Drag reduction is crucial for improving aerodynamic efficiency and enhancing energy conversion, such as wind turbines. Riblets inspired by shark skin are a promising approach in drag reduction technology. In this work, further inspired by the typical wind-eroded landform yardangs in nature, a novel passive metasurface of fluid mechanics, composed of low-high-low riblets (LHLRs), was proposed to achieve enhanced drag reduction performance. The aerodynamic drag reduction performance of LHLRs is validated by comparing them with skin-inspired riblets using a flow channel with an adjustable surface yaw angle. The surface turbulent flow characteristics are obtained via direct numerical simulation, then turbulence motion analysis explains the improved drag reduction performance of LHLRs. The results indicate that the drag reduction performance of the LHLRs is improved by 91.6 % compared to the shark skin-inspired riblets, and its robustness to wind yaw angles increases from 30 degrees to at least 45 degrees. Turbulence motion analysis reveals that LHLRs can weaken the transport of internal turbulence, further suppress turbulence penetration, and delay the formation of secondary vortices near the wall, thereby reducing dispersive stress and enhancing drag reduction performance. Moreover, the equivalent turbulence-free region between the primary and secondary riblets of LHLRs optimizes the near-wall turbulence distribution, leading to a modification of the optimal non-dimensional square root of the groove cross-section l+g in the riblets drag-change curve.

Accurate measurement of three-dimensional micro-aerodynamic forces is essential for the development of aerospace, micro air vehicles, robotics, and bio-inspired engineering. However, as the measured forces decrease, significant crosstalk interference and coupling between force components become evident. Due to limitations in measurement and installation methods, improving measurement resolution and precision of existing multi-axis sensors remains challenging. This paper presents a novel wind tunnel balance based on the air-floating principle. The balance achieves decoupling-free measurement of three orthogonal micro force components, with significantly suppressed inter-axis coupling. A self-designed calibration apparatus was used to calibrate the balance, demonstrating horizontal in-plane resolutions of approximately 1.28x10-5 N (z-axis) and 1.17x10-5 N (x-axis), and a normal-direction (y-axis) resolution of approximately 8.72 x 10-5 N. When measuring force of 1.0 x 10-3 N, the measurement precision was no greater than 0.12%. The balance's performance was validated by measuring forces on a single pigeon secondary feather at low wind speeds (1 5 m s-1) and various angles of attack (-20 degrees 20 degrees). The results show that the balance had accurately measured the component variations of force at O (10-4) O (10-2) N, revealing how the flexible vane curvature affects lift, drag, and spanwise forces. By eliminating complex decoupling processes, the proposed balance enables more precise and efficient micro-force measurements in multiple dimensions, offering significant advantages in micro-aerodynamics and demonstrating considerable value of the research on novel micro air vehicles.

Drag reduction and anti-icing are critical challenges in aircraft operations. Traditional anti-icing films are often inefficient. To meet the complex environmental demands of modern aviation, a dual-functional film combining drag reduction and anti-icing properties was developed. Using laser direct writing lithography, micro-riblet structures were fabricated on flexible PET films, which were then combined with a nanoparticle coating to create a superhydrophobic surface, achieving long-lasting drag reduction and anti-icing performance. The film exhibits a water contact angle of 156 degrees, delays ice formation by up to 201 s, and reduces ice adhesion strength to 49.8 kPa. Wind tunnel tests show a maximum drag reduction rate of 6.6 % under high Reynolds numbers. The film also demonstrates excellent mechanical durability, chemical stability, and self-cleaning performance. This integrated solution enhances resource efficiency and provides a novel approach for aviation technology optimization.

Fluid wall shear stress is a direct assessment of friction drag in turbulent boundary layers, which plays a crucial role in investigating aerodynamic optimization and drag reduction. Although optical sensors feature high sensitivities and strong immunity to electromagnetic interference, the conventional grating films undergo significant degradation at high temperatures, leading to deterioration of the sensing performance. To address the issue, this work proposes an optical wall shear stress sensor with a thermally stable high-reflectivity thin film structure, which adopts an aluminum oxide-gold-aluminum oxide (Al2O3-Au-Al2O3) three-layer structure. The grating film both alleviates stress concentration at the Si-Au interface and inhibits gold film agglomeration at high temperatures. A multi-objective genetic algorithm (MOGA) is employed to optimize the folded beam structure of the sensor, aimed at enhancing overall performance by balancing the sensitivity and response frequency. Based on microelectromechanical systems (MEMS) technology, sensor prototypes are fabricated for experimental verification. Under 1-kHz excitation, the sensor exhibits a dynamic wall shear stress sensitivity of 30.16 mV/Pa, and its coherence coefficient with the reference sensor reaches 0.997. Static calibration shows a sensitivity of 23.65 mV/Pa with a nonlinear error of 1.67 % over a 100-Pa range. Furthermore, tests in an arc-heated wind tunnel confirm the sensor's thermal stability and reliable dynamic response at 400( degrees)C, validating its applicability in high-enthalpy environments. This article provides a promising approach for measuring wall shear stress in high-temperature aerodynamic environments, such as aircraft engine combustion chambers and rocket engine nozzles.

