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This paper proposes a circulation control device based on dual synthetic jets (DSJs), and its control effect was verified by wind tunnel tests. The experimental pressure and aerodynamic forces were measured to test the control effect of lift enhancement and aerodynamic moment control. After the circulation control is applied, the negative pressure on the suction surface is decreased. Correspondingly, the positive pressure on the pressure surface is increased. The pressure measurement indicated that the pressure distribution trend in a direction favors the lift enhancement. The maximum increment of the lift coefficient was 0.2 when the momentum coefficient was 0.015. The lift–drag ratio was increased by a maximum of 5.4. Applying circulation control before the stall angle of attack can provide stable increments of the roll and pitch moments. In general, the circulation control method based on dual synthetic jets performs well for lift enhancement and aerodynamic moment control. [ABSTRACT FROM AUTHOR]

The high-lift Japan Aerospace Exploration Agency (JAXA) standard model (HL-JSM) has been numerically analyzed in order to further validate the HEMLAB code for realistic aircraft configurations. The numerical algorithm is based on highly efficient edge-based data structure for a vertex-based finite volume algorithm on hybrid meshes. The data pattern is arranged to meet the requirements of a vertex-based finite volume algorithm by considering data access patterns and cache efficiency. A fully implicit version of the numerical algorithm has also been implemented based on the Portable, Extensible Toolkit for Scientific Computation (PETSc) library in order to improve the robustness of the algorithm. The resulting algebraic equations, including the one-equation Spalart-Allmaras, are solved in a monolithic manner using the restricted additive Schwarz preconditioner combined with the flexible generalized minimal residual method [FGMRES(m)] Krylov subspace algorithm. The numerical method is also combined with the metric-based anisotropic mesh refinement library Python Adaptive Mesh Geometry Suite-INRIA (pyAMG) from National Institute for Research in Digital Science and Technology in order to improve the numerical accuracy. The numerical algorithm is initially applied to the two-dimensional L1T2 (National High Lift Programme) high-lift system, and then the calculations around the HL-JSM are carried out at relatively high angles of attack. The numerical results with the anisotropic mesh refinement library pyAMG indicate significant improvements in numerical accuracy. [ABSTRACT FROM AUTHOR]

The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengers and may even cause damage to the train and related tunnel structures. Therefore, controlling the train speed in the tunnel is extremely important. In this study, this problem is investigated numerically in the framework of the standard k-ε two-equation turbulence model. In particular, an eight-car urban rail train passing through a tunnel at different speeds (140, 160, 180 and 200 km/h) is considered. The results show that the maximum aerodynamic drag of the head and tail cars is most affected by the running speed. The pressure at selected measuring points on the windward side of the head car is very high, and the negative pressure at the side window of the driver's cab of the tail car is also very large. From the head car to the tail car, the pressure at the same height gradually decreases. The positive pressure peak at the head car and the negative pressure peak at the tail car are greatly affected by the speed. [ABSTRACT FROM AUTHOR]

Objective As the train operational speed increases, various braking methods become essential for ensuring high-speed train emergency safety braking. Wind resistance brakes, which complement wheel-rail adhesion brakes, have garnered extensive attention. The installation of wind resistance brake plates affects the train streamlined shape and can influence train operational safety under crosswind conditions. To ensure train operational safety and braking performance in high wind environments, it is necessary to thoroughly investigate the impact law of different brake plate configurations on train aerodynamic performance under crosswind conditions. Method Using three-dimensional, constant, incompressible Navier-Stokes equation and k-ε two-equation turbulence model, the influence of crosswind existence and varying brake plate heights on of high-speed train flow field and aerodynamic force are investigated. Result & Conclusion Simulation research results indicate that under crosswind conditions, the aerodynamic resistance on train carbody and brake plates increases along carbody direction, while the lateral force decreases. When the brake plate height increases from 0.5 m to 1 m, the proportion of brake plate resistance in overall resistance rises from 54.89% to 69.92%, with the maximum reaching 56 kN. The proportion of brake plate lateral force in overall lateral force is less than 1%, indicating that different brake plate heights have relatively little impact on train overall lateral force. The brake plates have a certain stopping effect on the incoming flow, and there is flow field interference between closely spaced brake plates. The influence of brake plates on lateral forces is minor. With proper preliminary design of brake plates, wind resistance brakes can be an effective train braking solution with minimal impact on train operational stability.

