Search Results (431)

Understanding the unsteady aerodynamic behavior of quadrotor unmanned aerial vehicle (UAV) is critical for improving flight stability, control, and performance, particularly in complex operational environments. In closely spaced multirotor configurations, coherent tip vortices shed from each blade convect downstream and form helical vortex streets that interact with subsequent blades and neighboring rotors. These interactions induce rapid fluctuations in local inflow velocity and effective angle of attack, resulting in transient lift variations, increased vibratory loads, and elevated acoustic emissions. This study presents a comprehensive computational investigation of quadrotor rotor interactions and wake dynamics using a large-eddy simulation (LES). Detailed analyses reveal that the formation and evolution of tip vortices and blade–vortex interaction phenomena significantly influence lift fluctuations and aerodynamic loading. The simulations capture transient wake structures and their effects on neighboring rotors, highlighting unsteady aerodynamic mechanisms that are not adequately predicted by conventional RANS or URANS approaches. Parametric studies examining vortex-street offset distance demonstrate the sensitivity of wake-induced instabilities to design and operational parameters. The results provide new physical insights into multirotor wake dynamics and establish the LES as a predictive framework for quantifying unsteady aerodynamic loading in quadrotor drones. The findings provide insights into the complex flow physics of multirotor systems, offering guidance for more accurate modeling, rotorcraft design optimization, and the development of control strategies that mitigate adverse unsteady aerodynamic effects. This study provides new insights into rotor–vortex-street interactions, with applications to multirotor UAVs, by isolating multi-vortex coupling effects and quantifying the influence of horizontal vortex spacing on unsteady aerodynamic loading, complementing existing high-fidelity LES research. Full article

To study the wind load characteristics of the construction steel platform of the high-rise core tube, considering the influence of safety net permeability and core tube interference, a large eddy simulation was used for unsteady numerical simulation. The pressure jump method was used to model the safety net, and the entrance turbulence was generated through the synthesis turbulence method to obtain the wind field distribution, wind pressure coefficient, and shape coefficient of the construction steel platform. The results indicate that there is a sudden drop in internal wind pressure at the entrance of the construction steel platform, and there are strong shear vortices and vortex shedding downstream of the platform. At 0° wind direction, the net wind pressure coefficient reaches a maximum of 1.3 at the center of the windward side, and a maximum negative value of −1.2 appears at the corners; as the wind direction angle increases, the maximum wind pressure coefficient decreases from 6.4 to about 5.3. The body shape coefficients of the windward side under three different wind directions are 0.563, 0.378, and 0.153, respectively. This indicates that the ventilation of the safety net reduces the wind load on the construction steel platform, resulting in a result lower than the standard value, and the standard value is conservative. The results of this study can provide data support and engineering reference for wind resistant design and structural optimization of construction steel platform structures. Full article

The global push for sustainable energy has elevated wind power as a key renewable source; however, turbine noise remains a critical barrier to deployment near populated areas. This study investigates the optimization of symmetric and asymmetric trailing-edge profiles to minimize aeroacoustic emissions. The primary novelty lies in the comparative analysis of a novel Pressure-Side Intruding Divergent model against standard sinusoidal serrations. Employing finite volume analysis in ANSYS, the preliminary results revealed that these targeted modifications significantly reduced noise propagation by 51.1% to 75.4%. By altering vortex shedding patterns and turbulent boundary-layer interactions, these findings provide actionable guidelines for balancing aerodynamic efficiency with environmental noise standards. Full article

An extreme rainfall event that occurred from 16 to 18 December 2021 along the coastal regions of Peninsular Malaysia (PM) caused widespread flooding and substantial socioeconomic impacts. This study investigates the mechanisms leading to this event, focusing on the roles of climatic phenomena and local terrains. Two atmospheric interactions play key roles in triggering the event. Firstly, a strong cold surge (CS) associated with the East Asian winter monsoon (EAWM) interacted with the easterly surge over the southern South China Sea, leading to the formation of Borneo vortex. Secondly, a strong northeasterly and CS largely contributed to enhancing and transporting the vortex towards the PM and across the Titiwangsa mountain ranges. The phase change of the Indian Ocean Dipole (IOD) facilitated the eastward propagation of the vortex. Sumatra and PM terrains significantly modulated vortex evolution and moisture convergence over the Strait of Malacca. These findings are analyzed to shed light on interactions between large-scale climate drivers and localized terrain in generating extreme rainfall, emphasizing the necessity of multi-scale analysis for model accuracy. Full article

