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In the present study, we experimentally investigate the liquid flow induced in a rotating drum (cylindrical tank with a short aspect ratio) aligned horizontally, focusing on the variation in the time-averaged and fluctuating flow structures with different fill ratios. For each fill ratio, controlled by varying the water height, we measure the velocity fields at different cross-sectional planes with particle image velocimetry while varying the rotational speed of the drum. Compared to the condition of a fill ratio of 1.0, in which the liquid inside the drum rotates forming a large-scale (solid-body rotation) organized flow structure, a substantial asymmetric flow structure shows up in partially-filled conditions driven by the imbalance between (i) the momentum diffusion along the radial direction and the centrifugal acceleration, and (ii) the downward (gravitational) flux of the induced flow. In addition to the mean flow structure, we examine the fluctuating velocity fields together with the dynamics of the free surface, and we also briefly discuss the difference between the liquid flow and granular (particle) flow in a partially-filled drum. We think that the present results provide valuable insights on the partially-filled liquid drum toward various engineering applications. [ABSTRACT FROM AUTHOR]

The issues of reliability and efficiency of operation of field and main oil and gas pipelines and control of energy characteristics during their operation are of no small importance. The efficiency of pipelines depends on the technical condition of facilities and equipment and the rationality of their use. The practice of operating pipelines shows that emergency and abnormal cases occur in them. Significant irregular pressure and flow pulsations are observed in pipelines. Waves of high and low shock pressure often occur and propagate along the pipeline. Along with density, additional pressure in the system from hydrodynamic impacts also arises from the elasticity of the pumped liquid and the pipeline itself. This pressure is determined by the elastic compression of the transported system and the elastic expansion of the pipeline as the pressure in it increases. The pipeline through which the multiphase flow is pumped, and its structures and other components must withstand dynamic loads. The work analyzes various modes of water impact. The volume of oil caused by its compression during hydraulic impact was calculated. The results of calculating the increase of an oil pipeline volume due to a dynamic impact are presented. [ABSTRACT FROM AUTHOR]

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

Water jet scouring technology is extensively applied in marine engineering, harbor maintenance, river training, and various other fields, showcasing a broad spectrum of potential applications. However, achieving a comprehensive understanding of the transient sand scouring characteristics of water jets remains challenging due to the inherent complexity of the coupled flow structure involving submerged jets and environmental fluids, along with the intricate dynamics of two-phase flow. This study, rooted in numerical simulation and experimental validation, introduces pulse characteristics into a submerged jet. A thorough investigation is conducted to explore the transient sand scouring characteristics and sand transport laws of the submerged jet under diverse working conditions. The results of this study revealed that the main reason for the asymmetry of the sand pit morphology is not the non-uniform distribution of sand grains, but more likely caused by turbulence effects. Simultaneously, within the initial 0.25 s of the pulse cycle, suspended sediment resulting from the pulsed jet in the preceding cycle gradually transports to the dune and its surrounding areas. Subsequently, from 0.25 s to 0.5 s, sediment on both sides of the pit's bottom undergoes movement and amalgamation with the sediment that remained unsettled during the previous cycle. The findings reveal that higher jet velocities significantly enhance sediment suspension, migration, and redeposition, leading to deeper erosion and the rapid formation of the sand pit's outline within 2 s. Additionally, the jet velocity and the impact distance are identified as critical factors influencing erosion depth and sediment dynamics. These insights advance the understanding of erosion mechanisms driven by pulsed jets, highlighting their impact on sediment transport processes. The research findings provide important guidance for dredging and ocean engineering fields and offer a theoretical basis for improving the understanding of submerged jet scouring mechanisms. [ABSTRACT FROM AUTHOR]

Intense energy flow near the dike head significantly influences the development of the dike field zone (DFZ), momentum exchange zone (MEZ), and mainstream zone (MSZ), leading to potential partial or full failure of the dike in the MEZ. To address this, laboratory experiments were conducted to observe flow changes and rate of energy reduction around a single impermeable dike, with alterations made to the pile group length (HL: half-length = 11.5 cm and FL: full length = 23 cm), location (U: upstream, D: downstream), and shape (C: Circular, DV: Delta Van, ST: Streamlined tapered, APF: Angled Plate footing). Modifications in the MEZ flow structure were studied to mitigate concerns about intense energy vortices and dike head flows. These piles helped to assess factors like flow deflection, backwater rise, energy reduction rate, velocity fluctuations, and discharge distribution percentages across the zones. The data revealed that when the pile group length was increased from HL to FL, there was an inverse effect on depth-averaged velocity, MEZ discharge distribution percentage, and flow deflection toward the DFZ. Conversely, there was a direct influence on the rise in backwaters, rate of energy reduction, and discharge distribution percentages in the DFZ. The U-FL-APF pile dike showcased optimal results, displaying a reduction in maximum energy by 52% and streamwise velocity by 96%, while also increasing the backwater rise and discharge distribution by 22% and of only 5% in the MEZ, respectively, compared to a single impermeable dike. During flood events, these suggested measures can mitigate the intensified swirls formed in the DFZ, protect the dike head from direct momentum exchanges in the MEZ, and enhance flow deflection into the MSZ.

