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The ditching processes of a blended-wing–body (BWB) aircraft under different initial speeds and pitch angles are simulated by numerically solving the unsteady Reynolds-averaged Navier–Stokes equations and the realizable [Formula: see text] turbulence model using the finite volume method. The volume-of-fluid model is adopted to capture the water–air interface. The six-degree-of-freedom model is employed to couple fluid dynamics and aircraft rigid-body kinematics. The global moving mesh is used to deal with the relative motion between the aircraft and the water. It is found that the plane composed of initial speed and pitch angle can be divided into two regions by a stability limit line, that is, the porpoising motion region (the aircraft takes coupled oscillatory motion between heaving and pitching) with large initial speeds and pitch angles and the stable motion region with low initial speeds and pitch angles. When the initial speed is large, the aircraft’s pitch-up moment peak and heaving amplitude are enhanced. Hence the aircraft carries out the porpoising motion. For the large initial pitch angle, the water entry depth of the aircraft increases and the waterline moves forward, which produces a more significant pitch-up moment peak and overload peak. As a result, the aircraft conducts the porpoising motion. The porpoising stability of the BWB configuration is obviously worse than the conventional and flying wing configurations. When the BWB aircraft ditches on water, the pilots should reduce the initial speed and pitch angle as much as possible to avoid the dangerous porpoising motion.

Airfoil trailing edge noise in low-to-moderate Reynolds number has multiple tonal noise. The frequency of the dominant tone has a ladder structure for the dependency on the free stream velocity, while the presence of the secondary tones is explained as an amplitude modulation by the primary single tone. However, during the jumping process, when the main tone is selected from two nearly equal strength tonal noise on the different ladders, the choice of the main tone and amplitude modulation theory are poorly investigated and lacks specific experiments at present. Hence, the switching process of trailing edge dominant tones of a NACA0012 airfoil at a Reynold number of around 130,000 is focused on by a simultaneous measurement of microphone and hot-wires at Beihang D7 aeroacoustics wind tunnel. The far field noise measurement confirms presence of two tones on time-average with a velocity range from 19.8m/s to 20.2m/s. For a freestream velocity of 20m/s, after selecting the time span by short-term Fourier transform, the wavelet contour maps of microphone present a random selection of the strongest tone, which is a switching tones pattern contradictory to the periodic amplitude modulation of only one tone. The simultaneous measurement results by two hotwires also show similar patterns with differences on the spanwise locations. This non-uniform spanwise alternation between frequencies rather than a consistent modification along the spanwise direction might contribute to the switching tones pattern in the microphone signals. A statistical analysis of the occurrence of two tones indicates that the switching tones pattern in sound pressure signals is greatly influenced by the spatial distribution of velocity on the spanwise direction as sound sources during the jumping process.

The ground effect aerodynamics and flow physics of a 2D dragonfly wing hovering (the Reynolds number is 157) in an inclined stroke plane are investigated via solving 2D unsteady incompressible laminar flow Navier–Stokes equations. An analysis road map is proposed to explain the influence of the ground on the flow field, pressure distribution on the wing surface, and the aerodynamic force. In the analysis road map, the flow relative to the wing surface induced by the wing motion and vortex is classified into vertical and parallel wing surface flows. The vertical flow impinges on the wing surface to form a positive pressure zone. In contrast, the parallel flow generates the boundary layer and further concentrated vortex and secondary vortex, which induce negative pressure on the wing surface. The ground impacts the flow relative to the wing in three ways: changing the trajectory of the shed vortex by the mirror effect, promoting the deformation and fusion of the vortices, and causing the cushion effect at extremely small ground clearance.