This investigation is to address the aerodynamic noise generated from laminar flow over a D-shaped cylinder at a low Reynolds number (Re). Proposed is a novel assembly of arc-shaped splitter plates to effectively reduce the aeolian tone for the D-shaped cylinder. The two-dimensional flow field is simulated at an Re of 160 to investigate the mechanism of reducing the sound of the arc-shaped plates. The radiated sound has been predicted by Ffowcs Williams and Hawkings (FW-H) acoustic analogy. To verify calculations, the predicted results of a circular cylinder have been compared with the data in the literature. The results reveal that the introduction of the arc plates decreases the lift and drag fluctuations as well as the vortex shedding frequency in comparison with the no-arc plate case. The pressure and velocity fluctuations in the wake zone are reduced by the arc plates due to vortex shedding suppression. The application of the arc plates shows an effective control of sound, leading to a maximum reduction in sound pressure level (SPL) by almost 34 dB. Full article

In fire emergency ventilation systems, EC (Electronically Commutated) internal-rotor axial fans are critical devices, but their high-speed operation generates aerodynamic noise often exceeding 90 dB (A). While struts are core structural components regulating flow field stability, their specific geometric impact on trailing-edge vortex shedding and noise generation mechanisms remains unclear. This study investigates three strut configurations: a hexagonal annular type, a hexagonal double-ring type, and a three-pronged type. A coupled numerical model was established using Large Eddy Simulation (LES) and the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. The Q-criterion was employed to analyze vortical structures, with numerical predictions validated against experimental measurements in a semi-anechoic chamber. The results quantitatively demonstrate that optimizing the strut geometry significantly mitigates unsteady flow separation. The three-pronged strut (Model C) effectively dispersed high-velocity airflow, reducing the peak turbulent kinetic energy (TKE) at the inlet by 30% compared to the original design (Model a). Furthermore, Model C achieved a 6.7 dB reduction in the sound pressure level at the blade-passing frequency (BPF), alongside a 14.1% reduction in pressure pulsation amplitude near the blade tip. Structural optimization of struts enables synergistic control over turbulence distribution and pressure fluctuations. By disrupting the phase coherence of shed vortices, the optimized design fundamentally suppresses aerodynamic noise, advancing axial fan design toward precise quantitative aeroacoustic optimization. Full article

The interaction between circular piers and turbulent open-channel flow generates complex three-dimensional structures, including horseshoe vortices at the pier base and wake vortices downstream. These structures increase vertical velocities, pressure fluctuations, and shear stresses, contributing to erosion and structural instability. Although these phenomena have been widely studied, limited attention has been given to surface geometric modifications as a flow-control strategy. This study employs Large Eddy Simulation (LES) to evaluate the influence of a hexagonal dimple pattern on circular piles in a free-surface channel. The dimples were defined by varying diameter, depth, and spacing to reduce vertical velocity and alter vortex formation. The computational domain represents a 0.40 m wide, 12 m long, and 1.2 m high rectangular channel, with an inlet mass flow of 9.4 kg/s and 0.10 m water depth. Model validation against particle image velocimetry (PIV) data showed 99% correlation, confirming numerical accuracy. Results demonstrate that textured surfaces modify flow dynamics by enhancing kinetic energy dissipation and generating micro-vortices that weaken dominant structures. The optimal configuration (6 mm diameter, 2 mm depth, 1 mm spacing) reduced downward vertical velocity by 42% and wake vortex shedding frequency by 24%, indicating improved hydraulic stability and erosion mitigation potential. Full article

Shark skin grooves, known to reduce hydrodynamic drag, have inspired riblet structures for flow control. This study investigates their application to airfoils, where flow separation at high angles of attack (AOA) compromises aerodynamic stability and wind turbine performance. Numerical simulations were conducted using the SST k–ω model in ANSYS Fluent to analyze riblets placed on the suction surface (SS) of an airfoil. The riblets—oriented perpendicular to the flow—have a fixed height and width of 1 mm, with total lengths varying from 0.1, 0.2, 0.5, and 0.7 of the chord length. The influence of riblet geometry on trailing-edge (TE) vortex shedding and drag reduction under stall conditions is examined in detail. The results indicate that appropriately sized riblets suppress secondary vortex formation and extend the 2S vortex-shedding regime. Conversely, poorly dimensioned riblets can advance Hopf bifurcation in the wake. Analysis of the transient boundary layer structure reveals that the suppression of vortex shedding is primarily due to riblets attenuating fluid pulsation and Reynolds stresses caused by turbulent bursts. Full article

