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An artificial chute cutoff was implemented to eliminate the danger caused by the lateral migration of meandering river in the upper Yellow River in 2018. However, the earlier studies on chute cutoff have not provided a clear understanding of the hydrodynamic and morphodynamic characteristics of this artificial chute cutoff. In this study, three field measurements have been conducted to reveal the channel morphology and flow structure of the artificial chute channel. The results show that, compared with the natural chute cutoff, a 20-m-deep scour hole and a 2.26-km-long scour belt formed in the diversion channel are the significant features of this artificial cutoff. Further, a dual counter-rotating helical cell separated by a distinct shear layer is observed at the scour hole. Therefore, the formation of scour hole is likely related to the helical cells. However, flow stagnation was not observed in the chute channel, but the flow recirculation and separation zones were observed. Among them, the flow separation zone observed on the right bank of the diversion channel promoted the formation of bar. The observed counterclockwise single helical cells aggravated the erosion of the left bank. These findings provide useful insights on the artificial chute cutoff with complex flow structure and channel morphology characteristics, which can be used to improve the conceptual models of chute cutoff. [ABSTRACT FROM AUTHOR]

The authors have solved scientific and technical problems of mathematical modeling and calculation of thermal efficiency, and also of structural characteristics of packed scrubbers of condensation water cooling of a gas in a film countercurrent regime. By simultaneous solution of the heat-balance equation and the expressions for thermal efficiencies of a packed scrubber in the gas and liquid phases, a relation has been established between the thermal efficiencies of condensation cooling of the gas and heating of the water. With an assigned temperature regime of cooling of the gas and its thermodynamic state, a required gas-phase thermal efficiency is computed. To calculate the actual thermal efficiency of a packed bed, use is made of a cellular model of the flow structure in the liquid and gas phases. An expression has been obtained for calculating the height of the packed bed from the assigned thermal efficiency, structural characteristics of the packing, and flow rates of the gas and water. Agreement with the existing experimental data has been shown and a calculation algorithm has been given. Conclusions on the most efficient packing structures have been drawn. [ABSTRACT FROM AUTHOR]

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

Gas–liquid two-phase flows are frequently encountered in chemical and nuclear industries. The study of gas–liquid flow structures is of great significance for understanding the mechanisms of the flow pattern transition. In this paper, a direct-image multi-electrode conductance sensor (DMCS) was used to detect the structure information of vertical gas–liquid flows. Recurrence plot (RP) and cost-based recurrence plot (CBRP) are validated using typical nonlinear systems, i.e. Lorenz system and Hénon map, and used to analyze the signals collected by the DMCS. The results indicate that the determinism (DET) derived from the CBRP is sensitive to flow pattern evolution, and can also demonstrate the internal differences in the same flow patterns. [ABSTRACT FROM AUTHOR]

This paper presents the findings from a research study using computational fluid dynamics (CFD) on the impact of different diameter Ball Tabulators Inserts (BTI) on the three-dimensional flow pattern and heat transfer characteristics within a circular tube. This analysis was carried under uniform heat flux conditions with different BTI diameters (1, 2, 3, 4, 5, 6, 7, and 8 mm). Fluid flow, pressure drop, dynamic pressure, velocity components, thermo-hydraulic, turbulent kinetic energy, and turbulent viscosity were analysed qualitatively and quantitatively. The performance evaluation results revealed that the characteristics of flow behaviour and the velocity field contours variations are closely associated with the BTI configurations. Also, the computational results indicated that the change in fluid flow velocity near the pipe wall and around the BTI is important parameters for the heat transfer enhancement as compared to that obtained without BTI under the same conditions. Moreover, using BTI presented a distinguished influence on the rate of heat transfer. Additionally, vortex flow through means of this kind of BTI is an important parameter in the enhancement of heat transfer. The use of BTI can enhance the rate of heat transfer performance by more than 46%. Furthermore, the maximum value for the PEF is found to be more than 1.03. [ABSTRACT FROM AUTHOR]

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

The mechanism of flow instability, which involves complex gas–liquid interactions and multiscale vortical structures, is one of the hot research areas in cavitating flow. The role of turbulence modeling is crucial in the numerical investigation of unsteady flow characteristics. Although large-eddy simulation (LES) has been used as a reliable numerical method, it is computationally costly. In this work, we used a hybrid Reynolds-averaged Navier–Stokes (RANS) and LES model, that is, stress-blended eddy simulation (SBES), to improve the prediction capability for the cloud cavitating flow. Our hybrid approach introduces a shielding function to integrate the RANS model with the LES applied only regionally, such as to large-scale separated flow regions. The results showed that the periodic shedding of cavity growth, break off, and collapse around a three-dimensional Clark-Y hydrofoil was reproduced in accordance with experimental observations. The lift/drag coefficients, streamwise velocity profiles, and cavity patterns obtained by the SBES model were in better agreement with the experimental data than those obtained by the modified RANS model. The re-entrant jet dynamics responsible for the break off of the attached cavity were discussed. Further analysis of vorticity transportation indicated that the stretching and dilatation terms dominated the development of vorticity around the hydrofoil. In conclusion, the SBES model can be used to predict cavitating turbulent flows in practical engineering applications. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model has been developed to study the flow structure in close binary systems with a magnetic field. The model uses a system of equations of modified magnetic hydrodynamics, which allows describing all the main dynamic effects associated with the magnetic field. It takes into account the processes of radiation heating and cooling, heating due to current dissipation, as well as magnetic field diffusion. The model allows calculations in a wide range of magnetic field values. Comparison of the calculation results with observational data confirms the reliability and high efficiency of the model. The paper presents the calculation results of the flow structure in a typical intermediate polar. It is shown that an accretion disk is formed in such a binary system, which has the following characteristic features: “hot line”, tidal shock waves, precession density wave, magnetospheric region, and accretion columns. In this case, the magnetic field in the disk is predominantly toroidal. The paper also presents the results of calculations for typical polars. In such systems, instead of an accretion disk, a collimated stream of matter is formed, moving along the magnetic field lines to the magnetic poles of the white dwarf. It is shown that in synchronous polars, variations of the mass transfer rate lead to a change in the spatial configuration of the flow. In asynchronous polars, changes in the flow structure for different phases of the beat period are observed as well as the processes of switching the flow between the magnetic poles of the accretor. Numerical calculations of the asynchronous system are performed under the assumption of the dipole configuration of the magnetic field for different values of the dipole offset relative to the center of the white dwarf. The paper presents a method for estimating this offset from observational light curves.

