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The actuator line method (ALM) is increasingly being preferred to the ubiquitous blade element momentum (BEM) approach in several applications related to wind turbine simulation, thanks to the higher level of fidelity required by the design and analysis of modern machines. Its capability to resolve blade tip vortices and their effect on the blade load profile is, however, still unsatisfactory, especially when compared to other medium-fidelity methodologies such as the lifting line theory (LLT). Despite the numerical strategies proposed so far to overcome this limitation, the reason for such behavior is still unclear. To investigate this aspect, the present study uses the ALM tool developed by the authors for the ANSYS® Fluent® solver (v. 20.2) to simulate a NACA0018 finite wing for different pitch angles. Three different test cases were considered: high-fidelity blade-resolved computational fluid dynamics (CFD) simulations (to be used as a benchmark), standard ALM, and ALM with the spanwise force distribution coming from blade-resolved data (frozen ALM). The last option was included to isolate the effect of force projection, using three different smearing functions. For the postprocessing of the results, two different techniques were applied: the LineAverage sampling of the local angle of attack along the blade and state-of-the-art vortex identification methods (VIMs) to outline the blade vortex system. The analysis showed that the ALM can account for tip effects without the need for additional corrections, provided that the correct angle of attack sampling and force projection strategies are adopted. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The repeatable and determinate pattern of asymmetric vortices at a regular state can be obtained by manually setting an artificial micro-perturbation (AMP) on the nose tip of a pointed-nosed slender body at a high angle of attack (AoA). Wind tunnel experiments and numerical simulations were conducted to investigate the predominant role of AMP in an asymmetric flow at α = 50°. The bi-stable asymmetric flow structures are presented when AMP rotates around the body axis. Thus, the corresponding side force acting on the slender body is shown as a square wave with two periods. The shear layer separation is presented as the separation lines to investigate the bi-stable asymmetry induced by the AMP. Results show that the AMP restricts the flow separation on the same side of the model with itself when it is located at windward. The separation location on the same side of the AMP moves to the leeward of the model (or the separation angle on the same side of the AMP increases); hence, the vortex rolls up from this side later than the other side. When the AMP is located at leeward of the slender body, it promotes the separation of flow on the same side of the model with itself. Thus, the separation location on the same side of the AMP moves to the windward of the model (or the separation angle on the same side of the AMP decreases) and the vortex rolls up from this side earlier the other side. [ABSTRACT FROM AUTHOR]

The present study numerically investigates the aerodynamic performance of the morphing airfoil and wing with leading edge (LE) and trailing edge (TE) parabolic flaps. Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart-Allmaras (S-A) turbulence model are employed to simulate the flow fields. Firstly, the parameterization method for the morphing airfoil with LE and TE parabolic flaps is proposed. Secondly, the influence of several design parameters, namely, LE droop angle, LE droop position, TE deflection angle, and TE deflection position, on the airfoil aerodynamics are further explored. Moreover, the aspect ratio (AR) effect for the wing based on the morphing airfoil is also investigated. Simulation results demonstrate that the parabolic flaps outperform the articulated flaps in lift generation, drag reduction, and aerodynamic efficiency enhancement, with an improvement in CL and L/D by 39.2% and 108.4% at α=4° , respectively. A larger LE droop angle can increase the stall margin, whereas the LE droop position barely influences airfoil aerodynamics at small angles of attack. The increment of the TE deflection angle significantly augments the lift. As the TE deflection position moves downstream, the suction peaks at the LE and TE are decreased and flow separation is also delayed. Furthermore, a larger AR can achieve higher efficiency, whereas a smaller AR is more beneficial for flow separation suppression. [ABSTRACT FROM AUTHOR]

This study investigates how the debris cloud structure and hazardous fragment distribution vary with attack angle by simulating a circular cylinder projectile hypervelocity impinging on a thin plate using the finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method. Based on the comparison and analysis of the experimental and simulation results, the FE-SPH adaptive method was applied to address the hypervelocity yaw impact problem, and the variation law of the debris cloud structure with the attack angle was obtained. The screening criterion of the hazardous fragment at yaw impact is given by analyzing the debris formation obtained by the FE-SPH adaptive method, and the distribution characteristics of hazardous fragments and their relationship with the attack angle are given. Moreover, the velocity space was used to evaluate the distribution range and damage capability of asymmetric hazardous fragments. The maximum velocity angle was extended from fully symmetrical working conditions to asymmetrical cases to describe the asymmetrical debris cloud distribution range. In this range, the energy density was calculated to quantitatively analyze how much damage hazardous fragments inflict on the rear plate. The results showed that the number of hazardous fragments generated by the case near the 35° attack angle was the largest, the distribution range was the smallest, and the energy density was the largest. These results suggest that in this case, debris cloud generated by the impact had the strongest damage to the rear plate. [ABSTRACT FROM AUTHOR]

This paper introduces a generic model for the study of aerodynamic behaviour relevant to fifth-generation high-performance aircraft. The model design is presented, outlining simplifications made to retain the key features of modern high-performance vehicles while ensuring a manufacturable geometry. Subsonic wind tunnel tests were performed with force and moment balance measurements used to develop a database of experimental validation data for the platform at a freestream velocity of 20 m/s. Numerical simulations are also presented and validated by the experiments and further employed to ensure the vortex behaviour is consistent with contemporary high-performance platforms. A sensitivity study of the computational predictions from the turbulence modelling approach is also presented. This geometry is the first in a suite of representative aircraft geometries (the Sydney Standard Aerodynamic Models), in which all geometries, computational models, and experimental data are made openly available to the research community (accessible via this link: https://zenodo.org/communities/ssam%5fgen5/) to serve as validation test cases and promote best practices in aerodynamic modelling. [ABSTRACT FROM AUTHOR]

