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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]

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]

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 used the two-dimensional fluid volume method to investigate the effect of vibration on the detachment and removal of droplets in the two-dimensional/three-dimensional flow channel of proton exchange membrane fuel cell (PEMFC). The vibration frequency was used as the main variable to study the dynamic process of droplets in the channel, and typical droplet flow modes and separation methods were determined. The water removal ability of the two-dimensional/three-dimensional flow channel under vibration conditions was evaluated using droplet breakage time and coverage rate as evaluation indicators. Finally, the orthogonal table method was used to analyze the effects of vibration frequency, vibration amplitude, wind speed, and droplet size on the water removal ability of the three-dimensional flow field. The results indicate that under vibration conditions, the main motion modes of droplets are rolling mode and crushing mode and that the drainage capacity of the three-dimensional flow field is much higher than that of the two-dimensional flow field in both modes. The impact of vibration on the removal of droplets in the flow channel in the crushing mode is more significant compared to the rolling mode, and the vibration frequency has a greater impact on the drainage efficiency of the three-dimensional flow channel compared to the vibration amplitude. This study is of great significance for understanding the dynamics of droplets in PEMFC gas channels under vibration conditions as well as for optimizing the design and operating conditions of these channels. [ABSTRACT FROM AUTHOR]

Research on three-dimensional (3D) flow velocity fields holds significant importance in aerodynamic performance design, energy power, and biomedicine. Nevertheless, current techniques for measuring three-dimensional flow velocity fields, such as tomographic particle image velocimetry (Tomo-PIV), have challenges in achieving accurate and high-resolution measurements of tiny structures in flow fields. Consequently, a 3D flow field super-resolution (SR) reconstruction method based on Swin-Transformer framework (SWINFlow-3D) has been proposed in this paper. SWINFlow-3D comprises stacked residual channel attention Swin-transformer blocks, each containing multiple Swin-Transformer standard layers, incorporating a hybrid attention mechanism that allows for integrating relevant information from several channels and gives greater importance to critical information. Second, a loss function for SR reconstruction of the flow field has been introduced, taking into account the physical constraints such as divergence and curl. Furthermore, the characteristics obtained by interpolation downsampling methods are different from those of real experiments. To address this limitation, we construct a dataset based on cross correlation downsampling. Simulation experiments are carried out on Johns Hopkins Turbulence Database isotropic turbulence data and cylindrical wake data. The results are subsequently compared with those of the interpolation approach and 3D flow field SR reconstruction method, and our model yields the best results for all the metrics. Ultimately, to ascertain the accuracy and practical applicability of the model in practical tests, we conduct experiments on jet data and cylindrical wake recorded by Tomo-PIV. The experimental results demonstrate that SWINFlow-3D with the loss function presented in this study can be used to effectively reconstruct the 3D flow field and flow features, exhibiting strong generalizability. [ABSTRACT FROM AUTHOR]

Cartesian cut-cell meshes are favored for their excellent complex geometric adaptability, orthogonality, and mesh generation convenience. However, the difficulty in constructing shape function for hanging-node and irregular cut-cell elements limits their use in a standard finite element method (FEM). Inspired by the point interpolation method shape function used in a smoothed finite element method (S-FEM) which adapts to the arbitrary shape of an element, this work proposes a cell-based S-FEM using Cartesian cut-cell meshes for incompressible flows. Four different types of cell-based smoothing domains (CSDs) are constructed and compared in the Cartesian cut-cell mesh, involving node-based CSD (NCSD), face-based CSD (FCSD), mixed CSD (MIXCSD), and tetrahedral CSD (T4CSD). The smoothed Galerkin weak form and semi-implicit characteristic-based split (CBS) scheme are employed for spatial discretization and stabilization of Naiver–Stokes (N–S) equations, respectively. Several numerical examples are utilized to compare the convergences, computational accuracy, and computational efficiency of proposed CSDs. The numerical results demonstrate that FCSD and T4CSD exhibit instability. Conversely, NCSD and MIXCSD exhibit good stability, and NCSD shows slightly higher computational accuracy than MIXCSD, but at a lower computational efficiency. Additionally, the results show that Cartesian cut-cell meshes offer superior computational accuracy compared to tetrahedral meshes. Therefore, the present method provides an attractive numerical technique for solving flow problems with complex geometries. [ABSTRACT FROM AUTHOR]

Deep-learning models garnered considerable attention in the field of fluid mechanics for physics discovery and approximation-model generation. This study aims to develop an approximation model to predict the flow field inside realistic fibrous filters based on an image-to-image approach to replace three-dimensional (3D) computational fluid dynamics (CFD) simulations, which are computationally expensive and difficult to apply to realistic fibrous filters. A data-driven framework is proposed using deep convolutional neural networks (CNNs) to provide a per-pixel prediction of the flow field. The model inputs are two-dimensional x-ray computed tomography images, whereas the outputs are the 3D distributions of the velocity vectors and pressure. High-resolution 3D CFD simulations are performed to create a database to train and test the CNN model. The model is applied to surgical and N95 face masks. The relative error of the CNN model over the test dataset is approximately 10% in regions with high velocity and pressure, and the model can provide a detailed high-resolution prediction of the flow field with a speedup of about three orders of magnitudes. A strict generalization test is conducted for completely unseen 3D segments with complex microstructures. The model generalizability still needs more improvements; however, the model can provide a low-resolution 3D flow field for those segments that can be used as the initial condition for CFD simulation to reduce the CFD computational time. This framework can be utilized for other types of filters and provides a basis for the design and optimization of fibrous filters. [ABSTRACT FROM AUTHOR]

