Search Results (1,000)

Ice accretion (icing) on aircraft surfaces is a significant safety risk through airfoil shape modification and reduction in aerodynamic efficiency. This process occurs when an aircraft flies through clouds of supercooled water droplets that freeze upon impact on exposed surfaces. To counter this hazard, electro-thermal de-icing systems integrate heaters in critical regions to melt ice and reduce performance losses. In this study, a multiphysics computational model is used to simulate ice accretion and electro-thermal de-icing on a NACA-0012 airfoil, accounting for factors such as airflow, droplet impingement, phase changes, and heat conduction. The model’s predictions are validated against experimental data, confirming its accuracy. A cyclic electro-thermal ice protection system (ETIPS) is then tested under both standard and severe supercooled large droplet (SLD) conditions, examining how droplet size and angle of attack affect de-icing performance. Simulations without an active de-icing system show severe aerodynamic degradation, including an 11.1% loss of lift and a 48.2% increase in drag at a ${12}^{\circ }$ angle of attack. For large droplets (median 200 $\mathsf{\mu }$m), the drag coefficient increases by 36.5%. Under harsh icing conditions, the effectiveness of the de-icing system is found to depend on droplet size, angle of attack, and heater placement. Even with continuous heater operation, ice continues to accumulate on the leading edge at higher angles of attack. While the ETIPS performs effectively against large droplets in heated zones, unheated regions experience significant ice buildup (especially with 200 $\mathsf{\mu }$m droplets). This indicates that additional or extended heaters may be necessary to ensure complete protection in extreme conditions. Full article

This study evaluates the tribological properties of poly-DL-lactic acid (PDLLA) nanosheets attached to shark-skin surfaces with varying textures. The main goal was to assess friction reduction in samples with different surface textures and investigate the influence of PDLLA nanosheets on tribological behaviors. Biomimetic shark skin was created using a polydimethylsiloxane (PDMS)-embedded stamping method (PEES) that replicates shark skin’s unique texture, which reduces friction and drag in aquatic environments. PDLLA nanosheets, with a controlled thickness of several tens of nanometers, were fabricated and attached to the PDMS surfaces. The morphological characteristics of the materials were analyzed before and after attaching the PDLLA nanosheets using scanning electron microscopy (SEM), revealing the uniformity and adherence of the nanosheets to the PDMS surfaces. Friction tests were conducted using force transducers to measure the friction coefficients of biomimetic shark skin, biological models, and flat PDMS and silicon substrates, allowing a comprehensive comparison of frictional properties. Additionally, sliding tests with human fingers were performed to assess friction coefficients between various fingerprint shapes and sample surfaces. This aspect of the study is critical for understanding how human skin interacts with biomimetic materials in real-world applications, such as wearable devices. These findings clarify the relationship between surface texture, nanosheets, and their tribological performance against human skin, thereby contributing to the development of materials with enhanced friction-reducing properties for applications such as surface coatings, substrates for wearable devices, and wound dressings. Full article

In response to growing demand for autonomous and energy-efficient offshore operations, unmanned sailboats have emerged as promising platforms for next-generation marine applications. As the primary control surface, the rudder plays a pivotal role in enabling precise maneuvering and maintaining course stability. This study proposes an asymmetric aft-twisted flap rudder integrating a symmetric streamlined main rudder with an asymmetric flap. The design aims to enhance lift generation at small deflection angles, thus improving the hydrodynamic performance and response characteristics of rudder systems. The flap size for the conventional symmetric rudder was first determined from computational fluid dynamics (CFD) simulation results. To further improve lift performance, a 45° curved transition section was introduced at the junction between the main rudder and the flap to enhance flow attachment and reduce viscous drag. Building on this configuration, the asymmetric twisted flap was incorporated into the improved rudder design. CFD results indicate that the lift coefficient increased by approximately 27%. Comparative CFD analyses with the conventional symmetric flap rudder and the streamlined rudder revealed distinct coupled flow characteristics under various combinations of rudder and flap angles. These findings offer valuable insights into the hydrodynamic optimization of control surfaces in autonomous marine systems. Full article

Long-span cable-supported bridges, such as cable-stayed and suspension bridges, are highly sensitive to wind-induced effects due to their flexibility, low damping, and relatively light weight. Aerodynamic analysis is therefore essential in their design and safety assessment. This study examines the aeroelastic stability of the Oued Dib cable-stayed bridge in Mila, Algeria, with emphasis on vortex shedding, galloping, torsional divergence, and classical flutter. A finite element modal analysis was carried out on a three-dimensional model to identify natural frequencies and mode shapes. A two-dimensional deck section was then analyzed using Computational Fluid Dynamics (CFD) under a steady wind flow of U = 20 m/s and varying angles of attack (AoA) from −10° to +10°. The simulations employed a RANS k-ω SST turbulence model with a wall function of Y+ = 30. The results provided detailed airflow patterns around the deck and enabled the evaluation of static aerodynamic coefficients—drag (C_D), lift (C_L), and moment (C_M)—as functions of AoA. Finally, the bridge’s aeroelastic performance was assessed against the four instabilities. The findings indicate that the Oued Dib Bridge remains stable under the design wind conditions, although fatigue due to vortex shedding requires further consideration. Full article

