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In this study, the round-trip motion of air-rich bubbles exhaled from a water vapor-rich bubble was investigated. The local heating of non-degassed water produced a vapor-rich bubble with a maximum diameter of 9 μ m, which intermittently exhaled air-rich bubbles with a radius of less than 1 μ m. The exhaled air-rich bubbles initially moved away from the heat source; however, as the air-rich bubbles fused and grew larger, they returned to the heat source and fused with the vapor-rich bubble. This round-trip motion of the air-rich bubbles is explained by the balance between the Marangoni and quasi-steady drag forces induced on the bubbles. As the quasi-steady drag force is approximately proportional to the bubble radius and the Marangoni force is proportional to the square of the bubble radius, a larger bubble correlates with a greater effect of the Marangoni force. To produce a quasi-steady drag force that can balance the increased Marangoni force, air-rich bubbles were attracted to the heat source against the flow created by the vapor-rich bubble. These results provide insight into the stabilization of water-vapor-rich microbubbles in non-degassed water, which can generate strong flows on the order of 1 m/s. [ABSTRACT FROM AUTHOR]

In this paper, a homogenized multiphase lattice Boltzmann (LB) model is established for parallelly simulating immiscible two-phase flow in both solid-free regions (pore scale) and porous areas (continuum scale). It combines the color-gradient multiphase model with the Darcy–Brinkman–Stokes method by adding a term that includes surface force and drag force of porous matrix to multiple-relaxation-time LB equation in moment space. Moreover, an improved algorithm is proposed to characterize and implement the apparent wettability in the locally homogenized porosity field. Validations and test cases are given to demonstrate the accuracy and robustness of this new model, as well as its applicability for trans-scale fluid simulation of transport and sorption behavior from porous (Darcy flow) area to free (Stokes flow) area. For practicality, the two-phase seepage flow in a composite rock structure with multiscale pores is simulated by this new model, and the effects of viscosity ratio and wettability on the displacement process are discussed. [ABSTRACT FROM AUTHOR]

This study investigates acoustic radiation forces on spherical objects generated by Bessel beams in a viscous fluid. Radiation forces on elastic spheres and shells of different materials are examined using viscid expression with the thermoviscous correction included, and the results are then compared with numerical simulations based on the finite element method. The Stokes drag force for zero-order Bessel waves was theoretically derived, and in turn, a practical example of negative radiation forces is proposed and investigated together with the gravity, the buoyancy, and the drag force from acoustic streaming. It is found that the negative pulling force exists even including the positive forces from the other sources; however, the parameter regions for pulling forces are reduced especially for small objects. This work helps the further study of particle manipulations by acoustic Bessel beams in viscous fluids and also guides the experimental realization of acoustic tractor beams. [ABSTRACT FROM AUTHOR]

Nanomaterials have achieved considerable prominence owing to their numerous applications such as thermal transport, heat exchangers, nuclear reactor cooling, paper production, microelectronics, thermal power plants, and architecture. Because of such thermal applications, the prime objective of the present analysis is to scrutinize the unsteady Darcy–Forchheimer flow of nanoliquid with Lorentz force. Stretching of the surface creates flow motion. Here three different types of nanoparticles, aluminum oxide ( $ \textrm{A}{\textrm{l}_\textrm{2}}{\textrm{O}_\textrm{3}} $ A l 2 O 3 ), copper ( $ \textrm{Cu} $ Cu ), and titanium dioxide ( $ \textrm{Ti}{\textrm{O}_\textrm{2}} $ Ti O 2 ), are used. Furthermore, water ( $ {\textrm{H}_\textrm{2}}\textrm{O} $ H 2 O ) is used as a base fluid. Heat expression is discussed through dissipation, radiation, heat generation, and Joule heating. Physical interpretation of entropy generation is discussed. The nonlinear partial system is reduced to a dimensionless ordinary system by appropriate dimensionless parameters. The resultant system is then solved by a numerical scheme (bvp4c technique). The influences of various involved parameters on entropy rate, velocity profile, and temperature are graphically examined. Drag force and thermal transport rate against flow variable are discussed. A larger Forchheimer number reduces velocity profile. A reverse trend is noted for temperature and velocity against volume fraction variable. An increment in magnetic variable augments entropy rate and temperature.. An improvement in entropy analysis is noted for Reynold number. Thermal transport rate declines for a higher stretching variable. An enhancement in entropy rate and temperature is noticed for radiation variable. An amplification in drag force is observed through volume fraction. An augmentation in magnetic effect leads to decline the thermal transport rate. Comparative studies for different nanoparticles are done. [ABSTRACT FROM AUTHOR]

Anaerobic membrane bioreactors (AnMBRs) have emerged as an effective technology for treating domestic and industrial wastewater. However, AnMBRs typically exhibit low membrane fluxes (<10 L/m2.h), which limits their wide application. Despite the use of various techniques to control membrane fouling, the relationships among these techniques and the challenges associated with their application remain unclear. Current literature categorizes membrane fouling control approaches into four classes, namely a reduction in the concentration of soluble microbial products (SMP), an increase in shear, an increase in particle size, and membrane optimization. Biological techniques are effective in reducing the concentration of SMP but limit the flexibility of reactor operation. The remaining three methods are non-biological techniques. Shear-induced lift force, permeation drag force, and the xDLVO theory on microparticles can be used to elucidate the mechanisms of these non-biological techniques, except for dynamic membranes. This indicates that other proposed additional forces may be disregarded. Non-biological techniques are associated with high energy costs and membrane damage. Hydrophilic membranes are effective but super-hydrophilic membranes have not been used in AnMBRs. Different materials rather than the membrane should be applied to create an electronic field for membrane fouling control. The application of dynamic membrane should not result in biofouling of a downstream water treatment process. Among current techniques, dosing flocculant is the most promising method for controlling membrane fouling, but developing an auto-flocculant dosing strategy is vital. Overall, this article provides an overview of current membrane fouling strategies and reveals their inherent relationships and challenges for their applications. [ABSTRACT FROM AUTHOR]