Numerical computations were conducted to investigate the vortex-induced oscillations of two adjacent circular cylinders, which are elastically supported by linear springs. The calculations were performed across a range of Reynolds numbers, spanning from 4200 to 42000. The cylinders were allowed to oscillate only in the transverse direction. The study aims to examine the influence of the spacing between two cylinders on their vibrations within the flow. The center-to-center spacing between the cylinders is varied between 1.2 and 4. The observed flow pattern exhibits different wake modes, accompanied by gap flow patterns. At a spacing ratio of 3, the response amplitude for both cylinders during lock-in is larger than that of a single cylinder. The characteristics of fluid forces, vortex patterns, output power as well as vibrational responses are extensively investigated in three different spacing configurations. [ABSTRACT FROM AUTHOR]

Two-layer thermal convection exists widely in nature. In the present work, an experiment was conducted to investigate the heat transport and flow structure in two-layer thermal convection. In a rectangular convection cell, two immiscible fluids, glycerol and 2 cs silicone oil, were used as the working fluids. In the lower-thin glycerol layer, the bottom boundary was subjected to a no-slip boundary condition (BC), and the interface was subjected to slip BC. The aspect ratio of glycerol layer (lower) was Γ1=10.4. The Rayleigh number and Prandtl number of the glycerol layer covered the ranges of 260≤Ra1≤6 000 and 3 708 < Pr1 < 7 000, respectively. In the upper-thick silicone oil layer, the boundary at the top was subjected to no-slip BC. The aspect ratio of silicone oil (upper) was Γ2=0.53. The Rayleigh number and Prandtl number of the silicone oil layer covered the ranges of 1.5×109≤Ra2≤2.0×1010 and 28 < Pr2 < 33. It is found that the two-layer thermal convection has different heat transfer efficiencies and flow structures in two regions. For region 1 where the heat flux is smaller than a certain value, the glycerol layer (lower) is in a stable stratified state. For region 2 where the heat flux is greater than the certain value, a cellular pattern was formed in glycerol layer and the global heat transport was sharply increased through a subcritical bifurcation. The heat transport of glycerol layer exhibits oscillatory instability at the critical Rayleigh number Ra1c=1 523, which is smaller than the theoretic value 1 708 of critical value Ra for the 2D infinite Rayleigh-Bénard convection (RBC) with both rigid BCs. It reveals that the slip BC makes the fluid become unstable easier and enhances the heat transport. A measurement with shadowgraph method was further conducted. The cellular pattern of glycerol layer, the interface and hot plumes were also studied.

This paper investigates the shape and hydrodynamic characteristics of the sand bed at the junction of urban pipelines and their relationship with the flow ratio. Various hydrodynamic and morphological features, including shear layers, spiral cells, and scour pits. The dataset used for analysis consists of a three-dimensional time-averaged velocity field, turbulence, bed morphology, and confluence morphology of equilibrium phases obtained under controlled laboratory conditions. For large flow ratios (q*), significant local erosion occurs near the downstream shear plane at the junction. When the flow of tributaries surpasses that of the main stream, the strength and downstream extension of the spiral cell blocks increase. The max Reynolds number shear stress predominantly concentrates in the middle region of the water depth, aligning with the turbulent kinetic energy representation of the shear layer. Keeping the flow ratio constant, the velocity, turbulent kinetic energy, and absolute Reynolds shear stress all escalate with increased flow. [ABSTRACT FROM AUTHOR]

This study investigates the aerodynamic performance of various trains with different nose shapes, using as the design variables two angles α , β for the head shape and the bluntness angle γ , without crosswind. The effects on aerodynamic performance, such as the train drag coefficient, pressure distribution along the train surface, flow structures around the train and the wake, and head pressure pulse, are analyzed. The results indicate that the increase in the train nose length for flat shapes decreases the C D values by 21.47 % and 19.11 % , decreasing the high-pressure region in the leading head. The duck nose configuration emerges as a compromise between drag reduction and nose length. Increasing the angle γ , a further drag reduction of 8.5 % is featured. Drag formation along the train is also analyzed. The steeper the variation in the geometry, the higher the peak intensity and the slope of the curve. Regarding the flow features around the train, two main counter-rotating vortices are captured in the wake. Moreover, the higher the nose length and the higher the bluntness angle γ , the weaker and narrower the wake. Again, a longer nose shape yields a softer jump in terms of pressure difference, crucial for train homologation and safety. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the evolution of rock fracture slug structures and decongestion strategies for natural gas extraction processes. For this purpose, the level set method was used to simulate the evolution of the slug structure under the effect of different flow ratios, fracture surface wettability, and fracture tortuosity. The results show that an increase in the water-to-gas flow ratio and fracture tortuosity leads to a significant increase in the proportion of slug structures in the fracture, while an increase in the surface contact angle leads to a decrease in the proportion of slug structures in the fracture. Based on the above slug structure evolution law, a quantitative characterization method for the slug structure of two-phase fluids considering the combined effects of the water–gas flow ratio, average wall contact angle, and flow channel tortuosity was developed. Subsequently, we engage in further discussion on the optimization of the extraction and decongestion process in natural gas extraction. [ABSTRACT FROM AUTHOR]

