Laser Powder Bed Fusion (LPBF) is an additive manufacturing process that builds parts by layer-by-layer spreading and selective laser melting of metal powders. The characteristics of the powder bed are closely related to laser parameters and the particle size distribution of the metal powder. However, the actual stacking height of the powder bed changes dynamically due to shrinkage during powder spreading, melting, and solidification. This study investigates the actual stacking height of metal powders by analyzing powder flow behavior during falling, spreading, melting, and solidification using the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). The results show that height shrinkage caused by powder spreading can be eliminated by increasing the gap between the blade and the working platform from 0μm to 20μm. The shrinkage rates due to solidification and liquid metal flow were found to be 8.5% and 31.5%, respectively. Furthermore, mathematical models relating the actual stacking height to layer thickness, number of layers, and solidification shrinkage were established, providing a theoretical foundation for LPBF processes with larger layer thicknesses, as well as for support structure design, printing accuracy, and allowance planning.

Abstract This study presents a surrogate-model-assisted Quasi-Newton optimisation framework for simultaneously improving the aerodynamic performance and radar stealth characteristics of an unmanned aerial vehicle (UAV). High-fidelity computational fluid dynamics (CFD) and computational electromagnetics (CEM) simulations are integrated through surrogate models generated via a face-centred central composite design within a design of experiments framework. Quadratic polynomial response surface equations are constructed for key aerodynamic and radar cross-section (RCS) metrics, enabling analytical gradient evaluation. A gradient-based quasi-Newton method with Broyden–Fletcher–Goldfarb–Shanno Hessian updates is employed to minimise a scalarised objective function combining normalised maximum lift coefficient, overall RCS and frontal RCS. Constraints are imposed on the lift-to-drag ratio ( $L/D \geq 10$ ) and static longitudinal stability ( ${C_{m0}} \geq 0$ ). Analytical derivatives from the response surface equations (RSEs) eliminate the need for direct numerical differentiation of CFD/CEM outputs, reducing computational cost and eliminating simulation noise. An interior-point sequential quadratic programming strategy is used to ensure satisfaction of nonlinear constraints during the optimisation process. The optimised UAV design demonstrates a $12{\rm{\% }}$ increase in maximum lift coefficient and a $30{\rm{\% }}$ reduction in both overall and frontal RCS compared to the baseline configuration. The results are confirmed through high-fidelity CFD and RCS simulations and are further validated experimentally in an anechoic chamber, with close agreement across all measured frequencies. The proposed methodology provides an efficient and experimentally verified approach for integrated aerodynamic and stealth optimisation in UAV design.

Abstract Transitional Reynolds-averaged Navier–Stokes (RANS) models have become relevant in the computational fluid dynamics (CFD) community as a practical approach to predict the transition to turbulence over the surface of aerospace configurations. These models capture the transition caused by the amplification of Tollmien-Schlichting waves, the bypass transition, and the stationary crossflow vortices. A fundamental aspect of transitional RANS models that still deserve continued attention is their numerical behavior. The source terms that are part of their formulation are commonly based on highly nonlinear functions, rendering more challenges in their convergence when compared to the underlying fully turbulent RANS models. The present work investigates the effects of smoothing these highly nonlinear, discontinuous functions that are embedded in the source terms of the Langtry-Menter transition model and its companion turbulence closure. There is particular interests in identifying improvements in the lift and drag coefficient convergence behavior. We consider the flat plate, the NACA 0012 and NLF(1)-0416 airfoils, and the 6:1 prolate spheroid configuration as test cases for transition caused by the amplification of Tollmien-Schlichting (TS) waves. We also consider flow conditions for which transition over the inclined 6:1 prolate spheroid is triggered by the amplification of stationary crossflow vortices. Our results show that the smooth functions lead to a faster convergence of the aerodynamic coefficients, which represents a reduced computational cost when compared to the original model.