The onset of flow-induced oscillations in valve-like configurations remains not completely understood, despite the wide relevance in fluid transport across human physiology and various industrial applications. The present work explores the excitation mechanisms of self-sustained oscillation with key operating parameters in a general-purpose configuration by means of high-fidelity simulations. The investigation is carried out with a partitioned framework that resolves the fluid field by a finite-difference fractional step scheme, discretizes the structural domain via an isogeometric method, and considers an immersed boundary forcing through the interpolation/spreading kernel built by moving-least squares. Our findings confirm the onset of flapping motion in valvular shells, jointly influenced by geometric parameters, structural properties, and flow conditions. Specifically, at a Reynolds number (Re) of 800 and shell aspect ratio of 1.0, a critical reduced velocity exists at around 6, bifurcating static and periodic oscillation modes. After this criterion, flexible shells flutter in the third-plate-mode natural frequency, with oscillation amplitudes approaching an asymptotic value, coupled with intensified vortex shedding, as the reduced velocity increases. Re mainly imparts a destabilizing effect on the fluid-shell system; a lower Re suppresses flow-induced vibrations through viscous dissipation, while a higher Re introduces three-dimensional complexities, asymmetrical oscillations, and quasi-periodicity in the flapping dynamics, especially within the critical regime of reduced velocity. The impact of shell aspect ratio is intricate; in contrast, the case with an aspect ratio of 1.3 displays more intensive flapping motion compared to the reference case of 1.0, whereas further increasing to 1.6 mainly shows stabilizing effects in the shell dynamics. [ABSTRACT FROM AUTHOR]

The internal flow within an evaporating sessile droplet is one of the driving mechanisms that lead to various particle deposition patterns seen in applications such as inkjet printing, surface patterning, and blood stain analysis. Despite decades of research, the causal link between droplet internal flow and particle deposition patterns has not been fully established. In this study, we employ a three-dimensional (3D) imaging technique based on digital inline holography to quantitatively assess the evolution of internal flow fields and particle migration in three distinct types of wetting droplets, namely water droplets, sucrose aqueous solution droplets, and sodium dodecylsulfate aqueous solution droplets, throughout their entire evaporation process. Our imaging reveals the three-stage evolution of the 3D internal flow regimes driven by changes in the relative importance of capillary flow, Marangoni flow, and droplet boundary movement during evaporation. Moreover, the migration of individual particles from their initial locations to deposition can be divided into five categories, with some particles depositing at the contact line and others inside the droplet. In particular, we observe the changing migration directions of particles due to competing Marangoni and capillary flows. We further develop an analytical model that predicts the droplet internal flow, deposition patterns, and determines the deposition mechanisms depending on their initial locations and evolving internal flow. The model, validated using different types of droplets from our experiment and the literature, can be further expanded to other Newtonian and non-Newtonian droplets, potentially serving as a real-time assessment tool for particle deposition in various applications. [ABSTRACT FROM AUTHOR]

In arbitrary water depths, the influence of uniform flow, which includes transverse and longitudinal flows, on the generation of three-dimensional (3D) freak waves is examined. A modified Davey–Stewartson equation is derived using potential flow theory and the multiscale method. This equation describes the evolution of 3D freak wave amplitude under the influence of uniform flow. The relationship between two-dimensional (2D) modulational instability (MI) and the generation of 3D freak waves, as represented by the modified 3D Peregrine Breather solution, is explored. The characteristics of 2D MI depend on the orientation of the longitudinal and transverse perturbations. In shallow waters, the generation of freak waves by MI is challenging due to the minimal orientation difference, and longitudinal flows hardly affect the occurrence of MI. Variations in relative water depth can contribute to forming shallow-water freak waves. In finite-depth waters, oblique modulation leads to MI, whereas in deep and infinite-depth waters, longitudinal modulation gains significance. In environments of finite-depth, deep, and infinite-depth waters, the divergence (convergence) effect of longitudinal favorable (adverse) currents reduces (increases) the MI growth rate and suppresses (facilitates) freak wave generation. [ABSTRACT FROM AUTHOR]

Coupled with Co-flow Jet (CFJ) technology, the Non-dominated Sorting Genetic Algorithm II was utilized for the multi-objective combination optimization of an optimized Co-flow Jet wing, based on National Advisory Committee for Aeronautics (NACA) 6421. A high-precision numerical simulation using the delayed detached eddy simulation model was performed on the optimized wing to investigate the three-dimensional flow separation characteristics after static stall. The stall improvement was investigated by adjusting the momentum coefficient of the injection. The results show that the optimized wing exhibits significant improvements in aerodynamic performance and corrected aerodynamic efficiency. At an angle of attack of 10°, the average lift increased by 16.25% and the drag decreased by 27.23% compared to the CFJ6421 wing, while effectively addressing the problem of low modified aerodynamic efficiency of the CFJ wing at lower angles of attack. By utilizing higher momentum and improving the boundary layer control capability, flow separation is effectively suppressed, thus achieving the goal of stall recovery of the CFJ wing. [ABSTRACT FROM AUTHOR]

