Flow Computational Fluid Research Articles

Numerical and Experimental Study on the Wave-Attenuation Effect According to the Height of a Two-Row Submerged Rectangular Structure

Coastal erosion, exacerbated by climate change and coastal development, presents increasing challenges for shoreline protection. This study investigates the effectiveness of submerged structures, specifically underwater breakwaters, in mitigating wave energy while supporting coastal ecosystems. The reflection and transmission coefficients of a two-row submerged rectangular structure at various heights were evaluated. Numerical simulations utilized the boundary element method (BEM) for potential flow analysis and computational fluid dynamics (CFD) for viscous flow assessment. Experimental validation was conducted in a two-dimensional wave tank at Inha University, measuring wave heights before and after interaction with the submerged structures. Results revealed that increasing structure height led to higher reflection coefficients and lower transmission coefficients. When the front structure was higher, the dissipation coefficient reached a maximum of 0.17. Maximum reflection and minimum transmission coefficients were observed under Bragg reflection conditions when the spacing matched half the incident wavelength. Discrepancies between CFD and BEM results were attributed to fluid viscosity effects. These findings underscore the potential of submerged structures to enhance wave attenuation, demonstrating that carefully optimized designs can significantly improve coastal protection.

Developing a Flow-Resistance Module for Elucidating Cell Mechanotransduction on Multiple Shear Stresses.

Fluid shear stress plays a pivotal role in regulating cellular behaviors, maintaining tissue homeostasis, and driving disease progression. Cells in various tissues are specifically adapted to physiological levels of shear stress and exhibit sensitivity to variations in its magnitude, highlighting the requirement for a comprehensive understanding of cellular responses to both physiologically and pathologically relevant levels of shear stress. In this study, we developed an independent upstream flow-resistance module with high fluidic resistances comprising three microchannels. The validity of the flow-resistance module was confirmed via computational fluid dynamics (CFD) simulations and flow calibration experiments, resulting in the generation of steady wall shear stresses ranging from 0.06 to 11.57 dyn/cm2 within the interconnected cell culture chips. Gene expression profiles, cytoskeletal remodeling, and morphological changes, as well as Yes-associated protein (YAP) nuclear translocation, were investigated in response to various shear stresses to authenticate the reliability of our experimental platform, indicating an increasing trend as the shear stress increases, reaching its maximum at various shear stresses. Our findings suggest that this flow-resistance module can be readily employed for precise characterization of cellular responses under various shear stresses.

Numerical study of water droplets in hydrogen recirculation ejectors for proton exchange membrane fuel cells

Gas ejectors play a vital role in recirculating anode hydrogen within proton exchange membrane fuel cells. Previous studies primarily use single-phase flow computational fluid dynamics to design ejectors, neglecting water phase changes and compromising accuracy. Here, we develop a two-phase flow model incorporating droplet injection in the secondary flow and a water condensation model to analyze the ejector’s behavior. Validated by previous experiments in six different conditions, our two-dimensional model captures dynamic interactions between the gas and liquid water phases, leading to predict entrainment ratio more accurately, with an average deviation of 3.08% compared to 24.04% for the single-phase model. Additionally, simulations have been done for six different cases comparing different degrees of humidification of the secondary hydrogen flow. Water droplet growth increases gas temperature and pressure in the mixing chamber while reducing velocity, lowering the entrainment ratio by over 30%. Injecting a certain amount of droplets into the secondary flow can effectively improve the efficiency of the mixing chamber. Integrating a heat exchanger in the hydrogen supply line increases overall temperature and decreases water condensation. This study provides an in-depth understanding of water phase behavior, further optimizes the hydrogen ejector, and improves the accuracy of its simulation.