To improve the aerodynamic efficiency of the aircraft, the article focuses on optimizing the L/D ratio through postponement of flow separation. Elevating the L/D ratio leads to diminished drag and delays stall occurrence at high angles of attack (α). The wing geometry adopts NACA 6-digit airfoils, specifically NACA 63418 and NACA 63415. Various aerodynamic devices are explored for their ability to defer flow separation, with passive aerodynamic devices being the prevalent choice. The primary goal of the research is to integrate rotational thin wire elements into the aerodynamic components of the wing, aiming to diminish drag, amplify lift, and enhance overall aerodynamic performance. The analysis spans a range of α, from 0° to 20°. The study encompasses two scenarios: one without the incorporation of aerodynamic devices and the other with their implementation. Comparative analyses of increases in CL and reductions in CD, with notable improvements observed at a 15o angle of attack, 28.47% increase in CL and 15.07% decrease in CD. Furthermore, the improved performance in the CL/CD, which increases substantially in stall conditions, thereby demonstrating the potential of these aerodynamic modifications to enhance overall aircraft performance. [ABSTRACT FROM AUTHOR]

We propose a novel framework for simulating ink as a particle-laden flow using particle flow maps. Our method addresses the limitations of existing flow-map techniques, which struggle with dissipative forces like viscosity and drag, thereby extending the application scope from solving the Euler equations to solving the Navier-Stokes equations with accurate viscosity and laden-particle treatment. Our key contribution lies in a coupling mechanism for two particle systems, coupling physical sediment particles and virtual flow-map particles on a background grid by solving a Poisson system. We implemented a novel path integral formula to incorporate viscosity and drag forces into the particle flow map process. Our approach enables state-of-the-art simulation of various particle-laden flow phenomena, exemplified by the bulging and breakup of suspension drop tails, torus formation, torus disintegration, and the coalescence of sedimenting drops. In particular, our method delivered high-fidelity ink diffusion simulations by accurately capturing vortex bulbs, viscous tails, fractal branching, and hierarchical structures. [ABSTRACT FROM AUTHOR]

Stellar-driven galactic winds regulate the mass and energy content of star-forming galaxies. Emission- and absorption-line spectroscopy show that these outflows are multiphase and comprised of dense gas clouds embedded in much hotter winds. Explaining the presence of cold gas in such environments is a challenging endeavour that requires numerical modelling. In this paper, we report a set of 3D hydrodynamical simulations of supersonic winds interacting with radiative and adiabatic multicloud systems, in which clouds are placed along a stream and separated by different distances. As a complement to previous adiabatic, subsonic studies, we demonstrate that hydrodynamic shielding is also triggered in supersonic winds and operates differently in adiabatic and radiative regimes. We find that the condensation of warm, mixed gas in between clouds facilitates hydrodynamic shielding by replenishing dense gas along the stream, provided that its cooling length is shorter than the cloud radius. Small separation distances between clouds also favour hydrodynamic shielding by reducing drag forces and the extent of the mixing region around the clouds. In contrast, large separation distances promote mixing and dense-gas destruction via dynamical instabilities. The transition between shielding and no-shielding scenarios across different cloud separation distances is smooth in radiative supersonic models, as opposed to their adiabatic counterparts for which clouds need to be in close proximity. Overall, hydrodynamic shielding and re-condensation are effective mechanisms for preserving cold gas in multiphase flows for several cloud-crushing times, and thus can help understand cold gas survival in galactic winds. [ABSTRACT FROM AUTHOR]

In this paper, we study the Cauchy problem of a two-phase flow system consisting of the compressible isothermal Euler equations and the incompressible Navier-Stokes equations coupled through the drag force, which can be formally derived from the Vlasov-Fokker-Planck/incompressible Navier-Stokes equations. When the initial data is a small perturbation around an equilibrium state, we prove the global well-posedness of the classical solutions to this system and show the solutions tends to the equilibrium state as time goes to infinity. In order to resolve the main difficulty arising from the pressure term of the incompressible Navier-Stokes equations, we properly use the Hodge decomposition, spectral analysis, and energy method to obtain the L 2 time decay rates of the solution when the initial perturbation belongs to L 1 space. Furthermore, we show that the above time decay rates are optimal. [ABSTRACT FROM AUTHOR]

This paper discusses the high heat transfer demand from application prospects. Hybrid nanofluid is a well-known liquid with higher heat transfer capabilities. Here, the time-dependent flow of hybrid nanocomposite, by hybridizing the metal (Cu) and metallic oxide (Al2O3) and inserting them into water-based nanofluid, is examined. The flow takes place over the upper half of a parabolic surface. The modified Buongiorno model is used to express the physical phenomenon in mathematical equations form. The governing system of partial differential equations (PDEs) is reduced to a system of ordinary differential equations (ODEs) by applying certain transformations. Computation of the final equations has been done by a numerical scheme, known as the Keller-box method. The significance of dimensionless flow causing physical parameters is shown through graphs and tables. The findings reveal that among the hybrid nanofluids with two types of nanoparticles varying from 0% to 5%, a nanofluid having 5% of both nanoparticles is the one with the maximum surface drag force and heat transport rate, which are 41.8% and 22.7% higher to water, respectively. A higher amount of Al2O3 than Cu results in a suitable hybrid combination for application purposes to produce higher cooling rate with less surface drag. Also, the thickness of the surface, unsteadiness, nanoparticles suspension and power index of wall temperature enhance the heat transfer rate. Thin parabolic surfaces experience less drag and have larger boundary layer thicknesses (momentum, thermal and concentration) as compared to thicker parabolic surfaces. Also, the addition of copper slows down the hybrid fluid flow field, but alumina magnifies the mobility of hybrid fluid. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of the flutter kick on the propulsive force generated by a stroke. Eight male swimmers performed 20 m front crawl trials under two conditions: the Whole Condition, involving maximum effort (T100%) and stroke frequencies at 70, 80, and 90% of T100%, and the Arm Condition, which excluded the flutter kick and matched stroke frequencies with the Whole Condition. Various parameters, including swimming velocity, stroke frequency, stroke length, three-dimensional (3D) resultant hand speed, and hand propulsion were calculated based on underwater 3D motion analysis and hand pressure distribution measurements. A two-way repeated-measures ANOVA was conducted to assess differences, considering the conditions and instructed frequencies as the two factors. There was no significant interaction between the condition and intensity for any of the variables. There was a significant main effect of condition on swimming velocity and stroke length, with these variables being 16.9–18.5% higher and 17.3–19.5% longer, respectively, in the Whole Condition compared to the Arm Condition. However, there was no difference in hand propulsion between the conditions, and it was clarified that the flutter kick did not affect hand propulsion at any swimming velocity. [ABSTRACT FROM AUTHOR]