The real-time computation of a three-dimensional pipe network flow is crucial for both pipe design and operational maintenance. This study devises a novel reduced-order configuration approach that combines the advantages of the acceleration characteristics of the reduced-order model and the structural applicability of the configuration model. First, a configuration model is established by categorizing sub-pipes extracted from a pipe network into sets based on the sub-pipes' type. Subsequently, reduced-order configurations are realized by a reduced-order model established for each type of configuration, enabling real-time computation of individual sub-pipes. Thus, the concatenation of sub-pipes allows the computation of an entire pipe network. A complex boundary–deep learning–reduced-order configuration model and a complex boundary–deep learning–reduced-order configuration–multi-source data–reduced-order configuration model integrated with a local multi-physical–discrete empirical interpolation method and a multi-source data fusion model are devised. These models were employed for the real-time computation and prediction of a three-dimensional velocity field for 300 snapshots composed of one to four sub-pipes extrapolated from a dataset of 294 pipe network snapshots composed of one to three sub-pipes. The maximum relative errors for snapshots from the dataset were similar to the limit precision of the proper orthogonal decomposition, with more precise accuracy than the relevant studies, indicating the excellent performance of our reduced-order configuration approach. [ABSTRACT FROM AUTHOR]

A great amount of thermodynamic losses and mechanical damages in industrial equipment occur due to the condensation phenomenon and two-phase flows in such equipment. In this study, supercooled vapor suction has been passively used in the 3D (three-dimensional) steam turbine stationary blade. Supercooled vapor suction is one of the techniques used in turbines for resisting corrosion and erosion. For the supercooled flow suction, the design is as follows: an embedded channel inside the turbine blade in the nucleation zone, which has the utmost non-equilibrium mode; furthermore, the impacts of the location and surface of the channels devised in the turbine blade for supercooled vapor suction on the following parameters have been investigated: the two-phase flow, the suction ratio, condensation losses, erosion ratio, the average droplet growth, and kinetic energy. Based on the results, in the optimal case (case F), the condensation losses, erosion ratio, average droplet radius, and kinetic energy decrease by 3%, 24%, 6.5%, and 2%, respectively; also, the suction ratio is 3.6%. The present research reveals that the supercooled vapor suction, due to a decrease in the surface necessary for the condensation, decreases turbine blade corrosion and erosion. This fact can provide the turbine designers with beneficial information. [ABSTRACT FROM AUTHOR]

We investigated the drag-reducing capabilities of a flexible coating on a rigid bluff body. Conducted in a wind tunnel, our experiments employed a rigid plate coated with a polyethylene membrane of various widths. The results indicated that the drag reduction, contingent on the membrane width, could reach up to 22.2%. Smoke-wire visualization corroborated the delay in flow separation and the emergence of narrower wake structures. This effect is ascribed to the self-adaptation of the flexible membrane to the fluid dynamics. Our study reveals that such passive flow control mechanisms are highly effective in complex, turbulent, three-dimensional flow conditions. [ABSTRACT FROM AUTHOR]

Understanding the flow behavior of non-Newtonian fluids from an industrial standpoint is crucial. Many industrial and technical activities, such as the extrusion of polymer sheets, the manufacturing of paper, and the development of photographic films, require non-Newtonian fluids. Heat and mass transport have various manufacturing uses. However, classical heat and mass transfer theories (Fourier and Fick laws) cannot anticipate thermal and solute relaxation time occurrences. The purpose of this investigation is to apply the modified Ohm law to the heat and mass transportation systems, which are established by generalized Fourier and Fick's equations, respectively. A three-dimensional Darcy–Forchheimer flow through a porous medium integrating Hall and ion slip effects is studied for a non-Newtonian fluid known as a "Casson nanofluid" with mixed convection across a stretched surface. To investigate heat transfer augmentation, the modified Buongiorno model for nanofluids is used. It covers practical nanofluid properties as well as the mechanics of random motion and thermo-migration in nanoparticles. These groups of Partial Differential Equations (PDEs) that represent the mathematical model are combined with the proper similarity transformations to create an ordinary differential equations system, which is then resolved using the power of the Lobatto IIIA method. Examples of numerical and graphical data are given to show how various physical constraints affect the variation for velocities, temperatures, mass transfer, dimensionless shear stress, as well as Nusselt and Sherwood numbers. It turns out that lowering the Casson fluid parameters' values reduces the velocity in the spatial coordinates (x, y). A rise in the Hall parameter's values ultimately leads to an improvement in the fluid. This paper sheds light on useful applications including power generation, conservation of energy, friction elimination, and nanofluidics. Nonetheless, the work highlights an important point: by carefully adjusting the Casson parameter, thermophoresis parameter, and Brownian motion parameter, the flow of a Casson fluid, including nanoparticles, may be controlled. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of real surface roughness on channel flow using direct numerical simulation assisted by a ghost cell immersed boundary method (DNS-GCIBM). The principles and implementations of DNS-GCIBM are first introduced. Two test cases, including the two-dimensional flow around a cylinder and the three-dimensional flow in a sinusoidal roughness channel are employed to demonstrate the practicability and accuracy of the proposed approach, especially in numerical studies on the rough wall-bounded flow. Using DNS-GCIBM, channel flows under conditions of Ma = 0.3 and R e τ ≈ 300 , with both the real-world and regular roughness surfaces are studied. The results are statistically analyzed using the triple decomposition technique. The outer layer similarity in the streamwise mean velocity and Reynolds stress profiles indicate that the impact of roughness on the boundary layer primarily localizes within roughness sub-layer. In the streamwise mean velocity profile, both regular and real-world roughness surfaces induce obvious increase to the roughness function Δ U + as roughness height Ra increases, while discrepancy of Δ U + between the two types of roughness can be found. Furthermore, turbulence statistics are sensitive to the variations of Ra. As Ra increases, it becomes challenging to organize coherent structures near the wall, resulting in the reduction of streamwise Reynolds stress intensity. In addition, although the skin friction coefficient and Δ U + are almost the same, the real-world roughness and the corresponding equivalent regular roughness manifest different flow structures near the wall. The real-world roughness contributes greater spatial inhomogeneity but lower turbulence intensity. [ABSTRACT FROM AUTHOR]

