Commercial Computational Fluid Dynamics Code Research Articles

Numerical evaluation of a PEM fuel cell with conventional flow fields adapted to tubular plates

In this research a 3D numerical study on a PEM fuel cell model with tubular plates is presented. The study is focused on the performance evaluation of three flow fields with cylindrical geometry (serpentine, interdigitated and straight channels) in a fuel cell. These designs are proposed not only with the aim to reduce the pressure losses that conventional designs exhibit with rectangular flow fields but also to improve the mass transport processes that take place in the fuel cell cathode. A commercial computational fluid dynamics (CFD) code was used to solve the numerical model. From the numerical solution of the fluid mechanics equations and the electrochemical model of Butler-Volmer different analysis of pressure losses, species concentration, current density, temperature and ionic conductivity were carried out. The results were obtained at the flow channels and the catalyst layers as well as in the gas diffusion layers and the membrane interfaces. Numerical results showed that cylindrical channel configurations reduced the pressure losses in the cell due to the gradual reduction of the angle at the flow path and the twist of the channel, thus facilitating the expulsion of liquid water from the gas diffusion layers and in turn promoting a high oxygen concentration at the triple phase boundary of the catalyst layers. Moreover, numerical results were compared to polarization curves and the literature data reported for similar designs. These results demonstrated that conventional flow field designs applied to conventional tubular plates have some advantages over the rectangular designs, such as uniform pressure and current density distributions among others, therefore they could be considered for fuel cell designs in portable applications.

Validation strategy for CFD models describing safety-relevant scenarios including LH2/GH2 release and the use of passive auto-catalytic recombiners

The ability to simulate the whole chain of physical phenomena that may occur following an accidental hydrogen release is mandatory for future safety studies on an industrial or urban scale. In cooperation with the RWTH Aachen University, Forschungszentrum Jülich develops numerical methods to predict safety incidents connected with the release of either liquid hydrogen (LH2) or gaseous hydrogen (GH2), using the commercial computational fluid dynamics (CFD) code ANSYS CFX. The full sequence from the release, distribution or accumulation of accidentally released hydrogen, until the mitigation of accident consequences by safety devices is considered. The paper describes the current development status, gives examples of the validation and concludes with future work to provide the full range of hydrogen release and recombination simulation.

Deforming grid generation and CFD analysis of variable geometry screw compressors

The most common type of twin screw machines are twin screw compressors. These normally contain rotors of uniform pitch and profile along the rotor length. However, in some cases such as in twin screw vacuum pumps with very large pressure ratios, the variable pitch rotors are often used to improve efficiency. The limited use of rotors with variable pitch and/or section profile is mainly due to manufacturing constraints. In order to analyse the performance of such machines by means of Computational Fluid Dynamics (CFD), it is necessary to produce a numerical mesh capable of calculating 3D transient fluid flows within their working domains.An algebraic grid generation algorithm applicable to unstructured grid, Finite Volume Method (FVM) for variable pitch and variable profile screw machines is described in this paper. The grid generation technique has been evaluated for an oil free air compressor with “N” profile rotors of 3/5 lobe configuration. The performance was obtained by calculations with commercial CFD code. The grid generation procedure provides mesh of the required quality and results from CFD calculations are presented to compare performance of constant pitch rotors, variable pitch rotors and variable profile rotors. The variable pitch and variable profile rotors achieve steeper internal pressure rise and a larger discharge area for the same pressure ratio. Variable pitch rotors achieve reduced sealing line length in high pressure domains.

A Numerical Study on the Improvement of the Performance of a Banki Wind Turbine

Banki wind turbine is a kind of vertical axis wind turbine (VAWT) with high solidity, and has been proved to have a relatively high starting torque and maximum power coefficient under low wind conditions. This study introduces an arc-shaped windshield to further improve the performance of Banki wind turbines. The windshield is placed in front of the turbine to deflect wind and reduce the negative torque on the blades in the upwind direction. Computational investigations are carried out to study the influence of the angle of the arc-shaped windshield on the performance of the turbine using the commercial computational fluid dynamics (CFD) code Fluent 13.0. The results demonstrated that the maximum power coefficient of the Banki wind turbine was increased by 66.9% with the optimal windshield angle of 60°. The maximum power coefficient was found to be 0.2784 at a tip speed ratio of 0.5 in the presence of the windshield.

