This study numerically investigates bilateral intakes around a broad-crested weir in a 90° river bend. The influence of interior intake angle (30°, 45°, 60°, 90°) and the effects of the sill and weir on discharge distribution is analysed. Results indicate that a 30° angle provides the most uniform flow and balanced discharge (each intake receives approximately 0.31 and 0.32 of the total flow at 35 l s−1). A 90° angle produces severe flow separation, reducing interior intake efficiency to no more than 0.04. The sill substantially reduces interior intake discharge, especially at 60°, where it falls to less than one-fifth of the no-sill value. Conversely, the broad-crested weir increases diverted discharge by factors of 2.9–14.4, depending on angle. This study demonstrates feasible water diversion from the inner bend and offers guidance for optimizing similar hydraulic systems.

Purpose This study aims to explore an investigation of stagnation-point flow and thermal transport characteristics of a radiative ternary hybrid nanofluid, consisting of engine oil as the base fluid, supplemented with nanoparticles of SiO2, Cu and ZrO2. It addresses the flow on a stretching/shrinking surface, accounting for the effects of velocity slip and melting. Design/methodology/approach The corresponding partial differential equations are then converted into self-similar equations and are solved using MATLAB’s bvp4c algorithm. Since the model has two solution branches, a linear stability analysis is conducted to select the physically relevant flow regime. The high level of statistical regression indicates the strength of the model, as evidenced by the significant F-statistic, low p-value and high coefficient of determination. Findings The findings indicate that a higher rate of melting and high rates of slip amplify momentum and thermal boundary layers, resulting in better heat transfer performance, and a decreased value of the parameters causes dual-solution behaviour and a delay in the boundary-layer separation. Originality/value Due to these features, the applications of the findings, in terms of polymer extrusion, storage of thermal energy, cooling of phase changes, the nano-lubrication systems and a sophisticated manufacturing process with high thermal loads, show high applicability.

Induced shape oscillations during bubble bouncing on substrates have been predicted to enhance mass transfer. However, the underlying physical mechanisms, including how bubble shape oscillations enhance mass transfer and whether this is governed by amplitude (low-order modes) or frequency (high-order modes), remain insufficiently understood. In this work, we hypothesize that bubble bouncing with shape oscillations enhances mass transfer by promoting interface renewal induced by circulation and concentration boundary layer separation. Within this framework, we further propose that the enhancement is primarily governed by low-order oscillation modes. A combination of optical methods with high spatiotemporal resolution - planar laser-induced fluorescence, particle image velocimetry and shadowgraphy - is employed to quantify the dissolved oxygen concentration field, the surrounding flow field and the bubble morphology. Additionally, a shape decomposition method is developed to analyze the oscillation modes of the bubble. Bubble bouncing accompanied by shape oscillations enhances mass transfer by approximately 20%, compared with the predictions of the classical model dominated by convection for moving bubbles. This enhancement results from the circulation and the concentration boundary layer separation, both driven by relatively large-amplitude oscillations of low-order modes during bubble bouncing, which promote interface renewal, as revealed by the spatiotemporal evolution of the flow and concentration fields. Building on these findings, an extended Sherwood number formulation is proposed, which takes bubble bouncing with shape oscillations in the low-order mode into account.

Improving the understanding and control of tip leakage noise is increasingly important for meeting future aviation noise-reductions targets. This study experimentally investigates porous tip treatments on a single stationary aerofoil, focusing on their effect on the two tip leakage noise sources, vortex-shedding and shear layer roll-up, both arising from the tip flow separation at the pressure side tip. Porous tip effectively reduces the roll-up noise source, with even a thin treatment of 1.6 mm providing reductions of almost 10 dB, whereas vortex-shedding noise radiation shifts toward lower frequencies and achieves almost full suppression for the thickness treatment of 10 mm. Localising the porous section to the mid-chord yields comparable noise reductions to full-chord treatments. Aerodynamic measurements indicate a modest lift reduction with the porous treatment compared to the hard-wall case, whereas drag remains largely unaffected for larger gaps.

