Flow Path Research Articles

Impact of Spatial Configuration of Bioretention Cells on Catchment Hydrological Performance Under Extreme Rainfall Conditions with Different Stormwater Flow Paths

Bioretention cells (BCs) are widely used to manage urban runoff due to their positive impact on runoff control. Current research primarily focuses on optimizing the internal structural design of bioretention cells, while studies on the interactions between their spatial configuration, topography, and land use types are limited. This study employs the Storm Water Management Model (SWMM) and uses extreme rainfall to analyze the influence of typical stormwater flow paths, determined by various land use types and topography, as well as the spatial configurations of bioretention cells on catchment hydrological performance. The results show the following: (1) Different stormwater flow paths significantly affect catchment hydrological performance, with series-type pathways performing best. (2) The spatial configuration of bioretention cells significantly influences catchment hydrological performance. Decentralized BCs under series-type pathways showed better performance for reducing total outflow and peak runoff, with reduction rates increasing by 7.1% and 8.8%, while centralized BCs better delayed peak times. (3) Stormwater flow paths affect BC efficiency in catchment hydrological performance. Decentralized BCs under a series-type stormwater flow path are recommended for priority use. This study provides a novel perspective for optimizing the spatial arrangement of BCs and urban stormwater management, thereby contributing to flood risk mitigation.

Tracing metal sources and groundwater flow paths in the Upper Animas River watershed using rare earth elements and stable isotopes

Groundwater flow paths and processes that govern metal mobility and transport are difficult to characterize in mountainous bedrock watersheds. Despite the difficulty in holistic characterization, conceptual understanding of subsurface hydrologic and geochemical processes is key to developing remediation plans for locations affected by acid mine drainage, such as the Upper Animas River watershed in southwestern Colorado, USA. Stable isotopes of water and rare earth elements were utilized to evaluate groundwater flow and metal sources within this complex catchment. Stable isotope samples collected from draining mine adits and springs display systematic spatial variation wherein sample sites at higher elevations have greater seasonal variability than sites at lower elevations. The Upper Cement Creek watershed, where multiple draining mines are present, displays the lowest seasonal variation in stable isotopic signatures, potentially indicating the presence of a large, well-mixed volume of groundwater storage or interbasin groundwater flow. Rare earth elements display statistically significant variation between different alteration styles in the catchment. Overprinting of regional propylitic alteration is evident based on enrichment of middle rare earth elements in acidic springs and mines that are not spatially associated with surficial exposures of acid generating alteration styles. Europium anomaly and middle rare earth enrichment signatures from two flooded mine tunnels on opposite sides of a watershed divide indicate connections to the same subsurface flooded mine workings.

Learning from history to improve the performance of blood purification devices and dialysis membranes: from engineering points of view.

Abel JJ, Rowntree LG and Turner BB (Baltimore Trio) proposed the concept of vividiffusion and developed a vividiffusion apparatus in 1912. In a 1914 paper, they laid out the most important rule of device design. We named this rule an ART law taken from the initials of the Baltimore Trio. The ART law means that a blood purification device with a shape that can secure as large a dialysis membrane area as possible for as small a volume of blood filling as possible will achieve high dialysis performance. Rather than using 8mm inner diameter collodion tubes in the original vividiffusion apparatus, the solution to the device shape that fits this rule is to hold down the tube from both top and bottom to make it as flat as possible, or if it is a flat membrane, to bring two flat membranes as close together as possible, and in the case of tubes and hollow fibers, to make their inner diameter as small as possible of approximately 200μm. In other words, the dialysis performance is greatly improved by narrowing the blood flow path. This is exactly the ART law, predicting the shape of today's blood purification devices.

