Search Results (707)

In cold and humid environments in high-latitude, high-altitude, and offshore regions, ice accretion sometimes occurs on airfoil blade surfaces, such as those of wind turbines. Therefore, a potential hazard exists for the equipment. For this reason, the aerodynamic characteristics of the airfoil blade degrade and power generation decreases. In the present study, the icing characteristics of airfoils in cold and foggy environments were investigated. A novel icing wind tunnel with a low LWC of 0.3 g/m³ and a small MVD of 10 μm was designed and built. An airfoil sample with the aerodynamic profile of NACA 0018 was selected, and the effects of the airfoil material and the temperature on the icing area, the thickness of ice, and the coverage scope of ice were tested and analyzed. The experimental results showed that the temperature had a more significant effect on the icing characteristics in comparison with the airfoil material. At the medium temperature, −7 °C in the present study, the icing area, the thickness of ice, and coverage scope all reached their maximum value. Specifically, the maximum cross-sectional icing areas (CIAs) on the aluminum airfoil at −4 °C, −7 °C, and −10 °C for 60 min were 35.088 mm², 66.357 mm^2, and 51.538 mm², respectively, and those on the FRP airfoil were 36.204 mm², 70.352 mm², and 47.814 mm², respectively. The FRP airfoil had a larger icing area and thickness of ice. In contrast, the aluminum airfoil had a larger coverage scope of ice, which was −0.10~0.15. In addition, the aerodynamic performance of the iced airfoil, including C_d and C_m, was also obtained through CFD. The research findings provided a foundation for further exploring the atmospheric icing of wind turbines and other structures with airfoil profiles. Full article

Flying-wing aircraft are more susceptible to wind disturbance due to their smaller wing loading, making gust alleviation critical for flight performance and safety. Conventional control surfaces may exhibit insufficient manipulation efficiency on such configurations, motivating the adoption of active flow control, particularly circulation control (CC) due to its favorable control efficiency. This paper presents an Active Disturbance Rejection Control (ADRC) framework for gust load alleviation (GLA) of flying-wing aircraft equipped with CC actuators, which enables real-time estimation and compensation of both gust disturbance and practical uncertainties and is validated through closed-loop wind-tunnel experiments under various sinusoidal gust conditions. An unsteady aerodynamic model with experimental data is established and simulations are performed for further investigation of alleviation performance and response characteristics under a wide range of gust conditions. Results show that both ADRC and PID exhibit degraded performance at higher gust frequencies and larger gust ratios, but ADRC achieves higher alleviation efficiency across the tested conditions. Furthermore, ADRC maintains satisfactory performance with actuator delays up to 0.04 s and outperforms PID under measurement noise and Dryden turbulence. These findings validate the effectiveness and robustness of ADRC for GLA, underscoring its practical potential for active flow control systems. Full article

Small multirotor UAVs frequently operate in crosswind conditions, yet the aerodynamic interaction between windward and leeward propeller pairs remains incompletely understood. This study investigates the performance of a quadcopter propeller system under lateral crosswind using steady-state RANS simulations with the Transition SST turbulence model, validated against wind tunnel measurements (thrust and torque deviations within $5.4\%$). A parametric matrix of five rotational speeds (8000–12,000 RPM) and six freestream velocities (0–10 m/s) is systematically examined. While thrust and power coefficients of all propellers increase monotonically with freestream velocity, the figure of merit ($FM$) of leeward propellers exhibits a previously unreported non-monotonic response: it decreases from hover, reaches a minimum near $6 \mathrm{m}/\mathrm{s}$, and partially recovers at higher velocities. Windward propellers show no such degradation. Our velocity contour and streamline analyses reveal that this behavior originates from windward wake ingestion into the leeward inflow region, which peaks at intermediate freestream velocities and is progressively alleviated as the stronger crosswind convects the wake downstream. The non-monotonic $FM$ response is therefore a direct consequence of the competition between wake-induced inflow degradation and freestream-driven aerodynamic augmentation. Our findings provide a systematic aerodynamic dataset essential for crosswind attitude control and propulsion system design in multirotor UAVs. Full article