This paper presents a dynamic model of a top-tensioned riser (TTR) subjected to combined vortex-induced vibration (VIV) and time-varying tension excitation. The model employs a van der Pol oscillator to simulate load excitation caused by vortex shedding and incorporates a tuned mass damper (TMD) to suppress nonlinear vibrations in the riser. The key contributions include, first, employing the Galerkin method to obtain a multi-mode approximate solution and analyzing it using single-mode approximate equations, and subsequently, applying a multi-scale approach to investigate the vibration reduction effect of the TMD under two typical resonance scenarios. By introducing a complex impedance term derived from the complex transfer function, the physical effect of the TMD is transformed into a frequency-dependent dynamic reaction force coupled to the riser’s equation of motion. The first involves 1:1 internal resonance between the structural frequency and vortex-induced frequency, while the second involves 1:2 parametric resonance between the structural frequency and the top tension frequency. Results indicate that when the structural frequency exhibits 1:2 parametric resonance with the top tension frequency, complex bifurcation behavior occurs, leading to large-amplitude structural responses. Findings demonstrate that TMDs effectively alter the system’s stability distribution and exhibit outstanding vibration-reduction efficiency under both typical resonance conditions. Full article

This paper focuses on the modeling and design of an adaptive vortex generator (AVG). The device is actuated through shape memory alloy (SMA) elements. The interest of the research community in these devices is due to their ability to improve the performance of the aircraft, directly altering and controlling the boundary layer. Their action consists of energizing the flow, thereby hindering separation. The peculiarity of the presented AVG architecture lies in its compactness and adaptability, which allows for its activation just for some specific phases that are not adequately covered by the conventional. This system can enable load alleviation in the cruise phase when a gust occurs (spoiler modality) and stall prevention in high-lift conditions (vane modality). These two working capabilities can be obtained by mounting the AVGs at different angles of incidence, with respect to the direction of the flow. The present paper is structured as follows. First, the project of RADAR, hosting the activities, is presented with specific focus on the main objectives and on the strategy of maturation of the technologies. Then, attention is paid to the simulations of the aerodynamic field produced by the AVG. These outcomes have driven the next part of the work, focusing on the identification of the architecture of the AVG. A dedicated finite element modeling approach was implemented to address the design task, even in the presence of SMA non-linear elements. Three main operational phases were simulated: (1) the stretching of the springs up to their connection to the architecture (pre-load phase); (2) the elastic recovery of the springs and the achievement of equilibrium with the hosting structure; and (3) the activation of the springs through heating to deflect the AVG. The simulations proved the capability of the system to produce the required deflection/deployment, even under the most severe load conditions. In particular, the simulations highlighted the capability of the system to produce a deflection of the vortex generator of 83.5 deg under the most severe load conditions, against the required value of 80 deg. This result was obtained by also keeping the structural safety factor at a value of four, in line with the wind tunnel facility requirement. Another key outcome of the dynamic analysis was the absence of coupling with vortex shedding, since the system resonance frequencies (135 and 415 Hz) are well outside the vortex-shedding frequency range (500–1400 Hz). Full article

Wind power has experienced rapid development due to its renewable advantages. To address the performance degradation of wind turbines caused by icing in alpine regions, this study integrates field testing and numerical simulation to analyze three key aspects for a 1.5 MW turbine: the underlying mechanism of icing impact, the effect of a de-icing coating on performance during ice-free operation, and the coating’s efficacy under active icing conditions. Results show that ice accretion causes a 25% power loss, induces severe flow separation and vortex shedding, and shifts the separation point forward to 15% chord length. Under ice-free conditions at an average wind speed of 8.3 m/s, the de-icing coating introduces a negligible power deviation of only 0.4%. In extreme cold, ice thickness on the coated blade section was measured at just 4.86 cm. The research demonstrates that de-icing the outer 10 m blade tip section substantially improves performance and confirms that the coating has a minimal aerodynamic footprint during normal operation while providing effective ice mitigation. These findings offer a scientific foundation for optimizing de-icing techniques and support the broader application of such coatings for wind turbines in cold climates. Full article

The trailing-edge design of a wind turbine airfoil is critical for balancing the aerodynamic performance and structural robustness of a wind turbine blade. In this paper, the S809 airfoil and its blunt trailing-edge variant, the S809-100 airfoil, are taken as the research objects. The aerodynamic and flow-field characteristics of both airfoils are analyzed by computational fluid dynamics, which is validated by U.S. National Renewable Energy Laboratory experiments and wind tunnel particle image velocimetry. The results show that the S809-100 airfoil achieves a higher lift coefficient across the entire angle of attack ($\alpha$) range 0–18°, with a superior lift-to-drag ratio within 8–12°. Three distinct states of aerodynamic response are identified for both airfoils, based on time series and spectral features of lift and drag coefficients, and flow-field structures: steady convergence state, periodic fluctuation state, and irregular fluctuation state. The two airfoils differ significantly in aerodynamic response transition with respect to $\alpha$: for the S809 airfoil, the aerodynamic response remains in a steady convergence state up to $\alpha =16°$ before shifting to a periodic fluctuation state, while for the S809-100 airfoil, it exhibits a periodic fluctuation state from $\alpha =0°$ and transitions to an irregular fluctuation state beyond $\alpha =14.2°$. This difference stems from trailing-edge thickening, which induces flow unsteadiness in the S809-100 airfoil. This shift in the aerodynamic response from the periodic fluctuation state to the irregular fluctuation state is attributed to the transition from single-frequency large-scale vortex shedding to a multi-scale vortex interaction, confirmed via spectral and flow-field analyses. This study focuses on the correlated flow structures of wind turbine airfoils and deepens the understanding of unsteady aerodynamic responses; the combined analysis of enhanced aerodynamic performance and induced unsteady fluctuation due to trailing-edge thickening offers a valuable reference for wind turbine blade design. Full article

