We used scat analysis to study the foraging habits of kenkéknem (Ursus americanus, American Black Bear) at Sun Peaks Ski Resort in Skwelkwék’welt, south-central Secwepemcúl’ecw, from May to late August 2023. The 20 scats (three in May, 10 in June, four in July, and three in August) showed the bears consumed largely green vegetation in the spring (1 May–21 June), scwicwéye (ants, primarily wood-nesting species) in early summer (22 June–31 July), and máts̓pe7 (wasps) and berries in late summer (1–30 August). Some vertebrate predation on voles (Microtus spp.) and other rodents was found. The most common vegetation in scats in spring was xwixwyúy̓sten (Equisetum spp., horsetail), which grows well in wet disturbed environments, such as the edge of ski trails. Wood-nesting ant species provided an important food source for bears in early and late summer. Given the importance of ants to the summer diet of bears, we recommend forest management in Skwelkwék’welt consider the importance of woody debris in providing suitable ant habitat.

Wing design in the last decades directed efforts and studies to improve the aircraft performance allowing fuel reduction, which implies more ecological and sustainable solutions and cost reduction for air transportation. Efficient design with a morph wing can fulfill such objectives. Different concepts of morph wing have been numerically investigated in this study proposing different wing configurations with the aim to improve aircraft performance in particular for the rolling maneuver. The assessment is performed by using an aerodynamic analysis based on a low fidelity 2D method such as the panel method, in combination with a 3D analysis using vortex lattice method, without considering elastic structural effects. The main morph wing concept is based on the constant morph of a part of the wing tip which has the aim of acting as a control surface hence as a substitution of the aileron for the rolling maneuver. The twist will then be applied linearly decreasing to the center of the wing. Within this concept three main configurations were evaluated: (a) the twist of the fixed airfoil section (Morph type M1 – rib twist), (b) the twist of the aileron which profile is changing according to a curvilinear law based on two morph angles (Morph type M2) and (c) both trailing edge and leading edge are morphed (Morph type M3). A comparison with a correspondent conventional aileron configuration at the same rolling moment coefficient showed an advantage of the morph wing in terms of drag coefficient with reductions that go up to 30%. It was also observed that in some cases such as M1 and M2C a morph deflection lower than 10° produce the same rolling moment coefficient of a typical small aircraft aileron deflection of 25°. Moreover, a parametric evaluation showed an optimum of the span wise parameter y rib to be 40% of the semi span b . Furthermore, a smoother distribution of the lift along the span wise direction will be determined in comparison with a conventional aileron. This also implies a smoother approach to stall conditions that can be beneficial for the pilot.

Airframe noise generated at wing trailing edges and high-lift devices, such as flaps, remains a major challenge during landing, with significant contributions in the low-frequency band of 500-1500 Hz. While solid surfaces reflect this acoustic energy, metallic porous materials can effectively absorb it through viscous and thermal dissipation within their internal pore structure. To address this, the present study examines the acoustic absorption characteristics of open-cell AlSi porous cylinders featuring controlled pore diameters between 0.3 mm and 2.25 mm. Measurements were conducted in an acoustic impedance tube according to the ISO 10534-2:2023 standard, using six cylindrical samples (28 mm diameter, 70 mm length). Two sets of measurements were performed for each sample (front and rear faces), and the average values were used. The findings indicate that the normal-incidence sound absorption coefficient α rises as pore size increases, reaching 0.93-0.97 at low frequencies of 500-700 Hz for the samples with the largest pores (1.8-2.25 mm). These results indicate that open-cell AlSi alloys offer strong low-frequencies sound absorption, positioning them as promising options for aeroacoustic noise mitigation, including applications such as porous trailing edge and hybrid flap designs.