The efficacy of compliant surfaces for load alleviation during aircraft manoeuvres or in turbulent gusts was investigated. A rectangular wing with a NACA0012 profile and a semi aspect-ratio of sAR = 5 was tested in a wind tunnel at a chord Reynolds number of 300,000 by means of lift, drag, wing root bending moment, flow fields, and compliant surface deformation measurements. The compliant surfaces with both ends fixed on the suction surface near the leading edge formed a hump which acted like rigid spoilers for separation control and led to substantial lift reduction. Similar lift reduction performance was also observed with leading-edge inverted compliant surfaces that exhibit steady large deflection to induce massive flow separations, thus led to a maximum lift reduction of 44% at the angle of attack of α = 10°. The trailing-edge inverted compliant surfaces with both steady deflections and limit-cycle flapping motions demonstrated a nearly constant lift reduction of up to Δ C L ≈ -0.28 by deflecting its wake flows upwards and reducing the circulation of the wing. When α increased beyond a critical value, both self-activated compliant spoilers and rigid spoilers with compliant hinges flipped over towards the upper surface, created massive flow separations over the wing and led to a maximum lift reduction of 32% at α = 10°. However, hysteresis loops in lift and drag appear when decreasing the angle of attack as both compliant and rigid spoilers remained on the upper surface of the wing and this requires future investigations. Nevertheless, to the best of our knowledge, this was the first time that compliant surfaces were employed for loads alleviation, and it provided a very cost-effective mechanism that can potentially eliminate the need for heavy mechanical surfaces such as trailing edge flaps or fluidic actuators.

Experimental studies were conducted to investigate the flow velocity distribution and turbulence intensity in a vortex settling tank (separator) and to examine changes when the flow rate is doubled. Two experiments were performed, each using a different flow rate through the tank. Variations in the turbulence structure were evaluated at two depths using measurements of instantaneous flow velocities obtained with a three-component acoustic Doppler velocimeter. The resulting changes in velocity and turbulence intensity, along with their spatial distributions within the settling tank, were analyzed. The findings showed that doubling the flow rate led to a threefold increase in average flow velocity near the tank walls, a twofold increase in turbulence intensity in the same region, and the expansion of zones with elevated local turbulence. Within these zones, the gradients of turbulence intensity rose substantially more than in other areas. The highest turbulence intensities were observed on the left side of the tank near the outlet deflector. Overall, the identified changes in the turbulence structure negatively impact the tank's performance, as they significantly increase flow velocity and turbulence intensity; however, this does not result in a significant decrease in the tank's efficiency.

Hydraulic Optimization of Shaft Hydropower Plant Intake Configurations Using 3D-CFD: the At-Bashy Case, Kyrgyzstan.

Arteriovenous fistula (AVF) failure in hemodialysis patients is strongly influenced by local hemodynamic factors such as elevated wall shear stress, flow separation, and vortex formation. In this study, computational fluid dynamics (CFD) simulations are performed to investigate the influence of anastomosis angle and blood rheology on AVF hemodynamics. Three non-Newtonian blood models (Carreau, power-law, and Casson) are first evaluated at 45°, 90°, and 135° anastomosis angles and validated against available experimental data. Based on shear stress prediction accuracy, the Carreau model is demonstrated as the best agreement and is selected for further simulations. Subsequently, AVFs with 45°, 90°, 110°, 120°, 135°, 145°, and 160° anastomosis angles are analyzed under maximum, medium, and minimum pulsatile flow conditions. Hemodynamic parameters including velocity patterns, wall shear stress distribution, vortex formation, and pressure drop between the proximal artery and vein are evaluated. Results indicate that increasing the anastomosis angle significantly reduces maximum wall shear stress, high-shear regions, vortex intensity, and pressure drop. Compared with the 45° configuration, the 160° angle reduced maximum shear stress by ~78% under peak flow conditions. Overall, obtuse anastomosis angles demonstrated improved hemodynamic performance, suggesting that larger angles may reduce thrombosis risk and cardiovascular burden in hemodialysis patients. Considering both hemodynamic performance and surgical feasibility, the 120° configuration is proposed as a clinically practical and effective option.

