Flow Characteristics Research Articles

Performance of Dodging Channels and Cofferdams Against Flood Flows in the Construction of Bener Dams

Bener Dam is one of the new dams built in Bogowonto River, in Guntur Village, Bener District, Purworejo Regency. Bener Dam was constructed to fulfill the irrigation and raw water demand, and also as a flood control, and a micro-hydro power plant, conservation, and tourism that can improve the economy. The diversion works of the Dam consist of the construction of a cofferdam and a diversion tunnel. The cofferdam and diversion tunnel need to be planned well to prevent the river from overflowing through the main dam and causing material losses and casualties. Therefore it is necessary to study the performance of cofferdam and the diversion tunnel of Bener Dam against the flood discharge. In this study, the diversion tunnel flood routing was carried out by HEC-RAS software version 4.1.0. The design flood uses return periods of 25 and 50 years. The flood routing simulation is carried out by two scenarios: the flow simulation on the existing conditions and the flow simulation on the diversion tunnel. The research results show that the Bogowonto River still can accommodate 25-year, and 50-year floods along the river channel. The cofferdam with a peak elevation of +235 m which is designed with a discharge of 410 m3/s is also capable of diverting the flood discharge with a return period of 25 years and 50 years. The diversion tunnel of Bener dam is planned by a horseshoe shape F, with a 25-year flood design with 7m tunnel diameter Based on the flood routing analysis, it was found that the maximum water elevation in the diversion tunnel was +221 m, and with outflow of 332 m3/s. The 50-year flood routing in the diversion tunnel results maximum water elevation of +222 m with an outflow of 396 m3/s. The flood simulation shows the flow characteristics in the diversion tunnel in the form of open channel flow because the tunnel is not filled by water. Then, the maximum flow velocity on the diversion tunnel is ±14.3 m/s which exceeds the permissible velocity so it can cause damage due to erosion and affect the amount of sediment transport.

Vertical Distribution of Rip Currents Generated by Intersecting Waves in a Sandbar–Groin Systems

To analyze the impacts of groins, sandbars, and channels on the three-dimensional features of rip currents, we conducted experimental investigations on the vertical distribution of rip currents under intersecting waves along barred beaches with channels. This study employed ADV flow velocity measurements at two distinct locations: within channel and on a sandbar. The results indicate that in nodal sections within channel and on a sandbar, the rip head region manifests surface flow characteristics, characterized by high velocities near water surface. In a rip neck location, the vertical distribution of rip currents on a sandbar exhibits greater variability, whereas within channel, the distribution is more homogeneous. The vertical distribution of rip currents in nodal sections within channel aligns with the logarithmic distribution law. The vertical distributions of the alongshore velocity of rip currents display a consistent pattern of higher at the top and lower at the bottom. However, this pattern varies slightly depending on the wave period. The presence of groins influences the fluctuation characteristics of the alongshore velocity of rip currents by regulating the nearshore circulation system. This results in the alongshore velocity of rip currents in channel pointing towards the groin. In contrast, the alongshore velocity of rip currents on sandbar, situated farther away from groin, exerts a weaker effect on the alongshore velocity of a rip current.

Numerical and experimental study of homogenization mechanism of high shear rotor‐stator mixer

AbstractUtilizing computational fluid dynamics (CFD) for analytical purposes, this study developed a fundamental model employing the multiple reference frame (MRF) method, facilitated by the CFX simulation platform. The investigation conducted numerical simulations of the flow field within the rotor‐stator assembly of a high shear mixer, guided by the Navier–Stokes equations and the standard k‐ε turbulence model. To quantify the homogenization efficacy of the high shear mixer under scenarios with and without energy consumption considerations, the study introduced two distinct parameters: the mixing index (γ) and the energy ratio mixing index (λ). The impact of structural parameters such as the number of rotor‐stator teeth, radial clearance, and tooth apex‐base axial clearance on the local flow characteristics—velocity, pressure, turbulent kinetic energy, shear rate distribution, net power consumption, and the specified indices—was meticulously analyzed. This analysis aimed to identify the optimal structural configurations for the mixer, considering energy efficiency and mixing effectiveness, and to determine the relative influence of these structural variations on the mixing index (γ) and the energy ratio mixing index (λ).

