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This study simulates wind effects on a standard tall building model as specified by the Commonwealth Advisory Aeronautical Council (CAARC). We generated data to enhance living conditions through passive flow control, which mitigates building weathering, reduces wind loads, and improves energy efficiency and natural ventilation. The research also aids building designers with robust numerical predictions. The validity of these results was confirmed by comparing drag coefficient (C D) values with those from previous studies. The findings demonstrate that passive flow control significantly reduces wind-induced drag forces on the building at various angles of attack (α) by altering wind-induced pressures, reducing vorticity, and decreasing vortex shedding magnitudes. The objective was to identify the optimal placement of segmented cladding materials with desired gaps between segments to allow airflow to influence temperature variations when exposed to wind at 293 K and a heat flux of 500 W/m2 at wind speeds of 1, 2, and 4 m/s (Reynolds numbers of 5.2 × 10³, 10.4 × 10³, and 20.8 × 10³). Using 2D numerical analysis, twenty-four different facade and building model combinations were simulated. This study offers practical guidance on facade selection and positioning to optimize wind resistance and enhance the livability and functionality of building environments. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics of two oscillating rigid spheres moving through an infinite porous medium saturated with Stokes fluid flow, addressing the problem of how fluid properties, permeability, frequency, and slip length influence the system. The objective is to model the interactions between the spheres, which differ in size and velocity as they move along the axis connecting their centers while applying slip boundary conditions to their surfaces. We derive the governing field equations using a semi-analytical method and solve the resulting system of equations numerically through a collocation technique. Our novel quantitative results include insights into the drag force coefficients for both in-phase and out-of-phase oscillations of each hydrophobic sphere, considering parameters such as diameter ratio, permeability, frequency, velocity ratios, slip lengths, and the distances between the spheres. Notably, when the spheres are sufficiently far apart, the normalized drag force coefficients behave as if each sphere is moving independently. Additionally, we present streamlines that illustrate the interactions between the spheres across a range of parameters, highlighting the novelty of our findings. A purely viscous medium and no-slip conditions are used to validate the numerical approach and results. [ABSTRACT FROM AUTHOR]

The high-speed movement of trains generates train-induced wind, commonly referred to as slipstream, which presents a specific safety concern for passengers and personnel. Yet, the fastening system employed to secure ballastless tracks, characterised by its complex shape, substantial quantity, and dense arrangement, remains inadequately investigated regarding its influence on train aerodynamics. In the present study, a sliding mesh technique was employed to comparatively examine the impact of different track configurations--trackless, track-only, and track with a fastening system--on the aerodynamic characteristics, slipstream formation, and wake turbulence induced by trains. The results indicate that the tracks and the fastening system increased the drag force coefficient by 0.73% and 2.05%, respectively, compared with no track. Additionally, tracks and the fastening system had a significant impact on the slipstream velocity near the train and ground. Tracks notably altered the shape of the wake near the ground, and the fastening system exacerbated this phenomenon. Further, the fastening system further intensified the generation of secondary vortices at track and footstep locations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study introduces a decentralized control framework designed to improve energy efficiency in vehicle platooning by optimizing inter-vehicle gaps to minimize aerodynamic drag, a significant factor in energy consumption. The proposed framework integrates extremum seeking control (ESC), a proportional integral derivative controller with feedforward compensation (PIDFC), and an extended state observer for estimating aerodynamic drag coefficients. Through this integration, the ESC dynamically adjusts inter-vehicle gaps to minimize the drag force based on the estimated aerodynamic drag coefficients, while the PIDFC ensures precise tracking of the optimized gaps and effectively addresses disturbances arising from aerodynamic variations. The results show that the proposed ESC with PIDFC converged to the optimal distance gaps 37.14% faster than the ESC with PPC, within a steady-state error of ± 1 % . Additionally, it improved the computational efficiency by 70.6%, compared to the ESC with PPC. Furthermore, it reduced the energy consumption by 15.3%, compared to the fixed-gap approach. These findings demonstrate the framework's potential to enhance the energy efficiency, scalability, and practicality, advancing sustainable and autonomous transportation systems. [ABSTRACT FROM AUTHOR]

Based on field observation at the north coast of the Zhanjiang Bay in southern China, the characteristics of wave attenuation due to the drag force of one mangrove species, Avicennia marina (Forsk.) Viern., were quantitatively analyzed. The results demonstrated that the mean significant wave height decreased by ~62% within a forest belt up to 80 m due to various bio-physical interactions. Affected by the unique vertical configuration of vegetation, the wave attenuation rate is positively correlated with water depth. The drag force within the forest can be approximated by the function C d = 0.7344 e 0.1409 A m , where Am is the projected area of the submerged obstacle at a certain water depth. The wave attenuation rate and the vegetation density (ρveg) in volume (‰) satisfy the fitting relationship of r = 5 × 10 − 4 · ρ v e g − 3.6 × 10 − 3 . These findings can accumulate quantitative information for studying the influence of mangrove vegetation on wave attenuation characteristics and provide necessary basic data for modeling studies to investigate the processes contributing to the attenuation capacity of mangroves. [ABSTRACT FROM AUTHOR]