When a pipeline is laid on the seabed, local scour often occurs below it due to sea currents. In practical engineering, there are some cases that two pipelines laid on the seabed need to cross with each other. The complex flow structures around two crossing pipelines make the scour characteristics different from that of an isolated single pipeline. In this study, scour below two crossing pipelines was simulated numerically using the CFD software Flow-3D. The study is focused on the effect of the intersecting angle on the equilibrium depth and time scale of scour below the crossing position. Five intersecting angles, i.e., α = 0°, 15°, 30°, 45° and 90°, are considered, where α = 0° and 90° represent two pipelines parallel and perpendicular to each other, respectively. The results show that the equilibrium depth and the time scale of scour below the two crossing pipelines are greater than those of an isolated single pipeline. The equilibrium depth and time scale of scour have the largest values at α = 0° and decrease with the increase of the intersecting angle. Finally, the flow structures around the crossing pipelines are presented to explain the scour process.

Following the construction of a reservoir, sediment is intercepted, which greatly reduces the sediment concentration in the discharged flow. This reduction causes riverbed scouring and flow structure adjustments downstream, thereby impacting the river habitat. This study used the generalized flume test with different bed sand compositions and discharge rates to simulate the scouring adjustment process of a sand pebble riverbed channel downstream of a reservoir. The results show that the bed sediment composition affects the water surface gradient, scour depth, turbulence intensity, and sand resistance directly after final scouring. Coarse-grained bed sediment demonstrated the greatest final turbulence intensity and sand resistance, while bed sediments with reduced coarseness exhibited a greater scouring degree; the resistance for sand grains of moderate coarseness showed the greatest change. Sand resistance was exponentially and positively correlated with the median grain size and the fractal dimension of bed sediment mass. The mass fractal dimension expression was suitable for the analysis of bed sand grain-size distribution; it contributed to the calculation of grain resistance with fewer hydraulic parameters. The relationship between the mass fractal dimension and the adjusted grain resistance was also established, which can aid the calculation of the resistance changes in sandy gravel-bed river reaches downstream of reservoirs, enabling the prediction of their effects on aquatic habitats.

• At various AoA, Five SJA parameters are optimised using a multi-objective optimiser. • By coupling a mesh generator to a CFD package, Over 2200 2D-CFD cases are automatically pre-processed and performed. • This paper shows how five SJA parameters need to be tuned for different AoA. • At pre-stall AoA, the injection Angle and SJA position are the key parameters to obtain the maximum lift and efficiency. • At post-stall AoA, higher momentum coefficient is required to obtain a full flow attachment. The use of Active Flow Control (AFC) technologies to modify the forces acting on streamlined bodies is one of the most active research fields in aerodynamics. For each particular application, finding the optimum set of AFC parameters which maximises lift, minimises drag or maximises lift-to-drag ratio (aerodynamic efficiency), has become a necessary design requirement. In the present paper, the AFC technology was applied to the Selig-Donovan 7003 (SD7003) airfoil at Reynolds number 6 × 10 4. Synthetic jets were employed to modify the lift and drag forces acting on the airfoil. Four angles of attack (AoA) of 4 ∘ , 6 ∘ , 8 ∘ and 14 ∘ were considered, alongside five AFC parameters: jet position, jet width, momentum coefficient, forcing frequency and jet inclination angle. A multi objective optimisation based on genetic algorithms (GA) was performed for each angle of attack to find the optimum combination of AFC parameters. Each GA generation was simulated using Computational Fluid Dynamics (CFD). A home-made GA package was linked with a mesh generator and the CFD solver, and the results were automatically fed back to the GA code. Over 2200 CFD simulations were performed in two dimensions, using the Spalart-Allmaras turbulent model. The motivation behind the current study is to understand the dependence of the optimum set of AFC parameters on the AoA. Results show that, as AoA is increased, the potential benefits of AFC become more pronounced, which allows for considerable improvement in aerodynamic efficiency. The physics involved in the interaction between the main flow and synthetic jet are clearly presented and clarifies that the physical phenomenon to obtain maximum efficiency is completely different at pre-stall and post-stall AoA. In particular, the aerodynamic efficiency was increased by 251% from baseline (no actuation) by using a moderate/finite momentum coefficient at AoA= 14 ∘ , while a mere 39% increase was obtained at AoA= 8 ∘. In addition, the interaction between the incoming flow and the synthetic jet pulsating flow at different injection angles has been thoroughly investigated. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the Rayleigh-Bénard convection (RBC) in two-dimensional cells with asymmetric (ratchet) roughness distributed on the top and bottom surfaces. We consider two aspect ratios of roughness γ = 1, 2 and the range of the Rayleigh number 1.0 × 106 ≤ Ra ≤ 2.0 × 1010 with the Prandtl number Pr = 4. The influences of the roughness on the heat transfer and the flow structure are found to be strongly dependent on both Ra and the roughness geometry. We find that the roughness can have a significant influence on the organization of the secondary corner rolls, and the corner rolls are evidently suppressed by the roughness for intermediate values of Ra. In the presence of the roughness, a sharp jump of the Nu values is identified as the Ra value is slightly increased, accompanied with the dramatic changes of the large-scale flow structure and the plume dynamics. The influences of the ratchet orientation on the heat transfer and the flow structure are discussed and analyzed. [ABSTRACT FROM AUTHOR]

