Transient Lift Research Articles

Data-driven transient lift attenuation for extreme vortex gust–airfoil interactions

We present a data-driven feedforward control to attenuate large transient lift experienced by an airfoil disturbed by an extreme level of discrete vortex gust. The current analysis uses a nonlinear machine-learning technique to compress the high-dimensional flow dynamics onto a low-dimensional manifold. While the interaction dynamics between the airfoil and extreme vortex gust are parametrized by its size, gust ratio and position, the wake responses are well captured on this simple manifold. The effect of extreme vortex disturbance about the undisturbed baseline flows can be extracted in a physically interpretable manner. Furthermore, we call on phase-amplitude reduction to model and control the complex nonlinear extreme aerodynamic flows. The present phase-amplitude reduction model reveals the sensitivity of the dynamical system in terms of the phase shift and amplitude change induced by external forcing with respect to the baseline periodic orbit. By performing the phase-amplitude analysis for a latent dynamical model identified by sparse regression, the sensitivity functions of low-dimensionalized aerodynamic flows for both phase and amplitude are derived. With the phase and amplitude sensitivity functions, optimal forcing can be determined to quickly suppress the effect of extreme vortex gusts towards the undisturbed states in a low-order space. The present optimal flow modification built upon the machine-learned low-dimensional subspace quickly alleviates the impact of transient vortex gusts for a variety of extreme aerodynamic scenarios, providing a potential foundation for flight of small-scale air vehicles in adverse atmospheric conditions.

Laminar separation bubble formation and bursting on a finite wing

The transient processes of laminar separation bubble (LSB) formation and bursting on a rectangular NACA 0018 wing are studied experimentally. A two-dimensional airfoil model is used as a baseline for the assessment of finite wing effects. The models are subjected to ramp changes in free-stream velocity causing the flow to switch between a state where an LSB forms and a state without reattachment. Lift force and particle image velocimetry measurements are used to relate the flow development to the aerodynamic loading. The lift coefficient of the airfoil exhibits substantial hysteresis, and the duration of the lift transients range from $10$ to $22$ convective time scales for bubble formation and $22$ to $30$ convective time scales for bursting. In contrast, the transient lift coefficients of the wing change gradually, with less hysteresis. The wing tip causes greater three-dimensionality in the separation bubble, whose thickness increases near the midspan where bursting is initiated. During bubble formation, the region of separated flow contracts towards the midspan. The gradual change in lift of the wing is linked to slower spanwise expansion and contraction of the separated flow region relative to the airfoil. On both models, the wavenumbers and amplitudes of disturbances in the separated shear layer rapidly change when reattachment initiates or ceases. Applying the bursting criterion of Gaster (Tech. Rep. Reports and Memoranda 3595. Aeronautical Research Council, London, 1967) to the bubble on the wing shows that bursting of the bubble at a single spanwise location is insufficient to cause complete spanwise failure of reattachment, and that the relationship between bursting parameters depends on spanwise position.

The perturbation of PAHs on mosses in Aberdeen, Scotland, as a consequence of social restrictions imposed during the COVID-19 pandemic

Air quality and the concentration of polycyclic aromatic hydrocarbons (PAHs) in urban environments are increasingly becoming a concern. Measuring air quality and PAHs, and linking these to specific activities, requires deploying and recovering sampling devices to capture and measure any changes. From May 2020 to June 2021, during the “lockdown” period of the COVID-19 pandemic, acrocarpous and pleurocarpous mosses were collected from five types of site in Aberdeen, United Kingdom, and the concentration of PAHs measured to track changes in PAHs as travel-related activities changed. The predominant types of PAHs found on mosses were of the four- and five-ring varieties, with the four-ring variety of PAH (medium molecular weight) becoming more dominant as the lockdown was lifted. However, for most sites, the concentration of PAHs was evidently perturbed by the transient lifting, reimposing, and then lifting of lockdown conditions, which either directly limited travel or changed people’s motivations to travel by car. Molecular diagnostic ratios or molecular marker parameters used to infer the source of PAHs varied little and were nearly always consistent with PAHs deriving from combustion in vehicle engines. Thus, even when travel was limited, PAHs were still derived from vehicle usage, although the overall concentrations on mosses were much lower. On average, the lowest PAH concentrations were found on mosses collected from a recreational park located the furthest from traffic. The highest PAH concentrations were observed on mosses collected from residential car parks during periods when the lockdown had been lifted. However, mosses from the same residential car parks had very low PAH concentrations during periods of travel restrictions, strongly suggesting that, for mosses, local factors and patterns of vehicle usage strongly determine their exposure to PAHs. Therefore, mosses within urban environments can be used for monthly monitoring of PAHs as they are able to detect changes induced by human behaviour.