The large-range uncertainties of specific impulse, mass flow per second, aerodynamic coefficients and atmospheric density during rapid turning in solid launch vehicles (SLVs) ascending leads to the deviation of the actual trajectory from the reference one. One of the traditional trajectory tracking methods is to observe the uncertainties by Extended State Observer (ESO) and then modify the control commands. However, ESO cannot accurately estimate the uncertainties when the uncertainty ranges are large, which reduces the guidance accuracy. This paper introduces differential inclusion (DI) and designs a controller to solve the large-range parameter uncertainties problem. When above uncertainties have large ranges, it can be combined with the ascent dynamic equation and described as a DI system in the mathematical form of a set. If the DI system is stabilized, all the subsets are stabilized. Different from the traditional controllers, the parameters of the designed controller are calculated by the uncertain boundaries. Therefore, the controller can solve the problem of large-range parameter uncertainties of in ascending. Firstly, the ascent deviation system is obtained by linearization along the reference trajectory. The trajectory tracking system with engine parameters and aerodynamic uncertainties is described as an ascent DI system with respect to state deviation, which is called DI system. A DI adaptive saturation tracking controller (DIAST) is proposed to stabilize the DI system. Secondly, an improved barrier Lyapunov function (named time-varying tangent-log barrier Lyapunov function) is proposed to constrain the state deviations. Compared with traditional barrier Lyapunov function, it can dynamically adjust the boundary of deviation convergence, which improve the convergence rate and accuracy of altitude, velocity and LTIA deviation. In addition, the correction amplitudes of angle of attack (AOA) and angle of sideslip (AOS) need to be limited in order to guarantee that the overload constraint is not violated during actual flight. In this paper, a fixed time adaptive saturation compensation auxiliary system is designed to shorten the saturation time and accelerate the convergence rate, which eliminates the adverse effects caused by the saturation. Finally, it is proved that the state deviations are ultimately uniformly bounded under the action of DIAST controller. Simulation results show that the DI ascent tracking system is stabilized within the given uncertainty boundary values. The feasible bounds of uncertainty is broadened compared with Integrated Guidance and Control algorithm. Compared with Robust Gain-Scheduling Control method, the robustness to the engine parameters are greatly improved and the control variable is smoother. [ABSTRACT FROM AUTHOR]

This paper highlights the results and comparison of the flow topology investigation above the unmanned combat aerial vehicle (UCAV) configuration, namely, multidisciplinary design configuration (MULDICON), with modified leading-edge profile at the apex region from a sharp to a blunt profile to reduce the complexity of the flow structure above the wing. It was found from the flow visualization results that at a low angle of attack, for instance, 10°, the onset of the flow separation took place near the apex region; the onset of a tip vortex at the wing tip was also detected. At a medium angle of attack, for instance, 15°, the onset of the flow separation moved further upstream with the formation of the apex vortex, and the magnitude of the tip vortex increased due to increasing incoming flow with increasing the angle of attack. At higher angle of attack, for instance, 20°, the apex vortex intensity increased and wing tip vortices shedding is observed. Furthermore, at an angle of attack of 25°, the configuration is partially stalled, while a complete stalled occurred at an angle of attack of 30°. The current results obtained from this study have shown that the configuration has a maximum lift coefficient of 0.8 obtained from the K-Omega-SST turbulence model while it is 0.93 calculated from the Spalart-Allmaras turbulence model, while the maximum drag coefficient is 0.31 and 0.35, respectively, when calculated for the K-Omega-SST turbulence model and the Spalart-Allmaras turbulence model at an AOA of 25°. The flow visualization results revealed that there is a single flow separation due to modified leading edge from sharp to blunt, thus flow complexity is reduced. [ABSTRACT FROM AUTHOR]

We illustrate a technique by which heterodyne-detected sum-frequency generation spectroscopy is performed at multiple angles of incidence in order to decompose components of the second-order susceptibility tensor when all beams are polarized parallel to the plane of incidence. As an illustration, we study the non-vibrationally resonant gold response. We benchmark our results by comparing with measurements obtained in a polarization scheme that isolates a single element of the susceptibility tensor. Our technique is particularly valuable in the case of metal substrates, where the surface selection rule often prevents spectra from being acquired in multiple beam polarizations. [ABSTRACT FROM AUTHOR]

