Search

To increase system efficiency and power density, the cathode air path of Polymer Electrolyte Membrane Fuel Cells (PEM FCs) is supercharged using electrically driven air bearing centrifugal compressors. To maximize system efficiency, the cathode air supply system must be designed to optimally fulfill the requirements of the PEM FC system while obeying the design constraints imposed by the electric compressor drive and the air bearing system. This article proposes a dedicated design process for PEM FC cathode air compressors. Using physically based component models, the impact of varying cathode stoichiometry and operating pressure on PEM FC system performance is assessed to derive the system efficiency optimal compressor operating strategy. The centrifugal compressor stage is subsequently designed to achieve optimum efficiency on this operating line using meanline performance models and three-dimensional computational fluid dynamics simulations. Novel test procedures and measurement equipment are employed to validate the compressor design. The design process is demonstrated using a PEM FC passenger car application as an example. It is shown that significant performance and efficiency gains are achievable when tailoring the cathode air supply system to the application at hand. In the given example, effective compressor efficiency is increased by Δηeff = 12%. Along with an optimized compressor operating strategy, an overall PEM FC system efficiency gain of Δηsys = 2.7% is achieved. [ABSTRACT FROM AUTHOR]

Nanofluid-based finned collector designs have been explored to enhance solar spectrum utilization and thermal efficiency in photovoltaic-thermal (PV/T) systems. Combining nanofluids with finned collector designs improves heat transfer processes. Over the past five decades, various research methods have been used to analyze system performance, including experimental studies, theoretical analysis, design modification, advanced technologies, and soft computing techniques. This research examines the impact of fin geometry on energy conversion of Water/Al2O3-based PV/T systems using 3D CFD modeling simulations using ANSYS Fluent and ANSYS Steady State Thermal software. This study found that the quadrilateral fin geometry produced the lowest PV temperatures, followed by each concentration's pentagon and triangle fin geometries. The PV temperature decreased as the electrical efficiency increased, with the quadrilateral fin geometry with 1% Water/Al2O3 fluid producing the highest efficiency of 12.83%. The amount of PV heat absorbed by the working fluid affects the output temperature, which causes thermal energy conversion to be inversely proportional to electrical efficiency. Pentagon fin geometry with 4% Water/Al2O3 fluid produces the highest thermal conversion of 22.28%. In addition, this study also found significant differences in results for the three fin geometries on the collector, but no significant differences for the six Water/Al2O3 working fluids studied. [ABSTRACT FROM AUTHOR]

This research uses 3D Computational Fluid Dynamics (CFD) simulations to investigate the downhole Natural Gas Separation Efficiency (NGSE) for multiphase pumping wells in the heterogeneous churn flow regime. Results explain the effects of key parameters such as liquid viscosity, intake port sizes/diameter, and casing diameter, on the NGSE. Methods are thus suggested to enhance the NGSE in oil field operations, and key improvements to the widely used mathematical formulations for viscous service are proposed. Transient numerical simulations were performed for a section of an experimental flow loop extracted from the literature, and the flow solution was obtained with the Volume of Fluid (VOF) model. For most simulations, turbulence effects were modelled with the [Formula: see text] turbulence model. The [Formula: see text] SST turbulence model was however considered for the sensitivity analysis on liquid viscosity. The final numerical results validated against the corresponding experimental data showed an average error of less than 6%. Combining past literature and current results confirms that (i), the NGSE is affected by the downhole geometry (i.e annulus space and pump intake port flow area geometry) and (ii), current analytical NGSE models are not ideal for multiphase viscous service (high viscosity Newtonian flow) in the heterogeneous flow regime. The widely used steady-state formulations might thus not be adequate for this flow regime.

The statistical tendency of an optically accessible single-cylinder direct-injection spark-ignition engine to undergo borderline/medium knocking combustion is investigated using 3D-CFD. Focus is made on the role of fuel surrogate formulation for the characterization of anti-knock quality and flame speed of the actual fuel. An in-house methodology is used to design surrogates able to emulate laminar flame speed and autoignition delay times of the injected fuel. Two different surrogates, characterized by increasing level of complexity, are compared. The most complex one (six components) improves the representation of the real fuel, highlighting the crucial role of accurate fuel kinetics to predict flame propagation and unburnt mixture reactivity. A devoted chemical mechanism including the oxidation pathways for all the species in the surrogate is also purposely developed for the current analysis. Knock is investigated using a proprietary statistical knock model (GruMo-UNIMORE Statistical Knock Model, GK-PDF), which can infer the probability of knocking events within a RANS formalism. Predicted statistical distributions are compared to measured counterparts. The proposed numerical/experimental comparison demonstrates the possibility to efficiently integrate complex-chemistry driven information in 3D-CFD combustion simulations without online solving chemical reactions: a combination of laminar flame speed correlations, ignition delay look-up tables, and a statistics-based knock model is adopted to estimate the percentage of knocking cycles in a GDI engine while limiting the computational cost of the simulations. [ABSTRACT FROM AUTHOR]