Politecnico di Milano is undergoing the design of a highly swept, low-aspect-ratio radio-controlled aircraft with reflex airfoils. This model is necessary to expand the automated flight-testing activities conducted inside the university, adding to the flying models a more unconventional one to verify the flight-testing technique implemented. Plain-type spoilerons were investigated as primary roll control devices and compared with conventional aerodynamic predictions and wind-tunnel data. The experimental tests assessed performance across spanwise and chordwise positions, angles of attack, and spoileron geometric variations. A normalized control effectiveness parameter, accounting for moment coefficient, spoileron surface area, and moment arm, was introduced to compare configurations. Results show consistent peak performance at intermediate incidence and highlight distinct degradation patterns near stall. Spanwise variations primarily affect roll authority, while yaw response remains weakly sensitive. Geometric analysis indicates span increases are more efficient than chord increases for equivalent performance, reducing actuator loads and aerodynamic penalties. Full article

Low-aspect-ratio flying-wing unmanned aerial vehicles (UAVs) are attractive drone platforms for civilian remote sensing, environmental monitoring, infrastructure inspection, disaster assessment, and persistent public-service monitoring because their integrated tailless layout offers high aerodynamic efficiency and payload volume. A trajectory-command-based three-loop nonlinear dynamic inversion (NDI) control architecture enhanced by a nonlinear disturbance observer (NDO) is designed to address the critical challenges of rapid time variation, strong nonlinearity, strong coupling, and restricted yaw authority in low-aspect-ratio flying-wing UAVs. The core innovation lies in the development of a trajectory-command-to-attitude kinematic mapping mechanism, integrated with the NDO for active torque compensation of lumped uncertainties and time-varying external disturbances. Leveraging a mathematical model of a low-aspect-ratio flying-wing UAV standard model, a three-loop NDI controller comprising angular rate, attitude, and trajectory command loops was designed based on the time-scale separation principle. The NDO was further designed to estimate lumped disturbances and provide feedforward compensation, thereby establishing an NDI-DO system that mitigates the high sensitivity of conventional NDI to modeling inaccuracies. Simulation and robustness tests involving typical high-angle-of-attack maneuvers (e.g., Cobra and Split-S maneuvers) demonstrated that the NDI-DO system achieved a reduction in angular-rate tracking error by over 77.2% compared to the baseline NDI. Furthermore, the permissible range of aerodynamic parameter perturbations was improved by 23%, significantly enhancing tracking fidelity and disturbance rejection. In a 3-DOF wind tunnel free-flight test, the NDI-DO system achieved a substantial expansion of the controllable angle-of-attack (attitude-stability) envelope from 72.9° to 99.19°, substantiating the high reliability and engineering utility of the control framework in post-stall nonlinear regimes. These results indicate that the proposed NDI-DO framework can support safer envelope expansion, autonomous upset recovery, and robust flight control for civilian flying-wing drones operating under uncertain aerodynamic and environmental conditions. Full article