Despite widespread recognition that confluences are characterized by complex hydrodynamic conditions, few studies have mapped in detail spatial patterns of flow at confluences and variation in these patterns over time. Recent developments in large‐scale particle image velocimetry (LSPIV) have created novel opportunities to explore the spatial and temporal dynamics of flow patterns at confluences. This study uses LSPIV to map two‐dimensional flow structure at the water surface at a confluence and to examine variation in this structure over time. Results show that flow within the confluence is characterized by a large region of flow stagnation at the junction apex, a region of low velocities at the downstream junction corner, and a region of merging of the two flows along a mixing interface within the center of the confluence. Interaction between the incoming flows varies over time in the form of episodic pulsing in which one of the two tributary flows first decelerates and then subsequently accelerates into the confluence. The cause of this pulsing remains uncertain, but it may reflect unsteadiness in the water‐surface pressure‐gradient field as the two flows compete for space within the confluence. No large‐scale vortices are evident within the mixing interface for the particular flow conditions documented in this study, but such vortices do occur along the margins of the stagnation zone where shearing action between fast‐moving and slow‐moving fluid is strong. The results of the study provide insight into the time‐dependent dynamics of the spatial structure of flow at stream confluences. Key Points: Large‐scale particle image velocimetry (LSPIV) reveals spatial and temporal variation in confluence flow structure at high spatial resolutionInteraction of incoming flows within a confluence is characterized by episodic pulsing of flow from the main tributaryFluid motion in a region of flow stagnation varies in direction over time and is influenced by large shear‐generated vortices [ABSTRACT FROM AUTHOR]

Vortex shedding phenomenon behind bluff bodies and its destructive unsteady wake can be controlled by employing active and passive flow control methods. In this quest, researchers employed experimental fluid dynamics (EFD), computational fluid dynamics (CFD) and an analytical approach to investigate such phenomena to reach a desired outcome. This study reviews the available literature on the flow control of vortex shedding behind bluff bodies and its destructive wake through the modification of the geometry of the bluff body. Various modifications on the bluff body geometries namely perforated bluff bodies, permeable and porous mesh, corner modification and wavy cylinder have been reviewed. The effectiveness of these methods has been discussed in terms of drag variation, wake structure modifications and Strouhal number alteration. [ABSTRACT FROM AUTHOR]

• 3D simulations on bubble coalescence in heated branching microchannels are performed. • The unique bubble coalescence dynamics and flow structures are presented. • Both the distribution and evolution of phase change heat transfer characteristics are provided. • Complex transport mechanisms during bubble coalescence process are well revealed. Understanding the bubble dynamics is essential to various two-phase applications. The three-dimensional numerical study on bubble coalescence with phase change in different heated branching microchannels (15°, 90°, and 180°) is performed. The detailed bubble dynamics, flow structures, and phase change heat transfer characteristics are respectively presented. Results show that during coalescence process, the bubble successively experiences three stages including liquid film formation, neck growth, and oscillation. It is interesting to point out that the sandwich structure (droplet exists within bubble) may occur in large-angle branching microchannels due to the classical Rayleigh-Plateau instability. Besides, the unique encircling coalescence phenomenon is found to occur in 90° branching microchannel, leading to the sudden increase in neck growth rate. Two distinct flow structures can be recognized, namely the smooth flow occurring in small-angle branching microchannels and the colliding flow occurring in large-angle branching microchannels. The fluid flow becomes quite chaotic under colliding flow structure, which significantly facilitates the convective heat transfer. The heat transfer enhancement for main channel is found to be limited because of the counter-balance mechanism of phase change heat transfer involved. The main channel produces the better heat transfer enhancement than the branching channel, and the best heat transfer enhancement occurs on the outer wall of main channel. This fundamental research sheds new light on the physical mechanisms of bubble dynamics in confined branching structures. [ABSTRACT FROM AUTHOR]