This study explores the characteristics of twin-screw pumps when operated in turbine, i.e., reverse mode as an alternative to traditional control valves in piping systems for recovering energy. Experimental and flow simulation methods are employed. By an overset grid technique, unsteady three-dimensional (3D) flow simulations are conducted, ensuring high cell quality and high spatial resolution, particularly in wall proximity and within the gaps. To assess viscosity effects, pump and turbine mode characteristics are analyzed for water and oil. Compared to water, a pronounced reduction of the flow rate dependence on pressure difference is revealed for highly viscous oil. The gap flow in oil is significantly affected by the spindles' rotational speed and direction, whereas water displays minimal influence. Analyzing the variation in gap sizes, a 50% reduction in the minimum flank gap width leads to a slight rise in volumetric efficiency with negligible overall efficiency effects. Our findings underscore that utilizing twin-screw pumps as turbines for high-viscosity fluids can potentially recover up to 50% of the energy instead of dissipating it by using conventional control valves. • The overset grid method is used for twin-screw machine flow simulations. • 3D flow field of twin-screw machines is analyzed. • Gap flow characteristics are explored, considering viscosity and speed variation. • The potential of using twin-screw pumps as turbines is evaluated. • Up to 50% energy are recuperated. [ABSTRACT FROM AUTHOR]

Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines' cooling system designs. [ABSTRACT FROM AUTHOR]

Transient flow characteristics and dissipation mechanism in pressurized pipeline were investigated based on 1D friction models and 3D turbulence models, where the pressure–density model was combined into the 3D continuity equation allowing for the elasticity of the fluid and the pipes. The applicability of 3D realizable k–ε and 3D SST (shear stress transport) k–ω turbulence models was verified with comparison to 1D traditional water hammer models and the experimental data for fast closing of the valve in the reservoir–pipe–valve system. The valve closure rule was instantaneously carried out using the grid slip CFD (computational fluid dynamics) technique. The SST k–ω turbulence model has the highest accuracy in predicting the pressure attenuation of transient flows. The 3D detailed flow field confirms that the asymmetric flows induced by the change of valve opening within approximately three-fourths of the pipe inner diameter before the valve are captured. In the pressure wave cycles, the unsteady inertia, axial pressure gradient, viscous shear stress and turbulent shear stress mainly influence the velocity variations. During the pressure wave propagation, the viscous and turbulent dissipation are critical in the pressure attenuation in the wall region; the viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation increases to the maximum values at y+ = 13–23. HIGHLIGHTS The 3D weakly compressible and dissipation mechanism models are introduced to investigate transient flow characteristics.; The asymmetric flows induced by the change of valve opening are captured well within approximately three-fourths of the pipe inner diameter before the valve.; The viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation has maximum influence at y+ = 13–23.;

A model for the approximation of cavitation-induced air release in three-dimensional flow simulations is proposed. A cavitating orifice flow is investigated. It is assumed that vapor vanishes in the proximity of the orifice, and bubbles further downstream consist essentially of air. The model is based on a homogeneous mixture assumption and comprises one main parameter, which needs to be adjusted to the experimentally measured degassing fraction. Experimental validation is based on transmission light images downstream of the orifice. In the proximity of the orifice, the inclusion of air release in the CFD simulation yields a better agreement to experimentally measured cavitation intensity than the consideration of pure vapor only. It is concluded that a considerably larger amount of air is released than is dissolved in the evaporated amount of liquid. The simulation results suggest that the released air mass corresponds to about 1% of the evaporated liquid mass. These observations may be a good basis for purposeful future experiments, which are indispensable for the development of a more predictive approach of cavitation-induced air release in 3D CFD methods. [Display omitted] • A compressible solver for cavitating flow is extended by air release. • Air release is modeled by a homogeneous mixture approach. • Inclusion of released air improves the match to shadowgraphy data. • Mass of released air equals about 1% of evaporated liquid mass. [ABSTRACT FROM AUTHOR]

Bu çalışmada doğalgazla çalışan direkt enjeksiyonlu benzinli bir motorda ateşleme zamanının yanma ve emisyonlar üzerine etkileri incelenmiştir. Farklı ateşleme zamanları için motorun 3000 devir şartlarında simülasyonlar gerçekleştirilmiştir. Yanma karakteristikleri ve emisyon oluşumlarını incelemek için üç boyutlu hesaplamalı akışkanlar mekaniği kodu olan ANSYS-Forte 19.0 kullanılmıştır. Tüm simülasyonlar farklı ateşleme zamanları için gaz kelebeğinin tam açık konumunda tekrarlanmıştır. Erken ateşleme zamanlamasında silindir içi basıncın yükseldiği görülürken, HC ve CO emisyonlarında düşüş gözlenmiştir. Ayrıca, erken ateşleme şartlarında düşen HC ve CO emisyonlarına rağmen NOx emisyonlarında artış görülmüştür. Sonuç olarak doğalgazlı motorlarda erken ateşleme zamanında daha yüksek yanma verimi elde edilmiştir.

In this study, we performed a computational fluid dynamics (CFD) modeling of tetracycline photocatalytic degradation using rGO/ZnO/Cu as the photocatalyst. The photoreactor was an unbaffled dished bottom tank with a backswept impeller and four lamp tubes. The CFD equations were solved for light intensity, velocity, pressure, and concentration fields in time-dependent modes of the fluid regime. Our model was more complex than the previous studies in several ways: we modeled the system is 3D instead of 2D, allowed variation of light intensity and pressure throughout the photoreactor, and traced the change of key parameters over time during the initiation phase until the steady state was reached. The flow pattern was solved and visualized in the presence of mixer in vertical and horizontal cuts. Experimentally measured concentrations over time matched model predictions well but also indicated the need for yet more complex models incorporating more factors that affect reaction rates. [ABSTRACT FROM AUTHOR]