Aeroelastic flutter design derivatives may be approximated by ignoring the sensitivity of the structural mode shapes. This fixed-mode derivative is less expensive to compute than the exact free-mode derivative (which accommodates the mode shape dependency) but also may provide inaccurate sensitivities for optimization. This work formulates both fixed- and free-mode flutter derivatives and demonstrates the conditions under which they are equivalent. Two different types of fixed-mode derivatives are also developed in this work. Using a cantilevered-plate demonstration problem with both shape and sizing design parameters, the accuracy of the free-mode derivative and the two fixed-mode derivatives is demonstrated via gradient-based optimization. [ABSTRACT FROM AUTHOR]

For the purposes of analyzing the stability of the tether system in the atmosphere, a mathematical model in the form of matrix based on the Euler kinematic equations is obtained, with consideration to changes in the kinetic moment. The experiment has shown that an increase in tether length leads to decrease the amplitude of angle of attacks of the spacecraft and the stabilizer and, as a result, increase the stability of the tether system. [ABSTRACT FROM AUTHOR]

Turbulence, flow separation, and shock dynamics challenge the modeling and analysis of high-speed aeroelastic behavior. Motivated by this, the importance of modeling the fidelity of the flow is explored in the aeroelastic response of a cantilever plate in an Ma=2.0 separating turbulent flow using unsteady Reynolds-averaged Navier-Stokes (URANS) and URANS-enriched local piston theory (LPT). Structural modeling assumptions are also evaluated using both linear and nonlinear representations. Close agreement in the predicted aeroelastic steady state is observed. However, large discrepancies in the dynamic aeroelastic response predictions are found and ultimately linked to the neglect of deformation-induced cavity pressure fluctuations and dynamic flow separation in the LPT model. Interestingly, the dynamic flow separation induces a fluid-driven limit cycle oscillation in the postflutter regime. Furthermore, structural nonlinearity is not found to have a strong impact on the conditions and configurations considered. [ABSTRACT FROM AUTHOR]

[Objective] As the train operational speed increases, various braking methods become essential for ensuring high-speed train emergency safety braking. Wind resistance brakes, which complement wheel-rail adhesion brakes, have garnered extensive attention. The installation of wind resistance brake plates affects the train streamlined shape and can influence train operational safety under crosswind conditions. To ensure train operational safety and braking performance in high wind environments, it is necessary to thoroughly investigate the impact law of different brake plate configurations on train aerodynamic performance under crosswind conditions. [Method] Using three-dimensional, constant, incompressible NavierStokes equation and k-e two-equation turbulence model, the influence of crosswind existence and varying brake plate heights on of high-speed train flow field and aerodynamic force are investigated. [Result & Conclusion] Simulation research results indicate that under crosswind conditions, the aerodynamic resistance on train carbody and brake plates increases along carbody direction, while the lateral force decreases. When the brake plate height increases from 0.5 m to 1 m, the proportion of brake plate resistance in overall resistance rises from 54.89% to 69.92%, with the maximum reaching 56 kN. The proportion of brake plate lateral force in overall lateral force is less than 1%, indicating that different brake plate heights have relatively little impact on train overall lateral force. The brake plates have a certain stopping effect on the incoming flow, and there is flow field interference between closely spaced brake plates. The influence of brake plates on lateral forces is minor. With proper preliminary design of brake plates, wind resistance brakes can be an effective train braking solution with minimal impact on train operational stability. [ABSTRACT FROM AUTHOR]

Copyright of Electric Drive for Locomotives is the property of Electric Drive for Locomotives Editorial Office 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.)

Abstract Given the influence of air intake from inclined shafts in existing tunnel ventilation systems on train comfort and aerodynamic safety, a numerical analysis method is used to study the comfort and aerodynamic safety of operating trains under three conditions—inclined shaft closed and inclined shaft open without and with air intake—and to explore the variation law of transient pressure and aerodynamic force (lift coefficient, transverse force coefficient, and overturning moment coefficient). Combined with practical engineering and requirements, the influence of inclined shaft air intake on train operation comfort and aerodynamic safety is analyzed. Through this research, the influence of using air intake from the inclined shaft of an existing tunnel, a ventilation scheme of the new Wushaoling Tunnel, on the comfort and aerodynamic force of trains is revealed, and the comfort and aerodynamic safety of trains in an actual project are evaluated, verifying the rationality of the ventilation scheme of the Wushaoling Tunnel.

Due to the limitations of wind tunnel speed and size, achieving a model’s Reynolds number equal to the actual Reynolds number is challenging and may lead to discrepancies between experimental and actual results. To investigate the effects of the Reynolds number on the aerodynamic forces and vortex-induced vibration (VIV) characteristics of a streamlined box girder, wind tunnel tests were conducted to study the variations in aerodynamic forces and surface pressures on the static main beam, as well as the VIV response and time–frequency characteristics of the aerodynamic forces on the dynamic main beam, as the Reynolds number varied. The results indicate that in static tests, as the Reynolds number increases, the drag coefficient of the main beam decreases, the lift coefficient slightly increases, and the pitching moment coefficient remains almost unchanged. The root mean square (RMS) values of the wind pressure coefficients show a significant Reynolds number effect, with values generally decreasing as the Reynolds number increases. In free vibration tests, as the Reynolds number increases, the onset wind speed of VIV increases from 14.35 m/s to 16.03 m/s, the maximum amplitude decreases from 0.076 to 0.004, and the VIV lock-in range narrows. The dynamic pressure results indicate that as the Reynolds number increases, the RMS values of the wind pressure coefficients decrease. At some measurement points, the dominant frequencies of the fluctuating pressure amplitude spectra deviate from the corresponding VIV frequency, and the correlation and contribution coefficients between the local aerodynamic forces and the overall vortex-induced force (VIF) decrease. These changes may explain the reduction in the VIV amplitude with an increasing Reynolds number. The motion state of the main beam has a minimal effect on the mean wind pressure coefficients and their Reynolds number effect, whereas it has a more significant effect on the RMS values of the pressure coefficients.