The fire performance of existing reinforced concrete (RC) bridge decks strengthened by external prestressing systems is investigated, with particular attention to the vulnerability of externally applied tendons under realistic fire scenarios. Fire exposure represents a critical condition for such retrofitted structures, as the structural response is strongly influenced by load level, prestressing effectiveness, and thermal degradation of the strengthening system. A comprehensive assessment framework is proposed, combining thermal and mechanical analyses applied to representative highway overpass bridges. The thermal input adopted for the analyses is first validated through computational fluid dynamics (CFD) simulations, aimed at evaluating temperature development in typical RC beam–girder grillage decks subjected to fire from below. The CFD study considers variations in clearance height and span length and confirms that, in the case of hydrocarbon tanker accidents with fuel spilled on the roadway, conventional fire curves commonly adopted in the literature provide a reliable and conservative representation of both the temperature levels reached and their rate of increase within structural elements, thus supporting their use for rapid and simplified assessments. The validated thermal input is then employed in an analytical fire safety procedure applied to several realistic bridge case-studies. A parametric investigation is carried out by varying deck geometry, span length, reinforcement layout, and the presence of external prestressing retrofit, allowing the evaluation of the reduction in bending capacity and the time-dependent degradation of mechanical properties under fire exposure. The results highlight the critical role of external prestressing in fire scenarios, showing that significant loss of prestressing effectiveness may occur within the first minutes of fire, potentially leading to critical conditions even at service load levels. Finally, a multi-hazard assessment is performed by combining fire effects with pre-existing aging-related deterioration, such as reinforcement corrosion and long-term prestressing losses, demonstrating a marked increase in failure risk and, in the most severe cases, the possibility of premature collapse under dead loads.

Intracoronary (IC) imaging-guided percutaneous coronary intervention (PCI) improves clinical outcomes in patients with high clinical and anatomical risk when compared to interventions guided by angiography alone. Recent Class I recommendations for the use of IC imaging guidance when performing PCI in left main stem or complex lesions may result in a significant uptake as the technology is embraced as standard of care. Routine application of IC imaging will provide interventional cardiologists with a wealth of high-fidelity intracoronary data on plaque composition and distribution. When paired with emerging data regarding the importance of plaque anatomical characteristics, developments in artificial intelligence and computational fluid dynamics, lesion stratification with IC imaging may herald the next paradigm shift in this field. In this review, we will explore this important emerging application of IC imaging to inform morphology-guided PCI, identify high-risk lesions for targeted therapies, and consider the prospects of harnessing automated image interpretation with artificial intelligence technologies to achieve an integrated physiological and morphological assessment. Lesion stratification with IC imaging has the potential to shape the future of interventional cardiology practice to guide therapies within and beyond the confines of the cardiac catheterisation laboratory.

Abstract Marine ecosystem restoration increasingly relies on artificial reefs (ARs) as critical tools for enhancing biodiversity and sustaining fishery resources. While ARs generate ecologically beneficial hydrodynamic features through upwelling and wake regions, the resulting near-seabed flow patterns can induce sediment scouring that compromises structural integrity and ecological functionality. Here, a systematic investigation of triangular ARs is presented. The hydrodynamic and ecological performance of these ARs (characterized by upwelling, wake region, and sediment scouring) is governed by three interdependent structural parameters: base angle (a), height (h), and length (l). Through three-dimensional computational fluid dynamics (CFD) simulations performed using OpenFOAM, combined with analysis of existing experimental scour data, we quantify the relationships between these structural parameters and three critical performance indices: upwelling index (Iu), wake index (Iw), and scour index (Is). Analysis using Generalized Linear Model (GLM) reveals that a exerts dominant control over both the Iu and Is, while h demonstrates limited influence on these indices. By developing a comprehensive performance index and employing Kriging interpolation with Bayesian optimization, we identify an optimal triangular AR configuration (α = 30.3°, h = 9.7 cm, l = 33.4 cm) that maximizes ecological benefits while minimizing scour effects. Our findings establish a quantitative framework for AR design optimization, advancing the development of sustainable marine infrastructure.