Improvement of bubble distribution characteristics through multi-objective optimization of flow characteristics of a swirling flow type microbubble generator with fixed blades

Swirling flow type microbubble generators with fixed blades (hereafter referred to as "bubblers") can be easily downsized and upsized and can be easily integrated into existing facilities. For this reason, bubblers have been used for mercury targets; however, there is a need to improve the bubble distribution characteristics. The objective of this study is to establish a technique to rapidly improve bubble distribution characteristics through multi-objective optimization of the flow characteristics of this bubbler using single-phase flow computational fluid dynamics (CFD) analysis. Therefore, design variables for the bubbler blades were defined by applying turbomachinery design methods, and four flow characteristics were subjected to multi-objective optimization using single-phase flow CFD analysis and the response surface methods. While the resulting optimized bubbler increased the pressure loss coefficient by 0.9 %, it improved the wall shear stress by 3.4 %, the swirl number by 10.0 %, and the pressure reduction coefficient by 14.3 % compared to the original bubbler. Furthermore, experiments showed that the optimized bubbler produced smaller bubbles than the original bubbler, demonstrating that the multi-objective optimization design method can significantly improve the bubble distribution characteristics while maintaining the same pressure loss coefficient.

Chemical Bath Deposition of NiFe Alloy Anode for Efficient Alkaline Water Electrolyzer Integration.

Green hydrogen production from water splitting is a feasible way for intermittent renewable energy storage and utilization, where the exploration and scale-up preparation of high-performance anodic oxygen evolution electrocatalysts are critical prerequisites for its industrial-level applications. Herein, a chemical bath deposition of FeNi3 intermetallic alloys onto Ni mesh support is performed, which delivers a current density of 0.62 Acm-2 at 1.72 V versus reversible hydrogen electrode for alkaline water oxidation in 1 m KOH and an excellent electrolysis stability at 0.2 A cm-2 for over 300 h. Moreover, via 3D computational fluid dynamics simulation and flow field optimization, a homogeneous deposition of ≈5400 cm2 NiFe anode is demonstrated within 4 min using the developed flow bath reactor. Once integrating the as-prepared NiFe anodes into alkaline electrolyzer stack, the voltage variation between each unit cell is below 40 mV at a total operation current of 71 A, or ca. current density of 0.2 A cm-2, confirming the uniformity of this batch synthesis protocol and its great potential for industrial alkaline water electrolysis.

Toward production zonal flow allocation using novel completion tracer dosing line and diffuser: Prototype laboratory flow loop experiments and computational fluid dynamics studies

Complex completion schemes with inflow control valves (ICVs) in multi-lateral wells are now the industry standard for modern fields. Understanding the production contributions from different production zones/laterals is of great importance in optimizing the zonal flow rates to prolong the field lifetimes, reduce water cuts and the associated costs, and achieve production targets. Furthermore, the improved operational efficiency can reduce the producers’ energy usages and carbon footprints for a more sustainable operation. For the past decade, inflow tracer technology based on embedding tracers in degradable polymer matrices, which are then placed in downhole completion zones at initial installation, has been used in understanding production zonal flow contributions in field demonstrations as well as in commercial projects. However, the current technology based on degradable polymers has the following limitations: (1) there are limited lifetimes for the degradable polymer matrices that will lose their functionality past their expiration dates, and (2) the tracers are released from the polymer matrices at a constant rate; so in order to create a transient for tracer flowback measurements the wells need to be shut-in for a period of time which will interfere with normal production and possibly, with the long-term productivity of the well. Here, we introduce an alternative approach for deploying inflow tracers that has no such limitations mentioned above. Specifically, we propose the installation of passive chemical tracer dosing lines connected to diffuser chambers at the annular regions downhole during completion. Pulses of tracers can be injected into the different production zones and monitored for their flowback characteristics on-demand. The passive tracer dosing lines and diffusers only require minimum upfront investments and have no limitations of lifetime compared to the degradable polymer matrices. Furthermore, the injection of tracer pulses into the annulus near production zones creates appropriate transient responses for their flowback measurements, which do not require well shut-in and will not affect normal production.Laboratory flow loop experiments and computational fluid dynamics (CFD) studies were performed to demonstrate the proposed methodology and to understand the underlying physics. Half-scale and quarter-scale flow loops made of transparent polyvinyl chloride (PVC) pipes that resemble annular regions near the ICVs were constructed with tracer dosing lines and diffusers attached within. Colored dyes were injected into the flow loops to visualize their flush out and flowback behaviors. In CFD studies, a two-step approach was used with first solving for the turbulent fluid flow profiles, and then solving for the tracer convection diffusion behaviors in the turbulent fields. The CFD model parameters were carefully matched with flow loop experiments to predict the possible real field responses. With appropriate diffuser design, we can achieve desirable zonal flow-rate-dependent tracer flowback responses with reasonable sampling times and injected tracer quantities.

