Search

Recently, the phenomenon of tail-sustained swaying of the 160 km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody's vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

AbstractRail models may be simplified at different levels in wind tunnel tests and numerical simulations. This work used delayed detached eddy simulations to analyze and compare the aerodynamic loads (drag, side force, lift, and rolling moment), surface pressure, and flow characteristics around a train model placed on subgrades with three different rail models: no-rail, simplified rail, and realistic rail. The simulations were conducted at a large yaw angle of 60°. The mean aerodynamic characteristics of the car bodies and bogies were similar with the simplified rail model and realistic rail model, while those were completely different without the rail model. The difference in aerodynamic loads between the no-rail model and the realistic rail model was as high as 53.1%, whereas the difference between the simplified and realistic rail models was only 7.7%. And for fluctuating aerodynamic characteristics of the train, there was still differences between the cases with the simplified and realistic models. Further, the rail model significantly impacted the flow (such as the velocity, turbulent kinetic energy, and vorticity) around the train, especially under the train, resulting in significant differences in the aerodynamic loads in time and frequency domains. For accurate and precise measurements of mean aerodynamic loads, incorporating a rail model (with the simplified model being sufficient) can improve accuracy by 48.0% and precision by 66.9%. When focusing on fluctuating aerodynamic loads, using a realistic rail model is essential to accurately capture amplitude-frequency characteristics. The rail model setup recommendations outlined in this work aim to enhance the accuracy and reliability of various wind tunnel tests and numerical simulations related to train aerodynamics. [ABSTRACT FROM AUTHOR]

The reliability of a pitch-plunge hypersonic airfoil in random fluctuating flow with both cubic and freeplay nonlinearity is examined. The Hopf bifurcation and dynamic responses of the hypersonic airfoil are performed. To analyze the reliability, the effects of stochasticity on the dynamic behaviors of the hypersonic airfoil model are discussed in detail. Several unwanted phenomena that result in the failure of the airfoil structure are induced by random fluctuations. Subsequently, the reliability of the airfoil model is defined and analyzed according to the first passage failure criteria. The effects of different parameters on the reliability are investigated. Furthermore, a nonlinear energy sink is introduced to suppress the vibration of the airfoil and enhance the reliability. Two-dimensional reliability regions of the airfoil model are given to provide the safety parameter region. The results show that the reliability of the airfoil model is significantly improved with the nonlinear energy sink. This work will provide new insights into the safety design of hypersonic aircraft. [ABSTRACT FROM AUTHOR]

The operation of wind turbines involves a complex interaction between aerodynamics, structural mechanics, and control systems. However, the control system is frequently overlooked. To investigate the impact of the control system on the aerodynamic characteristics and elastic deformations of wind turbines, this paper initially integrates the control system into the blade element momentum theory (BEMT) for calculating aerodynamic forces. Subsequently, the control system is incorporated into fluid-structure interaction (FSI) calculations to assess its influence on the overall performance of the turbine. The control system employs variable speed and pitch control, while the structural dynamics are modeled using the Euler-Bernoulli beam theory. When the control system is integrated with blade element momentum theory to calculate the aerodynamic forces of the wind rotor, it is observed that, below the rated wind speed, a portion of the torque error is transferred to the rotor speed. In contrast, above the rated wind speed, the entire torque error is transferred to the blade pitch angle (BPA). Crucially, when the control system is integrated, the rotor speed and BPA are no longer treated as known parameters. This approach enables the prediction of aerodynamic characteristics of the wind rotor, particularly under complex wind speed profiles. The control system exerts a significant influence on the FSI results, particularly in the range of wind speeds that correspond to larger blade deformations. This work can provide a reference for the calculation of aerodynamic characteristics and FSI of wind turbines under complex wind conditions. [ABSTRACT FROM AUTHOR]

Large quantities of sand carried by crosswinds often settle in the cabin of diesel locomotives operating in desert regions. This study adopts an Euler-Lagrange two-phase flow model to simulate sand movement and deposition in a running diesel locomotive through the ventilation grilles. The realistic sand particle diameter distribution obtained from the field test is incorporated by the Rosin-Rummler model in computational fluid dynamics software. The realizable k-ε turbulent model is adopted to simulate the turbulence. The operation of the locomotive on a straight track at 200 km/h with five different crosswind velocities is studied numerically. The simulation results indicate that the increment of crosswind speed leads to higher pressure on the grille and the velocity of the internal flow field. The relationship between the number of sand particles trapped inside the car and the incident angle (i.e., resultant wind angle) is discovered. It is evident that the majority of sand particles enter the compartment through the windward tail grilles. Therefore, the influence of adjusting the tilt angle of the tail grille on the sand entering the locomotive cabin is calculated. It is discovered that the compartment experiences the least sand deposition at a 30° title angle. Therefore, optimizing the tilt angle of the frame for grilles can significantly enhance the filtering of the grille. [ABSTRACT FROM AUTHOR]

The Riemann boundary value problem is a classic problem of complex analysis. It has numerous applications in hydrodynamics and aerodynamics. It is well-studied in the case of rectifiable curves, but results for non-rectifiable curves are relatively new. Here we apply a new approach to this problem on such curves to spirals, including those with infinite length. [ABSTRACT FROM AUTHOR]