This study employs numerical simulation to investigate the two-dimensional flow of a rectangular cylinder with an aspect ratio of 5, under various flow attack angles (α) and Reynolds numbers. The lift and drag coefficients, surface pressure distributions, and flow structures are analyzed using the HODMD method. The findings suggest that a rise in flow attack angle increases the lift and drag coefficients of rectangular cylinders, but the turning point of the Reynolds number leads to an opposite trend in the increase of drag coefficients. The sensitivity of the flow field is intricately related to the Reynolds number and flow attack angle. Additionally, the increase in both Reynolds number and flow attack angle enhances the complexity of the flow structure, particularly at the trailing edge, which is a sensitive part of applying flow control. HODMD analysis shows that the first three modes dominate dynamics. Odd-order modes contribute significantly to lift at low α , while even-order modes cancel each other. As α increases, the contributing modes of lift gradually shift from odd to even order. This study provides valuable insights for prospective flow control strategies and addresses vibration concerns in associated submerged structures. • Elevations in both α and Re amplify lift and drag coefficients' magnitude, volatility, and correlation. • HODMD analysis shows that odd-order modes contribute significantly to lift, while even-order modes cancel each other. • As α increases, the contributing modes of lift gradually shift from odd to even order. [ABSTRACT FROM AUTHOR]

• The dilute, dense and mid phases (intermediate region) are detected in BFB and TFB. • Solids holdup distribution of three phases is revealed. • Phase time fraction distribution of three phases is disclosed. • The phase time fraction distribution exposes flow structure traits from BFB to TFB. • Effects of static bed height and bed diameter on flow structure are dependent on U g. Bubbling and turbulent fluidized beds (BFB and TFB) are widely used in the chemical and energy industries, owing to their enhanced heat transfer and improved operation flexibility. In BFB and TFB, the gas-particle suspension is featured with a dilute phase (bubbles) and a dense phase. The gas exchanges between the bubbles and the dense phase often through an intermediate region, further enhancing the gas-particle contact. However, few comprehensive studies have been conducted on the intermediate region and the dense phase. In this work, the instantaneous solids holdup was obtained in BFB and TFB through optical fiber sensing. Subsequently, through the use of statistical signal analysis, solids holdup thresholds were proposed to discriminate between the bubbles, the intermediate region (named as 'mid-phase') and the dense phase. Finally, gas-particle segregation details were further revealed through the quantification of the different phases to advance the development of future modelling, design and scale-up processes. [ABSTRACT FROM AUTHOR]

The Characteristics of single and two- phase flow from a circular turbulent free jet from a nozzle of 10 mm diameter were investigated experimentally and numerically. The measurements were conducted for ReJ = 10007 - 31561. The velocity was measured at location from the nozzle y/D (0-8) in axial and radial directions. The two phase measurement were done by using natural construction sand as a solid phase of sizes (220,350,550) µm and loading ratios (mass flow ratio of sand to mass flow rate of air) in the range (0.18-1.38). Two phase air velocity of jet showed that the introducing of natural sand particles gives lower jet velocity attributed to momentum transfer to particles. The smaller particle size leads to lower values of velocity. The velocity found to be decreased with loading ratio increase. The numerical simulation was performed for single and two phase jet flow. RNG K-ε turbulence model was used to simulate the flow of fluid and the discrete phase model to simulate the particles flow. The results form numerical simulation showed a good agreement with experimental results.

Gas–liquid two-phase flow widely exists in petroleum, natural gas, and other industries. Recognition of flow structure is an important issue in the study of two-phase flow, and it is of great significance for the optimization of industrial processes. Therefore, how to recognize complex flow structures effectively represents a challenge. To cope with this problem, we develop a novel deep learning network to recognize flow structures under different flow conditions. In particular, we conduct vertical upward gas–liquid two-phase flow experiments to obtain the flow structure data set on the basis of images collected by a high-speed camera. Then, we design a branch-aggregation network (BAN), where the branch structure is utilized to increase the width of the network, and multilevel aggregation structure is used to fuse features of different levels. In recognition of flow structure, the proposed network achieves an accuracy of 99.60% with a fast convergence speed and shows the advantages in antinoise ability, which is significant for online recognition in industrial processes. The results indicate that BAN can be a feasible method to recognize complex flow structures. [ABSTRACT FROM AUTHOR]

The present study aims to describe flow structures and cavitation phenomenon in the submerged waterjet. A non-intrusive experimental work was performed. The waterjet was produced through a nozzle characterized by a short straight segment adjacent to the nozzle outlet. Waterjet pressures were varied from 5 to 22 MPa. The time-resolved particle image velocimetry (TR-PIV) was used to measure velocity distributions. The proper orthogonal decomposition (POD) method was employed to extract flow structures from the flowmeasurement results. Cavitation was created through increasing the waterjet pressure. A comparison of cavitation patterns at different waterjet pressures was implemented. Similarity of the distribution of average velocity is revealed as the waterjet pressure varies. The POD results indicate that two high-vorticity bands close to the nozzle, symmetrically distributed with respect to the nozzle axis, dominate the waterjet stream. Further downstream, small-scale flow structures are sparsely distributed and assume a low percentage of the total energy. Initial cavitation is featured by small-scale cavities which are formed near the high-vorticity zone. As the waterjet pressure increases, the volume fraction of cavitation increases and morphological features of cavitation change significantly as waterjet develops. At a later stage, stable cavity clouds are evidenced. A high relevance between vorticity distribution and cavitation cloud pattern is demonstrated. [ABSTRACT FROM AUTHOR]