This paper presents the results of wind tunnel experiments, where lift and drag coefficients were studied at various angles of attack and flow speeds, alongside numerical simulations conducted in ANSYS. The main objectives of this study are to investigate the aerodynamic characteristics and self-starting capabilities of three-bladed Darrieus rotors with asymmetrical blades and assess their efficiency. This study presents results on pressure distribution, velocity contours, and the impact of the angle of attack on pressure and aerodynamic characteristics. The results show that blades with asymmetric shapes achieve maximum values of lift and drag coefficients at angles of attack between 180° and 210°, with peak coefficients of Cx = 1.38 and Cy = 2.84, respectively. These findings indicate high effectiveness of the blades at low wind speeds, making them promising for use in WEIs where good starting characteristics and high power output are especially important. A good correlation was found between experimental data and numerical simulation results. This study contributes to the development of recommendations for optimizing the design and operating parameters of wind-driven powerplants, which in turn can improve their reliability and economic efficiency. Thus, the paper aims to expand the knowledge in the field of wind power engineering and to develop technologies to facilitate a wider adoption of wind-driven powerplants in the energy infrastructure of different regions. [ABSTRACT FROM AUTHOR]

The physical and aerodynamic properties of grain are very necessary in the development of pneumatic grain handling. These properties are influenced by moisture content and grain type. This study aimed to investigate the effect of moisture content and grain type on the physical and aerodynamic properties of rough rice and corn. In this study, three types of rough rice and corn, each in three levels of moisture contents were investigated. A completely randomized design, factorial 3 × 3 was used in the research. It was found that the physical properties consisting of major diameter (a), intermediate diameter (b), minor diameter (c), grain volume (Vp), grain weight (mp), particle density (Vp) and frontal area (Ap), and the aerodynamic properties consisting of terminal velocity (Vt), drag coefficient (Cd), drag force (Fd), and buoyant force (Fb) for both rough rice and corn were significantly affected by moisture content and grain type (p<0.05). It was also found that none of the evaluated equations could predict measured Vt accurately within the range of moisture content studied. Therefore, the use of theoretical equations to predict Vt should be done carefully. [ABSTRACT FROM AUTHOR]

In this study the computational analysis of the flow topology around two rectangular cylinders is performed using the lattice Boltzmann method. The cylinders are arranged in a staggered configuration, and both share the same aspect ratio. For simulations, the Reynolds number is kept constant at 150 while the gap spacing, between the cylinders, is varied within the range from 0 to 10 times the width of the cylinders. Four different flow patterns observed in this study are the isolated bluff structure, chaotic flow, modulated synchronized flow, and synchronized flow. The observed flow patterns and the corresponding fluid force parameters such as average drag coefficient, root-mean-square of the drag and lift coefficient, the amplitude of drag and lift, as well as the Strouhal number, are found to be strongly influenced by the gap spacing between cylinders. At low gap spacing values, a robust effect of jet flow disturbs the flow structure, which ultimately results in a complex flow structure in the wake and random fluctuations in drag and lift forces. With an increase in spacing values, the effect of jet flow on fluid flow characteristics gradually minimized, which results in a smooth periodic flow in the wake of both cylinders. [ABSTRACT FROM AUTHOR]

This study examines the variations in wake structures and fluid forces around a cluster of five square cylinders. The cylinders in the cluster are arranged such that a larger cylinder (the main cylinder) is surrounded by four similar but small-sized cylinders, which are very common in marine risers and axial pipe shrouds. The analysis uses an in-house developed code based on the lattice Boltzmann method. The gap spacing (g*) between the main and the surrounding cylinders varies from 0 to 10 while maintaining a fixed Reynolds number (Re) of 200. The accuracy and consistency of the code are first tested through simulations that examine the flow behind a single cylinder, revealing strong concurrence with the existing data. In the next step, the flow characteristics of the pentad arrangement are analyzed. Five diverse flow modes, including the extended single bluff body flow, stable symmetric flow, chaotic irregular shedding, antiphase symmetric flow, and modulated periodic flow, are observed depending on the gap distances. It is found that the small cylinders in the downstream position from the primary cylinder experience a negative mean drag at narrow gaps. In contrast, those at the upstream position are subjected to a positive drag force regardless of the gap spacing. The main cylinder has a higher drag coefficient compared to other cylinders for all gap spacing cases. The shedding frequencies appear similar for upstream and downstream smaller-size cylinders at higher spacing values, while the shedding frequencies for the main cylinder significantly deviate from the surrounding small cylinders. [ABSTRACT FROM AUTHOR]

In this work, the aerodynamic analysis of the original and modified Ahmed body was done. The principle of modification was the chamfer angle on the back sides of the Ahmed body like a boat tail, which was expected to decrease the magnitude of the drag force. The value of the aerodynamic coefficients was carried out using CFD modelling and data were validated in wind tunnel measurements. For those measurements, it was necessary to design simple aerodynamic balances, since the utilized wind tunnel was not equipped with any. It has been expected that the drag force coefficient of the modified model should be reduced compared to original geometry. [ABSTRACT FROM AUTHOR]

The large number and dense layout of rail fastening can significantly affect the aerodynamic performance of trains. Utilizing the Improved Delayed Detached Eddy Simulation (IDDES) approach based on the SST (Shear Stress Transport) k-ω turbulent model, this study evaluates the effects of the rail fastening system on the aerodynamic force, slipstream and train wake under crosswind conditions. The results indicate that in such conditions, compared to the model without rails, the rail and the fastening system reduce the drag force coefficient of the train by 1.69%, while the lateral force coefficients increase by 1.16% and 0.87%, respectively. The aerodynamic force can be considered virtually unchanged within the error allowance. However, the rail and the fastening system cause an inward shift of the negative pressure center on the leeward side of the train. The peak slipstream velocity near the ground in the rail and rail fastening system model is significantly lower than that in the situation without rails. Additionally, the rail and the fastening system not only induce two displacements in the vortex structure of the train but also accelerate the dissipation of shedding vortex and the rapid decrease of turbulent kinetic energy. [ABSTRACT FROM AUTHOR]