Inspired by the free-flight capabilities of the gannet in both aerial and underwater environments, a foldable-wing air–water cross-medium vehicle was designed. To enhance its propulsive performance and transition stability across these two media, aero-hydrodynamic performance analyses were conducted under three representative operating states: aerial flight, underwater navigation, and water entry. Numerical simulations were performed in ANSYS Fluent (Version 2022R2) to quantify lift, drag, lift-to-drag ratio (L/D), and tri-axial moment responses in both air and water. The transient multiphase flow characteristics during water entry were captured using the Volume of Fluid (VOF) method. The results indicate that: (1) in the aerial state, the lift coefficient increases almost linearly with the angle of attack, and the L/D ratio peaks within the range of 4–6°; (2) in the folded (underwater) configuration, the fuselage still generates effective lift, with a maximum L/D ratio of approximately 2.67 at a 10° angle of attack; (3) transient water entry exhibits a characteristic two-stage force history (“initial impact” followed by “steady release”), with the peak vertical load increasing significantly with water entry angle and velocity. The maximum vertical force reaches 353.42 N under the 60°, 5 m/s condition, while the recommended compromise scheme of 60°, 3 m/s effectively reduces peak load and improves attitude stability. This study establishes a closed-loop analysis framework from biomimetic design to aero-hydrodynamic modeling and water entry analysis, providing the physical basis and parameter support for subsequent cross-medium attitude control, path planning, and intelligent control system development. Full article

The low-altitude economy represents an important facet of emerging productive forces, and flying cars serve as key vehicles driving its development. This paper proposes an aerodynamic design for the aerial vehicle module of split-type flying cars, which meets the functional requirements for vertical takeoff, climb, and cruising, and provides a reference solution for urban air mobility. A multidisciplinary constraint-based approach was employed to define the design requirements of the aerial vehicle module, ensuring its capability to operate in various complex environments. Through theoretical analysis and Computer-Aided Design (CAD) methods, key geometric, aerodynamic, and stability parameters were developed and evaluated. After finalizing the design concept of the aerial vehicle module, aerodynamic analysis was conducted, and aerodynamic coefficients were assessed using Computational Fluid Dynamics (CFD) simulations across angles of attack ranging from −5° to 20°. The results indicated that the aerial vehicle module achieved a maximum lift-to-drag ratio of 13.40 at an angle of attack of 2°, and entered a stall condition at 13°. The aerodynamic design enhances the module’s stability under various operating conditions, thereby improving handling performance. Overall, the aerial vehicle module demonstrates favorable aerodynamic characteristics during low-altitude flight and low-speed cruising, satisfying the design requirements and constraints. Full article

Low Reynolds number flows are central to the performance of airfoils used in small unmanned aerial vehicles (UAVs), micro air vehicles (MAVs), and aerodynamic platforms operating in rarefied atmospheres. Consequently, a deep understanding of airfoil behavior and accurate prediction of aerodynamic performance are essential for the optimal design of such systems. The present study employs Computational Fluid Dynamics (CFD) simulations to analyze the aerodynamic performance of a cambered plate at a Reynolds number of 10,000. Two Reynolds-Averaged Navier–Stokes (RANS) turbulence models, $\gamma$–$R{e}_{\theta }$ and $k\text{-}{k}_L\text{-}\omega$, are utilized, along with the Unsteady Navier–Stokes (UNS) equations. The simulation results are compared against experimental data, with a focus on lift, drag, and pressure coefficients. The models studied perform moderately well at small angles of attack. The $\gamma$–$R{e}_{\theta }$ model yields the lowest lift and drag errors (below 0.17 and 0.04, respectively), while the other models show significantly higher discrepancies, particularly in lift prediction. The $\gamma$–$R{e}_{\theta }$ model demonstrates good overall accuracy, with notable deviation only in the prediction of the stall angle. In contrast, the $k\text{-}{k}_L\text{-}\omega$ model and the UNS equations capture the general flow trend up to stall but fail to provide reliable predictions beyond that point. These findings indicate that the $\gamma$–$R{e}_{\theta }$ model is the most suitable among those tested for low Reynolds number transitional flow simulations. Full article