Fluid-structure interaction simulation for multi-body flexible morphing structures

The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously. Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation. However, the unsteady aerodynamic characteristics with the fluid–structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation. In this paper, a fluid–structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated, and the aerodynamic characteristics during deformation were compared with different skin flexibility, flow field environment, actuation mode and actuation time. The numerical results show that for the steady aerodynamic, the skin flexibility can improve the stability efficiency. In the unsteady process, the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics, while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.

Aerodynamic Characteristics of a Z-Shaped Folding Wing

Z-shaped folding wings have the potential to enhance the flight performance of an aircraft, contingent upon its mission requirements. However, the current scope of research on unmanned aerial vehicles (UAVs) with Z-shaped folding wings primarily focuses on the analysis of their folding structure and aeroelasticity-related vibrations. Computational fluid dynamics methods and dynamic meshing are employed to examine the folding process of Z-shaped folding wings. By comparing the steady aerodynamic characteristics of Z-shaped folding wings with those of conventional wings, this investigation explores the dynamic aerodynamic properties of Z-shaped folding wings at varying upward folding speeds. The numerical findings reveal that the folding of Z-shaped folding wings reduces the lift-to-drag ratio, yet simultaneously diminishes the nose-down pitching moment, thereby augmenting maneuverability. Concerning unsteady aerodynamics, the transient lift and drag coefficients of the folded wing initially increase and subsequently decrease as the folding angle increases at small angles of attack. Likewise, the nose-down pitching moment exhibits the same pattern in response to the folding angle. Additionally, the aerodynamic coefficients experience a slight decrease during the initial half of the folding process with increasing folding speed. Once the wing reaches approximately 40°~45° of folding, there is an abrupt change in the transient aerodynamic coefficients. Notably, this abrupt change is delayed with higher folding speeds, eventually converging to similar values across different folding speeds.

Flow Control around the UAS-S45 Pitching Airfoil Using a Dynamically Morphing Leading Edge (DMLE): A Numerical Study

This paper investigates the effect of the Dynamically Morphing Leading Edge (DMLE) on the flow structure and the behavior of dynamic stall vortices around a pitching UAS-S45 airfoil with the objective of controlling the dynamic stall. An unsteady parametrization framework was developed to model the time-varying motion of the leading edge. This scheme was then integrated within the Ansys-Fluent numerical solver by developing a User-Defined-Function (UDF), with the aim to dynamically deflect the airfoil boundaries, and to control the dynamic mesh used to morph and to further adapt it. The dynamic and sliding mesh techniques were used to simulate the unsteady flow around the sinusoidally pitching UAS-S45 airfoil. While the γ-Reθ turbulence model adequately captured the flow structures of dynamic airfoils associated with leading-edge vortex formations for a wide range of Reynolds numbers, two broader studies are here considered. Firstly, (i) an oscillating airfoil with the DMLE is investigated; the pitching-oscillation motion of an airfoil and its parameters are defined, such as the droop nose amplitude (AD) and the pitch angle at which the leading-edge morphing starts (MST). The effects of the AD and the MST on the aerodynamic performance was studied, and three different amplitude cases are considered. Secondly, (ii) the DMLE of an airfoil motion at stall angles of attack was investigated. In this case, the airfoil was set at stall angles of attack rather than oscillating it. This study will provide the transient lift and drag at different deflection frequencies of 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, and 10 Hz. The results showed that the lift coefficient for the airfoil increased by 20.15%, while a 16.58% delay in the dynamic stall angle was obtained for an oscillating airfoil with DMLE with AD = 0.01 and MST = 14.75°, as compared to the reference airfoil. Similarly, the lift coefficients for two other cases, where AD = 0.05 and AD = 0.0075, increased by 10.67% and 11.46%, respectively, compared to the reference airfoil. Furthermore, it was shown that the downward deflection of the leading edge increased the stall angle of attack and the nose-down pitching moment. Finally, it was concluded that the new radius of curvature of the DMLE airfoil minimized the streamwise adverse pressure gradient and prevented significant flow separation by delaying the Dynamic Stall Vortex (DSV) occurrence.