Obtaining energy from low-emission sources is extremely important currently. The use of hydropower plants for electrical energy production proves to be advantageous. The most commonly used type of water turbines are Kaplan machines due to the highest efficiency they offer in a wide range of operation. There is a need to increase the reliability of operating machines due to the failure of the oil heads performing the task of supplying hydraulic oil to the interior of the rotating turbine shaft to control the Kaplan turbine rotor blades. An in-depth analysis of physical phenomena such as friction, mechanical vibrations, and heat transfer has been carried out. The assumptions for the construction of the FDHC early diagnostics system have been created. Methods of measuring the parameters have been defined, which have consequently assisted in creating an algorithm for the testing method of a working machine in real time. The 3D CFD simulation method has been applied and physical phenomena have also been implemented in order to enable the reconstruction of the actual processes taking place inside the working element. This has enabled the observation of changes in physical quantities in any cross-section and point of the component tested. These activities have made it possible to determine the critical measurement points of physical quantities in the model that can be applied to a real object. In order to confirm the correctness of the assumptions made for the construction of the FDHC system, the 3D CFD simulation has been compared with the results obtained during measurements carried out on a working hydro unit. The results of the measurements carried out with the thermal imaging camera have partly coincided with the results obtained in the computational model. [ABSTRACT FROM AUTHOR]

Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines’ cooling system designs.

According to the IEC 60041 standard, the pressure-time method (1D PTM) can be employed to determine the flow rate in hydraulic turbines. This method assumes a one-dimensional flow and applies to straight pipes with uniform cross-sections, with specific restrictions on the pipe length, fluid velocity, and distance between the measurement sections from any irregularities in the pipeline. However, challenges arise when applying this method in low-head hydropower plants due to the short lengths, irregularities like bends and developing flows in the intake. The present paper aims to improve the performance of the method in the presence of a bend. To this end, a test rig has been developed and measurements performed, including such geometry. The data are evaluated using the development of a newly proposed approach combining the 1D PTM based on an energy balance formulation and three-dimensional computational fluid dynamics (3D CFD) developed for axis-symmetrical accelerating flows. The updated methodology includes a correction of the experimental pressure measurements used in the 1D PTM to account for the effects of the Dean vortices present after the bend as well as the kinetic energy correction factors which deviate from known values in transient conditions. The results obtained under conditions involving the presence of bends either between or in close proximity to one show a significant improvement compared to the standard one-dimensional pressure-time method. • A laboratory setup is specially designed and built for testing the pressure-time method outside IEC-60041 recommendations. • A novel introduced which extends the method's applicability to account for developing flows affected by bends by incorporating 3D CFD. • Combining experimental data and 3D CFD analysis aims to enhance the traditional 1D PTM methodology. [ABSTRACT FROM AUTHOR]

The characterization and reproduction of tyre behaviour for vehicle modelling is a topic of particular interest both for real-time driver in the loop simulations and for offline performance optimization algorithms. Since the accuracy of the tyre forces and moments can be achieved by the accurate physical modelling of all the phenomena concerning the tyre-road interaction, the link between the tyre thermal state and the tyre frictional performance turns into a crucial factor. An integrated numerical methodology, allowing to couple the full 3D CFD (Computational Fluid Dynamics) flux within the internal chamber of the tyre with an equivalent discrete 3D structure model, is proposed with the aim to completely represent the tyre thermodynamic convective behaviour in the steady-state operating conditions. 3D CFD model enables the evaluation of the internal distribution of the gas temperature and of the thermal powers exchanged at each sub-wall in detail. This allows to increase the reliability of the tyre thermodynamic modelling with a particular reference to the proper managing of the aero-thermal flow of the brake disc impact on the rim temperature and therefore on the internal gas dynamics in terms of temperature and pressure, being able to optimize the tyre overall dynamic performance in both warm-up and stabilized thermal conditions. The steady RANS (Reynolds Averaged Navier–Stokes) simulations have been performed employing the 3D CFD model in a wide range of angular velocities with the aim to calculate the convective thermal flux distributions upon rim and inner liner surfaces. The simulation results have been then exploited to derive the convective heat transfer coefficients per each sub domain to be employed within the real-time tyre physical thermal model, with the peculiar advantage of an enhanced model reliability for thermal characteristics. To validate the proposed methodology, the tyre thermal model outputs, in terms of temperatures of internal and external layers, have been validated towards the acquired ones within the specific routine performed on tyre force and moment test bench, confirming an excellent agreement with the experimental data in the entire range of operating conditions explored. [ABSTRACT FROM AUTHOR]

This study investigates using tailor-developed combustion and air-handling system concepts to achieve high-efficiency, clean gasoline compression ignition (GCI) combustion, aimed at addressing a future heavy-duty ultralow NOx standard of 0.027 g/kWh at the vehicle tailpipe and the tightening CO2 limits around the world by combining GCI with a cost-effective engine aftertreatment system. The development activities were conducted based on a 15 L heavy-duty diesel engine. By taking an analysis-led design approach, a first-generation (Gen1) GCI engine concept was developed and tested, encompassing tailor-designed piston bowl geometry, fuel spray pattern, and swirl motion paired with a customized, fixed-geometry, two-stage turbocharging system and a high-pressure EGR loop with two-stage cooling. Across four key steady-state operating points, the Gen1 GCI concept demonstrated 85–95% lower smoke and 2–3% better diesel-equivalent gross indicated fuel consumption compared to the diesel baseline at 1 g/kWh engine-out NOx. By upgrading to a Gen2 air-handling concept that was composed of a prototype, single-stage, variable-geometry turbocharger and a less restrictive EGR loop, 1D system-level analysis predicted that the pumping mean effective pressure was reduced by 43–54% and the diesel-equivalent brake-specific fuel consumption was improved by 2–4%, thereby demonstrating the performance enhancement potential of refining the air-handling system.