Mosquitoes exhibit a distinctive and remarkable flight pattern, flapping their wings at a high frequency with relatively small stroke amplitude. However, until recently, the underlying aerodynamic mechanisms have remained unclear. Furthermore, there is a lack of understanding about their flight behaviors after blood-feeding and the corresponding aerodynamic characteristics. This study aims to explore this uncharted area, conducts experiments to acquire kinematic and morphological data and numerical simulations to obtain three-dimensional flow characteristic. Further analysis uncovers several key findings. Both before and after blood-feeding hovering exhibit a similar flapping wing pattern, characterized by downstroke and upstroke with three stages of each half stroke. After blood-feeding, there are significant increases in stroke amplitude, mid-downstroke duration, velocity, and flip angles. Additionally, body pitch, stroke plane tilt, and Reynolds number experience increments. In hovering, mosquitoes balance vertical force with weight, with substantial peaks observed in each stage, particularly during the mid-stroke. After blood-feeding, the vertical force experiences a 3.3-fold increase, with the majority of the increase occurring during the mid-downstroke. The study identifies three unsteady mechanisms for aerodynamic force generation without blood-feeding hovering, namely, added-mass force, delayed stall, and fast-pitching-up rotation. These mechanisms persist after blood-feeding, with a greater reliance on delayed stall to support increased weight. [ABSTRACT FROM AUTHOR]

Scale-adaptive simulations (SAS) of three-dimensional flow around a circular cylinder fitted with a passive version of a novel flow control method (passive Venturi actuator, PVA) are performed at a diameter-based Reynolds number of Re = 28 000. The PVA consists of one or more narrow slits located at the top and/or bottom sides of the cylinder that connected to the throat of the axial Venturi slit in this cylinder. The main purpose of the study is to investigate the influence of divergence angle and narrow slit location relative to the axial Venturi slit on the aerodynamic performance of the cylinder. To this end, four models were designed with various PVAs. Additional models, a plain cylinder (unmodified model) and a cylinder fitted with an axial Venturi slit (model without a narrow slit), were also used for quantitative comparison. SAS predicts that an additional 5% reduction in the time-averaged drag coefficient, ⟨ C D ⟩ , was observed when two narrow slits located on the surface at an angle of ±80° from the front stagnation line were fitted to the cylinder with an axial Venturi slit. Reducing the divergence angle of the PVA leads to improvements in ⟨ C D ⟩ and root mean square of fluctuating force coefficients, C D − rms and C L − rms . It is found that a cylinder with a PVA that has two narrow slits and a divergence angle of 6° can produce a 28.6% reduction in ⟨ C D ⟩ , a 58.5% reduction in C D − rms , and an 81.2% reduction in C L − rms , when compared to the plain cylinder. [ABSTRACT FROM AUTHOR]

This study presents a deep learning approach for predicting the flow field in the incompressible turbulent three-dimensional (3D) external flow around right-rhombic prism-shaped bluff bodies. The approach involves treating the nodes of the unstructured grid in the computational fluid dynamics domain as a point cloud, which is used as an input for a neural network. The neural network is trained to map the spatial coordinates of the nodes to the corresponding velocity and pressure values in the domain. The PointNet, a reliable solution in 3D vision tasks, is selected as the neural network architecture. Implementing this architecture makes it feasible to use irregular positions of the nodes of an unstructured grid as an input without needing interpolation. A dataset, comprising 3511 cases, is generated for training and testing the network. This is achieved by changing the geometric parameters of a right rhombic prism and varying its angle to the flow stream. Then, the continuity and momentum equations for turbulent flow are solved using a solver. Given the need for a larger number of points to accurately represent a 3D flow, the architecture of PointNet is modified. This modification involves adding extra layers and adjusting the number of neurons inside the layers to overcome this challenge. Once the training is completed, given the unseen samples from the test dataset to the model, our model can predict the velocity and pressure of the flow field at a speed that exceeds our conventional solver by several orders of magnitude with a maximum relative error of 4.58%. [ABSTRACT FROM AUTHOR]

Due to the limited length of cylinders, their use in practical engineering inevitably involves end effects, which results in three-dimensional flows at the ends of cylinders. These flow fields are the main factor influencing the aerodynamic and flow field characteristics of cylinders. Regarding a finite-length cylinder rotor, a specific pattern of tip vortices will form under the action of rotation, resulting in notable differences in the aerodynamic characteristics between an ideal two-dimensional cylinder and a finite-length cylindrical rotor. In the present study, the large eddy simulation method is used to systematically investigate cylinder rotors with various aspect ratios. By analyzing the sectional aerodynamic and flow field characteristics, the variation laws of the aerodynamic force, wind pressure, and flow field characteristics of cylinder rotors under the influence of end effects were summarized. The results show that the influence range and intensity of the tip vortices on the rotor flow field and sectional aerodynamic characteristics are dominated by the dimensionless rotating speed, which in turn affects the range of the end effects. The development trend of the tip vortices is analyzed and discussed from multiple aspects, including sectional aerodynamics, the pressure coefficient, and the flow correlation, and an attempt is made to explain changes in the phenomenon. [ABSTRACT FROM AUTHOR]