The optomechanical motion of a gold nanoparticle (GNP) dimer—a pair of optically bound GNPs—in fluid, manipulated by a Bessel beam, is theoretically studied using the multiple multipole (MMP) method. Since a Bessel beam possesses orbital angular momentum (OAM) and spin angular momentum (SAM) simultaneously, complicated rigid-body motions of the dimer can be induced. The mechanism involves the equilibrium between the optical force with the reactive drag force exerted by the fluid. Our results demonstrate that the dimer rotates around its center of mass (COM), while the COM performs an orbital revolution around the optical axis. Additionally, each individual GNP undergoes spinning. The directions of the GNPs' spin and the orbital revolution of COM depend on the handedness and the order (topological charge) of Bessel beam, respectively. Nevertheless, the rotation direction of the dimer depends on the size of GNP. In the case of a smaller dimer, the direction of dimer's rotation with respect to the COM is consistent with the handedness of the light. Conversely, a larger dimer performs a reverse rotation, accompanied by a precession during the orbital revolution. There are multiple turning points in the radius of the GNP for the alternating rotation of the dimer caused by positive or negative optical torque. Our finding may provide an insight to the optomechanical manipulation of optical vortexes on the motions of GNP clusters. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the problem of starvation lubrication of high-speed ball bearings due to temperature rise during operation and to avoid thermal failure of bearing lubrication. Design/methodology/approach: Under the quasi-statics model of grease lubrication, both the oil film dragging force and the rolling friction between the balls and raceways collectively counteract the gyroscopic torque. Initially, the static model for grease lubrication is solved, followed by calculating the generated heat using the local heat generation method and ultimately the multinodal thermal network model is solved, and the solved results of the quasi-statics are updated by the temperatures of the grease nodes based on the relationship of the grease temperature and viscosity, as well as the relationship of the viscosity and the film thickness. Findings: By comparing the numerical calculation results of bearings under different working conditions, the influence of starvation lubrication on the oil film thickness, oil film drag force and rolling friction of bearings is discussed, and it is found that the numerical calculation results of the outer ring temperature of bearings under the starvation lubrication due to the consideration of temperature rise are closer to the experimental values. Originality/value: This study reveals the dynamic characteristics of bearings under starvation lubrication, which is more practical and engineering guiding significance for the design of bearings, and introduces a new method and basis for the calculation of temperature rise of rolling bearings. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2024-0208/ [ABSTRACT FROM AUTHOR]

This study examines the influence of thermal radiation and heat source/sink of the tangent hyperbolic fluid on EMHD boundary layer flow through stretching sheets. Motile gyrotactic microorganism is considered in the fluid flow and the flow is analyzed with the impact of thermal radiation, heat source/sink, and electromagnetohydrodynamic. By utilizing the proper similarity transformations, partial differential systems are converted to ordinary differential systems. The Runge–Kutta fifth‐order method with shooting technique is used in the converted systems to solve numerically. Velocity, temperature, concentration, and microorganism density profile are discussed and represented graphically. The numerical values of drag force rate, heat transfer rate, mass transfer rate, and density of motile microorganisms are specified, compared, and results enhancement in heat transfer rate as 64.31% by radiation parameter, mass transfer rate as 97.28% by heat source/sink parameter and microorganism density rate as 28.33% by Peclet number, respectively. The buoyancy parameter diminishes the drag force by 30.39%. The multiple and quadratic regression coefficient for adjusted R2${R}^2$, multiple R2${R}^2$, residual standard error, F‐statistic, and p‐value is estimated for skin friction, Nusselt number, Sherwood number, and density of microorganism. It has significant applications which are widely used to transport biological material in bio‐microfluidics, enhance heat dissipation in high‐performance electronics, thermal management systems on spacecraft and satellites, and solar energy systems. [ABSTRACT FROM AUTHOR]

A deep understanding of the behavior of nonmetallic inclusions is essential for steel cleanliness control. The behavior of alumina inclusions at the liquid iron/argon gas interface is investigated using a high‐temperature confocal scanning laser microscope. The obtained images are used to determine the moving velocity of the inclusions on the interface. The obtained experimental data are quantitatively evaluated using the lateral capillary interaction model for multipole orders established by Danov–Kralchevsky while taking into account the resistive drag force. The attraction forces calculated from these data are in the range between ≈10−13 and ≈10−11 N. The best‐fitting model is assigned for each case. The multipole models almost counterbalance the drag force, indicating a good interpretation of the interaction between the inclusions. Moreover, the acting length of this interaction is examined and compared to the previous work on Ce2O3 inclusions. It is found that alumina inclusions generally exhibit a larger acting length at a large critical radius and a smaller acting length at a small critical radius when comparing them to their counterpart cerium oxide inclusions. Considering the particle shapes, high shape irregularity is better interpreted by higher orders of the multipoles. [ABSTRACT FROM AUTHOR]