Flow over shallow cavities is used to model the flow field and heat transfer in a solar collector and a variety of engineering applications. Many studies have been conducted to demonstrate the effect of cavity aspect ratio (AR), but very few studies have been carried out to investigate the effect of cavity height ratio (HR) on shallow cavity flow behavior. In this paper, flow field structure and heat transfer within the 3-D shallow cavity are obtained numerically for two height ratio categories: HR = 0.0, 0.25, 0.5, 0.75, and 1.0 and HR = 1.25, 1.5, 1.75, 2.0, 2.25, and 2.5. The governing equations, continuity, momentum, and energy are solved numerically and using the standard (K-ε) turbulence model. ANSYS FLUENT 14 CFD code is used to perform the numerical simulation based on the finite volume method. In this study, the cavity aspect ratio, AR = 5.0, and Reynolds number, Re = 3 × 105, parameters are fixed. The cavity’s bottom wall is heated with a constant and uniform heat flux (q = 740 W/m²), while the other walls are assumed to be adiabatic. For the current Reynolds number and cavity geometry, a single vortex structure (recirculation region) is formed and occupies most of the cavity volume. The shape and location of the vortex differ according to the height ratio. A reverse velocity profile across the recirculation region near the cavity’s bottom wall is shown at all cavity height ratios. Streamlines and temperature contours on the plane of symmetry and cavity bottom wall are displayed. Local static pressure coefficient and Nusselt number profiles are obtained along the cavity’s bottom wall, and the average Nusselt number for various height ratios is established. The cavity height ratio (HR) is an important geometry parameter in shallow cavities, and it plays a significant role in the cavity flow behavior and heat transfer characteristics. The results indicate interesting flow dynamics based on height ratio (HR), which includes a minimal value in average Nusselt number for HR ≈ 1.75 and spatial transitions in local Nusselt number distribution along the bottom wall for different HRs. [ABSTRACT FROM AUTHOR]

An annular venturi injector (AVI) was proposed to form an intermittent flow structure in airlift pump for a good pump performance. Experiments were conducted to investigate the performance of the airlift pump with this AVI by comparing with pump performance with traditional injectors, at a series of air flow rates . It was found that airlift pump with AVI had higher flow rates of output liquid and particle, than those with the traditional injectors. This AVI promoted the gas core to collapse and formed an intermittent flow structure in rising pipe. For this intermittent structure, its slug length, firstly increased to a maximal value with increasing gas flow rate and then remained stable even under a high gas flow rate, while its slug frequency decreased with gas flow rate and then remained to a minimal value under a high gas flow rate. [ABSTRACT FROM AUTHOR]

Culvert fishways can improve upstream fish passage in brooks and have been studied in relation to North American and Australian species. Research focusing on fish species from other world regions and, in parallel, effect of baffles on flow turbulence is rare. In this paper we present computational fluid dynamics of a sloped baffle culvert, called "stairs pipe". We aimed at evaluating if: (1) the flow met the requirements of Neotropical and European species; (2) the flow turbulence was acceptable for fish passage; (3) the flow limited fish movements. The average flow velocities for 5% slope and discharge rates of 5–13 L/s were lower than the prolonged speeds of three Neotropical species, namely, piau (Leporinus reinhardti), mandi (Pimelodus maculatus), and lambari (Piabarchus stramineus) and higher than the sustainable speeds of three European species, namely, dace (Leuciscus leuciscus), barbel (Barbus barbus), and brown trout (Salmo trutta). The turbulence flow characteristics i.e. levels of turbulence kinetic energy were similar to those produced by comparable culverts but higher than those in a fish ladder. The water jet created by baffles at an angle of 30° can limit fish movements, restraining them from jumping. The stairs pipe might improve upstream fish movement in different regions of world; nevertheless, further experimental research should concern the use of different swimming modes in the culvert flow. [ABSTRACT FROM AUTHOR]

As an essential part of riverine, lacustrine, and coastal wetland ecosystems, aquatic vegetation（AV） provides important ecosystem services, and many of the ecosystem services arise as AV has the ability to alter local hydrodynamic conditions. Studies on vegetated flow are helpful not only for scientifically illustrating the environmental and ecological effects of AV but also for guiding the practice of ecological restoration and pollution regulation in rivers and lakes. Considering two kinds of hydrodynamic environments（i.e.,unidirectional open-channel flow and waves）,this paper summarizes the main findings on the influence of AV on flow structures and sediment movement domestically and abroad. Under unidirectional open-channel flow conditions, research on the influence of AV on hydrodynamics has mainly focused on the flow resistance caused by AV and the turbulent flow structures and scales within canopy. Related studies on waves have mainly focused on the effect of AV on wave damping and the mean and turbulent flow structures. Dominated by hydrodynamic conditions, sediment movement under the influence of AV has recently received a lot of attention on the incipient sediment motion and bed load transportation under unidirectional flow conditions and sediment resuspension under waves. [ABSTRACT FROM AUTHOR]

Gas–liquid two-phase flow widely exits in production and transportation of petroleum industry. Characterizing gas–liquid flow and measuring flow parameters represent challenges of great importance, which contribute to the recognition of flow regime and the optimal design of industrial equipment. In this paper, we propose a novel complex network-based deep learning method for characterizing gas–liquid flow. Firstly, we map the multichannel measurements to multiple limited penetrable visibility graphs (LPVGs) and obtain their degree sequences as the graph representation. Based on the degree distribution, we analyze the complicated flow behavior under different flow structures. Then, we design a dual-input convolutional neural network to fuse the raw signals and the graph representation of LPVGs for the classification of flow structures and measurement of gas void fraction. We implement the model with two parallel branches with the same structure, each corresponding to one input. Each branch consists of a channel-projection convolutional part, a spatial–temporal convolutional part, a dense block and an attention module. The outputs of the two branches are concatenated and fed into several full connected layers for the classification and measurement. At last, our method achieves an accuracy of 95.3% for the classification of flow structures, and a mean squared error of 0.0038 and a mean absolute percent error of 6.3% for the measurement of gas void fraction. Our method provides a promising solution for characterizing gas–liquid flow and measuring flow parameters. [ABSTRACT FROM AUTHOR]