The article describes an interpolation–analytical method of reconstruction of the IAPWS-95 equations of state and the modified Benedict–Webb–Rubin equations of state with 32 terms (mBWR32). The method enables us to provide the thermodynamic closure in 3D computational fluid dynamics (CFD) calculations of turbomachinery flows with real working media, such as steam and Organic Rankine Cycle (ORC) fluids. The described approach allows for the sufficient accuracy of 3D flow calculations and does not require a significant increase in computational cost over perfect gas calculations. The method is validated against experimental data from measurements and compared with computational results from the model using the Tammann equation of state. Three turbine blading systems are considered—a multi-stage configuration from a low-pressure cylinder of a large-power steam turbine and two ORC microturbines working with organic media HFE7100 and R227ea. The calculation results obtained using the described method of approximation of the IAPWS-95 and mBWR32 equations exhibit satisfactory agreement with the experimental data, considering pressures, temperatures and enthalpies in key sections, as well as turbine power and efficiency in a wide range of changing thermodynamic parameters. In contrast, the Tammann equation of state provides acceptable results only for relatively small changes of thermodynamic parameters.

Lubrication of a wrist pin journal can become a limiting factor in the performance of internal combustion engines. A wrist pin journal is a hydrodynamic bearing with a radial clearance of only a few micrometers that is filled with a mixture of oil and air. Moreover, the radial clearance changes periodically with the piston motion and according to the working cycle of the internal combustion engine. Hence, a numerical study of the flow and oil transport inside a wrist pin journal requires an unsteady 3D two-phase model. Furthermore, the numerical model must include gravity and centrifugal forces, the unsteady rotation of the piston pin, and the oil feed on both sides of the piston pin boss. Presently, neither the oil feed surrounding the piston pin boss nor the mechanism transporting the oil into the gap between the piston and piston pin are fully understood. This study presents a numerical approach describing the lubrication inside the wrist pin journal. A particular aspect of the modeling is combining a structured mesh of hexahedron cells for the narrow gap and unstructured meshing in the surrounding geometry due to the difference in length scale of several orders of magnitude. The numerical model has been validated on test cases and experimental oil transport data obtained from a piston model experiment. The numerical results include images of complex 3D structures of oil and air fractions inside the oil film and in the regions surrounding the piston boss. [ABSTRACT FROM AUTHOR]

The key issue associated with the thermal power plant is the disposal of ash-water slurry and the process of its transportation is accomplished using long length pipelines. The designing of such pipelines is a vital endeavor of researchers and designers globally. In this perspective, numerical simulation of 42 mm diameter three-dimensional slurry flow pipeline carrying high concentration of mono-dispersed fine ash particles has been carried out. The study is enunciated by employing Eulerian- Eulerian two-phase model with RNG k-ɛ turbulence model with the aim of visualizing and understanding the characteristics of the slurry flow behavior. The coal ash slurry concentration varies between 50% to 70% (by weight) for velocity ranges, 1-3 ms-1. The modeling is done using Fluent commercial software with the intention of predicting the characteristics of flow for 300 μm particle size. It is observed that pressure drop upsurges non-linearly with solid concentrations and slurry velocity across pipeline. The obtained results of predetermined pressure drop are analytically compared with the experimental results. Moreover, the results are also compared with that of Eulerian-Langrange model using SST K-ω turbulence model and it is found that RNG k-ɛ turbulence model yields more accurate and desirable results. [ABSTRACT FROM AUTHOR]

Immersion cooling is an effective way to control the thermal load of high-power-density energy storage devices. Developing high-efficiency coolants is the core problem and research hotspot to improve immersion cooling performance. In this study, a novel ester coolant, pentaerythritol esters, for battery immersion cooling systems (BICS) was proposed by experiment, and its thermal properties were comparatively studied with other coolants. The effect of coolant flow rate and discharge rate on the thermal performance of BICS was studied. An increase in the discharge rate results in an increase in the maximum battery pack temperature and temperature non-uniformity. However, at a 3-C discharge rate, pentaerythritol esters with a flow rate of 0.015 kg/s can keep the temperature difference of the battery pack below 0.7 K. When the flow rate increases from 0.003 kg/s to 0.045 kg/s, the temperature rise of the battery pack can be reduced by 61%. For all coolants, when the flow rate increases from 0.025 kg/s to 0.045 kg/s, the power consumption increases by 2.3 times. Compared with mineral oil, at a flow rate of 0.045 kg/s, pentaerythritol esters can reduce power consumption by 55.4%. Combined with its renewable, biodegradable features, the novel pentaerythritol ester is a perfect option for the battery immersion coolant. • A novel kind of ester coolant has been experimental synthesized and tested. • A 3D CFD model for a BICS was constructed and verified. • The temperature difference in the pack can be controlled within 0.7 K using pentaerythritol esters at the 3-C condition. • Pentaerythritol esters exhibit a promising advantage as the coolant for BICSs. [ABSTRACT FROM AUTHOR]

Alteration of the flow characteristics in coronary vessels is correlated with coronary heart disease (CHD). In particular, wall shear stress (WSS) appears to be a hemody-namic key factor in the genesis of CHD. Since computational fluid dynamics (CFD) is a well-known method for the inves-tigation of WSS, it may be a valuable tool for the prediction of CHD. Latest imaging techniques, such as optical coher-ence tomography (OCT) in conjunction with angiography deliver precise 2D data sets of patient-specific vessel geome-try, which can be used for CFD analysis. Current CFD stud-ies utilize patient-specific geometries, but are lacking well defined physiologic inflow conditions.