Given the influence of air intake from inclined shafts in existing tunnel ventilation systems on train comfort and aerodynamic safety, a numerical analysis method is used to study the comfort and aerodynamic safety of operating trains under three conditions—inclined shaft closed and inclined shaft open without and with air intake—and to explore the variation law of transient pressure and aerodynamic force (lift coefficient, transverse force coefficient, and overturning moment coefficient). Combined with practical engineering and requirements, the influence of inclined shaft air intake on train operation comfort and aerodynamic safety is analyzed. Through this research, the influence of using air intake from the inclined shaft of an existing tunnel, a ventilation scheme of the new Wushaoling Tunnel, on the comfort and aerodynamic force of trains is revealed, and the comfort and aerodynamic safety of trains in an actual project are evaluated, verifying the rationality of the ventilation scheme of the Wushaoling Tunnel. [ABSTRACT FROM AUTHOR]

• A new spherical harmonic model of coma gas density is proposed. • An improved orbital model about a comet with coma gas, SRP, and non-spherical gravity is established. • A global grid method is used to search stable orbits around a comet. • The heliotropism and spatial distribution of stable orbits are analyzed. As a frontier field of deep-space explorations, the study of comets is of great value to planetary scientific research, resource exploration, and planetary defense. To date, only the ESA's Rosetta spacecraft successfully orbited the comet 67P. The orbital dynamical environment around comets is more complex than that of other small bodies, making the orbital stability around comets an important issue. The parameters of Rosetta's target, comet 67P/Churyumov-Gerasimenko, are used in this study of the orbital dynamics around a comet. The most unique perturbation around a comet is the aerodynamic force caused by the coma gas. However, the current numerical models are too complicated for analytical studies, and the current spherical harmonic model is too simple to reflect the actual distribution of the coma gas field accurately. To overcome the disadvantages of current models, a method is proposed to reduce the numerical model to a simplified analytical model. Then, the simplified model is fitted with a new spherical harmonic model, which is suitable for both numerical simulations and analytical studies. By considering perturbative effects of coma gas, solar radiation pressure (SRP), and non-spherical gravity of the comet nucleus, the orbital dynamical model is then established. Next, with a global search method, stable orbits around 67P/Churyumov-Gerasimenko are searched, and their characteristics are analyzed. It is found that the perturbative effect of the coma gas reduces the stability of the orbits. As the distance between the comet and the Sun increases, the stable orbital region will gradually shift from low inclinations to higher ones, and all of the stable orbits are heliotropic. According to the results, some candidate exploration orbits around the comet are finally identified. [ABSTRACT FROM AUTHOR]

Recent studies have shown that semi-aeroelastic hinge devices can enable larger aircraft wingspans. Such a device would be folded on the ground to meet airport width restrictions, locked during cruise for optimal aerodynamic performance, and released during maneuvers to alleviate flight loads. In contrast, this paper uses a wind tunnel experiment to study the aeroelastic behavior of floating wingtip fuel tanks. This device consists of a freely floating wingtip with an additional mass attached in the form of a liquid-filled fuel tank. The static aeroelastic results show that altering the fuel tank's filling level and position allows the wingtip to float at an optimal angle for aerodynamic efficiency across various angles of attack and fuel masses. Additionally, this paper shows that, with careful selection of the mass distribution of the wingtip, dynamic load alleviation comparable to the semi-aeroelastic hinge concept can be achieved during turbulence and one-minus-cosine encounters. Furthermore, the effect of fluid motion is shown to reduce incremental loads during random turbulence encounters by up to 10%; however, it has a negligible impact on the response to one-minus-cosine encounters. Such results are also confirmed by a numerical model incorporating a simple reduced-order fluid sloshing model. [ABSTRACT FROM AUTHOR]

Accurate aerodynamic distribution perception and real-time flight state evaluation are crucial for flight safety, e.g., stall detection. However, the observations are usually sparse due to limitations in sensor mounting space and cost, and a reconstruction technology is urgently required. Herein, a machine learning-assisted assimilation method based on sparse observations has been proposed. Different from the traditional reconstruction methods focusing on boundary condition correction, the proposed method formulates the flow field pressure distribution as a linear superposition of flow field modes, thereby forming a real-time reconstruction pattern that combines offline modal extraction using computational fluid dynamics (CFD) with real-time determination of modal weights using a neural network. In this study, CFD simulations were conducted under 800 different operating conditions for common modal extraction and model training. The weights of these modes were determined online based on merely five observations for reconstructing the full pressure field. A pressure reconstruction with a relative error of 6.1% and a mean square error of 0.003 was achieved within the prescribed condition range. The computational cost was just 2 ms for each reconstruction run, significantly faster than the 20 min required by the classical reconstruction ensemble transform Kalman filter. It also showed that the method maintains almost the same accuracy amidst 1.5% measurement noise. As practical examples, shock waves and the change of lift coefficient were analyzed using the proposed method, providing remarkable evidence for the capability of the method in supporting stall detection. These validate the method's effectiveness and explore its potential in real-time and accurate monitoring of an aircraft. [ABSTRACT FROM AUTHOR]