The precise perception of unsteady flow environments is critical for realizing 'fly-by-feel' flight control in next-generation aircraft. However, existing artificial hair sensors typically operate in a rigid, low-Cauchy-number regime and rely on scalar transduction, limiting their ability to resolve the flow direction without complex, dense arrays. In this study, we present a bio-inspired sensing system based on flexible magnetic cilia fabricated from a soft elastomer matrix. These sensors achieve a low elastic modulus that places them in a high-Cauchy-number regime, mechanically mimicking the compliance of seal whiskers and bat hairs. By synergizing this mechanical compliance with vector-sensitive magnetic transduction, we demonstrate that a single cilium can simultaneously resolve both the magnitude and direction of the airflow. Experimental validation on a non-slender delta wing confirms the array's ability to capture critical aerodynamic features, including leading-edge vortex migration, flow separation, and reattachment. Unlike traditional isotropic designs, this approach provides directional sensitivity at the single-sensor level, offering a scalable pathway for distributed aerodynamic monitoring.

A two-dimensional numerical investigation was conducted to evaluate the effects of plasma actuators (PLA) on the aerodynamic performance of a Darrieus vertical-axis wind turbine (VAWT). In the present study, PLAs mounted on turbine blades are employed to control flow separation. First, the flow field around the turbine and the induced field produced by the PLA are numerically simulated and validated. The influences of applied voltage, electrode length, and position on the power curve and flow features are explored. The performance of the PLA under optimal conditions is then evaluated for rotors with two to five blades, and the corresponding power curves are obtained. The results indicate that for a three-bladed rotor, the optimal use of the PLA increases the average power coefficient from 0.241 to 0.447. Moreover, due to the significant effectiveness of the PLA at low tip-speed ratios, the operational stability of the turbine is improved, and the difference between the maximum and minimum power coefficients of the three-bladed rotor over the tip-speed ratio (TSR) range of 1.64 to 3.3 is reduced from 0.24 to 0.09.

Flow passage optimization is an essential approach for enhancing the efficiency and operational stability of vertical mixed-flow pump units. To address the limitations of the traditional single-factor control variable method—which ignores parameter interaction effects and relies on empirical judgment for scheme screening, leading to low optimization efficiency and insufficient engineering adaptability—this study proposes a multi-factor interactive flow passage optimization methodology that deeply couples orthogonal experimental design with Computational Fluid Dynamics (CFD) simulations. A multi-indicator quantitative evaluation system encompassing “hydraulic loss, velocity uniformity, and weighted average angle” was constructed. Taking a large-scale drainage pumping station as the research object, key parameter combinations were systematically covered through orthogonal experiments. The optimal intake flow passage scheme was screened via CFD simulation, which was verified to have a hydraulic loss of only 0.104 m, an outlet velocity uniformity of 97.06%, and a weighted average angle of 84.82°, approaching the ideal vertical inflow, thereby effectively reducing flow impact losses. The optimal discharge flow passage scheme demonstrated smooth flow patterns without significant flow separation and was fully compatible with the spatial layout of the pumping station. Model test validation showed that under the design head condition of 7.1 m, the pump unit efficiency reached 77.34% with a flow rate of 11.38 m3/s. The error between CFD simulation and experimental results was less than 5%, meeting the design requirements. This study provides a scientifically efficient and engineeringly feasible technical pathway for flow passage optimization in similar vertical mixed-flow pump units.

Conventional thrust vector control nozzles are severely constrained by a single-pivot deflection paradigm, which induces asymmetric shock reflections and adverse boundary layer separation at large angles. Multi-segmented serial configurations offer a promising alternative to overcome these limitations by distributing the total deflection across multiple joint interfaces, thereby achieving large terminal angles and smooth flow-path curvatures. To realize such a configuration, this study draws inspiration from the abdominal bending mechanism of the damselfly Ischnura elegans during mating wheel formation. Real-time video recording and morphological characterizations identified abdominal segments VI and VII as critical for high-amplitude bending under load. Finite element analysis under muscular actuation elucidated the biomechanical synergy, which was rigorously verified through mesh convergence and material property sensitivity checks. Inspired by this biological system, a multi-segmented nozzle configuration incorporating discrete elastic elements and a centralized cable-driven layout was designed and evaluated using multibody dynamics and computational fluid dynamics. The nozzle achieved a continuous 61.20° deflection within 8 s under subsonic exhaust conditions, successfully stabilizing periodic supersonic shock structures and completely suppressing adverse boundary layer separation. These findings turn biological bending into a thrust vectoring method, giving insights for next-generation agile aerospace propulsion systems.