The stability analysis of laminar channel flow subject to spanwise thermal modulations is presented. Modulations create streamwise streaks and rolls, producing three-dimensional flow structures. It is shown that these structures induce a new type of instability which persists at low Reynolds numbers. Detailed characterization and quantification of this instability are given, including an explanation of its mechanism. It is shown that heating intensity and spatial distribution control this instability; its intensity increases with a reduction of the Prandtl number, and it can be induced by heating of either wall. [ABSTRACT FROM AUTHOR]

This work presents a novel two-fluid method based on our recently proposed viscosity model for red blood cells (RBCs)—for simulating three-dimensional (3D) blood flow in a microchannel of dimension comparable to the diameter of red blood cells and larger. Toward this, whole blood is assumed as a suspension of red blood cells in blood plasma, with each phase considered as interpenetrating continua having its separate mass and momentum conservation equations. The proposed approach-based performance study is presented after comprehensively validating it with experimental data for blood flow in a uniform, sudden expansion-constriction, and Y-shaped bifurcated rectangular microchannels over—an extensive range of size (25–330 μm), flow rates (11.8 μl/h–30 ml/h), and inlet hematocrit (0%–45%). The proposed approach effectively captures significant biophysical and biomechanical insights into blood flow. It highlights a migration of red blood cells toward the center of the microchannel and the formation of a cell-free layer near the wall. Notably, with the introduction of constriction and expansion in the microchannel, it predicts a fivefold enhancement of the cell-free layer. The Fahraeus and Fahraeus–Lindquist effects are also demonstrated in microchannels, with less than 300 μm characteristic dimensions. These findings are consistent with experimental evidence. In addition to experimentally evident phenomena, our simulations unveil several additional flow phenomena and features of blood flow in the microchannel. It is observed that the presence of confluence (merging flow) is more disturbing to the blood flow than the presence of diverging bifurcations (splitting flow). Furthermore, after the confluence, velocity profiles exhibit a local peak that persists up to the microchannel outlet. Primary contribution of this work lies in the proposal of a two-fluid method for simulating 3D blood flow in complex geometries. This approach provides a comprehensive understanding of blood flow dynamics in microchannels and can be applied to optimize dimensions and geometries during the initial phases of plasma separation microdevices development. [ABSTRACT FROM AUTHOR]

We investigate the control of three-dimensional flow separation around a finite wall-mounted square cylinder by applying suction at the side leading edge. Direct numerical simulations are conducted at a Reynolds number of 250, with suction ratios Γ of 0–2 (where Γ is the absolute value of the suction velocity divided by the free stream velocity). The effect of Γ on the aerodynamic forces acting on the cylinder is studied. The results show that suction reduces the aerodynamic forces, with the best control effect for the fluctuating lift coefficient (corresponding to a reduction of over 70%) achieved at Γ = 0.375. As the suction ratio increases, the pressure drag experienced by the square cylinder decreases. Simultaneously, the mean frictional drag force exerted on the square cylinder increases. The optimal mean drag coefficient (corresponding to a reduction of nearly 20%) is achieved at Γ = 1. The effect of the suction ratio on the flow topology in the wake is also investigated. Suction significantly suppresses the flow separation. As the suction ratio increases, the spanwise counter-rotating vortices in the streamwise and transverse directions decreases in size, and the downwash vortex shrinks, and shifts toward the free end of the square cylinder. The far-wake streamwise base vortex disappears when active suction is applied to the side leading edge. However, a new pair of base vortices splits from the original base vortex and persists into the far wake flow field, forming a quadrupole vortex structure with the tip vortex. [ABSTRACT FROM AUTHOR]

Conducting large-scale numerical computations to obtain flow field during the hypersonic vehicle engineering design phase can be excessively costly. Although deep learning algorithms enable rapid flow field prediction with high-precision, they require a significant investment in training samples, contradicting the motivation of reducing the cost of acquiring flow field. The combination of feature extraction algorithms and regression algorithms can also achieve high-precision prediction of flow fields, which is more suitable to tackle three-dimensional flow prediction with a small dataset. In this study, we propose a reduced-order model (ROM) for the three-dimensional hypersonic vehicle flow prediction utilizing proper orthogonal decomposition to extract representative features and Gaussian process regression with improved automatic kernel construction (AKC-GPR) to perform a nonlinear mapping of physical features for prediction. The selection of variables is based on sensitivity analysis and modal assurance criterion. The underlying relationship is unveiled between flow field variables and inflow conditions. The ROM exhibits high predictive accuracy, with mean absolute percentage error (MAPE) of total field less than 3.5%, when varying altitudes and Mach numbers. During angle of attack variations, the ROM only effectively reconstructs flow distribution by interpolation with a MAPE of 7.02%. The excellent small-sample fitting capability of our improved AKC-GPR algorithm is demonstrated by comparing with original AKC-GPRs with a maximum reduction in a MAPE of 35.28%. These promising findings suggest that the proposed ROM can serve as an effective approach for rapid and accurate vehicle flow predicting, enabling its application in engineering design analysis. [ABSTRACT FROM AUTHOR]

