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Scramjet combustors are emerging technologies in the aerospace industry, but this technology has a great challenge like air-fuel mixing at supersonic speed. Hence, worldwide many researchers are working on this concept and contributing to the efficient mixing and performance of scramjet. An innovative way has been created in this research to inject the fuel without altering any geometrical changes so that there won't be any pressure losses. Initially, the DLR scramjet combustor is considered with an inline arrangement of fuel injection nozzles. In the new model, the fuel injection nozzles are considered in a zigzag manner to interrupt the upcoming air flow stream over the wedge strut. The basic and new method of fuel injection is analyzed numerically by solving the three-dimensional fluid flow governing equations. The global one-step reaction mechanism is used to describe the combustion process between supersonic airflow and hydrogen fuel. The finite-rate eddy dissipation turbulence model explains the dynamic relationship between turbulence and chemical processes. The influence of fuel injection has been analyzed by visualizing the distribution of fuel in the radial direction, vortices development with new fuel injection, turbulence level, and the other flow properties in the strut downstream at different positions along the length of the combustor. Numerical results found that the new method of fuel injection improves fuel penetration in the radial direction and significantly improves the mixing of fuel and air as well. • Design of a wedge strut with in-line and wavy-line arrangement of fuel injection nozzles. • Numerical investigation of a scramjet with in-line and wavy-line configured fuel nozzles wedge strut. • Wavy-line fuel injection strut increases the recirculation region in the strut base. • Wavy-line fuel injection wedge strut increases the average turbulent reaction rate by 19.1%. • Wavy-line fuel injection scheme improve the mixing and combustion efficiency by 11.0% and 19.0%, respectively. [ABSTRACT FROM AUTHOR]

Landslides are characterized by intricate formation mechanisms and multiple triggering factors, posing serious threats to human life and property. Interferometric synthetic aperture radar (InSAR) has been extensively applied in landslide monitoring due to its all-weather operation, high precision, and wide spatial coverage. However, one-dimensional line-of-sight (LOS) deformation limits the ability to measure actual landslide displacement. Presently, many regions without the latest descending data, but they are in the overlapping position of two adjacent latest ascending track. Compared to using a single track, the method measuring three-dimensional deformation of landslides, combined with two ascending track InSAR datasets and pixel-level surface-parallel flow (PSPF) assumption, is presented. Based on the small baseline subset (SBAS) InSAR, the LOS deformation in two observations in the middle reaches of the Qingjiang River in China was measured. With pixel-level surface-parallel flow model, the three-dimensional deformation was obtained. It was further converted into the slope surface coordinate system, thus determining the direction of landslide movement. The findings effectively elucidate the primary displacement mode of landslides, with deformation rates ranging from −80 to 20 mm yr $^{ - 1}$ − 1 , which are significantly influenced by the slope angle and slope aspect. It is highly important to remotely identify the movement direction and analyse the failure mode of landslides. [ABSTRACT FROM AUTHOR]

Theoretical research has been done on the hydromagnetic three-dimensional nanofluid flow across an inclined stretching sheet in the presence of Brownian motion and thermophoresis. It is taken into account that there are two different kinds of water-based nanofluids that contain copper and alumina. Three-dimensional nonlinear-type similarity transformations are used to convert the governing boundary-layer equations into a collection of similarity equations, which are then numerically solved by MATLAB. Further, results obtained in some limiting cases are compared to some results that have already been published, and it is found that there is good agreement. The problem is controlled by a number of physical factors, and the impact of these factors on different flow distributions is thoroughly examined with the help of graphs and tables. It has been observed that the nanofluid has better heat transfer conductivity than the ordinary base fluid. [ABSTRACT FROM AUTHOR]

We study the capability of Large Eddy Simulation (LES) to predict fluid residence time in a ventilated room. Validation is performed against an experiment where the inlet vent slot width matches that of the room. On a coarse grid, the Smagorinsky subgrid-scale model has a detrimental effect on flow statistics, whilst the WALE and Germano–Lilly models perform well. A refined grid produces close agreement with the reference data. A simulation with a narrow inlet slot demonstrates that the flow becomes three-dimensional, with pairs of spiral vortices forming in the room and altering the recirculation pattern when compared to the wide inlet slot configuration. The obtained LES statistics show improvements in the prediction of velocity field over conventional RANS modelling techniques. Fluid age probability density functions show that a wide range of residence time values around the mean value can be observed within the room. LES is capable of providing accurate predictions in a simplified ventilated room, and residence time probability density function distributions can be useful for the improvement of ventilation strategies. [ABSTRACT FROM AUTHOR]

This paper concerns the well-posedness of subsonic flows in a three-dimensional finitely long cylinder with arbitrary cross section. We establish the existence and uniqueness of subsonic flows in the Sobolev space by prescribing the normal component of the momentum, the vorticity, the entropy, the Bernoulli's quantity at the entrance and the normal component of the momentum at the exit. One of the key points in the analysis is to utilize the deformation-curl decomposition for the steady Euler system introduced in [18] to deal with the hyperbolic and elliptic modes. Another one is to employ the separation of variables to improve the regularity of solutions to a deformation-curl system near the intersection between the entrance and exit with the cylinder wall. [ABSTRACT FROM AUTHOR]

The advances in the field of nanotechnology tends to improve the rate of heat extraction and transmission from foreseeable causes and has fascinated researchers and scientists. Furthermore, nanofluids are having a useful impact on various fields such as nuclear industries, powered lasers, chilling of microelectronic devices, solar energy capture, transformers oil cooling, and in cancer diagnosis. Hence, magnetohydrodynamic (MHD) three-dimensional bioconvective flow of nanofluid accommodating gyrotactic microorganisms over a wedge surface with zero nanoparticles mass flux boundary conditions is studied, using large Reynolds number approximation. The additional novelty of the study is the implementation of the revised Buongiorno model, which deliberates the effects of thermo-migration and Brownian diffusion of nanoparticles, together with passive control of nanoparticles fraction on the wedge surface. The self-similar form of conservation equations of energy, nanoparticle fraction, gyrotactic microorganisms, and momentum are handled numerically. T The results of the Blasius and the Hiemenz flows are retrieved as special cases of the model. It was found that the temperature of the nanofluid increases considerably when considering the nonlinear thermal radiation compared to the linear radiant heat. Increasing the strength of the Brownian diffusion increases the heat transport but reduces the mass transport. [ABSTRACT FROM AUTHOR]

This research leads to carrying out the productivity and the efficiency of the carbon nanotubes (CNTs) that have extensive applications in solar collectors. Due to the superior thermal as well as electrical properties, the use of CNTs has an important contribution to the nanotechnology revolution. Therefore, owing to the aforementioned vital points, this investigation intended to put forth the thermophysical properties of both single and multi-walled CNT nanofluids past a stretching surface. Additionally, an electrically conducting nanofluid flow phenomenon enriches due to the inclusion of dissipation (Ohmic heating) and external heat source/sink. The dimensional form of the three-dimensional fluid flow phenomena is transformed to a non-dimensional form with the use of similarity transformation and further numerical procedure is implemented to solve the nonlinear governing equations. The substantial significance of the characterizing parameters is presented briefly via figures and the comparative analysis with the earlier investigation is deployed through the table. However, the main findings of this study are as follows: A significant attenuation in the shear rate is marked for the enhanced inertial drag but it augments for the augmented values of the magnetization; further, particle concentrations of both the CNTs favor accelerating the fluid momentum as well as temperature distribution. [ABSTRACT FROM AUTHOR]