Flow stasis is a major hemodynamics determinant of thrombosis associated with flow separation in the cardiovascular system. Residence time provides a quantitative measure of flow stasis and can serve as a surrogate transport metric associated with thrombogenic potential. However, the experimental parameters governing reliable dye-based residence time quantification, including injection location, injection rate, and imaging configuration, remain insufficiently defined, particularly in milli-scale models. This study establishes a standardized and reproducible framework for residence time quantification using a backward-facing step geometry, a canonical benchmark that reproduces physiologically relevant separated flow structures. An in-house image processing algorithm was developed to quantify residence time from dye washout. Injection location, injection rate, and imaging modality were systematically varied under steady and pulsatile inflow conditions spanning laminar, transitional and turbulent regimes (Reynolds number 100–3000). Both profile and en face imaging were evaluated to replicate clinically relevant viewing perspectives. Systematic testing identified an optimal injection window (IHL = 0.5, 0.25 ≤ ILL ≤ 0.5) and injection rate of 0.2 ml/min that minimized flow disturbance and produced <5% trial-to-trial variability. Positioning the injection within this window introduced dye into the persistent low-velocity core of the recirculation region, enabling consistent dye retention and saturation across all flow regimes. Optimal borescope placement (IHL = 1 and ILL = 0.75) produced the smallest relative differences between imaging configurations. This work defines critical experimental parameters for reproducible dye-based residence time quantification, enabling characterization of dye-washout behavior and flow stasis conditions associated with thrombogenic potential in millimeter-scale models.

Surface roughness significantly influences flow behavior across natural phenomena and engineering applications. Accurate prediction of these effects is essential for engineering design, yet modeling roughness-induced transition remains challenging due to the intricate interactions among surface roughness, boundary-layer development, and laminar separation. This study develops a novel machine-learning-enhanced k−v2¯−ω transition model by introducing a transport equation for the roughness amplification factor Ar. The key correction function associated with Ar is explicitly derived using a multicase, computational-fluid-dynamics-driven machine-learning framework. The proposed model is assessed on canonical flat-plate boundary layers, airfoils, and turbine cascades under diverse flow conditions. Results demonstrate that the model effectively captures boundary-layer transition influenced by surface roughness and flow separation, achieving good agreement with both experimental and direct numerical simulation data. Further analysis reveals that Ar plays a critical role in amplifying disturbances and promoting earlier transition onset. Overall, the present machine-learning framework provides a promising pathway for extending traditional RANS transition models to incorporate complex physical effects.

Investigating the effects of streamwise riblets on flow separation in low-Reynolds-number compressor cascades using direct numerical simulation

We present an adaptive flow control strategy for a turbulent separated flow using online dynamic mode decomposition. The system dynamics are identified in real time, and a linear quadratic tracking controller regulates the separation location along a predefined target. Controller gains are updated continuously based on the new system updates, allowing for an adaptive formulation of real-time feedback control that can adjust to both variations in the freestream flow due to external disturbances and actuation-induced changes of the flow dynamics. The approach is demonstrated on a NACA4412 wing at Re=50,000 using direct numerical simulation at 0 and 10 deg angles of attack, outperforming steady blowing in moving the separation point downstream. At 10 deg, adaptive control increases lift to drag by approximately 60%. The framework is further extended to directly regulate the lift-to-drag ratio, illustrating its potential for real-time control of aerodynamic forces in unsteady, separated flows.