Loose and baggy clothing is required by the rules of ski cross and snowboard cross. However, it is known from the literature that fluttering garments increase the aerodynamic drag. The aim of this study was to investigate the influence of flexural rigidity and fabric weight on the coefficient of drag CD. Eleven fabrics (550 mm long, 320 mm wide) with different flexural rigidity (0.016–99 µNm) and fabric weight (0.1–2.4 N/m2) were tested in a wind tunnel on a cylinder (width 325 mm, diameter 125 mm) at speeds of 25 to 120 kph (Reynolds numbers Re 60 k-280 k). The general trend showed that fluttering fabrics that are heavier and stiffer create more drag force. All but one fabric had a smaller CD than the bare cylinder in the subcritical flow regime (CD ≈ 1.1), at least within a Re window of 80 k. One fabric had a consistently higher CD (average: 1.27) than the bare cylinder. The mean CD value of the other ten fabrics ranged from 0.87 to 1.07, with minimum CD values between 0.76 and 1. The CD advantage of the ten fabrics ended at the beginning of the critical flow regime of the bare cylinder between Re 200 k and 220 k. A regression analysis showed that the magnitude of the CD is more influenced by the flexural rigidity of a fabric, normalised to its weight, than by the weight itself, at least at Re < 250 k. The results of this study suggest that ski and snowboard cross athletes' suits should be made from light and flexible fabrics to reduce aerodynamic drag. [ABSTRACT FROM AUTHOR]

The article explores the modeling of filtered drag force in clustered particle-laden flows through large-scale interface-resolved simulations. It introduces a new correlation to consider mesoscale effects on drag force, emphasizing the importance of subgrid quantities like drift velocity and solid volume fraction variance. The study evaluates existing subgrid models and proposes a new model for solid volume fraction variance, showing promising accuracy in predicting drag force. Overall, the research provides valuable insights into modeling drag force in clustered particle-laden flows and suggests potential avenues for future studies. [Extracted from the article]

Drag coefficients (CD) are a key metric in quantifying the vegetation effect on riverine and coastal modeling. However, drag coefficients determined using various approaches under combined wave-current flows have not been comprehensively explored. In the paper, a three-dimensional (3D) numerical model was developed to study the wave dissipation induced by submerged canopies in both following and opposing currents. The results reveal the characteristics of variation of vegetation drag force under pure wave and combined wave-unidirectional flow, as well as the relationship between drag force and flow velocity. The calibration and direct measurement methods were applied to conduct the drag coefficients under various wave-current combinations. The temporal variation in horizontal velocity U, drag force F, and the drag coefficient within the aligned canopy and staggered canopy considering the combined effects of wave and current show different patterns. Moreover, the empirical relations between drag coefficients derived using different methods with Reynolds number (Re) and Keulegan-Carpenter number (KC) are proposed. Comparison of the CD-Re and CD-KC relations would provide insight into the understanding of wave dissipation by vegetation under combined wave-current flow conditions. [ABSTRACT FROM AUTHOR]

Flow over an Iranian bridge deck is studied under an actual extreme flood event happening similarly nowadays in many countries due to climate change. Rigorous transient fluid-structure interaction analyses using the realizable k-ε turbulence model and the VOF Method are conducted. Geotechnical and abutments damages are neglected. Water surface profiles, velocity vectors, and hydrodynamic coefficients are determined. Based on the latest hydrological regime, particularly in supercritical flows, the results are partially compared against the latest advanced design codes, to evaluate the performance of their hydrodynamic and hydraulic provisions in similar incidents. It was acknowledged that the flood loads recommended by the Federal Highway Administration (FHWA) are fairly acceptable, Eurocode-1 predicts them rather accurately but not in extreme cases, and the Australian Standard (AS-5100.2) is less effective due to over-estimation of the hydrodynamic loads. Instead, the latter offers comprehensive user-defined hydraulic conditions. Furthermore, upon gradual rise of the water level to thrice the deck height, bridge stability is found to be at risk due to highly turbulent states. It is recommended that due to such threats, re-evaluation of flood regime, as well as its distinct hydrodynamic properties have to be accounted for, when evaluating existing bridges or designing new ones. [ABSTRACT FROM AUTHOR]