Study on the Flow Characteristics of Heavy Oil-Water Two-Phase Flow in the Horizontal Pipeline.

Aiming at the problem of transportation for heavy oil during the middle-later development stages of the Lvda oilfield, based on the self-developed design of a visual circulating flow experimental apparatus for heavy oil-water two-phase flow-the flow regime characteristics and corresponding drag properties of the two-phase flow of Lvda viscous oil, which is simulated by 500# industrial white oil and water in a horizontal pipeline are investigated experimentally. According to the Kelvin-Helmholtz instability theory, the flow pattern transition criteria from stratified flow to annular flow (AF) are proposed. The effects of 0.11-0.90 m/s oil superficial velocities, 0.06-1.49 m/s water superficial velocities, and 0.09-0.93 input water cuts on the drag reduction effect of different flow regimes are analyzed. The experimental results indicated that with the increase of mixing velocity and water volume fraction, stratified flow, AF, oil plug flow, and dispersed oil lump flow are successively observed in the horizontal heavy oil-water two-phase flow, in which AF is the main flow pattern. As the Froude number increases to 4.0, the input water volume fraction does not change any more and remains at about 10% of the total flow rate in the process of converting from stratified flow to AF. The four delivery approaches can archive the reduction of transportation resistance for heavy oil at different degrees, in which the transportation of heavy oil surrounded by a water ring has the best effect of drag reduction. At the optimal working conditions of 0.61 m/s oil superficial velocity, 0.07 m/s water superficial velocity, and 0.10 input water cut, the pressure drop of water annulus conveying for heavy oil is only 1/62.54 of that of separate transport for pure heavy oil under the same oil flow rate.

A dynamic multigraph and multidimensional attention neural network model for metro passenger flow prediction

SummaryPassenger flow prediction is an important part of daily metro operation, and its accuracy affects the deployment of train resources management. Due to the complex spatiotemporal correlation characteristics of metro passenger flow, it is necessary to describe it to improve the accuracy of passenger flow prediction. However, the existing models mainly construct the weight matrix based on the static graph and the similarity between stations when describing the spatial correlation of station passenger flow but ignore the time‐varying characteristics of the spatial correlation of station passenger flow. To address this problem, this study introduces a dynamic multi‐graph and multidimensional attention spatiotemporal model. Specifically, the Graph Convolutional Neural Network combined with dynamic multigraph extracts spatial features and the Gated Recurrent Unit extracts temporal features of passenger flow. The multidimensional attention can obtain the spatiotemporal correlation of passenger flow data by assigning weights to them. Finally, this model has been used to conduct experiments on Beijing metro passenger flow datasets with time granularity of 10 and 15 min. The result indicates that the DGMANN model outperforms state‐of‐the‐art other deep learning methods in passenger flow prediction. In addition, the effectiveness of its key submodules has been verified through ablation experiments.

Effect of ferro nanofluids on mixed convection in an open cavity with phase change material

Numerical analysis of mixed convection flow in an open channel cavity was performed by placing PCM and using ferro nanofluids (water based Fe3O4 nanofluid) with different volume fractions (1.0%, 3.0% and 5.0%) as working fluids. The effect of different Richardson numbers under laminar flow conditions with constant Reynolds number was analyzed to reveal how the nanofluid volume fraction and PCM position in the cavity affect the flow and heat transfer characteristics. The main reason for considering the use of nanofluid as a working fluid with the PCM layer is the thermal control of the cavity. It has been determined that the use of ferro nanofluids has a positive effect on the thermal control of the flow by increasing the thermal energy storage capacity of the PCM. As the Ri number increased, the importance of mixed convection effects increased, and for the highest Ri number, natural convection played a dominant role, causing a 65.5% decrease in the heated wall dimensionless temperature. Since the heat flux applied for pure water at highest Ri number is one third of that applied for 5.0% nanofluid, the specified temperature increase is quite lower by comparing heat flux thanks to the nanofluid high convection capability. Different than pure water, in all PCM cases the rate of melting is higher for 5.0% ferro nanofluid due to the higher convective heat transfer. In the case of the PCM on the bottom wall, the highest thermal energy storage capacity was obtained for each working fluid and 50% more energy was stored compared to the right heated wall at the same Ri number. Moreover, the maximum average Nu number was determined for the bottom heated case and for the same Ri number at 5.0% ferro nanofluid which was obtained approximately twice as much as pure water when flow reached steady state.