The growing depletion of fossil fuel resources and rising energy costs underscore the need for efficient renewable energy technologies, such as unglazed transpired solar collectors (UTSCs). UTSCs harness solar energy to preheat outdoor air, thereby improving building energy efficiency and reducing reliance on conventional heating systems. This study presents a computational fluid dynamics (CFD) analysis of UTSC performance under Lithuanian winter conditions (ambient air temperature −2.64 °C, solar irradiance 733.45 W/m2, wind speed 1.93 m/s) using two- and three-dimensional models developed in ANSYS FLUENT. The 3D model simulates a realistic wall fragment with multiple repeating sheet metal profiles and an air gap, while the 2D model represents a longitudinal section applicable to generic UTSC configurations. Both models were validated against experimental data and used to evaluate airflow velocity, pressure distribution, and air temperature rise. The results indicate overall thermal efficiencies of 54.32% for the 3D model and 54.07% for the 2D model, demonstrating that simplified 2D models can achieve comparable accuracy while significantly reducing computational cost. These findings highlight the potential of high-resolution CFD modelling for optimizing UTSC design and enabling faster, more reliable assessments for integration in industrial and commercial building applications.

Urban underpasses are critical flood-prone hotspots during extreme rainfall, posing significant threats to urban resilience and infrastructure safety. However, a scale gap persists between catchment-scale hydrological models, which often oversimplify local geometry, and high-fidelity hydrodynamic models, which typically lack realistic boundary conditions. To bridge this gap, this study develops a multi-scale framework that integrates the Storm Water Management Model (SWMM) with 3D Computational Fluid Dynamics (CFD). The framework employs a unidirectional integration (one-way forcing), utilizing SWMM-simulated runoff hydrographs as dynamic inlet boundaries for a detailed CFD model of a 2.8 km underpass in Shanghai. Simulations across six design rainfall events (2- to 50-year return periods) revealed two distinct flooding mechanisms: a systemic response at the hydraulic low point, governed by cumulative inflow; and a localized response at entrance concavities, where water depth is rapidly capped by micro-topography. Informed by these mechanisms, an intensity-graded drainage strategy was developed. Simulation results show significant differences between different drainage strategies. Through this framework and optimized drainage system design, significant water accumulation within the underpass can be prevented, enhancing its flood resistance and reducing the severity of disasters. This integrated framework provides a robust tool for enhancing the flood resilience of urban underpasses and offers a basis for the design of proactive disaster mitigation systems.

The transition toward sustainable energy systems necessitates innovative solutions that reduce greenhouse gas emissions while improving fuel efficiency in existing combustion technologies. Hydrogen has emerged as a promising clean energy carrier; however, its widespread deployment is limited by challenges associated with large-scale transportation and storage. This study investigates a practical alternative in which hydrogen-rich syngas produced via steam methane reforming (SMR) is directly integrated into the diesel engine intake, thereby eliminating the need for fuel transport, storage, and separation while supporting a more sustainable fuel pathway. A validated computational fluid dynamics (CFD) model was developed to examine the effects of varying SMR gas mixture ratios (0–20%) on engine combustion, performance, and emissions. The findings reveal that increasing the SMR fraction enhances in-cylinder pressure by up to 15.7%, heat release rate by 100%, and engine power output by 102.5% compared to conventional diesel operation. Additionally, under SMR20 conditions, CO2 emissions are reduced by approximately 12%, demonstrating the potential contribution of this approach to decarbonization and climate mitigation efforts. However, the rise in in-cylinder temperatures was found to increase NOx formation, indicating the necessity for complementary emission control strategies. Overall, the results suggest that direct SMR syngas integration offers a promising pathway to improve the environmental and performance characteristics of conventional diesel engines while supporting cleaner energy transitions.

Helical static-mixer insert for pediatric and neonatal gas blending: RANS-CFD comparison of commercial and in-house monolithic designs.

Achieving adequate thermal comfort in classrooms in hot cities in southern Mexico is challenging. A heterogeneous distribution of air conditioning flow leads to thermal discomfort, affecting occupants’ academic performance and increasing energy consumption. This study evaluates the thermal comfort of occupants in an air conditioned classroom using computational fluid dynamics. We determined the effects of variations in air conditioning operating parameters (supply angle, velocity, and temperature) on PMV and modified PMV indices. An operating configuration of 60°, 3 m/s, and 22 °C ensures that thermal comfort remains within regulations while optimizing energy consumption, in contrast to the original PMV model. Using the modified PMV model, the values are 0.38 for students and 0.31 for the teacher, with percentages of dissatisfied individuals of 10% and 7.7%, respectively. This study demonstrates the importance of analyzing air conditioning operating parameters to enhance thermal comfort while reducing energy consumption.