Rock strength and stress dependence of local flow-path connectivity within faults or fractures: a preliminary overview of virtual and in-situ hydraulic tests

Abstract Global flow path connectivity along faults or fractures depends on the degree of local flow path connectivity within each fault or fracture and is a key control of groundwater flow and solute transport. However, the mechanical controls on spatial variations in local flow path connectivity within individual faults or fractures are poorly understood. Local flow path connectivity is quantifiable by the laboratory-scale flow dimensions (n lab) within individual faults or fractures, with a lower n lab indicating lower local flow path connectivity. Virtual hydraulic tests were performed on modeled individual fractures to derive a relationship between n lab and a mappable indicator, the ductility index (DI), defined by the mean stress, groundwater pressure, and rock tensile strength. The derived relationship was verified with data obtained from in-situ hydraulic tests of natural faults in rocks with low matrix permeability, poor swelling capacity, and few fracture mineral fillings, also incorporating the effect of linkage among faults in the field. The test results demonstrated that local flow path connectivity within faults or fractures can be high (n lab > 1.5) when DI < 2 but is generally low (n lab < 1.5) when DI > 2, depending on the level of effective-normal-stress-dependent (DI-dependent) fracture-normal displacement. This relationship between n lab and DI is valid even when the value of DI is varied, or the faults are sheared. These findings can be used to help map spatial variations in local flow path connectivity within faults or fractures from limited borehole data.

Coupling Driving Force–Pressure–State–Impact–Response–Management Framework with Hydrochemical Data for Groundwater Management on Sithonia Peninsula, Greece

Water scarcity in coastal tourist areas constitutes a critical environmental and socioeconomic sustainability issue. Hence, it is crucial to implement an integrated water resource management and protection plan. In this research, the DPSIR framework is coupled with hydrochemical data on groundwater resources in the fractured aquifer of the Sithonia Peninsula in Chalkidiki, North Greece. Geographical and demographic data, together with morphology, geology, hydrology, and groundwater quality data, were collected and evaluated to categorize the hydrosystem’s driving forces, pressures, states, impacts, and responses. The main pressures that affect groundwater quality in the study area are tourism, geological formation, and land use. Based on the analysis of the DPSIR framework, the absence of a landfill site, the inadequate operation of sewage treatment plants and biological wastewater treatment systems, and tourist activity contribute significantly to the degradation of groundwater quality. Additionally, the fractured rock aquifer develops preferential flow paths to pollutants through preexisting faults, which influence groundwater quality. The hydrochemical analysis of groundwater indicates seawater intrusion in the coastal area. The combination of DPSIR analysis and a water quality index based on ion ratios of groundwater samples identifies high-risk areas of seawater intrusion. Thus, it is essential to reinforce groundwater resources by implementing managed aquifer recharge, limiting unnecessary use of groundwater during the tourist season, and storing surface water during the wet period.

Predicting debris flow pathways using volume-based thresholds for effective risk assessment

Investigating the preferential flow path of a debris flow is crucial for quantifying the risk and developing mitigation strategies. Here, we examined 66 debris flows from the Western Ghats in India employing Rapid Mass Movement Simulation (RAMMS)::Debris Flow software to understand the kinematics of run-out. Our analysis revealed that the debris flow run-out in the study area follow two main routes: 60 along the existing stream channels (SC) and six following the steepest hill slope (SH). We further simulated these debris flows to identify their drivers, and derived a threshold that distinguishes between SC and SH-type debris flows. Our results indicate that the debris flow volumes greater than 7072 cu. m is SH-type, whereas those with smaller volumes are more likely to follow SC paths. The model’s accuracy was validated against field observations, achieving a success rate of 93% for SH-type flows and 85% for SC.

Pore-Scale Study of Fluid Displacement in Parallel-Layered Porous Media and Implications of Associated Distinct Flow Dynamics.

Fluid displacement within layered porous media is more complex than in nonlayered ones. Most of the previous studies placed a focus on the porous media with layerings perpendicular to the flow direction, and the effects of pore topology were often ignored. Therefore, this study aims to reveal the flow physics in porous media with layering parallel to the flow direction by accounting for the specific pore topology. Based on the phase-field method, a series of pore-scale numerical simulations were performed to investigate the dynamic displacement processes within layered porous media under various capillary numbers and wettability. The results showed that oil recovery was strongly affected by the heterogeneity of porous media in the capillary fingering regime compared to the viscous one. Besides, the alternative advancing phenomenon of the water fingers was suppressed in layered porous media. Compared with water wetting conditions, the viscous fingering regime of the invading water is more pronounced under oil wetting conditions. Last but not least, the center of mass of water flow paths can be used for fingering regime identification. These findings contribute to our better understanding of the flow dynamics of fluid displacement within layered porous media, which are of great significance to the industry related to oil recovery, underground storage of carbon dioxide and hydrogen gas, etc.