Two-phase flow exists widely in the industrial field, and its research is of great significance for industrial production. In this brief, we design a wire-mesh sensor system with 256 measurement points and conduct vertical upward gas-liquid two-phase flow experiments to capture the flow information under different flow conditions. We find that flow structure can be characterized by the gas-liquid distribution imaging obtained through the wire-mesh sensor. To obtain more detailed imaging, we apply super-resolution methods based on deep learning to improve the imaging quality and choose No-Reference Structural Sharpness to evaluate the effects. The results show that compared with traditional interpolation method, the deep learning-based super resolution can restore more abundant details such as edges and textures, thereby characterizing the flow structure more finely. This provides an important support for further analysis of the flow characteristics and flow regularity, which can effectively optimize the industrial process. [ABSTRACT FROM AUTHOR]

The process of removing corrosive gases from water at TPPs in packed columns of calciners and in columns of thermal deaerators with a storage tank in film mode is considered and a mathematical model is presented for calculating the efficiency of the desorption process. A cell model of the flow structure and an equation for calculating the mass transfer coefficient for a wave flow of a water film over the surface of a packing with artificial roughness are used. The value of the required height of the packing layer is obtained for the given density of irrigation with water and the efficiency of extracting gases dissolved in water. Formulas are given for calculating the parameters of a mathematical model: the coefficient of mass transfer in the wave film, the average velocity of water in the film, the dynamic retention of the liquid in the packing layer and the number of cells for complete mixing of the liquid phase. The possibility of using metal chaotic and regular packings is considered, and the results of calculations of the efficiency of mass transfer and the required height of the packing layer at various operating parameters of the desorption process are presented. The graphs of the required layer height for the given efficiency of mass transfer and the power spent on air supply to the desorber when using various nozzles of domestic and foreign production are presented. The article describes the operation of a thermal deaerator with a storage tank and outdated contact devices in a deaerator column at a TPP. The main mass transfer and hydraulic characteristics of modern nozzles for thermal deaerators are presented. Technical solutions have been developed that can be used when choosing a highly efficient metal chaotic packing with a rough surface, which provides an increase in the mass transfer coefficient in a liquid wave film and, accordingly, the efficiency of mass transfer. A variant for modernization of the deaeration column of the DSA-300 deaerator at the Kazan CHPP-3 by replacing outdated contact devices with a modern chaotic packing is shown. As a result of its application, compliance with the standards of water purification from dissolved oxygen is ensured at various loads on water and steam. [ABSTRACT FROM AUTHOR]

Wind tunnel tests for trains under large yaw angles are usually limited due to the width of the wind tunnel. Therefore, the leading car and a downstream dummy vehicle model are often employed instead of a real train, but there are no clear regulations regarding the shape of the end of the dummy vehicle. This paper studied the impact of the trailing edge shape of the downstream dummy vehicle on train aerodynamics subjected to crosswind based on the shear-stress-transport k-ω turbulence model of the delayed detached eddy simulation. Three types of end shapes, namely the rectangular end shape, the arc end shape, and the streamlined end shape were chosen for comparison, and the simulation results of the three-car-group train were selected as the benchmark. First, the reliability of the numerical method was validated by wind tunnel tests. Then, the aerodynamic coefficients under yaw angles of 0°–60° and the surface pressure distributions and flow structures around the train under the yaw angle of 60° of the head cars with different end shapes were compared and analyzed. [ABSTRACT FROM AUTHOR]

The paper presents experimental data on heat transfer and kinematic structure of steady and pulsating flows behind a rib. Several forcing frequencies and one non-dimensional amplitude of pulsation are considered. Distributions of heat transfer coefficient were obtained in the separation region. Optical measurements yielded the profiles of velocity and turbulent characteristics of flow at representative coordinates of the separation region.

Lean-premixed combustion technology has been adopted widely for heavy-duty gas turbine application. The multiple-swirl structure might shorten the flame brush length and reduce emissions. However, the inlet flow cannot be set equally for each swirl burner. The inlet guiding ring structure should be carefully adjusted and validated to reach the design goal. This paper introduces a typical geometry of heavy-duty combustor, which is designed with multiple swirler structures. The inlet guiding ring is a semicircle type. The parametric analysis is trying to investigate the axial location of the inlet guiding ring effect on the downstream multiple-swirl flow structure. Computational results show that both the Counter-Swirl and Co-Swirl configurations possess quite well aerodynamics which can support the recirculation establishment and flame stabilization. As the axial distance between the inlet guiding ring and swirl nozzle increases from 16 mm to 37 mm, the width of the recirculation will increase, which intensify the turbulence mixing for the pilot and main stage. Meanwhile, the length of the recirculation also increases, and the turbulence intensity keeps relatively strong. When the gap distance increases from 37 mm to 51 mm, the flow phenomenon would return to the condition like the case with an axial distance equal to 16 mm. Therefore, the condition with the axial gap distance 37 mm is quite critical. Thus, the flow field is quite sensitive to the inlet guiding ring location. [ABSTRACT FROM AUTHOR]