Modeling of particle transport and combustion phenomena in a large-scale circulating fluidized bed boiler using a hybrid Euler–Lagrange approach

The constantly developing fluidized combustion technology has become competitive with a conventional pulverized coal (PC) combustion. Circulating fluidized bed (CFB) boilers can be a good alternative to PC boilers due to their robustness and lower sensitivity to the fuel quality. However, appropriate engineering tools that can be used to model and optimize the construction and operating parameters of a CFB boiler still require development. This paper presents the application of a relatively novel hybrid Euler–Lagrange approach to model the dense gas–solid flow combined with a combustion process in a large-scale industrial CFB boiler. In this work, this complex flow has been resolved by applying the ANSYS FLUENT 14.0 commercial computational fluid dynamics (CFD) code. To accurately resolve the multiphase flow, the original CFD code has been extended by additional user-defined functions. These functions were used to control the boiler mass load, particle recirculation process (simplified boiler geometry), and interphase hydrodynamic properties. This work was split into two parts. In the first part, which is referred to as pseudo combustion, the combustion process was not directly simulated. Instead, the effect of the chemical reactions was simulated by modifying the density of the continuous phase so that it corresponded to the mean temperature and composition of the flue gases. In this stage, the particle transport was simulated using the standard Euler–Euler and novel hybrid Euler–Lagrange approaches. The obtained results were compared against measured data, and both models were compared to each other. In the second part, the numerical model was enhanced by including the chemistry and physics of combustion. To the best of the authors’ knowledge, the use of the hybrid Euler–Lagrange approach to model combustion is a new engineering application of this model. In this work, the combustion process was modeled for air-fuel combustion. The simulation results were compared with experimental data. The performed numerical simulations showed the applicability of the hybrid dense discrete phase model approach to model the combustion process in large-scale industrial CFB boilers.

Numerical simulation of immersion quenching process for cast aluminium part at different pool temperatures

The present paper outlines the recently improved Computational Fluid Dynamics (CFD) model to simulate the immersion quench cooling process. The main application area of the presented method is heat treatment of cast aluminium parts, mostly cylinder heads in automotive internal combustion engines, where an accurate heat treatment prediction plays an important role in conceptual and thermal analysis. In order to achieve low residual stress levels resulting from even temperature distribution during the cooling process, and thereby to prevent component failure during operation, the numerical model of the quenching process, as developed within the commercial CFD code AVL FIRE®, was improved by allowing for variable Leidenfrost temperature. Preliminary results of variable Leidenfrost temperature model together with the implementation of additional interfacial forces, such as lift and wall lubrication forces are presented. Only the enthalpy equation is solved in the solid domain to predict the thermal field, whereas the Euler-Eulerian multi-fluid modelling approach is used to handle the boiling two-phase flow and the heat transfer between the heated structure and the sub-cooled liquid. The results of the improved quenching model are compared with available measurement data for various water temperatures ranging from 303 K to 353 K. Using the step plate with variable thickness sections along its height as the model test case, different solid part orientations were investigated and obtained temperature profiles were analysed. The temperature histories predicted by the presented model correlate very well with the provided measurement data at different monitoring positions. The temperature distribution within the solid part, obtained from the CFD simulation, can therefore serve as a realistic input for subsequent Finite Element Analysis (FEA) of thermal stresses within the quenched solid part.

Numerical study of gas-cyclone airflow: an investigation of turbulence modelling approaches

A numerical study of unsteady single-phase vortical flow inside a cyclone is presented. Two different geometric configurations have been considered, with the goal of assessing several different turbulence modelling approaches for this class of problem. The models investigated include three Reynolds-averaged Navier–Stokes models: a commonly used two-equation eddy-viscosity model, a differential Reynolds stress model (DRSM) and an eddy-viscosity model sensitised to rotational and curvature (RC) effects which was recently developed and implemented into a commercial CFD (computational fluid dynamics) code by the authors. Results were also obtained using large eddy simulation (LES). The computational results are analysed and compared with available experimental data. The RC-sensitised eddy-viscosity model shows significant improvement over the standard eddy-viscosity model. The RC-sensitised model, DRSM and LES model predictions of the mean flowfield are in good agreement with the experimental data. The results suggest that curvature- and rotation-sensitive eddy-viscosity models may provide a practical alternative to more computationally intensive approaches.

