Search Results (2,798)

The aerodynamic calculation model of a high-speed train on the embankment under crosswind is built according to computational fluid dynamic (CFD) theory in order to obtain the aerodynamic forces on the train, and the running process of a high-speed train on the embankment is simulated on basis of multi-body dynamic theory. Furthermore, the crosswind aerodynamic performance and running reliability of a high-speed train on the embankment are studied. Considering the randomness of wind load, the influence of the embankment height, the embankment slope coefficient and the position of the upper/lower wind line, the aerodynamic characteristics of the train are analyzed. At the same time, taking the aerodynamic load as input, considering the different embankment heights, slope coefficients, mean wind velocities and train speeds, the change rules of failure probability for train operation with embankment height, train speed and wind velocity are analyzed, and then the probabilistic characteristic wind curve of the train and running safety area for the train under different embankment heights are obtained. The results show that the aerodynamic coefficients of the train gradually increase as the embankment height increases. When the embankment slope coefficient is the same, the absolute value of aerodynamic factor of the leading car is the largest. The aerodynamic factor of the train running on the downwind line is higher than on the upwind line. If the failure probability is given, the maximum operating speed of the train when the wind speed reaches a certain value can be determined through the probabilistic characteristic wind curve. Full article

Low-Reynolds-number micro aerial vehicles and lightweight deployment systems require aerodynamic configurations that provide vertical support and favorable passive responses to attitude disturbances. Winged seeds delay descent through autorotation, wing curvature, and mass distribution, offering a natural model for such designs. A three-dimensional model of a Hopea hainanensis-inspired double-winged samara was developed, and steady multiple-reference-frame (MRF) simulations were performed at seven rotating attitudes (−45, −22.5, −10, 0, 10, 22.5, and 45 degrees) and a nonrotating 90-degree reference. Aerodynamic forces, moments, surface pressure distributions, and streamline structures were compared. Negative deflections maintained relatively high vertical support, whereas the vertical force decreased progressively with positive deflection. The −45-degree attitude combined strong vertical support, limited lateral offset, and a restoring moment increment, producing the highest equal-weight score among the rotating cases. The pitching moment response varied nonlinearly with disturbance amplitude, and the static-restoring tendency became more evident over moderate and large deflections. Surface pressure distributions, streamline structures, and the equivalent aerodynamic line of action showed that redistribution of wing loading and migration of the effective moment arm jointly governed the force and moment variations. These results characterize the quasi-steady aerodynamic response under prescribed rotation and provide guidance for the passive aerodynamic design of low-Reynolds-number aerial vehicles and lightweight deployment systems. Full article

This article investigates the numerical simulation of heat-and-aerodynamic cycles in the ventilated air gap of a multilayer composite wall façade system in a hot climate using ANSYS 19/2 Fluent. Standard normative techniques rely on averaged, stationary boundary conditions and account for neither the height-wise inequality of solar exposure nor the dependence of air density and viscosity on barometric pressure and temperature, resulting in significant errors in predicting the actual heating of such structures. The model was calibrated on the authors’ own full-scale, in situ measurements of temperature, air speed and solar exposure in the ventilated gap of a nine-storey building, from which linear height-dependent surface-temperature relations were derived and used as boundary conditions for 3D models of façades 25 and 60 m tall. Thirty-two finite-volume experiments were performed under free convection (Boussinesq approximation), varying gap width (5 and 10 cm), inlet width (20 and 40 cm), barometric pressure (690 and 770 mmHg) and external air temperature (20 and 40 °C). Façade height proved the dominant factor (air speed up to 1.8 times higher, temperature 3–12.1 °C higher), followed by gap width (speed lower by 1.7 times, temperature by 3–5 °C), whereas pressure and inlet width altered the results by no more than 6%. Discrepancies with the standard calculation reached 10 °C in temperature and a two-fold difference in flow speed, confirming the need for verified CFD simulation when designing ventilated composite wall façades in hot climates. Full article