Rocket sled test avoids boundary effects in wind tunnel test and inconvenience of flight test, which is one of the feasible options for future single-stage-to-orbit. To analyze potential safety issues during payload separation and optimize the arrangement of testing sensors, different structural layouts and operating speeds of the rocket sled are conducted based on computational fluid dynamics and computational aeroacoustics. The hypersonic winged standard model is utilized as the load for these simulations. The analysis encompasses the evolution of shock waves, the forces exerted on the payload and noise propagation. Variations in flow field and aeroacoustic characteristics of rocket sled are analysed, revealing underlying physical mechanisms. It is observed that placing the payload in front of the thruster can reduce the head pressure, excessive wingspan may have an impact on the structural safety of the wingtip, and the regions of high sound pressure levels mainly exists in the middle and rear sections of the rocket sled. Moreover, as the Mach number increases, the characteristic frequency initially rises and then declines. These researches can serve as a valuable reference for the development of ground test systems and single-stage-to-orbit. [ABSTRACT FROM AUTHOR]

With the increasing popularity of vertical axis turbines (VATs), researchers are now focusing on their performance improvement. Instead of adopting conventional means of performance improvements such as augmentation techniques and exhaustive parametric design optimization, the bio-inspired turbine designs have become a center of attraction, especially during the last decade. This review article attempts to compile the bio-inspired designs belonging to the VATs. Bio-inspired designs implemented in Savonius, Darrieus, Nautilus, and Seed-inspired turbines are elaborated besides giving a detailed explanation of the corresponding bio-organism and natural phenomenon. How the working principles of bio-organisms emulated in the form of fluid dynamic design are explained thoroughly in this paper. The bio-inspired designs for VATs are then classified pragmatically for the future designs. Research gaps are highlighted for the aspiring researchers, and this is followed by the important strategies and allied challenges. [ABSTRACT FROM AUTHOR]

This paper explores the influence of engine modernization on the dynamic stability and performance of a general aviation aircraft. Utilizing an integral mathematical model, the study conducts a comparative analysis of the I-23 Manager piston-engine aircraft and its modified I-31T turboprop version, examining changes in aircraft dynamics depending on the power plant type. The modernization necessitated a redesign of the nose section of the fuselage, resulting in alterations to the external shape and flight properties of the aircraft. The research evaluates various dynamic stability parameters, including phugoid, short period, Dutch roll, roll, and spiral modes, under different flight conditions. Results indicate minimal changes in aerodynamic characteristics due to the engine type, yet significant improvements are observed in efficiency, noise reduction, and operational costs. The impact of the propulsion unit on the dynamic stability of the light aircraft was assessed as insignificant, suggesting that the strategy of modernizing an existing piston-driven aircraft by switching to a turboprop drive is indeed promising. With appropriate initial design assumptions, a modern turbine aircraft with strong flight qualities can be efficiently modernized in this way, without compromising the good flying properties of the existing plane. The outcomes are validated against flight tests, reinforcing the viability of integrating more sustainable and efficient propulsion systems into light aircraft. This study may therefore inform future design and regulatory decisions, providing a perspective on the implications of engine upgrades in the general aviation sector. [ABSTRACT FROM AUTHOR]

Copyright of Automotive Digest is the property of Automotive Digest 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.)

The accumulation of defects on wind turbine blade surfaces can lead to irreversible damage, impacting the aerodynamic performance of the blades. To address the challenge of detecting and quantifying surface defects on wind turbine blades, a blade surface defect detection and quantification method based on an improved Deeplabv3+ deep learning model is proposed. Firstly, an improved method for wind turbine blade surface defect detection, utilizing Mobilenetv2 as the backbone feature extraction network, is proposed based on an original Deeplabv3+ deep learning model to address the issue of limited robustness. Secondly, through integrating the concept of pre-trained weights from transfer learning and implementing a freeze training strategy, significant improvements have been made to enhance both the training speed and model training accuracy of this deep learning model. Finally, based on segmented blade surface defect images, a method for quantifying blade defects is proposed. This method combines image stitching algorithms to achieve overall quantification and risk assessment of the entire blade. Test results show that the improved Deeplabv3+ deep learning model reduces training time by approximately 43.03% compared to the original model, while achieving mAP and MIoU values of 96.87% and 96.93%, respectively. Moreover, it demonstrates robustness in detecting different surface defects on blades across different backgrounds. The application of a blade surface defect quantification method enables the precise quantification of different defects and facilitates the assessment of risk levels associated with defect measurements across the entire blade. This method enables non-contact, long-distance, high-precision detection and quantification of surface defects on the blades, providing a reference for assessing surface defects on wind turbine blades. Graphic Abstract [ABSTRACT FROM AUTHOR]

The effects of the erosion present on the leading edge of a wind turbine airfoil (DU 96-W-180) on its aerodynamic performances have been investigated numerically in the framework of a SST k–ω turbulence model based on the Reynolds Averaged Navier-Stokes equations (RANS). The results indicate that when sand-induced holes and small pits are involved as leading edge wear features, they have a minimal influence on the lift and drag coefficients of the airfoil. However, if delamination occurs in the same airfoil region, it significantly impacts the lift and resistance characteristics of the airfoil. Specifically, as the angle of attack grows, there is a significant decrease in the lift coefficient accompanied by a sharp increase in the drag coefficient. As wear intensifies, these effects gradually increase. Moreover, the leading edge wear can exacerbate flow separation near the trailing edge suction surface of the airfoil and cause forward displacement of the separation point. [ABSTRACT FROM AUTHOR]