The unsteady lift characteristics of a double-delta wing were studied using both experimental and numerical approaches, which were also compared with a single-delta wing with the same main wing sweep angle. It was found that by increasing the reduced frequency of pitching, the hysteresis effect of lift was magnified. Moreover, in the high reduced frequency case k = 0.48, the difference between the lift coefficients of single- and double-delta wings became rather subtle. The wing surface pressure distribution results indicated the flow phenomenon of dramatic lift losses was due to the effect of lower surface suction during the wing being pitched downstroke. It was observed that, as the reduced frequency became sufficiently high, the virtual camber effect induced by pitching could dominate the flow field, which would mitigate the impact of wing geometry on the lift characteristics.

For correct identification of vortices, this paper first analyzes the properties of the rigid vortex core and its induced flow field given by the Rankine vortex model, and it is concluded that the concentrated vortex structure should consist of the vortex core and the induced flow field (the potential flow region with a weak shear layer). Then the vortex structure is analyzed by using the Oseen vortex model. Compared with the Rankine vortex, the Oseen vortex is a concentrated vortex with a deformed vortex core. The vortex structure consists of the vortex core region, the transition region and the shear layer region (or the potential flow region). The transition region reflects the properties of the resultant vorticity of the same magnitude and the resultant deformation rate of the shear layer, and the transition region also determines the boundary of the vortex core. Finally, the evolution of leading-edge vortices of the double-delta wing is numerically simulated. And with different vortex identification methods, the shape and the properties of the leading-edge vortices identified by each method are analyzed and compared. It is found that in the vorticity concentration region, the vortices obtained by using ω, λ2, Ω criteria and Q criteria are basically identical when appropriate threshold values are adopted. However, in the region where the vorticity is dispersed, due to the influence of the flow viscous effect and the adverse pressure gradient, the results obtained by different vortex identification methods can be quite different, as well as the related physical properties, which need to be further studied.

There is an increasing need to develop a two-dimensional (2D) water entry model including the slamming and transition stages for the 2.5-dimensional (2.5D) method being used on the take-off and water landing of seaplanes, and for the strip theory or 2D+t theory being used on the hull slamming. Motivated by that, this paper numerically studies the transition stage of the water entry of a linear wedge with constant and varying speeds, with assumptions that the fluid is incompressible, inviscid and with negligible effects of gravity and surface tension, and the flow is irrotational. For the constant speed impact, the similitude of the declining forces of different deadrise angles in the transition stage are found by scaling the difference between the maximum values in the slamming stage and the results of steady supercavitating flow. The formulation of the hydrodynamic force is conducted based on the similitude of the declining forces in the transition stage together with the linear increasing results in the slamming stage. For the varying speed impact, the hydrodynamic force caused by the acceleration effect in the transition stage is formulated by an added mass coefficient with an averaged increase of 27.13% compared with that of slamming stage. Finally, a general expression of the hydrodynamic forces in both the slamming and transition stages is thus proposed and has good predictions in the ranges of deadrise angles from 5 deg to 70 deg for both the constant and varying speed impacts., 47 pages, 32 figures, 3 tables

The goal of this paper is to study the difference in aerodynamics and flow physics of an air jet impinging on a solid ground and a water surface at low subsonic Mach numbers with different heights ...

The difference in aerodynamic forces of a two-dimensional flapping wing hovering in unbounded flow field and ground effect is studied. The unsteady laminar Navier–Stokes equations are solved by the finite volume method to simulate the flow field around the wing. In the unbounded flow field, the correspondence between the aerodynamic force, pressure distribution on wing, and typical vortex structures is established, and then the high-lift mechanism of the flapping wing is further explained. In the ground effect, based on the lift variation, the dimensionless height H/ C ( H is the height of the wing above ground and C is the chord length of the wing) can be divided into transition and ground effect regimes. In the transition regime ( H/ C > 2.5), the lift decreases with the decreasing height, and the ground indirectly impacts the vortices near wing by changing the shed vortices in space. In the ground effect regime ( H/ C

In the traditional high-lift system design process, the aerodynamics optimization design and mechanism design are decoupled, which often introduces contradiction and trade-off between them. In this...