Transport of particles in flows is often modeled in a combined Eulerian–Lagrangian framework. The flow is evaluated on an Eulerian grid, while particles are modeled as Lagrangian points whose positions and velocities are evolved in time, resulting in particle trajectories embedded in the time-dependent flow field. The method essentially resolves the flow field in complex geometries in detail but uses a closure model for the particle dynamics aimed at including the essential particle–fluid interactions at the cost of detailed small-scale physics. Rarefaction effects are usually included through the phenomenological Cunningham correction on the drag force experienced by the particles. In this Lagrangian point-particle approach, any explicit reference to the finite size and the shape of the particles, and their local orientation in the flow field, is typically ignored. In this work we aim to address this gap by deriving, from fully-resolved Direct Simulation Monte Carlo (DSMC) studies, heuristic or closure models for the drag force acting on prolate and oblate spheroidal particles with different aspect ratios, and a fixed orientation, in uniform ambient rarefied flows covering the transition regime between the continuum and free-molecular limits. These closure models predict the drag in the transition regime for all considered parameter settings (validated with DSMC data). The continuum limit is enforced a priori and we retrieve the free-molecular limit with reasonable accuracy (based on comparisons with literature data). We also include in the models the capability to predict effects related to basic gas-surface interactions via the tangential momentum accommodation coefficient. We furthermore assess the validity of the proposed closure model for particle dynamics in proximity to solid walls. This investigation extends our previous work, which focused on small aspect ratio spheroids with exclusively diffusive gas-surface interactions [see Livi et al. (2022)]. The derived models are obtained for isothermal, subsonic flows relevant for particle contamination control in semiconductor manufacturing. • DSMC-enhanced drag force closures for particle tracking under rarefied gas conditions. • The drag force on finite-size spheroids in the transition regime of rarefied flows. • Towards algorithms for particle contamination control in semiconductor manufacturing. • Covering the device-to-nanoparticle scale separation in high-tech equipment. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai Jiao Tong University (1006-2467) is the property of Journal of Shanghai Jiao Tong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Satellite drag coefficients are crucial for determining the neutral mass densities that affect spacecraft operations in the thermosphere. Many studies typically utilize a constant drag coefficient of 2.2 to calculate the neutral density. However, due to the variability of space environment, uncertainties in the drag coefficient can lead to significant systematic discrepancies in neutral density measurements. Satellite drag coefficient may fluctuate in the thermosphere under various geomagnetic activities and altitudes. For the first time, we calculate the spherical satellite drag coefficient using data from the "Orbital Atmospheric Density Detection Experimental Satellite," referred to as the QX satellite. Our findings reveal that the drag coefficient can be estimated by thermospheric temperature and density, which are dependent on geomagnetic activity and altitude. At an altitude of ∼510 km, drag coefficients are adjusted to around 2.425, instead of the constant value of 2.2. Furthermore, the drag coefficient may decrease due to the significant influence of increasing geomagnetic activity, such as geomagnetic storms, on thermospheric density and temperature. These estimates of the drag coefficient can also be used to reduce discrepancies when deducing the ballistic coefficient. Consequently, using the estimated drag coefficient can accurately determine the QX‐derived neutral density, which agrees well with the density from Swarm‐B satellite. Plain Language Summary: Satellite drag coefficient is a key factor in advancing space engineering and understanding the impacts of space weather conditions on satellites in the thermosphere. It helps in calculating the neutral mass density associated with atmospheric drag force and estimating the satellite orbital lifetime. In this study, it is the first time calculating the spherical satellite drag coefficient using data from QX satellite, collected from 28 July 2022 to 30 June 2023. We investigate the response of the drag coefficient to thermospheric temperature and density under different geomagnetic activities and altitudes. These relationships allow us to estimate the spherical satellite drag coefficient, which in turn helps us improve the accuracy of determining the ballistic coefficient and the corresponding neutral mass density. Compared with the results of the drag constant of 2.2, the QX‐derived densities determined using the estimated drag coefficients, align well with the in‐situ observations from Swarm Precise Orbit Determination data. Overall, our results enhance the understanding of how the spherical satellite drag coefficient changes in response to variations in the thermosphere under different space weather conditions. We also suggest a method for estimating the drag coefficient, which has valuable applications in the calculation of neutral mass density. Key Points: We put forward a new method for determining drag coefficients using temperature and density affected by geomagnetic activity and altitudeGeomagnetic activity increases, associated with the enhancements in temperature and density, leading to a reduction of the drag coefficientUsing the estimated drag coefficients allows for accurate determination of QX‐derived density, which aligns well with Swarm‐derived density [ABSTRACT FROM AUTHOR]

Biofouling is a serious problem in marine aquaculture facilities, exerting several negative effects on cage structures. In this study, different materials of nets were placed in the Fujian Sea area of China, and the main biological adhesion species were determined. The drag force of different materials of fouled nets was studied by a physical test in a flume tank. The drag force coefficient of a clean polyethylene terephthalate (PET) net was 0.53. The drag force coefficients of ultrahigh-molecular-weight polyethylene (UHMWPE) and polyethylene (PE) nets were 161.2% and 133.5% higher, respectively, compared with those of PET nets. Crustaceans, mollusks, and algae were the main organisms that adhered to the nets. Compared with the clean nets, the drag force of PET, UHMWPE, and PE nets increased by 1.29–5.06 times, 1.11–2.85 times, and 0.55–2.46 times, respectively. Based on backpropagation (BP) neural network training, the relationship between biological characteristics (average adhesion thickness and density) and the drag force of three kinds of net materials was determined. The drag force of the biofouled net at various time points throughout the year can be predicted based on this model, which can guide the cleaning and maintenance of nets in cage structures. [ABSTRACT FROM AUTHOR]

Self‐supporting concrete shell structures are highly efficient in distributing loads, which can result in very reduced thicknesses (ultra‐thin), giving them remarkable slenderness. Due to their geometric complexity, it is difficult to predict how they interact with wind action. The main aim of the present study is to assess the mean surface pressure coefficient distribution in a shell with a triangular plan shape and three supports for different angles of wind incidence. To determine the distribution of surface pressure coefficients and lift and drag force coefficients, an experimental study was carried out in a wind tunnel, and a numerical simulation study was performed through computational fluid dynamics. The experimental and numerical results were analyzed and compared, and making it possible to identify the most critical surface zones and wind incidences when the shell is under the wind action. [ABSTRACT FROM AUTHOR]