Conventional vertical-axis wind turbines (VAWTs) rely on rigid blades that are heavy and require expensive materials and manufacturing processes to withstand aerodynamic loads. This study explores flexible sail-type blades as a low-cost alternative capable of achieving comparable performance. Small-scale sail-type VAWTs employing blades made out of fabric similar to maritime sails were designed, fabricated, and tested in a wind tunnel. One edge of each sail was hemmed to a vertical rod, while the opposite edge was secured at its end to top and bottom end disks. The turbine radius and height were fixed at 19 cm and 21 cm, respectively. Experiments were conducted in a wind tunnel and measurements included wind speed, turbine rotational speed, and the generator current and voltage. A total of 36 configurations were evaluated by varying four design parameters: number of sails (2, 3, and 6), chord length (10 cm and 15 cm), pitch angle (0°, 15°, 30°, and 45°), and blade shape (rectangular or trapezoidal). Performance was assessed using power output (P), power coefficient (Cp), and tip-speed ratio (TSR). Experimental results were validated by comparison with test data for a conventional rigid-bladed VAWT. The best-performing configuration was a three-sail turbine with rectangular blades, 15 cm chord length, and 0° pitch angle, producing 547 mW at 177 RPM, corresponding to a Cp of 0.053 at a TSR of 0.59. Numerical predictions using state-of-the-art codes were used to further assess sail-type VAWT performance. Under the test conditions considered, the sail-type VAWT not only showed better performance but also comparable self-starting capability compared to a rigid-bladed VAWT. However, due to the maximum wind speed limitation of the test facility, the complete Cp-TSR characteristic curve could not be determined. Moreover, preliminary estimates indicate a potential 24% reduction in total turbine capital cost and an overall 30% reduction in turbine mass of sail-type turbines over conventional HAWTs, demonstrating that flexible sail blades are a promising low-cost option that needs further investigation to realize their full potential. Full article

To investigate the multi-stage inflation mechanism of a supersonic reefed parachute cluster, an ALE-based fluid–structure interaction method is applied. The canopy permeability is modeled using the Ergun equation, and the virtual structure contact method is employed to handle contact issues induced by large canopy deformation. A flow-domain time-step updating strategy is employed to perform finite-mass inflation simulation. The accuracy of the adopted method is validated by wind-tunnel test data. Full-stage simulations from supersonic to subsonic regimes are conducted to investigate the canopy deformation, flow-field structure, system attitude, and aerodynamic response of the parachute cluster–payload system. The results demonstrate that the parachute cluster maintains stable overall attitudes throughout multi-stage inflation, with axial translation dominating and lateral interference remaining negligible. A steady bow shock with strong inter-canopy shock interaction is formed in the first supersonic stage, followed by prominent vortex shedding in the second transonic stage, and full wake isolation with optimal deceleration efficiency achieved in the third subsonic stage. Quantitative comparison with a single-parachute system reveals stage-dependent interference: higher peak load and stronger oscillations in the supersonic stage, and approximately twice the load in the transonic/subsonic stages. The findings can provide critical theoretical guidance and technical support for engineering implementation of supersonic reefed parachute cluster deceleration systems. Full article

Two-box edge girders are widely employed in bridge engineering owing to their superior mechanical properties. However, these girders are susceptible to vortex-induced vibrations (VIVs) due to their blunt configuration. Therefore, it is of great significance to study their VIV performance and specific suppression measures. Wind tunnel tests simultaneously measuring vibration and pressure and computational fluid dynamics (CFD) were performed to investigate the effects of sidewalk railing height and inclination angle on the VIV responses at different wind attack angles. Furthermore, surface pressure distribution, the relationship between distributed aerodynamic lift and the general vortex-excited force (VEF), and flow field characteristics were analyzed to elucidate the VIV suppression mechanism. Results indicate that vertical VIVs occur across all tested wind attack angles, with the most pronounced response observed at α = +5°. Both railing height and inclination angle significantly influence the VIV response, yet their influence patterns are different. Specifically, the VIV amplitude consistently increases with railing height across all wind attack angles, whereas the effect of the inclination angle varies depending on the wind attack angle. The leading and trailing edges of the upper surface and the trailing edge of the lower surface are identified as the critical areas responsible for VIV. The variations in fluctuating pressure coefficient and contribution value with railing configuration are generally consistent with those of the VIV response. Moreover, while the railing configuration does not alter the vortex shedding mode, it significantly modifies the vortex scale and pressure intensity, thereby resulting in distinct VIV responses. Full article