The energy conversion is proposed to analyze the effects of inertial force, surface tension, gravitational force and viscous force during the crown evolution of the drop impact phenomena. The incompressible laminar Navier–Stokes equations coupled with the volume of fluid model are solved numerically in the axisymmetric frame to simulate the impact process. The influences of both the ratio of the initial kinetic energy to the surface tension energy of the drop as well as the initial film thickness on the energy conversion during the impact process are studied in detail. The ratio of the initial kinetic energy to the surface tension energy of the drop can affect the energy conversion at a very early stage of the impact process, thus it can affect the occurrence of prompt splash significantly; while the initial film thickness can affect the energy conversion process during the whole impact process, and it is related to the occurrence of delayed splash. The energy conversion process corresponds to the type of impact phenomena, which is affected by the film depth significantly. according to the differences in energy curves and flow characteristics, the impact phenomenon is divided into three types: the drop impacts on shallow, medium and deep films. A typical impact process of the medium film is analyzed in detail. The impact process is divided into five stages, namely, crown formation, crown growth, crown stabilization, crown collapse and central jet formation. In the crown formation and growth stages, inertial force promotes the deformation of the liquid-gas interface and surface tension prevents the deformation; while in the crown collapse stage, inertial force prevents the deformation and surface tension does the opposite effect. During the whole process, the viscous force plays a prevention effect.

Experiments on the interactions between a single vortex/co-rotating vortices and the ground were conducted in a water channel using particle image velocimetry (PIV) measurements. Both the single vo...

This paper proposes an approximate solution for the varying speed impact of three-dimensional (3D) bodies on the water surface, with the assumptions that the fluid is considered to be incompressible, inviscid, weightless, and with negligible surface tension effects and the flow to be irrotational. The approximate solution provides a linear relationship between Cp and a dimensionless variable K, and the equation of body acceleration. These equations can be used to rapidly predict the pressure distribution on the body surface and the motions of the body. The predictions of the approximate solution match the computational fluid dynamics results very well for the varying speed impacts, including the normal and oblique impacts of a cone on the water surface and the normal impact of a pyramid on the water surface. The present approximate solution can be suitable for the two-dimensional, axisymmetric, and fully 3D impacts of bodies on the water surface with varying speed.

Hydrodynamic drag not only results in high-energy consumption for water vehicles but also impedes the increase of vehicle speed. The introduction of a low-viscosity gas lubricating film is assumed to be an effective and promising method to reduce hydrodynamic drag. However, the poor stability of the gas film and massive extra energy consumption restricts the practical application of the gas lubricating method. Herein, inspired by the microhairs with low surface energy wax covering the abdomen of water spiders, superhydrophobic sphere surfaces were designed. Attributed to numerous neighboring nanoneedle branches with low surface energy chemicals, an air-entrained cavity with a large surface area was captured and stabilized by the superhydrophobic sphere, changing its shape from a sphere to a streamlined body. The cavity continued attaching to the superhydrophobic sphere without bursting at a depth of 70.0-90.0 cm underwater and reduced the hydrodynamic drag by more than 90%. This work provides a simple, cost-effective, and energy-efficient way to stabilize the underwater gas-liquid interface to achieve a reduction in the hydrodynamic drag.

As an ultra-wide bandgap semiconductor, gallium oxide (Ga2O3) holds great application potential in deep-ultraviolet (DUV) photodetectors. While the performance of photodetectors based on crystalline Ga2O3 thin films grown on hard substrates has been continuously improved, photodetectors based on amorphous Ga2O3 grown on less-stringent substrates in a more convenient and accessible way emerged as alternative technology and received increasing attention. Herein, we choose thulium (Tm) for doping and grow amorphous Tm-Ga2O3 films on non-lattice-matched flexible mica substrates. Thanks to the larger bandgap of Tm2O3 (∼6.5 eV) and stronger Tm–O bond, the (Tm xGa1− x)2O3 films possess broadened bandgap and lessened oxygen vacancies compared to pure Ga2O3. Consequently, the photodetectors that were produced based on these amorphous (Tm xGa1− x)2O3 films exhibit high performances with both low dark current and fast response speed (36.47 pA and 0.07 s at x = 0.05) and well maintain the performance after multiple cycles of bending at radius as small as 5 mm. This work sheds light on the development of flexible devices based on amorphous (Tm xGa1− x)2O3 for solar-blind DUV detection.