This study investigates the impact of insufficient spanwise spatial resolution on the measurement accuracy of streamwise velocity fluctuations over rough walls. We use a direct numerical simulation (DNS) database of turbulent open-channel flow over three-dimensional sinusoidal roughness with varied wavelengths and roughness heights. Employing a triple decomposition, we investigate both the attenuation of the turbulent fluctuations (about the local mean), u ′ and the dispersive stresses (roughness-induced fluctuations of the time-averaged mean about the global mean), U ~ . A boxcar filter on DNS data is applied to investigate the effects of spanwise spatial filtering on these quantities. Our analysis reveals the significance of two key length-scale ratios for velocity measurements over rough walls: the wire length relative to the spatially and temporally plane-averaged Kolmogorov scale at the roughness crest ( l / ⟨ η ⟩ k ), and the wire length relative to the roughness spanwise wavelength ( l / Λ y ). We observe that maintaining l / ⟨ η ⟩ k constant while increasing l / Λ y attenuates the variance of U ~ and u ′ within the roughness sublayer. When fixing l / Λ y , an increase in l / ⟨ η ⟩ k influences the turbulent fluctuations across all wall-normal locations. These findings highlight the necessity of considering both length scales when evaluating spanwise spatial resolution in turbulence measurements over rough walls. [ABSTRACT FROM AUTHOR]

Tip-vortex cavitation is among the first forms of cavitation to appear around ship propellers. In the present study, the time-resolved three-dimensional flow field around non-cavitating and cavitating tip vortices in the wake of a marine propeller is investigated with tomographic PIV. The advance ratio of the propeller and the Reynolds number of the flow are kept constant, while the cavitation number is varied by changing the pressure inside the cavitation tunnel. The importance of masking the tip-vortex cavities before performing the tomographic reconstruction is firstly demonstrated, followed by a description of the applied masking algorithm. From the three-dimensional velocity vector fields, coherent structures of vorticity are identified using the Q-criterion. Three types of coherent structures are observed to populate the wake of the propeller, i.e. tip vortex, hub vortex, and secondary vortical structures. The secondary vortical structures surrounding the tip vortex appear to be progressively smaller in size and more chaotically-organized for decreasing cavitation number. This can be attributed to the pressure fluctuations induced by the cavity, which strengthen when the cavity size grows. [ABSTRACT FROM AUTHOR]

Understanding the fundamental structure of shock-containing elliptic jets is of great academic and engineering interest, but there are still many unknowns. The three-dimensional flow features of an underexpanded jet emerging from an elliptic convergent nozzle with an aspect ratio of 4.0 at the exit face are experimentally investigated by rainbow schlieren tomography (RST). The elliptic jet is discharged into quiescent air using an intermittent blowdown wind tunnel. The Reynolds number based on the equivalent diameter and flow properties at the nozzle exit is 3.0 × 10 5 . Multi-view rainbow schlieren images of the elliptic jet are taken by rotating the nozzle around its longitudinal axis, and the density field is reconstructed using the convolution back-projection (CBP) method. The three-dimensional density field of the elliptic jet is acquired with a nominal spatial resolution of approximately 13 μ m. The flow characteristics of shock-containing elliptic jets, such as the shock-cell length, the supersonic length, the switchover location, and the axis-switching location, are quantitatively revealed from the streamwise density profiles, the density contour plots in the minor-axis and major-axis planes where a method is proposed to quantitatively estimate the switchover and axis-switching locations. The shock-cell and supersonic lengths are quantitatively compared with the recently introduced analytical solution and scaling law, respectively. In addition, the shock structures and topology showing the spatial evolution in the streamwise direction of the near-field shock system within the elliptic jet are experimentally demonstrated for the first time. [ABSTRACT FROM AUTHOR]

Radial inlet distortion induced by boundary layer separation can significantly affect the aerodynamic performance of the compressor. The effect of radial inlet distortion on the flow structure is numerically investigated in a high load axial flow compressor. The inlet boundary is determined by the experimental results at the downstream of the distortion generator. The results reveal that tip distortion leads to a reduction in the stall margin, whereas hub distortion extends it. Radial distortion redistributes the main flow toward undistorted region due to the obstructive effect of lattice ring. The deficit in axial velocity with tip radial distortion causes the rotor to operate at a higher incidence angle near the casing, while hub radial distortion alleviates the tip blade loading. The detailed three-dimensional flow field analysis indicates that increased blade loading with tip distortion shifts the trajectories of both primary and secondary tip leakage flow toward the leading edge, thereby expanding the blockage region. Conversely, hub radial distortion unloads the rotor tip region, thereby reducing the blockage region induced by tip leakage flow. Additionally, with hub distortion, the location of separation line on the blade suction surface moves closer to the leading edge, and the flow separation around the trailing edge is intensified. [ABSTRACT FROM AUTHOR]

Numerical computations of the three-dimensional flow past dual-step cylinders using large eddy simulations are performed. The Reynolds number based on the diameter of the large cylinder, R e D , is fixed at 2000. The diameter ratio between the two cylinders is kept constant in all computations, i.e., D / d = 2 , where d is the diameter of the small cylinder. Investigations are carried out at different aspect ratios (ARs), defined as the ratio between the length of the large cylinder and its diameter L / D = 0.2 , 0.5 , 1.0 , 1.5. Vortex dislocation phenomenon is observed in all the cases near the step discontinuity. The higher AR cases, L / D = 1.0 , 1.5 , exhibit similar trends with regard to wake dynamics, while they are quite different in the lower AR cases, L / D = 0.2 , 0.5. Kelvin–Helmholtz instability is present in the wake of the dual-step cylinder with higher AR. Stable in-phase shedding and downwash characterize the wake of higher AR configurations, while oblique shedding (and flipping) is the key feature in the lower AR counterparts. Unique features are observed in the L / D = 1.0 configuration that marks the transition between shedding modes. [ABSTRACT FROM AUTHOR]

Hybrid turbulence models that can accurately reproduce unsteady three-dimensional flow physics across the entire range of grid scales and turbulence dynamics from Reynolds-averaged Navier–Stokes (RANS), through large-eddy simulation (LES), down to direct numerical simulations (DNS) are of increasing interest to the turbulence modeling community. However, despite decades of research and development, the basic tasks of eliminating poor-performing hybrid RANS-LES models and accelerating adoption of superior models through well-designed validation and verification have yet to occur. As a step in this direction, in this work we evaluate thirteen different hybrid RANS-LES models via systematic grid refinement of decaying homogeneous isotropic turbulence. We further derive a novel mathematical framework for assessing the energy partitioning dynamics of each Hybrid RANS-LES model, wherein model-to-model variations in energy partitioning can be interpreted as different feedback mechanisms operating on a low-dimensional nonlinear dynamical system. We found that model forms similar to the flow simulation methodology—also often termed very-large eddy simulation—are dynamically inconsistent with DNS at all resolutions. Additionally, we found a strong dynamical similarity in the feedback mechanisms of all models related to detached eddy simulation and partially averaged Navier–Stokes that is inherent to their general model forms. [ABSTRACT FROM AUTHOR]

This study employed large eddy simulation and a volume-of-fluid with discrete phase model to evaluate a swirl fuel injector's atomization performance. Addressing non-uniform atomization at low flow rates, the study optimized a swirl injector structure based on additive manufacturing advantages during re-modeling. Computational analysis revealed that vortex downstream and capillary bubbles caused non-uniformity in the prototype injector, mitigated by the optimized injector's three-dimensional flow channel. Comparative analysis showed similar parameters between the optimized and prototype injectors, except for significant improvement in circumferential uniformity at low flow rates (from 41.48% to 14.69%). The optimized injector's swirl structure, produced via micro laser powder bed fusion, exhibited precise dimensions and minimal surface roughness. Validation experiments without air inflow confirmed the computational results' reliability, with a minor discrepancy in circumferential uniformity (2.98%) and atomization cone angle (2.3°) for the prototype swirl structure. At low flow rates, the optimized structure showcased reduced circumferential non-uniformity (from 42.31% to 28.76%), underscoring its benefits. This interdisciplinary investigation underscores additive manufacturing's application in structural optimization and manufacturing. [ABSTRACT FROM AUTHOR]

