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This study employs a two-dimensional and incompressible flow of Herschel–Bulkley visco-plastic materials in order to investigate the hydrodynamic forces that are acting on a barrier that is located close to the inlet of a channel. As the benchmark configuration, the flow domain that has been selected is a channel that still contains the impediment. The two important parameters of the Herschel–Bulkley Model (HBM) are the yield stress τ y and power law index n. Obtaining special situations within the HBM, such as Newtonian, power-law, and Bingham fluids, can be accomplished by assigning certain values to these parameters at the appropriate times. Utilizing a numerical strategy grounded in the Finite Element Method (FEM), we tackle the nonlinearity of the governing equations as well as the viscosity models. As a result of this nonlinearity, FEM becomes an essential tool. The generation of a refined hybrid mesh is done in order to guarantee accuracy in the computations. The stable finite element pair ( ℙ 2 ∕ ℙ 1 ) has been selected for discretization purposes. The discretized nonlinear system is linearized with Newton's method and subsequently, a direct linear solver PARDISO has been employed in the inner iterations. The pressure, velocity, and viscosity profiles are plotted for various values of n and Bingham number (Bn). In addition, the velocity behavior is observed along the y-direction in a channel through line graphs. Code validation is done as a special case Bn = 0 and a good agreement is found with the results available in the literature. Finally, a correlation analysis has been performed for the drag coefficient C d and lift coefficient C l . [ABSTRACT FROM AUTHOR]

This research seeks to explore the behavior of Ree–Eyring nanofluid over an extended surface influenced by an inclined magnetic field within a permeable medium. The local thermal non‐equilibrium between the particle, liquid, and solid phases is represented by a three‐temperature model. The problem is addressed numerically using bvp4c code in MATLAB software. The findings are displayed in the format of tables and graphs. The study shows that higher values of the interface heat transfer parameter led to a decrease and increase in the fluid phase and solid phase Nusselt number, respectively. The velocity and concentration distributions decrease with increasing porosity coefficient. Nevertheless, the fluid phase temperature distribution shows an opposing trend. Furthermore, increasing the non‐Newtonian fluid parameter leads to a raise in the surface drag coefficient. [ABSTRACT FROM AUTHOR]

In this paper, the unsteady aerodynamic characteristics of a three-car grouped high-speed train (HST) with different bogie fairing configurations under the crosswind are studied using improved delayed detached eddy simulation (IDDES) at Re = 1.85 × 106. The numerical method results are validated against the previous wind tunnel experiments. There are three cases with original half-fairing configuration (HFC), non-fairing configuration (NFC) and full-fairing configuration (FFC), respectively. The numerical results show that the bogie fairing configuration has significant effects. Compared to the HFC case, the drag force coefficients of the head, middle and tail cars with NFC increase by 53.13%, 14.87% and 27.04%, and corresponding parts of the FFC case decrease by 49.98%, 24.40% and 12.41%, respectively. The FFC case can also optimize the pressure distribution on the windward and leeward sides of the HST, and the flow structure and vertex distribution around the car body are also optimized. In addition, the increasing encirclement of the fairing configurations reduces the maximum lateral flow velocity inside the bogie cavities by 70% for HFC and 50% for FFC compared to the NFC. Overall, the FFC presents better aerodynamic performance than the NFC and HFC cases under crosswind, which is recommended for the design of the HST. [ABSTRACT FROM AUTHOR]

This study investigates the potential of an optimized combination of active nose droop and active Gurney flap (CADAG) in a new flow control strategy to manage dynamic stall over a pitching blade section under variable Mach number flow. The optimization method employs the genetic algorithm coupled with a computational fluid dynamic (CFD) solver and artificial neural network. The base blade section belongs to a section positioned at r/R=0.865 of the rotor blade of the UH-60A helicopter in forward flight condition. A high relative angle of attack on the retreating side makes the flow susceptible to dynamic stall. A nose droop is employed to control the dynamic stall of the blade section, and a Gurney flap is used to maintain the balance of the generated lift of the blade during 360° of rotation. A comprehensive investigation is performed to determine the most significant parameters affecting the performance of the present combined active flow control. The ratio of the total generated lift to the drag is chosen as the objective function of the optimization. Results show that this ratio and the total generated lift in one rotation cycle increase by 193% and 13%, respectively, at the optimum condition of the present combined active flow control, while the ratio of the generated lift over the advancing side to the retreating side is equal to that of the base blade section. In addition, the dynamic stall hysteresis loop reduces significantly, and the maximum value of the drag coefficient and the negative aerodynamic damping decrease up to 87% and 83% compared to the base blade section, respectively. In general, the proposed innovative combined active flow control is an adjustable method to alleviate dynamic stall and improve the aerodynamic performance of rotary wings in different operation conditions. Practical Applications: The rotary blades are extensively used in rotorcraft, turbo engines, and wind turbines. Despite their massive use, they suffer from some essential issues, of which the most important one is the so-called dynamic stall. Dynamic stall is a complex phenomenon that limits the performance of the rotary blades. Due to the physics governing a rotary wing, such as a helicopter rotor blade, dynamic stall and flow separation are very common. Understanding dynamic stall physics and providing solutions to prevent it is still one of the main challenges of aerodynamic scientists. The present study introduces a novel adjustable method for practically alleviating the dynamic stall on helicopter blade section in forward flight conditions to improve its aerodynamic performance in different operational conditions. A comprehensive investigation is carried out to determine the key parameters affecting the proposed method. These findings can serve as a valuable tool for other researchers to develop various active flow control strategies. This article applies an optimization process using artificial neural networks, genetic algorithms, and CFD tools, which forms a comprehensive framework that can be easily extended to other applications. [ABSTRACT FROM AUTHOR]

Pulse opposing plasma synthetic jets (OPSJs) have potential for reducing the drag coefficient of hypersonic airfoils. This paper numerically investigated the effects and flow control mechanisms of a continuous nanosecond pulse OPSJ on the aerodynamic performance of a hypersonic airfoil. The results indicate that a continuous-pulse OPSJ reduces the airfoil drag coefficient by generating diffracted waves to shift the leading-edge shock wave. However, the flow control effectiveness of a pulse OPSJ decreases with the increase of the pulse sequence. The time-averaged lift-to-drag ratio of the airfoil decreased rapidly from 1.11 for the first pulse sequence to 0.94 for the third pulse sequence, followed by a gradual decrease. The thermal accumulation within the cavity triggers a blocking effect, impeding the heat exchange between the cavity and external fluid. This is the primary factor leading to the decreasing flow control effectiveness of continuous-pulse OPSJs. Furthermore, the results suggest that enhancing the mixing effect within the cavity can improve heat transfer between the cavity and the external flow, suppress thermal accumulation, and improve the flow control capability of continuous-pulse OPSJs in hypersonic flows. [ABSTRACT FROM AUTHOR]

A hybrid nanofluid is an amalgamation of two or more types of nanoparticles in a customary and possesses a variety of industrial applications. This exploration examines the blend of copper (Cu) and gold (Au), and engine oil as a hybrid nanofluid. The model considers the Hall current, Cattaneo–Christov (C-C) heat flux, thermal stratification, nonuniform heat source, and nonlinear thermal radiative effects for heat analysis. Ordinary differential equations (ODEs) are obtained through a similarity transformation scheme, and the model is visualized using a MATLAB function bvp4c. Graphs are presented to demonstrate the impact of various parameters on velocities and temperatures, and the wall drag coefficient and wall heat transfer rate are calculated and tabulated for both disks. The results show that a stronger Hall effect leads to a decrease in tangential velocity, while nonuniform heat sources increase fluid temperature. Thermal radiation and stratification have opposite effects on liquid temperature. It is interesting to note that for the radiation parameter at Rd = 0.5 , a higher heat transfer rate occurred at the lower disk, i.e., (N u 1 = − 3.63314) as compared to the upper disk (N u 2 = − 3.63324). Moreover, for the stratification parameter at S = 0.2 , it is observed that the heat transfer rate is lesser at the upper disk (N u 2 = − 3.64374) than at the lower disk (N u 1 = − 3.64274). Verification of the truthfulness of the proposed model is also included in the article. [ABSTRACT FROM AUTHOR]