The complex structure of the human nasal cavity makes it difficult to study the flow of air in it, therefore, at present, mathematical and computer modeling is used for this purpose. These studies are relevant due to the development of inhalation methods for introducing drugs into the nose, with the help of which operations can be performed. Within the framework of the Navier-Stokes system of equations, temperature and concentration using the ANSYS Fluent application, a three-dimensional test calculation of the air flow in the human nasal cavity was carried out at various modes of inhalation, normal and during exercise. A laminar model was used to close the Navier-Stokes equations, and the SIMPLE method was used to perform the relationship between velocity and pressure. In the graphics package AutoCAD, a geometric three-dimensional model of the nasal cavity was built, reconstructed from images of the nose in coronary sections. As a result of numerical simulation, the fields of velocity, pressure, temperature and concentration were obtained. The results obtained were compared with the experimental data from [10] and the numerical results from [3]. The analysis of these results in terms of the influence of the structure of the nasal cavity on the structure of the flow. The results obtained agree with the experimental data. It was found that the inhaled air is heated and humidified to the state of the nasal tissue, the shells increase the rate of local transfer of heat and moisture by improving mixing and maintaining thin boundary layers, the capacity of a healthy nose exceeds the requirements necessary for conditioning the inhaled air under normal breathing conditions. [ABSTRACT FROM AUTHOR]

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

Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 100–101). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase. [ABSTRACT FROM AUTHOR]

Flow development and eddy structure in an L‐shaped cavity with lids moving in the same directions have been investigated using both tools from topological and numerical methods. In particular, structural bifurcation near a nonsimple degenerate point is investigated by making a local analysis of the velocity field based on a Taylor series expansion. The streamlines of a Hamiltonian vector field system are simplified by using the homotopy invariance of the index theory. A series of bifurcation curves are constructed to determine the sequence of flow structures by which eddies are generated in the L‐shaped cavity. [ABSTRACT FROM AUTHOR]

The paper is devoted to the matter of energy losses prediction in axial turbine cascade based on CFD analysis. An intensive development of numerical modelling of flows in turbomachinery and the advent of various turbulence models open up major opportunities for blade row gas-dynamic efficiency estimation. Nowadays statistically significant data on the difference between predicted and experimental losses for flow conditions with Mach number near 1 and above are not available in public domain. Therefore the present paper offers analysis results for several turbine blade cascades of various geometries, that have detailed experimental data. Reynold's stress model in CFD analysis was used. The study has showed that the estimated and experimental data show satisfactory fit for isentropic Mach number along blade profile and significant difference in losses of energy when there is a skew shock waves system. The predicted losses are lower than experimental ones for the most flow conditions. [ABSTRACT FROM AUTHOR]

Regimes of continuous detonation of CH4/H2–air mixtures with mass fractions of H2 in the fuel equal to 0–1/5 are obtained in an annular combustor 503 mm in diameter with variation of the combustor geometry. The influence of the combustor geometry on the velocity and number of transverse detonation waves, pressure in the combustor, and specific impulse is considered. It is found that three-fold constriction of the combustor exit cross area allows obtaining two-wave regimes of continuous spin detonation in the pure methane–air mixture. Based on stagnation pressures measured at the combustor exit, the specific impulses in the case of continuous detonation are determined for different compositions of the fuel. [ABSTRACT FROM AUTHOR]

This study considers the effect of kinematics on the aerodynamic loads and flow structure around moving blades of micro air vehicles (MAVs) in deep dynamic stall. The transversal (pure heaving) and rotational (pure pitching) motions are considered distinctly to investigate the dynamic stall. An equivalent effective angle of the attack profile is given to both motions. This method helps to figure out the influence of kinematics on flow structures when all boundary conditions and effective angles of attack profiles are the same. An experiment is conducted in fully turbulent flow at Re = 1.5×104 to avoid any transition regime in the boundary layer, and make the results relatively independent of the flow characteristics. A NACA 0012 airfoil is chosen at high reduced frequencies (k = 0.25 and 0.375) and high angles of attack to reach deep dynamic stall conditions. Additionally, time-resolved particle image velocimetry (PIV) and post-processing are used to compute the aerodynamic loads using a control-volume approach. The flow field is also reconstructed using proper orthogonal decomposition (POD) to separate the flow structures in different modes. It is shown that the kinematics can significantly influence the flow structure and aerodynamic loads. In the pre-stall region, the pure pitching motion usually produces higher lift force, while the pure heaving motion has a higher lift peak. However, in the post-stall region, the pure heaving motion usually has higher lift than the pure pitching motion. The pure heaving motion produced lower drag force than the pure pitching motion. For pure heaving motion, the POD analysis reveals there is a high-energy mode in the flow structure that helps to make the vortices more stable compared to pure pitching motion. Furthermore, the pure heaving motion adds extra kinetic energy to the boundary layer, which decelerates the reversal flow and the transfer of the separation point on suction side of the airfoil. [ABSTRACT FROM AUTHOR]