The focus of this research was on the equivalent particle roughness height correction required to account for the presence of ice when determining the performances of wind turbines. In particular, two icing processes (frost ice and clear ice) were examined by combining the FENSAP-ICE and FLUENT analysis tools. The ice type on the blade surfaces was predicted by using a multi-time step method. Accordingly, the influence of variations in icing shape and ice surface roughness on the aerodynamic performance of blades during frost ice formation or clear ice formation was investigated. The results indicate that differences in blade surface roughness and heat flux lead to disparities in both ice formation rate and shape between frost ice and clear ice. Clear ice has a greater impact on aerodynamics compared to frost ice, while frost ice is significantly influenced by the roughness of its icy surface. [ABSTRACT FROM AUTHOR]

The energy crisis of the 1970s sparked growing concern over minimizing fuel consumption in water, land, and air transportation. Researchers fascinated by sharks' effortless swimming abilities investigated shark skin denticles and uncovered functions beyond drag reduction, such as antifouling, protection, and bioluminescence. Over the past five decades, significant progress has been made in comprehending drag reduction and antifouling functions of denticle structures; however, the investigation of other functions remains limited. Recent discoveries of diverse denticle morphologies have ignited a keen interest in obtaining morphogroups that can aid other functional studies. This work integrates advances in antifouling, hydrodynamics, aerodynamics, bioluminescence, and protective functions to provide a holistic understanding of their diverse roles. Additionally, this work also dictates multi‐functional adaptations of denticles and contributes to the relatively less‐explored but essential aspects, such as protective functions and denticle morphogroups. By examining these functions together, this work aims to uncover potential synergies and interactions, facilitating the development of multifunctional materials inspired by shark skin denticles. [ABSTRACT FROM AUTHOR]

The investigation of aerodynamics and the establishment of flow patterns around finite-length cylinders with various end shapes in a free, boundless air flow with longitudinal and transverse flow over a wide range of geometric and regime parameters is sketchy and does not have a wide range of geometric and regime parameters. This, in turn, affects the entire aerodynamics of the streamlined body. This paper considers the numerical simulation of a wind turbine made of combined blades. CFD (computational fluid dynamics) methods based on the realisable k-ε turbulence model were used in the study. The results on the influence of the position of the fixed blade on the angle of inclination are obtained (0°, 15°, 30°, 45°, and 60°). The authors found that the pressure of a fixed blade at an optimal angle increases the power coefficient Cp by 35–40%. The dependence of the Cp power coefficient on the rotational speed (speed coefficient) for a three-bladed wind turbine was also established, and it was determined that the maximum value of Cp = 0.28 at Z = 4.9. Based on the results obtained, it was determined that the wind turbine has a maximum power coefficient at an angle of inclination of 0 degrees. [ABSTRACT FROM AUTHOR]

The utilization of unmanned sailboats as a burgeoning instrument for ocean exploration and monitoring is steadily rising. In this study, a dual sail configuration is put forth to augment the sailboats' proficiency in its wind-catching ability and adapt to the harsh environment of the sea. This proposition is based on a thorough investigation of sail aerodynamics. The symmetric rigid wing sails NACA 0020 and NACA 0016 are selected for use as the mainsail and trailing wing sail, respectively, after considering the operational environment of unmanned sailboats. The wing sail structure is modeled using SolidWorks, and computational fluid dynamics (CFD) simulations are conducted using ANSYS Fluent 2022R1 software to evaluate the aerodynamic performance of the sails. Key aerodynamic parameters, including lift, drag, lift coefficient, drag coefficient, and thrust coefficient, are obtained under different angles of attack. Furthermore, the effects of mainsail aspect ratios, mainsail taper ratios, and the positional relationship between the mainsail and trailing sail on performance are analyzed to determine the optimal structure. The thrust provided by the sail to the boat is mainly generated by the decomposition of lift, and the lift coefficient is used to measure the efficiency of an object in generating lift in the air. The proposed sail structure demonstrates a 37.1% improvement in the peak lift coefficient compared to traditional flexible sails and exhibits strong propulsion capability, indicating its potential for widespread application in the marine field. [ABSTRACT FROM AUTHOR]

Summary This article addresses the safe tracking control problem of quadrotor unmanned aerial vehicles (QUAV) considering uncertain aerodynamics and unknown external disturbances. First, a robust adaptive backstepping controller is designed, where the bias of the control variable, that is, the tracking error of the attitude subsystem, is considered in the design process of the position subsystem. Meanwhile, the safe obstacle avoidance objective is realized by the quadratic programming (QP) method that combines the tracking controller with the exponential control barrier function (ECBF). Furthermore, an event‐triggered mechanism is used for the QP process to conserve computing resources. Simulation validates the feasibility and superiority of the proposed control scheme in presence of multi‐obstacle. [ABSTRACT FROM AUTHOR]