This article explores the trajectory of rockets and artificial satellites in the atmosphere, specifically focusing on the effects of drag forces. It discusses different types of orbits and highlights the lack of information on drag forces in high school textbooks. The article proposes a new calculation method to help students understand spiral motion caused by drag forces and also delves into the use of energy and power in analyzing these effects. The document further discusses the drag force experienced by objects in Earth's atmosphere, providing equations for different scenarios based on the Reynolds number. It also covers the motion of objects in circular paths and concludes with an equation describing the trajectory of objects experiencing drag force. The text emphasizes the study's focus on spherical objects passing through the stratosphere and troposphere, providing physical constants and presenting results of different mass values on the trajectory. The authors derived formulas for spiral trajectories based on energy loss caused by drag forces, and computational estimations showed that ideal spherical objects subjected to drag forces perform spiral motion. The study's findings can aid students and teachers in understanding the trajectory of objects experiencing drag forces. [Extracted from the article]

The article explores the issue of projectile motion with atmospheric drag, specifically focusing on vertical launch. The authors present an analytical solution for the projectile's position and maximum height over time, assuming a constant drag coefficient. They compare this solution with a numerical one that allows for a varying drag coefficient. The article emphasizes the importance of intermediate-level solutions in physics education and the need to consider drag forces in projectile motion problems. The authors also discuss the application of the analytical solution in studying volcanic eruptions and highlight its potential use in analyzing volcanic bomb trajectories. The research was supported by the European Research Council. [Extracted from the article]

Considerable parts of riparian forests around the world are covered by deciduous trees and tall shrub species with rigid trunk and flexible-broadleaf. Experiments are conducted on artificial rigid and flexible models to estimate drag coefficient and resistance to flow for deciduous trees in forest floodplains under nonsubmerged condition. The rigid and flexible models with similar size and configuration are tested in a laboratory flume to clearly determine the effects of vegetation flexibility and density, and the flow velocity and depth on the roughness coefficients. Ratios of the flexible to rigid drag forces and drag coefficients indicate considerable effects of flexibility on the roughness coefficients. In this study, the flexural rigidity of the tree leaf is used in the roughness equations to account for vegetation flexibility instead of the traditionally used tree trunk flexural rigidity. This is based on the assumption that foliage flexibility governs tree reaction to the flow for most species of deciduous trees and leafy tall shrub families. The developed roughness coefficient equations are scaled up to determine the variation of Manning's n -value with increase of flow depth for a riparian canopy of black willow. The estimated Manning's n -values are compared with the reported Manning n -values for the same black willow canopy. [ABSTRACT FROM AUTHOR]

The hydrodynamic coefficient of an underwater manipulator varies with changes in posture and flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6x10³ ≤ Re ≤ 3x104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = -90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25. [ABSTRACT FROM AUTHOR]

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Applying numerical simulation technology to investigate fluid-solid interaction involving complex curved boundaries is vital in aircraft design, ocean, and construction engineering. However, current methods such as Lattice Boltzmann (LBM) and the immersion boundary method based on solid ratio (IMB) have limitations in identifying custom curved boundaries. Meanwhile, IBM based on velocity correction (IBM-VC) suffers from inaccuracies and numerical instability. Therefore, this study introduces a high-accuracy curve boundary recognition method (IMB-CB), which identifies boundary nodes by moving the search box, and corrects the weighting function in LBM by calculating the solid ratio of the boundary nodes, achieving accurate recognition of custom curve boundaries. In addition, curve boundary image and dot methods are utilized to verify IMB-CB. The findings revealed that IMB-CB can accurately identify the boundary, showing an error of less than 1.8% with 500 lattices. Also, the flow in the custom curve boundary and aerodynamic characteristics of the NACA0012 airfoil are calculated and compared to IBM-VC. Results showed that IMB-CB yields lower lift and drag coefficient errors than IBM-VC, with a 1.45% drag coefficient error. In addition, the characteristic curve of IMB-CB is very stable, whereas that of IBM-VC is not. For the moving boundary problem, LBM-IMB-CB with discrete element method (DEM) is capable of accurately simulating the physical phenomena of multi-moving particle flow in complex curved pipelines. This research proposes a new curve boundary recognition method, which can significantly promote the stability and accuracy of fluid-solid interaction simulations and thus has huge applications in engineering. Graphic Abstract [ABSTRACT FROM AUTHOR]

The flow of carbon nanotubes (CNTs) via the Riga plate has a substantial influence, and it is used in the industrial sector, like fluid stirring, thermal reactors, semiconductors, tissue regeneration, gene delivery to organs, etc. However, the 3D Darcy–Forchheimer flow (DFF) of CNTs through the Riga plate with nonlinear thermal radiation and a non-uniform heat sink/source has not been investigated. As a consequence of this, the objective of this paper is to explore the impact of the nonlinear radiative DFF of water-based CNTs past a heated Riga plate with a non-uniform heat sink/source and homogeneous and heterogeneous reactions. In addition, the energy equation is constructed using the Cattaneo–Christov heat flux concept. By making use of appropriate variables, the governing flow models are mutated into a system of ordinary differential equations. These reduced equations are analytically and numerically computed by homotopy analysis method (HAM) and the bvp4c scheme. The brief discussion and visual depiction of the dominance of different factors on x- and y-direction velocities, thermal, nanoparticle concentration (NPC), surface drag coefficients, and local Nusselt number are presented in tables and figures. The growth of the Forchheimer number leads to a noticeable enrichment in the velocity profile in both directions. When the nanoparticle’s volume fraction and space-dependent heat source/sink parameters are increased, the thermal profile gets better. The NPC profile exhibits suppression as the intensity of both heterogeneous and homogeneous responses rises. [ABSTRACT FROM AUTHOR]

This study aims to numerically investigate the optimal conditions for fluid flow control around a single square cylinder with the help of a pair of attached flat plates. It is comparatively a new approach for controlling fluid flows as compared to the traditional solo plate flow control devices. The plates are attached adjacent to the both rear corners of the cylinder and their length (l) is varied from 0.1 to 4 times size of main cylinder while fixing the height (h) at 0.2. By varying the length, the plates manage to control the flow gradually. This study discusses how a steady wake can be achieved through control plates. Results indicate that the flow regime changes from unsteady to transitional at l=2.7 while for l>3.1 the steady flow appears. The streamlines visualizations reveal different flow structures termed as the oval-eye vortex, chain necklace vortex, sphere vortex, hair pin vortex and wooden eyes vortex-like structures. Among these the oval-eye vortex structure is found to have higher flow induced forces and shedding frequencies while the wooden eyes vortex structure is found to have minimal flow induced forces and shedding frequencies. After l=3.2, the plates’ efficacy is proven by a 100% reduction in Strouhal number, root-mean-square values of lift coefficient and amplitudes of lift and drag coefficients. This study reveals that l=3.2 is the best optimal value of plates length for complete wake and fluid forces control. [ABSTRACT FROM AUTHOR]