The paper discusses the strategy for aerodynamic prediction and analysis of a 56 m blade using Computational Fluid Dynamics (CFD) tools. The aim of this study is to simulate the flowfield around a 3 MW wind turbine blade to study the flow physics dominated by the three-dimensional effects. This blade incorporates flatback airfoils on the inboard region of the blade used to improve aerodynamic performance in the root region. In order to reduce computation time and complexity, only one-third of the domain is modeled and a periodic boundary condition is imposed on the 120° periodic faces. A k-ω SST turbulence model is used as a solver for this simulation. Several features pertaining to 3D flowfield behavior are captured and studied. A comparison is made of the results obtained from RANS with those obtained from Boundary Element Method (BEM)-based methods. The flow past the flatback regions of the blade did not separate at the sharp edges of the flatback corners, as predicted by 2D simulation due to the presence of a dominant radial flow component in the span-wise direction which caused the flow to wrap around the trailing edge of the blade without corner separation. The paper presents a comparison of the inflow angles from CFD to those predicted by BEM. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An Euler-Euler model for the two-phase flow (solid OC and gas fuel) is developed. • 3D unsteady numerical simulations of a CLC unit based on a DCFB are performed. • Good agreement between numerical results and experimental measurements is found. • Numerical results prove the ability of the approach to predict the CLC process. • The local and instantaneous CLC behavior is analyzed and discussed. Abstract In this paper, reactive unsteady three-dimensional numerical simulations of a chemical looping combustion (CLC) unit are presented. The configuration is a 120-kW pilot plant working with perovskite, CaMn 0.9 Mg 0.1 O 3− δ , as the selected oxygen carrier. Numerical simulations were performed using NEPTUNE_CFD code in the frame of an Euler-Euler approach by computing both gas and solid phases in an Eulerian technique, accounting for specific closures in order to model the interphase mass, and momentum and energy transfers. Heterogeneous reduction and oxidation (gas–solid) reactions were modeled by means of a grain model to account for the competing mechanisms of the chemical reaction onto the grain surface, the gaseous diffusion through the product layer around the grain, and the external transfer through the gas mixture surrounding the particle. Results from numerical simulations were assessed against experimental measurements and analyzed in order to acquire insight on the local behavior of reactive gas-particle flow in the CLC system. The theoretical/numerical tool developed in this work can be used for the design upgrade of crucial parts of the system in the stage of scaling-up from pilot to industrial plants. [ABSTRACT FROM AUTHOR]

Based on the Rayleigh bubble dynamics equation a mass transfer model for cavitation of binary alkane mixtures is presented. Raoult's and Dalton's law, simple mixing rules, and an accurate Equation of State are utilized. The model is implemented into an in-house CFD code. For solver validation pure species literature cases are taken. The method is applied to a lighter n -octane/ n -heptane and a heavier n -dodecane/ n -heptane mixture in a rarefaction tube and a hydrofoil test case. Segregation of the species is observed during cavitation due to their different mass transfer rates. While for the lighter mixture, mass transfer of both species only moderately deviates, a significantly higher mass transfer of n -heptane compared to n -dodecane is observed for the heavier mixture, where the saturation pressure differs two orders of magnitude between the mixture ingredients. The strong segregation of the heavier mixture is associated with a predominant amount of n -heptane in the vapor phase. As a consequence, vapor composition is strongly affected by the volatilities of mixture ingredients. [ABSTRACT FROM AUTHOR]

Coronary diseases are the main reason for death in the western world. Bio-fluid mechanical correlations with arterial diseases are in the focus of our research. To treat occluded vessels, stents are implanted. Stent implantations can be associated with blood flow disruptions leading to restenosis or thrombosis formation. Numerical flow simulation is a promising tool to evaluate the hemodynamic performance of cardiovascular implants, but is resource-intensive in time and computational power. Therefore, a reduction in grid size would be beneficial due to economic exploitation of computational cost. The purpose of this numerical investigation is to substitute the computational domain of a distal stented bifurcation with a stented straight vessel by using the right inlet condition. The deviation of the results of the two different methods to simulate the blood flow situation in a bifurcation is marginal. This inlet can be used for standardised simulations of bifurcations were lesions commonly occur.

The aim of this paper is to identify and investigate the potential and limitations of diesel-gas combustion concepts for high speed large engines operated in gas mode with very small amounts of pilot fuel (<5% diesel fraction). Experimental tests were carried out on a flexible single cylinder research engine (displacement 6.24 dm³) equipped with a common rail system. Various engine configurations and operating parameters were varied and the effects on the combustion process were analyzed. The results presented in this paper include a comparison of the performance of the investigated dual fuel concept to those of a state-of-the-art monofuel gas engine and a state-of-the-art monofuel diesel engine. Evaluation reveals that certain limiting factors exist that prevent the dual fuel engine from performing as well as the superior gas engine. At the same NOx level of 1.3 g/kWh, the efficiency of the dual fuel engine is ≈3.5% pts. lower than that of the gas engine. This is caused by the weaker ignition performance of the injected pilot fuel compared to that of the gas scavenged prechamber of the gas engine. On the other hand, the dual fuel concept has the potential to compete with the diesel engine. The dual fuel engine can be operated at the efficiency level of the diesel engine yet with significantly lower NOxemissions (3.5 g/kWh and 6.3 g/kWh, respectively). Since the injection of pilot fuel is of major importance for flame initialization, and thus for the main combustion event of the dual fuel engine, optical investigations in a spray box, measurements of injection rates, and three-dimensional (3D) computational fluid dynamics (CFD) simulation were conducted to obtain even more detailed insight into these processes. A study on the influence of the diesel fraction shows that diminishing the diesel fraction from 3% to lower values has a significant impact on engine performance because of the effects of such a reduction on injection, ignition delay, and initial flame formation. The presented results illustrate which operating strategy is beneficial for engine performance in terms of low NOx emissions and high efficiency. Moreover, potential measures can be derived which allow for further optimization of the diesel-gas combustion process. [ABSTRACT FROM AUTHOR]