The varying speed impact of wedge bodies on a water surface is studied numerically and theoretically to provide a fast and accurate prediction of the pressure on the wedge surface and the motion of wedge bodies during the free impact, which can be a two-dimensional (2D) model for the strip theory or 2D + t strategy. The fluid is assumed to be incompressible, inviscid, with negligible gravity effect and surface tension effect. The computational fluid dynamics (CFD) method is based on the volume of fluid (VOF) method and global moving mesh (GMM) method. Various cases of a varying speed impact are shown for the CFD method, and a linear relationship between the pressure coefficient Cp and a dimensionless variable K is observed. To clearly explain the linear relationship between Cp and K, we follow the potential theory to derive the Cp expression based on several assumptions on the free surface drawn from the CFD results. The Cp expression and the motion of wedge bodies for a free impact derived from it are considered as an approximate solution for a varying speed impact. The approximate solution is compared with the existing analytical models and the published experimental data. The approximate solution can work well for different deadrise angles, while the existing analytical models can only be used for small deadrise angles. Good agreement is also obtained between the approximate solution and the experimental test results, including the time history of wedge acceleration and the pressure on the wedge surface.

The interaction between the asymmetric vortex pair and the ground was experimentally investigated in a closed-circuit water channel for the current study. Particle image velocimetry tests were conducted to achieve the velocity measurements of flow fields at various crossflow planes. The vortex pair, with the reference circulation Reynolds number ReΓ ≈ 4490, was tested with various initial heights (h0/b0 = 1.5, 1.0 and 0.5) and circulation ratios (λ = 0.36:1, 1:0.36, 0.6:1, 1:0.6), with it being found that according to different interaction effects, the trajectory and merger of the vortex pair could be significantly affected. As the primary vortex pair approached the ground, a high turbulent kinetic energy region was observed between the secondary and primary vortical structures, which suggests violent interaction and accelerated circulation decay of the primary vortex. In addition, depending on the distribution of secondary vorticity and image vortices to the moving coordinate system, merging-promoting or -inhibiting effects were observed, which eventually affected the evolution of the primary vortex pair.

The impacts of a plate on an asymmetric water wedge with a constant speed and with varying speed are studied in this paper by considering the fluid to be incompressible, inviscid, weightless and with negligible surface tension effect and the flow to be irrotational. We derive the analytical solution for the impact with a constant speed with the help of Wagner’s function and Schwarz-Christophel mapping technique, and then proceed the numerical process given by following an iterative method. The verification is conducted by comparing the profile of free surface and the pressure distribution predicted by the present method and the published data. The impact with varying speed is first studied by VOF method and compared with the impact with a constant speed. An approximate solution is provided for the impact with speed that satisfies a power law of time based on the CFD results from VOF method. The approximate solution can provide an explicit expression for the pressure that is acting on the plate, which can describe the effects of the changing impact speed and the acceleration of plate.

The initial spray caused by a rolling aircraft elastic pneumatic tire is studied by Smoothed Particle Hydrodynamics method. The tire spray is divided into four types: bow wave, rooster tail, impact-generated side plume and wave-generated side plume. The distributions of the particles involved in the different types of spray in the initial unperturbed water film are studied, with the relationship between the momentum transfer, the relative position of water particles and the aircraft tire being proposed. The impact-generated side plume is caused by the direct impact of tire, while the wave-generated side plume is caused by the breakup of the wave developed by the tire. The particles involved in the wave-generated side plume all come from a parabolic region inside the strip of initial injected particles at a given time. The width of the parabolic region reduces with the increasing water depth. The strips and the kinematic characteristics of particles at any time are both similar. A model is developed to predict the direction and magnitude of the momentum transfer velocity in water film based on the similarity of the strips and the kinematic characteristics of the particles, which works well for the cases with small tire load and thick water film.