Boundary layer ingestion (BLI) propulsion offers notable benefits for blended wing body (BWB) aircraft, and understanding the interrelated effects of BLI and propulsion–airframe integration (PAI) is critical for early-stage design decisions. This study numerically applies combined momentum- and energy-based analyses to a closely coupled but non-integrated BWB–turbofan configuration enabling a continuous transition from non-BLI to BLI conditions. By introducing an idealized capture streamtube–airframe interaction force, the drag of BLI layout is decomposed into additional and external components, enabling quantification of a lift-to-drag ratio improvement of 1.7–2.6, corresponding to a 7.14–8.27% gain in power saving coefficient (PSC). Additional drag reduction, the primary contributor to total drag savings, is analytically attributed to inlet total pressure loss. The resulting decrease in required thrust under BLI shows strong mathematical correlation with jet dissipation reduction, revealing an intrinsic link between drag reduction and power saving. PAI exerts a significant influence on the BLI benefits, including nacelle cowl drag penalties, significant variations in shock wave location and strength, and notable suppression of both boundary layer and wake dissipation for the portion of cowl immersed in the airframe wake. These findings inform the transition from podded to BLI engine layouts. Full article

To address the trade-off between acoustic stealth and hydrodynamic efficiency in underwater glider design, this study proposes a coupled multi-physics parametric design framework for acoustic matching structures. Using the “Dolphin” glider as a case, geometric effects on acoustic scattering were analyzed by comparing spherical, capsule, and ellipsoidal structures under acoustic incidence. The ellipsoid configuration showed a superior performance and was further optimized through parameterized Myring profiles with length-to-diameter ratios (1.8–1.875) and sharpness factors (n = 1–5). Integrated CFD-BEM simulations revealed that the optimal design (ratio 1.875, n = 2) reduces the scattering sound pressure level by 1.8 dB at 1 kHz and drag coefficient by 14.2%. At 3 m/s, bow-direction target strength decreased by 6 dB, with 4.4 dB flow noise reduction. This methodology effectively resolves acoustic–fluid conflicts, advancing low-noise underwater vehicle design. Full article

This study presents the design, numerical analysis, and experimental validation of an innovative wind turbine blade incorporating an internal flow channel and tangential slots to harness the Coanda effect for enhanced aerodynamic performance. The primary objective is to improve thrust generation and lift while reducing drag, thereby increasing the efficiency of wind turbines and potential aerial propulsion systems. A three-dimensional blade model was developed in COMPAS-3D and fabricated using PET-G filament through 3D printing, enabling precise realization of the internal geometry. Computational fluid dynamics (CFD) simulations, conducted in ANSYS Fluent using a refined mesh and the k—ω SST turbulence model, revealed that the proposed blade design significantly improves pressure distribution and airflow attachment along the blade surface. Compared to a conventional blade under identical wind conditions (12 m/s), the innovative blade achieved a 12% increase in power coefficient, lift force of 33 N and drag force of 60 N, validating the efficacy of the Coanda-based flow control. Wind tunnel experiments confirmed the numerical predictions, with close agreement in thrust and lift measurements. The blade demonstrated consistent performance across varying wind velocities, highlighting its applicability in renewable energy systems and passive flow control for aerial platforms. The findings establish a practical, scalable approach to aerodynamic optimization using structural enhancements, contributing to the development of next-generation wind energy technologies and efficient propulsion systems. Full article

The effect of local scour on the hydrodynamic force upon a submarine pipeline under unidirectional flow has been numerically investigated. The flow field around the pipeline is obtained using the Navier–Stokes equations with the SST k-ω turbulence model, and the sediment transport model, considering suspended load and bed load, is accounted for. Firstly, the influences of the Reynolds number (1 × 10⁴ ≤ Re ≤ 1 × 10⁵) and Shields number (1.2 ≤ θ/θ_cr ≤ 2.5) on the scour below the pipeline are analyzed; then, the effect of local scour on the hydrodynamic force upon the pipeline is examined by comparing with the condition that the pipeline is put on the flat seabed. It is found that the presence of local scour leads to a significant effect on the hydrodynamic force acting on the pipeline. Additionally, the Reynolds number affects the hydrodynamic force significantly, while the Shields number has a relatively low effect. The reduction coefficient (λ) is adopted to quantify the influence of the local scour around the pipeline on the hydrodynamic force. According to the reduction coefficient, the presence of local scour increases the drag coefficient by about 10% when the Reynolds number is 1 × 10⁴, while it decreases the drag coefficient significantly when the Reynolds number is larger than 2 × 10⁴, and the reduction coefficient trends towards a constant value with the increase in the Reynolds number. Full article