Energy Harvesting Performance of Thick Oscillating Airfoils Using a Discrete Vortex Model

Abstract The energy harvesting performance of thick oscillating airfoils is predicted using an inviscid discrete vortex model (DVM). National Advisory Committee for Aeronautics (NACA) airfoils with different leading-edge geometries are modeled that undergo sinusoidal heaving and pitching with reduced frequencies, k=fc/U∞, in the range 0.06−0.14, where f is the heaving frequency of the foil, c is the chord length, and U∞ is the freestream velocity. The airfoil pitches about the midchord with heaving and pitching amplitudes of h0=0.5c and θ0=70 deg, respectively, known to be in the range of peak energy harvesting efficiencies. A vortex shedding initiation criteria is proposed based on the transient local wall stress distribution determined from computational fluid dynamics (CFD) simulations and incorporates both timing and location of leading-edge separation. The scaled shedding times are shown to be predicted over the range of reduced frequencies using a timescale based on the leading-edge shear velocity and radius of curvature. The convection velocity of the shed vortices is also modeled based on the reduced frequency to better capture the dynamics of the leading-edge vortex. An empirical trailing-edge separation correction is applied to the transient force results using the effective angle of attack modified to include the pitching component. Impulse theory is applied to the DVM to calculate the transient lift force and compares well with the CFD simulations. Results show that the power output increases with increasing airfoil thickness and is most notable at higher reduced frequencies where the power output efficiency is highest.

MATHEMATICAL MODEL AND SIMULATION OF FREE BALLOON LIFTOFF IN THE PRESENCE OF SURFACE WINDS

A mathematical model of free balloon launches in windy conditions is based on the conservation of the linear momentum in horizontal and vertical axes. Linear momentum conservation equations are represented by a set of four nonlinear first-order ODEs. Some ODEs were solved analytically, while the nonlinear Riccati ODE with variable coefficients for the vertical acceleration was solved using numerical ODE solvers. Transient aerodynamic lift and horizontal drag are caused by the slip flow over the balloon envelope. It takes free balloon ten half times to reach 90.9% of the wind velocity in a step function response. A launch condition was developed in terms of the minimum required envelope temperature for which the net aerostatic lift overcomes inert weight of a balloon. Perturbation analysis was used to explore changes in the net aerostatic lift. Simulations were performed to cases with and without envelope distortion and enhanced cooling due to forced convection. Since all balloon takeoffs are performed downwind, obstacle clearance becomes an issue due to rapid loss of aerodynamic lift. Balloons may stop climbing and even start descending shortly after liftoff despite intense heating representing real hazard.

A leading-edge vortex initiation criteria for large amplitude foil oscillations using a discrete vortex model

A leading-edge vortex initiation criterion of an oscillating airfoil is shown to provide a means to predict the onset of leading-edge separation. This result is found to collapse the occurrence of separation during the oscillation cycle when scaled using the leading-edge shear velocity determined from the foil oscillating kinematic motion. This is of importance in developing low order models for predicting energy harvesting performance, as is shown in this study using an inviscid discrete vortex model (DVM). Results are obtained for a thin flat airfoil undergoing sinusoidal heaving and pitching motions with reduced frequencies of k=fc/U∞ in the range of 0.06–0.16, where f is the heaving frequency of the foil, c is the chord length, and U∞ is the freestream velocity. The airfoil pitches about the mid-chord, and the heaving and pitching amplitudes of the airfoil are ho=0.5c and θ0=70°, respectively, illustrating results for conditions near peak efficiency for energy harvesting. The DVM uses a panel method, applicable to a wide range of foil geometries. An empirical trailing-edge separation correction is also applied to the transient force results. The vortex shedding criterion is based on the transient local wall stress distribution determined using a computational fluid dynamics (CFD) simulation, indicating the time and location of zero stress at the foil surface. In addition, the local pressure gradient minimum is also used as a local indicator. The effects of a wide range of Reynolds numbers on separation are shown for the given range of reduced frequencies. The use of the effective angle of attack, when modified to include the pitching component, is also shown to correlate the leading-edge vortex initiation time. The advantage of the proposed separation criteria is that it can be fully determined from the motion kinematics and then applied to a wide range of low order models. Model results are given for the transient lift force and compare well with the CFD simulations. It is noted that at higher reduced frequencies the DVM overpredicts portions of the transient loads possibly caused by the reversed viscous flow from the trailing edge.