Accurately determining the flow direction of drilling fluid in maxi-horizontal directional drilling (maxi-HDD) is essential for the precise calculation of parameters such as the minimum pressure required for drilling fluid circulation, volume of return drilling fluid, drag force of the drilling fluid, and borehole pressure. We propose a novel method for determining the flow direction and computing these physical parameters in maxi-HDD using the Bingham plastic model. An engineering case study was conducted to validate the applicability of the method. We analyzed the variation patterns of the minimum pressure required for drilling fluid circulation, flow rate, the drag force of the drilling fluid, and borehole pressure during the pipeline installation process. Furthermore, a parametric study was conducted to assess the influence of factors such as reaming, reaming differential, bentonite concentration, and the elevation difference between the bore entry and exit points on drilling fluid flow. The proposed method considers a wide range of parameters, including flow direction, elevation difference, and other relevant parameters. It offers a comprehensive tool for analyzing drilling fluid flow in maxi-HDD. [ABSTRACT FROM AUTHOR]

Satellites in very low Earth orbits can leverage the aerodynamics forces for control purposes. Three-axis attitude control can be achieved by adjusting the orientation of aerodynamic surfaces, benefiting from both drag and lift forces. However, complete control over the orbital motion of a satellite is unattainable using aerodynamic forces alone, as positive thrust cannot be generated. Nonetheless, this limitation does not apply when focusing on the control of a satellite formation. By properly modulating the orientation of panels, positive and negative relative forces can be generated. This paper shows that even in a formation of simple microsatellites, it is possible to achieve formation and attitude simultaneous control by using no other actuators than the aerodynamics surfaces. • Very Low Earth orbits are appealing but the large atmospheric density can be a problem. • The atmospheric forces can be used for control purposes. • Formation control and attitude control can be individually realized by using aerodynamic forces. • A GNC architecture is implemented to realized both goals with the same aerodynamic actuators. • Performance in keeping or acquiring a desired state (attitude and relative position) is promising. [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]

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]

A new autonomous underwater vehicle (AUV) has high maneuverability near the bottom and a direction turnaround ability, called the autonomous underwater helicopter (AUH). This paper numerically investigates the hydrodynamic performance of the AUH. A Reynolds-Averaged Navier–Stokes (RANS) equation, a computational fluid dynamics (CFD) technique, is applied to analyze the AUH's behavior. Investigations of the AUH's hydrodynamic characteristics become more obvious with a service speed in the range of 0.4–1.2 m/s. For the same velocity condition, the resistance of the AUH increases, and the irregular eddy at the rear of the AUH expands with changes in the angles of attack and the length/height ratio. Essential design characteristics including pressure, velocity distribution, and velocity streamlines are shown and analyzed. These insights can be used as a guideline to reduce drag force and optimize the AUH profile for future designs. It has great potential for improving the AUH's control algorithms. [ABSTRACT FROM AUTHOR]

The air-sea UAV is made to be able to fly, change from land to water, and navigate through submerged water. However, as it moves from the air to the water, it experiences a significant impact force. The UAV's structure and components run the risk of being harmed by this strong impact force. The accelerations and forces involved in the transition process must therefore be understood through quantitative research. The method was created using computational fluid dynamics (CFD), which can manage the process of water entry. The simulation and calculations were carried out using the Fluent software suite from ANSYS Inc. The research examined the UAV's wing and center bodies independently and separately. 3-D models were used for the analyses of the center body, while 2-D models were used for the wing-body analyses. The transition flow and submerged methods were taken into consideration in obtaining the impact load that a body experiences when transitioning into water. Because it was substantiated using experimental results from prior studies, the transient-time analysis-based transition technique was shown to be reliable. The steady-state analysis of the submerged flow method can be used to quickly comprehend the pressure and velocity distribution over a body immersed in or entering the water. However, because it fails to account for the water's initial acceleration upon entry, the steady-state simulation underestimates the drag force. The submerged flow method's findings indicate that a sharp nose centre body diminishes drag more successfully. The transition method evaluations for the UAV slender body reveal controllable drag and impact forces. Furthermore, the study demonstrates that wedge-shaped leading edges for the wing-body reduce impact but may not be optimal when considering airlift. As a result, this research provides useful data for air-sea UAV structural design and movement conditions. [ABSTRACT FROM AUTHOR]

The combined effects of particle concentration (0–20 vol%) and particle size on the hydrodynamics of a slurry bubble column were studied by computational fluid dynamics coupled with population balance model (CFD‐PBM) in a wide range of superficial gas velocity (0.02–0.20 m/s). This CFD‐PBM coupled model included multiple effects of particles, namely increased slurry viscosity, reduced drag force, promoted bubble coalescence, and attenuated liquid turbulence, among which turbulence attenuation was crucial. To quantify liquid turbulence attenuation, a mechanistic model was established by equating the energy dissipated by particle motion to the attenuated liquid turbulence energy calculated from turbulent energy spectrum. The turbulent energy dissipation rate was reduced by over 60% at a solid concentration of 20%. Using this model, the effects of particle concentration and particle size on overall gas holdup were well predicted. This model advanced our understanding of how particles affect the gas holdup in a slurry bubble column. [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]

As a means of influencing technological advancements in engineering applications and various fluid products, the generalized Fourier's and Fick's models have proven to be of great importance. Industries such as power station engineering, high thermal material processing, and bio-heat elements apply the concept of anomalous heat and mass transfer mechanism. The objective of this study is to stimulate the flow of a radiative magnetohydrodynamics Jeffery fluid over an expanding surface with anomalous heat and mass transfer dynamics subjected to nth order reaction and variable thermophysical properties. A set of similarity transformations is used to neutralize the governing equations into a nondimensionless form. To obtain the model parametric analysis, a numerical tool via the spectral local linearization method (SLLM) is deployed after transformation of the governing flow equation from a two-unknown partial differential equations to a one-variable ordinary differential equation. It is observed that the thermal boundary layer thickness is found to be enhanced with increasing parametric values of magnetic, Eckert and radiation parameters. For the radiation parameter R ∈ [ 0. 5 0 , 2. 5 0 ] , the skin drag force, Nusselt and Sherwood number increase by 0. 6 1 % , 4 8. 0 0 % and 0. 9 1 % , respectively. Additionally, a 2 0 0 % increment in the nth order parameter boosts the rate of heat transfer by 0. 7 8 %. while it downsizes the Sherwood number by 1 4. 3 2 %. [ABSTRACT FROM AUTHOR]