Dandelion seed-inspired low-Reynolds-number flyers represent a potential solution for exploring the extremely thin atmosphere of Mars. However, the flight dynamics of their natural prototype, the dandelion seed, remain incompletely understood. This paper establishes a flight dynamics model for the dandelion seed. Using the Runge-Kutta method to numerically integrate the model, the dynamic stability of bio-inspired micro-flyers with different beak lengths is investigated in ascending shear flows under various combinations of shear-rate amplitude and oscillation frequency. The results show that varying the beak length significantly affects the flyer’s moment of inertia. In most cases, the short-beaked flyer exhibits better stability, whereas a longer beak helps stabilize the flyer’s attitude under low shear intensity and high oscillation frequency. An increase in shear intensity induces chaotic motion in the long-beak flyer. In chaotic regimes, the vertical velocity distribution of the long-beaked flyer exhibits distinct symmetry breaking, enabling it to extract energy from the oscillatory flow, accumulate velocity, and thereby increase flight altitude and flight efficiency. Finally, a preliminary configuration of a dandelion seed-inspired Martian micro-flyer featuring a variable pappus structure and an adjustable beak length is proposed. Analogous to dandelion seeds exploiting thermal updrafts, the flyer is designed to achieve sustained flight by leveraging updrafts induced by thermal gradients near the Martian terminator. The findings provide new insights into the design of bio-inspired micro-flyers and into the dispersal mechanisms of Asteraceae seeds.

Skin friction, or wall shear stress is a fundamental parameter for characterizing turbulent boundary layer (TBL). Among various methods, the floating element (FE) method has long been advocated and developed. However, accurately measuring WSS for small-area samples remains challenging. This paper proposes air-bearing-based high-resolution micro skin-friction balance and a corresponding sliding-covering measurement method. As an extension of the traditional flush-mounted FE measurement method, it reduces errors caused by the edge gap and gap flow of the floating elements, and employs a clamping mechanism for high-precision assembly, thereby enhancing the measurement efficiency and accuracy for small-area samples. The error sources in balance calibration and measurement were carefully analyzed, with corresponding uncertainty calculated. The measurement range and resolution are +/- 0.12 Nand 2.5x10-7N, respectively. Fora smooth surface, assume the measured force is 1x10-4 N, and the measurement precision is approximately 0.047%. The balance is validated using a smooth-wall zero-pressure-gradient TBL. The measured skin-friction coefficient, equivalent to /infinity, generally follows a Coles-Fernholz relation = 2 [1/ ln (Re) + ]-2 within 3% (with chosen constant of = 0.384 and = 4.12) fora momentum-thickness-based Reynolds number Re = 1050 similar to 3361. Additionally, the skin friction on the surfaces of two envelope materials (EMs) used for airships was measured using the sliding-covering method. The results were compared with those of a smooth surface, revealing that the outer surfaces of EMs exhibited a drag reduction effect at low Reynolds numbers, with further potential for improvement in a broader range of Reynolds numbers. The balance measured the skin-friction differences between samples and revealed that the roughness of the samples affected the precision of the measurements. Asa direct measurement method, the results have higher reliability.

The porous and fluffy pappus structure of the dandelion is crucial for its stable flight. The pappus angle can be adjusted automatically in response to humidity to regulate flight capabilities. This study investigated the effect of pappus angle on flight dynamics using custom-made molds to fabricate dandelions with varying pappus angles. Aerodynamic drag was measured across wind speeds (0.1∼0.8 m s−1) using an air-bearing-based drag balance, while a hot-wire anemometer and particle image velocimetry analyzed wake vortex structures. Results showed that dandelions exhibit higher drag coefficients at low wind speeds, with larger pappus angles increasing drag and wake stability at higher Reynolds numbers. Smaller pappus angles led to lower local porosity, stronger shear effects, and rapid wake instability. Natural dandelions demonstrated superior vortex growth and spatial stability at high Reynolds numbers compared to artificial ones, highlighting the advantages of their complex three-dimensional pappus structure. Additionally, lateral vortex diffusion was constrained when the pappus angle exceeded 140°, limited by local porosity. These findings could inspire efficient unpowered aircraft designs.