This study conducted wind tunnel tests to verify a passive jet flow control method for suppressing the aerodynamic force on a chamfered square cylinder at a moderate Reynolds number, focusing on the influence of the opening parameters and the spanwise spacing ratio of hollow pipes on the jet flow control effect. The pressure coefficient distribution on the surface of the cylinder and the overall aerodynamic coefficient were considered in order to systematically analyze the influence of opening shape, opening number, opening height, pipe height, and pipe radial thickness, and to determine the optimal combination of opening parameters. Subsequently, we analyzed the influence of the spanwise spacing ratio on passive jet flow control. Furthermore, the optimal arrangement of the hollow pipe was derived by comparing the aerodynamic coefficients of uncontrolled and controlled cylinders. The results revealed that the passive jet hollow pipe significantly reduces the root mean-square value of the pressure coefficient and the fluctuation of the lift coefficient. Moreover, the platform area of the mean pressure coefficient at the leeward side of the cylinder increases and the mean drag coefficient decreases. The spectrum analysis results showed that the passive jet flow control pipe alters the frequency and intensity of vortex shedding in the wake region. All results indicated that the aerodynamic forces and wakes of a chamfered square cylinder are effectively controlled through jet flow control with perforated hollow pipes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature 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.)

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University 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.)

INTRODUCTION: STAR-CCM+ is a CFD software that uses continuum mechanics numerical techniques and is a tool for thermodynamic and fluid dynamics analysis. STAR-CCM+has expanded the functions of surface treatment, such as surface wrapper, surface remesh, and volume mesh generation. With the increase of train speed, the aerodynamic phenomena become more prominent, and the aerodynamic phenomena of high-speed trains in crosswind environment become more complicated. OBJECTIVES: Bogie is an important part of high-speed train. It is of great significance to study the aerodynamic performance Three groups of trains operating in a strong wind environment are modeled, and the surface pressure distribution characteristics of the car body and bogie, as well as the aerodynamic and aerodynamic torque distribution characteristics of each car and bogie, are analyzed when the train operates at 350km/h under a Class 12 crosswind condition. RESULTS: The results of the study show the variation rules of surface pressure, aerodynamic force and aerodynamic moment of the car body and bogie with wind speed. CONCLUSION: The windward surface pressure of the vehicle body increases linearly with the increase of wind speed, and the surface pressure of the roof and leeward side decreases linearly with the increase of wind speed. [ABSTRACT FROM AUTHOR]

Avian takeoff requires peak pectoralis muscle power to generate sufficient aerodynamic force during the downstroke. Subsequently, the much smaller supracoracoideus recovers the wing during the upstroke. How the pectoralis work loop is tuned to power flight is unclear. We integrate wingbeat-resolved muscle, kinematic, and aerodynamic recordings in vivo with a new mathematical model to disentangle how the pectoralis muscle overcomes wing inertia and generates aerodynamic force during takeoff in doves. Doves reduce the angle of attack of their wing mid-downstroke to efficiently generate aerodynamic force, resulting in an aerodynamic power dip, that allows transferring excess pectoralis power into tensioning the supracoracoideus tendon to assist the upstroke—improving the pectoralis work loop efficiency simultaneously. Integrating extant bird data, our model shows how the pectoralis of birds with faster wingtip speed need to generate proportionally more power. Finally, birds with disproportionally larger wing inertia need to activate the pectoralis earlier to tune their downstroke.

The impact of train heights on train aerodynamic performance is studied by using an improved delayed detached-eddy simulation (IDDES) method. The correctness of the numerical method has been verified by the existing wind tunnel and moving model experiments data. The aerodynamic drag, lift, slipstream, and wake flow are compared for three train heights. The results presented that the drag and lift increased by 6.2% and 23.8% respectively, with an increase in train height from 3.89m to 4.19 m. Compared with the 3.89m case, the maximum time-averaged slipstream at the platform location for 4.04 and 4.19mcases are increased by 2.0% and 4.3% respectively. Meanwhile, the wake topology for three cases is described and analyzed quantitatively. The downwash angle of the wake longitudinal flow is increased with the increasing train height, resulting in the mixing of the downwash flow and the ground flow in advance. The wake in the higher trains tends to develop outward and downward. Besides, the higher trains will also bring greater transient aerodynamic loads to the equipment above the train. It's recommended to shorten the maintenance period of the electrical equipment above the higher trains to ensure the devices' safety. [ABSTRACT FROM AUTHOR]