The development of magnetic separation technology using magnetic nanoparticles offers a promising avenue for targeted drug delivery and dealing with the upcoming water crises, environmental pollution and the gradual mineral resource depletion. In this study, a three-dimensional Lagrangian Discrete Phase Model (DPM) is carried out to simulate the performance of Fe3O4 nanoparticles to improve the separation process under the influence of an external magnetic field within a horizontal pipe. The crucial role of the drag force in capture efficiency (CE) prompted its examination, simulating various drag models for groups of particles. The Stokes-Cunningham model, showing a 3.59% average error is a suitable choice compared to experimental results. The research examines the impact of effective parameters, including flow velocity, magnetic field intensity, wire location, particle size and mass flow rate, and pipe diameter on CE and flow pattern. The results show that increasing nanoparticle concentration reshapes the flow pattern due to secondary flows without significantly changing separation efficiency. Moreover, decreasing flow velocity, diminishes drag force and enhances magnetic force impact. Specifically, reducing the velocity to a third increases CE by 37%. Furthermore, capture capacity varies approximately linearly with electric current. Due to the magnetic force's role as a volumetric force in interphase momentum transfer, the increase in particle size from 200 to 500 nm at 3 × 105 A enhances CE by nearly 50%. However, increasing the pipe diameter diminishes particle capture, attributed to higher Reynolds numbers. According to the results, the impact of increasing magnetic field intensity and particle size on CE improvement is notably more pronounced compared to the effect of flow velocity reduction. A comparative analysis of three injection types reveals that using the group injection type helps to select an appropriate injection location to increase CE and identify the final positions of nanoparticles. [ABSTRACT FROM AUTHOR]

Cilial pumping is a potent mechanism used to control and manipulate fluids on microscales. Recently, we introduced an electronically driven μ-cilial platform that can create arbitrary flow patterns in liquids near a surface with the potential for various engineering applications. This μ-cilial platform, however, utilized the coupling between elasticity and viscous drag to obtain pumping and had several limitations. For example, each cilium could only pump in one direction. Thus, to create bidirectional flows, it was necessary to fabricate and separately actuate two oppositely facing cilia. As another example, the generation of non-reciprocal cilial motions, a necessary condition for pumping at these scales, could only be achieved by matching the elastic stresses inherent in actuating the cilia with the viscous drag forces generated by the flows. This criterion severely restricted the frequency range over which the cilia could be operated and resulted in a small swept area, both of which restricted the volume of fluid being pumped in each cycle. These limitations contrast with the capabilities of natural cilia, which can achieve omnidirectional transport and operation over a broad range of frequencies. In natural cilia, these capabilities arise from their complex internal structure. Inspired by this strategy we designed hinged cilia and show they can achieve bidirectional pumping of larger fluid volumes over a broad range of frequencies. Finally, we demonstrate that even regular arrays of individually controlled hinged cilia can generate a variety of flow patterns using fewer cilia than in previous cilia metasurface designs. [ABSTRACT FROM AUTHOR]

The results of a numerical study of the configuration of chains of dust particles levitating in a gas-discharge plasma are presented. The studies have been carried out using an iterative model that self-consistently describes the motion of ions and dust particles under the action of an external electric field, an electric field (Coulomb) of each charged dust particle, a field of the plasma space charge (ions and electrons), which screens the charges of dust particles, and gravity for dust particles. The structural parameters of the chains of dust particles were calculated for different numbers of particles in them. It was found that when new particles are added to the chain, the center of the chain rises above the lower electrode. This is due to both a decrease in the charges of the lower dust particles due to the focusing of positively charged ions behind the upper particle, and a significant decrease in the ion drag force on the lower particles of the chain as a result of structural rearrangement of the entire chain. It is shown that the reduced charge of the chains decreases, and the reduced length of the chains has a maximum depending on the number of particles. [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]

The forebody length of a supercavitating vehicle requires careful consideration during the design process. Variations in this dimension have the potential to profoundly influence the supercavitation characteristics. In this numerical study, we qualitatively and quantitatively explore the characteristics of natural and ventilated supercavitating flow under various forebody lengths. We use the multiphase volume-of-fluid method and the large-eddy simulation framework coupled with the Schnerr–Sauer cavitation model. Three forebody lengths (LF = 10dc, 15dc, and 20dc, where dc is the diameter of the cavitator) are applied to the test model. The numerical simulations effectively predict variations in supercavity geometry, hydrodynamic force, and supercavitating internal flow under the influence of the forebody length. The results indicate that the time required to generate a clear supercavity for the model with a 10dc forebody length is ∼6% and 9% less than for the 15dc and 20dc forebody length models, respectively. Additionally, the 10dc forebody length model experiences about 5% smaller total drag force compared to the longer models. The variations in forebody length significantly influence the supercavitating internal flow and pressure distribution inside the supercavity. Specifically, the ventilation air is distributed as an outer layer of the supercavity for the 10dc forebody length model, whereas it moves along the surface of the models with 15dc and 20dc forebody lengths. In terms of pressure distribution, the 10dc forebody length model exhibits the highest local pressure compared to the models with longer forebody lengths. These observations provide insights into the physical mechanisms underlying the effects of forebody length on supercavity characteristics. [ABSTRACT FROM AUTHOR]