Heat stress remains a major constraint in dairy production. Mechanically cross-ventilated barns mitigate thermal load, but conventional in-line freestall layouts create wake interference that reduces airflow to downstream cows. This study used computational fluid dynamics (CFD), with numerical verification and benchmarking against empirical bluff-body correlations, to evaluate stall-level strategies for improving cow body sensible convective heat transfer. Simulations represented a head-to-head freestall section with anatomically realistic Holstein cows at inlet velocities of 0.5–3.0 m s⁻¹. Five configurations were examined: baseline in-line, staggered, staggered with an overhead baffle, single 45° vertical deflector, and double vertical deflectors. The staggered configuration increased the mean second-row cow body sensible convective heat-transfer rate by approximately 15–20% relative to the baseline, while the single deflector increased it by up to 29%. At 3.0 m s⁻¹, the double-deflector configuration produced an approximate 34% increase. A representative AOZ analysis at 1.0 m s⁻¹ showed that greater heat-transfer performance did not necessarily correspond to lower plane-wide velocity variation. These findings demonstrate that stall-level aerodynamic modifications can enhance cow body sensible convective heat transfer under controlled modeling assumptions. Full article

The aerodynamic characterization of propeller-driven UAVs is often constrained by the unfeasibility of testing the complete airframe–propeller assembly in a wind tunnel, since geometric scaling prevents simultaneous similarity of both the airframe and the propeller. To address this limitation, this work presents an integrated experimental–numerical methodology that reconstructs the full-scale free-air aerodynamic behaviour of a tractor-propeller UAV combining wind-tunnel measurements of the scaled airframe (without the propeller) and the full-scale propeller. Computational fluid dynamics (CFD) is not used to predict the full-scale UAV directly; it is used to predict differences between matched configurations, while the absolute aerodynamic level remains anchored to experiments. Dedicated CFD simulations are carried out to isolate three distinct physical contributions: scale effects, wind-tunnel blockage, and propeller installation effects. In the developed methodology, numerical simulations complement the experimental data to obtain corrected full-scale aerodynamic coefficients and propulsive maps together with a longitudinal force-equilibrium model used to determine the longitudinal force-equilibrium operating point. The reconstruction shows that scale and wind-tunnel blockage effects primarily alter the airframe aerodynamic characteristics, with a minor influence on equilibrium incidence, while propeller installation produces a substantial thrust augmentation due to airframe-induced inflow modification. Accounting for these effects leads to an overprediction of the propeller rotational speed by approximately $23\%$ when installation effects are neglected, demonstrating that the installed performance cannot be obtained by a linear superposition of isolated airframe and isolated propeller data. Full article

UAV-assisted greenhouse tomato pollination requires lateral airflow delivery toward flower clusters distributed along the crop canopy. To address this, an asymmetric duct was designed to passively redirect the rotor wake through geometric modification of three inner-wall curvature parameters (R₁, R₂, R₃). Three-dimensional CFD simulations were conducted to evaluate the effects of these parameters on airflow redirection and aerodynamic performance. Compared with a conventional symmetric duct, the asymmetric duct shifted the high-velocity wake from a predominantly vertical direction toward the canopy side. Among the three parameters, R₃ exerted the greatest influence: increasing R₃ from 20 to 65 mm improved the lift-to-drag ratio from 24.7 to 184.2 but reduced the airflow velocity delivered to the pollination region from 6.48 to 2.82 m·s⁻¹. The selected configuration (R₁ = 11 mm, R₂ = 20 mm, R₃ = 25 mm) delivered an airflow velocity of 6.03 m·s⁻¹ at an operating height of 1.44 m, with a lift of 7.04 N and a lift-to-drag ratio of 37.0. These results demonstrate that passive geometric asymmetry can redirect rotor-induced airflow toward the canopy side while balancing airflow delivery, operating height, and aerodynamic performance under greenhouse spatial constraints. Full article

