pitch and yaw, no clear evidence of such ogive vortex roll-ups can be observed. Instead, asymmetric flow separations occur over the fuselage’s port side and resemble bluff-body flow behavior. Additionally, these flow separations become more complex, and they interact more with the fuselage and fore- and aft-wings when the yaw angle increases. Lift and drag variations due to different pitch and yaw angle combinations are also documented. Finally, rolling and yawing moment results suggest that the present UAV possesses adequate flight stability unless the pitch and yaw angles are high.

Characterization of the chemical kinetics of dimethyl ether (DME) in a controlled trajectory - rapid compression and expansion machine (CT-RCEM)

A numerical study of the chemical kinetics of dimethyl ether (DME)-air mixture is presented when compressed in a controlled trajectory - rapid compression and expansion machine (CT-RCEM). CT-RCEM accurately steers the piston trajectory, allowing a broad operating condition range and an easy operation without needing hardware intervention. This feature enables us to modify the thermodynamic route of compression/expansion by choosing the appropriate piston trajectory. Based on the computational fluid dynamics (CFD) data, DME-air’s chemical kinetics is examined via reaction pathway analysis to understand the effect of the thermodynamic path of compression on the ignition delay. This work first shows how the creviced piston head effectively suppresses roll-up vortices, resulting in spatial uniformity of temperature, species, and, ultimately, a single dominant global reaction pathway of C, H, and O elements of DME. Next, this study shows that for a given compression ratio, the longer compression time, i.e., the longer residence time for more chemical reactions to progress by the end of compression (EOC), does not necessarily have higher reaction progress at the EOC, and in turn, lengthens the ignition delay. This counter-intuitive effect is due to the higher average core temperature of the shorter compression time piston trajectory right before EOC for sufficient time, which triggers the reactions much faster than the longer compression time piston trajectory and shortens the ignition delay. Hence, CT-RCEM’s novel feature, i.e., the ability to attain the same EOC thermodynamic state with different thermodynamic paths of compression, leading to different species build-up by EOC and thereby affecting ignition delay, provides essential information for a deeper understanding of chemical kinetics.

Linear stability analysis of a three-dimensional laminar separation bubble on a finite wing

Disturbance amplification in a laminar separation bubble forming on the suction surface of a cantilevered NACA0018 wing at an angle of attack of 6° and Reynolds number of 1.25 × 105 is studied using a combination of particle image velocimetry measurements and local and non-local linear stability analyses. The experimental measurements reveal the formation of largely two-dimensional velocity fluctuations leading to the formation of initially two-dimensional roll-up vortices in the separated shear layer at a nearly constant wavenumber and frequency, despite the substantial reduction in the effective angle of attack near the wing tip. The most amplified wavenumber and its growth rate are accurately predicted by linear stability theory outside of the regions of the separation bubble dominated by three-dimensional end effects, with negligible differences between local and non-local stability analyses. Near the wing root and tip, an increase in the magnitudes of spanwise velocities is observed within the laminar separation bubble, and linear stability calculations predict a relative increase in the amplification of spanwise wavenumbers with the same sign as the spanwise flow. However, the calculations show that the most amplified disturbance remains essentially two-dimensional across the entire wingspan.

Numerical Simulation and Wind Tunnel Test of a Variable Geometry Auxiliary Inlet for a Wide-Body Aircraft Environmental Control System

A variable geometry auxiliary inlet for a wide-body aircraft environmental control system with moveable deflectors operating in a large mass flow rate range is studied through numerical simulation and wind tunnel tests, which yields a design method for the variable geometry auxiliary inlet with high performance. The characteristics of the flow field are studied by numerical simulation. The results show that the favorable pressure gradient and the roll-up vortices are the major impetus that inhales the incoming flow into the inlet. The law of regulation and the performance variation under different conditions are obtained by wind tunnel test. The flow coefficient increases first but then decreases with the increase in the inlet opening, and the pressure rise ratio and total pressure recovery coefficient increase first and then decrease with the increase in the mass flow rate. In general, under the condition of a high Mach number (Ma > 0.4), the inlet opening of this test configuration should not exceed 50%. The deflectors can maintain the normal work of the environmental control system by moving properly to control the mass flow rate of the auxiliary inlet.

Evolution of unsteady vortex structures in the tip region of an axial compressor rotor

The evolution of unsteady vortex structures in the tip region of an axial compressor rotor is investigated based on delayed detached eddy simulation. The vortex structures are identified by the LTcri method, and the velocity fields are visualized by the particle tracing method. The results show that the evolution of the tip leakage vortex (TLV) can be divided into three phases: the generation phase, the development phase, and the dissipation phase. The unsteadiness of the flow field mainly appears in the dissipation phase as a consequence of the unsteady secondary tip leakage. There are three primary unsteady vortex structures caused by the tip leakage flow (TLF), and these vortex structures are related to each other as a feedback loop. The intermittent formation of the vortex ropes leads to the breakdown of the TLV and thus results in the roll-up of the backflow vortex (BFV) due to the radial velocity gradient. The secondary leakage of the BFV locally enhances the TLF jet and affects the formation of the vortex ropes in turn. This feedback loop causes the unsteady behavior of the TLF and has great impacts on the performance and stability of the compressors.

Aerodynamic Load Reduction on a Supercritical Airfoil Using Tilted Microjets

Microjets arranged on the wing surfaces of civil transport aircraft have been shown to have great potential in suppressing high-frequency gust loads. This paper presents a study of aerodynamic load reduction on a supercritical airfoil using tilted microjets by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The numerical method was first validated against the experimental and previous numerical data. Afterward, the subsonic and transonic flowfields around the supercritical airfoil were simulated with various angled microjets. The results show that both the lift reduction and the power efficiencies significantly increase as the blowing direction shifts downstream to upstream. The movement and weakening of the shock due to the jet are observed at α > 2 ∘ in transonic flow, resulting in a drag reduction compared to the baseline airfoil. However, the transient subsonic results revealed that the upstream jet induces a strong vortex shedding, which is suppressed in transonic flows. During jet deployment, there are three distinct phases: time lag, vortex rolling-up, and rebalancing, in that order. Once it reaches the trailing edge in subsonic flows, the starting vortex rapidly modifies the load and induced a strong roll-up vortex from the pressure surface. Nevertheless, in transonic flow, the rebalancing stage contributes to a greater reduction in lift due to the additional shock movement and weakening effect.

Wake Vortex Far-Field of a Generic Transport Aircraft Affected by Oscillating Flaps

The influence of oscillating trailing-edge flaps of a generic transport aircraft on the middle and far fields of the wake vortex system is investigated. The aim is to be able to reduce separation distances between aircraft during approach in order to increase capacity at airports. By introducing a certain disturbance by means of oscillating flaps in the near field, the long-wavelength Crow instability should be excited in the further downstream development. The evolution of the wake vortex system is investigated using a large-eddy simulation approach. The wake vortex system is examined up to 133 spans downstream for two high-lift configurations. A nonactuated configuration with statically deflected flaps is compared to a configuration with actuated flaps. The results show that the long-wavelength Crow instability cannot be excited by actuated trailing-edge flaps. However, a faster decrease of the dimensionless circulation over the downstream position can be observed for the actuated configuration compared to the nonactuated configuration, due to a faster diffusion of the rolled-up vortex pair. Furthermore, the averaged induced rolling moment on an aircraft [with the International Civil Aviation Organization’s (ICAO’s) classification of “light”] encountering the wake vortex of the actuated configuration (ICAO’s classification of “heavy”) is up to 32.5% lower than for a follower aircraft, which is entering the wake vortex of the nonactuated configuration.