Scaling laws for optimized power-law fluid flow in self-similar tree-like branching networks

The power-law fluid flow in tree-like self-similar branching networks is prevalent throughout the natural world and also finds numerous applications in technology such as oil recovery and microfluidic devices. We investigate analysis of optimal power-law fluid flow conditions and the optimal structures within tree-like branching networks, focusing on maximizing flow conductance under the constraint of the network tube’s volume and the surface area. The study considered fully developed laminar power-law fluid flow regimes without considering any losses in the network system. A key observation was the sensitivity of the dimensionless effective flow conductance to the network’s geometrical parameters. We found that the maximum flow conductance occurs when a dimensionless radius ratio β∗ satisfies the equation β∗=N−1/3 and β∗=N−(n+1)/(3n+2) under constrained tube-volume and surface-area, respectively. Here, N represents the bifurcation number of branches splitting at each junction, and n is the fluid power-law index. We further find that this optimal condition occurs when pressure drops are equipartition across each branching level. We validated our results with various experimental results and theories under limiting conditions. Further, Hess–Murray’s law is justified and extended for the shear-thinning and shear-thickening fluid flows for an arbitrary number of branches N. Further, in this study, we also derive the relationships between the geometrical and flow characteristics of the parent and daughter tubes as well as the generalized scaling laws at the optimal conditions for the other essential parameters such as tube-wall stresses, length ratios, mean velocities, tube-volume, and surface-area of the tube distributing within the networks. We find that the fluid power-law index n does not influence the constrained tube-volume scaling at the optimal conditions; however, the scaling laws vary with n under the constrained tube’s surface area. These findings offer valuable design principles for developing efficient transport and flow systems.

Cubic autocatalysis implementation in blood for non-Newtonian tetra hybrid nanofluid model through bounded artery

Abstract Tetra hybrid nanofluids are significant due to their unique properties like thermal and electrical conductivity enhancement, increased heat transfer, and improved fluid flow characteristics. This attempt proposes a tetra hybrid cross nanofluid model with the implementation of cubic autocatalysis in the context of blood flow passing through a stenosis artery. The model includes the effects of nanofluid, magnetic field, thermal radiation, and the cubic autocatalysis mechanism. This research investigates the innovative application of cubic autocatalysis within the context of blood flow through a tetra hybrid cross nanofluid model, specifically designed to simulate conditions within a stenosis horizontal artery. The equations governing the fluid flow are solved using the bvp5c method, and the numerical solutions are obtained for various parameter values. Specifically, the cubic autocatalysis mechanism profoundly impacts the velocity and concentration profiles of the blood flow. The proposed model and the obtained results provide new insights into the physics of blood flow passing through stenosis arteries. They may have important implications for the diagnosis and treatment of cardiovascular diseases. This article has a unique combination of tetra hybrid cross nanofluid model, cubic autocatalysis, and blood flow passing through the stenosis artery. These facts are not typically studied together in the context of blood flow.