Compressible flow through a branched duct and the motion of a sphere through a high blockage ratio pipe are two important and engaging topics throughout the years. The results of studies on these topics are of practical relevance to many fields such as the gas pipeline technology, air transport systems in gas turbines technology, and tube transportation, etc. However, studies on the motion of a sphere in a branched duct are scarce. Studies of the motion of a sphere in a near-vacuum tube could contribute to the development of a branched Hyperloop system in the future. In this study, we investigated the effect of the tube curvature radius and angle on the aerodynamic characteristics of a sphere during its motion in a branched tube. We examined, quantified, and compared the variation of the drag, side force, and pressure waves for the cases where a sphere enters a branch considering six curvature radii (from 500 to 3000 m), three angles (10°, 15°, and 20°), three speeds (100, 200, and 300m s-1), and two initial pressures (1/1000 and 1 atm) in simulations. The results indicated that the drag and side force vary only in the intersection region (region where the straight tube and branched tube intersect); before and after the intersection region, they are similar. With an increase in the curvature radius, the rate of drag reduction (FD/max(FD)) decreases, while the changes in the angle do not affect variation of drag and side forces. Furthermore, we compared the motion of a sphere in straight and branched directions and found out that the flow in front and behind the sphere was similar for both directions. [ABSTRACT FROM AUTHOR]

This paper examines the dynamic performance of the pantograph passing through an overlap section of the catenary system, using a China's high speed railway with the 4-span overlap as an example. The pantograph and catenary system are simulated as a lumped mass model and finite element model, respectively. The model is verified according to EN50318:2018. The model is also assessed against an experimental study of the contact force and uplift of contact wire at 300 km/h. Then the contact force and uplift of contact wire at the speed of 150–350 km/h are calculated. The research shows that when the pantograph passes through the overlap, the maximum contact force increases beyond 14%, the standard deviation of the contact force increases by more than 26%, and the increase of the vertical displacement exceeds 38%, which becomes more apparent with the increase of speed. Under the influence of aerodynamic force, when the running speed increases from 150 to 350 km/h, the mean contact force in the knuckle-downstream and knuckle-upstream orientation increase by 59.49% and 97.85%, respectively. As a result, the contact force and vertical displacement increase greatly when passing through the overlap section, which could affect the current collection quality. [ABSTRACT FROM AUTHOR]

Abstract The aerodynamic braking has become an attractive option with the continuous improvement of train speeds. The study aims to obtain the optimal opening angles of multiple sets of braking plates for the maglev train. Therefore, a multi-objective optimization method is adopted to decrease the series interference effect between multiple sets of plates. And the computational fluid dynamics method, based on the 3-D, RANS method and SST k-ω turbulence model, is employed to get the initial and iterative data. Firstly, the aerodynamic drag and lift are analysed, as well as the pressure and velocity distribution of the flow field with the braking plates open at 75°. Then, the aerodynamic forces of each braking plate pre and post optimization are compared. Finally, the correlation between each set of braking plates and the optimized objective is analysed. It is found from the results that the aerodynamic drag and lift of the train have significant differences with or without multiple sets of braking plates. Additionally, the design variable corresponding to the number of iterations of 89 is taken as the relative optimal solution, and its opening angles of braking plates (B2-B5) are 87.41°, 87.85°, 87.41°, and 89.88°, respectively. The results are expected to provide a reference for the opening angles design scheme for the future engineering application of high-speed maglev train braking technology.

This paper presents test data from vacuum and hover tests of a 2.8-ft-radius dihedral-anhedral tip composite rotor. The paper describes the blades, their fabrication, properties, instrumentation, the test conditions, and the data acquired. The blades were Mach-scaled to a generic but representative modern rotor. Vacuum chamber tests measured rotating frequencies and strains. Hover tests measured performance, blade loads, pitch-link loads, and strains under steady and cyclic loading conditions. Three-dimensional finite element structural models were developed to ensure completeness and consistency of property definition. The three-dimensional analysis was also used for a preliminary assessment of the test data. The test data revealed that the dihedral-anhedral tip influences the torsional and higher frequencies of a rotor blade significantly. The oscillatory blade loads show patterns consistent with the vertical center-of-gravity offset introduced by the tip. The surface strains reveal interesting higher-harmonic patterns of loading particularly near the dihedral junction. [ABSTRACT FROM AUTHOR]

Data-driven parametric reduced-order models (ROMs) in state-space form are valuable tools for rapid aeroelastic (AE) analysis and aerostructure control synthesis. However, the issue of state inconsistence (significant variations in model parameters over tradespaces) makes ROMs noninterpolatable, and therefore unable to accommodate use over broad flight parameter space. This paper presents a holistic framework that combines a system identification technique with state-consistence enforcement (SCE) and a genetic algorithm (GA) for the automated development of interpolatable AE ROMs across broad flight regimes. The SCE technique introduces a regularization term to the AutoRegressive model with eXogenous inputs (ARX) to specifically penalize model parameter variation between flight conditions. The GA autonomously guides the ROM development process toward optimal SCE-ARX hyperparameter selection that balances between model parameter variations and ROM accuracy. The GA-guided SCE-ARX approach is applied to build a parametric AE-ROM database at selected flight conditions, which, because of its state consistence, can be interpolated to create ROMs at any interstitial conditions, where training data or ROMs are not initially available, hence rapidly establishing the full coverage of the entire parameter space. The ROMs generated by the proposed method are compared with those by ARX, SCE, and GA-guided ARX in prediction accuracy. The individual and combined effects of SCE and GA on model parameter variation and ROM interpolatability are thoroughly investigated. The present method demonstrates the most accurate and robust performance for parametric ROM construction across the broad flight envelope. [ABSTRACT FROM AUTHOR]