River bends in actively developing lowland rivers exhibit complex flow characteristics owing to the mutual impacts of secondary current, large water-surface fluctuations, and flow separation within the bank. However, the understanding of the interface among mean flow patterns and turbulence in meandering during various hydrological circumstances remains limited. This paper addresses this knowledge gap by reviewing measurements acquired from Acoustic Doppler Current Profiler (ADCP) to analyze three dimensional flow velocities and to assess the influence of hydrologic variability on flow field in a bend. The study investigates the flow patterns at different flow stages and their relationship with changes in bed shear stress. Particularly, observations from the highly curved R c/B ≤ 3 bends of the Gomti River reveal the flattening and deformity of velocity profile of the primary flow owing to the advection of momentum from the secondary motion. It is noteworthy that in highly-curved bends, the greatest flow velocity consistently results in the inner bank, indicating that the influence of secondary flows extends beyond the confines of the bend. The variation of secondary current, streamlines, bed shear stress, and velocity components in response to hydrologic variability is examined. The study identifies variations in general shapes of streamline at various water depths in the bend study. Analysis of bed shear stress (BSS) distribution employing two separate techniques, the turbulent kinetic energy and shield stress approach demonstrate that the largest shear stress arises from bend entry to the apex region near the inner bank. Overall, this research provides valuable insights into the flow dynamics of stream bends and their response to hydrologic variability. [ABSTRACT FROM AUTHOR]

The study is focused on the flow parameters of the slotted impinging jet associated with its heat transfer performance. The analysis is performed for the circular and slotted jets of square, cross, and oval sections for flow outlet to target plate distance of L/D = 1 to 4. The Reynolds number range of 12700 - 23000 is used in this study to analyze the heat transfer pattern using liquid crystal sheet. The numerical analysis is carried out using CFD. The axial velocity peak (u/U0 = 2.124) is observed for the square jet corresponding to r/D = 0.33 at L/D = 1 and the peak reduces with increasing L/D distances. Higher intensity of average radial velocity (ur/U0 = 1.44) is observed close to the impinging plate for the slotted jet at L/D = 1 at 0.5 = r/D = 1.4 compared with radial velocity (ur/U0 = 0.91) of circular jet. Nusselt number distribution has little dependence for circular jet on the separation distance as the variation is marginal at L/D = 4 when compared to L/D = 1 and 2, the slotted jet however shows marked variation of Nusselt number (136.8 at L/D = 1, 135.2 at L/D = 2 and 113.5 at L/D = 4) in the region at X/D = 1.5. The highest values of turbulence intensity (TI = 0.206) is observed at r/D = 0.5 for the square jet at L/D = 3. [ABSTRACT FROM AUTHOR]

The three-dimensional lattice Boltzmann method (LBM) is used to simulate the motion of a spherical squirmer in a square tube, and the steady motion velocity of a squirmer with different Reynolds numbers (Re, ranging from 0.1 to 2) and swimming types is investigated and analyzed to better understand the swimming characteristics of microorganisms in different environments. First, as the Reynolds number increases, the effect of the inertial forces becomes significant, disrupting the squirmer's ability to maintain its theoretical velocity. Specifically, as the Reynolds number increases, the structure of the flow field around the squirmer changes, affecting its velocity of motion. Notably, the swimming velocity of the squirmer exhibits a quadratic relationship with the type of swimming and the Reynolds number. Second, the narrow tube exerts a significant inhibitory effect on the squirmer motion. In addition, although chirality does not directly affect the swimming velocity of the squirmer, it can indirectly affect the velocity by changing its motion mode. [ABSTRACT FROM AUTHOR]

The hydrodynamic coefficient of an underwater manipulator varies with changes in posture and flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6x10³ ≤ Re ≤ 3x104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = -90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25. [ABSTRACT FROM AUTHOR]

This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model's accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier. [ABSTRACT FROM AUTHOR]

This study aims to numerically investigate the optimal conditions for fluid flow control around a single square cylinder with the help of a pair of attached flat plates. It is comparatively a new approach for controlling fluid flows as compared to the traditional solo plate flow control devices. The plates are attached adjacent to the both rear corners of the cylinder and their length (l) is varied from 0.1 to 4 times size of main cylinder while fixing the height (h) at 0.2. By varying the length, the plates manage to control the flow gradually. This study discusses how a steady wake can be achieved through control plates. Results indicate that the flow regime changes from unsteady to transitional at l=2.7 while for l>3.1 the steady flow appears. The streamlines visualizations reveal different flow structures termed as the oval-eye vortex, chain necklace vortex, sphere vortex, hair pin vortex and wooden eyes vortex-like structures. Among these the oval-eye vortex structure is found to have higher flow induced forces and shedding frequencies while the wooden eyes vortex structure is found to have minimal flow induced forces and shedding frequencies. After l=3.2, the plates’ efficacy is proven by a 100% reduction in Strouhal number, root-mean-square values of lift coefficient and amplitudes of lift and drag coefficients. This study reveals that l=3.2 is the best optimal value of plates length for complete wake and fluid forces control. [ABSTRACT FROM AUTHOR]