This study aims at investigating the ballistic resistance and energy absorption in woven E-glass composite panels, considering different projectile nose shapes and oblique incidence angles. To that scope, three-dimensional finite element (FE) models of both projectiles and the laminated target are developed and numerical investigations are carried out using Abaqus Explicit solver. The composite damage model's constitutive law encompasses nonlinear material response, material properties degradation, progressive failure, and an element deletion strategy. The cohesive surface technique is used to represent the interface between two adjacent plies in the laminate, and the traction-separation law is used to characterize the behaviors of interlaminar degradation and failure. Material responses attributable to fiber rupture, matrix cracking, and plasticity caused by micro-matrix cracking due to shear loading are taken into account with suitable damage evolution laws. The computational framework is first validated against the experimental results reported in the literature by performing ballistic impact tests on the target laminate with conical, hemispherical and blunt-ended projectile, and the numerical results showed a good comparison in terms of residual velocity. Subsequently the framework is explored in simulating more complex failure mechanisms, with particular emphasis on the influence of the impact angle of obliquity, a parameter that is not usually analyzed in the literature. In that regard, the effects of normal and oblique impact on the damage morphologies and ballistic behavior of the fabric composite target in terms of energy absorption, impact contact force, and projectile residual velocity are conducted and analyzed, comparatively. The findings showed that the ballistic impact behavior of target composite is substantially influenced by projectile nose shape and incidence angle obliquity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper sets out to investigate the vortex flow of spinnaker yacht sails, which are low-aspect-ratio highly cambered wings used to sail downwind. We tested three model-scale sails with the same sections but different twists over a range of angles of attack in a water tunnel at a Reynolds number of 21 000. We measured the forces with a balance and the velocity field with particle image velocimetry. The sails experience massively separated threedimensional flow and leading-edge vortices convect at half of the free-stream velocity in a turbulent shear layer. Despite the massive flow separation, the twist of the sail does not change the lift curve slope, in agreement with strip theory. As the angle of attack and the twist vary, flow reattachment might occur in the time-average sense, but this does not necessarily result in a higher lift to drag ratio as the vorticity field is marginally affected. Finally, we investigated the effect of secondary vorticity, vortex stretching and diffusion on the vorticity fluxes. Overall, these results provide new insights into the vortex flow and associated force generation mechanism of wings with massively separated flow. [ABSTRACT FROM AUTHOR]

This study presents the empirical comparison between the wing root and wingtip corrugation patterns of dragonfly wing in the newly-built wind-tunnel at the IAUN. The main objective of the research is to investigate the effect of wingtip and wing root corrugations on aerodynamic forces and the flow physics around the cross-sections at Re=10000 and the angle of attack of 0° to 30°. For this aim, two cross-sections are extracted from wing root (first cross-section) and wingtip (second cross-section). The first cross-section has corrugations with higher density than the second cross-section. The comparison of lift coefficients obtained from pressure distribution and force measurement indicates an acceptable agreement between the results. Also, Particle Image Velocity (PIV) technique is used to measure the velocity field. The results show that all corrugation patterns do not have positive effects on the aerodynamic forces. The second cross-section can generate considerable aerodynamic forces compared to the first cross-section. At a=25°, the lift coefficient generated by the second cross-section is 90% and 25% higher than that of the first cross-section and the flat plate, respectively. Based on results, corrugations in the wing root's vicinity have a crucial role in the solidity of insect wings; however, corrugations in the wing tip's vicinity play a vital role in generating adequate aerodynamic forces. The comparison conducted in the current research reveals the second cross-section is an appropriate replacement for the flat plate in MAVs due to generating more essential forces for flight. [ABSTRACT FROM AUTHOR]

A new acoustic metamaterial plate (AMP) is proposed herein. The plate incorporates Helmholtz resonators that are periodically embedded at intervals shorter than acoustic wavelengths. This metamaterial plate exhibits extraordinary sound transmission loss (STL) at the resonance frequency of the Helmholtz resonators compared to a conventional flat plate. The STL of the AMP can be theoretically analyzed using the effective mass density and flexural rigidity. At the resonant frequency, the dynamic density of the AMP becomes much larger than that of a conventional solid flat plate with the same mass. When the Helmholtz resonant frequency is tuned to the coincidence frequency of the AMP, the dip in transmission loss owing to the coincidence effect is not observed. The frequency band, wherein high STL occurs, is narrow; however, the frequency band can be widened by embedding multiple resonators with slightly different resonant frequencies. Numerical experiments are also performed to demonstrate the acoustic performance of the proposed system. In the simulation, Helmholtz resonators with the 2.1-kHz resonant frequency are embedded at 20-mm intervals inside a 6-mm-thick flat glass plate. Analytical solutions of this system agree well with numerical solutions for various incidence angles of incoming plane waves. In this configuration, we find that the degradation of STL caused by the coincidence effect is nearly eliminated for waves that are incident at random angles. [ABSTRACT FROM AUTHOR]

The structural and the optical properties of different Si nanostructures have been compared. Detailed optical properties of Si nanowires arrays of different optical lengths, fabricated by facile electroless etching technique, have been reported. The theoretical calculation of exponential sine profile at constant λ = 600 nm shows a better explanation in terms of gradient index with optical length for vertical nanowires. The observations signify the possibility of strong light trapping due to an exponential gradient towards the high index along the nanowires and the existence of dense subwavelength features. The optical admittance (Ƶ) shows a strong impact on optical distance (Z) for Z < H, owing to the electromagnetic wave interaction with the nanowires that perceive a different Ƶ at the oblique angle of incidence (AOI). In addition, the experimental reflectance data and the theoretical model for transverse electric and transverse magnetic modes predict that an optical length of 5 μm can exhibit a very low reflectance value. This indicates that the Si nanowires are polarization insensitive over a wide range of AOI (0°–80°). Moreover, Raman spectra showed a very strong light confinement effect in the first order transverse optical band with increasing etching depths. The morphological dependent resonance theory predicts a strong localized light field confinement in the lower wavelength regime for SiNWs. The effect on the strong resonant absorption modes was further correlated with the simulation results obtained by using COMSOL. The obtained results are likely to enhance the maximum absorption of SiNWs for various photonic applications. [ABSTRACT FROM AUTHOR]