Introduction: The aim of this study was to assess the validity and reliability of a hydraulic resistance device (HRD) for monitoring sprint split times under different loads within and between sessions. Methods: Three 20-m sprints with low (15 N), medium-low (40 N), medium-high (50 N), and high (130 N) HRD resistance levels (loads) were performed on two separate occasions 14 days apart. Twenty-four student athletes (24.8 ± 3.8 years) participated in the first session and 13 (24.1 ± 3.2 years) of them in the second session. Resisted sprints split times over a distance of 0-20 m (t0-5, t0-10, t0-20, t5-10, t10-15, t15-20) were measured simultaneously with magnetic incremental encoder embedded in the HRD and a system of single-beam timing gates. Results: The results showed acceptable to high within session (ICC3,1 = 0.91-0.99; CV = 0.92%-3.38%) and between session (ICC3,1 = 0.82-0.99; CV = 1.62%-4.84%) reliability of HRD for measuring all split times at all loads. The minimal detectable change between sessions ranged from 3.3% at high load to 9.9% at low load. The HRD systematically underestimated timing gates times at all loads (bias = 2.01-11.08%), yet good to excellent consistency was observed between the HRD and timing gates, specifically for t0-10 and t0-20 (ICC3,k lower 95% CI = 0.84-0.99). Discussion: Due to high reliability and good validity in monitoring resisted sprint times, the HRD holds potential for practical and research applications. [ABSTRACT FROM AUTHOR]

This investigation studied numerically the aerodynamical effects of different modifications in a model of a common sedan. Four car modifications as spoiler, wing profile spoiler, standard diffuser and curved diffuser and their combinations were reported. Using a three-dimensional sedan model created with Computer-Aided Design software, the modifications are applied and assessed their influence on aerodynamics at speeds ranging from 60 to 120 km/h. The spoiler, wing spoiler, standard diffuser and curved diffuser reducing the lift forces experienced by the vehicle. Three cases, spoiler, wing spoiler, and curved diffuser increase the drag forces Combining a curved diffuser and a spoiler significantly decreases lift forces by an average of 77.8%, albeit with a 15.3% increase in drag forces, by 120 km/h The synergy of a curved diffuser and a wing spoiler achieves a substantial 63.3% reduction of net vertical forces, with only a 7.9% increase in drag forces, by 120 km/h, offering improved control with lesser energy consumption in comparison to other combinations. Results show that modifications, greatly influence airflow interaction, with effects varying by speed. Importantly, the impact of using two modifications is not a simple sum of their individual effects; and it must be assessed thoughtfully alongside airflow alterations. [ABSTRACT FROM AUTHOR]

In order to enhance the stability of the tilt transition process, a new configuration of Quad-Tiltrotor UAV was presented in this paper. Firstly, numerical simulation was used to calculate and analyze the aerodynamic interaction between the front rotor/fuselage/rear rotor during the transition state mode. The calculation model of the isolated rotor, front-rear rotor, front rotor-fuselage, and front rotor-rear rotor-fuselage combination states are established. Besides, the effects of pitch, roll, and yaw moment on the fuselage at different tilt angles are analyzed. It is concluded that the front rotor is the leading factor in the aerodynamic interference of the whole UAV in the different combination states. The research results can provide a reference for the optimization design of the overall layout, structure, and flight control strategy of the cross-shaped quad-tiltrotor UAV, and can also provide solutions for the logistics application of urban air traffic. [ABSTRACT FROM AUTHOR]

Wedge tail airfoils refer to the addition of a wedge section to the tail of an airfoil. This modification has demonstrated greater efficiency in increasing the lift forces compared to the base airfoil design. Such airfoils are particularly important in scenarios where increased lift forces are required, such as in the fast and efficient maneuvering of marine and aerospace vehicles. This study aimed to predict the flow fields and aerodynamic coefficients of wedge tail airfoils using a multi-head perceptron (MHP) network and classical machine learning (ML) algorithms, including k-nearest neighbors, decision tree, and random forest. These predictions were based on airfoil sections, x–y grid coordinates, Mach number, and angle of attack, eliminating the need to solve the Navier–Stokes (NS) equations. The database required for training the MHP network and the ML models were generated using the Ansys solver, which solved the NS equations. The results of the models were compared, and it was observed that the MHP network consistently outperformed the others in terms of prediction accuracy. Additionally, the prediction process demonstrated a significant speed improvement of 125 times compared to conventional computational fluid dynamics techniques. Once the training was completed, the flow fields and aerodynamic coefficients for a wedge tail airfoil could be obtained within seconds. [ABSTRACT FROM AUTHOR]

This paper investigates the aerodynamic performance of a system of multiple vehicles (three) propelled by an electric fan/compressor system in a closed low-pressure environment. The study was conducted on a 2-D axisymmetric model of multiple vehicles traveling at the same cruising speed inside a tube. The flow field was computed using the unsteady RANS model. The results demonstrate a significant improvement in aerodynamic performance when using a multiple-vehicle system equipped with an air-breathing electrical engine. The combined use of multiple-vehicle and the air-breathing propulsion system eliminated the piston effect at low Mach numbers and reduced transonic range effects at higher Mach numbers. Consequently, a considerable enhancement in aerodynamic performance over the single-vehicle model was attained. A minimum of 11% and a maximum of 57% reduction of further in average system drag was achieved for M = 0.3 and 0.7, respectively. An increase in thrust was also observed in the multiple-vehicle system over the single-vehicle system. The results of the study demonstrated the advantage of using an air-breathing multiple-vehicle system as an efficient and environmentally friendly high-speed transportation system. [ABSTRACT FROM AUTHOR]