Navigating Hemodynamic Insights: A Promising Future with Four-dimensional Flow MRI and Computational Fluid Dynamics in Transjugular Intrahepatic Portosystemic Shunt Management.

Navigating Hemodynamic Insights: A Promising Future with Four-dimensional Flow MRI and Computational Fluid Dynamics in Transjugular Intrahepatic Portosystemic Shunt Management.

Realization of Bio-Coal Injection into the Blast Furnace

The steel industry accounts, according to the International Energy Agency, for ~6.7% of global CO2 emissions, and the major portion of its contribution is from steelmaking via the blast furnace (BF) route. In the short term, a significant reduction in fossil CO2 emissions can be achieved through the introduction of bio-coal into the BF as part of cold bonded briquettes, by injection, or as part of coke. The use of bio-coal-containing residue briquettes was previously demonstrated in industrial trials in Sweden, whereas bio-coal injection was only tested on a pilot scale or in one-tuyere tests. Therefore, industrial trials replacing part of the pulverized coal (PC) were conducted. It was concluded that the grinding, conveying, and injection of up to 10% of charcoal (CC) with PC can be safely achieved without negative impacts on PC injection plant or BF operational conditions and without losses of CC with the dust. From a process point of view, higher addition is possible, but it must be verified that grinding and conveying is feasible. Through an experimentally validated computational fluid flow model, it was shown that a high moisture content and the presence of oversized particles delay devolatilization and ignition, lowering the combustion efficiency. By using CC with similar heating value to PC, compositional variations in the injected blend are not critical.

A New Development of Cross-Correlation-Based Flow Estimation Validated and Optimized by CFD Simulation

The accurate measurement of mass flow rates is important in nuclear power plants. Flow meters have been invented and widely applied in several industries; however, the operating environment in advanced nuclear power plants is especially harsh due to high temperatures, high radiation, and potentially corrosive conditions. Traditional flow meters are largely limited to deployment at the outlet of pumps, on pipes, or in limited geometries. Cross-correlation function (CCF) flow estimation, on the other hand, can estimate the flow velocity indirectly without any specific instruments for flow measurement and in any geometry of the flow region. CCF flow estimation relies on redundant instruments, typically temperature sensors, in series in the direction of flow. One challenge for CCF flow estimation is that the accuracy of the flow measurement is mainly determined by inherent, common local process variation across the sensors, which may be small compared to the uncorrelated measurement noise. To differentiate the process variations from the uncorrelated noise, this research implements periodic fluid injection at a different temperature than the bulk fluid before the temperature sensors to amplify process variation. The feasibility and accuracy of this method are investigated through flow loop experiments and Computational Fluid Dynamics (CFD) simulations. This paper focuses on a CFD simulation model to verify the previous experimental results and optimize CCF flow estimation with different configurations. The optimization study is carried out to perform a grid search on the optimal location of the sensor pair under different flow rates. The CFD results show that the optimal sensor spacing depends on the flow rate being measured and provides guidance for sensor location implementation under various anticipated flow rates.