Acceleration of objects in fluids widely exists in biological propulsions and contains rich unsteady fluid mechanisms. In this paper, the instantaneous drag force on accelerating normal flat plates (circular, elliptical, square, and rectangular plates) in a wide range of dimensionless acceleration ( a * = 1 6 ∼ 2) is measured, and the underlying mechanism for force generation is investigated. At first, we find that the drag force coefficient generally scales with the square root of a * when a * < 1.0 , coinciding with the scaling law given by Reijtenbagh et al. (PRL. 2023,130,174001). However, the drag force coefficient more linearly scales with a * rather than a * when a * > 1.0 , thereby indicating acceleration plays two distinct roles on the force generation depending on a * . Moreover, two scaling laws are built to quantitatively describe the two distinct roles of a * on the drag force generation. Based on fluid impulse, the drag force is largely contributed by the added mass of the accelerating plates (added mass force) and vorticity generation fed by the shear layer on the edge of the plates (vortex creation force). When a * < 1.0 , the vortex creation force scales with a * and almost contributes to the total drag force. When a * > 1.0 , the added mass force scaling with a * contributes to most of the drag force. Furthermore, the two force generation mechanisms associated with acceleration ( a * ) are independent, and a criterion based on the energy ratio is proposed to identify the transition of the two force generation mechanisms. The present results uncover the role of acceleration in force generation and explain the inconsistencies of using one quasi-steady model in describing the force on accelerating plates. [ABSTRACT FROM AUTHOR]

Offshore floating photovoltaic (FPV) systems are subjected to significant aerodynamic forces, especially during extreme wind conditions. Accurate estimation of these forces is crucial for the proper design of mooring lines and connection systems. In this study, detailed CFD simulations were performed for various PV panel configurations, and using these CFD simulation correlations were developed to estimate lift and drag forces as a function of the number of panels. These correlations provide valuable tools for designing large-scale FPV systems with multiple PV modules. Additionally, this study investigates the potential of using breakwaters to reduce aerodynamic forces on FPV systems. Breakwaters, typically used to mitigate wave impacts, can also serve as wind barriers, significantly reducing wind forces before they reach the FPV array. Aerodynamic simulations with and without a breakwater were conducted using CFD to assess this effect. The results show a substantial reduction in lift and drag coefficients, especially for angles of attack up to 10 degrees, demonstrating the effectiveness of the breakwater in protecting the FPV system. However, beyond this threshold, the effectiveness of the breakwater of 2 m reduces. These findings highlight the importance of strategic breakwater placement and heights and their role in enhancing FPV system resilience. The insights gained from this study are critical for optimizing breakwater design and placement, ensuring the structural integrity and performance of FPV systems in varying environmental conditions. The data generated will also contribute to future design improvements for floating PV systems. [ABSTRACT FROM AUTHOR]

The angle of attack plays a pivotal role in determining the performance of an aircraft wing, a critical component of its overall design. This angle, defined as the angle between the chord line of the wing and the relative wind direction, has a profound impact on the lift and drag forces experienced by the wing. When the angle of attack is low, the wing generates lift with minimal drag. However, at higher angles of attack, the wing encounters increased drag and may reach a stall condition. Understanding the influence of the angle of attack on an aircraft wing is crucial in both design and operation, significantly impacting the aircraft's capabilities in takeoff, climb, navigation, and landing. Therefore, a comprehensive comprehension of the relationship between the angle of attack and wing performance is imperative for ensuring safe and efficient aircraft operation. This study is dedicated to elucidating the effect of the angle of attack on aircraft performance, focusing on the variation in aerodynamic coefficients for two distinct airfoils. Employing Computational Fluid Dynamics (CFD) analysis via SolidWorks, the research examines NACA airfoil types, specifically NACA 2412 and NACA 4412, each featuring different cambers. The selected angles of attack for the investigation range from 0° to 20°, with a constant flow rate of 43 m/s. The findings reveal that the NACA 2412 airfoil exhibits a higher lift-to-drag ratio near to 20 compared to 6 in NACA 4412 airfoil. This insight provides valuable information for optimizing the aerodynamic performance of aircraft wings, contributing to the enhancement of overall efficiency and safety in aviation. [ABSTRACT FROM AUTHOR]

In this paper, a novel surrogate model for shape-parametrized vehicle drag force prediction is proposed. It is assumed that only a limited dataset of high-fidelity CFD results is available, typically less than ten high-fidelity CFD solutions for different shape samples. The idea is to take advantage not only of the drag coefficients but also physical fields such as velocity, pressure, and kinetic energy evaluated on a cutting plane in the wake of the vehicle and perpendicular to the road. This additional "augmented" information provides a more accurate and robust prediction of the drag force compared to a standard surface response methodology. As a first step, an original reparametrization of the shape based on combination coefficients of shape principal components is proposed, leading to a low-dimensional representation of the shape space. The second step consists in determining principal components of the x-direction momentum flux through a cutting plane behind the car. The final step is to find the mapping between the reduced shape description and the momentum flux formula to achieve an accurate drag estimation. The resulting surrogate model is a space-parameter separated representation with shape principal component coefficients and spatial modes dedicated to drag-force evaluation. The algorithm can deal with shapes of variable mesh by using an optimal transport procedure that interpolates the fields on a shared reference mesh. The Machine Learning algorithm is challenged on a car concept with a three-dimensional shape design space. With only two well-chosen samples, the numerical algorithm is able to return a drag surrogate model with reasonable uniform error over the validation dataset. An incremental learning approach involving additional high-fidelity computations is also proposed. The leading algorithm is shown to improve the model accuracy. The study also shows the sensitivity of the results with respect to the initial experimental design. As feedback, we discuss and suggest what appear to be the correct choices of experimental designs for the best results. [ABSTRACT FROM AUTHOR]