The interaction of a tank impacting a water surface is an extremely complex nonlinear multiphase flow phenomenon. In this study, experiments and numerical simulations are used to systematically investigate the flow physics and load characteristics of a tank corner impacting a water surface. Free surface flow at different fall heights (200–800 mm) and inclination angles (0°–15°) was obtained through free fall experiments. The volume of fluids method and overset grid technology were used to simulate the water impact process of a three-dimensional structure accurately. For typical bubble flows, the numerical and experimental results agree well. On the basis of the three-dimensional flow characteristics and pressure distribution, flow behaviors, such as fluid climbing, corrugation disturbances, and air cavity effects, are analyzed. Bubble flow has a significant effect on the behavior mode of the impact load. In particular, the bubbles at the upper wall play a key role in the load characteristics at different locations. In addition, the influences of corrugations inside the tank's corner and the impact velocity on fluid flow were investigated. These results provide beneficial references for an in-depth understanding of the fluid flow and load characteristics between a tank and fluid. [ABSTRACT FROM AUTHOR]

This work introduces a new higher-order accurate super compact (HOSC) finite difference scheme for solving complex unsteady three-dimensional (3D) non-Newtonian fluid flow problems. As per the author's knowledge, the proposed scheme is the first ever developed higher-order compact finite difference scheme to solve 3D non-Newtonian flow problems. The proposed scheme is fourth-order accurate in space and second-order accurate in time, utilizing only seven adjacent grid points at the (n + 1) th time level for the finite difference discretization. A time-marching methodology is employed with pressure calculated via a pressure-correction strategy based on the modified artificial compressibility method. Using the power-law viscosity model, we tackle the benchmark problem of a 3D lid-driven cavity, systematically analyzing the varied rheological behavior of shear-thinning (n = 0.5), shear-thickening (n = 1.5), and Newtonian (n = 1.0) fluids across different Reynolds numbers (R e = 1 , 50 , 100 , 200). Both Newtonian and non-Newtonian results are carefully investigated in terms of streamlines, velocity variation, pressure distributions, and viscosity contours, and the computed results are validated with the existing benchmark results. The findings demonstrate excellent agreement with the existing results. It is found that for shear-thinning fluid (n = 0.5), u velocity is higher near the top moving wall than the case of Newtonian (n = 1.0) and shear-thickening fluid (n = 1.5) for all Re values. This extensive analysis, using the new HOSC scheme, not only increases our understanding of non-Newtonian fluid behavior but also provides a robust foundation for future research and practical applications. [ABSTRACT FROM AUTHOR]

Pressure drop effectively reflects the state of water in PEMFC channels and gas diffusion layers. In order to study the regularities in pressure drop and the characteristics of the under-rib convection in the PEMFC at different temperatures, a three-dimensional multiphase flow model was presented, which considers the formation and transport of water inside the cell, as well as the mechanisms governing the conversion between different states of water (liquid water, water vapor and membrane water). The model was imported into Fluent using user-defined functions to simulate and analyze under-rib convection characteristics within the fuel cell at different temperatures. A fuel cell testing system was established to perform tests on polarization curves and anode pressure drop at different temperatures. The results show that the model agrees well with the experiment data, with a maximum error of 5.34%. The anode pressure drop shows a step-level characteristic with three segments: a normal segment, an increasing segment and a stepped segment. As the temperature increases, both the average anode pressure drop and the velocity vector of reactants gradually increase. Notably, the peak velocity vector is observed in the rib-turning region, where heightened under-rib convection is evident. [ABSTRACT FROM AUTHOR]

The transition towards a sustainable energy landscape necessitates efficient and scalable technologies for renewable energy storage. Water electrolysis, a process that converts electrical energy into chemical energy stored in hydrogen, holds immense potential for integration with intermittent renewable sources. However, the performance and efficiency of water electrolyzers are impeded by the complex multiphase flow dynamics involving bubble nucleation, growth, and transport within the electrochemical cell. This study employs state-of-the-art three-dimensional multiphase flow simulations to unravel the intricate interplay between bubbles and the electrochemical processes in a parallel-electrodes flow-based electrolyzer (PE-FBE). By accurately capturing bubble-electrolyte interfaces, the simulations quantify the detrimental effects of bubbles on overpotentials, current density distribution, and bubble distribution. Crucially, the impact of critical parameters, including flow rate, bubble nucleation size, surfactant addition, and applied current, on these performance metrics is systematically investigated. The findings reveal strategies to mitigate bubble-induced losses, enhance current uniformity, and improve hydrogen purity, paving the way for optimized electrolyzer designs and efficient renewable energy storage. The impact of bubble dynamics on current streamlines and performance within a parallel-electrodes flow-based electrolyzer is highlighted. [Display omitted] • Investigated bubble dynamics in a parallel-electrodes flow-based electrolyzer (PE-FBE). • 3D simulations revealed the impact of bubbles on overpotential and current density uniformity. • Addition of surfactants reduces bubble coalescence and improves hydrogen purity. • Larger bubble nucleation sizes result in better current uniformity and improved efficiency. • High electrolyte flow rates decrease bubble overpotential but require more pumping power. [ABSTRACT FROM AUTHOR]

Land subsidence, marked by a decline in surface elevation, poses a significant threat to urban infrastructure and safety. Accurate subsidence information and a reliable prediction model are crucial for prevention and control. In this study, we used persistent scatterer interferometric synthetic aperture radar (PSInSAR) technology to obtain long-term land subsidence data and analyzed subsidence characteristics in Decheng District. By integrating hydrogeological and groundwater data, we developed a three-dimensional groundwater flow and one-dimensional compaction model through numerical simulation. Furthermore, the subsidence data monitored by PS-InSAR were used to further constrain and validate the model. The evolution trend of land subsidence under different groundwater exploitation scenarios was predicted and analyzed. The results showed that from May 2017 to December 2021, the cumulative maximum subsidence in Decheng District reached -173 mm. The subsidence area is mainly concentrated in the northern area, and its subsidence center is near Qiaoyuan Town. According to the Land Subsidence Prevention and Control Plan of Dezhou City, Shandong Province (2018-2025), we set up different groundwater mining scenarios with the goal that the rate of land subsidence in the key prevention and control area is less than 35 mm/yr in 2025.The Fluidsolid coupled model prediction analysis results indicated that a 30% reduction in groundwater exploitation is reasonable. [ABSTRACT FROM AUTHOR]

Solute transport in unsaturated conditions is important in various applications and natural environments, such as groundwater flow in the vadose zone. Studies of unsaturated solute transport show complex characteristics (e.g. non-Fickian transport) due to larger variations in the pore-scale velocities compared to transport in saturated conditions. However, the physical processes at the pore scale are still not completely understood because direct three-dimensional observations at the pore scale are very limited. In this study, single-phase and two-phase solute transport was directly characterized by performing tracer injection experiments in a sintered glass and Bentheimer sandstone sample. These experiments were imaged by continuous scanning with fast laboratory-based micro-computed tomography. The network-scale flow velocities and transport properties were characterized by using the pore-based transient concentration fields to determine the tracer's arrival time and filling duration in every pore. Important measures for dispersion (the scalar dissipation rate and filling duration) were determined and indicated a wide range in pore-scale velocities and the existence of stagnant and flowing pores for the unsaturated experiments. Furthermore, we performed the first quantification of the mass transfer coefficient between stagnant and flowing pores on three-dimensional experimental data. We also calculated the tortuosity directly from the interstitial velocity and the pore-based velocity. This was found to be 13% higher in unsaturated conditions compared to saturated conditions. Our results indicate that pore-scale structural heterogeneity increases the differences between saturated and unsaturated solute transport. This study thus provides further insight into pore-scale spreading and mixing of dissolved substances in unsaturated porous media. [ABSTRACT FROM AUTHOR]