GPU-powered CFD-DEM framework for modelling large-scale gas–solid reacting flows (GPU- rCFD-DEM) and an industry application

The coupling of CFD (computational fluid dynamics) and DEM (discrete element method) is extensively used for simulating gas–solid reacting flows in various industrial processes, while its high computational cost limits its industry applications, especially large-scale systems with a large number of particles and complex geometries. This paper reports a robust highly efficient GPU (graphics processing unit) − powered CFD-DEM coupling approach that is, for the first time, capable of simulating large-scale gas–solid reacting flow systems with complex geometries (GPU- rCFD-DEM). The fluid flow calculations are performed using CPU parallelization, while the particle flow simulations leverage GPU parallelization, and the coupling calculations between CFD and DEM are fully implemented on GPU. The model includes advanced coupling strategies to enhance numerical stability, especially when handling complex geometries with unstructured CFD meshes. The developed model is validated through experimental measurements and its computational performance is evaluated by comparison with previous GPU-based simulations. It shows good agreement with the experiments and superior performance compared to the traditional coupling method. The model is then applied to simulate raceway dynamics and coke combustion in an industrial-scale blast furnace, showcasing its effectiveness in handling complex geometries and a huge number of particles in gas–solid reacting flows. This work provides an efficient and robust solution for numerically simulating industrial applications of gas–solid reacting flow systems.

Optimization of a radial-axial turbine at the stage of center line of fluid flow calculation

Optimization of a radial-axial turbine at the stage of center line of fluid flow calculation

Experimental and numerical study of the added resistance and seakeeping performance of a new unmanned survey catamaran

Experimental and numerical methods were employed to investigate the added resistance and seakeeping performance of an innovative unmanned catamaran for offshore surveying. Model experiments validated numerical results from viscous flow computational fluid dynamics (CFD) modeling using the unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the potential flow method. URANS modeling precisely predicted the catamaran's performance in regular waves, and the potential flow method offered effective short-term predictions in irregular waves. Simulations were performed at three velocities (4, 6, and 8 knots). The results highlight the fundamental relationships between added resistance and motion responses with changing wave conditions. The extreme motion responses generated by typical actual sea conditions are summarized. The added resistance and motion responses are greatest when the wavelength is slightly longer than the length of the catamaran and the encounter frequency, fe, is ∼1.2. The optimal velocity of the catamaran is 6 knots. The seakeeping performance of the catamaran was assessed using existing indicators for manned vessels. Compared with manned vessels, unmanned survey vessels are more tolerant of first-order motion response but require stricter limitations on second-order accelerations in each degree of freedom.

Dynamic wetting performance and resin-flow behavior of two-level selective laser-etched metal surface in resin transfer moulding process of fiber-metal laminates

ABSTRACT In selective laser etching for the interfacial strengthening of Fiber Metal Laminates (FMLs), the wettability of customized structured features significantly affects their overall mechanical properties. For two-level features, their complicated geometry makes the evaluation of wettability difficult, which introduces challenges to feature design. In this study, a sandwich FMLs comprising an AA2024-O metal skin and a plain-woven carbon-fiber fabric core is investigated. Three types of two-level feature interfaces are designed and introduced into the FMLs structure. To understand the effect of two-level features on the resin flow and dynamic wetting progress in resin transfer molding, two-phase flow Computational Fluid Dynamics numerical models coupled with porous media and level-set numerical methods are built. The feasibility of the numerical simulation in the qualitative analysis was verified by comparing the results with those of the testing porosity values from X-ray scanning. In addition, the mechanisms of pore formation and transportation are revealed. These results indicate that the deeper groove structure in the etched features plays an important role in discharging residual air and determining the transformation of pores to reduce porosity. The permeability orientations of the porous media and surface structure both have significant impacts on the flow behavior and formation of pores.

Topological "Shape" in Micellar Dynamics.

For micelles, "shape" is prominent in rheological computations of fluid flow, but this "shape" is often expressed too informally to be useful for rigorous analyses. We formalize topological "shape equivalence" of micelles, both globally and locally, to enable visualization of computational fluid dynamics. Although topological methods in visualization provide significant insights into fluid flows, this opportunity has been limited by the known difficulties in creating representative geometry. We present an agile geometric algorithm to represent the micellar shape for input into fluid flow visualizations. We show that worm-like and cylindrical micelles have formally equivalent shapes, but that visualization accentuates unexplored differences. This global-local paradigm is extensible beyond micelles.