The movement of submerged flexible vegetation leads to an increase in resistance to the stream flow. In this study, a formula that can directly calculate the drag force on a highly flexible submerged vegetation, called Ceratophyllum, by using the vegetation swaying characteristics and the flow field information in a steady‐uniform open‐channel flow is derived. The drag force on submerged flexible vegetation is characterized by the time‐averaged flow velocity, turbulence intensity, and the additional force arising from the vegetation swaying. Based on the results of the numerical models in the previous studies (Wang et al., 2022a, 2022b, https://doi.org/10.1017/jfm.2022.598, https://doi.org/10.1017/jfm.2022.899), the drag coefficient is determined. It is revealed that the drag coefficient is influenced by a combination of factors, including the flow conditions, and the distribution and movement characteristics of vegetation. The drag coefficient decreases with an increase in velocity and is approximately linearly related to the cubic power of the bulk flow velocity. In the case of an inter‐plant spacing of 0.5 times the initial plant height, the drag coefficient ranges from 10.72 to 2.11, as the Reynolds number varies from 20,000 to 50,000. Besides, the vegetation distribution density and the relative submergence influence the drag coefficient. In this context, the drag coefficient decreases linearly with an increase in the inter‐plant spacing. For the Reynolds number equaling 50,000, the drag coefficient ranges from 2.11 to 2.02, when the inter‐plant spacing varies from 0.5 to 2 times the plant height, and from 2.47 to 1.79, when the flow depth varies from 1.5 to 3 times the plant height. Key Points: A formula for the drag force on submerged flexible vegetation in an open‐channel flow is proposedThe drag coefficient is inversely proportional to and linearly varying with the cubic power of the bulk flow velocityThe drag coefficient decreases with an increase in the inter‐plant spacing and the submergence depth [ABSTRACT FROM AUTHOR]

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]

Ideal tree exhibits fractal characteristics, where the branch angle plays a significant role in shaping the morphology of trees, thereby influencing their wind resistance capabilities. Nevertheless, investigation into the aerodynamic effects of branch angle on trees with leaves remains relatively scarce. By subjecting various tree morphologies to controlled wind conditions, this study scrutinizes the aerodynamic responses and resulting loads experienced by one-order sympodial trees with differing branch angle configurations. The results reveal that the tree experiences unstable oscillations induced by irregular leaf vibration with an increase in wind speed, resulting in a rise in drag coefficient. Meanwhile, despite a higher drag force observed in the tree with higher branch angle at wind speeds below 20 m/s, the tree exhibits superior reconfiguration capabilities, enabling it to withstand stronger winds effectively. Subsequently, a reconfiguration process for the one-order sympodial tree is proposed, exhibiting a wavy streamlining effect. Finally, it is found that the sympodial tree structure can be regarded as a high-frequency filter to dissipate high-frequency branch vibration energy. The findings from this research endeavor hold significant implications for enhancing our understanding of the aerodynamics of trees with different morphology and the cultivation and selection of urban trees. [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]

Purpose: An experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the subcritical range of Reynolds number 1 × 105 ≤ Re ≤ 1.8 × 105. To study the interaction effect, hemispherical shapes of various sizes are attached to the upriver of the D-shaped bluff body model. The diameter of the hemisphere (b1) varied from 0.25 to 0.75 times the diameter of the D-shaped model (b2) and its gap from the D-shaped model (g/b2) ranged from 0.25 to 1.75 b2. Design/methodology/approach: The experiments were carried out in a low-speed open-circuit closed jet wind tunnel with test section dimensions of 1.2 × 0.9 × 1.8 m (W × H × L) capable of generating maximum velocity up to 45 m/s. The wind tunnel is equipped with a driving unit which has a 175-hp motor with three propellers controlled by a 160-kW inverter drive. Drag force is measured with an internal six-component balance with the help of the Spider 3013 E-pro data acquisition system. Findings: The wind tunnel results show that the hemispherical forebody has a diameter ratio of 0.75 with a gap ratio of 0.25, resulting in a maximum drag reduction of 67%. Research limitations/implications: The turbulence intensity of the wind tunnel is about 5.6% at a velocity of 18 m/s. The uncertainty in the velocity and the drag coefficient measurement are about ±1.5 and ±2.83 %, respectively. The maximum error in the geometric model is about ±1.33 %. ractical implications: The results from the research work are helpful in choosing the optimum spacing of road vehicles, especially truck–trailer and launch vehicle applications. Social implications: Drag reduction of road vehicle resulting less fuel consumption as well as less pollution to the environment. For instance, tractor trailer experiencing approximately 45% of aerodynamics drag is due to front part of the vehicle. The other contributors are 30% due to trailer base and 25% is due to under body flow. Nearly 65% of energy was spent to overcome the aerodynamic drag, when the vehicle is traveling at the average of 70 kmph (Seifert 2008 and Doyle 2008). Originality/value: The benefits of placing the forebody in front of the main body will have a strong influence on reducing fuel consumption. [ABSTRACT FROM AUTHOR]

The drag force exerted on a body moving in a fluid is empirically known to follow a linear drag law at low Reynolds numbers and a quadratic drag law at very high Reynolds numbers. The major challenge with the empirical description of the drag lies in the uncertainty of the description of the drag coefficient as a function of velocity. If the function is precisely known, it may be possible to find a general formula for the drag, which would, in principle, be applicable for all Reynolds numbers. The general law can consequently be tested using the linear and quadratic drag laws within their validity regimes to confirm its reliability and validity. The current absence of such a general law implies that the prediction of the dynamics of a body moving under drag forces in the intermediate regime of the Reynolds number can only be approximate and inaccurate since it is not guided by any valid law. In this study, we derive a general relation for the drag force, which may be applicable in all the Reynolds number regimes. We achieve this through a simple transformation of Newton's second equation for uniformly decelerated motion. It turns out that our general relation is a modification of the linear drag law. The effect of the introduced correction term in the dynamics of a projectile is evidently promising, as can be seen in the more realistic results generated. [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]