This paper investigates the idea of substituting the first stage of a conventional axial-flow compressor and its inlet guide vane (IGV) row with a variable rotor tandem (VRT) stage to reduce the size and weight of axial-flow compressors. It is expected that a tandem stage gains higher pressure ratio than a conventional stage, and simultaneously, its variable stagger rotor provides more flexibility in handling unsteady phenomena at low mass flow rates. A three-dimensional numerical model based on Reynolds-Averaged Navier–Stokes equations is developed to conduct this investigation. To validate the numerical model, experimental tests are conducted on a tandem single-stage axial-flow compressor test bench in the Dana laboratory of Amirkabir University of Technology, to compare the performance map with numerical results. The validated numerical model is then employed to simulate the performance of both front and aft variable rotor blades. The proposed tandem stage effectively performs the IGV duty, suppresses instabilities at low mass flow rates, and eventually extends the compressor's stable operational range. This proves that a VRT stage is an efficient active surge-control system tool. The detailed survey of the three-dimensional flow field reveals that the aft tandem rotor blade stagger angle is more effective in increasing the stall margin and decreasing the minimum operational mass flow rate than the front row of blades. It is observed that when the aft blades rotate in the direction of decreasing the tandem blades' gap area, the flow momentum increases and causes the compressor stability at lower mass flow rates. [ABSTRACT FROM AUTHOR]

The sodium-cooled fast reactor (SFR), a fourth-generation nuclear reactor, utilizes liquid sodium as a coolant and offers advantages like operation at atmospheric pressure and the use of spent nuclear fuel. Understanding flow characteristics around fuel rod bundle is crucial for securing cooling performance and safety. This study investigates the flow characteristics in a 37-pin wire-wrapped fuel rod bundle of SFR from three-dimensional flow fields measured by magnetic resonance velocimetry. Aimed at enhancing the understanding of coolant flow dynamics crucial for reactor safety and efficiency, the study successfully captures and validates three-dimensional, three components of mean velocities. Key discoveries include phase differences between wire position and high velocity regions, evidence of upstream flow influence by wire structures, and secondary flows such as edge swirling induced by wire blockage. The research offers detailed insights into subchannel velocities and flow split factors, contributing to improved SFR design and safety. [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]

Alumina stands out as a highly prevalent ceramic material in contemporary applications. Serving as a prime illustration of an electrical insulator, alumina boasts superior temperature resistance, chemical stability, and enhanced thermal conductivity. Its useful effectiveness spans extends to various sectors including medicine, industry, household products, as well as the manufacturing of electrical components and batteries. Considering these important applications, this study develops a mathematical framework to analyze MHD mixed convective three-dimensional nanofluid flow incorporating alumina nanoparticles over an extending surface. Initial assumptions constrain the nanofluid flow to exhibit rotation. A significant aspect of this study revolves around examining the impact of nanoparticle size and nanolayer characteristics on the nanofluid and highlighting its innovative contribution. The modeled equations have been evaluated numerically by using bvp4c MATLAB command. It is concluded that the higher magnetic factor augments the thermal distribution and secondary velocity distribution while retards the primary velocity distribution. Upsurge in rotation factor has augmenting impact on thermal distribution while it has retarding impacts on primary and secondary velocity distributions. Escalation in empirical factor causes augmentation in the primary velocity and temperature distributions while it retards the secondary velocity distribution. It is also noticed that growth in Nusselt number is greater in case of escalation of nanolayer in comparison of upsurge in nanoparticles' diameter. The results of this work have also been confirmed with available results in the literature through a comparative analysis. [ABSTRACT FROM AUTHOR]

Optimizing the heat extraction performance of geothermal systems is a long-standing issue in the study of geothermal energy. Besides the heat extraction in fractured hot rock, minimizing the heat loss during water flowback through boreholes is also critical for the system performance. Here, we conducted a series of experimental and numerical studies to understand the controlling factors of heat extraction rate and efficiency and to explore practical approaches for the optimization of heat extraction performance in a geothermal borehole. We performed water flow experiments to observe the heat extraction from neighboring hot granite and reproduced the heat extraction process using a three-dimensional water flow model. Our results show that the heat extraction rate first increases with a higher flow rate to the maximum value and then decreases with a further rise in flow rate. The heat extraction efficiency decreases constantly with a higher flow rate. To improve the heat extraction performance with both the heat extraction rate and efficiency approaching the maximum values, we scaled up the laboratory-scale borehole and found that the heat extraction performance is enhanced with a triangular zone of heat extraction and a reduced zone of low-temperature water along a field-scale borehole. We finally discovered that a proper control of borehole geometry, such as section diameters along a multi-section borehole and bending angle of borehole trajectory, is a feasible strategy to modulate the heat extraction performance in a geothermal borehole and to replenish the heat loss during water flowback. Highlights: Experimental and numerical studies are conducted to understand the controlling factors of heat extraction rate and efficiency. Heat extraction performance is enhanced with a triangular zone of heat extraction and a reduced zone of low-temperature water. Multi-section borehole is a feasible strategy to modulate the heat extraction performance in a geothermal borehole. Proper bending angle of borehole trajectory is another feasible strategy to optimize the heat extraction performance. [ABSTRACT FROM AUTHOR]

This study aims to investigate the flow characteristics of water–sand mixture in fractured porous media through a series of laboratory experiments. The experiments focus on examining the transport characteristics of water–sand mixture with varying grain sizes, glass bead gradations, sand mass fraction and outlet conditions. The results show that an increase in grain size causes a more pronounced nonlinear variation in large pressure gradient, resulting in a predominantly longitudinal flow pattern with a 'multi-arc' flow state. Water–sand mixture with various glass bead gradations exhibits aggregation effects in porous media. The discrete element method–computational fluid dynamics (DEM–CFD) two-way coupling method is used to simulate water–sand flow in fractured porous media using the three-dimensional particle flow code (PFC3D). The simulation shows that the fracture has a more significant constraint effect than the pore due to the significant variation in internal contact force. A response surface optimization method is utilized to establish multi-factor response models. The correlation between flow, fracture inlet pressure, pore inlet pressure and water–sand mass is analyzed to predict accurately the variation of water–sand outflow. Based on the least square method, multivariate regression fitting equations are developed using sand grain size, gradation and sand mass fraction to predict the dynamics of fluidity I and non-Darcy factor β. The equations are found to be effective in forecasting the dynamics of these factors and provides valuable insights for assessing. These results can be used to predict the movement behavior of fluid in fracture-pore composite media and provide theoretical guidance for preventing disasters such as water–sand inrush. Highlights: A shift in the flow pattern of water-sand mixture from a grid-like structure to a multi-arc structure is found as the size of sand particles increases. Water–sand flow in fracture–pore channel is established based on the DEM–CFD two-way coupling method. Multi-factor response models for water-sand outflow are established by using the method of response surface optimization. Multiple regression fitting equations are established based on the least squares method to predict the evolution of fluidity I and non-Darcy factor β. [ABSTRACT FROM AUTHOR]