The greater thrust-vector angles can be obtained in the axisymmetric divergent bypass dual throat nozzle (ADBDTN). Meanwhile, the axisymmetric divergent bypass dual throat nozzle also has a certain flow adaptive capability and can solve the starting problems existing in the non-vectored state. In the present paper, the results of experimental investigations on the vectoring characteristics of the axisymmetric divergent bypass dual throat nozzle are given. By comparing the structures of the flow field obtained from experiments and numerical simulations as well as the wall static pressure distributions along the flow direction and circumferential direction, it can be seen that, as the nozzle pressure ratio (NPR) increases, flow reaches a critical state near the nozzle exit, and incompletely expanded flow in the cavity continues to accelerate after flowing out of the nozzle, a diamond-shaped structure with alternating shock and expansion wave systems appears downstream of the nozzle exit, and the flow field structures in the cavity are no longer changed when NPR ≥ 6. In addition, the static pressure distributions on the upper and lower wall surfaces of the cavity of the nozzle obtained from the experiments are in good agreement with the results of the numerical simulations, and the wall static pressures in the cavity are basically symmetrically distributed at various circumferential angles. [ABSTRACT FROM AUTHOR]

Large wood in rivers can lead to accumulations in the river channel, affecting local flow structures, aquatic habitats, and the river's topography. This plays a crucial role in the ecological restoration of the river. This paper presents flow field measurements downstream of six types of logjams at different flow velocities using acoustic Doppler velocimetry (ADV) for artificially designed engineered logjams. The results indicate that the presence of logjams reduces the flow velocity and increases the turbulent kinetic energy in the wake region, and as the distance downstream increases, the flow velocity and turbulence intensity in the wake region gradually return to the upstream level. The minimum values of normalized flow velocity under different conditions are located in the region of the bottommost logs. The differences in normalized flow velocity at various flow rates are not significant. Jets are less likely to be generated in logjams with larger and more concentrated projection areas, but the strength of the jet is influenced by the physical structure of the logjam (projection area, gap ratio). The flow distribution behind the logjam is primarily influenced by the proportion of the projected area in different regions. Changes in the vertical physical structure of the logjam have minimal effect on the lateral flow distribution. Flow velocity in the gap area (b0) at the bottom of different logjams is influenced by their physical structure. The larger the overall blockage area of the logjams, the larger the flow velocity in the bottom gap area will be. The flow velocity in the bottom gap area of a densely placed logjam is mainly influenced by the gap ratio. The velocity of flow in the gap area can impact the initiation and deposition of sediment near the logjam. However, the internal structure complexity of the logjam does not significantly affect river energy dissipation and flow attenuation. This study broadens the applicability of certain theoretical models and explores the impact of logjams on river ecology and channel geomorphology. The findings can serve as a theoretical foundation for ecological restoration, timber management, and logjam construction in rivers. [ABSTRACT FROM AUTHOR]

To study the influence of an elbow inlet on the rotating stall characteristics of a waterjet propulsion pump (WJPP), a three-dimensional internal flow field in a WJPP under a straight-pipe inlet and elbow inlet is numerically simulated. By comparing the hydraulic performance of WJPP under the two inlet conditions, the internal relationship between the inlet mode and the flow pattern in the pump is clarified. Based on unsteady pressure fluctuation characteristics and wavelet analysis, the influence of the inlet mode on the rotating stall is revealed, and the stall transient propagation characteristics under critical stall conditions are analyzed. The disturbance effects of the inlet channel geometry disappear under low flow rate conditions, the main disturbance is induced by the high-speed countercurrent, and the flow pattern under the elbow inlet is better than that under the straight-pipe inlet. Under the straight-pipe inlet, the single-stall nucleus in the WJPP temporarily experiences a low-frequency and high-amplitude disturbance, which subsequently transforms into a mode of multi-stall nuclei with high-frequency circumferential disturbance. Under the elbow inlet, the rotating stall always maintains a mode of high-amplitude and low-frequency disturbance, which represents the transient characteristics of a single stall core propagating in the circumferential direction inside the channel. The results of this study have a reference value for structural design optimization in a WJPP.

The hydrodynamic coefficient of an underwater manipulator varies with changes in posture and flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6×103 ≤ Re ≤ 3×104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = −90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25.

This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model’s accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier.

Abstract This work considers the flow field as two-dimensional turbulent flow and studies the steady-state properties of heat transfer and the pressure of the suspension nozzle. An adiabatic wall parallel to the moving wall and two slit entrances at either end of the adiabatic wall make up the rectangular flow field. The SST $$k - \omega$$ k - ω turbulence model is used in the turbulence computation. Both qualitative and quantitative analyses are conducted on the distribution of the flow field, temperature field, local Nusselt number, local pressure coefficient, average Nusselt number, and average pressure coefficient under various combination conditions. The findings indicate that when the suspension nozzle's flow field varies greatly, wall-jet velocity ratio is 0.1. A rise in Jet inclination angle is not helpful for the wall's suspension, and it has minimal effect on the flow field. The flow field is greatly influenced by separation space-slit width ratio. Larger separation space-slit width ratio values are advantageous for the wall's heat transmission but unfavorable for the wall's suspension. The flow field is most influenced by wall-jet velocity ratio. The wall's ability to convey heat is stronger the higher the wall-jet velocity ratio, but its ability to support weight falls.