This paper presents the parameter influence of upstream deflector on the performance of vertical axis wind turbines (VAWTs). For this purpose, two counter-rotating straight-bladed VAWTs and the upstream deflector have been simulated via three-dimensional (3D) computational fluid dynamics (CFD), which is validated against experimental data. Parameter Influence of upstream deflector on VAWTs output power is investigated in this study. From the CFD results, it is observed that when the turbine is positioned outside the near-wake region, the aerodynamic power can increase significantly.) This research indicates that performance of VAWTs can be greatly improved by properly choosing parameters of the deflector. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical hydrodynamic performance assessment of a 1:50 scale model offshore floating–moored Oscillating Water Column (OWC) wave energy converter. The device is a tension–leg structure with four vertical mooring lines. The performance of the OWC device was investigated for several design parameters including regular and irregular wave conditions of different heights and periods, power take–off (PTO) damping and mooring line pre–tension. A 3D Computational Fluid Dynamics (CFD) model using RANS–VOF approach was constructed and validated against experimental results for regular waves showing good agreement. It was found that the hydrodynamic efficiency of the floating–moored OWC device follows the same general trend as a fully–constrained (fixed) model, but the addition of surge motion in the floating device improved the energy production efficiency over a broader bandwidth around the chamber resonance. Increasing the incoming wave height resulted in a higher efficiency for low–frequency waves, but noticeable reductions in the efficiency were observed in the intermediate– and high– frequency zones. The effectiveness of utilizing offshore OWC devices in deep–water was demonstrated by increasing the extracted energy by a maximum of 7.7 times and 5.7 times when regular and irregular wave heights were doubled, respectively. Decreasing the mooring line pre–tension slightly increases the energy extraction efficiency in the intermediate–frequency zone. [ABSTRACT FROM AUTHOR]

In this paper, two kinds of pulse feed including sinusoidal pulse flow (SPF) and intermittent pulse flow (IPF) were applied at the entrance of the ultrafiltration (UF) module with hollow fiber membrane, which were more effective for flux enhancement. As compared to compared to continuous flow at the same average velocity, the improvement of permeation flux could reach up to 80% for SPF and 44% for IPF, respectively. The mechanism of pulse feeding on flux enhancement was explored and a comprehensive analysis of the shear stress distribution along the membrane surface has been performed by a three-dimensional computational fluid dynamics (3D CFD) model. Additionally, comparison of pressure drop between pulse feed and steady flow was done to evaluate energy consumption. Results indicated that sinusoidal pulse flow (SPF) led to higher shear force and higher efficiency in UF process than IPF, which is consistent with experiments. [ABSTRACT FROM AUTHOR]

A numerical study has been carried out to investigate heat transfer enhancing flow field in 28 geometrically different sinusoidally, spirally corrugated tubes. To vary the corrugation, the height of corrugation e / D and the length between two successive corrugated sections p / D are varied in the ranges 0–0.16 and 0–2.0 respectively. The 3D Unsteady Reynolds-averaged Navier–Stokes (URANS) equations combined with the transition SST turbulence model are solved using the finite volume method to obtain the fully-developed flow field in a repeatable section of the heat exchangers at a constant wall temperature and at Re = 10 , 000 . By studying the wide range of geometrically different tubes, the flow conditions vary significantly. At low corrugation heights, only a weak secondary flow centred in the corrugated section is present. At higher corrugations heights, the tangential velocity component increases and eventually exceeds the axial velocity component causing the highest pressure to be located at the centre of the corrugated section. At these high corrugation heights, a further increase in corrugation height will at best only result in a small increase in Nusselt number but at a significantly higher pressure loss. To assess the performance as a heat exchanger, the ratio of enhanced Nusselt number to enhanced friction factor η = ( Nu / Nu s ) / ( f / f s ) 1 / 3 compared to the non-corrugated tube is used. Using this parameter, the simulations show a decrease in performance at higher corrugation heights. To link the detailed flow fields to the performance as a heat exchanger, non-dimensional correlations for heat transfer, pressure loss, and performance parameter are given. [ABSTRACT FROM AUTHOR]

This work describes a 3D computational fluid dynamic model, which characterizes the hydrodynamic behavior of a mixing strategy applied to egg-shaped reactors that lack a mechanical stirring device. The model is based on Navier-Stokes and material balance equations without a chemical reaction. To describe the behavior of mixing, initial water feed flows of 6, 7.5 and 9 mL s−1were used. An experimental validation was subsequently carried out using a pulse technique, with NaCl as a tracer. The residence time distributions were quantitatively determined. Then, the degradation process of the wastewater sludge was characterized by studying the time dependence of the dynamic viscosity, the concentration of volatile solids and the density of wastewater sludge. The data resulting were introduced into the validated model, and five feed flows from 9 to 13 mL s−1, the best performance found was with feed flow of 11 mL s−1. [ABSTRACT FROM PUBLISHER]