As a three-dimensional flow channel, the laminated filter has a complex structure, and it is easy to appear phenomena such as too short blocking time and increasing head loss caused by sand interception in the operation process. According to the relationship between head loss and cross-sectional area, an annular flow channel laminated filter was proposed. The circumferential flow channel was added on the lamination surface, which increased the flow direction of the flow channel and played the role of dividing the radial flow channel, achieving the purpose of hierarchical multi-layer filtration in the lamination and improving the number of available flow channels. In order to explore the advantages and disadvantages of the linear flow channel and annular flow channel laminated filter for irrigation water filtration capacity. Through indoor comparative experiments, 120 mesh laminated filter, namely the filter particle size of 125 μm was used to test the head loss and filtration performance of the two filters under four kinds of sand grading median particle size (106, 121, 126 and 165 μm), three kinds of sediment content (0.10, 0.15 and 0.2 g/L) and five kinds of inlet flow (1.5, 2.0, 2.5, 3.0 and 3.5m3 /h), a total of 60 groups of tests. The dependent variables were the head loss, the sediment retention capacity and the median particle size of the interception, and the independent variables were the inlet flow, the sediment concentration and the median particle size of the inlet. The evaluation indexes were the head loss, the plugging uniformity, the sediment retention capacity and the particle size distribution of the interception sediment. The multiple regression equation was established to verify the correlation between the head loss and the filtration capacity. The entropy weight method was used to determine the optimal lamination of the head loss and the filtration capacity. The results show that: under the condition of clear water, the maximum flow head loss of the annular flow laminated filter is 9.1% lower than that of the trapezoidal linear filter. Under the condition of sandy water, the time for the head loss to reach 8m is 1.5～10 times longer than that of the trapezoidal linear filter, and the maximum head loss is reduced by 52.5%. The total sediment retention capacity is increased by 0.5%～6.3%, and the average sand removal rate is increased by 0.22% for the sand with the median particle size greater than 110μm. The siltation channels of the trapezoidal linear filter account for 25%～ 86% of the total number of channels of the trapezoidal lamination, while no siltation phenomenon is observed in the operation cycle of the annular lamination. The head loss of the two kinds of laminated filters was positively correlated with the sediment concentration, inlet flow and inlet median particle size, the sediment retention was positively correlated with the sediment concentration, inlet flow and inlet median particle size, and the interception median particle size was positively correlated with the sediment concentration and inlet median particle size. The annular flow channel laminated filter was more suitable for irrigation water with high sediment concentration and high median particle size distribution than the trapezoidal linear laminated filter. Therefore, the optimal laminated filter can be designed by considering the change of the geometric distribution of the flow channel of the laminated filter, which can reduce the filter head loss and extend its backwashing cycle without reducing the filtration capacity. [ABSTRACT FROM AUTHOR]

In the context of controlling axial fan aerodynamic noise, one effective approach involves the redesign of the blade. In the present study, a novel blade design was formulated for a specific model of axial flow fan, targeting the mitigation of the tip leakage vortex (TLV) and subsequent reduction of noise levels. The assessed noise-reduction blades have perforations drilled from the leading edge (LE) to the pressure surface (PS) of the blades. By impeding the tip leakage flow (TLF), these perforations effectively weaken the TLV. The three-dimensional non-constant flow field within the channel is computed employing the shear stress transport (SST) turbulence model. The aerodynamic noise prediction, which is based on the Lighthill's acoustic analogy theory, shows that the designed blades can effectively reduce the aerodynamic noise of the axial fan. Specifically, enhancing the ratio of inlet area to outlet area of the ventilation holes leads to an improved noise reduction effect. Notably, for ratios of 0.44 and 1.06, the designed blades exhibit noise reductions of up to 3.3 dB(A) and 3.9 dB(A), respectively. Meanwhile, the static efficiency of these two fans is reduced by 0.50% and 0.26%, respectively. The study thus provides good theoretical support for the design of axial flow fans in the context of noise reduction. [ABSTRACT FROM AUTHOR]

This research work aims to theoretically examine the influence of various factors on the three-dimensional nanofluid flow. The study includes parameters such as temperature ratio coefficient, Prandtl numbers, Schmidt, Soret, Dufour, Biot, expansion ratio coefficient, Power index, and nanoparticle volume fraction parameter, as well as the effect of non-linear thermal radiation and magnetic parameter on the behavior of the nanofluid. These characteristics significantly impact the flow of the three-dimensional boundary layer in the presence of an expansion plate. To facilitate the investigation, we have selected nanofluids that contain water-based copper and aluminum oxide for this study. We have developed a model of a system of partial differential equations (SYS-PDEs) with non-linear terms. Based on selected similarity equations, the SYS-PDEs with non-linear terms has been transformed into a system of ordinary differential equations (SYS-ODEs) whose terms are non-linear. To approximate and solve the obtained SYS-ODEs, we utilized a modified spectral Chebyshev polynomials' first derivative pseudo-Galerkin spectral method. Additionally, we conducted an error analysis discussion to ensure the credibility of our results. We presented our analysis in graphical form and provided comments on each figure along with the effects of the various parameters studied. Consequently, we concluded that the power low is an essential factor affecting the flow's behavior, such as the nanofluid's velocity, temperature, and concentration. [ABSTRACT FROM AUTHOR]

Natural rock fractures often exhibit non-matching characteristics at certain scales, leading to uneven aperture distributions that significantly affect fluid flow. This study investigates the impact of the mismatch between the upper and lower surfaces on the flow through three-dimensional rough fractures. By applying fractal theory, a rough upper surface of the fracture is generated, and different degrees of mismatch are introduced by adding random noise to this surface. This approach enables the construction of a variety of three-dimensional rough fracture flow models. Numerical simulations, which involve directly solving the Navier-Stokes equations, are used to simulate flow through a rough single fracture, assessing the effects of various degrees of mismatch between the surfaces. The study also examines how the inclusion of the matrix alters flow characteristics. The results demonstrate that the Forchheimer equation accurately describes the nonlinear flow behavior in fractures with different degrees of mismatch. The increased mismatch intensifies the uneven distribution of fracture apertures, causing the flow velocity to shift from uniform to discrete and the streamlines to become increasingly curved. The overall tortuosity of the flow path increases and the formation of 'concave' and 'convex' areas leads to vortex zones, promoting nonlinear seepage. The correlation between both viscous and inertial permeability with the degree of mismatch is negative, whereas the impact of matrix permeability on the flow capacity of the fracture shows a positive correlation with a mismatch. [ABSTRACT FROM AUTHOR]

This article uses a finite-element approximation approach for solving a three-dimensional flow problem of a nanofluid influenced by heat transfer due to nanoparticles over a non-linearly stretching sheet within an unbounded domain. Utilising similarity transformations, a well-posed coupled system of nonlinear ordinary differential equations is derived from the governing partial differential equations describing the flow and heat transfer processes. The resulting system is then solved by using quadratic Lagrange polynomials as basic functions over a mesh of different finite elements through the Galerkin finite element (GFE) technique. This implementation is based on a regular grid utilising Lagrange polynomials for solving the converted equations. The effects of various parameters of interest are efficiently discussed with the help of graphs and numeric tables. Both numerical and exact solutions are compared favourably, demonstrating a high level of accuracy. It is noteworthy that the GFE method emerges as a much more stable numerical technique than the other existing analytic and semi-analytical methods. Furthermore, the adopted finite-element method reduces the dimensionality of Sobolev's space's finite-dimensional subspace and also improves the solution's convergence rate. Moreover, the velocity is negative, and its magnitude increases as the stretching rates ratio increases due to the downward flow in the vertical direction. The temperature and heat transmission from the sheet are barely impacted by Brownian motion due to the dominance of other forces and length scales involved in the heat transfer process. [ABSTRACT FROM AUTHOR]