This paper investigates the aerodynamic forces on a 600-m-high supertall building based on field measurements during Super Typhoon Mangkhut and wind tunnel test on a 1∶500 scaled model of the monitored building. The local wind force coefficients and their power spectral densities obtained by the full-scale measurements and the model experiment are compared and discussed. The comparative study shows that the wind tunnel test provides conservative mean local drag coefficients and root-mean-square (RMS) local lift coefficients, whereas for the RMS local drag coefficients, the model experiment reproduces smaller predictions at higher levels than those from the onsite measurements. Moreover, to explore the deviations between the full-scale and model-scale results, the Reynolds number effects in the range of 5.5×104 to 1.8×108 on the local wind forces and the Strouhal number are investigated. It is found that the Reynolds number has evident effects on the local wind force coefficients, although its influence on the Strouhal number is negligible. This combined study of field measurements and wind tunnel test aims to enhance the understanding of the aerodynamic forces on high-rise buildings during strong windstorms and provide useful information for the wind-resistant design of supertall buildings. [ABSTRACT FROM AUTHOR]

The flow past the rotating circular cylinder and the effect of buoyancy on heat transfer characteristics are studied numerically for the Reynolds number of 20 and 40 and the Prandtl number of 0.7. The lift and drag coefficients, Strouhal number, and local Nusselt number on the cylinder are studied under the sway of combined buoyancy (at the Richardson number varies from 0 to 2) and different rotational directions. Although the interaction between buoyancy and rotation is a puzzling heat transfer problem, the direction of rotation is found to have significant effects on the flow patterns and heat transfer rate. The main innovation of the present work is to determine the extreme points of Nusselt numbers when different conditions are applied. For a positive rotation, the maximum local Nusselt number is at θ=225o, and the minimum local Nusselt number is at θ=100o. In contrast, for a negative rotation, the maximum and minimum local Nusselt numbers are at θ=140o and θ=270o, respectively. Applying Taguchi method, it is found that average Nusselt number is more dependent on Reynolds number than other factors. Additionally, it can be concluded that the direction of rotation can be used as a powerful tool to adjust the heat transfer rate and the required value of drag and lift. Consequently, without applying different rotation speeds, it would be difficult to stabilize the flow, and with the aid of Taguchi method, it is determined that rotation is deciding factor in stabilizing flow patterns. The results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, based on Euler-Bernoulli beam theory, the vibration of a helicopter blade is studied. In this regard, the partial differential equation of motion is obtained and solved for a clamped beam numerically. The aerodynamic forces are introduced in terms of the pilot parameters included the collective pitch, lateral cyclic, longitudinal cyclic, and built-in twist on the blade deformation. Moreover, the effects of the blade rotational angular velocity, flight altitude, the blade length, and induce velocity on the blade deflection are studied. The results show that the blade deformation will be oscillating in terms of time and it is very sensitive to the control parameters, its geometry, and the environmental conditions. Moreover, it is observed that the pilot coefficients have more effect on the blade deformation in comparison with other parameters. [ABSTRACT FROM AUTHOR]

Due to the complicated geometric shape, it's difficult to precisely obtain the aerodynamic force of high-speed trains. Taking numerical and experimental data as the training data, the present work proposed a data-driven rapid prediction model to solve this problem, which utilized the Support Vector Machine (SVM) model to construct a nonlinear implicit mapping between design variables and aerodynamic forces of high-speed train. Within this framework, it is a key issue to achieve the consistency and auto-extraction of design variables for any given streamlined shape. A general parameterization method for the streamlined shape which adopted the idea of step-by-step modeling has been proposed. Taking aerodynamic drag as the prediction objective, the effectiveness of the model was verified. The results show that the proposed model can be successfully used for performance evaluation of high-speed trains. Keeping a comparable prediction accuracy with numerical simulations, the efficiency of the rapid prediction model can be improved by more than 90%. With the enrichment of data for the training set, the prediction accuracy of the rapid prediction model can be continuously improved. Current study provides a new approach for aerodynamic evaluation of high-speed trains and can be beneficial to corresponding engineering design departments.

To study the aerodynamic characteristics of the convex structure of a surface-monitoring device on a high-speed train and to evaluate its impact on the aerodynamic performance of the high-speed train, numerical simulation research was conducted on three different layouts of the monitoring device. The computational fluid dynamics (CFD) method was used for the simulation study, and the unsteady compressible NS equation was used as the control equation. Hexagonal grid technology was used to reduce the demand for the grid quantity. The rationality of the grid size and layout was verified through grid independence research. To increase the accuracy of the numerical simulation, the γ-Reθ transition model and improved delayed detached eddy simulation (IDDES) method were coupled for the simulation research. The aerodynamic characteristics of the different operation directions and configurations were compared and analyzed. The research results showed that the windward side of the single pantograph detection device experienced positive pressure, and the sideline and leeward sides experienced negative pressure. Increasing the fillet radius of the sideline could appropriately reduce the aerodynamic resistance. When the speed was about 110 m/s, the drag force coefficient of the detection device was 210~410 N, and the lateral force was small, which means that it had little impact on the overall aerodynamic force of the train. According to the results of the unsteady analysis of the layout with a large space, the resistance during forward travel was greater than that during negative travel. The streamlined upwind surface was conducive to reducing the scope of the leeward separation zone and the amplitude of the pressure fluctuation in the leeward zone, and it thus reduced the resistance. For the running trains, a vortex was formed on their leeward surface. The pressure monitoring results showed that the separated airflow had no dominant frequency or energy peak. The possibility of the following train top and other components experiencing resonance damage is low. [ABSTRACT FROM AUTHOR]