Numerical investigation of flow around a square cylinder in accelerated flow

To investigate the flow field evolution and resultant aerodynamic characteristics of a square cylinder during flow acceleration, large-eddy simulations were undertaken to simulate flow with a dimensionless acceleration rate ap of 0.0048. The adopted ap resembles that is likely to be experienced during a severe downburst wind storm. The tested incidence angle α ranges from 0° to 45° and the time-dependent Reynolds number Re [Re = U(t)D/v, where U(t) is the time-dependent inflow velocity and D and v are the cylinder length and the kinematic viscosity, respectively] varies from 0 to 5 × 104 throughout the simulation. Results revealed that the flow around a square cylinder in accelerated flow evolves through three distinct temporal flow phases: namely, Phase I (Ia and Ib) where no vortex shedding (the instantaneous lift force through this period is zero) is observed, Phase II, where periodic vortex shedding and associated lift force oscillations are initiated and enhanced, and Phase III where stable vortex shedding occurs. Phase I can be further broken down into Phase Ia, which is characterized by laminar shear layer separation and the existence of steady recirculation vortices in the near wake region, and Phase Ib (only present at α = 0° and 45°) which is distinguished by the presence of quasi-steady recirculation vortices behind the cylinder. Aside from the variation of flow patterns, the transient lift and drag coefficients and the wind pressure distributions, as well as the spatial evolution of three-dimensional flow structures and pressure distributions, are also elucidated in detail.

Roles of wing flexibility and kinematics in flapping wing aerodynamics

Insects are excellent fliers because of their ability to generate precise wing kinematics and deform their wings for the sufficient production of unsteady aerodynamic forces. Most of the previous studies on the effects of wing kinematics on the aerodynamics have been limited to the use of rigid wings, and leaves the contribution of wing flexibility unknown. Here, an experiment was conducted to investigate the effect of varied sweep duration and timing of rotation on the unsteady aerodynamic characteristics of hovering flexible and rigid wings at Re of 104. This study found that the forces generated by the flexible wing showed a conspicuous phase delay, which was more sensitive to the change in sweep duration than the timing of rotation. The transient negative lift associated with rigid wings undergoing delayed and advanced wing rotations totally disappeared in the flexible case. A digital particle image velocimetry (DPIV) measurement at the middle of stroke revealed a slight difference in the vortical structures surrounding the two wings in terms of proximity to the shed trailing-edge vortices (TEVs). Also, the linearly twisted nature of the flexible wing caused the coherent leading-edge vortex (LEV) to be stabilized throughout the wingspan. This increased the radial limit of the delayed stall from 3.6c in the rigid wing to 4.8c in the flexible wing. In general, the flexible wing with symmetric and delayed wing rotations generated the higher efficiency. The corresponding net force vectors were tilted in an almost vertical direction in comparison to the rigid wing. This is an indication that natural fliers adopt specific wing kinematics in addition to their wing deformation for the upward titling of their net force vector, which will significantly enhance their aerodynamic performance.

Modeling the Flow State Sensitivity of Actuation Response on a Stalled Airfoil

In this work, we perform direct numerical simulations of leading-edge momentum injection of a NACA0009 airfoil at poststall angles of attack. It is found that the lift response is highly dependent upon the instantaneous state of the wake at the time of actuation, which is characterized by the phase of the vortex-shedding limit cycle present in the unactuated system. In particular, we find that actuating at a phase of the limit cycle corresponding to the maximum lift gives the largest maximum in transient lift response, whereas actuating near the lift minimum gives a smaller initial transient lift enhancement and can lead to a significant reduction in the amplitude of the limit cycle. As well as characterizing this phase dependency, we develop a reduced-order model that can capture this behavior. This is achieved by applying dynamic mode decomposition with control to a concatenation of velocity and lift measurements from several training datasets. The resulting models can accurately capture the dynamics of the training datasets as well as for phases not included in the training data. We show that for this method of actuation, multiple control objectives with the same actuator can be achieved.