AbstractIn order to investigates the flow and heat transfer characteristics under supersonic mainstream conditions among three typical film hole-configurations—cylinder hole (CH), fan-shaped hole (FSH), and laidback fan-shaped hole (LFSH), this study conducted numerical simulation using the ANSYS CFX and based on the assumption of compressible flow. The results indicate that the cooling effectiveness of the CH dramatically decreases as the blowing ratio increases, while FSH and LFSH improves. When the supersonic mainstream encounters the coolant, flow structures such as oblique shock waves, expansion waves, and mixing layers et al., will be generated around the film holes, which have an impact on the flow and heat transfer characteristics. Under the conditions of same blowing ratio, the shock wave intensity of LFSH is significantly lower than the other two holes and the kidney vortices formed by the CH develop further along the mainstream direction. While the strength of the kidney vortices formed by the FSH and the LFSH is weaker. Additionally, the LFSH incurred the least total pressure loss from before the shock wave to after the oblique shock wave. Specifically, at a blowing ratio of 0.8, it achieved a reduction of approximately 20% in total pressure loss compared to the CH. [ABSTRACT FROM AUTHOR]

It is proposed to determine the main parameters of the structure of flows in objects by velocity profile without taking response curves using the indicator method in heat and mass transfer apparatuses and reactors. A formula is derived for calculating the variance (central moment of the second order) and the flow structure function for a half-open vessel. An algorithm is also proposed for calculating the average residence time, the Peclet number of longitudinal diffusion for a one-parameter diffusion model, the number of cells and the differential response function of a combined model with a sequential connection of ideal displacement and mixing zones for a cell model. Moreover, calculation of the distribution density of the differential and integral response curves corresponding to a given velocity profile is provided. [ABSTRACT FROM AUTHOR]

The flow structures of jet impingement dominate heat and mass transfer process, even the whole thermal performance. In this study, we have inspected the flow structures and mechanism of nanofluid jet impingement onto a dimpled target surface with different design parameters. Investigations are performed for the relative depth of dimple (δ / D), the jet-to-plate spacing (H / d), nanoparticle volume concentration (ϕ), and Reynolds number (Re) ranging to explore the mechanism of flow structure variations. Results indicate that these parameters have a significant effect on the flow structure of nanofluid jet impingement near the dimpled target surface. The flow begins to separate after passing the edge of the dimple along with the curvature of a dimple. δ / D will affect the form and location of flow separation and reattachment, and ϕ will affect the intensity of separation flow. The length of the flow separation bubble varies in different H / d cases. When H / d increases, the impinging energy and the velocity near the dimple edge decreases. The different Re has little effect on the length of the flow separation bubble and the tendency of the pressure coefficient (Cp). These results can provide further mechanism inspiration for the design of the flow structure of nanofluid jet impingement. [ABSTRACT FROM AUTHOR]

The confluence between a pipe and an open channel is a common pattern. This study analyses the flow characteristics of pipe and channel confluences by examining the bed morphology and turbulent structure. A general process-response model of the hydro-morpho-sedimentary processes is proposed. The study also investigates the transport of contaminated sediment carried in the drainage pipe at the discharge outlet. The bed morphology at the confluence of the pipe and channel is characterized by a scour hole at the pipe outlet, a scour hole bar and a deposition zone. Above the scour hole and deposition zone, the inner shear layer exists with intense turbulence and low velocities between them. Contaminated sediments accumulate on the inner side of the channel, with coarser particles (D50 > 2.28 × 10–4 m) near the pipe outlet and finer particles carried downstream. The findings of this study could be helpful to pollutant transport management in natural confluences. [ABSTRACT FROM AUTHOR]

The presented study aims to reveal flow and heat transfer characteristics as a translating aluminum plate is impinged by high-temperature gas discharged from inclined slot nozzles. The computational fluid dynamics (CFD) and the fluid-solid interaction (FSI) techniques were used to simulate the impingement process. A comprehensive comparison of flow, heat transfer, and structural parameters was implemented. The results indicate that twin vortices are produced between the two inclined nozzles. When the velocity ratio increases from 0.1 to 1.0, the vortex at the left expands, while the right one is compressed. Meanwhile, average Nusselt number and the pressure coefficient exhibit opposite variation tendencies. The highest average pressure coefficient of 0.45 arises at a velocity ratio of 0.5. As the plate-nozzle distance increases, characteristic flow structures are developed, and the distributions of temperature and the pressure coefficient are uniformized. The maximum Nusselt number decreases from 473 to 266 when the nondimensional plate-nozzle distance increases from 4 to 8. Large deformation occurs at the middle part of the plate. High equivalent stress is concentrated at the front and rear ends of the plate, which is insensitive to the velocity ratio and the plate-nozzle distance. [ABSTRACT FROM AUTHOR]