Spatial and Temporal Distribution and Flow Characteristics of High-Quality Development of Modern Service Industry in Chinese Sub-provincial Cities

Based on the new development concept of the service industry, this paper constructs a comprehensive evaluation index system for the high-quality development of modern service industry from a total of 22 indicators in four dimensions, namely, development efficiency, structural optimization, innovation agglomeration and industrial scale. The composite index of 15 sub-provincial cities in China from 2013 to 2022 was measured by entropy weight method, describing the current development status and development differences of each city, and with the help of Kernel density estimation method and Dagum Gini coefficient method, the law of inter-city evolution was inscribed, which revealed the spatial differences of the four major geographic regions and their sources and contributions. The study shows that the overall high-quality development of the service industry in the 15 cities is at a relatively low level, with obvious differences, but all of them are on a slowly rising trend. According to the division of the four major geographic regions, the northeast region has the largest intra-regional differences, and the eastern region has the smallest intra-regional differences. Meanwhile, the spatial imbalance between regions is still aggravating, and there is a clear differentiation between the development level of the eastern and western regions.

Improving flow dynamics and storage longevity of a low-cost phosphorescent fingerprint powder.

An inexpensive, commercially available doped strontium aluminate phosphor with long-lived afterglow was prepared as a luminescent fingerprint dusting powder suited for challenging, highly patterned substrates; however, prolonged exposure to humidity was found to reduce that powder's affinity for fingermarks. Here, an enhanced preparation for synthesizing that fingerprint dusting powder is presented that prevents powder aggregation and loss of function upon exposure to humid environments. This was achieved by introducing a flow regulator during synthesis: hydrophobic silica SIPERNAT® D10 or SIPERNAT® D17. Increasing the hydrophobicity of the powder prevents aggregation by inhibiting the uptake of water, thereby improving the material's flow dynamics and transfer behavior from brush to fingermark. The angle of repose and flow characteristics made by the modified powders were quantified, with excellent affinity for fingermarks observed, even after being stored under 85% (±5%) humidity for 4 weeks. A preliminary comparison of the performance of the modified hydrophobic powders relative to the unmodified precursor revealed that more of the SIPERNAT® treated powder typically adhered to fingermarks while simultaneously imparting less background development. In addition, fewer clumps of particulate were observed in the developed fingermarks after addition of a hydrophobic flow regulator. This technical report outlines the updated method for synthesizing the fingerprint powder, with summarized flow performance results, and a demonstration of the modified powder's affinity for simulated fingermark evidence.

Effect of inlet distortion on internal flow and performance of a contra-rotating fan operating with single-stage impeller

To establish a theoretical foundation for the rational selection of contra-rotating fans operating with a single-stage impeller under inlet distortion. Unsteady numerical simulations were conducted using the SST k-ω turbulence model to analyze the airflow fields, respectively, for the single-stage operation of front impeller (SSOFI) and the single-stage operation of rear impeller (SSORI) of the fan. The internal flow characteristics with single-stage operation under both distorted inlet condition (DIC) and uniform inlet condition (UIC) were studied. Furthermore, a comparison of the performance parameters of the fan, including total pressure and total pressure efficiency, was conducted. Focusing on the SSOFI with satisfactory operational performance of the contra-rotating fan, this study aims to reveal the propagation of inlet distortion inside the fan and reveal the influence mechanisms of inlet distortions on the performance of the fan. The results indicate that the impact of inlet distortion on the flow field is primarily concentrated in the upstream area of the front-stage impeller for SSOFI. However, the flow disturbance from the exit of the front-stage impeller to the diffuser is relatively minimal. For SSORI, the inlet distortion exacerbates the adverse effect of the front stage impeller as the front guide vane on the flow inside the rear stage impeller. The entropy loss in the two-stage impellers is significantly higher than that under the uniform inlet condition, and the turbulence level in the diffuser is intensified. While the efficiency of the fan is significantly influenced by the inlet condition and operating stages, their impact on the total pressure is small. Specifically, under uniform inlet conditions, the total pressure efficiency for SSOFI exceeds that of SSORI by 4.9 %, whereas the difference rises to 11 % under inlet distortion condition.