AdversaFlow: Visual Red Teaming for Large Language Models with Multi-Level Adversarial Flow.

Large Language Models (LLMs) are powerful but also raise significant security concerns, particularly regarding the harm they can cause, such as generating fake news that manipulates public opinion on social media and providing responses to unethical activities. Traditional red teaming approaches for identifying AI vulnerabilities rely on manual prompt construction and expertise. This paper introduces AdversaFlow, a novel visual analytics system designed to enhance LLM security against adversarial attacks through human-AI collaboration. AdversaFlow involves adversarial training between a target model and a red model, featuring unique multi-level adversarial flow and fluctuation path visualizations. These features provide insights into adversarial dynamics and LLM robustness, enabling experts to identify and mitigate vulnerabilities effectively. We present quantitative evaluations and case studies validating our system's utility and offering insights for future AI security solutions. Our method can enhance LLM security, supporting downstream scenarios like social media regulation by enabling more effective detection, monitoring, and mitigation of harmful content and behaviors.

Chemical Solution Mitigates Stuck Inflow Control Devices in Horizontal Completion

Summary Horizontal open holes covering long reservoir sections can be benefitted by installing inflow control devices (ICDs) along the lateral to even the production contribution from the entire heterogeneous permeability profile. During the drilling and completion process, the well can be shut in for prolonged periods of time. Though the ICDs are designed to withstand the buildup of debris, they are still subjected to the accumulation of weighting and bridging materials existing in the drilling fluid, such as calcium carbonate (CaCO3). This debris deposits on the internal diameter of the valves or the flow control device, preventing proper shifting against the seats, or blocking the flow path of the devices. Recovering the function of the ICDs requires a chemical treatment. In high-permeability formations, it is undesirable to have acid contact the rock since this may compromise the mechanical integrity of the formation or trigger further solids buildup in the ICDs. Therefore, an acid designed to dissolve the solid deposits on ICDs but not penetrating the formation is required. In this study, a modified coreflood setup was designed and an acid-based chemical treatment was formulated to remove solid deposition on the ICD. The goal was to dissolve the CaCO3 scale on the ICD with minimal penetration into the formation to avoid formation softening. The core assembly simulates the geometry of the ICD completion system with a core matrix behind the ICD operating space. Calcite marble was used to represent the scale deposited on the ICDs, while Indiana limestone was used to represent the reservoir rock. Several acid formulations were tested using the custom-designed coreflood setup. One acid blend composed of a strong organic acid [methane sulfonic acid (MSA)] mixed with hydrochloric acid (HCl) and a second blend of HCl and mutual solvent (glycol-based solvent) showed the desirable effect of dissolving the scale deposits (calcite marble in this case) with minimum to no penetration into the formation matrix. The success of the two acid systems in dissolving CaCO3 deposits on the ICDs was confirmed by analyzing the pressure data during the coreflooding experiment, as well as from analyzing the post-treated core samples using computed tomography (CT) scan. Simulation of completion design in the laboratory is a key factor in testing and designing acid treatments to overcome scale problems in the field. Single-phase acid systems containing no gelling or emulsifying agents were tested and proved capable of dissolving the solids deposited on the ICDs with minimum to no formation contact. This will result in an economical and easier one-step treatment in the field, avoiding the complexity encountered with pulling the whole completion string out of the wellbore to be treated with acid on the surface and then reinstalling it back into the well.