Advanced technologies in both aseptic filling and environmental monitoring are coming together to improve the resilience and sterility assurance of aseptic processing. Continuous, real-time environmental monitoring using biofluorescent particle counters (BFPCs) to detect viable and nonviable particles during the aseptic filling process for injectable drugs is gaining traction as an accepted alternative to conventional methods such as active air sampling instruments. Evolving regulatory guidance, including EU Annex 1 guidelines, are increasingly recommending the adoption of isolator technology as well as continuous environmental monitoring during GMP processes, including technologies that offer real-time feedback during drug product manufacturing. Computational flow dynamics and airflow visualization studies are additional tools that support the design of equipment and determination of locations for environmental monitoring. The current nutrient culture media growth-based environmental monitoring, rooted in science from 150 years ago, is unable to keep pace with recent technological advances and the ability to immediately react to an out-of-control state. Here we examine the design of an isolator that eliminates human intervention and indirect product contact parts during aseptic fill finish operations and present computational fluid dynamics (CFD) studies verified by airflow visualization, along with the incorporation of BFPCs at critical areas. Also, we report the results of the interference study characterizing the baseline results for detection of total particles (nonviable plus viable) using a BFPC within a robotic gloveless isolator during dynamic and static operating conditions. The results of our study using BFPCs demonstrate that airflow in the robotic gloveless isolator provides protection of critical areas from contamination during the tub peeling process and that the stoppering process in this environment does not generate detectable particles. During dynamic conditions and material transfer, the study demonstrates the design of the robotic gloveless isolator prevents false positives from interfering with materials during normal operations.

Due to the demand of unmanned helicopters for drag reduction and rain-proof, the helicopter nacelle must be sealed. It will lead to a decrease in the heat transfer efficiency of the radiator, and the output power of the engine will drop dramatically. The helicopter's flight safety will be seriously jeopardized, especially when the helicopter is hovering (maximum engine power is needed). Currently, active cooling by equipping the radiator with a fan is the only solution, and the heat transfer efficiency of the radiator could be controlled by fan. Therefore, the performance of the fan directly affects the flight safety of the whole system. In this study, the Airfoils 30, suitable for low Reynolds number flows, is adopted to design the fan blade considering the characteristics of helicopter heat sink miniaturization and high integration. Then, a three-dimensional CFD (computational fluid dynamics) k-omega SST model is developed to investigate the effects of fan blade torsion angle, chord length, mounting angle and the number of blades on the performance of the fan. Furthermore, the constraints of radiator dimension, air flow resistance on the performance of the fan are considered comprehensively to finalize the new fan configuration. The optimised parameters of fan suitable for high flow rate (above 1.17kg/s) are chord length is55mm, torsion angle is 26°, mounting angle is 39° and the blade number is 7. The fan efficiency increases about 13.6%. The power consumption decreases about 9.5% (about 73 W). The fan rotational speed decreases 10.5%. The improvement of fan efficiency is a key measure for energy conservation and carbon reduction in unmanned helicopter systems. The 73 W power consumption of the fan decrease indicates that 1.2kg green-house gas emission reduces per day. The lower power consumption will result in a 0.14% cruising endurance increase. The fan is then manufactured by additive manufacturing based on CFD optimization results. This deep integration between CFD and additive manufacturing reduces trial and error costs and energy consumption. It also shows the promising future of UAV components autonomous manufacturing. Finally, the experiment is conducted in lab under 40℃. The experimental results indicate that the maximum output power of the engine is over than 90kW. Based on the helicopter main rotor performance curve, the helicopter could hover indefinitely with 500kg loading under 40°C. It is a criterion to identify the designing success.