Small wind turbines operating in low wind speed regions have not had any significant success. In addition, small wind speed regions occupy a large area of the world, so they represent a potential area for installing small wind turbines in the future. In this paper, a method to design an efficient airfoil for small wind turbines in low wind speed conditions using XFLR5 and CFD simulations is implemented. Because the impact of the airflow on the blade surface under low Re number conditions can change suddenly for small geometries, designing the airfoil shape to optimize the aerodynamic performance is essential. The tuning of the key geometric parameters using inversion techniques for better aerodynamic performance is presented in this study. A two-dimensional model was used to consider the airflow on the airfoil surface with differences in the angle of attack. The original S1010 airfoil was used to design a new airfoil for increasing the aerodynamic efficiency by using V6.57 XFLR5 software. Subsequently, the new VAST-EPU-S1010 airfoil model was adjusted to the maximum thickness and the maximum thickness position. It was simulated in low wind speed conditions of 4–6 m/s by a computational fluid dynamics simulation. The lift coefficient, drag coefficient, and CL/CD coefficient ratio were evaluated under the effect of the angle of attack and the maximum thickness by using the k-ε model. The simulation results show that the VAST-EPU-S1010 airfoil achieved the greatest aerodynamic efficiency at an angle of attack of 3°, a maximum thickness of 8%, and a maximum thickness position of 20.32%. The maximum value of CL/CD of the new airfoil at 6 m/s was higher than at 4 m/s by about 6.25%. [ABSTRACT FROM AUTHOR]

The utilization of unmanned sailboats as a burgeoning instrument for ocean exploration and monitoring is steadily rising. In this study, a dual sail configuration is put forth to augment the sailboats' proficiency in its wind-catching ability and adapt to the harsh environment of the sea. This proposition is based on a thorough investigation of sail aerodynamics. The symmetric rigid wing sails NACA 0020 and NACA 0016 are selected for use as the mainsail and trailing wing sail, respectively, after considering the operational environment of unmanned sailboats. The wing sail structure is modeled using SolidWorks, and computational fluid dynamics (CFD) simulations are conducted using ANSYS Fluent 2022R1 software to evaluate the aerodynamic performance of the sails. Key aerodynamic parameters, including lift, drag, lift coefficient, drag coefficient, and thrust coefficient, are obtained under different angles of attack. Furthermore, the effects of mainsail aspect ratios, mainsail taper ratios, and the positional relationship between the mainsail and trailing sail on performance are analyzed to determine the optimal structure. The thrust provided by the sail to the boat is mainly generated by the decomposition of lift, and the lift coefficient is used to measure the efficiency of an object in generating lift in the air. The proposed sail structure demonstrates a 37.1% improvement in the peak lift coefficient compared to traditional flexible sails and exhibits strong propulsion capability, indicating its potential for widespread application in the marine field. [ABSTRACT FROM AUTHOR]

Technologies regarding solar heating, ventilation and air-conditioning (S-HVAC) are aimed at making modern 3D numerical forms that address the Sutterby flow ternary nanofluids circulating onward the convective heating and extendable seats. Heat transport includes joule heating, heat source or sink along with thermal radiation. Using fitting modifications, mathematically conveyed partial differential equations of energy, fixation and strength may decrease into ordinary differential equations (ODEs). They determine ODEs beyond dimension, and for this, the mathematical process is utilized. Copper–silver–aluminum alloys/sodium alginate (Cu–Ag–AA7075/C6H9NaO7) was used to address the behavior of this research work. The natural attributes, for example, heat movement and surface drag coefficients, are numerically prepared and shown in figures and tables when there is an alteration in distant factors. The field of temperature was raised to develop the Biot number. This heat transport rate was hiked to 34.0839% although the shear stress rate was hiked to 32.8043% in the single nanoparticle case compared to the triple nanoparticle case. To validate the analysis, a comparison between the presented and existing is reported under certain assumptions on the flow parameters. It is found that the results are reliable and in line with the existing ones. [ABSTRACT FROM AUTHOR]

The flow structure around limited-size vegetation patches is crucial for understanding sediment transport and vegetation succession trends. While the influence of vegetation density has been extensively explored, the impact of the relative diameter of vegetation stems remains relatively unclear. After validating the reliability of the numerical model with experimental data, this study conducted 2D-URANS simulations (SST k-ω) to investigate the impact of varying relative diameters d/D under different vegetation densities λ on the hydrodynamic characteristics and drag force of vegetation patches. The results show that increasing d/D and decreasing λ are equivalent, both contributing to increased spacing between cylinder elements, allowing for the formation of element-scale Kármán vortices. Compared to vegetation density λ, the non-dimensional frontal area aD is a better predictor for the presence of array-scale Kármán vortex streets. Within the parameter range covered in this study, array-scale Kármán vortex streets appear when aD ≥ 1.4, which will significantly alter sediment transport patterns. For the same vegetation density, increasing the relative diameter d/D leads to a decrease in the array drag coefficient C ¯ D and an increase in the average element drag coefficient C ¯ d . When parameterizing vegetation resistance using aD, all data points collapse onto a single curve, following the relationships C ¯ D = 0.34 ln a D + 0.78 and C ¯ d = − 0.42 ln a D + 0.82 . [ABSTRACT FROM AUTHOR]

This study presents a computational analysis of fluid flow characteristics around two staggered arranged square cylinders using the Lattice Boltzmann Method (LBM). With Reynolds number (Re) fixed at 200, numerical simulations explore the influence of varying gap ratios (G) ranging from 0 to 10 times the cylinder size. Emphasis is placed on understanding the impact of cylinders spacing on flow structure mechanisms and induced forces. Investigation of fluid flow parameters includes vorticity behavior, pressure streamlines, and variations in drag and lift coefficients alongside the Strouhal number under different values of G. From the results, four distinct flow patterns emerge: single bluff body flow, flip flopping flow, modulated synchronized flow, and synchronized flow, each exhibiting unique characteristics. This study reveals the strong dependence of fluid forces on G, with low spacing values leading to complex vortex structures and fluctuating forces influenced by jet flow effects. At higher spacing values, proximity effects between cylinders diminish, resulting in a smoother periodic flow. The Strouhal number, average drag force and the rms values of drag and lift force coefficients vary abruptly at narrow gaps and become smooth at higher gap ratios. Unlike the tandem and side-by-side arrangements the staggered cylinders arrangement is found to have significant impact on the pressure variations around both cylinders. Overall, this research could contribute to a comprehensive understanding of staggered cylinder arrangements and their implications for engineering applications. [ABSTRACT FROM AUTHOR]

Sail-assisted propulsion is an important energy-saving technology in the shipping industry, and the development of foldable wingsails has recently become a hot topic. This type of sail is usually composed of multiple elements, and its performance at different folding configurations is very sensitive to changes in incoming airflow, which result in practical operational challenges. Therefore, original and optimized three-element wingsails (bare and concave) are modeled and simulated using the unsteady RANS method with the k-ω SST turbulence model. Next, certain key design and structural parameters (such as angle of attack, apparent wind angle, and camber) are employed to characterize the auxiliary propulsion performance, and the differences are explained in combination with the flow field details. The results show that, in the unfolded state, the aerodynamic performance of the concave wingsail is better than that of the bare wingsail, exhibiting higher lift coefficients, lower drag coefficients, and a more stable surface flow. In the fully folded state, wherein both the nose and flap are rotated, the thrust performance of the concave wingsail remains superior. Specifically, at an angle of attack of 8 degrees, the thrust coefficient of the concave wingsail is approximately 23.5% higher than that of the bare wingsail, indicating improved wind energy utilization. The research results are of great significance for engineering applications and subsequent optimization design. [ABSTRACT FROM AUTHOR]