The interaction of wings with vertical gusts is still not well understood, especially at the lower Reynolds numbers relevant to small Uncrewed Aerial Systems. Studies at higher Reynolds numbers with relatively slowly developing gusts have shown that morphing wing camber is effective at mitigating gusts, while at low Reynolds number, gusts are understood to be a leading edge phenomena relatively unaffected by the trailing edge. This study evaluates one-way trailing edge morphing and oscillating trailing edge motions with respect to the ability to mitigate vertical gust impacts. The results show that, for the gust condition tested, one-way trailing edge morphing at low Reynolds number acts similarly to higher Reynolds number studies. However, the long duration of the gust tested showed that one-way trailing edge morphing can only mitigate gusts for a certain length of time, after which stall occurs. Oscillating the trailing edge is shown to mitigate gusts in a similar fashion to prior studies on oscillating wings, where predictable oscillatory lift is possible. However, oscillating the trailing edge is only able to generate a predictable lift behavior for a certain length of time, after which the leading edge effects of the gust dominate over trailing edge motion. Higher oscillation frequency and Strouhal number are shown to have a detrimental effect on the predictability of lift during gust interactions, but have no effect altering the time at which highly unsteady stall dynamics occur.

Particle image velocity of the gust-induced flowfield and lift for the elastic wing are measured simultaneously in the wind tunnel test. The experimental results indicate that the wing’s pronounced elastic motion alters the flow acceleration performance of the gust, which brings a challenge to control at varying gust frequencies. To address this, a deep reinforcement learning (DRL) control is presented for the first time in a gust alleviation wind tunnel test, which is not only trained but also tested using only experimental data. A GLA wind tunnel test is conducted with a seamless morphing trailing edge (TE). From the perspective of the phase offset between the gust and the morphing TE, the controller can adjust the TE morphing to its optimal phase across different gust frequencies, varying inflow velocities, and gust amplitudes. Hence, the aerodynamics induced by the morphing TE can cancel out the gust-induced lift, which can be suppressed significantly. Specifically, at U∞=10 m/s, GR=0.08, and fg=3.0 Hz, the gust-induced lift coefficient is alleviated by 76.0%. Furthermore, the presented DRL controller can also take effect under superimposed multifrequency sinusoidal gusts.

Serration manufacturing effects on propeller trailing edge noise mechanisms

This study presents a comprehensive experimental investigation of flutter, post-flutter, and limit-cycle oscillations (LCOs) in very flexible swept-back wings, extending the Pazy wing benchmark to 10 and 20° sweep. Wind-tunnel tests on two models, each with leading-edge (LE) or trailing-edge (TE) tip weights, revealed two distinct flutter mechanisms: a low-speed, high-frequency hump flutter (LE) and a high-speed, low-frequency hard flutter (TE). Flutter onset sensitivity to deformation varied significantly: the hump flutter of the LE configuration was extremely sensitive to wing deformation, while the hard flutter in the TE configuration showed minimal sensitivity. Post-flutter responses exhibited superharmonic vibrations scaling with amplitude, while LCO tests identified small-amplitude, non-stall-driven oscillations and large-amplitude, stall-driven cases with subharmonics. The results demonstrate that mode coupling, rather than sweep-induced aerodynamics, governs flutter and nonlinear responses in these wings and provide a high-fidelity data set for validating nonlinear aeroelastic models.

Electric submersible pumps (ESPs) are widely used in oil production to lift multiphase fluids, yet the presence of oil-water mixtures can substantially complicate performance prediction and compromise operational stability, especially in multistage systems. This study investigates the internal flow dynamics and energy characteristics of a three-stage ESP under different oil-water ratios using Euler-Euler two-phase simulations validated against experimental data. Quantitative results show that both total head and hydraulic power decrease gradually as the oil content increases, with reductions of 1.29% and 1.75%, respectively, when the oil volume fraction rises from 0.1 to 0.3. A critical oil volume fraction of 0.3-0.4 is identified, at which phase inversion occurs from an oil-in-water to a water-in-oil regime, leading to an abrupt drop in total head to 18.47 m. The first-stage impeller is particularly sensitive to changes in oil-water ratio: unstable vortices near the pressure side are progressively suppressed with increasing oil content, reducing energy loss and improving efficiency, whereas downstream stages exhibit greater robustness. At the 0.5-span location, oil-dominated regions occupy up to 60% of the first-stage impeller blade chord, with marked accumulation near the suction-side trailing edge. In contrast, subsequent stages display more fragmented and disordered phase distributions due to shear-induced breakup. Overall, these findings provide new insights into the phase-inversion mechanism, inter-stage flow evolution, and energy-dissipation characteristics, offering practical guidance for optimizing ESP design and operation under oil-water multiphase conditions.