The double-row hydraulic sluicing model is widely used in deep-sea mining collecting systems. However, there has been limited research focusing on its flow contributions and the relationship with particle motions. In this paper, a double-row hydraulic sluicing collector with high pickup efficiency is designed. The flow characteristics, the mechanics of the flow field, and the movement of particles in the collector are analyzed in detail through numerical calculations and experiments. The flow contributions and the collecting mechanism are clearly highlighted through aspects such as the frequency of pressure fluctuations and flow-induced vortices. The high-speed jet rolls upward after hitting the ground, forming a high-pressure area on the ground. The upwelling in the collection area is generated by the combination of the high-pressure area and the upward rolling of fluid. Regarding the particles, it is observed that particle motion can be divided into two main stages, rapid acceleration, followed by slow deceleration. Some particles may fall back when rising. Additionally, the analysis of fluid forces on the particles indicates that drag force and pressure gradient force have significant influence on particle motion. [ABSTRACT FROM AUTHOR]

The dynamics of liquid droplets surfing over the surfactant-infested free surface of another liquid have been explored experimentally. We analyze the motion of oil droplets that has been initiated through the creation of a surface tension gradient resulting from the deposition of a drop of surfactant at the water surface contained in the petri dish. The experiments reveal that the location of surfactant deposition with respect to the droplet position influences its motion. Due to the presence of a surface tension gradient, the footprint area of the droplet reduces and its shape changes. We have studied the temporal variation in the velocity (| v x |) of the droplets in relation to their proximity to a wall. Based on the evolution of droplet shape and change in droplet velocity, the drop dynamics can be experimentally divided into four distinct zones. Results indicate that in zone-1, | v x | grows with t as | v x | ≈ t n , where n is between 0.8 and 1.0. The scaling argument shows that in this zone, the surface tension force dominates the drag force, and thereby, | v x | of the droplets increases linearly with t expressed as | v x | ∝ t. The experimental investigation and the scaling law exhibit a reasonable agreement. In zone-2, | v x | remains more or less constant, as it is postulated that the surface tension force balances the drag force. In zone-3, a decrease in surface tension force results in a deceleration of the droplets. In zone-4, the deceleration becomes more prominent as the droplet approaches the petri dish wall. [ABSTRACT FROM AUTHOR]

We present a combination of laboratory experiments and computational fluid dynamics (CFD) simulations to understand the wind-induced drag force and drag coefficient for Saccharum contortum seeds. Seed drop experiments indicate that the settling fall velocities of hair-equipped seeds are within 1–2 m/s, compared to 2.34 times higher settling fall velocity of the seed without hairs. The experimental data illustrate a power-law relationship between drag coefficient ( C d ) and Reynolds number (Re) under the free fall condition: C d ∼ R e − 1.1 . CFD simulations show that both viscous and pressure drag force components are important in contributing to wind drag. The presence of hairs substantially increases pressure drag, and its relative importance depends on hair number and orientation. Seed morphology including hair number and orientation influences the drag coefficient under different flow directions relatively to the seed body. The lower drag coefficient observed with crossflow wind compared to free fall suggests that seeds encounter less air resistance while drifting horizontally in the wind, favoring extended flying time and distance. Based on the varying drag coefficients under different conditions, we propose the incorporation of varying drag coefficients in future wind-driven seed dispersal models. [ABSTRACT FROM AUTHOR]

A debris flow, with terraced fields as the source area, broke out on June 25th, 2018 in the Xiaotuga area of Yunnan Province, China, and this kind of debris flow is rarely recorded. Two purposes in this study: (1) the influence of flow drag force on slope stability; (2) back-analyze the movement process of debris flow. First, the geological background and movement of this debris flow were described based on a field investigation. Then, drag force, calculated by the laminar flow theory, is added to the slope stability calculation model, which elaborates the initiation process of this disaster. Moreover, dynamic simulation software (DAN3D) was used to simulate the kinematic process of the debris flow with a variety of combination models. The study shows that the terrace area can quickly produce surface runoff and create a drag force under rainfall conditions, which is the essential reason for the initiation of debris flow. In addition, the use of the FVV (Frictional-Voellmy-Voellmy) model is found to provide the best performance in simulating this type of debris flow, which reveals that it lasts approximately 200 s and that the maximum velocity is 12 m/s. [ABSTRACT FROM AUTHOR]

Strong metal‐support interaction (SMSI) has drawn much attention in heterogeneous catalysts due to its stable and excellent catalytic efficiency. However, construction of high‐performance oxide‐capsulated metal nanostructures meets great challenge in materials thermodynamic compatibility. In this work, dynamically controlled formation of oxide‐capsulated metal nanoparticles (NPs) structures is demonstrated by ultrafast laser plasmonic nanowelding. Under the strong localized electromagnetic field interaction, metal (Au) NPs are dragged by an optical force toward oxide NPs (TiO2). Intense energy is simultaneously injected into this heterojunction area, where TiO2 is precisely ablated. With the embedding of metal into oxide, optical force on Au gradually turned from attractive to repulsive due to the varied metal‐dielectric environment. Meanwhile, local ablated oxides are redeposited on Au NP. Upon the whole coverage of metal NP, the implantation behavior of metal NP is stopped, resulting in a controlled metal‐oxide eccentric structure with capsulated oxide layer thickness ≈0.72–1.30 nm. These oxide‐capsulated metal NPs structures can preserve their configurations even after thermal annealing in air at 600 °C for 10 min. This ultrafast laser plasmonic nanowelding can also extend to oxide‐capsulated metal nanostructure fabrication with broad materials combinations (e.g., Au/ZnO, Au/MgO, etc.), which shows great potential in designing/constructing nanoscale high‐performance catalysts. [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]