Coach car is a commonly used mode of transportation, due to its large passenger capacity, in case of accidents, it will cause enormous human casualties and economic losses. To improve the braking performance of coach car, an aerodynamic plate is installed on the top of coach car to assist braking. Based on RANS (Reynolds average Navier-Stokes) equations and SST (Shear-Stress Transport) k-ω turbulence model, the aerodynamic performance of coach car with different aerodynamic parameters is analyzed by computational fluid dynamics method. The numerical algorithm and setting are verified by wind tunnel tests. In this paper, the influence of four parameters, including car speed, plate configuration of maximum opening angle, installation position, and plate height, on the aerodynamic drag and lift coefficient of coach car is discussed by using control variable method and orthogonal test method. The conclusions of the two methods are consistent, that is, the optimal combination of plate configuration is that installation position, maximum opening angle, and height are 10 m, 80°, and 1 m, respectively. According to the results of range and variance analysis, the order of influence of aerodynamic parameters on the aerodynamic drag and lift coefficient is installation position, maximum opening angle, height, and car speed. [ABSTRACT FROM AUTHOR]

The automotive industry continuously enhances vehicle design to meet the growing demand for more efficient vehicles. Computational design and numerical simulation are essential tools for developing concept cars with lower carbon emissions and reduced costs. Underground roads are proposed as an attractive alternative for reducing surface congestion, improving traffic flow, reducing travel times and minimizing noise pollution in urban areas, creating a quieter and more livable environment for residents. In this context, a concept car body design for underground tunnels was proposed, inspired by the mako shark shape due to its exceptional operational kinetic qualities. The proposed biomimetic-based method using computational fluid dynamics for engineering design includes an iterative process and car body optimization in terms of lift and drag performance. A mesh sensitivity and convergence analysis was performed in order to ensure the reliability of numerical results. The unique surface shape of the shark enabled remarkable aerodynamic performance for the concept car, achieving a drag coefficient value of 0.28. The addition of an aerodynamic diffuser improved downforce by reducing 58% of the lift coefficient to a final value of 0.02. Benchmark validation was carried out using reported results from sources available in the literature. The proposed biomimetic design process based on computational fluid modeling reduces the time and resources required to create new concept car models. This approach helps to achieve efficient automotive solutions with low aerodynamic drag for a low-carbon future. [ABSTRACT FROM AUTHOR]

A new study aims to clarify the analytical and mathematical dimensions of the tangent hyperbolic fluid through the plate and cone with useful uses in technical devices like the handling of biomass pyrolysis and viscometer. The presence of chemical process and mixed convection in the natural characteristics of liquid is taken into account. By implementing the homotopy analysis approach, the achieved coupling system is inspected. The influence of the flow control variables on the related profiles is evaluated quantitatively and qualitatively in order to get a full understanding of the current pagination. Through the deep study, it is calculated that convective thermal and surface drag factor for the plate is greater in magnitude than for the cone. The superiority is also observed for the plate in the thermal field relative to that in the cone. The results shows that the heat transfer improves as Hartmann number (M) and Brownian motion factor (Nt) increase but it decreases with an increase of thermophoresis factor (Nb). Also it can be found that effect of drag coefficient is more pronounced or higher for cone as compared to plate. [ABSTRACT FROM AUTHOR]

Renewable energy sources are essential to address climate change, fossil fuel depletion, and stringent environmental regulations in the subsequent decades. Horizontal-axis wind turbines (HAWTs) are particularly suited to meet this demand. However, their efficiency is affected by environmental factors because they operate in open areas. Adverse weather conditions like rain reduce their aerodynamic performance. This study investigates wind turbine power prediction under rainy conditions by integrating Blade Element Momentum (BEM) theory with explainable artificial intelligence (XAI). The S809 airfoil's aerodynamic characteristics, used in NREL wind turbines, were analyzed using ANSYS FLUENT and symbolic regression under varying rain intensities. Simulations at a Reynolds number (Re) of 1 × 106 were performed using the Discrete Phase Model (DPM) and k– ω SST turbulence model, with liquid water content (LWC) values of 0 (dry), 10, 25, and 39 g/m3. The lift and drag coefficients were calculated at various angles of attack for all the conditions. The results indicated that rain led to reduced lift and increased drag. The innovative aspect of this research is the development of machine learning models predicting changes in the airfoil coefficients under rain with an R 2 value of 0.97. The proposed XAI framework models rain effects at a lower computational time, enabling efficient wind farm performance assessment in rainy conditions compared to conventional CFD simulations. It was found that a heavy rain LWC of 39 g/m3 could reduce power output by 5.7% to 7%. These findings highlight the impact of rain on aerodynamic performance and the importance of advanced predictive models for optimizing renewable energy generation. [ABSTRACT FROM AUTHOR]

Long-span highway–railway double-deck truss bridges are mostly located in urban centers, where noise pollution and traffic safety issues have a great impact. The fully enclosed barrier has excellent sound insulation and windproof performance and has been widely used in double-deck truss bridges in recent years. However, the large volume and the low air permeability rate will affect the aerodynamic characteristics of the bridge, resulting in vortex-induced vibration (VIV). To analyze how the fully enclosed barrier influences the highway–railway bridge VIV performance, this study analyzes the Huangjuetuo Yangtze River Bridge, combined with the wind tunnel test and the numerical calculation method to study different variations of the static three-force coefficient, the change of VIV response, and its influence mechanism after setting the fully enclosed barrier. The results show that the static three-force coefficient of the double-deck truss bridge changes significantly, the drag coefficient increases, and the absolute values of the lift coefficient and the moment coefficient decrease after the fully enclosed barrier is set. The aerodynamic performance of the bridge is significantly reduced after the fully enclosed barrier is set, and the amplitude and range of the VIV response are increased. Vertical bending VIV increased by an average of 58.5%, and torsional VIV increased by an average of 21.9%. Considering driving comfort and safety, attention should be paid to the double-deck truss bridge with a fully enclosed barrier. [ABSTRACT FROM AUTHOR]

The flow around a finite square cylinder with suction control at the side and a free-end leading edge is investigated through direct numerical simulations at a Reynolds number of 250. The absolute value of the ratio (Γ) between the suction velocity and the free-stream velocity is in the range of 0 < Γ ≤ 2. The results show that suction reduces the drag and fluctuating lift on the square cylinder. The optimal control effectiveness for reducing the fluctuating lift coefficient C l ′ and the average drag coefficient C d ¯ is achieved at Γ = 0.375 and 0.75, respectively ( C l ′ reduced by over 70% and C d ¯ reduced by nearly 20%). This is superior to the control effect achieved by active suction control only at the side leading edge. Compared to suction applied only at the side leading edge, adding suction at the free-end leading edge suppresses the flow separation on the top surface of the square cylinder. Moreover, with increasing suction ratios, the tornado-like Tip Vortex scale at the free-end of the square cylinder decreases, and the root mean square of streamwise velocity fluctuation at various spanwise planes decreases. Additionally, a data-driven balanced model-based dominant flow mode identification method is adopted to identify the dominant modes of the flow field at the z / d = 0 plane at different suction ratios. The results show that suction can suppress the influence of the square cylinder on the far wake, and as the suction ratio increases, the area of the free flow expands. [ABSTRACT FROM AUTHOR]

Oscillation characteristics in a cavity are investigated under real experimental conditions through unsteady numerical simulations of the time-evolving oscillatory damping of a high-Mach-number freestream over a two-dimensional forward-facing cavity. The post-disturbance flow field is taken as the initial condition. Temporal variations in the flow field and wall resistance coefficient are obtained. The forward-facing cavity experiences underdamped oscillatory behavior when subjected to disturbances. The convergence of the oscillations is influenced by the cavity volume, with significant reductions in cavity damping observed when stagnation regions develop within the cavity. During the initial phase of disturbance, each oscillation cycle consists of gas injection and jet phases. In the former, external gas stagnates within the cavity, resulting in a gradual increase in internal density and pressure. High-temperature regions extend from the external flow into the cavity, and bow shocks approach the cavity wall, adversely affecting aerodynamic drag reduction and thermal protection for aircrafts. In the jet phase, the flow field structure resembles the opposing jet. As the gas is expelled, the internal cavity pressure decreases, forming a cold jet that envelops the cavity's surface. The temperature within the boundary layer on the surface decreases, and bow shocks are pushed away from the wall, resulting in thermal-protection and drag-reduction effects. Transitions between phases induce instability in the internal flow states within the cavity. During the transition from the gas injection phase to the jet phase, the wall drag coefficient reaches its peak value; the reverse transition results in the lowest wall drag coefficient. [ABSTRACT FROM AUTHOR]