Abstract The influence of turbulence on the aerodynamics of a NACA0012 wing and the behavior of the associated wingtip vortex is investigated at a chord-based Reynolds number of 5000. The study is conducted through water tunnel experiments using a half-wing setup with an aspect ratio of 6 and an angle of attack of 10 degrees. At this low Reynolds number, relevant for aerodynamics at low-speed, the flow over a stationary wing exhibits laminar separation. Longitudinal Particle Image Velocimetry (PIV) measurements show a laminar flow separation over the wing upper surface and its reduction with increased incoming turbulence. Four turbulence conditions are tested: three different passive grids and one baseline (no-grid) configuration, yielding turbulence intensities ranging from 1.4 to 8.2%. Transverse PIV measurements are conducted over three cross-sections up to 24 chord lengths downstream of the wing trailing edge, to characterize the vortex dynamics. At the wingtip, the flow rolls up into a single coherent tip vortex, which exhibits significant unsteadiness in the form of a dominant displacement mode, as Proper Orthogonal Decomposition (POD) shows. In the no-grid case, the vortex exhibits significantly lower-frequency and higher-amplitude motion than in the grid-generated turbulence cases. This indicates that, at low Reynolds numbers, vortex meandering can arise either from unsteady perturbations linked to large-scale flow separation on the wing under low turbulence intensity, or from the direct receptivity of the vortex to freestream turbulence at higher turbulence levels. These results highlight the coexistence and relative importance of two distinct sources of disturbance—wing-separated flow and inflow turbulence—in governing wingtip vortex dynamics. Graphic abstract

Wind tunnel and rotation testing of a flexible trailing edge for wind energy turbine blades

The present study experimentally investigates the onset of ventilation of surface-piercing hydrofoils. Under steady-state conditions, the depth-based Froude number $\textit{Fr}$ and the angle of attack $\alpha$ define regions in which distinct flow regimes are either locally or globally stable. To map the boundary between these stability regions, the parameter space $(\alpha , \textit{Fr})$ was systematically surveyed by increasing $\alpha$ until the onset of ventilation while maintaining a constant $\textit{Fr}$ . Two simplified model hydrofoils were examined: a semi-ogive with a blunt trailing edge and a modified NACA 0010-34. Tests were conducted in a towing tank under quasi-steady-state conditions for aspect ratios of $1.0$ and $1.5$ , and for $\textit{Fr}$ ranging from $0.5$ to $2.5$ . Ventilation occurred spontaneously for all test conditions as $\alpha$ increased. Three distinct trigger mechanisms were identified: nose, tail and base ventilation. Nose ventilation is prevalent at $\textit{Fr} \lt 1.0$ and $\textit{Fr} \lt 1.25$ for aspect ratios of $1.0$ and $1.5$ , respectively, and is associated with an increase in the inception angle of attack. Tail ventilation becomes prevalent at higher $\textit{Fr}$ , and the inception angle of attack exhibits a negative trend. Base ventilation was only observed for the semi-ogive profile, but it did not lead to the development of a stable ventilated cavity. Notably, the measurements indicate that the boundary between bistable and globally stable regions is not uniform and extends to significantly higher $\alpha$ than previously estimated. A revised stability map is proposed to reconcile previously published and current data, demonstrating how two alternative paths to a steady-state condition can lead to different flow regimes.