Crosswind protection on high-speed railway bridges is important for train running safety; however, bridge-mounted wind barriers may also increase wind loads on the bridge deck and barrier-supporting structure. Previous studies have mainly evaluated wind-barrier performance according to reductions in train aerodynamic loads, whereas direct experimental quantification of the trade-off between train protection and bridge lateral load increase for different barrier geometries remains limited. This study compares vertical and curved wind barriers through wind-tunnel tests using a 1:30 sectional model of a train–bridge system at a reference wind speed of 10 m/s. Barrier porosities in the range of 20–50% and wind attack angles ranging from −6° to 6° were considered. Train-surface pressure distributions and static three-component aerodynamic coefficients of both the train and bridge were measured simultaneously. A lateral load benefit–penalty index was introduced based on the train lateral load-reduction ratio and the bridge lateral load-increase ratio to enable the relative comparison of the tested barrier configurations, while steady Reynolds-averaged Navier–Stokes simulations were used to interpret the underlying flow mechanisms. Both barriers reduced the aerodynamic loads on the train, but the vertical barrier provided stronger train-side shielding at the cost of a larger increase in bridge lateral load. At 30% porosity and a wind attack angle of 0°, the vertical barrier reduced the train side-force coefficient by 75.4% and increased the bridge side-force coefficient by 89.2%, whereas the corresponding values for the curved barrier were 57.6% and 39.4%, respectively. Within the tested ranges, the curved barrier consistently achieved higher index values because its flow-guiding effect reduced pressure concentration and limited the additional lateral load on the bridge. The vertical barrier is therefore more suitable when maximum train protection is the primary objective, whereas the curved barrier provides a better balance between train protection and bridge wind-load control. Full article

This report presents an experimental study focused on parametric optimization of an electric vertical take-off and landing (eVTOL) wing–propeller lifting system. The experiments were conducted in a wind tunnel equipped with a Particle Image Velocimetry (PIV) system, and a wing–propeller thrust and power measurement test stand was used. The total mission flight energy was evaluated and compared for three different propeller-to-wing gross area ratios and three mission profiles. Two principal configurations of the wing–propeller lifting system were considered, corresponding to the hovering and cruising stages of flight. In these configurations, both the propellers and the tilting wing sections were oriented according to the requirements of hover and cruise operation. The total flight energy was adopted as the figure of merit and was calculated for all design points. The figure of merit was then analyzed as a function of the propeller-to-wing gross area ratio. The results allowed the determination of optimal configurations for different hover times. Finally, the total flight energy obtained from the experiments was calculated and compared with the corresponding simulation results. Full article

Vortex-induced vibration (VIV) poses a significant serviceability concern for wide streamlined box girders of long-span suspension bridges. This study investigates the VIV performance and aerodynamic mitigation of a wide streamlined box girder with a width-to-depth ratio (B/D) of approximately 10 through sectional model wind tunnel testing. The original cross-section was found to exhibit pronounced heaving and torsional VIV at positive wind angles of attack, with amplitudes considerably exceeding the prescribed serviceability limits. A systematic experimental investigation was conducted to evaluate the influence of three geometric parameters, i.e., wind fairing inclination angle, inspection rail position, and pedestrian railing porosity and panel arrangement, on VIV performance. Experimental results demonstrate that reducing the wind fairing inclination angle from 65° to 45° is the most effective mitigation measure. An appropriate porosity of the pedestrian railing is shown to substantially improve VIV performance. Furthermore, under equivalent overall porosity, a uniformly distributed alternation of solid and ventilated panels yields markedly superior VIV suppression compared with continuously sealed arrangements. Subsequent flutter and aerostatic wind tunnel tests confirm that the recommended cross-section preserves the favorable flutter stability and aerostatic performance of the original design. Strouhal number analysis reveals that the VIV lock-in is governed by St ≈ 0.12. Notably, the St number obtained from the pitching moment coefficient is nearly twice that obtained from the lift coefficient. Full article

Panel-based aeroelasticity models are commonly used to conduct mid-fidelity aeroelastic analysis. The unsteady vortex lattice method (UVLM) in particular is used when non-linear aerodynamic corrections are needed, for example by utilizing the $\alpha$-convergence method. While this method is well tested for non-linear corrections in high-Reynolds transonic flows for both steady and unsteady cases, its effectiveness has not been well researched in unsteady low-Reynolds flows. This paper tests the effectiveness of the $\alpha$-convergence method in this regime by comparing modeling results with original wind tunnel test results. In the steady aeroelastic displacement tests, the aerodynamic non-linearity improved the modeling results significantly, with an error under $\pm 10\%$ at all tested angles of attack, compared to a maximum error of $-30.8\%$ for the aerodynamically linear models. In the flutter test case, the aerodynamic non-linearity had less of an impact, with structural non-linearity being more important in this case. However, the maximum flutter speed error for the aerodynamically non-linear model was still lower, at $-14.4\%$, compared to $+19.6\%$ for the aerodynamically linear model. Full article