Many outdoor devices require effective snow prevention solutions, yet existing passive anti-icing technologies are inadequate for snow repellency due to the variability of snow properties. This study addresses this gap by proposing a bioinspired micro-grooved anti-snow structure that minimizes van der Waals forces through reduced contact area and mitigates capillary effects via a V-shaped design, facilitating the separation of liquid water at the interface. Snow-shedding performance is shown to be highly sensitive to surface roughness, with the periodic smoothness of micro-grooves significantly reducing mechanical interlocking with snow. In contrast, hierarchical superhydrophobic structures strongly interlock with ice grains, preventing spontaneous snow-shedding even at extremely low adhesion forces. By embedding superhydrophobic nanoparticles into the micro-groove structure, this study presents a multifunctional design that integrates anti-icing, anti-snow, and water-repellent properties. Experimental results demonstrate that the structure effectively balances adhesion reduction and snow-shedding performance, showing promising potential for photovoltaic solar power systems and large-scale architectural applications.

The dynamic behavior of droplets on superhydrophobic microstructured surfaces plays a crucial role in applications such as self-cleaning, thermal management, and anti-icing. While previous studies have extensively investigated droplet impact dynamics, the effect of the droplet-to-microstructure size ratio (D/S) on rebound behavior remains insufficiently understood. This study systematically examines the influence of D/S on impact dynamics, revealing a transition from inertia-dominated macroscopic effects to adhesion-governed localized interactions. At larger D/S, inertia and surface tension primarily dictate retraction, leading to symmetric rebound. However, as D/S decreases, intensified contact line pinning prolongs contact time and suppresses rebound, fundamentally altering retraction dynamics. A previously unreported transition in droplet retraction identified, where localized constraints progressively hinder contact line motion, shifting the governing mechanism from inertia-driven to adhesion-controlled behavior. To further elucidate this transition, a theoretical framework is established to characterize the role of D/S in contact line dynamics, linking size-dependent interfacial interactions to droplet mobility. These findings provide new insights into droplet impact physics and serve as a theoretical foundation for optimizing superhydrophobic surfaces in applications such as anti-icing and spray cooling.

Droplet impact behavior on superhydrophobic surfaces plays a crucial role in various thermal management applications, particularly in anti-icing, condensation heat transfer, and moisture control. While extensive studies have focused on freezing-induced adhesion, rebound failure can also occur under non-freezing conditions, where conventional explanations are insufficient. In this study, we systematically conducted droplet impact experiments on cold superhydrophobic surfaces under controlled temperature difference (Delta T) conditions between the droplet and the surface. The results demonstrate that rebound behavior is primarily governed by Delta T rather than the individual temperatures of the droplet and surface. When Delta T exceeds a critical threshold of 15 degrees C, droplet rebound begins to fail due to intensified interfacial condensation, which forms liquid bridges inside surface microstructures and significantly increases energy dissipation. This temperature-difference-driven interfacial condensation mechanism provides new insights into dynamic wetting failure under thermal gradients, and suggests potential strategies for improving surface design in condensation management, anti-icing, and coldenvironment heat exchange systems.

Micro-scale droplet impact behavior is widely observed and holds critical significance in various fields such as inkjet printing, anti-icing, and spray cooling. However, current research has primarily focused on millimeter-scale droplets, leading to a lack of understanding regarding the dynamics of micro-scale droplets. To address this gap, our research systematically analyzed the impact and rebound behaviors of droplets of various sizes on microstructur surfaces, revealing the significant influence of droplet size on dynamic characteristics. The results revealed that micro-scale droplets exhibit markedly distinct morphological evolution during spreading, contraction, and rebound compared to millimeter-scale droplets. As droplet size decreases, the minimum rebound velocity threshold significantly increases, contact time extends substantially, and viscous dissipation becomes the primary energy loss mechanism in micro-scale droplets, resulting in a dramatic decrease in the restitution coefficient. Based on energy balance analysis, we developed a theoretical model to characterize the restitution coefficient of micro-scale droplets, demonstrating strong concordance with the experimental results. This research provides novel insights into the dynamic behavior of micro-scale droplets and offers theoretical support for surface design in diverse applications such as biomedical printing, aircraft anti-icing, and electronic device cooling.