This study investigates the aerodynamic effects of biomimetic wavy trailing edges inspired by natural designs, focusing on their application to a swept-back NACA 0012 airfoil under free-flight conditions. Numerical simulations were conducted using a three-dimensional numerical model with k−ω SST turbulence modeling at a Reynolds number of 3 × 104. The study was performed under steady-state conditions. Reynolds-Averaged Navier–Stokes (RANS) were used in the simulation. The baseline wing was modified with sinusoidal trailing edges, varying wave amplitude and wavelength in both chordwise and spanwise directions to assess their impact on lift, drag, and stall characteristics. Experimental validation was conducted in a low subsonic speed wind tunnel using 3D-printed scaled models, with comprehensive data collection on lift and drag coefficients, pressure distribution, and flow visualization. The results indicate that the wavy trailing-edge configuration maintains comparable lift to the clean wing at low angles of attack (AOA < 8°), while providing substantial aerodynamic enhancement beyond 8°, with improved lift generation and delayed stall. This demonstrates its potential for improving post-stall stability and aerodynamic efficiency in low-Reynolds-number flight regimes. Results demonstrate that a moderate wave amplitude of 20% tip chord length at 8° angle of attack enhances lift by 11.8%. The optimum parametric wavy wing delays the stall by approximate 6° associated with an increase in CLmax by 31% compared to a conventional straight edge. The findings highlight the potential of wavy trailing edges for improving aerodynamic efficiency and stability, particularly for small aircraft and UAVs.

Rim-driven propellers (RDPs) have attracted renewed attention as an efficient propulsion concept for integrated electric propulsion systems, yet their structural configuration inherently limits duct geometry modification, and viscous losses associated with boundary layer separation near the duct trailing edge remain a key performance constraint. In this study, a vortex generator-based flow control strategy is proposed as a practical means of improving RDP performance without altering the duct geometry. Reynolds-averaged Navier–Stokes (RANS) simulations were conducted to examine the effects of vortex generators installed on the outer surface of the duct, with numerical reliability ensured through a grid convergence index (GCI) analysis. A steady-state multiple reference frame (MRF) approach was employed, and the resulting flow characteristics were analyzed using velocity profiles, line integral convolution (LIC) visualization, pressure field analysis, and distribution of the flow field in the wake. The results show that the vortex generators effectively delay boundary layer separation near the duct trailing edge by re-energizing the near-wall flow, thereby enhancing flow attachment and pressure recovery. Consequently, consistent improvements in thrust coefficient and propulsive efficiency are achieved over the entire range of advance ratios, while the increase in torque coefficient remains negligible. These findings demonstrate that vortex generator-based flow control offers a practical and effective approach for enhancing the open-water performance of rim-driven propellers under structural constraints.

Abstract This paper investigates the aerodynamic interaction between a row of compressor blades and a downstream cylindrical probe, using unsteady, three-dimensional simulations. The study demonstrates the probe influence on rotor performance as a function of probe size and rotor proximity, identifies the physical mechanisms driving rotor–probe interactions, and quantifies the resulting probe measurement errors. A probe downstream of a rotor row causes each blade passage to deviate periodically from the steady, axisymmetric characteristic, as they pass the probe. In this study, the largest rotor disturbance occurs for a probe of diameter 14% blade chord, located 30% chord downstream of the rotor trailing edge. The flow coefficient, ϕ, moving with the rotor passage, varies between −10.4% and +5.5% compared to a case with no downstream probe. The total-to-total pressure rise coefficient, ψtt, increases by up to 7.7%. These rotor–probe interaction effects are driven by the unsteady response of the rotor passage to the potential field of the probe. In the stationary frame, measurement error occurs because the probe is exposed to the disturbed flow field, leading to maximum average errors of Δϕ=+7.5% and Δψtt=+8%. The magnitude of the rotor disturbance decreases as the probe is moved away from the trailing edge of the blades and when probe size is reduced. Decreasing probe size close to the blade row reduces the rotor disturbance more than moving a large probe downstream. Including a stator blade row downstream of the probe leaves the physical mechanisms unchanged.