Synergy between heterogeneous catalysis and homogeneous radical reactions for pharmaceutical waste destruction: Perspective

Enormous quantities of pharmaceuticals are consumed by humans leading to a growing and continuous release of harmful components into the environment. Existing conventional water treatment plants are designed mainly for eliminating biodegradable organics and nutrients and cannot degrade pharmaceuticals and personal care products efficiently enough due to their chemical stability. Advanced oxidation processes using radicals generated from ozone can be efficiently combined with heterogeneous catalysis for treatment of wastewater containing pharmaceuticals and personal care products. From the technology viewpoint, elimination of pharmaceuticals from water by heterogeneously catalyzed ozonation should done in a continuous fixed bed reactor. The structured catalysts can be prepared by additive manufacturing using 3D-direct printing of supports/catalysts allowing a high degree of freedom in both the composition and design of the final catalytic material for a fixed bed heterogeneous-homogeneous reaction. Structured materials can exhibit non-periodic structure, such as for example semi-ordered structures, inspired by nature. For periodic and semi-periodic structures, heat and mass transfer should be investigated using computational fluid dynamics and flow imaging methods, guiding further design of novel architectures and subsequently allowing in combination with the materials development efficient control of activity and selectivity. The innovative catalytic reactor engineering should include experimental and numerical investigation of the stage wise injection of the oxidation agent, variation of the reactor cross-section size, changing the distance between the catalyst beds and introduction of the recycle loops.

Into the boundary layer behavior of segmented grinding wheels and its illustration on Ti6Al4V

Segmented grinding wheels, with active abrasive regions and passive slots, have been reported as a promising choice for controlling the grinding force via an intermittent cutting scheme. With an appropriate selection of feed and other operating variables, segmented grinding could mark its merits of improved thermal performance and grinding efficiency, typically in difficult-to-machine aerospace materials. However, the formation of a boundary layer around a rotating grinding wheel is always a barrier to effective cutting fluid delivery in the grinding zone. This article attempts to investigate the boundary layer characteristics of segmented grinding wheels, typically with a comparison of 8-segmented and 32-segmented grinding wheels with a non-porous electroplated structure and its comparison with traditional porous grinding wheel configuration. The regression model proposed in this article can predict boundary layer thickness and tangential air velocity in the grinding zone during the rotation of the wheel. A closer look at flow aspects has been covered using computational fluid flow modeling/simulation, followed by experimental assessments through particle image velocimetry and shadowgraphs. The influence of segmentation and its configuration (typically the number of segments) have been illustrated through a case study of wet grinding on Ti6Al4V.

Noninvasive Advanced Cardiovascular Magnetic Resonance-Derived Fontan Hemodynamics Are Associated With Reduced Kidney Function But Not Albuminuria.

Kidney disease is the most important predictor of death in patients with a Fontan circulation, yet its clinical and hemodynamic correlates have not been well established. A total of 53 ambulatory patients with a Fontan circulation (median age, 16.2 years, 52.8% male patients) underwent advanced cardiovascular magnetic resonance assessment, including 4-dimensional flow imaging and computational fluid dynamics. Estimated glomerular filtration rate (eGFR) <90 mL/min per 1.73 m2 was observed in 20.8% and albumin-to-creatinine ratio >3 mg/mmol in 39.6%. The average eGFR decline rate was -1.83 mL/min per 1.73 m2 per year (95% CI, -2.67 to -0.99; P<0.001). Lower eGFR was associated with older age, larger body surface area at examination, longer time since Fontan procedure, and lower systemic ventricular ejection fraction. Higher albumin-to-creatinine ratio was associated with absence of fenestration at the Fontan operation, and older age and lower systemic ventricular ejection fraction at the assessment. Lower cross-sectional area of the Fontan conduit indexed to flow (r=0.32, P=0.038), higher inferior vena cava-conduit velocity mismatch factor (r=-0.35, P=0.022), higher kinetic energy indexed to flow in the total cavopulmonary connection (r=-0.59, P=0.005), and higher total cavopulmonary connection resistance (r=-0.42, P=0.005 at rest; r=-0.43, P=0.004 during exercise) were all associated with lower eGFR but not with albuminuria. Kidney dysfunction and albuminuria are common among clinically well adolescents and young adults with a Fontan circulation. Advanced cardiovascular magnetic resonance-derived metrics indicative of declining Fontan hemodynamics are associated with eGFR and might serve as targets to improve kidney health. Albuminuria might be driven by other factors that need further investigation.