The match of rotor and stator blades significantly affects the flow field structure and flow-induced pressure pulsation characteristics inside the pump. In order to study the effects of the rotor and stator matching mode on the complex flow field and pressure pulsation of a centrifugal pump with a vaned diffuser, this paper designs three different vaned diffusers (DY5, DY8 and DY9) and uses the DDES (Delayed Detached Eddy Simulation) numerical method combined with structured grids to simulate the unsteady flow phenomena of the model pump under rated conditions. The results show that, under different rotor and stator matching modes, the pressure pulsation spectrum is dominated by the blade passing frequency and its harmonics. The matching mode of the rotor and stator significantly affects the time–frequency domain characteristics of the pressure pulsation inside the pump, and it is observed that the pressure pulsation energy of vaned diffusers with more blades is significantly smaller than that of fewer-blade vaned diffusers in comparison to the energy of the pressure pulsation at the blade passing frequency and within the 10–1500 Hz frequency band. Combined with the distribution characteristics of the complex flow field inside the pump, it can be found that increasing the number of vaned diffuser blades can reduce the energy of flow-induced pressure pulsation, improve the distribution of high-energy vortices in the interaction zone and stabilize the flow inside the centrifugal pump effectively. [ABSTRACT FROM AUTHOR]

This work considers the flow field as two-dimensional turbulent flow and studies the steady-state properties of heat transfer and the pressure of the suspension nozzle. An adiabatic wall parallel to the moving wall and two slit entrances at either end of the adiabatic wall make up the rectangular flow field. The SST k - ω turbulence model is used in the turbulence computation. Both qualitative and quantitative analyses are conducted on the distribution of the flow field, temperature field, local Nusselt number, local pressure coefficient, average Nusselt number, and average pressure coefficient under various combination conditions. The findings indicate that when the suspension nozzle's flow field varies greatly, wall-jet velocity ratio is 0.1. A rise in Jet inclination angle is not helpful for the wall's suspension, and it has minimal effect on the flow field. The flow field is greatly influenced by separation space-slit width ratio. Larger separation space-slit width ratio values are advantageous for the wall's heat transmission but unfavorable for the wall's suspension. The flow field is most influenced by wall-jet velocity ratio. The wall's ability to convey heat is stronger the higher the wall-jet velocity ratio, but its ability to support weight falls. [ABSTRACT FROM AUTHOR]

The important aspects of increasing hydrodynamic efficiency, improving performance and technical characteristics of various heat and mass transfer equipment, as well as ensuring the required regime and flow conditions of fluids with different viscosities have been analyzed. Such heat transfer equipment includes radiators that contain tubes for circulating heat transfer medium. When solving related issues, in addition to studying the flow characteristics of various fluids in circular horizontal tubes (capillaries), it is necessary to determine the conditions, under which the flow of fluid inside capillaries and circular tubes of small diameter is laminar, so it can be described by the Poiseuille equation. The experimental data on determining water flow rates in horizontal circular tubes of various diameters are presented. The dependence of the volumetric flow rate on the pressure drop has been determined. It was shown that the basic parameters that determine the flow characteristics of fluids in horizontal tubes are the tube radius and fluid dynamic viscosity. A flow of distilled water in tubes with diameters of 0.95, 1.6 and 2.0 mm was analyzed at a gauge pressure ranging from 0.266 to 4.000 kPa. It was found that when using a 0.95 mm diameter tube, the dependence of the volumetric flow rate on the gauge pressure remains linear in the entire analyzed range of pressures. An increase in the tube radius increases the likelihood of flow velocity fluctuations and the appearance of a radial velocity component (i.e., the occurrence of the elements of a turbulent fluid flow structure). The water flow regime in tubes with diameters of 1.6 and 2.0 mm deviates from the laminar at pressures exceeding 1.3 and 1.0 kPa, respectively. The dependence of the volumetric flow rate on pressure for a 40% aqueous solution of calcium chloride, as well as transformer, transmission, and engine oils with dynamic viscosities ranging from 0.002 to 0.182 Pa · s remains linear up to the tube diameters of 5–6 mm. The results of studying fluids with different viscosities are presented in the form of a nomogram illustrating the ratio of the tube radius raised to the fourth power to the fluid viscosity as a function of the tube radius. By analyzing this relationship, it becomes possible to predict the flow characteristics of the studied fluid at given tube radius and dynamic viscosity values. The obtained results can be used when designing and operating various heat transfer devices, such as radiators with tubes for circulating a heat transfer medium. [ABSTRACT FROM AUTHOR]

Ice can change the leading-edge profile of the airfoil and affect the overall aerodynamic performance of the airfoil. Studying the effects of simplified horn ice shapes on the flow field structures can provide a valuable reference for aircraft anti-icing/deicing design. Detailed experimental measurements of the flow field structures of the airfoil with different horn ice shapes were carried out in a low-speed direct wind tunnel using the particle image velocimetry technique. Three simplified ice shapes and the original ice shape were tested at different angles of attack. The results showed that, within the scope of the present study, there was a maximum 35.11% difference in the flow field parameters between the airfoil with simplified ice shapes and the airfoil with the original ice shape. Compared with the original ice shape case, the separation bubbles of the simplified ice shape cases were farther away from the leading edge and trailing edge of the airfoil. Among the three ice shape simplification methods, adding connecting lines between rectangular ice tips was found to have the optimum simplification effects in the flow structures and the airfoil performances. Using this simplification method, the maximum flow field differences at various angles of attack were within 14.88% in the selected two regions. [ABSTRACT FROM AUTHOR]