Numerical simulations were performed to analyze the external flow field characteristics of a non-pneumatic tire (NPT) with flexible spokes. The simulation results revealed that the acute shoulders and cavities formed by spokes are the principal contributors to the high aerodynamic drag and ventilation moment (VM). By changing the parameters of the shear bands, a significant reduction in the aerodynamic drag coefficient (Cd) and ventilation moment could be achieved. Taking the minimum aerodynamic drag coefficient and ventilation moment as optimization objectives, a five-factor and four-level orthogonal experiment was designed with the spoke thickness, spoke radial length, spoke curvature, spoke outer offset rate, and spoke inner offset rate as the design parameters. The optimal combination of spoke parameters was obtained by range analysis and variance analysis, with the reduction of Cd and VM by 6.25% and 16.55%, respectively. Meanwhile, the feasibility of optimization parameters of the shear bands and spokes was confirmed by mechanical performance test. [ABSTRACT FROM AUTHOR]

This research is the first attempt to examine the hydrodynamic loads of nonlinear solitary waves on bridge decks near a coastline. We employ laboratory experiments and a large eddy simulation model to simulate the wave motion and wave loads on a partially submerged rectangular deck near a sloped beach. The measured wave heights and wave loads from wave flume experiments verify the accuracy of the computational fluid dynamics model. A series of parametric studies investigates the effects of wave height, submergence, and beach slope on the wave loads of the bridge deck. The simulation results revealed that the hydrodynamic forces are linearly proportional to the wave height, and the dimensionless force coefficients depend on the submergence ratio and beach slope. For the mild slope case (θ = 18.5°), the wave load during the run-up stage is larger than that during the run-down stage. The largest drag coefficient CD = 0.58, lift coefficient CL = 0.45, and pitch moment coefficient Cm = −0.21 occur when the deck is initially above the still wave level. On a steeper slope (θ = 30°), the run-down current could generate a large downward force and a clockwise moment when the bridge deck is close to a shoreline. Hereafter, coastal bridges should consider the impact of the run-down flow during tsunamis and storm surges. [ABSTRACT FROM AUTHOR]

We perform two-dimensional particle resolved direct numerical simulations of the steady cross flow past a pair of interacting circular and non-circular cylinders with the cut-cell method, a sub-class of non-body-conforming methods that provides a sharp description of the boundary, is strictly mass and momentum conservative, and can be easily extended to adaptive grids. We use hierarchically refined Cartesian meshes where we place a reference cylinder (i) at the center of the domain and vary the location of a neighboring cylinder (j). We consider a large parameter space defined by the radius of curvature 2 / ζ i and 2 / ζ j ranging from 1 to 0, the angles of incidence α i and α j at values of 0 ° and 45 ° , the center-to-center gap ratio G ranging from 1.5 to 20, the alignment angle θ measured between the free-stream flow and the line connecting the centers of the cylinders, ranging from 0 ° to 360 ° , and finally the Reynolds number Re varied from 1 to 20. Specifically, we investigate the force and flow disturbances introduced by the neighboring cylinder on the reference cylinder, with a focus on the normalized hydrodynamic drag and lift coefficients and the associated prevailing flow regimes. Our study highlights the substantial impact of both the gap ratio G and the alignment angle θ in delineating distinct flow regimes, each exhibiting distinctive flow characteristics and consistent trends in pressure distributions and variations of the normalized drag and lift coefficients. Generally, the flow and force disturbances become more pronounced when significant interactions between the cylinders occur, whether due to proximity, wake interference, or both. We identify a critical threshold for G, beyond which the flow and force disturbances induced by the neighboring cylinder markedly diminish, except in scenarios dominated by significant wake interactions. Our investigation shows that the documented trends in the flow and force variations exhibit remarkable similarity at Re of 10 and 20, but expectedly deviate at R e = 1. Finally, we propose an empirical model to predict the hydrodynamic disturbances between two circular cylinders based on the modulation of the drag C d , i and lift C l , i coefficients. Leveraging the periodic nature of C d , i and C l , i as a function of the relative angular alignment θ of the neighboring cylinder, we use Fourier series expansions demonstrating accurate reconstruction of the data across a wide parameter space. Furthermore, our model exhibits promising predictive capabilities when applied to unexplored parameter ranges, encompassing scenarios involving non-circular cylinders and interpolated regions of Re and G. [ABSTRACT FROM AUTHOR]

The development tendency of lightweight and higher-speed regarding trains goes against the safety and comfort requirement of high-speed trains, especially in the scenario of the train running on bridges within crosswind environments. Wind barriers have been proven to be an effective measure to guarantee the train's operation security. In this paper, a new type of wind barrier consisting of the fence-type wind barrier form and open hole-type wind barrier form has been proposed. Then, a series of wind tunnel tests about the large-scale section model of a large-span suspension bridge installed with different wind barriers have been conducted. The effects of three different forms of wind barrier including fence-type, open hole-type, and combined-type on the aerodynamic characteristics of the train-bridge system have been analyzed. The windproofing effectiveness and the protection mechanism of the combined-type wind barrier on the train-bridge system have been revealed through the measured aerodynamic characteristics. The results show that the installation of open hole-type, fence-type, and combined-type wind barriers at a height of 4 m and a ventilation rate of 19% yields a maximum reduction in the train drag coefficient of 67.70%, 72.92%, and 97.21%, respectively. Moreover, the combined-type wind barrier can improve the train-bridge system's aerodynamic performance and trains' running safety on bridges when comparing with the open hole-type and fence-type wind barriers. The proposed combined-type wind barrier can provide a more efficiency and practical way for the high-speed train's running safety on the bridge. [ABSTRACT FROM AUTHOR]

The microscale gas–particle interaction is the determining process for the macroscopic flow behaviors of gas–particle systems. Anisotropic Stefan flow is often manifested at the surface of the biomass particle when thermally decomposed. However, the influence of the anisotropic Stefan flow on the gas–particle interactions is not well understood. To this end, particle-resolved direct numerical simulations were carried out in this research to explore the momentum interactions between the gas flow and a static particle emitting mass flux at its surface. A signed distance function based immersed boundary method is first extended to account for the Stefan flow at the gas–particle interface and successfully validated by comparing with literature results in the case of no Stefan flow or uniform Stefan flow. It is found that the presence of the outward uniform Stefan flow leads to an expanded wake formation and the intensity of the vortex (Re ≥ 40) is enhanced as result of the Stefan flow. Subject to the impact of anisotropic Stefan flow parallel to the main flow, the low-speed region in the front and rear of the particle is reduced when the Stefan flow goes inwards, resulting in the increase in the drag coefficient. As the Stefan flow is outward, the low-speed region in the front of the particle is pushed forward by the emitting gas and the velocity magnitude in the wake region is increased, which behaves like an enlargement of the gas cushion and leads to a significant reduction of the drag coefficient comparing with a uniform Stefan flow. In contrast, the impact of anisotropic Stefan flow with the direction perpendicular to the main flow on the fluid–particle drag interaction is less significant due to the fact that the flow structure in the front and rear regions is not significantly disturbed. [ABSTRACT FROM AUTHOR]