By using the finite volume method with volume of fluid model and global dynamic mesh technique, the effects of Froude number and geometry on the water entry process of a 2-D ellipse are investigated numerically. For the time history of the vertical force, the computational fluid dynamics (CFD) results match the experimental data much better than the classical potential-flow theories due to the consideration of the viscosity, turbulence, surface tension, gravity, and compressibility. The results show that the position of peak pressure on ellipse shifts from the spray root to the bottom of ellipse at a critical time. The critical time changes with the geometry and Froude number. By studying the vertical force, the ellipse water entry process can be divided into the initial and late stages based on the critical dimensionless time of about 0.1. The geometry of the ellipse plays a dominant role in the initial stage, while the Froude number is more important in the late stage of entry. The classical Wagner theory is extended to the ellipse water entry, and the predicted maximum value of vertical force coefficient in the initial stage is 4πa/b that matches the CFD results very well, where a and b are the horizontal axis and vertical axis of the ellipse parallel and perpendicular to the initial calm water surface, respectively.

During the take-off and landing of aircrafts from/on water-contaminated runways, the tire-generated water spray can endanger flight safety, such as engine spray ingestion and spray impingement drag. In this paper, the flow physics and chine control of the spray generated by an aircraft rigid tire are studied by the Smoothed Particle Hydrodynamics (SPH) method. The SPH method is validated by a NASA experiment. The forming and developing progresses of the front and side sprays are described in detail. It is found that the parabolic stripe of initial ejected particles at a given time is the boundary between the spray source region and the non-disturbed region in water film, and the stripes at any time are similar. The effects of tire speed and water film depth on spray angles are evaluated. The chines can effectively control the spray angles by reducing the vertical velocity component of the ejected particles and increasing the lateral component. The arc chines are more effective in controlling the spray than the linear chines.

The ditching performance of a BWB aircraft is studied using the numerical method. The unsteady Reynolds-Averaged Navier-Stokes equations and the Realizable k − e turbulence model are solved by the finite volume method, the implicit volume-of-fluid model is adopted to capture the water-air interface, the six-degree-of-freedom model is employed to couple fluid dynamics and aircraft rigid-body kinematics, and the global moving mesh is used to deal with the relative motion between the aircraft and the water. The accuracy of the present numerical method is validated by the high-speed ditching experiment of a 3D flat plate. The porpoising motion of the BWB aircraft during ditching is discovered for the first time, and this motion is independent of the initial pitch angle, i.e., the amplitude and period of the motion and load curves are coincident for different initial angles. The porpoising motion is determined by a couple of hydrodynamic and aerodynamic loads, and the total load peak is mainly caused by the former. The hydrodynamic load is mainly from the staggered positive-negative pressure stripe on the aircraft belly. The variation in aerodynamic load is mainly induced by the compression work in the dynamic ground effect.

The aerodynamics and flow physics of a close-coupled canard configuration W40C60 (the sweep angles of the wing and canard are 40° and 60°, respectively) with sharp leading edge at the angle of attack of 12.0° in static ground effect are investigated by the Delayed Detached Eddy Simulation grounded on Spalart–Allmaras turbulence model. With the ride height decreasing, the lift, drag, nose-down pitching moment and lift to drag ratio of W40C60 increase nonlinearly. In the unbounded flow field, both the canard lift increment and the wing lift decrement due to Wing/Canard Interference (WCI) stem mainly from the leeward surface. With the ride height decreasing, the canard lift increment due to WCI will increase and the wing lift decrement due to WCI will decrease, which is because both the canard and wing windward surface lift increments due to WCI increase significantly with the decreasing ride height. The windward surface lift behaviors are also interpreted as that the windward surface pressure increment of canard and wing of W40C60 due to ground effect is larger than that of the canard alone and the wing alone, respectively. This is because the WCI increases the effective chord length so that the effective dimensionless ride height of W40C60 is smaller than those of the canard alone and the wing alone at the same nominal dimensionless ride height.