Study on the Influence of Reservoir Wettability on Shale oil Flow Characteristics by Molecular Dynamics Simulation

Study on the Influence of Reservoir Wettability on Shale oil Flow Characteristics by Molecular Dynamics Simulation

Study on the bubble breakup and internal flow characteristics in the pulsed jet ejector

To intensify the bubble breakup in the ejector, a novel pulsed jet ejector is designed in this work. The pulsed jet is introduced into the ejector by one fluidic oscillator. A high-speed camera experiment is conducted to capture the progress of bubble breakup. The intensification mechanism of pulsed jet on bubble breakup in ejector is investigated by numerical simulation. The experimental results indicate that the introduction of the pulsed jet effectively induces the occurrences of pressure fluctuations and vortex collision, prompting the deformation of bubbles to produce microbubbles. It is also found that the bubble diameter and number of microbubbles mainly depend on the process of bubble breakup in the divergent section, and the bubble diameter distribution is significantly influenced by the variation of Reynolds number. The variations of the vortex structure are induced by the pulsed jet, which is a key factor influencing mixing efficiency and bubble breakup effects. In addition, pulsed jet ejectors have superior mixing performance compared to conventional ejectors.

Comparative investigation of activation energy and biot number on quadratic convective flow of a radiating micropolar fluid

In this study, we evaluate the significance of activation energy for initiating a chemical reaction in a two-dimensional laminar flow of a micropolar fluid over a semi-infinite inclined plate. The internal heat transfer mechanism of fluid is modeled with considerations of radiation and convective thermal boundary conditions. The momentum equation uses quadratic density relations in the concentration and temperature differences in buoyancy. In addition, flow through a porous medium surrounded by an inclined plate is modeled by the Darcy-Forchheimer model. Using a spectral successive linearization approach achieves the numerical results for the dimensionless equations. Basic characteristics of flow are examined for a range of dimensionless physical parameters. Quadratic convection is observed to have a stronger impact on the physical components of the flow than linear convection. In addition, compared to the linear illustration, the quadratic convection scenario results in a 14 % − 19 % increase in surface drag and heat transmission rate and a 5 % − 9 % decrease in mass transfer rate. Further, a higher activation energy corresponds with a higher concentration of micropolar fluid. Furthermore, as the radiation and Biot number rise, the velocity and rate of heat transfer correspondingly increase. We believe that the obtained results apply to aerosol technologies and polymeric mixtures used under extreme temperatures and concentrations.

Analysis of scale effect on the propulsion discrepancy of a four-waterjet system

This paper focuses on the scale effect on the propulsion discrepancy and the correlating flow characteristics of a high-speed ship with four waterjets. The propulsion discrepancy of a four-waterjet-propelled ship in model test is observed in previous study (Gong et al. Ocean Eng. 2019, 180, 211–222). Current study further performs a systematic analysis of the scale effect on several hydrodynamic coefficients (net thrust, lateral/vertical forces and torque) and flow field details (velocity, TKE and pressure). It is noted that the net thrust discrepancies are amplified in model-scale simulations and tests due to the scale effect, and the lateral/vertical force discrepancies of waterjet units are gradually decreasing with the increase of advanced speed in both scales. Stable hydraulic performance of the inner and outer pumps is observed although there are minor differences in the inflow quality, while stronger turbulence intensity exists near the channel faces in full scale due to the induction effect of the impeller.

Furnace MILD combustion versus its open counterpart in hot coflow

The open jet flame in hot co-flow (JHC) has been frequently utilized for fundamental investigations of Moderate or Intense Low-oxygen Dilution (MILD) combustion due to its controllable conditions and relatively easy measurement capabilities. However, practical MILD combustion must take place within a combustor that is enclosed. Therefore, it is necessary to examine the similarity and disparity of combustion characteristics between two flame configurations. This issue is addressed currently. Specifically, we investigate the flow mixing, ignition, and combustion, as well as emission characteristics of non-premixed and premixed JHC and cylindrical furnace (FUR) flames at various values of the environmental temperature (Te) and central jet Reynolds number (Re). For the open non-premixed flames, we employ both previous single-tube JHC (SJHC) combustor and presently modified JHC (MJHC) one that uses the same nozzle configuration as the FUR burner. It is revealed that significant differences occur in flow, combustion and emission characteristics between the SJHC and FUR cases. On the other hand, both non-premixed and premixed MJHC configurations exhibit high similarity to the corresponding FUR cases in terms of upstream flow mixing and combustion features. Moreover, different CO and NOx emissions result from open JHC and close furnace flames due to different post-combustion configuration and residence time. Accordingly, future experiments on non-premixed MJHC and premixed JHC flames are highly recommended for better understanding practical MILD combustion.