The influence and validity of wall boundary conditions for non-equilibrium fluid flows described by the Boltzmann equation remains an open problem. The substantial computational cost of directly solving the Boltzmann equation has limited the extent of numerical validation studies to simple, often two-dimensional, flow problems. Recent algorithmic advancements for the Boltzmann–Bhatnagar–Gross–Krook equation introduced by the authors [Dzanic et al., J. Comput. Phys. 486, 112146 (2023)], consisting of a highly efficient high-order spatial discretization augmented with a discretely conservative velocity model, have made it feasible to accurately simulate unsteady three-dimensional flow problems across both the rarefied and continuum regimes. This work presents a comprehensive evaluation and validation of wall boundary conditions across a variety of flow regimes, primarily for the purpose of exploring their effects on momentum transfer in the low Mach limit. Results are presented for a range of steady and unsteady wall-bounded flow problems across both the rarefied and continuum regimes, from canonical two-dimensional laminar flows to unsteady three-dimensional transitional and turbulent flows, the latter of which are the first instances of wall-bounded turbulent flows computed by directly solving the Boltzmann equation. We show that approximations of the molecular gas dynamics equations can accurately predict both non-equilibrium phenomena and complex hydrodynamic flow instabilities and show how spatial and velocity domain resolution affect the accuracy. The results indicate that an accurate approximation of particle transport (i.e., high spatial resolution) is significantly more important than particle collision (i.e., high velocity domain resolution) for predicting flow instabilities and momentum transfer consistent with that predicted by the hydrodynamic equations and that these effects can be computed accurately even with very few degrees of freedom in the velocity domain. These findings suggest that highly accurate spatial schemes (e.g., high-order schemes) are a promising approach for solving molecular gas dynamics for complex flows and that the direct solution of the Boltzmann equation can be performed at a reasonable cost when compared to hydrodynamic simulations at the same level of resolution. [ABSTRACT FROM AUTHOR]

A conservative implicit scheme in the finite volume discrete velocity method framework is proposed for solving the three-dimensional steady flows of molecular gases in all flow regimes from continuum one to free-molecular one. This work is based on the Boltzmann–Rykov model equation, which is a nonlinear relaxation model and can describe the thermodynamic non-equilibrium of diatomic gas flows. The macroscopic equations are solved implicitly together with the Rykov model equation to find a predicted equilibrium distribution first at each iteration step. As a result, the collision term of the Rykov model equation can be discretized in a fully implicit way for fast convergence in all flow regimes. At the cell interface, an asymptotic preserving simplified multi-scale numerical flux is developed to relieve the limitation of grid size and time step in all flow regimes, which can keep the multi-scale property and achieve high computational efficiency. The integral error compensation technique is used to keep the scheme conservative and greatly reduce the number of unstructured discrete velocity space (DVS) meshes. Furthermore, an empirical criterion based on the numerical experiments of the Apollo 6 command module is suggested to guide the generation of three-dimensional unstructured DVS. The accuracy and efficiency of the present method are demonstrated by a number of three-dimensional classic cases, covering different flow regimes. [ABSTRACT FROM AUTHOR]

In this article, we address the capabilities of physics-informed neural networks (PINNs) in assimilating the experimentally acquired mean flow of a turbulent separation bubble occurring in a diffuser test section. The training database contains discrete mean pressure and wall shear-stress fields measured on the diffuser surface as well as three-component velocity vectors obtained with particle image velocimetry throughout the volumetric flow domain. Imperfections arise from the measurement uncertainty and the inability to acquire velocity data in the near-wall region. We show that the PINN methodology is suited to handle both of these issues thanks to the incorporation of the underlying physics that, in the present study, are taken into account by minimizing residuals of the three-dimensional incompressible Reynolds-averaged Navier–Stokes equations. As a result, measurement errors are rectified and near-wall velocity profiles are predicted reliably. The latter benefits from the incorporation of wall shear-stress data into the PINN training, which has not been attempted so far to the best of our knowledge. In addition to demonstrating the influence of this novel loss term, we provide a three-dimensional, highly resolved, and differentiable model of a separating and reattaching flow that can be readily used in future studies. [ABSTRACT FROM AUTHOR]

Synthetic jet has shown promising applications in active flow control in recent years. Tomographic particle image velocity (Tomo-PIV) is an emerging flow field measurement, which can obtain three-dimensional flow field with a high spatial and temporal resolution to help us better understand the evolution of synthetic jet. Therefore, this paper uses a time-resolved Tomo-PIV system to measure and analyze the three-dimensional flow evolution of a submerged two-orifice synthetic jet. The measurement is conducted for stroke length L = 1.9, 2.6, and 3.0 while keeping the orifice diameter D and the distance between the two orifices s constant. Research results reveal that the three-dimensional flow evolution can be described as follows: first, two independent vortex rings form at the outlet of the orifice plate; next, these two vortex rings interact with each other and merge into a non-circular vortex ring, which then undergoes axis switching and vortex reconnection, with the tendency of splitting into two vortex rings. Furthermore, the position where the axis-switching finishes coincides with the location of the maximum mean streamwise velocity. When the stroke length of the synthetic jet is 2.6, the non-circular vortex ring undergoes a collision of vortices after the completion of the axis switching, resulting in the phenomenon of vortex ring bifurcation. However, the non-circular vortex ring fails to split into two vortex rings for stroke lengths of 1.9 and 3. Moreover, the entrainment of the synthetic jet increases with the increase in stroke length. [ABSTRACT FROM AUTHOR]