Enhanced understanding of flow structure in braided rivers is essential for river regulation, flood control, and infrastructure safety across the river. It has been revealed that the basic morphological element of braided rivers is confluence-bifurcation units. However, flow structure in these units has so far remained poorly understood with previous studies having focused mainly on single confluences/bifurcations. Here, the flow structure in a laboratory-scale confluence-bifurcation unit is numerically investigated based on the FLOW-3DR® software platform. Two discharges are considered, with the central bars submerged or exposed respectively when the discharge is high or low. The results show that flow convergence and divergence in the confluence-bifurcation unit are relatively weak when the central bars are submerged. Based on comparisons with a single confluence/bifurcation, it is found that the effects of the upstream central bar on the flow structure in the confluence-bifurcation unit reign over those of the downstream central bar. Concurrently, the high-velocity zone in the confluence-bifurcation unit is less concentrated than that in a single confluence while being more concentrated than that observed in a single bifurcation. The present work unravels the flow structure in a confluence-bifurcation unit and provides a unique basis for further investigating morphodynamics in braided rivers. [ABSTRACT FROM AUTHOR]

The present study examines numerically a three-dimensional (3D) laminar and stationary flow around an idealized metal foam cell shaped as an empty cube with cylindrical edges. The physical configuration adopted consists of an isolated cell placed inside a plane channel crossed by air as a working fluid. The numerical investigation is carried out using the dimensionless Navier-Stokes equations resolved by finite volume method. The flow configurations given for several Reynolds numbers are described entirely using 2D and 3D maps. The plane maps give streamlines at the side and top fiber planes: the vertical side of the cell is normal to the flow. In addition, the critical locations and zones characterizing the flow are also localized: the saddle points, separation nodes, attachment points, foci of the recirculation zones, and the attachment lines. For the Reynolds number in the range 75 ≤ Re ≤ 500, the results show that the topography of the streamlines at the vertical plane in the middle of the lateral fibers of the cell (z = 5.3Dp) is developed into arc-shaped vortex rollers in the gap. In the wake, two saddle points reveal the zones of influence of these spiral structures, formed by two vortices (Bt and Nw) and zones of upwash and downwash. At a high value of Re (Re = 500), the upwash weakens but does not disappear. Two recirculation bubbles are associated with the two saddles, in the gap and the wake of the upper fibers, parallel to the flow. At Re =500, the distribution flow loses its symmetry and displays matter transfer between the two recirculation. The displacement of the saddle point in the wake is 9.65 times that in the gap. No vortex shedding is observed in the wake of cell due to the nullity of the frequency shedding (f = 0).The results indicate also that decreasing the pore diameter favors recirculation inside the cell gap. These recirculation lengths (Lrz, Lry) located respectively in the wake of planes z = 5.3Dp and y = Dp reduce the drag coefficient in equal proportion (51%) in the range 75 ≤ Re ≤ 500. It appears that the wake of the lateral fibers of the z=5.3Dp plane contributes better to the drag coefficient. We consider that the predominance of downwash associated with the instability of saddle point S.2 in the wake when Re increases leads to a decrease in the drag coefficient in the wake. [ABSTRACT FROM AUTHOR]

The mixing of a passive impurity in a random flow in the limit of weak molecular diffusion, when there is a range of scales between a small diffusion scale and a relatively large correlation length of the gradient of the flow velocity field, is considered. In this range of scales, to describe the evolution of the initial distribution of the impurity in space near a certain Lagrangian trajectory, it is sufficient to approximate the velocity field by a linear profile. Second- and fourth-order correlation functions of the impurity concentration are related to the statistics of the affine deformation of a small volume element of the liquid. Meanwhile, the pair correlation function reflects the extension statistics only in the principal direction, and the fourth-order correlation function reflects in its angular singularities the complete extension statistics in a three-dimensional flow. In a two-dimensional flow, the behavior of the fourth order correlation function in angular singularities has different properties and significantly depends on the diffusion coefficient. The conclusions are valid for any time-uniform gradient of the velocity field and are practically significant for the measurement of this statistics. [ABSTRACT FROM AUTHOR]

This study explored the three-dimensional flow characteristics in a recirculation zone near a permeable buttress in curved channels with varying curvatures. Understanding these characteristics is crucial for managing natural river bends, as rivers often meander, with backwater zones formed behind obstructions, such as mountains in the riverbed. The direct comparison of the recirculation zones across different bend types revealed the correlation between the flow characteristics and bend curvature. However, previous studies have focused on flow velocities and turbulent kinetic energy without a probability density analysis. This analysis provided a more comprehensive understanding of the flow characteristics. Gaussian kernel density estimation was applied in this study to observe the distribution of the flow velocities, turbulent kinetic energy, and turbulent kinetic energy dissipation rate. The results indicated that the longitudinal time-averaged flow velocity in the recirculation zone typically ranged from −0.2 m/s to −0.8 m/s, with all the skewness coefficients exceeding 0. The horizontal time-averaged flow velocity in the recirculation zone fell between −0.175 m/s and −0.1 m/s. The skewness coefficients were negative at water depths of 16%, 33%, and 50% within the 90° and 180° bends, indicating a non-normal distribution. The probability density distribution of turbulent kinetic energy in the recirculation zone was skewed, ranging from 0 to 0.02 m2·s−2, with the skewness coefficient almost always greater than 0. The plot demonstrated multiple peaks, indicating a broad distribution of turbulent kinetic energy rather than a concentration within a specific interval. This distribution included both the high and low regions of turbulent kinetic energy. Although the overall rate of turbulent kinetic energy dissipation in the recirculation zone was relatively low, there were multiple peaks, suggesting the localized areas with higher dissipation rates alongside the regions with lower rates. These findings were significant for managing the meandering river channels, restoring the subaqueous ecosystems, understanding the pollutant diffusion mechanisms in backwater areas, the sedimentation of nutrient-laden sediments, and optimizing the parameters for spur dike design. [ABSTRACT FROM AUTHOR]

Estimating the flow velocity and discharge in rivers is of particular interest for monitoring, modeling, and research purposes. Instruments for measuring water level and surface velocity are generally mounted on bridge decks, and this poses a challenge because the bridge structure, with piers and abutments, can perturb the flow field. The current research aims to investigate the applicability of entropy theory to estimate the velocity distribution and the discharge in the vicinity of river bridges. For this purpose, a computational fluid dynamics (CFD) model is used to obtain three-dimensional flow fields along a stretch of the Paglia River (central Italy), where a historical multi-arch bridge strongly affects flood flows. The input data for the entropy model include the cross-sectional bathymetry and the surface velocity provided by the numerical simulations. A total of 12 samples, including three different flow conditions at four cross-sections, one upstream and three downstream of the bridge, are considered. It is found that the entropy model can be reliably applied upstream of the bridge, also when forced with a single (i.e., the maximum) value of the surface velocity, with errors on total discharge below 13 % in the considered case. By contrast, downstream of the bridge, the wakes generated by the bridge piers strongly affect the velocity distribution, both in the spanwise and in the vertical directions and for very long distances. Here, notwithstanding the complex and multimodal spanwise distribution of flow velocity, the entropy model estimates the discharge with error lower than 8 % if forced with the river-wide distribution of the surface velocity. The present study has important implications for the optimal positioning of sensors and suggests the potential of using CFD modeling and entropy theory jointly to foster greater knowledge of river systems. [ABSTRACT FROM AUTHOR]