Conversion of carbon dioxide (CO2) to methanol in a traditional reactor (TR) with catalytic packed bed faces the challenge of lower reactant conversion due to thermodynamic limitations. On the contrary, membrane reactors selectively remove reaction products, enhancing the conversion, but it is still limited, and existing designs face challenges of structural integrity and scale-up complications. Therefore, for the first time, a ceramic membrane microchannel reactor (CMMR) system was developed with 500 µm deep microchannels, incorporated with catalytic membrane for CO2 conversion to methanol. Computational fluid dynamic (CFD) simulations confirmed the uniform flow distribution among the microchannels. A catalytic LTA zeolite membrane was synthesized with thin layer (~45 µm) of Cu-ZnO-Al2O3 catalyst coating and tested at a temperature of 220 °C and 3.0 MPa pressure. The results showed a significantly higher CO2 conversion of 82%, which is approximately 10 times higher than TR and 3 times higher than equilibrium conversion while 1.5 times higher than conventional tubular membrane reactor. Additionally, methanol selectivity and yield were achieved as 51.6% and 42.3%, respectively. The research outputs showed potential of replacing the current industrial process of methanol synthesis, addressing the Sustainable Development Goals of SDG-7, 9, and 13 for clean energy, industry innovation, and climate action, respectively.

This article analyzes the applications of computational fluid dynamics (CFD) in addressing the issue of flow patterns in a realistic urban landscape, specifically in the Metropolitan Area of Monterrey. CFD enables the simulation of physical phenomena such as turbulence, which is useful for studying the transport behavior of pollutants in urban environments. The computational model was obtained from satellite imaging and covered a surface of about 1.134 km × 1.227 km. It was composed of 173 urban blocks, representing around 3570 houses, including hospitals, schools, recreation centers and other gathering places. The population of the urban landscape was estimated at around 11,400 inhabitants. Three velocity scenarios, low, average, and high (air gusts), were simulated, using data from a local weather station. The Reynolds numbers (Re) ranged from 1.9 × 106 to 21.2 × 106, falling within the fully developed turbulence regime, which was modeled using the renormalization group (RNG) k–ε turbulence model. Results showed that the mean velocity patterns were preserved independent of the Reynolds number (Re) and were characterized by regions of high velocity in the main avenues, as well as other regions of low velocity between urban blocks. This methodology may also be applicable for understanding the flow patterns of similar urban regions composed of irregularly arranged low-rise blocks.

Inspired by the movements of sea turtle forelimbs, this study presents a bio-inspired underwater flapping wing with three degrees of freedom. This flapping wing mechanism can more accurately simulate the rotational motion of a sea turtle’s forelimbs to generate greater propulsive force. The highlight is the gear transmission mechanism arranged along the wingspan, enabling a preset increasing twist angle along the wingspan. Computational fluid dynamics simulations are conducted to evaluate the hydrodynamic performance of the proposed flapping wing system. The effects of different spanwise twist angles along the wingspan on thrust generation are quantitatively analyzed, as well as the influence of key kinematic parameters, including the longitudinal flapping angle, spanwise increasing twist angle, and elevation angle. The results indicate that, compared with a uniform twist angle, the spanwise increasing twist significantly increases the peak thrust during specific phases of the flapping cycle. It is further revealed by flow field analyses that the formation of vortices near the trailing edge enhances the propulsive force in the streamwise direction. To further validate the proposed concept, a prototype of the mechanism is fabricated and experimentally tested under low-frequency actuation, confirming the feasibility of the mechanical design. Overall, these results demonstrate the potential of the proposed approach for bio-inspired underwater propulsion and provide useful guidance for future flapping wing mechanisms and kinematic design.

In this paper, we propose a complete formulation of the Lattice Boltzmann Method adapted for quantum computing. The classical collision, based on linear equilibrium distribution functions and streaming steps, are reformulated as linear algebraic operations. The inherently non-unitary collision operator is decomposed using Singular Value Decomposition and the Linear Combination of Unitaries technique. Bounce-back boundary conditions are incorporated directly into the collision matrix, while the streaming step is realized through conditional unitary shift operations on spatial registers, controlled by lattice velocity indices encoded in the distribution function register. This formulation ensures that the streaming step remains purely unitary. The resulting quantum circuit is implemented using Qiskit and validated against Couette flow and Poiseuille flow benchmarks. The simulation accurately reproduces the expected velocity profile, with relative errors below 1 0 − 4 . This work establishes a foundational framework for quantum fluid solvers and provides a pathway toward quantum computational fluid dynamics.