Comparing the Utility of Coupled Aero-Hydrodynamic Analysis Using a CFD Solver versus a Potential Flow Solver for Floating Offshore Wind Turbines

There has been a great effort towards development of renewable energy systems to combat global warming with significant interest towards research and development of floating offshore wind turbines (FOWTs). With commercial projects such as Hywind Scotland, Hywind Tampen and others, there is a shift of industry attention from bottom-fixed offshore turbines to FOWTs. In this work, we focus on comparing industry standard Potential Flow (PF) methods versus Computational Fluid Dynamics (CFD) solvers for a scaled version of the IEA 15 MW turbine and associated FOWT system. The results from the two solvers are compared/validated using experimental thrust values for the fixed turbine. The motions and the thrust for the FOWT system are then compared for the two solvers along with hydrodynamic properties of the floater hull. The wake features downstream of the turbine are analyzed for the fixed and floating turbine using the CFD solver. The wake from the CFD solver is also compared with a simplified PF model. Finally, a simplified cost-benefit analysis is presented for the two solvers to compare the usefulness and utility of a CFD solver as compared to presently used industry-standard PF methods.

Computational Fluid Dynamics Calculations of Moderator Heat and Fluid Flow of Small Modular Heavy Water Reactor

Abstract The heavy water reactor concept Teplator is a pressure channel type reactor with independent systems for the primary coolant and the moderator. The present study analyses the low-pressure moderator cooling system of Teplator during full-power operation. The moderator is heated from neutron thermalization, gamma rays absorption, fission product decay, and decay of activation products. Additionally, heat transfer from the coolant channels has to be taken in the analyses of the moderator cooling system. Preliminary thermal-hydraulic analyses of the cooling system are supplemented by computational fluid dynamics (CFD) simulations of heat and fluid flow in the moderator's vessel, emphasizing flow-type regimes. Results from CFD simulations showed that the buoyancy-dominated flow (case MF-22) resulted in a higher thermal stratification and high moderator temperature close to the upper plate of the moderator vessel. The inertia-dominated flow regime MF-90 resulted in good mixing of the moderator and a low thermal stratification in the vessel. Finally, the midmass flow rate regime MF-45 was identified as a transitional region from a buoyancy-dominated to a mix-type regime.

Development of a piston-actuated 3D bio-printer with performance prediction system for the reliable printing of tubular structures

3D bio-printing is a promising approach for creating tubular structures within the human body by precisely controlling the distribution of cells. While several 3D bio-printers have been developed for printing tubular structures, achieving reliable and repeatable construction of effective human tubular structures remains a challenge. This paper presents a piston-actuated 3D bio-tubular structures printer that uses a rotary rod-support printing method and a printing performance prediction system. The printing performance prediction system is based on a two-phase flow computational fluid dynamics model that simulates the tubular structure forming process and provides optimal printing setup parameters, such as extrusion nozzle movement speed, nozzle height, and rod rotating speed. Experimental testing has validated the performance prediction system, which achieved a fair prediction accuracy with an average error of around 10%. The proposed bio-printer and prediction system have the potential to improve the efficiency and effectiveness of tubular structure printing for various biomedical applications.