A volume penalization-based immersed boundary technique is developed and thoroughly validated for fluid flow problems, specifically flow over bluff bodies. The proposed algorithm has been implemented in an open source field operation and manipulation (OpenFOAM), a computational fluid dynamics solver. The immersed boundary method offers the advantage of inserting a complex solid object inside a Cartesian grid system, and therefore, the governing equations can be applied to such a simpler grid arrangement. For capturing the fluid–solid interface more accurately, the grid is refined near the solid surface using topoSetDict and refineMeshDict utilities in OpenFOAM. In order to avoid any numerical oscillation and to compute the gradients accurately near the interface, the present volume penalization method (VPM) is integrated with a signed distance function, which is also referred to as a level-set function. Benchmark problems, such as flows around a cylinder and a sphere, are considered and thoroughly validated with the results available in the literature. For the flow over a stationary cylinder, the Reynolds number is varied so that it covers from a steady two-dimensional flow to an unsteady three-dimensional flow. The capability of the present solver has been further verified by considering the flow past a vibrating cylinder in the cross-stream direction. In addition, a flow over a sphere, which is inherently three-dimensional due to its geometrical shape, is validated in both steady and unsteady regimes. The results obtained by the present VPM show good agreement with those obtained by a body-fitted grid using the same numerical scheme as that of the VPM, and also with those reported in the literature. The present results indicate that the VPM-based immersed boundary technique can be widely applicable to scientific and engineering problems involving flow past stationary and moving bluff bodies of arbitrary geometry. [ABSTRACT FROM AUTHOR]

The end wall loss of modern highly loaded low pressure turbine (LPT) has been greatly increased, due to the enhanced secondary flow loss and boundary layer separation loss. Thus, it is of great significance to develop effective flow control strategies to improve the end wall flow condition and aerodynamic performance of modern LPT. This research carried out a numerical investigation on the coupled flow control strategy, which combined non-axisymmetric end wall contouring (NEC) and root tangential lean (RTL), based on a highly loaded LPT cascade (Zweifel = 1.59). Meanwhile, the optimization process was used to get the optimal design parameters of the coupled method NEC&RTL. The results indicate that the optimal coupled configuration can reduce the total pressure loss coefficient by 12.68% and the non-dimensional secondary kinetic energy by 23.91%. Compared with the reference cascade without modification, the coupled method is found to improve the end wall flow conditions: the passage vortex is weakened both in size and strength, mainly attributed to the smaller cross-passage pressure gradient resulting from NEC; the closed separation bubble near end wall and the three-dimensional separation flow before trailing edge are eliminated, due to the great downward pressure gradient near end wall resulting from RTL; and the counter vortex is eliminated and the slender back flow is weakened under the additional coupling flow control effect of NEC&RTL. Therefore, the coupled flow control method can not only highlight the advantages of the independent methods, but also induce external flow control superiorities, demonstrating the application prospect of the coupled flow control strategy on the highly loaded LPT. [ABSTRACT FROM AUTHOR]

Due to costs and practical constraints, field campaigns in the atmospheric boundary layer typically only measure a fraction of the atmospheric volume of interest. Machine learning techniques have previously successfully reconstructed unobserved regions of flow in canonical fluid mechanics problems and two-dimensional geophysical flows, but these techniques have not yet been demonstrated in the three-dimensional atmospheric boundary layer. Here, we conduct a numerical analogue of a field campaign with spatially limited measurements using large-eddy simulation. We pose flow reconstruction as an inpainting problem, and reconstruct realistic samples of turbulent, three-dimensional flow with the use of a latent diffusion model. The diffusion model generates physically plausible turbulent structures on larger spatial scales, even when input observations cover less than 1% of the volume. Through a combination of qualitative visualization and quantitative assessment, we demonstrate that the diffusion model generates meaningfully diverse samples when conditioned on just one observation. These samples successfully serve as initial conditions for a large-eddy simulation code. We find that diffusion models show promise and potential for other applications for other turbulent flow reconstruction problems. [ABSTRACT FROM AUTHOR]

The utilization of oscillating water column (OWC) converters with existing hydraulic/coastal structures has emerged as a crucial approach for the development of economically viable and environmentally sustainable green power generation devices. Integrating OWC converters into offshore wind turbine (OWT) monopiles is a promising solution in wind power industrialization. This paper presents an experimental investigation of the flow characteristics of an OWT-OWC system under regular wave conditions, focusing on the evolution of vortex structures. Particle image velocimetry (PIV) is employed to measure the flow field surrounding the OWC converter under different wave heights and wave period conditions. Based on the measured velocity field data, the evolution of vortices is examined using the Q-criterion. The results indicate that the wave period significantly affects the flow patterns. Specifically, an increase in wave period enhances the three-dimensional nature of the flow field. The vortices outside the OWC chamber are observed to connect and form a three-dimensional vortex ring, hindering efficient wave energy conversion. Conversely, the variation in wave height exhibits limited impact on the flow field evolution. However, as the wave height increases, the vortex strength and asymmetry experience a significant rise, making it difficult to form a stable three-dimensional vortex ring. Moreover, based on optimal geometric design considerations, it is recommended to increase the lateral angle and height of the sidewall openings to prevent vortex ring formation and minimize obstructions, while ensuring the structural safety of the OWT. [ABSTRACT FROM AUTHOR]