Using pulsed femtosecond laser irradiation, we demonstrate the creation of an array of microgrooves within a single laser spot on metals. The orientation of these grooves is not limited to being parallel to the plane of the laser beam's propagation but can orient at any angle up to 30° from parallel. We control the orientation of the microgrooves by proportionally varying the laser's polarization. Polarization, angle of incidence, and structural evolution dynamics have been thoroughly studied to help us understand this phenomenon. Our studies suggest that the formation of angled microgroove arrays is due to a feedback effect occurring between defect-focused ablation and polarization-dependent laser-induced periodic surface structures. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the refraction and reflection of longitudinal (LD) waves at plane interface between micropolar elastic solid (MES) and electro-microelastic solid (EMS) half-spaces. A LD wave is taken to be impinge obliquely at the plane interface between MES and EMS half spaces. The ratios of amplitude of different type of refracted and reflected waves have been obtained numerically and results have been depicted graphically with the help of MATLAB Graphical routines. This has been observed that the mentioned amplitude ratios depend on the material properties and angle of incidence of incident waves. Also few particular cases have been discussed and then obtained result is compared with the exist ones. This study is very useful for the researchers pursing the research in the field of wave propagation and solid mechanics. [ABSTRACT FROM AUTHOR]

To understand the jet flow characteristics of turbofan separate exhaust system, a parametric design method based on the initial Class Shape Transformation function was developed. HBPR and UHBPR turbofan separate exhaust systems were designed. Furthermore, the jet flow characteristics of the HBPR turbofan exhaust system under take-off condition with zero angle of attack were studied based on numerical simulation. The jet flow characteristics of the HBPR and UHBPR turbofan exhaust system under take-off condition with high angle of attack were also simulated. The effects of angle of attack and bypass ratio on the jet flow characteristics were investigated and the related flow mechanisms were analyzed. Results show that the axisymmetric plumes of the HBPR turbofan exhaust system are distributed around the engine axis under take-off condition with zero angle of attack. With the plug wake as the center, the core flow, the fan/core shear layer, the fan flow, the fan/free stream shear layer and the free stream are wrapped around the plug wake from inside out. Vortexes appear in the lee area at the back of the cowl and jet flow under take-off condition with high angle of attack. These vortexes cause cross sectional secondary flow and expose the highvelocity core flow to the low-velocity free stream. The contact area and velocity gradient in the mixing region among the free stream, fan flow and core flow increase. Therefore, the mixture among jet flow and free stream strengthens. So the high-velocity region, the high-vorticity region, and the high turbulence kinetic energy region shorten by 55.1%, 47.7% and 50.9% respectively. The vorticity values and turbulence kinetic energy level peak on the upper side of the exhaust plumes increase by about 30% and 87% respectively. Relative to these parameters from the HBPR turbofan exhaust system, the jet velocity peak value of UHBPR turbofan decreases by 5.5% under take-off condition with high angle of attack. The vorticity values and turbulence kinetic energy level reduce due to decreased velocity gradient in shear layers downstream of the nozzle exit plane. The turbulence kinetic energy level peak on the upper side of the exhaust plumes decreases by 29.3%. The reasons are that the contact area between high-velocity core flow and the free stream decreases due to thicker fan flow and the velocity gradient in the core flow and free stream mixing region decreases because of the lower core flow velocity. [ABSTRACT FROM AUTHOR]

The unsteady vortex evolution of NACA 0012 airfoil is numerically investigated at low angles of attack ranging from 0° to 10° where the separation is performed from the trailing edge. The Reynolds number ranges between 1000 and 4000. The laminar separation bubble at the trailing edge is observed and the main flow features are presented. It is found that, the increase of the angle of attack and Reynolds number result higher lift to drag ratio by an extensive decrease of the drag coefficient below 8° angle of attack. The transition from the steady condition to periodic force evolution has been revealed with a detailed flow field analysis at different angles of attack and Reynolds numbers. The critical angle is defined as the angle of attack where the onset of oscillations starts with a dominant fundamental frequency of oscillation. The angle of attack where the laminar separation bubble (LSB) is observed is also revealed in the current study. Both the LSB formation angle and the critical angle of attack is found to decrease with the increase of the Reynolds number from 1000 to 4000. [ABSTRACT FROM AUTHOR]

Both underwater and wave gliders are known as autonomous unmanned energy-saving vehicles which have recently found applications for monitoring the world ocean. The paper under consideration discusses simplified mathematical models of these platforms enabling the straightforward parametric investigation into relationships between their parameters and performance. In its first part the paper discusses equations describing the motion of an underwater glider (UG) in a vertical plane as a basis for derivations relating geometric, kinematic and hydrodynamic characteristics of UG and its lifting system with relative differential buoyancy and pitch angle. Obtained therewith are formulae for the estimation of the UG glide path speed, lift-to-drag ratio, range of navigation and endurance. The approach is exemplified for typical cases of the UG conceived as winged bodies of revolution and flying wings. The calculated results feature dependencies of the UG speed on its configuration and volume as well as on the angle of attack for different magnitudes of relative buoyancy. Also considered is an optimal mode of operation, based on the maximization of the lift-to-drag ratio. The second part of the paper is dedicated to the estimation of the thrust and speed of a wave glider (WG), comprising a surface module (float) and underwater module represented by a wing, with the use of a simplified mathematical modeling intended to clarify the influence of the parameters upon the performance of the WG. The derivations led to an equation of forced oscillations of the vehicle accounting for the interaction of the upper and lower modules, connected by a rigid umbilical. The exciting impact of progressive waves of a given length and amplitude is found through the calculation of the variation of a buoyancy force in accordance with the Froude–Krylov hypothesis. The derivatives of time-varying lift with respect to kinematic parameters, entering the equation of vertical motion of the WG, as well as coefficients of instantaneous and time-averaged thrust force, are found by resorting to the oscillating hydrofoil theory. The derivation of the available thrust and the approximate calculation of the drag of the vehicle with account of wave and viscous components enable the evaluation of the speed of the WG for the prescribed geometry of the craft and wave motion parameters. [ABSTRACT FROM AUTHOR]