The internal flow structures of detonation wave were experimentally analyzed in an optically accessible hollow rotating detonation combustor with multiple chamber lengths. The cylindrical RDC has a glass chamber wall, 20 mm in diameter, which allowed us to capture the combustion self-luminescence. A chamber 70 mm in length was first tested using C 2 H 4 O 2 and H 2 –O 2 as propellants. Images with a strong self-luminescence region near the bottom were obtained, confirming the small extent of the region where most of the heat release occurs as found in our previous research. Based on the visualization experiments, we tested RDCs with shorter chamber walls of 40 and 20 mm. The detonation wave was also observed in the shorter chambers, and its velocity was not affected by the difference in chamber length. Thrust performance was also maintained compared to the longer chamber, and the short cylindrical RDC had the same specific impulse tendency as the cylindrical (hollow) or annular 70-mm chamber RDC. Finally, we calculated the pressure distributions of various chamber lengths, and found they were also consistent with the measured pressure at the bottom and exit. We concluded that the short-chamber cylindrical RDC with equal length and diameter maintained thrust performance similar to the longer annular RDC, further expanding the potential of compact RDCs. [ABSTRACT FROM AUTHOR]

Predicting the velocity distribution of double horizontal axis tidal turbines (DHATTs) is significant for the effective development of tidal streams. This current research gives an account on double turbine wake theory and flow structure of DHATT connected to single support by using the joint axial momentum theory and computational fluid dynamics (CFD) method. Characteristics of single turbine wake were previously studied with two theoretical equations predicting the initial upstream velocity closer to the turbine, and it's lateral distributions along the downstream of the turbine. This current works agreed with the previous wake equations, which was used for predicting the velocity region along the downstream of the turbines. Flow field separating the two turbines is complicated in nature due to the indirect disturbance of turbines and no report was found on this central region. The Central region in the downstream flow is initially suppressed due to the blockage effects with a high velocity close to the free stream. Lateral expansion of two turbine wakes penetrated the central region with velocity reduction and followed by the flow recovery further downstream. This work provides more understandings of the wake and its central mixing region for double turbines with a proposed theoretical model. [ABSTRACT FROM AUTHOR]

The problem of calculating the thermal efficiency of the liquid and gaseous phases in a countercurrent fi lm-type cooling tower has been solved. From the joint solution of the heat balance equation and expressions for the thermal efficiencies of the cooling tower liquid and gaseous phases, the relationship between the efficiencies of water cooling and air heating in the blocks of sprinklers has been established. At the given temperature regime of water cooling and thermodynamic state of moist air, the thermal efficiency of the liquid phase was determined and then the obtained relation was used to determine the thermal efficiency of the gas phase to be provided by the blocks of sprinklers. To calculate the efficiency of the blocks of sprinklers, a cellular model of flow structure was used. An expression is obtained for calculating the height of the blocks at the given efficiency of the gas phase and construction characteristics of packing and of water and air flow rates. Agreement with experimental data is shown, and the algorithm of calculation is given. [ABSTRACT FROM AUTHOR]

The Ω caving in riverbanks is one of the typical bank erosion patterns occurred in alluvial rivers which develops quickly and increases the instability of dikes. The numerical simulation of this type of bank erosion is still a challenging task. The Zhinancun bank caving developed at the lower Yangtze River was investigated in this paper,and a 3-D numerical method for modeling the Ω caving in the riverbank was proposed based on the mechanism of bank erosion. The sediment transport capacity in the circumfluence zone was calculated by considering the influences of turbulence intensity. The simulated results indicated that the velocity close to the riverbed is larger than that in the upper layers in the circumfluence zone during the processes of riverbank collapse,which becomes the driving factors for the riverbed scouring and thus bank erosion. The determination of the sediment transport capacity has a great influence on the simulated shape of the bank which can be more accurately simulated by considering the effect of turbulence intensity. This study could improve our understanding of the mechanism of riverbank collapse. [ABSTRACT FROM AUTHOR]

Labyrinth seals installed in turbine machines serve for decreasing the working fluid leakage through the clearances between the rotating and stationary structural elements in order to increase its flowrate through the flow path. The operational efficiency and reliability of all types of turbine machines (steam, gas, and hydraulic turbines; compressors; fans; pumps; etc.) depend to an essential extent on the type of seals (labyrinth, groove, etc.), which determine the working fluid leakage and intensity of hydrodynamic forces acting on the rotor. Therefore, those who design turbine machines should use a close-to-reality model of the flow pattern in labyrinth seals. Such a model was developed in the 1970s by A.G. Kostyuk with his coworkers at the Moscow Power Engineering Institute and is quite widely used in analyzing the dynamics of turbine machines. However, the procedures for thermal and aerodynamic design analyses of turbine machines, as well as relevant standards and handbooks, do not contain a description of this model nor do they contain recommendations for using it. At present, such a state of things becomes especially dangerous in connection with wide application of numerical methods of 3D design and analysis, when the use of an inadequately selected flow model (in particular, in seals) may give rise to essential errors. The article presents a review and scrutiny of the used numerical and experimental models of shroud seals; their drawbacks are shown, and a model adequately representing a real flow is described. [ABSTRACT FROM AUTHOR]

Results of experimental investigations in a flow-type annular cylindrical combustor with an outer diameter of 503 mm are reported. The influence of air addition to products of continuous spin detonation of CH4/ m H2–air mixtures on the parameters of detonation waves, the pressure in the combustor, and the specific impulse is considered. It is demonstrated that air injection into detonation products increases the velocity of continuous spin detonation, the pressure in the combustor, and the thrust, whereas the specific flow rate of the fuel decreases. [ABSTRACT FROM AUTHOR]

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