The aircraft water spray test on water-contaminated runways is of great significance in the civil aircraft airworthiness certification. It is a very complex strongly nonlinear multiphysics process ...

Wind tunnel tests of five propellers with different blade tip widths are carried at pitch angles between 20.5° and 40°. The aerodynamic performance are provided, which can be treated as a supplement of the high altitude airship propeller database. The influences of the blade planform and advance ratio on both power coefficient and propulsive efficiency are analyzed. It is found that at advance ratio below 0.8, the propeller with narrow tip has higher efficiency but limited power coefficient. While at advance ratio above 0.8, the propeller with wider tip has the advantages of higher power coefficient and acceptable efficiency. The variation of the propulsive efficiency with planform and advance ratio is dominated by the radial distributions of the airflow angle and interference angle.

The energy conversion is proposed to analyze the effects of liquid properties on the formation of an ejecta sheet, prompt splashing, and crown evolution. The incompressible laminar Navier–Stokes equations coupled with the volume-of-fluid (VOF) model are solved numerically in an axisymmetric frame to simulate the impact process. Based on the energy conversion curves and liquid–gas interface shapes, the Weber number is shown to be the main dimensionless quantity controlling the impact process, especially with regard to crown evolution. However, the Reynolds number does have some influence on the drop impact process, especially during the stage of ejecta sheet formation and prompt splashing. By studying energy conversion during the impact process, the crown evolution is shown to be accelerated significantly with decreasing Weber number, but is hardly affected by the Reynolds number. A linear relation is found between the time to the moment of crown stabilization (when the crown height reaches its maximum value) and the square root of the Weber number. The relationship between the Weber number and the energy distribution at the moment of crown stabilization is also studied.

The pitching oscillations (α from 0° to 60°) of a close-coupled coplanar canard configuration were investigated at various reduced frequencies ( k = 0.0375 , 0.075, 0.15, 0.3, 0.6 and 1.2). Both experiments and numerical simulations were carried out to study the differences of dynamic flow characteristics for the configurations with and without a canard ( k = 0.0375 and 0.6). It was found that lift hysteresis occurred for both a delta wing and canard configuration at various reduced frequencies. At k ≥ 0.6 , the orientation of the lift hysteresis loop of the canard became reversed. During the upstroke pitching, a transition phenomenon occurred, in which the canard-wing vortices switched from a counter-rotating vortex system to a co-rotating one. This is due to variation of the effective angle of attack and the canard vortex formed over the lower surface during pitching at k ≥ 0.3. As the wing pitched downstroke, the canard vortex and its mirror brought strong downwash flow close to the symmetric plane, which created a high positive pressure region on the upper surface of the wing and eventually led to substantial lift loss.

The experiments were conducted in a water tunnel facility and were aimed at investigating the merging process of co-rotating wake vortices in ground effect. A corresponding two-dimensional analytical model was also introduced based on experimental results. The two like-sign vortices were generated with equal size and strength above the ground plane. The evolution of vortex pair was attained by using particle image velocimetry at a series of downstream locations. The main finding is that the ground effect promotes the merging process and accelerates the vortices' rotation around one another. Vertical movements, known as vortex rebound, and lateral movements are observed. The ground effect also leads to the emergence of a secondary vortex ( SV ), which adds to the complexity of the vortex system. Prediction of the modified potential model, which takes vortex decay, viscous drag and the evolution of the SV into account, is compared with the experimental data. The results show that the vortex merging and rebound of a co-rotating vortex pair is successfully predicted and the prediction of vortex orientation and lateral motion are also improved by this model.