Saturated flow film boiling on a sphere has been numerically studied in this work for both vertical and horizontal flow configurations. The simulations were performed using a numerical methodology developed by the authors for boiling flows on three-dimensional unstructured meshes. For interface capturing, the coupled level set and volume of fluid method is used. The interface evolution, vapour wake dynamics and heat transfer have been thoroughly investigated by varying the saturated liquid flow velocity, sphere diameter and wall superheat. The relative importance of both the buoyancy and the inertial forces is described in terms of the Froude number $(Fr)$. The vapour bubble evolves periodically at low $Fr$ values, while a stable vapour column develops at high $Fr$ values. The interface evolution pattern obtained in the present work is in good agreement with the results of experimental studies available in the literature. For all the values of $Fr$ , a stable vapour column develops for a large-diameter sphere and releases vapour bubbles of varying sizes. Furthermore, for a large-diameter sphere, surface capillary waves are observed at the interface, similar to the observations of some of the experimental studies available in the literature. The flow in the liquid and vapour wakes appears to be strongly coupled. The heat transfer in the present work is estimated using the spatially and temporally averaged Nusselt numbers. Finally, an fast Fourier transform analysis of the space-averaged Nusselt number reveals a strong interaction among the different forces. [ABSTRACT FROM AUTHOR]

There are several uses for bio-convection mechanisms, such as in sedimentary pools, fuel models, and microbially accelerated oil restoration. These are the basis of motile microorganisms which are applied to improve the mixability of fluid and tiny nanoparticles because they are accountable for biological transmission procedure. This work examines the bio-convective nanoparticles fluid flow and electrically conducting incompressible magneto-hydrodynamic flow of nanofluid towards a chemically reactive stretchable surface. Buongiorno model is considered here, which incorporates Brownian motion and thermophoretic diffusion, is employed in this study to explain how nanofluids improve heat transfer. The controlling boundary layer nonlinear PDEs are converted into ODEs by utilizing certain suitable similarity approaches. Numerical scheme is adopted to solve the transformed ordinary differential equations. The main findings of this research are that the magnetic field slows motion of the fluid when the thermal and mass buoyancy forces speed it up, and that thermophoretic diffusion increases the temperature and concentration of dimensionless fluids, resulting in stronger concentration and thermal boundary layers. The Brownian motion, concentration exponent, and chemical reaction parameters show an inverse relationship between temperature and concentration. Additionally, the first-order chemical reaction creates a lighter concentration boundary layer while the magnetic field's presence due to impact of thermal and mass buoyancies helps to lower the heat transfer rate and shear stress. The findings show that while the Nusselt number and wall shear stress values are declining, the microorganism number is increasing. [ABSTRACT FROM AUTHOR]

Surface treatment processes such as mass finishing play a crucial role in enhancing the quality of machined parts across industries. However, accurate measurement of the velocity field of granular media in mass finishing presents significant challenges. Existing measurement methods suffer from issues such as complex and expensive equipment, limited to single-point measurements, interference with the flow field, and lack of universality in different scenarios. This study addresses these issues by proposing a single-camera-based method with deep learning to measure the three-dimensional velocity field of granular flow. We constructed a complete measurement system and analyzed the accuracy and performance of the proposed method by comparing the measurement results with those of the traditional DIC algorithm. The results show that the proposed method is very accurate in measuring spatial displacement, with an average error of less than 0.07 mm and a calculation speed that is 1291.67% of the traditional DIC algorithm under the same conditions. Additionally, experiments in a bowl-type vibratory finishing machine demonstrate the feasibility of the proposed method in capturing the three-dimensional flow of granular media. This research not only proposed a novel method for three-dimensional reconstruction and velocity field measurement using a single-color camera, but also demonstrated a way to combine deep learning with traditional optical techniques. It is of great significance to introduce deep learning to improve traditional optical techniques and apply them to practical engineering measurements. [ABSTRACT FROM AUTHOR]

Based on existence results for the Stokes operator and its solution properties in manifolds with cylindrical ends by Große et al. and Kohr et al., the Stokes flow in a three‐dimensional compact domain Ω+$$ {\Omega}^{+} $$ with circular openings Σj(j=1,2)$$ {\Sigma}_j\kern0.1em \left(j=1,2\right) $$ through which the fluid enters and leaves Ω+$$ {\Omega}^{+} $$ through unbounded cylindrical pipes the Stokes flow is modeled as a mixed boundary value problem Ω+$$ {\Omega}^{+} $$ whereas in the cylindrical ends, the velocities and pressures are constant on every straight line in the cylindrical directions with initial values from the openings Σj$$ {\Sigma}_j $$ of Ω+$$ {\Omega}^{+} $$. These values equal the velocities and pressures which are obtained from the mixed boundary values' solution in Ω+$$ {\Omega}^{+} $$ at the openings Σj$$ {\Sigma}_j $$. [ABSTRACT FROM AUTHOR]

The unsteady three-dimensional flow of nanofluid over a stretching surface in the presence of a magnetic field and thermal radiation are investigated. Zero nanoparticle flux at the wall has been considered. Buongiorno's model for nanofluid has been used in this study. Employing similarity transformations, the governing partial differential equations are transformed to ordinary ones and the transformed equations are then solved numerically by using the shooting technique with the help of Runge–Kutta method. The computed results are compared with previously reported work and found in excellent agreement. Fluid velocity initially decreases with the increase of the unsteadiness parameter. Temperature and nanoparticle volume fraction both increase with the increase of unsteadiness parameter. Due to the increase of thermal radiation temperature increases, nanoparticle volume fraction decreases initially but increases away from the surface. The effect of the other governing parameters on velocity, temperature and concentration fields are discussed through their graphical representations. Besides, the local skin friction coefficient, local Nusselt number and local Sherwood number are presented through graphs. [ABSTRACT FROM AUTHOR]

The purpose of this study was to quantify the accuracy of partial volume-corrected three-dimensional volume flow (3DVF) measurements as a function of spatial sampling beam density using carefully-designed parametric analyses in order to inform the target applications of 3DVF. Experimental investigations employed a mechanically-swept curvilinear ultrasound array to acquire 3D color flow (6.3 MHz) images in flow phantoms consisting of four lumen diameters (6.35, 4.88, 3.18 and 1.65 mm) with volume flow rates of 440, 260, 110 and 30 mL/min, respectively. Partial volume-corrected three-dimensional volume flow (3DVF) measurements, based on the Gaussian surface integration principle, were computed at five regions of interest positioned between depths of 2 and 6 cm in 1 cm increments. At each depth, the color flow beam point spread function (PSF) was also determined, using in-phase/quadrature data, such that 3DVF bias could then be related to spatial sampling beam density. Corresponding simulations were performed for a laminar parabolic flow profile that was sampled using the experimentally-measured PSFs. Volume flow was computed for all combinations of lumen diameters and the PSFs at each depth. Accurate 3DVF measurements, i.e., bias less than ±20%, were achieved for spatial sampling beam densities where at least 6 elevational color flow beams could be positioned across the lumen. In these cases, greater than 8 lateral color flow beams were present. PSF measurements showed an average lateral-to-elevational beam width asymmetry of 1:2. Volume flow measurement bias increased as the color flow beam spatial sampling density within the lumen decreased. Applications of 3DVF, particularly those in the clinical domain, should focus on areas where a spatial sampling density of 6 × 6 (lateral x elevational) beams can be realized in order to minimize measurement bias. Matrix-based ultrasound arrays that possess symmetric PSFs may be advantageous to achieve adequate beam densities in smaller vessels. [ABSTRACT FROM AUTHOR]

Porous materials are increasingly being used in the design of floating structures in coastal and ocean engineering, but there is a lack of numerical tools that can aid in the design of a movable floating porous structure. To close this gap, the existing volume-averaged numerical model for flow interacting with a fixed porous body was extended to floating scenarios by (1) using the relative velocity in the porous friction force, (2) calculating rigid body motion using volume integral of porous body force, and (3) modifying a dynamic mesh algorithm for a mobile porous body. As a demonstration, the developed model was applied to a porous floating structure consisting of cubically packed uniform spheres. Two sets of model applications were involved. The first set considered three-dimensional flow around a fixed porous block placed beneath the free surface. The measured total force on the block under wave or steady flows was predicted accurately with an error less than 10%. The second set involved a two-dimensional wave interacting with a floating porous block representing a breakwater. For free-floating conditions, the model can accurately predict the dynamic response of the structure, including the time varying movement of its rigid body and the mean drift. For mooring-restrained conditions, the mooring force and wave transmission coefficients were also predicted well with an error less than 20%. The proposed numerical approach can be applied to other floating structures with a rigid volumetric porous body. Future research is also required to study the microscopic pore flows, upon which more detailed parameterization of the porous media can be derived. [ABSTRACT FROM AUTHOR]