Stay cables are slender and lightly damped structural members that are highly sensitive to wind action. Although the aerodynamic effects of rain rivulets, ice accretion, snow accretion, and surface roughness on bridge cables have been widely investigated, the influence of architectural illumination attachments installed along stay cables remains insufficiently understood. Such attachments modify the original circular cable cross-section and may alter aerodynamic force coefficients, vortex-shedding characteristics, wake structure, and galloping tendency. This study investigates the aerodynamic characteristics of bridge stay cables modified by illumination attachments with different shapes, dimensions, and installation gaps. Large-eddy simulation was performed using OpenFOAM 5.0 to resolve the unsteady flow around a reference circular cable and ten illumination-modified cable configurations at a representative subcritical Reynolds number of R_e = 9.42 × 10⁴. The numerical model was first verified using benchmark aerodynamic properties of a circular cylinder and then validated against force measurements obtained from closed-circuit wind-tunnel experiments. The results show that illumination attachments significantly affect the drag and lift characteristics of stay cables, particularly at oblique wind attack angles. Among the representative wind attack angles considered, the drag coefficient generally increases when the attachment is exposed laterally or obliquely to the incoming flow, whereas the lift coefficient is strongly affected by attachment shape and angular orientation. Rectangular and double-rectangular attachments produce stronger wake disturbance, greater pressure asymmetry, and more complex vortex structures than circular attachments. The preliminary Den Hartog analysis further indicates that sharp-edged and direct-contact attachments may increase galloping susceptibility, whereas smaller circular attachments and separated-gap configurations show more moderate aerodynamic behavior. These findings indicate that illumination systems should not be treated as purely architectural accessories, but should be considered in the aerodynamic assessment and wind-resistant design of cable-supported bridges. Full article

Distributed aerodynamic sensing is a key requirement for future fly-by-feel UAV systems. Inspired by mechanosensory systems found in flying animals, this paper investigates the use of a bio-inspired optically tracked flexible pillar sensor array for aerodynamic sensing and stall detection on a washed-out NACA0012 aerofoil. Experiments were conducted in a low-speed water tunnel, with flow at chord-based Reynolds $Re=70\times {10}^3$ and the pillar sensors set to measure local flow conditions. Sensor calibration and dynamic characterisation were performed prior to testing. Time-resolved flow visualisation measurements were used to validate sensor response and investigate local flow phenomena. The results demonstrated that flexible pillar sensors can capture early indications of stall through monitoring of spanwise mean deflection, flow reversal events associated with incipient and fully separated flow, and characteristic low-frequency oscillations. The findings demonstrate the potential of distributed bio-inspired sensor arrays to enhance stall detection and enable real-time aerodynamic monitoring in future fly-by-feel UAV systems. Full article

Coupled shear wall systems are widely used in tall buildings due to their high lateral stiffness and effectiveness in controlling wind-induced serviceability responses. Reliable assessment of their behavior under realistic wind loading requires accurate load representation and properly calibrated numerical modeling. This study investigates the performance of coupled shear wall systems under wind loads derived from wind tunnel testing, where surface pressure time histories were extracted from the TPU Aerodynamic Database and used to generate equivalent full-scale, time-varying wind loads. The preliminary design of a 20-story building was established in ETABS based on current design codes. Detailed nonlinear time-history analyses were subsequently performed in OpenSees to assess the performance under three different wind hazards for the original and refined design, where shear walls were modeled using the Multiple-Vertical-Line-Element Model (MVLEM). Several wind demand indicators, including drift ratios, floor accelerations, and component and cladding performance were evaluated. The results demonstrate that the performance-based design framework enables the identification of critical vulnerabilities that may not be fully captured by conventional code-based drift and strength checks, particularly regarding localized damage accumulation and serviceability-related demands. Additionally, the refined configuration, while requiring only a 4.33% increase in total baseline concrete volume, effectively reduced peak roof drift by 60%, allowing reliable control of dynamic behavior and prevention of structural yielding, as well as ensuring the maintenance of both structural integrity and operational serviceability for the investigated high-rise configuration during severe wind events. Nevertheless, the findings are limited to the investigated building configuration and aerodynamic conditions considered in this study. Full article