Lightweight method for injection rate prediction of supersonic gas flow from pintle-type hydrogen injector

Research on hydrogen engines has been actively pursued to achieve carbon neutrality in the transportation sector. To optimize the combustion characteristics of hydrogen engines under various driving conditions, active and precise control of the hydrogen injection flow rate is crucial. Lightweight prediction for hydrogen injection rates from pintle-type injectors, which are widely used in hydrogen engines, is required for the control of the injection rate as well as the model-based engine development. However, lightweight injection rate prediction for gaseous fuel has been conducted solely for hole-type injectors and not for pintle-type injectors that have an annular internal flow path with complex configurations. In this study, a lightweight methodology is introduced to predict the hydrogen injection rate of pintle-type hydrogen injectors based on the compressible flow theory of converging-diverging nozzles with minimum mass flow rate data obtained with a safer surrogate gas. The validity of the method for various injection conditions and gases (nitrogen, helium, and hydrogen) is discussed. The methodology demonstrated prediction accuracy of over 92% for nitrogen and helium injection rates under different injection pressures (1.5–4 MPa) and ambient pressures (0.1–2 MPa). The versatility of the prediction methodology for various gases, including hydrogen, was also confirmed. The error sources were analyzed thoroughly based on the dynamic characteristics of the pintle behavior and differences in gas properties.

Energy Flow Path Planning and Multi-Load Constant Voltage Outputs in Domino WPT System Based on Current Phase Configuration

Energy Flow Path Planning and Multi-Load Constant Voltage Outputs in Domino WPT System Based on Current Phase Configuration

Topology design and theoretical modelling of one-way flow path

Topology design and theoretical modelling of one-way flow path

Water Table Fluctuations Control Nitrate and Ammonium Fate in Coastal Aquifers

AbstractCoastal aquifers experience water table fluctuations that push and pull water and air through organic‐rich soils. This exchange affects the supply of oxygen, dissolved organic carbon (DOC), and nitrogen (N) to shallow aquifers and influences groundwater quality. To investigate the fate of N species, we used a meter‐long column containing a sequence of natural organic topsoil and aquifer sediments. A fluctuating head was imposed at the column bottom with local, nitrate‐rich groundwater (16.5 mg/L NO3‐N). We monitored in‐situ redox potential and collected pore water samples for analysis of inorganic N species and DOC over 16 days. Reactive processes were more complex than anticipated. The organic‐rich topsoil remained anaerobic, while mineral sediments beneath alternated between aerobic, when the water table dropped and sucked air across preferential flow paths, and anaerobic conditions, when the water table was high. A fluid flow and reactive transport model shows that when the water table rises into organic‐rich soils, it limits the flow of oxygen, while the soils release DOC, which stimulates the removal of nitrate from groundwater by denitrification. At the end of the experiment, we introduced seawater to the column to mimic a storm surge. Seawater mobilized N and DOC from shallow soil horizons, which could reach the aquifer if the surge is long enough. These processes are relevant for groundwater quality in developed coastal areas with anthropogenic N sources, as climate change and rising seas will drive changes in water table and flood dynamics.

Investigation of a Notable Landslide under Complex Hydrogeological Conditions at Pak Tam Road, Sai Kung, Hong Kong

On 8 June 2022, an intense rainstorm triggered multiple landslides in the northeastern area of Hong Kong. One of these landslides occurred at the registered soil and rock cut slope adjoining Pak Tam Road in the Sai Kung East Country Park with significant social consequences and widespread media attention. An investigation of this notable landslide was undertaken to study the probable causes and mechanism of the failure, as well as the hydrogeological conditions of the slope. The landslide was a large‑scale rain‑induced sliding failure caused by adversely orientated relict joints within the weathered rock profile. Coupling effects of inadequate slope maintenance, steep slope profile and tension cracks rendered the slope particularly vulnerable to landsliding under severe rainfall. Additionally, heavy seepage was observed from some weep holes within the same slope, which suggested the presence of complex hydrogeological conditions. Field mapping and site‑specific ground investigation revealed preferential flow paths along a network of soil pipes and relict joints in the groundmass that prompted the subsurface flow and the build-up of a transient perched groundwater table. The landslide highlighted the importance of proper and regular slope maintenance of slopes in Hong Kong, and the need of assessing the site holistically when modifying the site with engineering works. A robust design solution is strongly advocated for stabilising slopes.