The aim if this paper is the analysis of a lubrication circuit adopting two simulation models to study the influence of three different lubrication oils. First, the oils pump performance were analyzed with a tri-dimensional simulation model, realized with the commercial code PumpLinx ® , which allowed to obtain the performance curves of the oil pump, varying the oils. Then the lubrication circuit was studied with a 1D model, realized with the commercial code LMS AMESim ® , and the behaviour of the lubrication circuit was analyzed in terms of pressure drops and components oil consumption. The adopted oils were: 0W30; 5W40 and10W60. In previous activities, both models showed good correlation with experimental data. Analyzing the models results, it was noted that the pressure behavior in the lubrication circuit is highly influenced by the oil, especially for low engine speed and high temperatures. The adopted methodology, that couples mono-dimensional and tri-dimensional models, allowed to analyze the oil influence in a lubrication circuit, avoiding excessive computational cost, but with an acceptable accuracy [ABSTRACT FROM AUTHOR]

A numerical and experimental characterization of the performance of a High Temperature Polymer Electrolyte Membrane Fuel Cell (HT PEM FC) is presented. Starting from the fluid dynamic optimization performed in a previous work, a detailed 3D CFD-electrochemical model of a single HT PEM FC is developed, in order to describe the internal fluid dynamic fields coupled to the electrochemical reactions. To validate the numerical activity, an experimental campaign has been conducted on a single-cell prototype built ad-hoc, with both pure H 2 and Syngas anodic feeding. The results of both the numerical and experimental investigations are compared to the performance of commercial HT PEM Fuel Cells, proving the good accuracy of our numerical method as well as the consistency of the experimental setup. [ABSTRACT FROM AUTHOR]

A skeletal mechanism (144 species) and a corresponding reduced mechanism (62 species) were developed on the basis of the most recent detailed n-heptane mechanism by Lawrence Livermore National Laboratories (LLNL, version 3.1, 2012) (Mehl et al., 2011, "Kinetic Modeling of Gasoline Surrogate Components and Mixtures Under Engine Conditions," Proc. Combust. Inst., 33, pp. 193-200), in order to assess the mechanism's performance under various practical combustion conditions. These simplified mechanisms were constructed and validated under shock tube conditions. Three-dimensional computational fluid dynamics (3D CFD) simulations with both simplified mechanisms were conducted for the following modeling applications: ignition quality tester (IQT), diesel engine, and homogeneous charge compression ignition (HCCI) engine. In comparison with experimental data, the simulation results were found satisfactory under the diesel condition but inaccurate for both the IQT and HCCI conditions. For HCCI, the intake temperature used in the simulation had to be increased 30 K in order to be consistent with the engine data provided by Guo et al. (2010, "An Experimental and Modeling Study of HCCI Combustion Using n-Heptane," ASME J. Eng. Gas Turbines Power, 132(2), 022801). Exploration of possible causes is conducted leading to the conclusion that refinement in the mechanism is needed for accurate prediction of combustion under IQT and HCCI conditions. INSET: 3. [ABSTRACT FROM AUTHOR]

ABSTRACT The present paper is the second part of a combined (experimental and computational) study on stall cells (SCs) on a rectangular wing. In the first part, tuft data were used in order to geometrically characterize a stabilized SC resulting from a localized spanwise disturbance introduced by a zigzag tape. Here, pressure measurements on the model and in the wake and aerodynamic polars at midspan are reported. The wing model had an aspect ratio value of 2, the Reynolds number was 106 and the range of angles of attack ( α) was from −6° to 16°. Experimental results confirm previous findings. Furthermore, two-dimensional and three-dimensional Reynolds Averaged Navier-Stokes RANS simulations are used in order to better understand the structure of SCs. 3D simulations reproduce the experimental data with a 3° delay in α and permit a qualitative analysis. It is found that the SC vortices start normal to the wing surface and extend downstream in the wake; the evolution of the SC vortices in the wake is in strong interaction with the separation line vortex and the trailing edge line vortex; as the SC vortex develops downstream in the wake, its centreline is contracted towards the SC centre; the wing wake is pushed upstream at the centre of the SC and downstream at the sides by the SC vortices; spanwise lift and drag distributions always attain their minimum at the SC centre. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the use of computational fluid dynamics (CFD) to predict the solid separation efficiency of a hydrodynamic separator. The numerical difficulty concerns the discretization of the geometry to simulate both the global behavior and the local phenomena that occur near the screen. In this context, a CFD multiscale approach was used: a global model (at the scale of the device) is used to observe the hydrodynamic behavior within the device; a local model (portion of the screen) is used to determine the local phenomena that occur near the screen. The Eulerian-Lagrangian approach was used to model the particle trajectories in both models. The global model shows the influence of the particles' characteristics on the trapping efficiency. A high density favors the sedimentation. In contrast, particles with small densities (1,040 kg/m³) are steered by the hydrodynamic behavior and can potentially be trapped by the separator. The use of the local model allows us to observe the particle trajectories near the screen. A comparison between two types of screens (perforated plate vs expanded metal) highlights the turbulent effects created by the shape of the screen. [ABSTRACT FROM AUTHOR]

Abstract: The main target of nowadays engine designers is to focus on exhaust emissions, fuel consumption and engine performance, so during the design phase of a new internal combustion engine, all the aspects related to friction and mechanical power loss must be deeply considered. And then, also the friction related to engine lubrication system must be analyzed and studied. In this paper a tridimensional CFD analysis of the lubrication circuit oil pump of a modern high-performance engine manufactured by Aprilia will be shown. The model was build up with PumpLinx®, a commercial CFD 3D code by Simerics Inc.®, taking into account all the phenomena associated to the fluid cavitation. The model was validated by data of an experimental campaign performed on a hydraulic test bench, at the Industrial Engineering Department of the University of Naples, Federico II. [Copyright &y& Elsevier]