A Numerical Study on the Improvement of Suction Performance and Hydraulic Efficiency for a Mixed-Flow Pump Impeller

This paper describes a numerical study on the improvement of suction performance and hydraulic efficiency of a mixed-flow pump by impellers. The design of these impellers was optimized using a commercial CFD (computational fluid dynamics) code and DOE (design of experiments). The design variables of meridional plane and vane plane development were defined for impeller design. In DOE, variables of inlet part were selected as main design variables in meridional plane, and incidence angle was selected in vane plane development. The verification of the experiment sets that were generated by2kfactorial was done by numerical analysis. The objective functions were defined as the NPSHre (net positive suction head required), total efficiency, and total head of the impellers. The importance of the geometric design variables was analyzed using2kfactorial designs. The interaction between the NPSHre and total efficiency, according to the meridional plane and incidence angle, was discussed by analyzing the2kfactorial design results. The performance of optimally designed model was verified by experiments and numerical analysis and the reliability of the model was retained by comparison of numerical analysis and comparative analysis with the reference model.

Prediction of Particles-Air Movement in Silo during Filling Operation

Awareness of dust explosion hazards during silo filling operation is important for safety measures. Thus, information on particles-air flow field is required to assess the likelihood of the hazard. Flow field visualization via experimental investigation associated with difficulties and risks. Hence, in the present study, a modeling formulation using commercial computational fluid dynamics (CFD) code, FLUENT software was employed to predict an insight of flow field distribution, in terms of mean and root mean square (RMS) velocities vectors in cylindrical silo during axial filling. According to the simulation results, predicted flow field has a great influence to the silo height and distance to the silo wall due to gravitational force and movement of fugitive dust and re-circulation of air. The results showed that the predicted data were in very good agreement with experimental data obtained from the literature. The maximum error was around 10%. The study has gone some way towards enhancing our understanding of the particles-air behavior inside industrial equipments during filling operation.

Influence of Spacer Grid Outer Strap on Fuel Assembly Thermal Hydraulic Performance

The outer strap as a typical structure of a spacer grid enhances the mechanical strength, decreases hang-up susceptibility, and also influences thermal hydraulic performance, for example, pressure loss, mixing performance, and flow distribution. In the present study, a typical grid spacer with different outer strap designs is adopted to investigate the influence of outer strap design on fuel assembly thermal hydraulic performance by using a commercial computational fluid dynamics (CFD) code, ANSYS CFX, and a subchannel analysis code, FLICA. To simulate the outer straps’ influence between fuel assemblies downstream, four quarter-bundles from neighboring fuel assemblies are constructed to form the computational domain. The results show that the outer strap design has a major impact on cross-flow between fuel assemblies and temperature distribution within the fuel assembly.

Optimization of Solar Tower Hybrid Pressurized Air Receiver Using CFD and Mathematical Optimization

Solar receivers used for central tower Concentrated Solar Plants (CSPs) use either a surface-based or volumetric heat transfer region. Volumetric receivers are more efficient but require more sophisticated and expensive materials that can withstand the elevated temperatures (in excess of 1000°C). If pressurized air is used as heat transfer fluid (HTF) in order to increase both the density and heat capacity of the HTF, the volumetric receiver needs to be located in a pressure vessel with a pressurized quartz window located at the aperture of the concentrator. An alternative approach to utilize pressurized air in a pseudo-volumetric fashion is to populate a volumetric region with piped pressurized air (Kretzschmar & Gauché, 2012). This tubular-type volumetric receiver provides the challenge of enabling maximum heat transfer without causing hot spots on the side of the solar irradiation source. Heat transfer would not be as effective as for a true volumetric receiver because the heat transfer area is limited by the tube wall. A Computational Fluid Dynamics (CFD) model is generated of the solar receiver cavity. The commercial CFD code ANSYS Fluent v14.5 is used to evaluate the heat transfer between the incoming solar flux and the HTF. The incoming solar irradiation is modeled using the Discrete Ordinates (DO) radiation model ANSYS Fluent. The DO model also predicts the resulting thermal radiation in the conjugate heat transfer problem. The geometry is parameterized in order to allow for the selection of design variables in a formal design optimization formulation. Results include typical CFD results of a candidate geometry to illustrate the solar irradiation input, the effect of tubular layout as well as temperature and heat flux distributions that provide candidate objective functions for optimization. Recommendations are made for the implementation of the optimization process.