The variation in thrust generation with respect to Reynolds number was numerically evaluated for an oscillating foil with combined pitching and heaving motion at a range of reduced frequencies, amplitudes, and phase offsets. Laminar scaling (R e − 0.5 ) was found accurate for a reasonable range of average angle of attack ( α ¯ < 20 °). However, quantitative evaluation of laminar scaling using statistical measures indicates that its capability in predicting thrust variation weakens at higher reduced frequencies and amplitudes. This coincides with an increase in α ¯ above 20°. Evaluation of the pressure and viscous forces revealed a dominance of the former toward total thrust generated at high frequencies for all cases, which also coincided with lower coefficient of determination (R2) for laminar scaling. The chordwise variation of pressure and skin friction coefficient provided further evidence indicating that pressure, in contrast to the skin friction, did not achieve an asymptotic trend with increasing Reynolds number, especially at higher frequencies and for all phase offsets. Qualitative evaluation of the developing leading edge vortex structure at increasing reduced frequencies and Reynolds numbers also supported the quantitative assessment of chordwise pressure variations. Empirical incorporation of Reynolds number into the complete scaling model was hence completed, which further validates the laminar scaling (R e − 0.5 ) of propulsive thrust generation in oscillating foils with a coupled motion. [ABSTRACT FROM AUTHOR]

In the natural world, numerous flying creatures generate both thrust and lift by flapping their wings. Aerodynamic mechanisms of forward flight with flapping wings have received much attention from researchers. However, the majority of previous studies have simplified the forward-flight motion of flapping wings to be uniform, and there has been no detailed evaluation of the validity of this simplification. Motivated by this, aerodynamic characteristics of a self-propelled flapping wing with a non-zero angle of attack were investigated. The results showed that the asymmetric leading-edge vortex produced in the wing's upstroke and downstroke leads to transient thrust, driving the self-propelled wing to move with variable forward velocities. Compared to the uniform forward-flight cases, significant losses in lift and severe changes in the flow field were observed in self-propelled flapping wings. In addition, the changes in the aerodynamic performance—including the forward propulsion speed, lift, and power efficiency—of the self-propelled flapping wing with changes in various dimensionless parameters were also investigated. The heaving amplitude was shown to have significant effects on lift and propulsion speed of the self-propelled flapping wing, while the effects of ratio between the airfoil density and fluid density as well as the Reynolds number, were relatively small. In most conditions, when the Strouhal number was in the range 0.2–0.4, the self-propelled flapping wing performed well in terms of both lift generation and propulsive efficiency. These research results suggest that it is necessary to consider the fluctuating forward speed in aerodynamic modeling of propulsive flapping wings. [ABSTRACT FROM AUTHOR]

Copyright of Ordnance Industry Automation is the property of Editorial Board for Ordnance Industry Automation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this paper is to numerically investigate a new curved design of a counter flow double-pass solar air heater with arched baffles placed in the second duct. Due to high inertia of the flow and curved nature of design, fluid in second channel tend to move away from the absorber plate and thus, reduces the thermal efficiency significantly. In order to overcome this deficiency, new design parameters are introduced in the second duct in terms of arched baffles and their design is optimized for various geometric parameters such as angle of attack, variable pitch ratio etc. for best thermo-hydraulic performance. It was observed that arched baffles accelerate the flow near the absorber and facilitate the formation of large secondary vortices that enables multiple attachment zones at the absorber plate. Enhancement in thermal and hydraulic performances are discussed in terms of flow visualization, local Nusselt number, thermal effectiveness and friction factor ratio. Maximum enhancement of Nu in roughened curve counter double-pass solar air heater with baffle angles α/90 = 0.5 at P/d = 6 are found in the range of 20–28%, higher than without baffles. Moreover, two new regression correlations are developed for prediction of thermo-hydraulic performance in terms of geometrical and flow parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: Winglets play a major role in saving fuel costs because they reduce the lift-induced drag formed at the wingtips. The purpose of this paper is to obtain the best orientation of the winglet for the Office National d'Etudes et de Recherches Aérospatiales (ONERA) M6 wing at Mach number 0.84 in terms of lift to drag ratio. Design/methodology/approach: A computational fluid dynamics analysis of the wing-winglet configuration based on the ONERA M6 airfoil on drag reduction for different attack angles at Mach 0.84 was performed using analysis of systems Fluent. First, the best values of cant and sweep angles in terms of aerodynamic performance were selected by performing simulations. The analysis included cant angle values of 30°, 40°, 45°, 55°, 60°, 70° and 75°, while for the sweep angles 35°, 45°, 55°, 65° and 75° angles were used. The aerodynamic performance was measured in terms of the obtained lift to drag ratios. Findings: The results showed that slight alternations in the winglet configuration can improve aerodynamic performance for various attack angles. The best lift to drag ratio for the winglet was achieved at a cant angle of 30° and a sweep angle of 65°, which caused a 5.33% increase in the lift to drag ratio. The toe-out angle winglets as compared to the toe-in angles caused the lift to drag ratio to increase because of more attached flow at its surface. The maximum value of the lift to drag ratio was obtained with a toe-out angle (−5°) at an angle of attack 3° which was 2.53% greater than the zero-toed angle winglet. Originality/value: This work is relatively unique because the cant, sweep and toe angles were analyzed altogether and led to a significant reduction in drag as compared to wing without winglet. The wing model was compared with the results provided by National Aeronautics and Space Administration so this validated the simulation for different wing-winglet configurations. [ABSTRACT FROM AUTHOR]