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Background: Vortex-induced vibration may cause adverse effects on the safety and usability of bridges. The study of the vortex-induced vibration of bridges is mainly based on empirical mathematical models. Nevertheless, with these models, it is difficult to solve for all complex fluid-structure interaction problems for all types of section models. Purpose: The major aim of this study is to identify the aerodynamic load on bridge deck in wind tunnel test, which can be generally applied on various bridge decks. Methods: In this research, a wind tunnel experiments with a centrally slotted box deck are performed, two lock-in regions of vortex-induced vibration are found during the experiments. An unscented Kalman filter with unknown input method is applied to identify wind-induced forces. Pure aerodynamic force and nonlinear self-excited force are separated directly at both vortex induced vibration lock-in regions. Conclusions: Aerodynamic stiffness and damping at different wind speeds in the vortex-induced vibration phase are identified and proven to show dependence on wind speeds. Based on the calculated standard deviation of forces, the percent of nonlinear self-excited force over all wind-induced forces can be up to 83%, and a minimal percentage of 30% indicates that the nonlinear self-excited cannot be ignored in lock-in phases. The identified values at two lock-in regions are discussed and compared as well. Results indicate the stiffness and damping show similar change pattern in the two lock-in regions. The approach of this research can be applied to obtain system information of vortex-induced vibration events for section models of different bridge deck types. [ABSTRACT FROM AUTHOR]

The increased use of electrothermal ice protection systems (ETIPSs) in various industries (manned and unmanned aviation, energy production) requires improvements to de-icing efficiency, ice shedding predictability, and energy consumption. To achieve these, a coupled numerical and experimental investigation of ETIPS's ice removal (ice shedding) mechanism is presented in this paper. Idealized ETIPS de-icing experiments performed in the icing wind tunnel of the von Karman Institute show several ice shedding mechanisms. A one-dimensional phase change solver developed for ice melting simulations highlights the water layer thickness influence over the ice shedding process. Coupled numerical-experimental results are employed to develop an idealized ice shedding model. The model is validated in realistic de-icing experiments in a second experimental campaign in the icing wind tunnel of the LeClerc Icing Research Laboratory. [ABSTRACT FROM AUTHOR]

An ideally flexible laser may function in unison with minute fluctuations in nature. Lasers made solely from liquids are promising toward this end, but they are intrinsically unstable and have been inapplicable to steady operation under ambient conditions unless they are enclosed in a tailored container or a matrix to prevent the evaporation of the liquid. Here, a simple methodology is reported to form a self‐standing spherical microlaser that is composed fully of liquid and operates steadily even under atmosphere. The robustness and spherical morphology of the droplets are achieved by using ionic liquid as the liquid medium and gently casting the droplets on a substrate covered with hydrophobic nanoparticles to enhance the metastability of the contact angle. The resulting droplets are highly robust and work as efficient long‐lasting laser oscillators. The lasing wavelength is sensitively shifted when the droplets are subjected to a faint breeze or moisture, which is associated with the deformation of the droplet. The morphological and optical responses of the droplet under gas convection are consistently supported by aerodynamic and electromagnetic simulations. The droplets are readily scalable with an inkjet printer without the need for any further treatments. [ABSTRACT FROM AUTHOR]

The wind tunnel experiment is conducted on a simplified aircraft model with rigid and two kinds of elastic wings to investigate the effect of wing 3-D deformation on the aircraft aerodynamic performance. The results show that two elastic wings exhibit different aerodynamic performances, which are classified as the lift-enhancement wing and the drag-reduction wing. For the lift-enhancement wing, the stall angle is delayed from 8° to 15° with a corresponding lift increment of 64.3% compared with the rigid wing. It is shown that the lift enhancement of the aircraft model is accompanied by the torsional vibration mode of the wing, which results in the significant improvement of wing circulation. For the drag-reduction wing, the aerodynamic performance is dominated by the time-averaged deformation, which couples the bending and twisting. The wing twist reduces the effective angle of attack, as well as the frontal area, and contributes to the decreased wake deficit. Meantime, the bent wings function as barriers to the cross flow resulting in a reduction of lift-induced drag. As a result, the drag coefficient is reduced from 0.115 to 0.098 with a reduction of 14.8% at angle of attack of 12°. [ABSTRACT FROM AUTHOR]