This paper presents time-resolved, three-dimensional measurements coupling particle trajectories with flow fields around settling spheres in Newtonian fluids. The experiments cover a range of particle Reynolds numbers (Re), spanning from 1.6 to 6. Our calculated drag coefficients, derived from sphere trajectories, closely align with values reported in the literature. Notably, our high spatial resolution reveals oscillations, potentially corresponding to the "streamwise oscillations" phenomenon discussed by Horowitz and Williamson ["The effect of Reynolds number on the dynamics and wakes of freely rising and falling spheres," J. Fluid Mech. 651, 251 (2010)]. For a single sphere, we extract the three-dimensional flow field using particle tracking velocimetry. Discrete particle tracks are meticulously interpolated onto a regular grid using a fine-scale reconstruction based on the vortex-in-cell method. Leveraging the known sphere position, we introduce a sphere-centered coordinate system, enabling time-averaging of flow properties. Additionally, we interpolate and analyze the pressure field on the sphere's surface, employing proper orthogonal decomposition to unveil distinct pressure fluctuation modes. [ABSTRACT FROM AUTHOR]

Physics informed neural networks (PINNs) have demonstrated their effectiveness in solving partial differential equations (PDEs). By incorporating the governing equations and boundary conditions directly into the neural network architecture with the help of automatic differentiation, PINNs can approximate the solution of a system of PDEs with good accuracy. Here, an application of PINNs in solving three-dimensional (3D) Navier–Stokes equations for laminar, steady, and incompressible flow is presented. Notably, our approach involves deploying PINNs using feed-forward deep neural networks (DNNs) without depending on any simulation or experimental data. This investigation focuses on 3D square channel flow and 3D lid-driven cavity flow. For each case, one deep neural network was trained using only the governing equations and boundary conditions. Finally, the PINNs' results were compared with the computational fluid dynamics results. The goal was to assess the ability of PINNs (with DNN architectures) to predict the solution of Navier–Stokes equations in the 3D domain without any simulation or experimental data (unsupervised learning). [ABSTRACT FROM AUTHOR]

We investigated the dynamics of highly turbulent thermally driven anabatic (upslope) flow on a physical model inside a large water tank using particle image velocimetry (PIV) and a thermocouple grid. The results showed that the flow exhibited pronounced variations in velocity and temperature and, importantly, could not be accurately modeled as a two-dimensional quasi-steady flow. Five significant findings are presented to underscore the three-dimensional nature of the flow, namely, the B-shaped mean velocity profiles, B-shaped turbulent flux profiles, synthetic streaks that revealed particles flowing perpendicular to the laser sheet, average vorticity maps revealing helical structure splitting, and identified vortices shooting away from the boundary toward the apex plume. Collectively, these findings offer novel insights into the flow behavior patterns of thermally driven complex terrain flows, which influence local weather and microclimates and are responsible for scalar transport, e.g., pollution. [ABSTRACT FROM AUTHOR]

Through comparing with the tandem circular and elliptic cylinders with the same characteristic dimensions, the behavior of flow and flow-induced noise generated around the tandem seal-vibrissa-shaped cylinder is studied based on delayed detached-eddy simulation model and acoustic analogy approach. The co-shedding pattern of flow developed around the tandem cylindrical-like bars is investigated. The spatial modes, mode energy, and mode coefficients of turbulent flow around the geometries are analyzed through spectral proper orthogonal decomposition. Results show that the lift fluctuations of downstream bar are stronger than those of upstream bar, and more aerodynamic noise is radiated from the downstream bar than from the upstream bar. The alternative arrangement of nodal and saddle planes of seal-vibrissa-shaped cylinder introduces three-dimensional flow separations and suppresses the shear layer interactions, inhibiting the regular vortex shedding of Kármán vortex street occurring in the tandem cylinder wake. The reversed vortex shedding generated by two adjacent saddle surfaces in the wake of seal-vibrissa-shaped cylinder balances the lateral force and mitigates the lift fluctuations greatly, thereafter reduces the aerodynamic noise generated by wall pressure fluctuations introduced by unsteady fluctuating forces exerting on the surfaces of geometries. Compared to the tandem circular and elliptic cylinders, the good noise reduction effect with sound pressure level reduced at main frequency range has been achieved from the tandem seal-vibrissa-shaped cylinder. The calculated spectra and amplitude levels of aerodynamic noise agree well with the experimental measurements from the anechoic wind tunnel, verifying the accuracy of the numerical simulations. [ABSTRACT FROM AUTHOR]

This study introduces a novel method for imposing wall boundary conditions in smoothed particle hydrodynamics (SPH). SPH is a particle method based on the Lagrangian approach, primarily employed in fluid analysis as a part of numerical computation methods. Due to its ability to discretize space using particles, SPH excels in handling analyses of free surface flow or multiphase flow with intricate boundary surfaces. However, there is a drawback in modeling wall boundaries using particles, as resolving the particle deficiency problem necessitates multi-layered boundary particles to be arranged behind the wall boundary. This leads to difficulties in implementing complex shapes and adds computational expense. To address this issue, this study suggests the use of boundary segments for wall boundary modeling and specifically employs triangular segments for three-dimensional expansions. For robust application of boundary conditions, a method considering both Poisson's equation and geometric configurations is proposed. The proposed method is independent of the segment density, which facilitates efficient and flexible modeling. In addition, by imposing accurate boundary conditions from the wall, the stability and accuracy of the solution are enhanced. The performance of the proposed method is validated through numerical examples, compared with various analytical and experimental results. [ABSTRACT FROM AUTHOR]