During takeoff and landing processes, the aerodynamic characteristics of a delta wing configuration aircraft are influenced by the dynamic ground effect (DGE). In this paper, the DGE during the landing process of a 65° sweep delta wing (VFE-2) with sharp leading edge is numerically studied at AOA = 23°. The unsteady compressible Reynolds-Averaged Navier–Stokes equations and Spalart–Allmaras turbulence model are discretized using the finite volume method. With the ride height decreasing, the lift, drag and nose-down pitching moment increase nonlinearly, and the increments become larger with the sink velocity increasing. The DGE can be divided into three regions based on the aerodynamics and flow physics. In the large ride height region, the aerodynamic forces in DGE remain unchanged with the ride height decreasing, and they are equal to those in static ground effect (SGE) as long as the angles of attack (AOAs) are equal; the ground effect (GE) can be neglected. In the medium ride height region, the aerodynamic forces in DGE increase slowly with the ride height decreasing, and they are still equal to those in SGE as long as the AOAs are equal; SGE governs the flow. In the small ride height region, the aerodynamic forces in DGE increase significantly with the ride height decreasing, and they are much larger than those in SGE although the AOAs are equal; SGE and compression work effect govern the flow together. Among them, SGE stagnates the airflow under the delta wing, increasing the pressure on the windward surface; simultaneously, it enhances the primary vortex strength, promotes its breakdown and drives it outward along the span. The compression work effect further increases the pressure on the windward surface; however, it has little influence on the airflow over the delta wing.

A numerical study of the transient deformation and drag properties of impulsively started decelerating drops in axisymmetric flows is conducted. The incompressible Navier–Stokes equations coupled with the volume of fraction method are solved. The differences in the deformation and drag characteristics between the accelerating and decelerating drops are elucidated. The Weber number We has a significant influence on the drag properties of the round drops; however, the effect of the Ohnesorge number Oh is small. A dynamic droplet drag model is provided based on the computational fluid dynamics results to predict the drag coefficient of a decelerating drop. In addition, the flow of liquid drops past an RAE2822 airfoil is considered, and its drag is evaluated using the drag model.

The aerodynamic response to sideslip is crucial for an aircraft’s lateral stability, especially for configurations incorporating vortex flow, on which sideslip causes asymmetric vortex behavior and brings extra complexity. In this work, vortex flow over a close-coupled canard configuration under sideslip is simulated using delayed detached-eddy simulation, with the angle of attack varying up to the poststall regime. Sideslip-induced distinctions in both vortex dynamics and canard/wing-vortex interaction are analyzed to explain the nonlinear response of the configuration. The results reveal that the effect of sideslip differs significantly upon different angle-of-attack regimes. At a medium angle of attack, the spanwise extension of the low-pressure area due to windward vortex core expansion results in superior windward lift against the leeward side, but the relatively low pressure retained due to delay of the leeward vortex breakdown is the main motivation that leeward lift surpasses windward at a high an...

The unsteady aerodynamic characteristics of a 50° sweep delta wing performing pitching oscillations at angle of attack between 0° and 60° were tested in a water channel facility. Both force and velocity measurement results were analyzed and compared with the numerical simulation results for the pitching reduced frequency of 0.069 and 0.55. Both lift hysteresis and an unsteady phenomenon of leading-edge vortex (LEV) evolution were observed, which were significantly influenced by the pitch rate of the wing. As the wing pitch rate became sufficiently high, instead of being dissipated and convecting downstream, the LEV remained over the suction surface of the wing, which provide additional lift overshoot at a high angle of attack. In addition, as the wing pitched downstroke due to the negative induced camber effect, the lower surface of the wing turned from a pressure surface to a suction one and hence, there were significant lift losses.