Analysis of Cyclone Spinning Effect with Different Guide Vane Heights

In order to explore the influence of change in the structural parameters ofguide vane cyclones on the cyclone spinning effect, this paper mainly used numerical simulations and physical experiments to analyze the energy of the hydrodynamic flow of acyclone with different guide vane heights by taking the structuralparameters of the guide vane height as the research object. The results show that the rotational kinetic energy of the water flow inside the cyclone was almost zero in the upstream and straight sections of the guide vane section, and it only existed in the leading edge section of the guide vane. In the twisted section of the guide vane, the rotational kinetic energy increased along the flow path, while it decreased in the downstream section of the guide vane. An increase in the height of the guide vanes led to an increase in local mechanical energy loss at the leading and trailing edges of the guide vanes of the cyclone. In the guide vane section, the mechanical energy loss of the water flow remained almost constant along the path, but the mechanical energy loss was faster for cyclones with greater heights. During the deflection of the guide vane, pressure energy was converted into kinetic energy, and the higher the height of the guide vane, the greater the kinetic energy growth and mechanical energy consumption. The proportion of additional mechanical energy loss in the total loss increased with the increase in guide vane height, and the influence of guide vane height was greater than that of the Reynolds number. The mechanical efficiency ηdecreased with the increase in guide vane height, whereas the mechanical efficiency increased slightly with the increase in Reynolds number. The research results in this paper provide a theoretical basis for further optimizing the structural parameters of cyclones.

Coupled vibration characteristics of a drive system during automatic transmission power shifting

To elucidate the vibration principle and effectively mitigate noise during power shifting in an automatic transmission, this study investigates a power split automatic transmission. The transmission principle and power flow path are analyzed using the centralized mass method and Lagrange equation. A vibration model that encompasses both clutches and gears is established for the coupling system. The dynamic model and vibration principle of clutches during power shifting are determined. Subsequently, the dynamic vibration characteristics are solved considering engine speed as a time-domain excitation source, while analyzing the dynamic transmission error. By optimizing gear modification parameters and structural stiffness, measures to reduce both dynamic transmission error and vibrational response during power shifting are obtained. Through vehicle-based vibration analysis and testing, a comparison is made between optimized gear parameters’ vibrational response characteristics and noise test data; revealing significant improvement in vibration performance by 3%–6%. A new approach is suggested for studying the vibration characteristics and dynamic response of automatic transmissions during power shifting, which provides both theoretical importance and practical benefit in effectively minimizing vehicle vibrations and noise.

Effect of Different Pressures on Polymer Flow at a Contraction Path: A Real-Time Numerical Approach

The complexity of polymer flow through a contraction arises from the simultaneous occurrence of shear and elongational strains near the entrance of the contraction path (die). Although this phenomenon has been extensively studied, the effect of plunger motion on the flow toward the contraction path remains underexplored. This study investigated the rheological behavior of thermoplastic polymers at a contraction flow path to enhance the understanding of their flow and rheological behavior, including variations in velocity, pressure, viscosity, and shear rate under varying loads. Polypropylene (PP), a semicrystalline polymer with a low melting point, was used as the test material. The operating temperature was set to 180 °C, and the displacement of the plunger, marked with black lines at its initial and final heights, was recorded under loads of 0.3, 0.6 and 0.85 MPa. The displacement rates were analyzed using MATLAB. A dynamic mesh approach in ANSYS 19 was employed to simulate the real-time motion of the plunger, incorporating a user-defined function developed in C language to control the dynamic boundary motion. The numerical approach successfully simulated the rates of plunger displacement (speed) and predicted the viscosity of PP within the paths (barrel and die). Results indicated that the plunger speed increased with pressure. The pressure generated by the plunger created a driving force that overcame the resistance to flow within the barrel. Higher pressure from the plunger resulted in a greater driving force, which increased the flow rate of the polymer melt through the barrel. On the other side, as the polymer melt flowed from a large cross-sectional area to the contraction flow area, the velocity of the polymer molecules increased, resulting in a pressure drop in the PP melt. Polymer molecules became oriented and stretched in the flow direction upon entering the contraction area, further increasing the shear rate. Consequently, the reduced cross-sectional area in the contraction increased the flow rate, elevated the shear rate, and decreased the viscosity, facilitating polymer flow through the contraction.