The effect of transient needle lift on the internal flow and near-nozzle spray characteristics for modern GDI systems investigated by high-speed X-ray imaging

The development of the injector nozzle is a dynamic area in regard of several technical aspects. At first, the internal flow influences the near-field spray characteristics via various phenomena such as cavitation and turbulence. However, these phenomena are not fully understood due to their extremely fast, complex and multiscale nature. Furthermore, it governs the spray targeting inside the combustion chamber. High-speed X-ray imaging of GDI injector nozzles is performed in this study. The experimental results presented are related to the internal flow and primary breakup of discharged liquid jets. The injectors used are equipped with nozzles made of aluminum which have been specially developed for these investigations to enhance optical accessibility. The visualization of the needle motion, in-nozzle flow and the primary breakup region provides several exciting observations. First, the needle lift tracking exhibits short overshooting right before the steady-state of the injection phase. This event leads to a short-term, however, significant change in the associated performance of the breakup. This phenomenon is found to be a consequence of the transient behavior of the in-nozzle flow. It is shown that under some circumstances hydraulic flip may occur during this overshooting period. The primary jet breakup region is visualized and evaluated by means of image processing. Thus, the transient behavior of liquid jet expansion is quantified in the vicinity of the nozzle. It is observed that the liquid jet direction deviates from the hole axis already at the nozzle outlet, which is caused by internal flow characteristics.

Probing microcavity switching events on the picosecond time scale using quantum dots as a broadband internal fluorescent source

We report on ultrafast all-optical switching experiments performed on pillar microcavities containing a collection of quantum dots (QDs). Using QDs as a broadband internal light source and a detection setup based on a streak camera, we track in parallel the frequencies of a large set (>10) of resonant modes of an isolated micropillar during the entire duration of switching events and with a 2 ps temporal resolution. Being much faster and more convenient than standard approaches based on pump–probe spectroscopy, this method is very well suited for in-depth studies of cavity switching, noticeably in view of applications in the field of quantum photonics. We report as a first demonstrative example an investigation of the switch-on time constant τon dependence as a function of the pump power and the observation of a remarkably low value of τon(≈1.5 ps) for optimized pumping conditions. As a second illustration, we report the observation of a transient lifting of the degeneracy of a polarization-degenerate cavity mode, induced by a non-centrosymmetric injection of free carriers.

Evaluation of vorticity forces in thermo-sensitive cavitating flow considering the local compressibility

The correlation between hydrodynamic forces and cavity evolution has been widely investigated but has not been deeply revealed. This study uses force element method to analyse the characteristics of force evolution along with cavitation around a NACA0015 hydrofoil. A modeling framework using the mixture two-phase flow model considering the energy convection and compressibility is proposed, to investigate the compressibility and thermal effects in the thermo-sensitive cavitating flow. Moreover, a force element method is applied for evaluating vorticity forces. The evolution of lift and drag coefficients under different cavitation numbers is mainly studied. Results indicate that, with increasing cavitation number, the time-averaged lift and drag coefficients firstly rise and then decline. However, the drag coefficient decline trend is greater than the lift coefficient. Combined with cavity evolution, the transient lift and drag evolution is analysed. Positive lift elements are mainly concentrates on the cavity surface and transport with cavity development, but the rupture of detached cavity and the pressure wave will inhibit the growth. The lift force reaches its peak when the cavity forms with the attached cavity that is completely detached from the hydrofoil surface, because of the volume of positive lift element reaches its maximum. Except for the shearing fracture of leading edge with the effect of fluid impact, the evolution of drag elements is similar to the lift. This studies shows that the force element method can well reveal the mechanism of force evolution due to the cavitation.

Aerodynamic characteristics of morphing wing with flexible leading-edge

The morphing wing can improve the flight performance during different phases. However, research has been subject to limitations in aerodynamic characteristics of the morphing wing with a flexible leading-edge. The computational fluid dynamic method and dynamic mesh were used to simulate the continuous morphing of the flexible leading-edge. After comparing the steady aerodynamic characteristics of morphing and conventional wings, this study examined the unsteady aerodynamic characteristics of morphing wings with upward and downward deflections of the leading-edge at different frequencies. The numerical results show that for the steady aerodynamic, the leading-edge deflection mainly affects the stall characteristic. The downward deflection of the leading-edge increases the stall angle of attack and nose-down pitching moment. The results are opposite for the upward deflection. For the unsteady aerodynamic, at a small angle of attack, the transient lift coefficient of the upward deflection, growing with the increase of deflection frequency, is larger than that of the static case. The transient lift coefficient of the downward deflection, decreasing with the increase of deflection frequency, is smaller than that of the static case. However, at a large angle of attack, an opposite effect of deflection frequency on the transient lift coefficient was demonstrated. The transient lift coefficient is larger than that of the static case when the leading edge is in the nose-up stage, and lower than that of the static one in the nose-down stage.