A machine learning algorithm is here proposed with the objective to identify homogeneous flow regions in computational fluid dynamics solutions. Given a numerical compressible viscous steady solution around a body at high Reynolds numbers, the task is to select the grid cells belonging to the boundary layer, shock waves, and external inviscid flow. The Gaussian mixture algorithm demonstrated to overcome some of the limitations and drawback of the currently adopted deterministic region selection methods, which require the adoption of case-dependent cutoff inputs, topological information, and final human check. This paper shows an example of application of this selection method performing an accurate breakdown of the aerodynamic drag in viscous and wave contributions by a classical far-field method. The new algorithm essentially leads to the same results of the reference method in terms of drag decomposition; slight differences could only be found in the shock-wave/boundary-layer interaction zone, where the drag breakdown is inherently ambiguous. [ABSTRACT FROM AUTHOR]

Abstract The bamboo weevil beetle, Cyrtotrachelus buqueti, has evolved a particular flight pattern. When crawling, the beetle folds the flexible hind wings and stuffs under the rigid elytra. During flight, the hind wings are deployed through a series of deployment joints that are passively driven by flapping forces. When the hind wings are fully expanded, the unfolding joint realises self‐locking. At this time, the hind wings act as a folded wing membrane and flap simultaneously with the elytra to generate aerodynamics. The functional characteristics of the elytra of the bamboo weevil beetle were investigated, including microscopic morphology, kinematic properties and aerodynamic forces of the elytra. In particular, the flapping kinematics of the elytra were measured using high‐speed cameras and reconstructed using a modified direct linear transformation algorithm. Although the elytra are passively flapped by the flapping of the hind wings, the analysis shows that its flapping wing trajectory is a double figure‐eight pattern with flapping amplitude and angle of attack. The results show that the passive flapping of elytra produces aerodynamic forces that cannot be ignored. The kinematics of the elytra suggest that this beetle may use well‐known flapping mechanisms such as a delayed stall and clap and fling.

This paper presents a flexible lattice variable sweptback wing (FLVSW) concept based on the flexible main beam and lattice that allows the sweptback angle to be varied by 80 deg. The whole FLVSW concept is an integral structure consisting of rigid and flexible parts. The rigid parts are the wing ribs that maintain the shape of the wing and transfer the aerodynamic loads. The flexible parts are mainly composed of the flexible main beam and the flexible lattice, which meet the requirements of supporting aerodynamic loads and deformation of the wing. The surface of the FLVSW is divided into parallel partitions by the wing ribs, and each partition is closed by superimposed skin strips. A prototype model was designed and manufactured based on the Talon first-person-view (FPV) platform performance parameters and considering the finite element analysis of the FLVSW concept under the effect of the drive mechanism and aerodynamic loads. Through testing the structural response of the manufactured prototype model under the driving and static deadweight loads, it was demonstrated that the structure could be driven smoothly and exhibited no deleterious deformations at various sweep angles. In this way, the feasibility of the FLVSW drive mechanism and the design process was verified. [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.)

The aerodynamic braking has become an attractive option with the continuous improvement of train speeds. The study aims to obtain the optimal opening angles of multiple sets of braking plates for the maglev train. Therefore, a multi-objective optimization method is adopted to decrease the series interference effect between multiple sets of plates. And the computational fluid dynamics method, based on the 3-D, RANS method and SST k-ω turbulence model, is employed to get the initial and iterative data. Firstly, the aerodynamic drag and lift are analysed, as well as the pressure and velocity distribution of the flow field with the braking plates open at 75°. Then, the aerodynamic forces of each braking plate pre and post optimization are compared. Finally, the correlation between each set of braking plates and the optimized objective is analysed. It is found from the results that the aerodynamic drag and lift of the train have significant differences with or without multiple sets of braking plates. Additionally, the design variable corresponding to the number of iterations of 89 is taken as the relative optimal solution, and its opening angles of braking plates (B2-B5) are 87.41°, 87.85°, 87.41°, and 89.88°, respectively. The results are expected to provide a reference for the opening angles design scheme for the future engineering application of high-speed maglev train braking technology. [ABSTRACT FROM AUTHOR]

The design of flapping wing micro aerial vehicle (FWMAV) imposes several challenges with reference to dimensional stability for micro mechanism assembly and ability to withstand cyclic loading conditions. Earlier manufacturing methods such as injection moulding and wire cut electrical discharge (EDM) machining necessitate more human efforts, time-consuming and increase cost of preparation of mould. The 3D printing (3DP) process seems to be well suited to manufacture small and intricate parts with good accuracy and reduces the labour cost. In this article, three 3DP technologies with various polymer materials such as Polyjet (Polymethyl methacrylate), Multijet (Polypropylene–light) and Stereolithography (Polypropylene Fumarate) are exploited to fabricate micromechanical linkages of FWMAV mechanism. The structural characteristics of these 3DP materials are evaluated using Finite Element Analysis. The aerodynamic performance of 3D printed mechanism assemblies is evaluated for various angle of attack at diverse wind speed conditions using the developed test rig. Wind tunnel experimental results revealed that low elastic modulus materials produced more amount of lift and high elastic modulus materials experienced less drag. These experimental results suggested that 3DP can be utilized to manufacture small batch of micro mechanism components as an alternative to injection moulding and wire cut EDM. [ABSTRACT FROM AUTHOR]