This study employed numerical simulations to investigate the three-dimensional hydrodynamic structure of a channel obstructed by submerged rigid canopies. After validating the model using existing experimental data, a series of numerical experiments varying the canopy density and the blocking ratio were conducted. The results indicate that submerged canopy, different from emergent canopies, triggers the generation of three-dimensional coherent vortices. When canopies expand laterally, the scale, location, and evolution characteristics of cross-sectional secondary flows vary. The direction of secondary circulation at the canopy top of the fully covered vegetation channel is affected by the river width/depth ratio. Three-dimensional coherent vortices are jointly controlled by vertical and transverse Reynolds stresses. When the channel is seriously blocked, the degree of momentum exchange in the mixing layer does not change significantly. The boundary friction effect dominates the momentum exchange process near the wall. An equation coupling the drag length scale and blocking ratio with the vertical coherent vortex penetration length is proposed, indicating that the penetration length increases exponentially with both variables. Higher canopy density exhibits a stronger resistance to the vertical coherent vortex penetration length. In the process of canopy lateral expansion, the evolution time of the outer vortex to scale stability is longer than that of the inner vortex. The significance of research on the three-dimensional vortex structure of rigid submerged vegetation is established based on previous studies and existing conclusions. [ABSTRACT FROM AUTHOR]

Natural channels often take the form of compound channels during flooding events. The unsteadiness of floods is crucial for flood management and river-floodplain ecosystems. However, the impact of unsteady flow on three-dimensional hydrodynamic processes within compound channels remains poorly understood. This study employed a validated two-dimensional/three-dimensional numerical model to examine how unsteady features influence key hydrodynamic indicators of compound channels, such as velocity distribution, turbulence characteristics, and discharge partitioning between the main channel and floodplain. A definitive positive correlation was found between water level fluctuation amplitudes and integrated discharge during unsteady events, as well as between mean water levels and mean discharges. The proportion of discharge conveyed by the main channel relative to the total was directly linked to the water depth ratio. The exchange at the main channel–floodplain interface exhibits a dual-layer flow pattern: surface waters spill into the floodplain, while deeper waters are siphoned into the main channel. Unsteady conditions principally modulate the intensity of these exchanges, altering hydraulic interactions and water transfer between areas. Pronounced wall shear stresses were detected at the main channel–floodplain interface due to swift channel flows and momentum exchange at the floodplain margin, with maxima adjacent to the floodplain edge correlating with peak flow velocities. Under deep conditions, cross-sectional flow across the compound channel's mixing layer was essentially two-dimensional. These findings elucidate the complex hydrodynamics inherent to unsteady overbank flows while holding implications for enhancing floodplain management and advancing the understanding of unsteady fluvial hydraulics. [ABSTRACT FROM AUTHOR]

Steady solutocapillary convection and instability near the air–liquid interface are studied. First, under the assumption of the conically similar viscous flow, an exact axisymmetric solution of the steady solutocapillary convection near the air–liquid interface is determined due to a constant mass flux. It is shown that the constant mass flux and the radial surface tension cause the divergent motion at the interface and the Marangoni convection beneath the interface. Then, the linear stability of the steady solutocapillary convection in response to the azimuthal disturbance is analyzed. At a given Peclet number (or Schmidt number), the steady basic flow loses its stability when the Reynolds number is beyond its critical value. It is found that for the fixed Schmidt number, the critical Reynolds number increases monotonously as the harmonic wave number of the azimuthal disturbance increases. However, for the fixed Peclet number, a nonlinear relationship between the critical Reynolds number and the harmonic wave number of the azimuthal disturbance is found. The structures of iso-concentration lines and velocity fields in the three-dimensional flow system depend on the disturbance harmonic wave number, which is dominated by both the radial and the azimuthal surface tensions. This study provides a profound understanding of the soluble surfactant-driven instability of a divergent flow near the air–liquid interface, which is of great significance for practical applications in the micro-fluidics related to chemistry and biology. [ABSTRACT FROM AUTHOR]

This study systematically investigates the flow birefringence of cellulose nanocrystal (CNC) suspensions. The aim is to clarify the importance of the stress component along the camera's optical axis in the stress-optic law (SOL), which describes the relationship between birefringence, the retardation of transmitted polarized light, and the stress field. More than 100 datasets pertaining to the retardation of CNC suspensions (concentrations of 0.1, 0.3, 0.5, and 1.0 wt%) in a laminar flow field within a rectangular channel (aspect ratios of 0.1, 1, and 3) are systematically obtained. The measured retardation data are compared with the predictions given by the conventional SOL excluding the stress component along the camera's optical axis and by the SOL including these components as second-order terms (2nd-order SOL). The results show that the 2nd-order SOL gives a significantly better agreement with the measurements. Based on the 2nd-order SOL, the retardation at the center of the channel, where the effect of the stress component along the camera's optical axis is most pronounced, is predicted to be proportional to the square of the flow rate, which agrees with the experimental data. The results confirm the importance of considering the stress component along the camera's optical axis in the flow birefringence of CNC suspensions at high flow rates, even for quasi-two-dimensional channel flow. [ABSTRACT FROM AUTHOR]

This study investigates a dual-stage axial-flow fan within a specific power plant context. Numerical simulations encompassing both steady-state and stall conditions were conducted utilizing the Reynolds-averaged Navier–Stokes (RANS) equations coupled with the Realizable k–ε turbulence model. The findings reveal that, under normal operating conditions, there exists a positive correlation between the mass flow rate and outlet pressure with gas density while displaying a negative correlation with dynamic viscosity. Regardless of the changes in air density, the volumetric flow rate at the maximum outlet pressure of the fan remains essentially the same. When a stall occurs, the volumetric flow rate rapidly decreases to a specific value and then decreases slowly. The analysis of the three-dimensional flow field within the first-stage rotor was performed before and after the rotational stall occurrence. Notably, stall inception predominantly manifests at the blade tip. As the flow rate diminishes, the leakage area at the blade tip within a passage expands, directing the trajectory of the leakage vortex toward the leading edge of the blade. Upon reaching a critical flow rate, the backflow induced by the blade tip leakage vortex obstructs the entire passage at the blade tip, progressively evolving into a stall cell, thereby affecting flow within both passages concurrently. [ABSTRACT FROM AUTHOR]

In this study, a CFD computational model has been established to properly simulate complex correctly expanded supersonic flow generated by a three-dimensional C–D nozzle for the purpose of Thrust Vector Control (TVC) simulations. Jet tabs affixed to the perimeter of the nozzle exit are used to achieve thrust vectoring. This study focuses on the estimation of the force on the tabs due to the jet issued from the C–D nozzle using Ansys 19.2 three-dimensional density based solver, implicit formulation with SST K–ω turbulence model. The force is calculated for different tab configurations based on tab sector angles of 60°, 90°& 120° for the designed Mach number and X/D ratio of 0.7. The nozzles with Mach 1.6, Mach 1.8 and Mach 2.0 designed using SolidWorks are compared. It has been observed that with an increase in sector angle, tab force increased by an average of 70 % for sector angle of 60° to 90° and 36 % for sector angle of 90° to 120°. [ABSTRACT FROM AUTHOR]