The water-exit problem of active ventilation vehicles has complex cavity dynamics and hydrodynamic characteristics. This study explores the influence of the ventilation parameters on the dynamic evolution of the cavity and the hydrodynamic forces by experimentation. The full development of cavities is beneficial for hydrodynamic stability. The ventilation parameters focus on two influencing factors: the ventilation opening type and the ventilation angle between the direction of gas flow and the axis of the vehicle. The former includes porous structure, ventilation hole, and ventilation seam, while the latter includes 30° and 90°. Compared to the cases of holes and seams, the cavities formed under the porous structure opening condition have larger diameters and shorter lengths. This is not conducive to the hydrodynamic performance, which includes frictional resistance, pressure drag, and impact pressure at the closure point. When the cavity transits from a partial state to a supercavity state, the frictional resistance no longer changes significantly, and the axial drag coefficient tends to be stable. The increase in the cavity diameter leads to an increase in the pressure drag and the impact pressure at the cavity closure. The ventilation angle mainly affects the stability of the internal pressure and the morphology of the cavity. This work can provide reference for the design of artificial cavity of underwater vehicles. [ABSTRACT FROM AUTHOR]

Analysis of 40 years of tide gauge data and reanalysis wind stresses from the Middle Atlantic Bight (MAB) indicate that along‐shelf wind stresses are a dominant driver of coastal dynamic sea level (sea level plus atmospheric pressure) variability at daily to yearly time scales. The sea‐level response to along‐shelf wind stress varies substantially along the coast and is accurately reproduced by a steady, barotropic, depth‐averaged model (Csanady, 1978, https://doi.org/10.1175/1520‐0485(1978)008<0047:tatw>2.0.co;2, Arrested Topographic Wave). The model indicates that the sea‐level response in the MAB depends primarily on the along‐shelf distribution of the along‐shelf wind stress, the Coriolis frequency, the bottom drag coefficient, and the cross‐shelf bottom slope. The along‐shelf wind stress varies along the MAB shelf due primarily to changes in the shelf orientation. The sea‐level response depends on both the local and upstream (in the sense of Kelvin wave propagation) along‐shelf wind stresses. Consequently, sea‐level variability at daily, monthly and yearly time scales along much of the central MAB coast is more strongly driven by upstream winds along the southern New England shelf than by local winds along the central MAB shelf. The residual coastal sea‐level variability, after removing the wind‐driven response and the trend, is roughly uniform along the MAB coast. The along‐coast average of the residual sea level at monthly and yearly time scales is caused by variations in shelf water densities primarily associated with the large annual cycle in water temperature and interannual variations in salinity. Plain Language Summary: Winds parallel to the coast (along‐shelf) are an important driver of coastal sea level variability that contributes to coastal flooding and erosion. This study examines the relationship between along‐shelf winds and coastal sea level along the East Coast of the United States from North Carolina to Massachusetts from tide gauges for the 40 year period from 1982 to 2021. The along‐shelf winds vary in this region due to changes in the coastline orientation. The sea level variability at a given tide gauge depends not only on the local winds, but also winds to the north and east of the tide gauge because of a tendency for sea level variations to preferentially spread along the coast from the northeast toward the southwest. A simple, wind‐forced, model that includes this preferential along‐coast spreading accurately reproduces the observed coastal sea level variations in this region. Key Points: Along‐shelf wind stress is a major driver of coastal sea‐level variability in the Middle Atlantic Bight at daily to yearly time scalesThe sea‐level response varies along the coast and depends on both local and remote along‐shelf wind stressesA steady, barotropic, depth‐averaged model proposed by Csanady, 1978, https://doi.org/10.1175/1520‐0485(1978)008<0047:tatw>2.0.co;2 accurately reproduces the observed sea level response [ABSTRACT FROM AUTHOR]

Sprinkler irrigation is widely used in agriculture because it allows for rational use of water. However, it can induce negative effects of soil erosion and of surface waterproofing. The scholars of these phenomena use the numerical integration of the equation of motion, but if there was an analytical solution, the study would be facilitated, and this solution could be used as software for regulating sprinklers. Therefore, in this study, the solution of the differential equation of the flight of droplets produced by sprinklers in the absence of wind was developed. The impossibility of an exact analytical solution to the ballistic problem due to the variability of the drag coefficient of the droplets is known; therefore, to find the integrals in closed form, the following were adopted: a new formula for the drag coefficient; a projection of the dynamic's equation onto two local axes, one tangent and one normal to the trajectory and some linearization. To reduce the errors caused by the latter, the linearization coefficients and their calculation formulas were introduced through multiple non-linear regressions with respect to the jet angle and the initial droplet speed. The analytical modeling obtained, valid for jet angles from 10° to 40°, was compared to the exact numerical solution, showing, for the total travel distance, a high accuracy with a mean relative error MRE of 1.8% ± 1.4%. Even the comparison with the experimental data showed high accuracy with an MRE of 2.5% ±1.1%. These results make the analytical modeling capable of reliably calculating the travel distance, the flight time, the maximum trajectory height, the final fall angle and the ground impact speed. Since the proposed analytical modeling uses only elementary functions, it can be implemented in PLC programmable logic controllers, which could be useful for controlling water waste and erosive effects on the soil during sprinkler irrigation. [ABSTRACT FROM AUTHOR]

Generating more usable power annually from the river and tidal currents is essential to improving cost-effectiveness. Among various alternative options, the performance improvement of the blade foil has been considered in this work. When the fluid over the blade surface loses kinetic energy, flow separation occurs. The lift forces are reduced by flow separation, which finally results in less power production by the horizontal axis current turbine. To extract more power, it is necessary to overcome this flow separation. This paper presents a passive flow control method using tubes at regular intervals on the blade section to improve its performance considering its application on a horizontal axis current turbine. The tube inlet and outlet positions are determined by analyzing the force coefficients, glide ratio, and stall angle for a specific angle of attack. Finally, the performance characteristics are compared between the baseline and the modified hydrofoil. The maximum lift coefficient of the hydrofoil is increased by 15.7%. Also, the maximum glide ratios are considerably increased beyond the stall of the baseline profile. From the numerical results, it can be concluded that tubes inserted at regular intervals on the hydrofoil significantly increase its performance at a higher angle of attack. [ABSTRACT FROM AUTHOR]

This paper presents a close-formation flight of two unmanned aerial vehicles (UAVs) and the aim of the study is to improve the understanding of the vortex effects between fixed-wing UAVs in a swarm using computational fluid dynamics (CFD) tools. To validate the numerical method, results of a variable-density wind tunnel test from the literature were used. This numerical CFD analysis was used to determine the lift coefficient (CL) and the drag coefficient (CD) values for a single UAV at various angles of attack. When examining the aerodynamic impact areas behind the UAV, the longitudinal distance between the two UAVs is not particularly effective for close flight. Therefore, CFD analyses were carried out on the two UAVs for both vertical and lateral distances. The optimum position for close-formation flight was identified using CL/CD ratios. The results of the analysis indicate that the most effective flights, across all lateral positions, occur when the two UAVs are vertically at the same height. In terms of aerodynamic efficiency, the most effective points for close-formation flight for wingspan b are at lateral distances of 0.875 b and 1 b. At these positions, flight efficiency can be increased by approximately 11.5%. [ABSTRACT FROM AUTHOR]