Accurate prediction of automotive aerodynamic wind noise is important for cabin comfort and early-stage styling, yet conventional CFD and wind-tunnel workflows are too expensive for rapid design iteration. This paper proposes a point cloud surrogate that combines farthest-point sampling with a Transolver-derived, physics-inspired slice-attention mechanism. Here, physics-inspired denotes a representation-level inductive bias; the model does not impose governing-equation residuals, conservation constraints, or physics-based losses. Exterior meshes are converted into 10,240-point geometric inputs and assembled into a controlled dataset of 867 sedan and SUV variants generated at 120 km/h and zero yaw. On the random test split, the model obtains RMSE values of 2.30 dB(A), 2.56 dB for SPL, and 0.0068 for the dimensionless articulation index (AI), with 0.80 s single-sample inference on an RTX 4090. Repeated-seed and grouped-split analyses indicate a favorable accuracy–latency trade-off while also showing a measurable performance decrease for held-out vehicle families. A single-vehicle wind-tunnel comparison confirms strong frequency-trend correlation but reveals a mean simulation over-prediction of 2.70 dB; therefore, the current surrogate should be interpreted primarily as an emulator of the simulation labels rather than a universally unbiased predictor of measured cabin noise. Full article

Efficient maximum power extraction in variable-speed wind energy conversion systems (WECSs) remains challenging because of nonlinear turbine dynamics, continuously varying wind conditions, measurement disturbances, and mechanical-parameter uncertainties. This study presents a robust nonlinear integral backstepping control (BC) strategy for generator-speed regulation within a Tip-Speed Ratio (TSR)-based Maximum Power Point Tracking (MPPT) framework. The proposed controller combines nonlinear backstepping stabilization with integral compensation to improve reference tracking and reduce persistent tracking errors. The turbine-generator mechanical inertia is explicitly incorporated into the control formulation, providing a physically consistent representation of the mechanical dynamics and enabling systematic evaluation of parameter uncertainty. A comprehensive comparative assessment is conducted in MATLAB/Simulink using four control strategies: proportional-integral (PI), integral-proportional (IP), sliding-mode control (SMC), and the proposed integral BC. The controllers are evaluated under five complementary scenarios: variable wind speed, measurement noise, abrupt stepwise wind-speed variations, ±20% mechanical-inertia uncertainty, and a 10-ms rotor-speed measurement delay. Performance is assessed using the Integral of Squared Error (ISE), Integral of Absolute Error (IAE), and Integral of Time-weighted Absolute Error (ITAE), together with statistical measures across the five scenarios. Under the baseline variable-wind condition, BC achieves ISE = 24.4164, IAE = 1.539, and ITAE = 0.716, outperforming PI, IP, and SMC in all three indices. Under abrupt stepwise wind-speed variations, BC further achieves ISE = 0.00110, IAE = 0.0056, and ITAE = 0.0529, demonstrating rapid transient error suppression. The proposed controller remains stable under ±20% mechanical-inertia variations and a 10-ms measurement delay. Across the five scenarios, BC achieves the lowest mean ISE, IAE, and ITAE values of 19.353, 1.231, and 2.642, respectively, as well as the lowest standard deviations for ISE and IAE. SMC exhibits particularly consistent performance under measurement noise and the lowest standard deviation for ITAE. Overall, the results demonstrate that the proposed integral BC provides the most favorable balance of tracking accuracy, transient performance, and robustness among the investigated strategies. The improved rotor-speed regulation supports operation near the optimal TSR and effective aerodynamic power extraction. The findings highlight the potential of the proposed approach for robust MPPT control of variable-speed WECSs. Full article

Circulation control is an efficient active flow control technique that enhances aerodynamic lift by injecting a tangential jet near the trailing edge, altering the circulation around the airfoil. This study investigates the influence of three key geometric parameters—Coanda surface radius, slot height, and jet angle—on the aerodynamic performance of a NACA4309-based circulation-control airfoil (NACA4309-CCA) operating under a fixed ground clearance (hg/c = 0.14), representative of high-speed aerodynamically alleviated marine vehicles. Numerical simulations are performed using the Reynolds-averaged Navier–Stokes equations with the SST k-ω turbulence model. The results show that increasing r/c enhances lift up to a limit (r/c ≈ 0.017), beyond which flow separation occurs, reducing lift. For a fixed momentum coefficient (=0.01), an optimal h/c = 0.0007 balances jet momentum and mass flow, yielding the highest lift. The jet angle study reveals that the maximum lift (CL = 2.684) is achieved at θ ≈ 10°, but θ = 0° (CL = 2.581) is recommended for practical implementation due to simpler geometry and stable attachment, with only a 3.84% loss in lift relative to the maximum. The findings provide comparative numerical trends for the design of circulation-control systems on aerodynamically alleviated marine vehicles under the investigated conditions. Full article