Numerical Study on the Effect of Back Cavity on the Aerodynamic Behavior of a Non-Axisymmetric Casing Treatment for Transonic Axial Compressors

Abstract For decades, aeronautic engineers have studied the potential of Casing Treatments (CT) to improve the aerodynamic operability of tip-limited compressors. Axial Slot Casing Treatment (or ASCT) has shown very good results on modern transonic compressor. One possible variant of ASCT uses a circumferential back cavity that links the slots outside the compressor main flow path. This study does a back-to-back comparison of two CT designs that differ only by the presence or the absence of the back cavity. The influence of both CT designs on a transonic rotor performances and aerodynamics are presented. CT flows are detailed and analyzed. The analysis focuses on fluid exchanges between the CT and the main flow path. This study is based on CFD simulation; CFD results are, at first, confronted with available experimental data and then analyzed. Detailed CT flows analyses show that the presence of the cavity reduces the amplitude of the velocity fluctuations and allows for a more uniform redistribution of the recirculated mass flow. The presence of the back cavity reduces significantly the flow mass transfer between the main flow and the front part of the slots. In addition, the synchronization between the rotor blade passage and the extraction cycle, by the rear part of the slots, differs when back cavity is present or not. Because of these differences, the back cavity reduces the influence of the CT on rotor efficiency at the cost of a reduction in its capability to improve stall margin.

Acoustic Modes in an open Box Cavity with variable Depth using two distinct Wind Tunnels

Abstract Cavity resonances in ducts is a classical problem that has involved researchers from very different fields over time. More recently the aerospace community became engaged again due to resonances found within the flow path of aero-engines, for example in bleed cavities in the low pressure compressor section. These resonances can lead to problems with the structural integrity of upstream components, and thus warrant investigation. The paper compares the results of the same cavity geometry within two wind tunnels of different dimensions and operational setups. The intention of the study is to isolate the Rossiter modes from any other geometric modes that are due to the wind tunnel's test section geometry. This isolation allows the modification of the model of Rossiter and the cavity depth model of East to improve the predictive capability over a larger range of Mach numbers and for deeper cavities. The experiments were performed for an operating range from low subsonic to transonic Mach numbers. The analysis focuses on modifying the constants in both the Rossiter model and the cavity depth model proposed by East along with investigating the phenomenon of mode switching for Rossiter modes. The analyses show a good repeatability of the data set between the two wind tunnels displaying strong resonances at similar operating points. An independence from Reynolds number of the acoustic frequency generation is demonstrated within the operating range. A mode switching behavior is identified with the shallowest and deepest cavity showing multiple mode transitions within the operating range.

Impact of Gas Diffusion Layer Compression on Electrochemical Performance in Proton Exchange Membrane Fuel Cells: A Three-Dimensional Lattice Boltzmann Pore-Scale Analysis.

Proton exchange membrane fuel cells (PEMFCs) are being pursued for applications in the maritime industry to meet stringent ship emissions regulations. Further basic research is needed to improve the performance of PEMFCs in marine environments. Assembly stress compresses the gas diffusion layer (GDL) beneath the ribs, significantly altering its pore structure and internal transport properties. Accurate evaluation of the PEMFC cathode's electrochemical performance at the pore scale is critical. This study employs a three-dimensional multicomponent gas transport and electrochemical reaction lattice Boltzmann model to explore the complex interplay between GDL compression and factors such as overpotential, pressure differential, porosity, and porosity gradient on PEMFC performance. The findings indicate that compression accentuates the reduction in oxygen concentration along the flow path and diminishes the minimum current density. Furthermore, compression exacerbates the reduction in current density under varying pressure conditions. Increased local porosity near the catalyst layer (CL) enhances oxygen accessibility and water vapor exclusion, thereby elevating the mean current density. Sensitivity analysis reveals a hierarchy of impact on mean current density, ranked from most to least significant: overpotential, porosity, compression, porosity gradient, and pressure difference. These insights into the multicomponent gas transfer dynamics within compressed GDLs inform strategic structural design enhancements for optimized performance.