Commercial Computational Fluid Dynamics Code Research Articles

Retraction Note to: Numerical simulation on pollutant dispersion from vehicle exhaust in street configurations.

The impact of the street configurations on pollutants dispersion from vehicles exhausts within urban canyons was numerically investigated using a computational fluid dynamics (CFD) model. Three-dimensional flow and dispersion of gaseous pollutants were modeled using standard κ − e turbulence model, which was numerically solved based on Reynolds-averaged Navier–Stokes equations by the commercial CFD code FLUENT. The concentration fields in the urban canyons were examined in three cases of street configurations: (1) a regular-shaped intersection, (2) a T-shaped intersection and (3) a Skew-shaped crossing intersection. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated against wind tunnel results in order to optimize the turbulence model. Numerical predictions agreed reasonably well with wind tunnel results. The results obtained indicate that the mean horizontal velocity was very small in the center near the lower region of street canyon. The lowest turbulent kinetic energy was found at the separation and reattachment points associated with the corner of the down part of the upwind and downwind buildings in the street canyon. The pollutant concentration at the upwind side in the regular-shaped street intersection was higher than that in the T-shaped and Skew-shaped street intersections. Moreover, the results reveal that the street intersections are important factors to predict the flow patterns and pollutant dispersion in street canyon.

Numerical investigation on vibration and noise induced by unsteady flow in an axial-flow pump

Full-scale structural vibration and noise induced by flow in an axial-flow pump was simulated by a hybrid numerical method. An unsteady flow field was solved by a large eddy simulation-based computational fluid dynamics commercial code, Fluent. An experimental validation on pressure fluctuations was performed to impose an appropriate vibration exciting source. The consistency between the computed results and experimental tests were interesting. The modes of the axial-flow pump were computed by the finite element method. After that, the pump vibration and sound field were solved using a coupled vibro-acoustic model. The numerical results indicated that the the blade-passing frequency was the dominant frequency of the vibration acceleration of the pump. This result was consistent with frequency spectral characteristics of unsteady pressure fluctuation. Finally, comparisons of the vibration acceleration between the computed results and the experimental test were conducted. These comparisons validated the computed results. This study shows that using the hybrid numerical method to evaluate the flow-induced vibration and noise generated in an axial-flow pump is feasible.

Design and Performance Analysis of Cooling Tower Axial Fan Using the Thin Airfoil Theory and CF D. (Dept. M ( Power ))

Numerical algorithms for the flow of cooling tower axial fans in the flow wise direction and span-wise direction have been transformed and solved by the Matlab application with a graphical user interface to obtain the optimum axial fan design. The analyses of the velocity and pressure distributions were achieved using the thin airfoil theory. The fan has a single rotor with no inlet or outlet guide vanes and produces a large amount of flow rate and a small pressure rise. Then, the air flow governing equations for the new design were solved using the commercial computational fluid dynamics (CFD) code ANSYS CFX-16.0. A comparison between the new design and an existed design (usually a mean line design approach) of the ammonia cooling tower fan in El-Delta for Fertilizers Company in Talkha City, Egypt was done. The efficiency of the new design is higher than that of the existed one. The new designed fan is capable to deliver more air flow or the same flow rate at higher pressures with the same power requirement. This enables the installation of new high resistance fill, which increases the area of contact between air and water to increase cooling efficiency.

3D CFD modeling of a PEM fuel cell stack

A single-phase, three-dimensional model has been implemented to simulate the fluid flow, heat transfer, electrochemical reaction and species transport in a Proton Exchange Membrane Fuel Cell stack with five single cells including the membrane, gas diffusion layers, catalyst layers, flow channels and current collectors. A commercial computational fluid dynamics (CFD) code, Ansys 15.0®, was used to solve the numerical model. The numerical results showed the detailed distributions of mass fractions of hydrogen and oxygen, as well as the heat sources and temperature through five membrane electrode assemblies inside the stack. The species concentration always was higher at inlets and it was reduced gradually along the channels. The lowest temperature was observed at the inlet of the cathode where oxygen is supplied at temperature of 300 K. Likewise, the heat sources in PEM fuel cell are tightly related with the current density distributions through membrane electrodes assembly. Moreover, the results were validated by polarization curves and experimental data obtained from experiments carried out in a Horizon PEM fuel Cell (H-100). Furthermore, this model can be used as an important step for improving the stack design and proposing a new cooling method.