Momentum and heat transfer from spherical sections in Bingham plastic fluids

Label-free and direct separation of white blood cells (WBCs) remains one of the major challenges in the field of efficient leukocyte separation. To address this challenge, we propose a WBC sorting strategy based on inertial microfluidics and 3D-printing technology, which employs a single inertial microfluidic chip to perform four consecutive high-throughput separation steps between red blood cells (RBCs) and WBCs. Specifically, the chip features a trapezoidal cross-section spiral channel to achieve size-dependent, stable spatial separation of cells along the inner and outer channels. After the conceptual design, the UV cured 3D printing technology is employed to fabricate the inertial chip and its fixture. Subsequently, mixed polystyrene microparticles are used as test objects to verify the sorting performance of the inertial chip, and the results indicate that the optimal separation flow rate is ∼1700 . This corresponds to a maximum WBC throughput of ∼1.12×107cells/h during a single-pass separation under the current 1:100 dilution condition, assuming a whole-blood WBC concentration of 1.1×107cells/mL. Ultimately, the diluted whole-blood samples are used to examine the four-cycle consecutive sorting strategy, and the results demonstrated that this strategy, proposed in this work, could directly obtain WBCs from blood samples with a recovery efficiency of ∼94.9% and a purity of ∼85.5%. Related experiments indicate that this strategy which is centered on the 3D-printed chip offers high reliability and sensitivity for label-free WBC sorting from blood cells. With the aid of state-of-art additive manufacturing technology, it is promising that our strategy could be widely applied on fields including cell analysis and disease diagnosis.

Industrial dust pollution threatens occupational health and production safety, driving the urgent need for optimized filtration technology. Filter plate geometry critically regulates flow fields, filtration performance, and energy consumption. This study numerically modeled a dust collector with a flat filter plate and three corrugated filter plates of different curvatures (λ = 1/8, 2/8, 3/8). Using the SST k‑ω turbulence model, discrete phase model, and JKR adhesion theory, the effects of curvature on flow distribution, turbulent kinetic energy, pressure field, and dust deposition were investigated. Quantitatively, compared with the flat plate (λ = 0), the corrugated plate with λ = 1/8 reduces the pressure drop by 3.5% (from 256.4 Pa to 247.3 Pa) by increasing the effective filtration area. Further increasing curvature to λ = 3/8 significantly improves deposition uniformity and suppresses local filter cake accumulation, though a slight pressure drop rebound occurs due to intensified flow separation. Mechanistically, curvature induces periodic pressure fluctuations and multi-peak turbulent kinetic energy, enhancing particle migration while balancing airflow uniformity. These results demonstrate that the optimal curvature range for balancing energy consumption and deposition performance is λ = 2/8–3/8.

Abstract This paper presents an experimental investigation of the properties of long electrical arcs immersed in a crossflow. The insights gained from these experiments can be applied in numerous fields: one of which is lightning protection of aircraft. Upon initial attachment to the airplane, the lightning arc column can sweep along the plane's surface due to the relative motion between the two in a process known as the swept-stroke. The first set of experiments corresponds to meter-scale low-current D.C. arcs (3 A) attaching to an aeronautic airfoil in low speed flow (1-4 m/s), extending prior work that considered an anodic airfoil to the negative polarity case. The dynamic and electrical properties of the arc channel, as well as the dynamic motion of the cathodic arc root, are investigated through high-speed imaging, particle image velocimetry (PIV), and electrical measurements. The influences of wind speed, airfoil angle of attack (AoA), and counter-electrode configuration are explored. The second set of results applies the same data processing to high-speed videos from a previous experimental campaign conducted at ONERA on meter-long high-current D.C. arcs (200-600 A) subject to high-speed flow (40-60 m/s). Unlike the anodic arc root, the cathodic arc root is observed to either stall or sweep along the airfoil surface. In general, the root trails the leading edge of the arc column, which is advected by the flow, with the degree of lag depending on the experimental conditions. These findings enable analysis of how flow separation, boundary layer dynamics, arc regimes, and cathode emission processes influence the physical behavior of the arc column and root over two orders of magnitude in current and one order of magnitude in wind speed, providing insight into the coupled phenomena governing the swept-stroke.