CFD modelling study of heat transfer in a coiled agitated vessel

Computational fluid dynamics (CFD) modelling of heat transfer studies in a helical coiled agitated vessel with varying heat input has been carried out using commercial CFD code FLUENT (Version 6.3.26). The study using two agitators namely propeller and disk turbine is proposed to evaluate the CFD predictions of heat transfer performances as well as to provide a detailed insight into the process. The simulations have been performed for the three-dimensional and time-independent flow. The standard k-e model was adopted to capture the turbulent nature. The temperature contours in both axial and radial directions are also discussed. The CFD predicted Nusselt number agrees well with the experimentally reported value and the discrepancy is found to be less than ±7%.

연료 종류 및 당량비에 따른 Flame Spray 화염장의 열-유동 특성 연구

The present study aims to investigate the flow characteristics with respect to fuel type and equivalence ratio in the flame spray coating process. The flame spray flow is characterized by much complex phenomena including combustion, turbulent flows, and combined heat transfer. The present study numerically simulated the flam spray process and examined the gas dynamics involving combustion, gas temperature and velocity distributions in flame spray process by using commercial computational fluid dynamics (CFD) code of FLUENT (ver. 13.0). In particular, we studied the effect of fuel type and equivalence ratio on thermal and flow characteristics which could substantially affect the coating performance. From the results, it was found that the gas temperature distributions were varied with different fuels because of reaction times were different according to the fuel type. The equivalence ratio also could change the spatial flame distribution and the characteristics of coated layer on the substrate.

Air Quality Modeling of Santhepet Street Canyon of Mysore City Using FLUENT

Automobile transport has become an inherent part of human life, and the adverse effect like air pollution is becoming more drastic. Vehicular traffic is leading to deterioration of air quality in the streets of Mysore city in recent years. It is very important to assess the impact of traffic related air pollution to take administrative decisions for improving air quality. In the present study, an attempt has been made to study the street canyon air quality by monitoring the concentration of pollutants like Suspended Particulate Matter (SPM), Sulfur dioxide (SO2) and Nitrogen dioxide (NO2) in Santhepet street canyon of Mysore city. Pollutants are monitored for 8 hours using instrument High Volume Air Sampler (HVAS) at two sampling stations in the canyon. During sampling period, the meteorological condition such as temperature, wind speed and humidity are found to be 33 0 C, 3-4km/hr and 50% respectively. The pollutants SPM, SO2 and NO2 concentration at sampling station 1 are 943.89, 15.73 and 1319.57 µg/m 3 and concentration of pollutants in sampling station 2 are 520.69, 13.93 and 350.87µg/m 3 respectively. Computational Fluid Dynamics (CFD) is a tool which assists in modeling the airflow and dispersion of pollutants among complex urban street canyons. FLUENT is the most widely used commercial CFD code for a range of flow applications. An attempt has been made to study the dispersion of the pollutants inside an urban street canyon using FLUENT.

Optimization Design of Refuse-Incinerating Power Plant With Air-Cooled Heat Exchanger

As a newly developed industry, refuse incinerating power plants with air-cooled heat exchanger (ACHE) systems benefit both environment and energy savings. Since the exhaust steam of power plant is cooled in the atmosphere, the pressure of the exhaust steam fluctuates with variation of air temperature. As a result, the generated electric power of a power plant with an ACHE system is considerably influenced by meteorological conditions in the region where this type of power plant is built. The present work studies three different designs of a refuse-incinerating power plant with ACHE for a real project. Under the local meteorological conditions, the overall flow and temperature fields of the air in the whole power plant, especially around the air-cooled heat exchanger, are numerically investigated with the commercial computational fluid dynamics (CFD) code FLUENT and the feasibility of the project is then evaluated. In addition, a comparison of these three designs is also provided, including the performance of the exchangers and the fans, the collocation of the exhaust gas pipe, and the costs of the ACHE system.

Analysis of Start-Up Characteristics of a Honeycomb Regenerator

A three-dimensional numerical model is established which is for studying the unsteady thermal process in honeycomb regenerator. The numerical simulation was performed using FLUENT, a commercial Computational Fluid Dynamics (CFD) code, to compare simulation results to the test data. The temperature distribution of flue gas and air along the length way were obtained. The influence of switching time on the heat exchange is investigated as well. And the factors that influencing the best switching time were studied. The work in this study provides a theory basis and guide to the exploitation and appliance of HTAC system and the results of the numerical calculation can be used as the foundation of engineering design. The results may be utilized for design of porous media reactors and process optimization.