Kelps are resilient organisms, capable of thriving in high-energy wave environments. However, when hydrodynamic drag forces exerted by the wave environment exceed the kelps' structural limits, individuals become dislodged. Floating kelps generally follow ocean currents, traveling long distances until air-filled structures fail or the epibiont load becomes too great, causing them to sink to the seafloor. The ability of kelp to disperse over vast offshore and nearshore systems makes them important for organic subsidy and as a dispersal vector for marine organisms. Previous research on dislodged macroalgae focused on context-specific rafts, limiting insights into the broader ecological role of floating kelp. This study employed a site-specific Lagrangian trajectory model to describe the spatial distribution of floating Ecklonia maxima along the South African coastline. The model incorporated buoyancy and sinking using site-specific morphological data. Findings revealed that the distribution of floating E. maxima is influenced by oceanographic conditions, and seasonal patterns were also evident. Mesoscale features played a vital role in kelp accumulation on the surface and seafloor and acted as barriers to dispersal. This study offers essential insights into kelp's role as an organic subsidy and provides numerical evidence for kelp's potential as a carbon sink, contributing to a better understanding of kelp ecosystems and their ecological functions. [ABSTRACT FROM AUTHOR]

In this study, a realistic model of the respiratory tract obtained from CT medical images was used to solve the flow field and particle motion using the Eulerian–Lagrangian approach to obtain the maximum particle deposition in the bronchial tree for the main purpose of optimizing the performance of drug delivery devices. The effects of different parameters, including particle diameter, particle shape factor, and air velocity, on the airflow field and particle deposition pattern in different zones of the lung were investigated. In addition, a genetic algorithm was employed to obtain the maximum particle deposition in the bronchial tree and the effect of the aforementioned parameters on particle deposition. Reverse flow, vortex formation, and laryngeal jet all affect the airflow structure and particle deposition pattern. The mouth–throat region had the highest deposition fraction at various flow rates. A change in the deposition pattern with an increased deposition fraction in the throat was observed owing to the increased diameter and shape factor of the particles, resulting from the higher inertia and drag force, respectively. The particle deposition analysis showed that three parameters, shape factor, diameter, and velocity, are directly related to particle deposition, and the diameter is the most effective parameter for particle deposition, with an effect of 60% compared to the shape factor and velocity. Finally, the prediction of the genetic algorithm reported a maximum particle deposition in the bronchial tree of 17%, whereas, based on the numerical results, the maximum particle deposition was reported to be 16%. Therefore, there is a 1% difference between the prediction of the genetic algorithm and the numerical results, which indicates the high accuracy of the prediction of the genetic algorithm. [ABSTRACT FROM AUTHOR]

The present analysis aims to scrutinize the importance of 3D viscoelastic-nanofluid having gyrotactic motile microorganisms and Cattaneo-Christov heat and mass fluxes over the Riga plate. The flow of current analysis occurs due to the stretching sheet. The Riga plate is frequently used in sophisticated sensor and magnetic lubrication structures. This is a specific electromagnetic actuator that contains a span-shaped arrangement of contrasting/alternating electrodes and a permanent magnet and allows for precise flow regulation. The technical efficiency of nanofluids is apprehended by the assessment of the Buongiorno process, which permits us to analyze the attractiveness of Brownian motion and thermophoresis diffusion. Thermal radiation has a key role in the energy equation and most of the available literature, it has been used linear. In this study, thermal radiation has been used nonlinearly. The transmuted non-linear ODE's traced with shooting technique and results of physical parameters are sketched by implementing bvp4c solver via computational software MATLAB. Numerous essential flow parameters are graphically shown to be of physical significance. The drag force, thermal gradient, concentration, and microorganism's rates are calculated under the effect of various embedded constraints. [ABSTRACT FROM AUTHOR]

This study explores the impact of end electric current on the performance of a marine magnetohydrodynamic (MHD) propulsion motor or thruster using a comprehensive 3D numerical simulation. The investigation focuses on various operating parameters, such as electromagnetic and drag forces, efficiency, losses, current, and different pressure components. To validate the numerical findings, a scaled-down experimental setup is utilised. The results demonstrate that certain operating parameters of MHD motors are not affected by the three-dimensional characteristics of their channels. These parameters, including fluid velocity, can be accurately calculated using the analytical model based on the effective electric current of the motor. Conversely, other operating parameters of MHD motors are significantly influenced by the end effects in their channels. For example, the overall efficiency, which depends on the total electric current of the motor, should be calculated using a more precise simulation method. [ABSTRACT FROM AUTHOR]

Featured Application: This study presents a new pullback load calculation model from the perspective of pipe–borehole wall contact. Pipeline pullback load is a crucial basis for drill rig selection and pipeline strength design. This paper presents a new pullback load calculation model from the perspective of pipe–borehole wall contact. The pipe–borehole wall contact analysis includes the distribution of contact pressure and the relationship between the external load and compressive displacement. The friction force between the pipe and the borehole wall was calculated based on the pipe–borehole wall contact analysis and adhesion theory without depending on the empirical friction coefficient. The effects of the eccentricity were also considered when calculating the fluid drag force. Through case studies, we verified the applicability of the model and discussed the possible reasons for the errors between the theoretical and field-measured results. This study can provide a helpful tool for analyzing the pipe–borehole wall contact and pullback loads for horizontal directional drilling. [ABSTRACT FROM AUTHOR]

Understanding the agglomeration behavior between inclusions during steelmaking is crucial to control steel quality and cleanliness. This work reviews the state-of-the-art lateral capillary interaction between inclusions attached to the gas/steel or slag/steel interfaces, which is an essential aspect of inclusion agglomeration. The origin of the lateral capillary force, the methodologies to measure the force, and the development of the capillary theory are discussed. High-temperature confocal scanning laser microscopy (CSLM) has been intensively used for the in situ observation of inclusion agglomeration at the gas/steel or slag/steel interfaces. To calculate the lateral capillary force between inclusions from a series of 2D CSLM images, the particle mass, the inter-particle distance, and the drag force on the inclusions are the main input parameters. We compared the capillary force between two ellipsoidal particles obtained from different particle radius approximations (long and short radii, arithmetic mean, equivalent and effective radius, and equivalent volume), separation distances (inter-center and inter-surface), and capillary models (Yin's, Chan's, Mu's, K–P, and sub-particle models). The results highlight the importance of consistency in the parameters used in the force calculation from CSLM images and capillary models. [ABSTRACT FROM AUTHOR]