The linear stability of a suspension of phototactic algae is investigated numerically with particular emphasis on the effects of angle of incidence of the illuminating oblique collimated irradiation. The solutions show a transition of the most unstable mode from stationary to overstable state or vice versa for certain parameters at the variation in angle of incidence. Furthermore, a transition from mode 2 to mode 1 instability is observed at the variation of angle of incidence for some parameter values. Oscillatory instabilities are also frequently observed in the rigid upper surface case at the increment in angle of incidence. [ABSTRACT FROM AUTHOR]

Three major factors lead to the deviation of actual power output of a photovoltaic (PV) panel from the rated value: irradiance, temperature and spectral factor. While the first two are well characterized, spectral factor remains less explored. Spectral factor depends on the spectral irradiance as well as the spectral response of the material. So far, normal irradiance is assumed for the estimation of the spectral factor which excludes one major factor, i.e. the angle of incidence (AOI). Here it is demonstrated that AOI has a strong effect on spectral factor due to multiple reasons. For a chosen PV material of monocrystalline Si, the AOI-dependence is obtained through the following parameters: reflectivity of a bare cell and a covered panel, the transmissivities of the cover system and the effective AOI on the PV cell after multiple refractions. When all these factors are incorporated in the estimation of spectral factor, a systematic underestimation (∼4.5%) is observed for the conventional method. Further the modified definition is tested for a chosen location of Kanpur, India for annual variations. Again a significant underestimation is noticed (∼3.5%), the value of which is expected to be higher for higher latitude locations due to greater obliquity of insolation. The effect of angle of incidence on the absorption and conversion is studied for a monocrystalline silicon solar photovoltaic panel. The spectral factor is demonstrated to be sensitive to the angle of incidence which alters the reflectivity, transmissivity of the cover system and the effective angle of incidence on the layer of photovoltaic material. [Display omitted] • AOI-dependence on spectral factor (SF) is estimated for m-Si PV module. • AOI-dependent spectral reflectivity is measured for bare PV cell. • AOI-dependent spectral transmissivity of cover material is measured. • Strong AOI dependence on SF-estimation is observed. • Seasonal variations of SF are illustrated for Kanpur, India. [ABSTRACT FROM AUTHOR]

Because a fluctuating incoming flow can affect with the unstable shock train movement, a numerical study was performed to analyze the effects. For the base flow with constant incoming and downstream flow conditions, the fundamental frequency and dominant role of the first separation shock are confirmed. The oscillations of the first separation shock are not always strengthened with an increase of the excitation amplitude at the resonant frequency. It is found that with a specific amplitude, the pressure peak in the shock wave/boundary layer interaction is enhanced, which can effectively suppress the upstream movement of the separation shock. However, a further increased excitation results in a wider oscillation region and greater pressure fluctuation. The non-negligible effects of the core flow enhance the oscillation of the separation shock. • Separated shocks on both sides periodically dominate and deflect the incoming flow. • Shock oscillations are not always strengthened with an enhanced excitation. • Favorable pressure gradient has a positive effect on the shock train motion. • Pressure peak in the boundary layer affects the suppression of the backpressure. [ABSTRACT FROM AUTHOR]

A numerical investigation has been made into the interaction of slender (5–20 calibers) steel cylinder strikers with orthotropic compost plates at velocities of up to 2000 m/s. The said interaction has been modeled in a threedimensional formulation within the framework of the phenomenological approach of continuum mechanics using the method of finite elements and the proprietary EFES software suite. We have identified the effects of orientation of elastic and strength parameters of a composite and a striker angle of attack on the destruction of a plate and the behavior of the striker in the process of its penetration into the plate. It is shown that the existence of an attack angle of the striker in its interaction with the plate results in the loss of the striker stability and exerts a substantiated effect on the destruction of the barrier. [ABSTRACT FROM AUTHOR]

In this project work, experiments are carried out in low-speed subsonic wind tunnel and 30-port multitube manometer used to study the aerodynamics characteristic of cambered airfoil model NACA5520 with different velocity range and various angle of attack. Experiments were made to investigate the pressure distribution over the airfoil under velocity range from 5m/s, 10m/s, 15 m/s, and 20 m/s and various x/s locations as 0.25, 0.5, and 0.75. The pressure measurements were taken using a multi-tube manometer and pitot-static tube over the cambered airfoil at different angles of attack. Hence, the distribution of the pressure coefficient (Cp) is calculated for the different operating conditions on the tapered blade. Also, the effect of pressure distribution over the tapered blade at different velocities and AOA is studied in spanwise location of the blade. [ABSTRACT FROM AUTHOR]