This article presents a validation study of the popular aeroservoelastic code suite OpenFAST leveraging weeks of measurements obtained during normal operation of a 2.8 MW land-based wind turbine. Measured wind conditions were used to generate one-to-one turbulent flow fields (i.e., comparing simulation to measurement in 10 min increments, or bins) through unconstrained and constrained assimilation methods using the kinematic turbulence generators TurbSim and PyConTurb. A total of 253 bins of 10 min of normal turbine operation were selected for analysis, and a statistical comparison in terms of performance and loads is presented. We show that successful validation of the model was not strongly dependent on the type of inflow assimilation method used for mean quantities of interest, which had median modeling errors per wind-speed interval generally within 5 %–10 % of the measurement. The type of inflow assimilation method did have a larger effect on the fatigue predictions for blade-root flapwise and tower-base fore–aft quantities, which surprisingly saw larger errors from the assumed higher-fidelity assimilation methods. Avenues for further work are discussed and include possible improvements to the aerodynamic, structural, and controller modeling that may offer insight on the origin of the up to ∼ 40 % median overprediction of fatigue for these quantities. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of blade flexibility on the aerodynamics and wake of large offshore turbines using a flexible actuator line method (ALM) coupled to the structural solver BeamDyn in large-eddy simulations. The study considers the IEA 15 MW reference wind turbine in close-to-rated operating conditions. The flexible ALM is first compared to OpenFAST simulations and is shown to consistently predict the rotor aerodynamics and the blade structural dynamics. However, the effect of blade flexibility on the loads is more pronounced when predicted using the ALM compared with using the blade element momentum theory. The wind turbine is then simulated in a neutral turbulent atmospheric boundary layer with flexible and rigid blades. The significant flapwise and torsional mean displacements lead to an overall decrease of 14 % in thrust and 10 % in power compared to a rotor with no deformation. These changes influence the wake through a reduced time-averaged velocity deficit and turbulent kinetic energy. The unsteady loads induced by the rotation in the sheared wind and the turbulent velocity fluctuations are also substantially affected by the flexibility and exhibit a noticeably different spectrum. However, the influence of these load variations on the wake is limited, and the assumption of rigid blades in their deformed geometry is shown to be sufficient to capture the wake dynamics. The influence of the resolution of the flow solver is also evaluated, and the results are shown to remain consistent between different spatial resolutions. Overall, the structural deformations have a substantial impact on the turbine performance, loads, and wake, which emphasizes the importance of considering the flexibility of the blades in simulations of large offshore wind turbines. [ABSTRACT FROM AUTHOR]

This study presents findings from a wind tunnel experiment investigating a model wind turbine equipped with aft-swept blades. Utilising particle image velocimetry, velocity fields were measured at multiple radial stations. These allow the derivation of blade-level aerodynamic parameters, including bound circulation, induction values, inflow angle, angle of attack, and forces normal and tangential to the rotor plane. The measured local lift coefficient aligns well with the lift polar of the design airfoil, validating the experimental approach. The resulting public dataset provides a comprehensive aerodynamic characterisation of rotating swept blades in controlled conditions. It can serve as a baseline for future experimental research on swept wind turbine blades. Furthermore, it is valuable in validating numerical models of varying fidelity simulating swept wind turbine blades. The provided blade-level aerodynamics are particularly relevant to lower-fidelity models such as blade element momentum theory and lifting-line algorithms. At the same time, the measured flow fields can be compared against higher-fidelity simulation results from computational fluid dynamics. [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.)

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.)

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.)

Usually at the design stage of a gas turbine unit (GTU) the nominal operating mode is considered. This mode is defined by the axial exit of the flow from the turbine, in order to reduce losses with the exhaust velocity. Axial entry into the diffuser is optimal, due to the absence of incidence angle on the support struts. Struts are the integral part of the diffuser, where the rear bearing support of the turbine rotor is located. However, the GTU operates for a long time both in the nominal and in variable modes. Partial modes are characterized by significant incidence angles on the struts, which leads to flow separation and a notable increase in pressure losses in the diffuser. Maintaining a satisfactory flow in the diffuser in a wide range of modes is an important issue. In this paper, the stage-diffuser system is studied by experimental and numerical methods in a wide range of modes. This study shows that at the last stage when the flow angle is less than 50°, the flow in the diffuser acquires an asymmetric character with the developed vortices. This means that numerical simulation in an engineering approach cannot repeat the nature of the flow at low load modes. Nevertheless, a comparison of the total parameters of the experiment and simulation shows close agreement (a difference of about 5%) even for modes with large incidence angles on the diffuser struts. [ABSTRACT FROM AUTHOR]