This study presents a two-dimensional computational fluid dynamics analysis of a vertical-axis Savonius-type wind turbine under atmospheric conditions representative of an educational environment located in the Ecuadorian Andean region. Unlike previous studies conducted under sea-level meteorological conditions, this research is performed under high-altitude conditions (2723 m a.s.l.). The unsteady flow around the rotor was simulated using a two-dimensional approach based on the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, discretized with the finite volume method and coupled with the k–ω Shear Stress Transport (SST) turbulence model. The rotor rotation was modeled using sliding mesh technique, employing a second-order implicit time scheme to ensure numerical stability and adequate temporal resolution. The numerical model was configured for a tip speed ratio of 0.8 and a wind speed of 3.9 m/s. The time step was defined based on a constant angular advancement of the rotor per time iteration, ensuring numerical stability and adequate temporal resolution. The aerodynamic torque was obtained by integrating the pressure and viscous forces acting on the blades, allowing the calculation of the mechanical power generated and the power coefficient. The results showed a periodic and stable torque behavior after the initial transient cycles, yielding an average torque of 0.7687 N·m and a mechanical power of 5.17 W, while the power coefficient reached a value of 0.2102. Analysis of the flow fields revealed the formation of a low-velocity wake downstream of the rotor, regions of high turbulent kinetic energy associated with periodic vortex shedding, and a significant pressure difference between the advancing and returning blades, confirming that turbine operation is dominated by drag forces. The numerical results were validated through comparison with previous studies, showing good agreement and demonstrating the reliability of the proposed Computational Fluid Dynamics (CFD) approach. This study highlights the potential of Savonius turbines for low-power applications in urban and educational environments, as well as the usefulness of CFD as a tool for evaluating and optimizing their aerodynamic performance. Full article

The hollow fiber membrane humidification modules are used for indoor humidification in hot–dry regions and heating in winter. The module is composed of several flexible hollow fiber membranes, which are bent and displaced by gravity and fluid forces. This paper is a further study of previous work that reveals the internal relationship between the forces generated by vortex shedding and fiber vibration. The central trajectories of fibers in the flow field are described for various pulsating flow and fiber structure parameters. The effects of fiber displacement on fluid flow, heat transfer, and mass transfer performance at different parameters are discussed. The results show that the fiber displacement in the flow field consists of two components: (i) deformation caused by fluid drag force and gravity and (ii) periodic vibration caused by periodic lift and drag force as vortices shed at the fiber surface. The fiber vibration facilitates the vortex shedding on the fiber surface, which enhances the convective heat and mass transfer performance on the fiber surface. The average friction factor (f_m,v), Nusselt number (Nu_m,v), and Sherwood number (Sh_m,v) increased by 12.9%, 39.3%, and 20.0%, respectively, when the fiber vibrated compared to non-vibration. This implies that inducing fiber vibration can optimize the heat and moisture transfer performance. Full article

Efficient energy harvesting from open-channel flows offers a sustainable solution for powering distributed sensing systems in water infrastructure. This study investigates a piezoelectric wake-excited membrane vortex-induced vibration (VIV) energy harvester through a combined numerical and mechanical approach. The device features an upstream cylindrical bluff body that generates a periodic vortex street, exciting a downstream flexible membrane equipped with surface-mounted piezoelectric patches. A one-way coupled CFD–FEM framework implemented in ANSYS was employed to assess the effects of membrane length, material stiffness, and flow conditions on hydrodynamic loading, structural deformation, and deformation power. Results show that membrane length mainly affects oscillation amplitude and force levels, whereas material stiffness has a stronger influence on membrane deformation and RMS mechanical power. Among the investigated materials, low-stiffness polyethylene yields the highest deformation power, while none of the analysed configurations reaches a full lock-in condition within the explored parameter range. Complementary mechanical analysis revealed that the stiffness of commercial piezoelectric patches significantly reduces local strain, thereby constraining the practically harvestable energy in the present baseline configuration. Spectral power density analysis identified the dominant shedding frequency and its harmonics, confirming that the flow response is governed by a coherent periodic excitation. These findings highlight key design trade-offs in wake-excited membrane harvesters and provide useful guidance for the future optimisation of self-powered hydraulic monitoring systems. Full article