Understanding the strengths and limitations of the modeling capacity of surface flooding in urbanized floodplains is of utmost importance as such events are becoming increasingly frequent and extreme. In this study, we assess two computational models against laboratory observations of surface urban flooding in a reduced‐scale physical model of idealized urban districts. Four urban layouts were considered, involving each three inlets and three outlets as well as a combination of three‐ and four‐branch crossroads together with open spaces. The first model (2D) solves the shallow‐water equations while the second one (3D) solves the Reynolds‐averaged Navier‐Stokes equations. Both models accurately predict the flow depths in the inlet branches. For the discharge partition between the outlets, deviations between the computations and laboratory observations remain close to the experimental uncertainties (maximum 2.5 percent‐points). The velocity fields computed in 3D generally match the measured surface velocity fields. In urban layouts involving mostly a network of streets, the depth‐averaged velocity fields computed by the 2D model agree remarkably well with those of the 3D model, with differences not exceeding 10%, despite the presence of helicoidal flow (revealed by the 3D computations). In configurations with large open areas, the 3D model captures generally well the trajectory and velocity distribution of main surface flow jet and recirculations; but the 2D model does not perform as well as it does in relatively channelized flow regions. Visual inspection of the jet trajectories computed by the 2D model in large open areas reveals that they substantially deviate from the observations. Plain Language Summary: Advancing our modeling capacity of urban flooding is of utmost importance for improving the design of risk reduction measures. During extreme urban flooding, complex flow patterns develop in urban environments, involving three‐dimensional flow structures. Though, urban floods are commonly simulated with two‐dimensional computational models. So far, no detailed comparison between flow fields predicted by two‐ and three‐dimensional computational models were conducted and assessed against reference data such as experimental observations for representative configurations of urban flooding. In this study, we assess two computational models against laboratory observations of urban flooding in a reduced‐scale physical model of an idealized district. Key Points: Predictions of 2D and 3D computational models were compared against laboratory experiments representing urban flooding in a steady‐stateBoth models perform equally well to predict upstream flow depth, outlet discharge partition, and velocity field in street networksIn urban layouts with large open spaces, only the 3D model accurately predicts the velocity field [ABSTRACT FROM AUTHOR]

The flow around two tandem circular cylinders in proximity to a wall is investigated using particle image velocimetry (PIV) for Re = 2 × 103. The spacing ratios L/D are 1, 2, and 5, and the gap ratios G/D are 0.3, 0.6, and 1. The proper orthogonal decomposition (POD) method and λ c i vortex identification method are used to investigate the evolution of flow structure, and the influences of L/D and G/D on flow physics are shown. At L/D = 2 and G/D = 0.3, a "pairing" process occurs between the wall shear layer and the upstream cylinder's lower shear layer, resulting in a small separation bubble behind the upstream cylinder. At L/D = 1, the Strouhal number (St) increases with decreasing G/D. At three gap ratios, the St gradually decreases as L/D increases. At G/D = 0.3, there is nearly a 49.98% decrease from St = 0.3295 at L/D = 1 to St = 0.1648 at L/D = 5, which is larger than the reductions in cases of G/D = 0.6 and G/D = 1. The effects of L/D on the evolution of flow structure at G/D = 0.6 are revealed in detail. At L/D = 1, the vortex shedding resembles that of the single cylinder. As L/D increases to 2, a squarish flow structure is formed between two cylinders, and a small secondary vortex is formed due to induction of the lower shear layer of the upstream cylinder. At L/D = 5, there is a vortex merging process between the upper wake vortices of the upstream and downstream cylinders, and the lower wake vortex of the upstream cylinder directly impinges the downstream cylinder. In addition, the shear layers and wake vortices of the upstream cylinder interact with the wake of the downstream cylinder as L / D increases, resulting in reductions in velocity fluctuations, and the production and turbulent diffusion of turbulent kinetic energy are decreased behind the downstream cylinder. [ABSTRACT FROM AUTHOR]

Water jet scouring technology is extensively applied in marine engineering, harbor maintenance, river training, and various other fields, showcasing a broad spectrum of potential applications. However, achieving a comprehensive understanding of the transient sand scouring characteristics of water jets remains challenging due to the inherent complexity of the coupled flow structure involving submerged jets and environmental fluids, along with the intricate dynamics of two-phase flow. This study, rooted in numerical simulation and experimental validation, introduces pulse characteristics into a submerged jet. A thorough investigation is conducted to explore the transient sand scouring characteristics and sand transport laws of the submerged jet under diverse working conditions. The results of this study revealed that the main reason for the asymmetry of the sand pit morphology is not the non-uniform distribution of sand grains, but more likely caused by turbulence effects. Simultaneously, within the initial 0.25 s of the pulse cycle, suspended sediment resulting from the pulsed jet in the preceding cycle gradually transports to the dune and its surrounding areas. Subsequently, from 0.25 s to 0.5 s, sediment on both sides of the pit’s bottom undergoes movement and amalgamation with the sediment that remained unsettled during the previous cycle. The findings reveal that higher jet velocities significantly enhance sediment suspension, migration, and redeposition, leading to deeper erosion and the rapid formation of the sand pit’s outline within 2 s. Additionally, the jet velocity and the impact distance are identified as critical factors influencing erosion depth and sediment dynamics. These insights advance the understanding of erosion mechanisms driven by pulsed jets, highlighting their impact on sediment transport processes. The research findings provide important guidance for dredging and ocean engineering fields and offer a theoretical basis for improving the understanding of submerged jet scouring mechanisms.