Wall shear stress is one of the key parameters in turbulent boundary layers, playing a pivotal role in aerodynamic optimization and fuel efficiency enhancement. Although MEMS-based direct measurement stands as the most promising approach for wall shear stress quantification, the inherent limitations of floating sensing structures under harsh environments lead to mechanical failure, representing persistent technical barriers in practical applications. This work presents a novel MEMS sensor equipped with a protective floating cover plate, achieving high-robustness measurement through coordinated structural-process innovations. Based on the Dual Silicon-On-Insulator (DSOI) fabrication process, a protective floating configuration is developed. The critical process techniques, including deep silicon etching, wet etching of glass through vias, and silicon-glass anodic bonding synergistically establish protection for the sensing structures. The established electromechanical coupling mathematical model elucidates quantitative mapping relationships between critical structural parameters and sensing performance. Experimental characterization reveals a linear sensitivity of 28.3 mV Pa−1 and a resonance frequency of 2.9 kHz. In supersonic tunnel experiments at Mach 2.0, the sensor achieves unprecedented full-cycle dynamic capture from establishment through stabilization to dissipation with millisecond-level transient response characteristics. This work provides a robust, high-precision solution for aerodynamic and fluid dynamics applications, paving the way for improving energy efficiency and flow control strategies.

Iron oxides are widely used for electrochemical energy storage, however, low conductivity and poor reversibility still limit their potential. In this paper, we proposed a simple hydrothermal pore-making and subsequent in-situ electrochemical redox method to synthesize hierarchical porous Fe3O4 nanoparticle anodes. Benefiting from the self-supporting electrode design and abundant surface area and pore pathways, the ion transport efficiency and conductivity of the anode are enhanced, and the generation of inert phases induced by excess charge buildup is also greatly mitigated. Ex-situ X-ray diffraction shows that the crystal structure remains stable with nearly zero strain generation throughout the charging and discharging process. Due to this structural advantage, the P-Fe3O4@CC electrode exhibits a specific capacitance of 1918.3 F g-1 in KOH (at 2 A g-1), with 97.3 % capacity retention after 10,000 cycles. Notably, the assembled symmetric supercapacitors P-Fe3O4@CC//P-Fe3O4@CC and asymmetric supercapacitors P-Fe3O4@CC//CoNi-LDH@CC exhibit maximum energy densities of 158.0 Wh kg-1 (at 2.0 kW kg-1) and 108.9 Wh kg-1 (at 1.5 kW kg-1), respectively. This study confirms the effectiveness of the synergistic effect of hierarchical porous structure and anti-spinel crystal structure to enhance charge storage and structural stabilization for Fe3O4 anodes.

Understanding the dynamics of droplet impact on superhydrophobic cold surfaces is essential for developing effective anti-icing strategies in low-temperature environments. However, most previous studies have focused on millimeter-scale droplets, and the behavior of microscale droplets, which are common in practical environments, remains largely unexplored. To address this gap, we conducted systematic experiments spanning millimeter to micrometer scales and characterized the outcomes using phase diagrams, maximum spreading factors, contact times, and restitution coefficients. The results show that the spreading stage consistently follows the classical inertia-capillarity scaling and remains unaffected by temperature reduction or droplet size. In contrast, the retraction stage is highly temperature sensitive and strongly size dependent. As surface temperature decreases, contact time is markedly prolonged due to slower retraction, restitution coefficients decline, and smaller droplets increasingly lose their rebound ability under supercooled conditions. To explain this behavior, we propose a thermal diffusion-dynamics timescale criterion that clarifies the size-dependent mechanism of freezing onset. The criterion decreases with droplet size and shows that smaller droplets complete interfacial cooling more readily within the limited dynamic window, which triggers localized freezing. This work deepens the understanding of droplet impact dynamics on cold interfaces and provides theoretical foundations for the rational design of anti-icing and de-icing surfaces in microdroplet environments.

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Micro-drop ejection technology has been widely employed in cell analysis, drug delivery, microreactors, and various other fields due to its high accuracy and resolution, which can accurately control and dispense liquid materials. However, the current development of this technology faces challenges due to nozzle diameter limitations. Smaller droplets require finer nozzles for ejection. Nevertheless, fine nozzles cause significant fluid resistance, hindering micro-droplet ejection. Overcoming the constraint posed by nozzle and achieving high- precision micro-droplets ejection has become a challenging task for the industry. Inspired by the phenomenon of cavity collapse in nature, we have developed a micro-droplet ejection technology based on actively controlling the cavity collapse within the confined interface. By analyzing the formation and collapse of the liquid cavity, we have identified three ejection modes: no droplet, single droplet, and satellite droplet, and further delineated the boundary conditions for minimizing droplet size and ejecting satellite-free droplets. Using this technology, we achieved precise control over droplet size within a defined range, with the minimum droplet diameter reaching 34 % of the nozzle diameter. Furthermore, the continuous ejection of single droplets demonstrated excellent stability and repeatability. This innovative technology could provide a novel approach to achieve high accuracy and controllability in micro-droplets ejection, liberating it from nozzle constraints, thus expected to play a significant role in the fields of biomedical research, chemical engineering, and printed electronics.