Research on the Flow Characteristics of Power-Law Fluids in Self-Priming Sewage Pumps

Research on the Flow Characteristics of Power-Law Fluids in Self-Priming Sewage Pumps

Numerical investigation of flow characteristics in the front and rear chambers of centrifugal pump and pump as turbine

To investigate the flow characteristics in front chamber and rear chamber in pump mode and pump as turbine mode, a 3D computational model of a centrifugal pump was established, including the front and rear chamber. Based on Realizable k-ε turbulence model, numerical calculations of incompressible flow were carried out for internal viscous flow in two operating modes. Further analysis was conducted on the flow stability and hydraulic losses under two modes using energy gradient theory and entropy production theory. The numerical simulation results are within reasonable error compared to the experimental results in pump operation mode, which ensures the reliability of the numerical calculation method. The results indicate that the volumetric efficiency in both two modes is on an upward trend with increasing flow, but the volumetric efficiency of the pump mode is more significantly affected by changes in flow; the distribution patterns of dimensionless circumferential velocity and dimensionless radial velocity in the front and rear chambers under two operating modes are similar, but the distribution pattern of dimensionless radial velocity in the front chamber in turbine mode is significantly different from other operating conditions; flow instability is most likely to occur at the outlet of impeller, and the energy loss in clearance of wear-rings is greater than that in the pump chamber.

Investigation of the minimum filling amount of ionic liquid in the multi-stage ionic liquid compressor

Ionic liquid compressors are the ideal solution for hydrogen refueling stations, and multi-stage compression is an inevitable choice for achieving high-pressure refueling, such as 90 MPa level. However, the initial filling amount of the ionic liquid in the compression chamber is lacking basis as the characteristics of gas-liquid two-phase flow during the reciprocating movement of the liquid piston are not understood. This study numerically investigates the variation characteristics of the gas-liquid interface in the compression chambers under different structural and operating parameters of a five-stage ionic liquid compressor. Based on the fluctuation feature of the phase interface, the minimum liquid piston heights in each stage that ensure effective sealing for the compression chamber with different stroke-to-diameter ratios (r) are determined. Finally, the mathematical relationship for calculating the minimum ionic liquid filling amount related to structural parameter r and suction pressure is established, which provides guidance for the design of the ionic liquid compressor.

Impact of Reverse Buoyancy on Heat and Mass Transfer in MHD Flow of PbLi Within a Poloidal Duct in a Typical DCLL Liquid Breeder Blanket

The typical dual-coolant lead-lithium (PbLi) design of a liquid breeder blanket in a magnetic confinement fusion reactor involves the utilization of PbLi as the working fluid to effectively remove neutron heat. However, the nonuniform heating of neutrons with a significant radial gradient induces a buoyancy effect, resulting in the formation of vortexes ices within the downward flow duct. These vortexes have an adverse impact on the heat and mass transfer characteristics of the magnetohydrodynamic (MHD) flow of PbLi. The simulations in this work employed a MHD buoyant mixed-convection solver to resolve the characteristics of PbLi flow and a one-way coupled Lagrangian method to analyze the qualitative characteristics of tritium transport in PbLi flow. The results indicate that buoyant reverse flow can create vortexes that contain hot spots in the PbLi fluid, which can significantly impede heat transport. Additionally, the vortex causes tritium recirculation in the flow field and retention, resulting in adverse effects on tritium transport.