The results of studies of the flow structure of a horizontal bead mill with a centrifugal system for separating bead particles from a ground suspension are presented. Diffusion, cellular, and recirculation flow-structure models are used to describe the residence time of the dispersed material in the bead mill. To determine the parameters of these models, F-response curves are used, which are obtained by the stepwise perturbation method under various operating conditions of the mill. As a result of the research, it is established that the structure of the flows of bead mills of this design is best described by the recirculation model. [ABSTRACT FROM AUTHOR]

Regimes of detonation burning of a two-phase mixture consisting of TS-1 aviation kerosene and air in a radial vortex chamber 500 mm in diameter with exhaustion toward the center and geometry variations at the combustor entrance and exit are obtained and studied. Air is injected into the combustor through a vortex injector, and kerosene bubbled with air is injected through oppositely directed channels. Optical registration of the process is performed through transparent windows in the combustor by a high-speed camera with a frequency of 420 000 fps. The flow pattern observed in the combustor with free exhaustion and an expanding nozzle is continuous spin detonation with one detonation wave rotating with a velocity of 1.68–2.17 km/s close to the Chapman–Jouguet detonation velocity or pulsed detonation with radial waves with a frequency of 0.14–0.26 kHz. Mounting of radial partitions yields pulsed detonation or combustion. In continuous spin detonation, the air flow rate is 3.6–11.7 kg/s, the kerosene flow rate is 0.2–0.77 kg/s, and the equivalence ratio varies from 0.63 to 2.5. [ABSTRACT FROM AUTHOR]

Numerical calculations were performed to study the vortex-induced vibration (VIV) of a circular cylinder, which was elastically supported by springs of linear and cubic terms. These simulations were conducted at high Reynolds numbers ranging from 4200 to 42,000. To simulate the cylinder's motion and the associated aerodynamic forces, Computational Fluid Dynamics were employed in conjunction with dynamic mesh capabilities. The numerical method was initially verified by testing it with various grid resolutions and time steps, and subsequently, it was validated using experimental data. The response of cubic nonlinearities was investigated using insights gained from a conventional linear vortex-induced vibration (VIV) system. This 2D study revealed that both the amplitude and frequency of vibrations are contingent on the flow velocity. The highest output was achieved within the frequency lock-in region, where internal resonance occurs. In the case of a hardening spring, the beating response was observed from the lower end of the initial branch to the upper end of the initial branch. The response displacement amplitude obtained for the linear spring case was 27 mm, whereas in the cubic nonlinear case, the value was 31.8 mm. More importantly, the results indicate that the inclusion of nonlinear springs can substantially extend the range of wind velocities in which significant energy extraction through vortex-induced vibration (VIV) is achievable. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the previously unexplored effects of ice cover and submerged vegetation on flow structure. Experiments were undertaken under both open channel and ice-covered flow conditions. The bed material consisted of three non-uniform sands. The findings revealed that when vegetation patches were present on the bed and an ice cover was present, the velocity profiles exhibited a distinctive pattern with two peak values. Turbulent kinetic energy (TKE) also exhibited two peaks, one above the vegetation bending height and another at the sheath section, with a decreasing trend towards the ice cover. Furthermore, quadrant analysis showed that when the flow surface is covered by an ice cover, the contributions of inward and outward events increased compared with those observed in an open channel flow. In most cases, these contributions surpassed the sweep and ejection events. The findings enhance our understanding of vegetation's response to diverse surface conditions and have practical implications for river management and environmental engineering. [ABSTRACT FROM AUTHOR]

Rivers as a natural drainage of a watershed have always been of interest in draining the runoff resulting from precipitation, especially during floods. Due to the formation of most cities and villages on the banks of rivers and the construction of structures in their floodplains, during floods, the pattern of river flow always undergoes changes, so it is necessary to study the interaction of flood flows of meandering compound channel in these areas. In this research, by using Flow3D software, which is a powerful software in the field of computational fluid dynamics, the flow structure and bed shear stress in meandering compound channel under the effect of structural density of floodplain during floods have been investigated. For this purpose, six types of structural density of 0, 8, 16, 11, 25 and 44% have been used on the floodplain using non-submerged blocks with distances of 7, 14, 21, 28 and 35 cm. The results of the numerical simulation showed that with the increase of structural density in the floodplain from zero to 44%, the average velocity of the main channel, the maximum water surface elevation and the amount of flow passing through the main channel increased by 51%, 25% and 84% respectively. Also, with the increase in structural density on the floodplain, the amount of bed shear stress has increased so that the maximum bed shear stress has increased from 1.32 to 4.61 pascal (250 percent) and moves towards the center of the main channel. [ABSTRACT FROM AUTHOR]