The legs of flying insects play a critical role in enabling seamless transitions between aerial and terrestrial environments. These appendages serve multiple functions, including landing, walking, jumping, and transitioning from jumping to flight (takeoff). Such capabilities have inspired engineers to seek similar multimodal mechanisms in Flapping-Wing Aerial Robots (FWARs) to expand their operational versatility across diverse environments. However, designing multimodal mechanisms with distinct kinematic and propulsive characteristics remains challenging, particularly in the domain of autonomous jump takeoff for FWARs, where research remains relatively sparse. In this study, inspired by the jumping takeoff strategy and hindleg kinematics of the Asian migratory locust (Locusta migratoria), we propose a functional bio-inspired jumping takeoff mechanism that extracts selected mechanical principles of the locust jumping system, including elastic energy accumulation, temporary mechanical locking, and rapid energy release. The mechanism employs a gear–crank–slider transmission system and utilizes one-way bearings to regulate the locking and disengaging states, enabling the storage and rapid release of energy for jump takeoff, thereby achieving autonomous takeoff of the robot. Adams dynamic simulations show that at a torsion spring angle of 40°, the mechanism achieves a maximum resultant velocity of 1.955 m/s, a jump height of 168.2 mm, and a horizontal displacement upon landing of 134.6 mm. Ansys Fluent (2024 R2) simulations under multiple operating conditions further confirm that the aerodynamic performance is optimal at a takeoff angle of attack(α) of 5° with a torsion spring angle(β) of 40°, yielding a lift-to-drag ratio of 3.005. This work presents a functional bio-inspired jumping takeoff mechanism based on selected mechanical principles of locust jumping, providing a potential approach for improving the autonomous takeoff capability of small-scale FWARs. Full article

This paper presents a numerical investigation of the effect of rotational speed on the development of leakage flow in a low-speed axial fan equipped with a rotating shroud. Rotor deformation induced by centrifugal forces and aerodynamic loading is taken into account through a one-way coupling between steady CFD simulations and static FEM analyses. Aerodynamic and structural results obtained at four rotational speeds are validated against available experimental data collected by the same research group, and the different leakage flow patterns associated with rotor deformation are correctly reproduced. Subsequently, the deformed geometries corresponding to two rotational speeds and operating at the same non-dimensional flow coefficient are used to perform URANS simulations. The numerical results provide insight into the leakage flow behavior within the gap between the rotating shroud and the stationary casing, a region that cannot be experimentally investigated due to optical access limitations. It is shown that the leakage flow rate through the gap shows limited sensitivity to rotor deformation, as it scales with rotational speed, and it is fed by two main contributions: a flow directly extracted from the rotor outlet and a recirculating flow developing along the mounting panel. Conversely, the non-dimensional angular momentum flow rate is larger at the lower rotational speed, corresponding to the case in which the leakage flow is rapidly re-ingested by the rotor. This indicates that the centrifugal effects associated with the leakage flow swirl are not responsible for the observed change in leakage flow pattern. Finally, significant periodic and non-periodic components are identified within the leakage flow. These components are expected to contribute to the formation of the large-scale structures impinging on the rotor blades and thus generating significant noise. Full article

This study presents the design and flight demonstration of an aerobatic RC aircraft equipped with a morphing-wing using a compliant mechanism-based flexible structure. Unlike conventional hinged control surfaces, the proposed morphing wing provides an aerodynamic surface through elastic deformation, which can reduce aerodynamic discontinuities compared to conventional hinged wings. The flexible morphing rib was designed to ensure structural flexibility by combining fishbone and corrugated structures, and four flexible ribs constitute one module, making up four modules of the entire wing. Flight tests were conducted to evaluate the roll maneuverability of the UAV using roll rate and a nondimensional roll performance index. Experimental results showed that the morphing-wing UAV achieved stable and sufficient roll control performance under limited control input conditions, while demonstrating maneuverability comparable to or better than that of a conventional hinged control surface when the aileron deflection angle was limited. These results confirm the feasibility of compliant morphing wings as an alternative to traditional mechanical control surfaces and demonstrate their potential application to future high-efficiency UAV systems. Full article