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]

In this study, drag force and surface pressure measurements were conducted on a 1/32 scaled truck-trailer combination model. The experimental tests were carried out between the ranges of 312×10³-844×10³ Reynolds Numbers in a suction type wind tunnel. The aerodynamic drag coefficient (CD) and distribution of pressure coefficient (CP) were experimentally determined for the truck and trailer combination. The regions with a large amount of pressure coefficients were determined on the truck-trailer by using flow visualizations. The aerodynamic structure of truck-trailer combination models was improved by passive flow control methods on 4 different models. By using a newly designed spoiler on Model 1, the drag coefficient was reduced by 10.01 %. On Model 2, after adding a trailer rear extension with a spoiler, the reduction was obtained at 11.35 %. For the model 3 which is obtained by adding a side skirt to model 2, the improvement reached 18.85 %. The model 4 was composed of model 2 and a bellow between the truck and trailer. The drag force improvement was obtained at 22.80 % for model 4. [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]

This paper introduces a low-boom aircraft optimization design method guided by equivalent area distribution, which effectively improves the intuitiveness and refinement of inverse design. A gradient optimization method based on discrete adjoint equations is proposed to achieve the fast solution of the gradient information of target equivalent area distribution relative to design variables and to drive the aerodynamic shape update to the optimal solution. An optimization experiment is carried out based on a self-developed supersonic civil aircraft configuration with engines. The results show that the equivalent area distribution adjoint equation can accurately solve the gradient information. After optimization, the sonic boom level of the aircraft was reduced by 13.2 PLdB, and the drag coefficient was reduced by 60.75 counts. Moreover, the equivalent area distribution adjoint optimization method has outstanding advantages, such as high sensitivity and fast convergence speed, and can take both the low sonic boom and the low drag force of the aircraft into account, providing a powerful tool for the comprehensive optimization design of supersonic civil aircraft by considering sonic boom and aerodynamic force. [ABSTRACT FROM AUTHOR]

The initial flow past an impulsively started rotating and translating circular cylinder is asymptotically analysed using a Brinkman penalization method on the Navier-Stokes equation. In our previous study (J. Fluid Mech., vol. 929, 2021, A31), the asymptotic solution was obtained within the second approximation with respect to the small parameter, ϵ, that is of the order of 1/λ. Here, λ is the penalization parameter. In addition, the Reynolds number based on the cylinder radius and the translating velocity is assumed to be of the order of ϵ. The previous study asymptotically analysed the initial flow past an impulsively started translating circular cylinder and investigated the influence of the penalization parameter λ on the drag coefficient. It was concluded that the drag coefficient calculated from the integration of the penalization term exhibits a half-value of the results of Bar-Lev & Yang (J. Fluid Mech., vol. 72, 1975, pp. 625-647) as λ→∞. Furthermore, the derivative of vorticity in the normal direction was found to be discontinuous on the cylinder surface, which is caused by the tangential gradient of the pressure on the cylinder surface. The present study hence aims to investigate the variance on the drag coefficient against the result of Bar-Lev & Yang (1975). First, we investigate the problem of an impulsively started rotating circular cylinder. In this situation, the moment coefficient is independent of the pressure on the cylinder surface so that we can elucidate the role of the pressure to the hydrodynamic coefficients. Then, the problem of an impulsively started rotating and translating circular cylinder is investigated. In this situation, the pressure force induced by the unsteady flow far from the cylinder is found to play a key role on the drag force for the agreement with the result of Bar-Lev & Yang (1975), whereas the variance still exists on the lift force. To resolve the variance, an alternative formula to calculate the hydrodynamic force is derived, assuming that there is the pressure jump between the outside and inside of the cylinder surface. The pressure jump is obtained in this analysis asymptotically. Of particular interest is the fact that this pressure jump can cause the variance on the lift force calculated by the integration of the penalization term. [ABSTRACT FROM AUTHOR]

In this paper, using interfacial slip on the boundary, the exact solution is obtained for the Stokes flow through a couple stress fluid sphere which is embedded (implanted) in a porous medium with Brinkman's condition. Analytical computations are derived for the stream functions and drag. For the drag force, special conditions are deduced that satisfy the literature's facts. Graphs are created and the numerical results are tabulated. It is noticed that in the external viscous fluid case the porosity parameter and the drag coefficient are directly correlated and for the external couple stress fluid case with raises in slip parameter the coefficient of drag reduces. [ABSTRACT FROM AUTHOR]

Drag and lift are two important parameters to evaluate a vehicle's aerodynamic performance. Aerodynamic resistance (drag force Fd) prevents the movement of the vehicle and has a value proportional to the square of the velocity. That is, when the speed increases twice, the aerodynamic drag will increase fourfold. This article presents a plan to design a sport utility vehicle model with improved aerodynamics by using Ansys Fluent software to analyze pressure distribution areas that affect aerodynamics and the body. Based on the results obtained, the areas of stress and maximum pressure concentration have been identified. From this, a plan to improve the vehicle's exterior design has been proposed. After many iterations of the design and model optimization process, the aerodynamic drag coefficient CD was reduced by 3.06% compared to the original model. The revised design option is equipped with an airflow diffuser under the vehicle; the lifting resistance coefficient has been reduced from 0.0902 to 0.038, equivalent to 58.2%. The new proposed design of the model has reduced the vehicle's frontal drag by 2.04%. The research results have determined the aerodynamic coefficients CD and CL of the model car. Based on the results received, it is possible to compare them with the manufacturer's announced parameters and propose new design options that still ensure aesthetics. [ABSTRACT FROM AUTHOR]