Although β-Ga2O3 is considered an excellent candidate for solar-blind photodetectors (PDs) owing to its direct bandgap (4.9 eV) and high stability, the cut-off wavelength often oversteps the DUV region, reducing the rejection ratio of the PD. Moreover, oxygen vacancies, which always appear in β-Ga2O3 films, act as trap centers hindering carrier recombination and significantly lowering response speed. To disentangle these issues, we propose in this work to modify β-Ga2O3 by incorporating Sc to form ternary (ScGa)2O3 alloys. Thanks to the wider bandgap of Sc2O3 (∼5.7 eV) than Ga2O3 and stronger Sc–O bonding than Ga–O, the (ScGa)2O3 alloy films exhibit a wider bandgap (5.17 eV) with fewer oxygen vacancies compared with pure-Ga2O3, as expected, which eventually lead to an ultra-low dark current (0.08 pA at 10 V) and faster response times (τrise: 41/149 ms; τdecay: 22/153 ms) of the alloy film-based PDs. Furthermore, the peak and cut-off response wavelengths of the (ScGa)2O3 PD are blue shifted relative to the pure Ga2O3 PD, resulting in a higher rejection ratio (>500 vs ∼317). The Sc-alloying strategy, taking advantage of wider bandgap of Sc2O3 and stronger Sc–O bonding to widen the bandgap while reducing the intrinsic carriers and oxygen vacancies in the (ScGa)2O3 alloy, is expected to be generally applicable to the design of other wide-bandgap oxide alloys for developing high-performance UV photodetectors with a low dark current and high response speed.

In this paper, numerical method is used study the extreme impact load and its physical causes during the wavy aircraft ditching. the finite volume method and VOF method are used to capture the free surface, six degrees of freedom model and global motion mesh to deal with the relative motion between water and aircraft. and simulate the forced landing process of the aircraft. By choosing the place with the largest vertical velocity relative to the water as the impact position, the extreme impact load on the fuselage is predicted. In this paper, during the impact stage of the wavy water surface, the fuselage encountered an impact peak which is unforeseen on the calm water surface, and the magnitude of the impact peak was related to the sinking speed of the aircraft relative to the water surface. This paper also compares the movement attitude and overload history of aircraft ditching under five sea conditions with different wave height, and gives the influence rules of wave height on the extreme impact load and the peak values of other parameters, which provides a reference for the design of aircraft load distribution.

An approximate solution is proposed for the impact of wedge bodies on wedge-shaped water surfaces with varying speed, based on the similarity solution of the impact with a constant speed. The approximate solution can give fast predictions of the pressure distribution on the wedge surface and the motion of the wedge bodies in the initial stage where the impact speed is high and the peak acceleration occurs. In this study, the impact speed in the initial stage is large enough that we can simplify the water to be incompressible, weightless and inviscid, the effect of surface tension to be negligible, and the flow to be irrotational. Thus, the velocity potential can be introduced to describe the problem with complex variables. First, the similarity solution for the impact with a constant speed is derived based on Wagner’s function and Schwarz–Christoffel formula, and it agrees well with the existing methods. Second, the approximate solution for the impact with varying speed is proposed based on the above similarity solution and the CFD results, by neglecting the jet region where the pressure coefficient is small. The approximate solution can give the explicit expressions of pressure coefficient and wedge body’s acceleration. In the range (-2, 1) of dimensionless variable K , the prediction of the approximate solution matches the CFD results very well.

The co-rotating vortex pair merger in the convergent and divergent channel flow was investigated in both equal and unequal cases. The crossflow flow phenomenon of vortex pair merger was acquired by applying particle image velocimetry in a series of streamwise locations. The main finding is that the resultant single-side-wall deflection convergent and divergent channel flow can vary the merging rate and merging trajectories of the equal vortex pair. In the unequal vortex merger, distortion and absorption of the weaker vortex by the stronger vortex were observed, which is different from the mutual induction phenomenon in the equal strength vortex pair case. Furthermore, it was found that the flow converging and diverging have common effects on the merging process in both equal and unequal vortex merger. In the convergent channel flow, vortex pair separation experienced early reduction at upper stream locations, and the merger was accelerated. As the vortex pair developed further downstream, the difference in the merger progress among different channel flow environments becomes less significant, which is believed to be due to the combined effect of pressure gradient and developing time variations.