Feeding strip significantly enhances continuous cast slab quality. To clarify its impact on inclusion distribution, a mathematical model coupling flow, solidification and inclusion motion have been developed. The upper recirculation, lower recirculation, and unformed recirculation flow occur during continuous casting. Under the resultant forces of drag, virtual mass, pressure gradient, Saffman, gravity, buoyancy, etc., the inclusion motion can be divided into two stages: Injection and Split flow. Feeding strip mainly affects inclusion motion by altering the drag, virtual mass, pressure gradient, and Saffman forces, which are closely related to the molten steel flow. After feeding strip, the lower recirculation on the strip feeding side is compressed, while it on the no-feeding side is expanded. The unformed recirculation flow on strip feeding side squeezes the flow below lower recirculation on no-feeding side. A higher strip feeding speed promotes downward inclusion motion, increasing the chance of being captured between the slab edge and strip. Unformed recirculation flow guides inclusions on the no-feeding side toward the slab edge, while expanded flow directs them toward the center. Consequently, inclusions on strip feeding side gradually gather between slab edge and quarter, while inclusions on no-feeding side first gather toward center and then toward edge of slab with increased strip feeding speed. [ABSTRACT FROM AUTHOR]

In this paper, an analytical and numerical technique are examined in order to analyse the Stokes flow determination problem due to a viscous sphere droplet moving at a concentric instantaneous position inside a spherical interface separating finite and semi-infinite immiscible fluid phases. Here, when only one of the three phases of the fluid (micropolar fluid) has a microstructure, attention is focused on this case. The motion is considered when Reynolds- and capillary-numbers are low, and the droplet surface and the fluid-fluid interface have insignificant deformation. A general solution is obtained in a spherical coordinate system based on a concentric position to analyse the slow axisymmetric movement of the micropolar fluid, considering microrotation and velocity components. Boundary conditions are initially fulfilled at the fluid-fluid interface and subsequently at the droplet surface. The normalised hydrodynamic drag force applying to a moving viscous droplet appears to be a function of the droplet-to-interface radius ratio, which increases monotonically and becomes unbounded when the droplet surface touches the fluid-fluid interface. The numerical outcomes of the normalised drag force acting on the viscous droplet are derived for different values of the parameters, and are presented in a tabular and graphical framework. A comparison was made between our numerical outcomes for the drag force and the pertinent data for the special cases found in the literature. [ABSTRACT FROM AUTHOR]

Shelterbelts provide essential protection against wind erosion and soil degradation, as well as protection for fruit-bearing plants and crops from strong winds. Enhancing their sheltering capabilities requires optimizing their pattern and orientation, as well as defining their height and desired canopy shape, according to the desired performance. In this work, Large Eddy Simulation is employed to investigate the flow field and windbreak effectiveness of single and double-arranged shelterbelts characterized by different geometry and resistance to the air passage for neutral atmospheric condition. In particular, the canopy of the shelterbelts is modeled as an isotropic porous medium immersed in atmospheric boundary layer flow using the Darcy–Forchheimer model. Results show that a shelterbelt with a rectangular-shaped cross-section and a large canopy height results in the most significant reduction in mean wind speed and TKE, thus providing a large wind-protection region. As the spacing distance of double-arranged shelterbelts increases, the protection zones formed by both shelterbelts are reduced. The systematic comparisons of flow patterns, drag force coefficients, and windbreak effectiveness indicators of a series of single and double-arranged shelterbelts are essential for optimizing the design and management of shelterbelts. [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]

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]

This work pursues the closure for the effective reaction rate based on fine‐grid two‐fluid model (TFM) simulations in reactive gas‐solid flows. It is found that the mesoscale mechanism in the solid‐catalyzed reaction is constrained by the kinetic regime (KR) and the external mass transfer‐controlled regimes (EMTR). Thus, a filtered reaction rate model ηsubgrid considered two different regimes is proposed. The mesoscale effectiveness factor proposed in previous work is adopted in KR. A filtered interphase mass transfer model QM, which is constructed by analogy to the interphase heat transfer model, is used in EMTR. ηsubgrid shows a good predictability in two regimes via a priori test. The fidelity of ηsubgrid is also assessed via a filtered TFM simulation. The results indicate that the simulations incorporating corrections for the drag force and reaction rate yield better agreement with the fine‐grid simulations for both mass fraction and reaction rate profiles. [ABSTRACT FROM AUTHOR]

To improve the aerodynamic efficiency of the aircraft, the article focuses on optimizing the L/D ratio through postponement of flow separation. Elevating the L/D ratio leads to diminished drag and delays stall occurrence at high angles of attack (α). The wing geometry adopts NACA 6-digit airfoils, specifically NACA 63418 and NACA 63415. Various aerodynamic devices are explored for their ability to defer flow separation, with passive aerodynamic devices being the prevalent choice. The primary goal of the research is to integrate rotational thin wire elements into the aerodynamic components of the wing, aiming to diminish drag, amplify lift, and enhance overall aerodynamic performance. The analysis spans a range of α, from 0o to 20o. The study encompasses two scenarios: one without the incorporation of aerodynamic devices and the other with their implementation. Comparative analyses of increases in CL and reductions in CD, with notable improvements observed at a 15o angle of attack, 28.47% increase in CL and 15.07% decrease in CD. Furthermore, the improved performance in the CL/CD, which increases substantially in stall conditions, thereby demonstrating the potential of these aerodynamic modifications to enhance overall aircraft performance.