This paper focuses on the hydrodynamic interaction between a semipermeable spherical particle and a laminar flow of couple stress fluid. The framework of the flow is divided into two regions, in which the non‐Newtonian characteristics of the couple stress fluid are governed by classical Stokes equations and the permeable region is governed by Darcy's law. The asymptotic series expansion involves the stream functions in terms of modified Bessel's function and Gagenbauer's polynomials for the inner and outer regions. The graphical analysis demonstrating the superior outcomes of numerous parameters such as the couple stress parameter, the permeability parameter, and the couple stress viscosity ratio on the drag coefficient is conducted, and the outcomes are discussed comprehensively. The present study discovered that the drag of a semipermeable sphere is greater than that of a couple stress fluid sphere. A continuous reduction in the pressure distribution is observed with the rising value of the couple stress parameter. However, an increasing value of the couple stress parameter in the semipermeable medium contributes to increasing the tangential stress with respect to the distance from the surface. The current study's findings could be useful in analyzing significant clinical and industrial applications such as the filtration process for wastewater treatment, the design of the digestive system, fluid–solid disperse systems, and the petroleum industry. However, experimental verification is required for the proposed work. [ABSTRACT FROM AUTHOR]

We investigate the three-dimensional (3-D) flow around and through a porous screen for various porosities at high Reynolds number Re = O(104). Historically, the study of this problem has been focused on two-dimensional cases and for screens spanning completely or partially a channel. Since many recent problems have involved a porous object in a 3-D free flow, we present a 3-D model initially based on Koo & James (J. Fluid Mech., vol. 60, 1973, pp. 513-538) and Steiros & Hultmark (J. Fluid Mech., vol. 853, 2018 pp. 1-11) for screens of arbitrary shapes. In addition, we include an empirical viscous correction factor accounting for viscous effects in the vicinity of the screen. We characterize experimentally the aerodynamic drag coefficient for a porous square screen composed of fibres, immersed in a laminar air flow with various solidities and different angles of attack. We test various fibre diameters to explore the effect of the space between the pores on the drag force. Using PIV and hot wire probe measurements, we visualize the flow around and through the screen, and in particular measure the proportion of fluid that is deviated around the screen. The predictions from the model for drag coefficient, flow velocities and streamlines are in good agreement with our experimental results. In particular, we show that local viscous effects are important: at the same solidity and with the same air flow, the drag coefficient and the flow deviations strongly depend on the Reynolds number based on the fibre diameter. The model, taking into account 3-D effects and the shape of the porous screen, and including an empirical viscous correction factor that is valid for fibrous screens may have many applications including the prediction of water collection efficiency for fog harvesters. [ABSTRACT FROM AUTHOR]

Savonius, a type of vertical-axis wind turbine, is a small-scale energy conversion device suitable for low wind speeds, such as those characteristic of Indonesian wind speeds, yet has low efficiency. Savonius is a drag-type turbine. Drag force on the surface is affected by roughness or wavyness. The purpose of this study is to analyze the impact of applying wavy (zigzag) variations to the concave surface of Savonius blades on their performance. This was achieved by the use of 3D computational fluid dynamics simulation at TSR 0.6 with a velocity inlet of 5 m/s. The model was semicircular, zigzag on the concave surface on semicircular with t = 0.75, t = 0.25, and t = 1 mm. The result of this study's CRDR maximum is 1,817 at the zigzag model with t = 1 and CRDR avrg =1.24. The average drag coefficient increased by 14 percent compared to the conventional semicircular rotor. The maximum Cp value is also found at t = 1 mm, which is 0.315. The power coefficient increased by 29 percent compared to the conventional semicircular rotor. The total pressure on the blade shows the highest model with t = 1 mm at the same angle of attack (a = 30). Zigzag on the concave surface affects blade pressure, which improves the performance of the Savonius rotor. [ABSTRACT FROM AUTHOR]

In this study, models for the wake capture lift and drag force coefficients of a hovering flapping wing were presented using numerical fluid dynamics simulation to improve the blade element theory. The investigated wing is inspired by the fruit fly and has combined flapping and pitching movements. The effect of changing the wing acceleration time at the start (Δ τ A ) and end of the half cycle (Δ τ D ), as well as the Reynolds numbers in the range of 136–6800, on wake capture using the Taguchi orthogonal array test design, is investigated using the numerical fluid dynamics method, and the values of average lift and drag coefficients due to wake capture are obtained. These force coefficients were applied to linear and nonlinear regression methods to obtain the mathematical model, and a model for its changes was extracted. Finally, to obtain the instantaneous coefficients, the extracted models were placed in the normal distribution function, and the final instantaneous model was obtained. Examining the verification cases of the application of these wake capture relationships with the blade element theory, as well as the effects of translational force, rotational force and added mass force, revealed that this developed theory is capable of correctly predicting the wake capture force's initial peak. The force coefficient trend in the final quasi-steady model with wake capture is similar to the computational fluid dynamics (CFD) results, according to a qualitative examination of the lift and drag force coefficients in a half cycle. This demonstrates a significant result: this theory, which is divided into four parts: transnational, rotational, added mass and wake capture, adequately covers the general physics of these complex movements. [ABSTRACT FROM AUTHOR]