Flow past bluff bodies (e.g., circular cylinders) forms a canonical context for teaching external flow separation, vortex shedding, and the coupling between surface pressure and hydrodynamic forces in offshore engineering. Conventional laboratory implementations, however, often fragment local and global measurements, delay data feedback, and omit intelligent modeling components, thereby limiting the development of higher-order cognitive skills and data literacy. We present a low-cost, modular, data-enabled instructional hydrodynamics platform that integrates a transparent recirculating water channel, multi-point synchronous circumferential pressure measurements, global force acquisition, and an artificial neural network (ANN) surrogate. Using feature vectors composed of Reynolds number, angle of attack, and submergence depth, we train a lightweight AI model for rapid prediction of drag and lift coefficients, closing a loop of measurement, prediction, deviation diagnosis, and feature refinement. In the subcritical Reynolds regime, the measured circumferential pressure distribution for a circular cylinder and the drag and lift coefficients for a rectangular cylinder agree with empirical correlations and published benchmarks. The ANN surrogate attains a mean absolute percentage error of approximately 4% for both drag and lift coefficients, indicating stable, physically interpretable performance under limited feature inputs. This platform will facilitate students’ cross-domain transfer spanning flow physics mechanisms, signal processing, feature engineering, and model evaluation, thereby enhancing inquiry-driven and critical analytical competencies. Key contributions include the following: (i) a synchronized local pressure and global force dataset architecture; (ii) embedding a physics-interpretable lightweight ANN surrogate in a foundational hydrodynamics experiment; and (iii) an error-tracking, iteration-oriented instructional workflow. The platform provides a replicable pathway for transitioning offshore hydrodynamics laboratories toward an integrated intelligence-plus-data literacy paradigm and establishes a foundation for future extensions to higher Reynolds numbers, multiple body geometries, and physics-constrained neural networks. Full article

Subsea pipelines with intermittent spanwise arrangements are commonly encountered in offshore engineering, yet their complex hydrodynamic interactions remain insufficiently understood. In this study, three-dimensional numerical simulations were conducted to investigate the hydrodynamics of intermittently spanning cylinders at a Reynolds number of 40,250. The hydrodynamic coefficients and flow fields of cylinders with different gap ratios e/D, total spanning ratios L/H, and individual spanning ratios l/D were investigated (where e is the gap height, D is the diameter of the cylinder, L is the total spanning length, H is the length of the cylinder, and l is the individual spanning length). Moreover, this work validates the applicability of existing hydrodynamic prediction formulas for spanning cylinders under complex spanning conditions, as proposed by previous researchers. Numerical results show that the existing formulas can accurately predict the drag coefficient ${\overline{C}}_D$ of spanning cylinders under different uniform l/D ratios, but it fails to provide reliable predictions for the lift coefficient ${\overline{C}}_L$. These findings provide critical insights for optimizing the design of subsea pipelines and marine structures with intermittent spanwise arrangements. Full article

Savonius drag-based rotors, a type of vertical-axis wind turbine (VAWT), are well-suited for urban environments—particularly residential rooftops—owing to their compact design and ability to capture wind from all directions. However, their relatively low efficiency and narrow operational range pose significant challenges, such as limited energy output under variable wind conditions and reduced performance across a broad range of tip speed ratios. To address these issues, this study explores flow augmentation using strategically placed deflectors, referred to as Wind Accelerators and Guiding Rotor Houses (WAG-RHs). Four different configurations, including double, triple, oblique, and straight designs, were evaluated against both omni-directional guide vanes (ODGVs) and a conventional rotor. The findings show that the ODGV configuration successfully extends the operational range from a tip speed ratio of 0.5 to 0.6—termed the extended performance point (EPP)—and increases the power coefficient ($C_p$) by up to 300% compared to the conventional design. Among all setups, the straight WAG-RH configuration proved most effective, not only achieving the EPP but also delivering a 385% and 264.3% increase in local and AVE $C_p$ values, respectively compared to the conventional rotor. It also outperformed the ODGV-equipped rotor by 25%, thanks to its radial and dual-plane arrangement. Full article

The optimization of polymer extrusion processes is crucial for improving product quality and manufacturing efficiency in plastic industries. This study aims to investigate the viscoelastic flow behavior of high-density polyethylene (HDPE) through an extrusion die with an internal mandrel, focusing on the effects of die geometry and flow parameters. A two-dimensional (2D) numerical model is developed in COMSOL Multiphysics using the Oldroyd-B constitutive equation, solved using the Galerkin/least-square finite element method. The simulation results indicate that the Weissenberg number (Wi) and die geometry significantly influence the dimensionless drag coefficient (Cd) and viscoelastic stress distribution along the die wall. Furthermore, filleting sharp edges of the die wall surface effectively reduces stress oscillations, enhancing flow uniformity. These findings provide valuable insights for optimizing die design and improving polymer extrusion efficiency. Full article