In this paper, the non-destructive assessment of thermo-mechanical characteristics of extremely rigid structures made up of natural composites fibers is conducted. Higher-force dynamic mechanical investigation has allowed for new insights, which is not possible with the regularly employed static and impact test methods. Natural fibers made up of composite sandwich panels with aluminum and aramid honeycomb cores are studied. Various panel cores of equal stiffness and damping capabilities are compared over flight frequencies ranging from 1 to 100 Hz. It was discovered that the exhaustion of the natural fiber sandwich panels depends on both the core material and the applied static load. Additionally, temperature sweeps were carried out, and it was discovered that they can identify variations in the post processing of the natural fiber laminated panels and show the variations in the transition temperature of the matrix material. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive framework for optimising vehicle performance, integrating advanced simulation techniques with optimisation methodologies. The aim is to find the best racing line, as well as the optimal combination of parameters and control inputs to make a car as fast as possible around a given track, with a focus on energy deployment and recovery, active torque distribution and active aerodynamics. The problem known as the Minimum Lap Time Problem is solved using optimal control methods and direct collocation. The solution covers the modelling of the track, vehicle dynamics, active aerodynamics, and a comprehensive representation of the powertrain including motor, engine, transmission, and drivetrain components. This integrated simulator allows for the exploration of different vehicle configurations and track layouts, providing insights into optimising vehicle design and vehicle control simultaneously for improved performance and energy efficiency. Test results demonstrate the effect of active torque distribution on performance under various conditions, enhanced energy efficiency and performance through regenerative braking, and the added value of including parameter optimisation within the optimisation framework. Notably, the simulations revealed interesting behaviours similar to lift-and-coast strategies, depending on the importance of energy saving, thereby highlighting the effectiveness of the proposed control strategies. Also, results demonstrate the positive effect of active torque distribution on performance under various conditions, attributed to the higher utilization of available adherence. Furthermore, unlike a simpler single-track model, the optimal solution required fine control of the active aerodynamic systems, reflecting the complex interactions between different subsystems that the simulation can capture. Finally, the inclusion of parameter optimisation while considering all active systems, further improves performance and provides valuable insights into the impact of design choices. [ABSTRACT FROM AUTHOR]

The perch landing maneuver of a wing-deforming unmanned aerial vehicle (UAV) was investigated through a framework that uses the free, open-source OpenFOAM with 6 degrees of freedom (6DOF) simulations. The framework uses a moving grid to follow the trajectory of the UAV, reducing computational resources. Together with the ability to allow internal grid deformation, sliding mesh, and algorithm addition, it can accurately mimic the entire landing process. Different wing deformation speeds, additional elevator rotation and emulated propeller lift were added to the 6DOF simulations to investigate their effects on the landing maneuver. The results showed that the wing deformation retraction speed has a considerable effect on the trajectory and velocity of the UAV. The wing deformation reduced the forward velocity of the UAV by 32%, from 13.89 to 9 m/s. With the elevator control, the velocity was reduced to 5 m/s. Lastly, and an activation time of 1 s for the emulated propeller lift can further decrease the velocity to around 4.2 m/s. A better algorithm for the emulated propeller lift may be able to give a superior performance. This framework allows us to understand the underlying perch landing maneuver aerodynamics. It can also be used on problems like fast-turning agile and flapping wing flight. [ABSTRACT FROM AUTHOR]

This study explores the implications of the number of blades on the performance of both open and shrouded rotors. By conducting a thorough experimental analysis at a fixed solidity ratio, this research seeks to enhance our understanding of rotor dynamics and efficiency. Two-, three-, four-, and five-bladed rotors were designed and manufactured to have the same solidity ratio. This leads to smaller chord distribution values for higher blade numbers. The experimental analysis aims to quantify the effects of the number of blades and provides a comparative analysis of performance differences between the two rotor configurations (shrouded and open). For the open rotor, results indicate that increasing the number of blades has a minimal impact on overall performance. This is due to the decrease in the tip loss factor being counterbalanced by a decline in efficiency caused by the two-dimensional airfoil performance, which results from a smaller chord and a lower Reynolds number. In contrast, the shrouded rotor exhibits a noticeable performance decay with an increased blade count. Since tip loss is inherently absent in shrouded designs, the decline is primarily attributed to the two-dimensional airfoil performance. This decay occurs while maintaining a constant solidity ratio, highlighting the significant effect of blade count on shrouded rotor efficiency, thereby contributing to the optimization of rotor design in various engineering applications. [ABSTRACT FROM AUTHOR]

In 2021, the Ingenuity helicopter performed the inaugural flight on Mars, heralding a new epoch of exploration. However, the aerodynamics on Mars present unique challenges not found on Earth, such as low chord-based Reynolds number flows, which pose significant hurdles for future missions. The Ingenuity's design incorporated a Reynolds number of approximately 20,000, dictated by the rotor's dimensions. This paper investigates the implications of flows at a Reynolds number of 50,000, conducting a comparative analysis with those at 20,000 Re. The objective is to evaluate the feasibility of using larger rotor dimensions or extended airfoil chord lengths. An increase in the Reynolds number alters the size and position of Laminar Separation Bubbles (LSBs) on the airfoil, significantly impacting performance. This study leverages previous research on the structure and dynamics of LSBs to examine the flow around a cambered plate with 6% camber and 1% thickness in Martian conditions. This paper details the methods and mesh used for analysis, assesses airfoil performance, and provides a thorough explanation of the results obtained. [ABSTRACT FROM AUTHOR]