Bionic serrated blades with three configurations for a voluteless centrifugal fan are proposed to improve the aerodynamic performance and suppress the noise, including triangular serrated blade (T-BLE), square serrated blade (S-BLE) and semi-circular serrated blade (C-BLE). The improved delayed detached eddy turbulence model and Ffowcs Williams-Hawkings acoustic model are employed to deal with the flow fields and acoustic characteristics. The models are first validated by comparing the experimental results and simulation data in terms of the aerodynamic and noise tests. Then, a comprehensive analysis of flow field characteristics and acoustic performance of a voluteless fan is conducted. Results indicate that the aerodynamic performance of serrated blades decreases due to the reduced air-exhaust area, with the T-BLE showing a 1.6% reduction. The improvement in wake flow pattern, vortex formation and separation for triangular serrations is pronounced. The serration designs significantly suppress primary tonal noise at the 13th blade passing frequency and other broadband noise. The total sound pressure levels of the T-BLE, S-BLE and C-BLE decrease by 6.27 dB, 4.06 dB and 5.14 dB, respectively. The serration structures inhibit noise generation and propagation by weakening periodic unsteady interactions between wake vortices and stationary flow. In general, the T-BLE achieves better noise reduction while maintaining the same aerodynamic performance.

This study experimentally investigates the bleeding flow characteristics downstream of isotropic porous square cylinders as a function of permeability and pore configuration across a broad range of Darcy numbers ( $2.4 \times 10^{-5} \lt \textit{Da} \lt 2.9 \times 10^{-3}$ ). The porous cylinders, constructed with a simple cubic lattice design, were fabricated using a high-resolution three-dimensional printing technique. This novel design method, based on a periodic and scalable lattice structure, allows fine control over the number of lattice pores along the cylinder width, $D$ , and the corresponding permeability, independently of porosity. Permeability was carefully determined by measuring the pressure drop and superficial velocity for each porous structure considered in this study. High-resolution particle image velocimetry measurements were conducted in an open-loop wind tunnel to characterize the downstream flow structures. The results reveal that bleeding flow characteristics near the cylinder trailing edge are strongly influenced by both permeability and pore configuration. These structural behaviours are further explored using an analogy to multiple plane turbulent jets. This approach identifies three distinct flow regions downstream of porous square cylinders, determined by the structural pattern of the bleeding flow. Additionally, an analytical framework is developed to model the longitudinal extent of the merging region by integrating the momentum equation, incorporating the Darcy–Brinkman–Forchheimer model, with a boundary layer assumption. The analytical model is validated against experimental data, demonstrating its capability to predict the key dynamics of bleeding flow evolution. Our results provide new insights into the fluid dynamics of porous bluff bodies, establishing pore configuration and permeability as dominant parameters governing downstream flow structures.

ABSTRACT The strong fluid–structure interaction (FSI) between the membrane structure and the surrounding airflow directly impacts the wind pressure distribution and structural stability, which are concerned with structural safety. This paper comparatively investigates the FSI of open and closed‐type saddle‐shaped membrane structures under wind loads, in terms of wind pressure distribution and flow field characteristics. First, a bidirectional FSI numerical simulation, integrated into this vortex dynamics‐based framework, was implemented for the spatial membrane structure in laminar flows. The accuracy of the simulation was verified based on previous wind tunnel tests, from the perspective of both structural vibration and flow field. Subsequently, leveraging the framework's ability to track vortex evolution, a comparative analysis of wind pressure distribution and velocity trajectories was conducted for both configurations. Finally, the framework enabled a deep analysis of how vortex structures–their formation, development, and dissipation–influence structural vibration. The results indicate that the peak wind pressure coefficients of the open membrane structure at the leading edge under 0° and 90° wind directions reach 0.5 and 0.7, respectively. At a 45° wind direction, the flange area becomes a risk focus due to conical vortices. For closed membrane structures, the minimum average wind pressure coefficients under 0° and 90° wind directions were −0.52 and −1.0, respectively, with significant overall wind suction force. The open‐type membrane structures exhibit both positive and negative pressure zones at all wind directions. Airflow separation results in wind pressure peaks at the leading edge of the windward side. Wind direction obviously affects the type of vortex structure, and the more sufficient vortex development would lead to increased trailing edge amplitude. Then, the local dynamic response of open‐type membrane structures should be paid more attention. However, closed‐type membrane structures experience upward lifting at all wind directions. The enhanced stiffness of the internal gas would reduce pulsations, and therefore the risk of structural overall instability should be considered as priorities.