Experimental study of the effective parameters on the offshore wind turbine's airfoil in pitching case

Nowadays, wind energy plays a great role in the world's energy production. Detection and experimental measurement of the effective parameters on the transient lift and drag coefficients in the blades are very important in the wind turbine design. In this study, the aerodynamic coefficients of an oscillating wind turbine airfoil are evaluated. Due to the unsteady nature of the wind turbine's surrounding flow, blades are chosen according to the oscillating motion, which creates unsteadiness. The experiments are carried out using the constructed system in the Laboratory of Aerodynamics in the Hakim Sabzevari University. Firstly, experimental data were validated with the published experimental data. These coefficients operate as an oscillating force and result in increasing the fatigue tension. Therefore, the effective parameters in this paper, including reduced frequency, mean angle of attack, amplitude, and Reynolds number, were studied on the hysteresis loops in terms of real experimental conditions. Furthermore, in the last section of the research, the airfoil is corrected based on the entropy analyze results. Afterward, the unsteady aerodynamic coefficients corrected airfoil will be measured. The results show that a more suitable airfoil could be chosen based on the wind turbine's rotation frequency.

Leading-edge vortex formation and transient lift generation on a revolving wing at low Reynolds number

Both the transient formation and the stable attachment of leading-edge vortex (LEV) contribute to the high lift generation of an insect wing when it revolves at high angles of attack. In this study, we examined the LEV formation and the transient lift generation on a revolving wing with Reynolds number at 1500 and aspect ratio at 3, using combined computational and experimental methods. The wing started from stationary with a constant angular acceleration within a prescribed chord length of travel at its radius of gyration (i.e. λa), ranging from 0.25 to 2, and then revolved at a constant velocity. Our results showed that the rate of LEV development saturated when λa<1, resulting in a minimum chord length of travel of 2.5 to arrive at a steady LEV. This minimum travel distance agreed well with the prediction based on the vortex formation criterion proposed in other vortex generators. On the other hand, the instantaneous lift generation was strongly dependent on the instantaneous wing velocity and acceleration and therefore exhibited no saturation as λa decreases, which is seen in the LEV formation. The lift generation was attributed to the evolution of tangential vorticity according to the vortex impulse theory. Finally, the instantaneous volume-averaged LEV circulation at different angles of attack scaled well with the instantaneous velocity normal to the leading edge.

Modeling of transient hydrodynamic lifting forces of sailing yachts and study of their effect on maneuvering in waves

The calculation of hydrodynamic lifting forces sustained by a sailing yacht's hull performing maneuvers in regular incident waves is reported. The mathematical model involves the application of the lifting surface theory for transient flows, implemented through the numerical scheme of the vortex lattice method and corrected for linear thickness effects of the simulated body geometry. The mathematical influence of the waves appears through the derivation of the wave potential and it is employed in a kinematic sense via the introduction of an additional inflow velocity component on the lifting surface. Validation with data derived from experiments in calm water showed very good agreement. Additionally, the variation of the side force coefficient while sailing in waves has been quantified in terms of the amplitude of oscillation due to the wave orbital velocities. The formulation is intended to upgrade the respective computational component in a mathematical model previously developed by the authors, for the maneuvering motions of sailing yachts. Parametric studies of maneuvering and course-keeping demonstrate a sensitivity of the yacht to wave steepness and heading angles, with a deficit in sustaining capacity appearing for lower wind speed.

Leading-Edge Vortices: Mechanics and Modeling

The leading-edge vortex (LEV) is known to produce transient high lift in a wide variety of circumstances. The underlying physics of LEV formation, growth, and shedding are explored for a set of canonical wing motions including wing translation, rotation, and pitching. A review of the literature reveals that, while there are many similarities in the LEV physics of these motions, the resulting force histories can be dramatically different. In two-dimensional motions (translation and pitch), the LEV sheds soon after its formation; lift drops as the LEV moves away from the wing. Wing rotation, in contrast, incites a spanwise flow that, through Coriolis tilting, balances the streamwise vorticity fluxes to produce an LEV that remains attached to much of the wing and thus sustains high lift. The state of the art of vortex-based modeling to capture both the flow field and corresponding forces of these motions is reviewed, including closure conditions at the leading edge and approaches for data-driven strategies.