Nowadays, high aerodynamic load has made blade separation an issue for compact axial compressors under high-altitude low-Reynolds-number conditions. In this study, herringbone grooves inspired by bird feathers were applied to suppress the suction side separation and reduce loss. To study the effect of bio-inspired herringbone grooves on the aerodynamic performance of compressor cascades, a high subsonic compressor cascade was taken as the research object. Under the conditions of different Reynolds numbers, the effects of herringbone grooves of different depths on the flow separation were numerically studied. The research results show that at a high-Reynolds-number condition (Re = 5.6 × 105), the sawtooth-shaped wake induced by herringbone grooves increases the turbulent mixing loss near the suction surface, and the blade performance deteriorates. At a low-Reynolds-number condition (Re = 1.3 × 105), the span-wise secondary flow and micro-vortex structure induced by the herringbone grooves effectively suppress the laminar separation on the suction surface of the blade, and there is an optimal depth for the herringbone grooves that reduces the profile loss by 8.33% and increases the static pressure ratio by 0.55%. The selection principle of the optimal groove depth with the Re is discussed based on the research results under six low-Reynolds-number conditions. [ABSTRACT FROM AUTHOR]

Because fixed-wing unmanned aerial vehicles (UAVs) require high-speed taxiing for takeoff and landing, the aircraft's stability during taxiing is critical. However, despite research on the taxiing stability of fixed-wing UAVs conducted in taxiing motion simulations employing various tire models, the applicability of the models to fixed-wing UAV taxiing simulations remains unclear, as does the rationale behind the parameter settings in the models. Therefore, in our study, we measured the forces acting on the tires of a fixed-wing UAV under various conditions, including tire loads of 1.6–3.6 kg and tire slip angles of 0–40 deg. Based on the results, we modified conventional tire models and assessed their applicability in taxiing simulations. Among our findings, the parameter values of the models significantly differed from those used in crewed aircraft taxiing simulations, and the presence or absence of load parameters in the lateral force tire models significantly affected the dynamics. Furthermore, the aerodynamics acting on the aircraft enhanced the straight-line stability during taxiing, resulting in reduced forces on the tires. [ABSTRACT FROM AUTHOR]

In this work we construct a surrogate model using artificial neural networks (ANN) to predict the steady-state behavior of an unmanned combat aircraft. We employ various strategies to improve the model's accuracy, including the consideration of design tolerances, creating independent surrogate models for the different flow regimes and encoding non-numeric input features. We also explore alternative machine learning models, albeit they demonstrated a lower reliability than ANNs. Two scenarios are considered for the target variable: one focusing solely on predicting the pitching moment coefficient, and the other incorporating the roll moment coefficient as well. We investigate different methods for handling multiple targets, finding that constructing a single model with multiple outputs consistently outperforms developing separate models for each target variable. Overall, the ANN provides predictions that show excellent agreement with the experimental data, demonstrating its effectiveness and reliability in aerodynamic modeling. [ABSTRACT FROM AUTHOR]

Modern fighter aircraft increasingly need to conjugate aerodynamic performance and low observability. In this paper, we showcase a methodology for a gradient-based bidisciplinary aero-stealth optimization. The shape of the aircraft is parameterized with the help of a CAD modeler, and we optimize it with the SLSQP algorithm. The drag, computed with the help of a RANS method, is used as the aerodynamic criterion. For the stealth criterion, a function is derived from the radar cross-section in a given cone of directions and weighed with a function whose goal is to cancel the electromagnetic intensity in a given direction. Stealth is achieved passively by scattering back the electromagnetic energy away from the radar antenna, and no energy is absorbed by the aircraft, which is considered as a perfect conductor. A Pareto front is identified by varying the weights of the aerodynamic and stealth criteria. The Pareto front allows for an easy identification of the CAD model corresponding to a chosen aero-stealth trade-off. [ABSTRACT FROM AUTHOR]

As part of the strategy to achieve net-zero Greenhouse Gas (GHG) emissions in international maritime shipping, there is ongoing exploration into the use of wind propulsion systems as auxiliary ship propulsion devices. When considering a rigid sail as the wind propulsion system, evaluating the performance of a single sail is relatively simple. However, assessing the performance of multiple sails is more challenging due to the interference between the sails and between the sails and the hull. In this study, the thrust characteristics of two rigid sails attached to a ship are investigated by using Computational Fluid Dynamics (CFD). This includes considering the interference effects between the sails themselves and between the sails and the hull. The research reveals the innovative optimized angle of attack for maximizing thrust under tailwind conditions. At 150° in relative wind direction, the best performance is achieved with a low angle of attack on the fore side sail and a high angle of attack on the aft side sail. At 180° in relative wind direction, a high angle of attack on the fore side sail and a low angle of attack on the aft side sail yield the best results. Here, a "low" angle of attack means that the lift force is greater than the drag force, while a "high" angle of attack means the drag force is greater than the lift force. In this study, the force in the ship's forward direction is only focused on optimizing the angles of attack of the two sails. However, the side forces caused by the sails are also significant for the ship's sailing conditions. Therefore, future work will involve optimizing the angles of attack under drifting conditions. [ABSTRACT FROM AUTHOR]