The dynamics of a droplet on an inclined plane containing a chemical step, implying a heterogeneity in the wettability, have been widely studied because of their relevance to many applications. However, the modeling of such dynamics remains inaccurate due to the lack of implementation of contact angle hysteresis. In this work, we implement a chemical potential wetting boundary condition that includes hysteresis in a well-balanced lattice Boltzmann simulation to address that specific shortcoming. We investigate the behavior of droplet dynamics including this hysteresis force, and subsequently, also probe the effects of chemical step strength, inclination angle, and droplet volume on the droplet dynamics. We observe that the dynamics at the leading and the trailing edges of the droplet are significantly impacted by hysteresis effects and the chemical step strength. In addition, we conclude that for varying inclination angles, the hysteresis contribution is comparable to other contributing forces in the precise manipulation of the droplet.

The study of biomimetic structures in the fields of acoustics and fluid mechanics is of great significance, as they can mimic and exploit the efficient flow-control mechanisms found in nature to enhance the performance of fluid machinery, reduce energy losses, and achieve noise reduction. In this work, the application of biomimetic hydrofoils to underwater flow-induced noise suppression is investigated. The NACA66 (National Advisory Committee for Aeronautics) hydrofoil is selected as the baseline model, and its trailing edge is modified into a serrated shape to explore the corresponding hydrodynamic and acoustic characteristics. Large eddy simulation (LES) combined with the permeable surface Ffowcs Williams and Hawkings (FW-H) equation is employed, and the results confirm that the biomimetic structure can effectively suppress flow-induced noise. The serrated trailing edge of the biomimetic hydrofoil guides the formation of local vortices, effectively delaying boundary-layer separation, reducing turbulence intensity in the wake region, and shifting the onset of flow separation downstream, thereby enhancing flow stability. The serrated structure also reduces pressure loss. Compared with the baseline hydrofoil, the lift coefficient of the biomimetic design increases by 3.9%, while the drag coefficient rises by 4.4%. This indicates that the modified hydrofoil proposed in this study effectively improves hydrodynamic performance, thereby enhancing its engineering application prospects in equipment with stringent requirements for lift characteristics and flow control capabilities. Compared with the baseline hydrofoil, the biomimetic design exhibits a remarkable noise reduction effect at a monitoring radius of 15 m. At the monitoring point, the noise sound pressure level (SPL) is mainly concentrated in the low- to mid-frequency range, while the high-frequency SPL remains relatively low. A comparison of the SPL between the biomimetic and baseline hydrofoils at the same receiving point shows that the biomimetic hydrofoil achieves a significantly lower SPL in the low- to mid-frequency band. The maximum difference in the dominant frequency SPL reaches 15 dB. These results demonstrate that optimizing the trailing-edge shape of the hydrofoil can, within a certain range, improve its hydrodynamic performance and acoustic characteristics. This provides new insights into low-frequency noise suppression for underwater propulsors and theoretical support for noise reduction design in underwater propulsors and fluid machinery.

Secondary flow plays a pivotal role in flow separation within turbomachinery, impacting the performance of pump-jet propulsors through associated secondary flow losses. Past research has predominantly concentrated on water wing models, leading to limited insights into more intricate turbomachines. This study explores methods for extracting secondary flow characteristics in pump-jet propulsors through numerical simulations employing large eddy simulation, coupled with vortex identification techniques and analysis of velocity and pressure fields. Notable features of secondary flow include the tip leakage vortex and root shedding vortex, the latter exhibiting reverse flow and pronounced oscillations at the suction side's trailing edge. The distribution of driving forces and secondary flow intensity is evaluated using S3 flow surface theory, revealing a substantial influence of Coriolis forces at the blade root. This study proposes an innovative approach utilizing helical line techniques to form S3 approximate flow surfaces, facilitating thorough extraction of secondary flow characteristics at both blade tips and roots. This research fills existing gaps in the study of secondary flow phenomena in pump-jet propulsors, contributing valuable methodologies and a theoretical framework for evaluating secondary flow energy dynamics and related noise generation, thereby advancing the understanding of these critical elements in fluid mechanics and propulsion systems.