Even simple behaviors arise from the simultaneous activation of multiple regions in the brain. Thus, the ability to simultaneously stimulate multiple regions within a brain circuit should allow for better modulation of function. However, performing simultaneous multifocus ultrasound neuromodulation introduces challenges to transducer design. Using 3-D Fullwave simulations, we have designed an ultrasound neuromodulation array for nonhuman primates that: 1) can simultaneously focus on multiple targets and 2) include an imaging aperture for additional functional imaging. This design is based on a spherical array, with 128 15-mm elements distributed in a spherical helix pattern. It is shown that clustering the elements tightly around the 65-mm imaging aperture located at the top of the array improves targeting at shallow depths, near the skull surface. Spherical arrays have good focusing capabilities through the skull at the center of the array, but focusing on off-center locations is more challenging due to the natural geometric configuration and the angle of incidence with the skull. In order to mitigate this, the 64 elements closest to the aperture were rotated toward and focusing on a shallow target, and the 64 elements farthest from the aperture were rotated toward and focusing on a deeper target. Data illustrated that this array produced focusing on the somatosensory cortex with a gain of 4.38 and to the thalamus with a gain of 3.82. To improve upon this, the array placement was optimized based on phase aberration simulations, allowing for the elements with the largest impact on the gain at each focal point to be found. This optimization resulted in an array design that can focus on the somatosensory cortex with a gain of 5.19 and the thalamus with a gain of 4.45. Simulations were also performed to evaluate the ability of the array to focus on 28 additional brain regions, showing that off-center target regions can be stimulated, but those closer to the skull will require corrective steps to deliver the same amount of energy to those locations. This simulation and design process can be adapted to an individual monkey or human skull morphologies and specific target locations within individuals by using orientable 3-D printing of the transducer case and by electronic phase aberration correction. [ABSTRACT FROM AUTHOR]

The flapping wings or fins in an in-line arrangement are a common scene in flocks and schools, as well as flying creatures with multiple pairs of wings, e.g., dragonflies. Conventional studies on these topics are underpinned by tandem plunging airfoils in either a vertical or a declined stroke plane. The former model mostly considers a symmetrical pitching motion, and the latter model fails to separate the effect of the asymmetric pitching from that of the declined incoming flow. However, our study focuses on the tandem airfoils with vertical plunging and asymmetric pitching in a horizontal freestream and, therefore, explains the effects of asymmetric pitching on tandem plunging airfoils. Using numerical methods, the aerodynamic performance and vortical structures of the tandem airfoils are examined, and the effects of the non-zero geometric angle of attack (α0), phase angles in the plunging and pitching motion (φ and θ), and inter-foil spacing (G/c) are discussed. Our results show that the tandem arrangement is beneficial to enhance the propulsion thrust while retaining the lifting capacity of the airfoil at a non-zero α0. The effects of φ and G/c are coupled since they both determine the interaction between the hind airfoil and the leading-edge vortex in the wake and the out-of-phase mode is suggested for the tandem airfoils at G/c = 1 to enhance both lift and thrust. For a tandem airfoil with in-phase mode, the optimal G/c is around 1.5 to 2. Moreover, the asymmetric pitching of the in-phase plunging airfoils should be synchronized to retain the enhanced performance. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To solve the problem regarding the impact angle of the missile, this paper proposes a novel guidance law, which can control the missile to hit the target at the desired angle. The key of the guidance law is selecting a moving point on the collision line as the virtual target, and the tactical requirements can be fulfilled by the missile directly pursuing the virtual target. The Lyapunov stable theory is used to prove the convergence of the proposed guidance law. The guidance command is generated by a PID controller to make the missile towards the virtual target. The proposed guidance law makes the lateral acceleration of the missile converge to zero, which leads the angle of attack to zero, and it theoretically guarantees the flight path angle equals the attitude angle. Numerical simulations demonstrate this impact angle control guidance law is very accurate and robust. Regardless of whether the initial heading error is large or small, the missile which employs the proposed guidance law can always hit the target from the preset direction and the guidance process is smooth. [ABSTRACT FROM AUTHOR]

Lung ultrasound (LUS) is nowadays widely adopted by clinicians to evaluate the state of the lung surface. However, being mainly based on the evaluation of vertical artifacts, whose genesis is still unclear, LUS is affected by qualitative and subjective analyses. Even though semi-quantitative approaches supported by computer aided methods can reduce subjectivity, they do not consider the dependence of vertical artifacts on imaging parameters, and could not be classified as fully quantitative. They are indeed mainly based on scoring LUS images, reconstructed with standard clinical scanners, through the sole evaluation of visual patterns, whose visualization depends on imaging parameters. To develop quantitative techniques is therefore fundamental to understand which parameters influence the vertical artifacts' intensity. In this study, we quantitatively analyzed the dependence of nine vertical artifacts observed in a thorax phantom on four parameters, i.e., center frequency, focal point, bandwidth, and angle of incidence. The results showed how the vertical artifacts are significantly affected by these four parameters, and confirm that the center frequency is the most impactful parameter in artifacts' characterization. These parameters should hence be carefully considered when developing a LUS quantitative approach. [ABSTRACT FROM AUTHOR]

Principal angle of incidence and quasi-polarizing angle methods are performed to determine the spectral dependences of the principal angle of incidence and quasi-polarizing angle of copper polycrystalline metal at range of wavelengths from 500 nm - 650 nm. Using the principal angle of incidence method, the spectral dependences of the optical constants of copper sample are determined. In case of the quasi-polarizing angle method, the intensity of the reflection of p- polarized component is measured at different angles of incidence for each wavelength. The angle of incidence at which the intensity has minimum value is referred to the quasi polarizing angle for this wavelength. The results show that the quasi polarizing angle is found to be close to the value of the principal angle of incidence for the copper sample at each wavelength. [ABSTRACT FROM AUTHOR]