The Π-shaped composite girder is widely used in the construction of long span cable-stayed bridges, but its poor vortex-induced vibration (VIV) performance seriously affects its application prospects. The VIV performance and aerodynamic optimization measures of a Π-shaped composite girder are studied by using wind tunnel tests. The tests show that the VIV of the original Π-shaped section occurs at each wind attack angle, and the amplitude can be reduced by setting guide vanes and the lower central stabilizer at the bottom of the I-beam. The change of the inclination angle of guide vanes has a significant impact on the VIV suppression performance of the combined aerodynamic measures. The configuration with a 30° guide vane inclination angle exhibited optimal performance for VIV suppression, achieving the greatest reduction in amplitude. The VIV suppression mechanisms of the combined aerodynamic measure are studied by using computational fluid dynamics (CFD) numerical simulation. The calculation results show that the windward-side guide vane in the 30° inclination guide vane combination measure can significantly improve the flowing condition around the upstream section and cooperate with the lower central stabilizer to weaken the Kármán vortex of the Π-shaped section wake, thereby suppressing the girder’s VIV. Changing the inclination angle of the guide vane not only affects the generation of vortices near the guide vane itself but also affects the improvement of the lower central stabilizer on the vortex shedding state on the lower side of the section, thereby significantly improving the VIV suppression performance of the combined aerodynamic measure.

This study presents an eccentric pipe separator (EPS) designed according to the shallow pool principle and Stokes’ law as a compact alternative to conventional gravitational tank separators for offshore platforms. To investigate the internal oil-water flow characteristics and separation performance of the EPS, both field experiments with crude oil on an offshore platform and computational fluid dynamics (CFD) simulations were conducted, guided by dimensional analysis. Crude oil volume fractions were measured using a Coriolis mass flow meter and the fluorescence method. The CFD analysis employed an Eulerian multiphase model coupled with the renormalization group (RNG) k-ε turbulence model, validated against experimental data. Under the operating conditions examined, the separated water contained less than 50 mg/L of oil, while the separated crude oil achieved a purity of 98%, corresponding to a separation efficiency of 97%. The split ratios between the oil and upper outlets were found to strongly influence the phase distribution, velocity field, and pressure distribution within the EPS. Higher split ratios caused crude oil to accumulate in the upper core region and annulus. Maximum separation efficiency occurred when the combined split ratio of the upper and oil outlets matched the inlet oil volume fraction. Excessively high split ratios led to excessive water entrainment in the separated oil, whereas excessively low ratios resulted in excessive oil entrainment in the separated water. Crude oil density and inlet velocity exhibited an inverse relationship with separation efficiency; as these parameters increased, reduced droplet settling diminished optimal efficiency. In contrast, crude oil viscosity showed a positive correlation with the pressure drop between the inlet and oil outlet. Overall, the EPS demonstrates a viable, space-efficient alternative for oil-water separation in offshore oil production.

Abstract This research investigates the aerodynamic flow behavior and noise contribution of various cavity configurations designed to reduce aerodynamic noise in a simplified DSA 350 SEK pantograph model, scaled to 1/10. The cavities are classified into dual-shape and single-shape designs, with four distinct models (concave–convex, convex–concave, convex, and concave) analyzed in three sizes. A base cavity with a sloped edge at θ = 80° serves as a reference for comparison. Computational fluid dynamics (CFD) simulations are performed to evaluate flow characteristics, followed by the Ffowcs Williams and Hawkings (FW–H) aeroacoustic analogy is applied to estimate far-field sound pressure levels (SPLs). The results demonstrate that the convex-edged cavity improves aerodynamic performance by reducing the root-mean-square (RMS) drag and lift coefficients from 0.026 to 0.023 and from −0.06 to −0.038, respectively, and lowering the mean drag and lift coefficients from 0.23 to 0.18 and from −1.3 to −0.85, relative to the base cavity, thereby mitigating both steady and unsteady aerodynamic forces. Noise predictions, obtained from receivers positioned 2.5 m away in the scaled model at a train speed of 300 km/h, show reductions in noise levels from 81.9 to 77.3 dB at the top receiver and from 68.4 to 63.1 dB at the side receiver. Incorporating the pantograph into the optimal and base cavity designs reveals further aerodynamic improvements, with the optimal cavity reducing the pantograph’s aerodynamic noise by 2.7 dB(A) in total sound power. Sound pressure levels decrease by 2.3 dB(A) at the top receiver and 1.8 dB(A) at the side receiver compared to the base cavity.