Investigation of the parallel efficiency of a PC cluster for the simulation of a CFD problem

Previously, large-scale fluid dynamics problem required supercomputers, such as the Cray, and took a long time to obtain a solution. Clustering technology has changed the world of the supercomputer and fluid dynamics. Affordable cluster computers have replaced the huge and expansive supercomputers in computational fluid dynamics (CFD) field in recent years. Even supercomputers are designed in the form of clusters based on high-performance servers. This paper describes the configuration of the affordable PC hardware cluster as well as the parallel computing performance using commercial CFD code in the developed cluster. A multi-core cluster using the Linux operating system was developed with affordable PC hardware and low-cost high-speed gigabit network switches instead of Myrinet or Infiniband. The PC cluster consisted of 52 cores and easily expandable up to 96 cores in the current configuration. For operating software, the Rock cluster package was installed in the master node to minimize the need for maintenance. This cluster was designed to solve large fluid dynamics and heat transfer problems in parallel. Using a commercial CFD package, the performance of the cluster was evaluated by changing the number of CPU cores involved in the computation. A forced convection problem around a linear cascade was solved using the CFX program, and the heat transfer coefficient along the surface of the turbine cascade was simulated. The mesh of the model CFD problem has 1.5 million nodes, and the steady computation was performed for 2,000 time-integrations. The computation results were compared with previously published heat transfer experimental results to check the reliability of the computation. A comparison of the simulation and experimental results showed good agreement. The performance of the designed PC cluster increased with increasing number of cores up to 16 cores The computation (elapsed) 16-core was approximately three times faster than that with a 4-core.

Computational Fluid Dynamics Simulation of the Exterior Flow Field around an Aerodynamic Reference Model

The exterior flow field around a Ford notchback automobile aerodynamic reference model was investigated using a commercial Computational Fluid Dynamics (CFD) code, Ansys Fluent. Two computational domains were set up in order to represent different model mounting conditions. According to the comparisons, good simulation accuracy could be obtained using the steady state k-ω SST model with small size near wall mesh (y+<5) simulations. The comparatively large prediction errors of the surface pressure coefficient of the model centerline happened in two positions. One is the roof trailing edge, where the flow separation begins. The other is the saddle point on the deck lid centerline, where the reverse flow emerges. These differences between the CFD and experiment were possibly due to the unstable wake. This wake instability would be the reason of the differences between the Ford notchback model transverse vortices and the typical notchback car wake structures.

CFD Analysis of the Coolant Mixing within the Upper Plenum of a Pressurized Water Reactor (PWR)

In this study, a Computational Fluid Dynamic (CFD) model is established to obtain the 3-D flow characteristic, temperature distribution of the pressurized water reactor (PWR) upper plenum and hot-legs. In the CFD model, the flow domain includes the upper plenum, the 61 control rod guide tubes, the 40 support columns, the three hot-legs. The inlet boundary located at the exit of the reactor core and the outlet boundary is set at the hot-leg pipes several meters away from upper plenum. The temperature and flow distribution at the inlet boundary are given by sub-channel codes. The computational mesh used in the present work is polyhedron element and a mesh sensitivity study is performed. The RANS equations for incompressible flow is solved with a Realizable k-ε turbulence model using the commercial CFD code STAR-CCM+. The analysis results show that the flow field of the upper plenum is very complex and the temperature distribution at inlet boundary have significant impact to the coolant mixing in the upper plenum as well as the hot-legs. The detailed coolant mixing patterns are important references to design the reactor core fuel management and the internal structure in upper plenum.

Two-Phase CFD Study of Coolant through a 5×5 Rod Bundles with Grid Spacers

A numerical study using computational fluid dynamics (CFD) under air/water two-phase flow condition without thermal transmission is carried out utilizing the commercial CFD code CFX. A detailed geometry of 5×5 rod bundles with two grid spacers in the Pressurized Water Reactor (PWR) is set up for analyzing. The Multiple Size Group (MUSIG) model based on the population balance equation is employed to describe the characteristic of flow field in which the dispersed phase has a large variation in size, and the breakup and coalescence interaction among different sizes of the bubbles. The effects of the size fraction at inlet, the size group quantities, the breakup and coalescence coefficients, the momentum transfer model, and so on, are studied. The results demonstrate that various parameters and two-phase model have different impacts on the analysis results. The detailed CFD modeling methodology for two-phase flow conditions in PWR fuel assemblies is developed according to the above-mentioned investigations. The flow field patterns and air/water phase distributions in the computational results shows that the two-phase modeling methodology in the present work is reasonable.