This study numerically evaluates the performance of flow control using fluidic oscillators on the NACA 0015 airfoil with a flap at different flap angles and different pitch angles of the oscillators. An inline array of fluidic oscillators is located just in front of the flap. Aerodynamic analysis was carried out using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations in a computational domain that consists of the external domain around the airfoil and the internal domains in three fluidic oscillators. Flap angles of 20°, 40°, and 60° were tested with a fixed angle of attack of 8°. For each flap angle, the effects of the pitch angle of the oscillators on the aerodynamic performance were evaluated in a range of 60° to the negative value of the corresponding flap angle. It was found in this work that the oscillator jets parallel to the flap showed the best performance, which was achieved by using negative pitch angles and also bending the outlets of the oscillators. The results indicate that the aerodynamic performance varies significantly with the flap and pitch angles. [ABSTRACT FROM AUTHOR]

Summary: This article attempts to study the high angle of attack maneuver from the perspective of switched system control. In view of the complex aerodynamic characteristics, an improved longitudinal attitude motion model is presented, which is a switched stochastic nonstrict feedback nonlinear system with distributed delays. The significant design difficulty is the completely unknown diffusion and drift terms and distributed delays with all state variables. Based on a technical lemma and neural networks, an improved smooth state feedback control law for nonstrict feedback systems is proposed without any growth assumptions. To eliminate the influence of distributed delays, an improved Lyapunov–Krasovskii function is constructed, which skillfully removes the constraint of the upper bound of the delay change rate. Then, by combining the average dwell‐time scheme and stochastic backstepping technique, an adaptive neural network tracking control law is designed, which extends a newly proposed switched system stability condition to the stochastic switched system. Theoretical analysis and flight control simulation experiments are provided to illustrate the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In a Fizeau interferometer, off-axis illumination will lead to fringe optimization. Primarily due to the unique structure of our interferometer, we first analyze the influence of the optical properties of the parallel plate as a part of the interferometer on the optimal incident angle. Generally, the incident angle determination is mainly based on the graphing method proposed by Langenbeck and the estimation formula proposed by Kajava. However, Langenbeck's method is cumbersome, and the error of Kajava's estimation formula is large. Based on the predecessors, this paper proposes a modified method of determining the optimal angle of incidence and further derives more accurate optimal angle expressions than Kajava's. By simply substituting the wedge angle of the wedge cavity and the reflectivity of the cavity, the optimum incidence angle can be obtained immediately. Thus, it eliminates the tedious and complex process of finding the optimum incident angle by graphing method and makes the formula method the simplest method to find the optimum incident angle. Finally, the comparison of the interference intensity at the optimum incidence angle calculated by the improved method and normal incidence is given. It is found that the beam has a good suppression effect on the sub-peak when it is incident at the optimum incident angle calculated by the method in this paper. [ABSTRACT FROM AUTHOR]

The flow field around a finite-span flat wing in pitch motion is modeled by means of large-eddy simulation. The effect of moderate sweep angles on the stability of the leading-edge vortex (LEV) is investigated. The relative stability of LEVs on flapping profiles can be improved by moderating LEV growth through spanwise vorticity convection and vortex stretching. The LEV growth over an unswept wing and two sweep angles, namely, Λ = 15 ° ; 30 ° , is studied by investigating the spanwise flow. The calculated results are in good agreement with experimental data, establishing confidence in the approach. Results show that sweeping the wing profile increases not only the scale of the secondary vortices but also expedites the initiation of the vortices at lower angles of attack. For the sweep angle of Λ = 30 ° , increasing the angle of attack is associated with annihilation of vorticity and thereby limits the vortex growth as a necessary condition for LEV stability. Analysis shows that increasing the sweep angle results in a higher circulation intensity, especially in the inner region of the wing, and significant spanwise flow is observed through the vortex core. The pattern of vorticity remains stable and attached to the surface as the angle of attack continues to grow for the swept wing, while the patterns of vorticity depart the wing surface for the unswept wing. It is suspected that sweeping the wing can control the scale of the vortex by introducing a substantial vortex stretching. [ABSTRACT FROM AUTHOR]

To measure airborne particulate matter concentration over a wide range, a measurement system is mounted on various types of moving vehicles, such as high-speed trains, small drones, and airplanes. Depending on the purpose and range of measurement, the size of the moving vehicle used varies, and the sampling flow rate of the measurement system mounted on the vehicle also varies accordingly. Therefore, an isokinetic sampling inlet with a size suitable for each mobile measurement system must be used. In this study, the aspiration ratio according to various sizes of double-shrouded probes developed to enable representative sampling, including under high-speed flow conditions, was investigated. Considering the various speed ranges of the moving vehicle and relative angle between the moving direction of the vehicle and the surrounding flow direction, the free-stream velocity range around the double-shrouded probe was set to 0–300 km/h and the angle of attack was set to 0–30°. As the angle of attack increased, the aspiration ratio tended to decrease. When the angle of attack is fixed, we found that the aspiration ratio of the double-shrouded probe of various sizes can be made non-dimensional using the square root of the Stokes number. Based on these results, it is expected that the size of the double-shrouded probe suitable for various mobile measurement systems can be easily determined, and accurate measurement of dust concentration is possible through quick prediction of the aspiration ratio according to the velocity of the moving vehicle and angle of attack. Copyright © 2021 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The study presents test results concerning resistance to impingement erosion caused by solid particles transported in the gas stream. The angle at which the erosive jet affected the HVOF-sprayed coatings made using the Ni-WC flux-cored wire amounted to 30° and 90°. The study included microhardness measurements and the microscopic metallographic specimens of the deposited (sprayed) coatings. [ABSTRACT FROM AUTHOR]