The unsteady buzz characteristics of a dorsal supersonic bump inlet for a flying-wing configuration are investigated using wind-tunnel tests and three-dimensional unsteady numerical simulations. This study focuses on off-design operation at a freestream Mach number of 1.8, with particular attention to the effects of angle of attack and downstream throttling on shock motion, pressure oscillation, and inlet stability. Wind-tunnel measurements show that the onset and development of buzz are highly sensitive to angle of attack. At high angles of attack, pressure oscillations first appear near the inlet compression surface and subsequently develop into large-amplitude fluctuations at the aerodynamic interface plane. The dominant experimental buzz frequency is approximately 60–70 Hz, and the numerical prediction of 71 Hz agrees well with the measured dominant frequency of 66 Hz. The simulations further reveal a strongly three-dimensional buzz cycle in which asymmetric separation over the bump, spanwise accumulation and discharge of low-energy flow, and alternating inlet blockage and recovery govern the large-amplitude shock excursion. The oscillatory flow field is dominated by shock–system expulsion and ingestion on the spanwise side with stronger back-pressure tolerance, accompanied by the formation of strong and weak shear layers during different stages of the cycle. These results provide insight into the buzz mechanism of dorsal bump inlets and support the assessment of starting performance and stable operating limits for supersonic inlets integrated with flying-wing configurations. Full article

Efficient removal of stones and soil from harvested hazelnuts remains a critical challenge in postharvest processing, especially in regions where mechanization is limited. There is a growing need to optimize cleaning systems to improve grain quality, reduce labor, and support scalable operations. This study investigates the optimization of air velocity, feed rate, drop distance, and impurity mixture in a horizontal wind tunnel pneumatic separation system designed for hazelnut postharvest cleaning. Using both classical statistical analysis and Random Forest (RF) modeling, the performance metrics, grain purity, grain loss, and net contaminant removal, were evaluated across variable settings. The results reveal significant influences of air velocity and drop distance on cleaning efficiency, with optimal performance achieved at 25 m/s, 500 kg/h, and a 60–70 cm drop range. Machine learning models achieved high predictive accuracy (R² > 0.9), confirming their utility for performance forecasting. This integrated approach offers robust recommendations for machine parameter settings, supporting mechanized cleaning solutions to enhance efficiency and reduce manual labor in hazelnut production. Full article

To address the challenges posed by the complex flow fields of civil aircraft thrust reversers and the difficulty of quantitatively decoupling multiple interference factors in wind tunnel tests, this paper employs numerical simulation methods to conduct an in-depth investigation into the aerodynamic characteristics and environmental interference effects of a scaled thrust reverser test configuration. The results indicate that the Fan Pressure Ratio (FPR) is the primary factor governing deceleration efficiency, while an increase in the freestream Mach number exerts a significant streamwise constraining effect on the reverse jets. Under sideslip conditions, the asymmetric interference moment induced by lateral dynamic pressure superimposes positively with the inherent stability of the configuration, thereby enhancing the directional recovery capability during crosswind rollout. Analysis of wind tunnel interference reveals that the boundary layer on the static floor induces a “ground cushion effect,” leading to an overestimation of lift; meanwhile, the support structure interference results in an overall increase in aerodynamic loads. This study elucidates the physical essence of thrust reverser flow fields within confined spaces, providing critical theoretical support for the design of test schemes and the correction of experimental data. Full article