During this research, aerodynamic shape optimization is conducted on the Ahmed body with the drag coefficient as the objective function and the ramp shape as the design variable, while aero-structural optimization is conducted on NACA 0012 to reduce the drag coefficient for the aerodynamic performance with the shape as the design variable while reducing structural mass with the thickness of the panels as the design variables. This is accomplished through a gradient-based optimization process and coupled finite element and computational fluid dynamics (CFD) solvers under fluid–structure interaction (FSI). In this study, DAFoam (Discrete Adjoint with OpenFOAM for High-fidelity Multidisciplinary Design Optimization) and TACS (Toolkit for the Analysis of Composite Structures) are integrated to optimize the aero-structural design of an airfoil concurrently under the FSI condition, with TACS and DAFoam as coupled structural and CFD solvers integrated with a gradient-based adjoint optimization solver. One-way coupling between the fluid and structural solvers for the aero-structural interaction is adopted by using Mphys, a package that standardizes high-fidelity multiphysics problems in OpenMDAO. At the end of the paper, we compare and discuss our findings in the context of existing research, specifically highlighting previous results on the aerodynamic and aero-structural optimization of wind turbine blades. [ABSTRACT FROM AUTHOR]

This study employs the XBeach surfbeat model (XBSB) to explore the effects of vegetation on wave attenuation and dune erosion in a case study of Mexico Beach during Hurricane Michael. The XBSB model was validated against laboratory experiments of wave-induced dune erosion and wave attenuation by vegetation. In the case study of vegetation on dunes in Mexico Beach during Hurricane Michael, different vegetation drag coefficients were evaluated to investigate the effects of vegetation on wave attenuation and dune erosion. LiDAR data of dune profiles before and after Hurricane Michael were used for model validation. The findings reveal that vegetation on dunes significantly affects wave attenuation and dune erosion. Under vegetated conditions, as the vegetation drag coefficient value increases, wave attenuation also increases, leading to a reduction of dune erosion. An increase in vegetation density enhances wave attenuation in the vegetated area, including reductions in significant wave height and flow velocity. However, the rate of change in attenuation decreases as the vegetation density increases. Through simulations under regular wave condition on Mexico Beach, an optimal vegetation density was identified as 800 units/m2. Beyond this density, additional vegetation does not substantially improve wave attenuation. Furthermore, the position of the dune crest elevation is related to the location where the alongshore flow velocity begins to decrease. The findings highlight the essential role of coastal vegetation in enhancing coastal resilience against hurricanes. [ABSTRACT FROM AUTHOR]

Fish in nature can extract the vortex energies from the environment to enhance their swimming performance. This paper numerically investigated the hydrodynamic characteristics and the energy-saving advantages of an undulating fish-like body behind the vortical flows generated by an upstream cylinder. The numerical model was based on a robust ghost cell immersed boundary method for the solution of incompressible flows around arbitrary complex flexible boundaries. We examined the dynamic characteristics, the swimming performance, and the wake structures of the downstream fish under different locations and diameters of the cylinder in a wide range of Strouhal numbers. It was found that the average drag coefficient was significantly reduced in the presence of the upstream cylinder, while the RMS (root mean square) lift coefficients were very close for different locations and diameters of the cylinder as well as in the fish-only case. Therefore, the downstream fish gain efficiency and thrust enhancement by capturing energies from the vortex flows, which are more significant for smaller Strouhal numbers (St). However, the swimming efficiency converges to near 0.12 at St = 1.2 for different locations and diameters of the upstream cylinder, just slightly higher than that of the fish-only case. The fish can experience the thrust in not only the von-Kármán vortex street, but also the reversed one. In addition, the fish can be situated in the extended shear layer region and the fully developed wake region dependent on the position and diameter of the upstream cylinder, leading to abundant wake modes such as the splitting, coalescing, and competing of vortices. [ABSTRACT FROM AUTHOR]

The two-dimensional laminar flow over a simultaneously pitching-heaving teardrop airfoil is studied numerically. The influence of frequency and amplitude on the wake structure and aerodynamic performance is investigated at a constant Reynolds number, Re=2640. The computational modeling accurately depicts the changes in the wake structure that occur between the von Karman, reverse von Karman and deflected conditions. Investigations at low flapping frequencies and amplitudes identified the presence of additional wake structures that had not been reported previously. The interaction between the flapping frequency and vortex shedding frequency appears to govern the formation of such multiple vortex wakes. The wake structures identified are presented in the form of a wake map where the transitions between the wake structures are visible. This study correlates the wake arrangement with the variation in force coefficients and explains why the presence of a reverse von Karman street is necessary but not a sufficient condition for thrust production. The time history of the drag coefficient and the phase relation between lift and drag show the dynamics of the wake. The variation of force coefficients and efficiency at different flapping conditions is evaluated, and the influence of flapping parameters is assessed. The underlying vortex interactions that influence the aerodynamic performance are identified. The development and distribution of stress fields developed due to periodic fluctuations behind the flapping airfoil have not been discussed previously. The velocity fluctuations in the wake due to the periodic flapping are presented, and regions of maximum stress distribution are identified. [ABSTRACT FROM AUTHOR]

Understanding the aerodynamic characteristics of landfalling typhoons is of great importance for both wind engineering and meteorology. This study comparatively investigated the near‐surface wind profiles and aerodynamic parameters over coastland and coastal sea areas using typhoon observational data collected by Doppler wind lidars and wind tower anemometers during the passage of 15 typhoons that made landfall over China during 2009–2020. Specifically, the three surface aerodynamic parameters of roughness length, friction velocity, and drag coefficient (Cd) were obtained using the logarithmic law wind profile method. Results showed that the near‐surface wind profiles became much closer to the power law wind profile with increase in wind speed. The values of roughness length and friction velocity over the coastal sea were found to exceed those over coastland areas when the 10‐m wind speed (U(10)) was larger than 18 m s−1. The critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1. There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the sea, which has never been reported in previous observational studies. Finally, a formula for Cd was proposed to describe the variation in Cd with U(10) under the condition of onshore wind over land, which is expected to be applied in the typhoon surface layer scheme to improve numerical simulation of landfalling typhoons. Plain Language Summary: Typhoons are one of the most destructive natural disasters that cause severe economic losses and human casualties in many parts of the world. Understanding the typhoon wind field is important for designing high‐rise buildings and improving weather forecast. In order to understand how the near‐surface wind field change in coastal regions, we measure it using specialized observation instruments during the passage of 15 typhoons that made landfall over China and analyze the results of the measurements. We find that the aerodynamic characteristics of typhoons over coastland are very different from those over the coastal sea. A specialized surface aerodynamic parameter called drag coefficient, which represents the momentum transport efficiency on the sea/land surface, is found to reach its maximum value when the 10‐m wind speed is 24 m s−1 over the coastal sea. Interestingly, two peaks are observed in the plot of drag coefficient as a function of 10‐m wind speed under the condition of onshore wind over the coastal sea, which has not been reported before in any other related studies. Further development of the typhoon numerical models should take these results into account. Key Points: Values of roughness length and friction velocity over the coastal sea were found to exceed those over the coastland for U(10) > 18 m s−1Critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the coastal sea [ABSTRACT FROM AUTHOR]

A large-eddy simulation was implemented for the flow around a cylindrical observation tower to investigate the effects of the tower structure on wind speed and drag coefficient. The mean wind velocity accelerates above the tower because flow separation occurs at the leading edge of the top of the tower. The drag coefficient is strongly linked to the Reynolds shear stress. Above the tower, the Reynolds shear stresses change from negative to positive within the recirculation zone and return to a negative value in the latter half of the tower because of the steep velocity gradients near the top of the tower. The change in the Reynolds shear stress results in an inaccurate drag coefficient. When one anemometer is used, a location at over 10 m above the top of the tower is suitable for measuring the drag coefficient accurately. When two anemometers are used, the Reynolds shear stress can be measured more accurately. Although the effects of the tower on the drag coefficient are not entirely removed, the use of two anemometers is a promising approach to estimate the drag coefficient in a tower. [ABSTRACT FROM AUTHOR]