This study investigates using tailor-developed combustion and air-handling system concepts to achieve high-efficiency, clean gasoline compression ignition (GCI) combustion, aimed at addressing a future heavy-duty ultralow NOx standard of 0.027 g/kWh at the vehicle tailpipe and the tightening CO2 limits around the world by combining GCI with a cost-effective engine aftertreatment system. The development activities were conducted based on a 15 L heavy-duty diesel engine. By taking an analysis-led design approach, a first-generation (Gen1) GCI engine concept was developed and tested, encompassing tailor-designed piston bowl geometry, fuel spray pattern, and swirl motion paired with a customized, fixed-geometry, two-stage turbocharging system and a high-pressure EGR loop with two-stage cooling. Across four key steady-state operating points, the Gen1 GCI concept demonstrated 85–95% lower smoke and 2–3% better diesel-equivalent gross indicated fuel consumption compared to the diesel baseline at 1 g/kWh engine-out NOx. By upgrading to a Gen2 air-handling concept that was composed of a prototype, single-stage, variable-geometry turbocharger and a less restrictive EGR loop, 1D system-level analysis predicted that the pumping mean effective pressure was reduced by 43–54% and the diesel-equivalent brake-specific fuel consumption was improved by 2–4%, thereby demonstrating the performance enhancement potential of refining the air-handling system. [ABSTRACT FROM AUTHOR]

A CFD approach, in which the full equations are solved in the time domain, is proposed to calculate noise reduction of a cleaner and a complex exhaust muffler without mean flow. First, two modelling approaches are used to deal with the outlet boundary and to calculate noise reduction of the cleaner without a filter element. The calculated results agree quite well with measurements. Further, the noise reduction of the cleaner with a filter element and the muffler with E-glass roving in one of its chambers is calculated with the simpler but fairly accurate modelling approach. The calculated results are not as in good accordance with measurements as they are when the porous material is not taken into account, but still are attained with considerable accuracy, especially for the results of the exhaust muffler with approximately homogeneous porous material. [ABSTRACT FROM AUTHOR]

The study of a vehicle moving through a lateral wind gust has always been a difficult task due to the difficulties in granting the right similitude. The facility proposed by Ryan and Dominy has been one of the best options to carry it out. In this approach, a double wind tunnel is used to send a lateral moving gust on a stationary model. Using this idea as a starting point, the ISAE has built a dedicated test bench for lateral wind studies on transient conditions. Experimental work has been carried out by means of time-resolved PIV, aiming at studying the unsteady interpenetration of the two flows coming from each wind tunnel. Meanwhile, a 3D CFD model based on URANS was set up, faithfully reproducing the double wind tunnel. Both the experimental and numerical results are compared, and the evolution of the reproduced wind gust is discussed. Conclusions are finally determined about the validity of this kind of test bench for ground vehicle applications. [ABSTRACT FROM AUTHOR]

Abstract: Spatially 1D simulations of exhaust gas catalysts are often used in the automotive industry because of short computation times. In fully 3D CFD-based model, the computational requirements increase by several orders of magnitude. A novel approach to 3D simulations of complete exhaust gas aftertreatment systems is proposed in this paper. It is based on a modular combination of standard CFD tool with a user-defined 1D channel model. The employment of external 1D channel model enables more effective computations and gives maximum freedom in definition of realistic reaction kinetics, including non-linear rate laws and fully transient solution of adsorbed components. The approach is validated by comparison of the results from the stand-alone 1D model and single channel CFD simulation. Dynamic simulations of CO oxidation light-off and lean/rich operation of NO x storage catalyst (NSRC, LNT) are then conducted in a test geometry with 10 representative channels and skewed inlet/outlet pipes. Finally, a complex system including bent pipes and conical expansion/constriction parts is simulated with 80 representative channels. It is demonstrated that relatively large deviations can exist between the individual channels. Non-uniform inlet flow distribution affects light-off behaviour as well as breakthrough of adsorbed components, and it may also lead to a different extent of catalyst ageing in individual channels. The combined 3D CFD and 1D channels simulation approach represents an effective tool for analysis of such problems and can help with the design of more efficient exhaust gas aftertreatment systems. [Copyright &y& Elsevier]

In order to forecast and to follow the dispersion of odours around its treatment sites, SIAAP which treats wastewater for the entire region around Paris, developed and implemented an innovative tool called SYPROS. SYPROS is based on the 3D CFD dispersion tool Fluidyn-PANEIA and uses a Lagrangian puff model for real time calculations, together with a source definition module for determining the source emission rates in real time. In order to adjust the source emission the so-called remapping process has been implemented. A case study for the implementation of the comprehensive tool SYPROS on the Seine Aval site is described. [ABSTRACT FROM AUTHOR]

Abstract: From an automotive manufacturer point of view, polymer electrolyte membrane (PEM) fuel cells have evolved, over the past couple of decades, from a laboratory experiment to one of the most probable successors to the internal combustion engine. High efficiency, modularity and local zero emission of greenhouse gases are only some of the advantages of this technology. On the downside, cost, durability targets and the deployment of an hydrogen distribution infrastructure remain challenges to be addressed in order for the fuel cell electric vehicle to make it into mass production. This work presents the comprehensive 3D modeling approach of the AVL FIRE fuel cell module, including coupled thermal, electric, fluidic, and electrochemical phenomena. The model is validated with experimental data obtained on a full size industrial PEM fuel cell designed by PSA. A good agreement between simulation and experiment can be achieved in average as well as local current densities proving the validity of the model. Shortcomings of the model in predicting the fuel cell performance for different inlet gas humidities are identified indicating that further improvement of the membrane model is required. [Copyright &y& Elsevier]