Riblets can be potentially employed to passively reduce the turbulent friction drag. However, the drag reduction performance of riblets does not currently meet expectations, which could assist in emission reduction and energy conservation in green transportation. This study proposes and validates a topological form of hierarchical nested riblets (HNR) that significantly enhances the drag reduction performance. To explore the drag reduction enhancement mechanism, direct numerical simulations are performed for flow simulation on the riblet surface under different Reynolds numbers. The results show that under the riblet dimensionless spacing of the riblet s(+)approximate to 21, the drag reduction performance of the HNR surface improves by about 70% compared to that of the uniform riblet surface, which is inspired by shark skin. From the perspective of turbulence statistics, the HNR surface reduces the turbulent mixing near the wall, weakening the momentum transfer. Furthermore, the transient flow field shows that the secondary riblet in HNR prevents some turbulent flow and streamwise vortices from entering the groove, considerably weakening the dispersive stress induced by the secondary flow. Moreover, owing to the influence of the secondary riblet, small-scale turbulence develops and strengthens into large-scale turbulent motion, which is advantageous to the boundary layer flow and results in drag reduction improvement.

Actuators play a crucial role in modern distributed electric grids and renewable energy network architectures, implementing control actions based on sensor data to ensure optimal system performance and stability. This paper addresses the economic dispatch (ED) problem of distributed DC microgrids with renewable energy. In these systems, numerous sensors and actuators are integral for monitoring and controlling various parameters to ensure optimal performance. A new event-triggered distributed optimization algorithm in the discrete time domain is employed to ensure the minimum production cost of the power grid. This algorithm leverages data from sensors to make real-time adjustments through actuators, ensuring the maximum energy utilization rate of renewable generators (RGs) and the minimum cost of conventional generators (CGs). It realizes the optimal synergy between conventional energy and renewable energy. Compared to the continuous sampling optimization algorithm, the event-triggered control (ETC) optimization algorithm reduces the frequency of communication and current sampling, thus improving communication efficiency and extending the system’s lifetime. The use of actuators in this context is crucial for implementing these adjustments effectively. Additionally, the convergence and stability of the DC microgrid are proven by the designed Lyapunov function. Finally, the effectiveness of the proposed optimization algorithm is validated through simulations of the DC microgrid.

Aircraft icing has a significant impact on flight safety,as ice accumulation on airfoils and engines can cause aircraft stalls.Developing anti-icing technology that can adapt to harsh and cold environment presents a challenge.Here,we propose a new anti-icing skin with micro-nano structure inspired by the bamboo leaf called Fargesia qinlingensis.A multilayer non-uniform height(MNH)micro-nano structure is proposed based on the Fargesia qinlingensis surface structure.The anti-icing mechanism of the MNH micro-nano structure is revealed.The flexible large-area MNH micro-nano structure is fabricated based on hierarchical assembly method.Compared with the smooth surface,the ice adhesion strength of the prepared bio-inspired surface is reduced by 80％,indicating that the MNH micro-nano structure inspired by Fargesia qinlingensis has ice-phobic effect.Based on this,an anti-icing hybrid skin based on bionics and electric heating is developed.The anti-icing hybrid skin has successfully completed the anti-icing function flight test on the UAV.To realize the effective anti-icing function under super cold conditions,the anti-icing hybrid skin has been applied on a certain type of UAVs.The bio-inspired anti-icing skin has broad application prospects in large transport aircraft,helicopters,wind power generation,and high-speed trains.

Existing wetting theories have difficulty accurately describing advancing/receding processes on micro-structured surfaces. A strategy is proposed to solve this problem by recognizing it as a liquid–vapor interface geometrical question. The wetting chip method is proposed to realize the microscopic observation of liquid–vapor interface variations. A wetting model based on the liquid–vapor interface shape (LVIS model) is established to describe the analytical relationships between the apparent contact angles, liquid–vapor interface radius, substrate geometry, and chemical nature of liquid. The LVIS model is divided into four typical time points and three transition stages, and its predictions agree with the experimental measurements. In contrast to traditional theories, the apparent contact angles in a quasi-equilibrium state should be separated into advancing and receding processes, and in this state, apparent contact angles vary with changes in the parameters of micro-pillar width and spacing. This strategy has the potential to accurately describe the wetting process on micro-structure surfaces.