This study investigates the influence of small control cylinders on the fluid dynamics around a square cylinder using the Lattice Boltzmann Method (LBM). Varying the gaps (L) between the main and control cylinders from 0 to 6, four distinct flow regimes are identified: the solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS). The presence of control cylinders results in significant reductions in flow-induced forces, with drag coefficient (CD) and root mean square values of drag and lift coefficients (CDrms and CLrms) decreasing by approximately 31%, 90%, and 81%, respectively. The SFDF flow regime exhibits the lowest fluid forces compared to other regimes. The effects of tiny control cylinders on the fluid flow characteristics of a square cylinder are examined using the Lattice Boltzmann Method (LBM) in this research work. The gaps (L) between the main and control cylinders are varied in the range from 0 to 6. The size of each control cylinder is equal to one-fifth of the primary cylinder. According to the findings, there are four distinct flow regimes as the gap spacing varies: solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS) for gap spacing ranges 0 ≤ L ≤ 0.2, 0.3 ≤ L ≤ 0.9, 1 ≤ L ≤ 3, and 3.2 ≤ L ≤ 6, respectively. Additionally, it has been noted that the amplitude of variable lift force is reduced when the gap separation between the main and control cylinders is increased. When compared to solo cylinder values, it is found that the presence of small control cylinders in the flow field results in a considerable reduction of flow-induced forces. The SFDF flow regime was determined to have the lowest fluid forces compared to the other flow regimes studied. Our findings highlight the efficacy of small control cylinders in mitigating flow-induced forces and controlling flow characteristics. The LBM proves to be a valuable computational technique for such fluid flow problems. [ABSTRACT FROM AUTHOR]

When the high-speed elevator is running, the air in the hoistway is rapidly compressed and released to form the piston effect. Especially when the car and counterweight intersect, the piston effect makes the aerodynamic force of the car and counterweight change sharply, affecting the stability of elevator operation. In this study, a three-dimensional car counterweight intersection model is constructed, and a multi-region dynamic layered method is proposed to calculate the aerodynamic flow field in the whole moving process, the changes of aerodynamic drag force and aerodynamic lateral force of the car and the counterweight under different length ratio, blockage ratio and spacing are analyzed and simulated, and the influence of structural changes in the hoistway on the aerodynamic flow field is studied. Furthermore, the accuracy of the numerical results is verified by the real elevator test. Finally, the results show that when the car intersects the counterweight in the hoistway, the interaction between the car and the counterweight is enhanced, and the drag force coefficient and lateral force coefficient of the car suddenly change, and return to the normal state after the intersection, with the decrease of length ratio and spacing and the increase of blockage ratio, the sudden change degree of drag force also increases, and the sudden change of lateral force of the car is mainly affected by the car counterweight spacing, and increases with the decrease of spacing. [ABSTRACT FROM AUTHOR]

Aircraft icing deteriorates aerodynamic performance and reduces stall angle of attack, the fast convergence rate of tracking error is required to stabilize the aircraft when aircraft icing occurs. The state-of-the-art control methods for icing aircraft mostly assume that the icing of aircraft is instantaneous. Aiming at these issues, a fixed-time angle of attack-constrained control strategy is designed considering dynamic icing process. In order to explore the variation of aerodynamic coefficients in the process of dynamic icing, an ice wind tunnel experiment is implemented, and the relationship between lift coefficient, drag coefficient and pitching moment coefficient with angle of attack and icing intensity is obtained by fitting method. In order to prevent the stalling problem caused by the decrease of the stalling angle of attack in the process of dynamic icing, a method to determine the stalling angle of attack based on deep neural network is proposed. Considering the asymmetric and time-varying angle of attack constraint, a fixed-time convergent angle of attack-constrained robust control method is designed. The ice wind tunnel experiment shows the process of dynamic icing of the airfoil, and the simulation results verify the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) simulations have been extensively used in designing air distribution systems for controlled environment agriculture (CEA). In recent years, more application studies using CFD simulations can be found for vertical farms due to the increasing interest in indoor vertical farming systems. However, it is well-known that CFD simulations are sensitive to many computational parameters and settings. The requirement of a crop response model in the CFD simulation for a vertical farm makes it even more complicated. Despite increased interest, guidelines for CFD simulations in vertical farms are scarce based on a literature study. Therefore, a systematic sensitivity analysis is conducted for a small generic multi-layer vertical farm with sole source lighting, which was the object of study in the literature before. The impact of a wide range of computational and physical parameters is investigated, including grid resolution, turbulence model, turbulence intensity, discretisation scheme, drag coefficient of the crops and computational time. The analysis shows that in this case (inlet Re = 46,923, Ar = 0.078, cultivated with lettuce), the RNG k-ε turbulence model outperforms other commonly used two-equation turbulence models. Compared to the experimental results from the literature, the simulation results from the first-order upwind scheme show large discrepancies, especially on the coarse grid. Although the influence of drag coefficient on the airflow inside the crop canopy is pronounced, little difference is observed in the air distributions in the vertical farm away from the crops. • Literature review on computational settings in CFD simulations of indoor farming. • Validation of RANS CFD simulations including a crop response model. • RNG k-ε turbulence model outperforms the other two-equation turbulence models. • First-order upwind discretisation scheme shows large discrepancies. • Influence of the momentum sink of lettuce canopy on the air distributions is limited. [ABSTRACT FROM AUTHOR]

In the approach of metric-based geometric parameterization, the concept of database filtration and proper orthogonal decomposition manipulation quantitatively enhances the generation of new geometric parameters so that the problem-oriented information is reflected in aerodynamic design. Compared with the conventional approach that applies only geometric filtration, this paper incorporates performance filtration so that the problem-oriented information is no longer limited to geometric constraints, thereby enabling the guidance of optimization direction in a more informed manner. This paper focuses on the pressure distribution of samples and their relationship with geometric variations. A variational autoencoder is employed to extract the dominant features of the aerodynamic potentials that an initial geometry can attain in optimization. The authors believe that the aerodynamic potential is reflected in how the pressure distribution differs from that of the initial geometry. Then, samples have to meet the performance filtration criterion based on pressure distribution proposed by designers according to their aerodynamic understanding of the optimization problem. Finally, the remaining collection of qualified samples generates new geometric parameters via proper orthogonal decomposition. The conventional and new approaches were validated in a two-dimensional airfoil case of drag coefficient optimization; the lift-to-drag ratio improved by 17.07% using the traditional method, and by 38.20% using the new approach. The pressure distribution shows that the performance filtration approach produces more supercritical properties than the geometric filtration approach. This implies that the performance filtration approach can capture more intricate details related to the aerodynamic performance of the airfoil. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the hydrodynamic forces acting on wood debris accumulations. Tests were performed under steady subcritical flow conditions by letting debris elements accumulate against an obstacle. We analyze the influence of a variety of variables involved in the problem, namely the Froude number, the blockage ratio, the geometric parameters of the dam, its porosity, and the debris type. Resulting forces are expressed through a typical drag coefficient formula, where the coefficient depends on the Froude number and the blockage ratio, but is independent of the geometric characteristics of the debris accumulation. The model is validated against literature data, providing both best-fit and safe-side predictors. Practical Applications: Wood debris can build up on bridge piers and decks, which increase the water's force on these structures. In this paper, we offer a straightforward method to estimate these forces. We have calibrated an empirical model using data from laboratory experiments and checked its accuracy against information from existing studies. With this model, one can input the basic characteristics of the flowing water (such as its depth, width, and speed) and the size of the debris pile facing the flow. The model then provides the drag coefficient, which, in turn, allows determining the drag force acting on the debris pile. [ABSTRACT FROM AUTHOR]