Dethridge wheel for pico-scale hydropower generation: An experimental and numerical study

This study aims to assess the potential of the Dethridge wheel for developing power from very low head sites in open channel flow. The Dethridge wheel has been in use since early 20th century for measuring flow in irrigation canals. Being robust and simple in design, this technology served as a reliable flow metering solution for more than a century. Working in a similar principle to the conventional waterwheel, this wheel could be a viable option of power generation for decentralized application in remote areas. Two different methods, experimental and numerical, are used for investigating the potential of the wheel. An experimental approach in which a physical model of the Dethridge wheel is built and tested at the hydraulics laboratory of Darmstadt University of Applied Sciences. Whereas a three dimensional numerical model of the Dethridge wheel is simulated using a commercial Computational Fluid Dynamics (CFD) code Flow-3D. Efficiency of around 60% is achieved in the model tests. Computed results are also in good agreement with the physical model results. The results from the physical and the numerical model are presented in this paper.

Numerical simulation of thermal runaway and inhibition process on the thermal polymerization of styrene

In order to achieve safer operating conditions of styrene polymerization process and effective inhibition of runaway reaction, computational fluid dynamics (CFD) technology is applied to simulate the thermal polymerization of styrene. A three-dimensional geometry model of the stirred reactor is established with a tool of SolidWorks. The computational model is carried out with a commercial CFD code (FLUENT). The effect of the viscosity, the impeller speed, the temperature probe location and the diluent addition location are investigated. The simulation results indicate that the three-dimensional model is useful for revealing the distribution of temperature and divergence of thermal runaway and inhibition process on the thermal polymerization of styrene.

수증기-메탄 혼합비에 따른 개질 튜브 내 온도 및 화학반응 특성

본 연구의 목적은 실제 산업현장에서 사용되는 수소 개질로 내 개질가스의 수증기-메탄 혼합비에 따른 튜브 내 온도 및 화학반응 특성을 수치 해석하는 것이다. 탄화수소의 수증기 개질반응은 800 K - 1000 K 이상의 고온에서 발생하기 때문에 대류, 전도 및 복사 열전달을 고려한 복합 열전달을 고려해야 한다. 수치해석은 상용 전산유체역학(CFD) 코드(ANSYS Fluent V.13.0)를 사용하였다. 본 연구에서 해석을 위해 Reynolds-Averaged Navier-Stokes, 운동량 및 에너지 방정식을 사용하고, 화학반응이 발생하는 튜브 내부는 니크롬 재질의 다공성 영역으로 가정하였다. 개질 튜브 내 온도 및 화학반응 특성을 비교하기 위해 메탄과 수증기의 혼합비를 1-6으로 증가시켜 비교 분석하였다. 수치해석 결과, 메탄에 대한 수증기 비율이 높을수록 튜브 내부의 온도가 증가하고, 메탄의 전화율이 증가한다. 그러나 수소 개질량은 수증기와 메탄의 비율이 5일 때 가장 많은 것을 알 수 있다. The aim of numerical study is the investigation of the solid and fluid temperatures in a reformer tube and chemical reaction characteristics of different steam-carbon ratio. We considered conjugate heat transfer contain radiation, convection and conductive heat transfers. This is because steam reforming reaction of hydrocarbon occurred high temperature conditions up to 800 K- 1000 K by using commercial computational fluid dynamics (CFD) code (Fluent ver. 13.0). For numerical simulation, the Reynolds-Averaged Navier-Stokes, momentum and energy equation were employed. In addition, inside of reformer tube is assumed as the porous medium to consider the Nichrome-based catalyst. To analysis characteristics of tube temperature in chemical reaction, we changed steam-methane ratio(SCR) from 1 to 6. As increased SCR, the higher tube temperature and methane conversion were observed. It was obtained that the highest hydrogen production held in SCR of 5.