Floating offshore wind turbines (FOWTs) experience unbalanced loads and platform motion due to the coupling of variable wind and wave loads, which leads to output power fluctuation and increased fatigue loads. This paper introduces a new blade pitch control strategy for FOWTs that combines fuzzy logic with a linear quadratic regulator (LQR) and a proportional-integral (PI) controller. The fuzzy PI controller dynamically adjusts the PI control gains to regulate rotor speed and stabilize output power. Fuzzy LQR is employed for individual pitch control, utilizing fuzzy logic to adaptively update feedback gains to achieve stable power output, suppress platform motion, and reduce fatigue load. Co-simulations conducted with OpenFAST (Fatigue, Aerodynamics, Structures, and Turbulence) and MATLAB/Simulink under diverse conditions demonstrate the superiority of the proposed method over traditional PI control. The results show significant reductions in platform pitch, roll, and heave motion by 17%, 27%, and 48%, respectively; blade out-of-plane, pitch, and flapwise bending moments are reduced by 38%, 44%, and 36%; and the tower base roll and pitch bending moments are reduced by up to 29% and 22%, respectively. The proposed control scheme exhibits exceptional environmental adaptability, enhancing FOWT's power regulation, platform stability, and reliability in complex marine environments. [ABSTRACT FROM AUTHOR]

As the velocity of a train increases, the corresponding air pumping power consumption of the brake discs increases proportionally. In the present experimental study, a standard axle-mounted brake disc with circumferential pillars was analyzed using a 1:1 scale model and a test rig in a wind tunnel. In particular, three upstream velocities were selected on the basis of earlier investigations of trains operating at 160, 250, and 400 km/h, respectively. Moreover, 3D steady computational fluid dynamics (CFD) simulations of the flow field were conducted to compare with the wind tunnel test outcomes. The results for a 3-car train at 180 km/h demonstrated: (1) good agreement between the air resistance torques obtained from the wind tunnel tests and the related numerical results, with differences ranging from 0.95% to 5.88%; (2) discrepancies ranging from 3.2 to 3.8 N · m; (3) cooling ribs contributing more than 60% of the air resistance torque; (4) the fast rotation of brake discs causing a significantly different flow field near the bogie area, resulting in 25 times more air pumping power loss than that obtained in the stationary brake-disc case. [ABSTRACT FROM AUTHOR]

The design of an aircraft's internal structure, and therefore the appropriate choice of material type, is a direct function of the performed tasks and the magnitude and type of the acting loads. The design of a durable aircraft structure with appropriate stiffness and lightness requires knowledge of the loads that will be applied to the structure. Therefore, this paper presents the results of an aerodynamic experimental test and numerical analysis of a newly designed jet-propelled aerial target. The experimental tests were carried out in a low-speed wind tunnel for a wide range of angles of attack and sideslips. Moreover, they were performed for various configurations of the airplane model. In addition, the results of the experimental test were supplemented with the results of the numerical analysis performed using computational fluid dynamics methods. During numerical analysis, specialized software based on solving partial differential equations using the Finite Volumes Method was used. This article presents the methodology of the conducted research. The results of the aerodynamic analysis are presented in the form of diagrams showing the aerodynamic force and moment components as a function of the angle of attack and sideslip. In addition, qualitative results of the flow around the plane have been presented. The results obtained prove that the adopted methods are sufficient to solve these types of problem. The aerial system was positively verified during the qualification tests of the system at the Polish Air Force training range and finally received the type certificate. [ABSTRACT FROM AUTHOR]

Small‐scale multirotor drones often require careful consideration of many aspects including the selection of structural parameters and the propulsion system. Double‐layer staggered octocopters (DLSOs) are a type of arrangement with advantages in structural layout and aerodynamic performance compared with other configurations, which can conserve structural space and restrict the aerodynamic interaction between the rotors. For the purpose of increasing thrust, reducing weight, and maximizing power efficiency, DLSOs are designed with the optimal combination of structural parameters and propulsion systems using noncustomized products. The optimization process is divided into two steps. First, utilizing the simulation results from Latin hypercube design‐guided sample points, a surrogate model is established by the radial basis function (RBF)–based neural network to forecast the thrust of the staggered rotors. An optimal structural configuration of the DLSO is then obtained by applying the adaptive geometry estimation–based multiobjective evolutionary algorithm (AGE‐MOEA). Second, based on an improved propulsion system sizing method, the propulsion system, including motors, electronic speed controllers (ESCs), and batteries, is further optimized using standard methods and noncustomized propulsion system product data, to minimize weight and maximize power efficiency. The optimized DLSO has greatly enhanced its total thrust and power efficiency when compared to some well‐known market products. [ABSTRACT FROM AUTHOR]

Abnormal carbody vibrations can significantly affect the safety and stability of high-speed trains. In this study, we conducted field measurements to analyze low-frequency swaying of a high-speed train on the Chinese alpine railway line. The test results reveal that the tail vehicle of the train swayed laterally in certain sections of the track, resulting in vehicle lateral stability index exceeding the limit. The swaying frequency of the carbody was mainly distributed in the range of 1.4–1.5 Hz. The causes of abnormal swaying were analyzed by establishing a computational fluid calculation model. Computational fluid dynamics calculations revealed that lift force, side force, and yaw moment were higher for the tail vehicle compared to the head and middle vehicles. The train-track coupled dynamics simulation results demonstrate that aerodynamics disturbances may be the key factor to intensify the abnormal swaying of the high-speed train tail vehicle. [ABSTRACT FROM AUTHOR]