CFD investigation of nucleate boiling in non-circular geometries at high pressure

Boiling flows are commonplace in the nuclear industry. Computational Fluid Dynamics (CFD) is slowly beginning to be used to deliver the relevant two-phase thermal hydraulic analyses required for nuclear applications. This paper presents a blind assessment of the capabilities of the commercial CFD code STAR-CCM+ against measurements for a vertically upward mildly subcooled boiling flow approaching saturation in a rectangular channel at a pressure of 41bar. The available measurements comprised transverse distributions and cross-sectional area averages of void fraction at numerous axial positions along the channel. The predictive ability of several combinations of turbulence, wall heat flux partitioning, interfacial area transport and lift force models was tested. In general, good agreement was obtained for the area-averaged void, with the most mechanistic modelling combination reproducing the measurements accurately. Reasonable agreement was also observed for the distributions of transverse void, however this agreement could not be maintained beyond the channel entrance. The transition from near-wall to core void peaking exhibited in the experiments, attributable presumably to a bubbly to churn-turbulent flow regime transition, could not be reproduced accurately with any of the modelling combinations used, and the basic qualitative trend was captured only in part. Suggestions for future investigation are outlined subsequently.

Finite-volume ray tracing using Computational Fluid Dynamics in linear focus CSP applications

The modelling of solar irradiation in concentrated solar power (CSP) applications is traditionally done with ray-tracing methods, e.g. the Monte Carlo method. For the evaluation of CSP receivers, the results from ray-tracing codes are typically used to provide boundary conditions to Computational Fluid Dynamics (CFD) codes for the solution of conjugate heat transfer in the receivers. There are both advantages and disadvantages to using separate software for the irradiation and heat transfer modelling. For traditional ray-tracing methods, advantages are the cost-effectiveness of the Monte Carlo method in modelling reflections from specular surfaces; the ability to statistically assign a sun shape to the rays; the statistical treatment of reflectivity and optical errors (e.g. surface slope errors), to name a few. When considering a complex mirror field and a complex receiver with secondary reflective surfaces, especially with selective coatings to enhance absorption and limit re-radiation losses, standard ray tracers may be limited in specifying emissivity and absorptivity, which are both specular and temperature dependent, and are hence not suitable as radiation analysis tool. This type of scenario can be modelled accurately using CFD, through the finite volume (FV) treatment of the radiative transfer equation (RTE) and a banded spectrum approach at an increased computational cost. This paper evaluates the use of CFD in the form of the commercial CFD code ANSYS Fluent v15 and v16 to model the reflection, transmission and absorption of solar irradiation from diffuse and specular surfaces found in linear CSP applications. 2-D CFD solutions were considered, i.e. line concentration. To illustrate and validate the method, two sources were used. The first source was test cases from literature with published solutions and the second a combined modelling approach where solutions were obtained using both FV and ray tracing (with SolTrace). For all the test cases, good agreement was found when suitable modelling settings were used to limit both ray-effect and false scattering errors.

CFD Analysis of Aggregation and Breakage of Li-Ion Precursor in Taylor-Reactor

In this work, aggregation and breakage of Li-ion precursor in Taylor-reactor are studied for various simulation condition, i.e., agitation rate, particle property, and reactor direction. The mean particle size and distribution is important to electrochemical performance of cathode materials. The population balance equation (PBE) is solved for coupling between particle interaction and fluid dynamic. The quadrature method of moments (QMOM) is implemented in a commercial computational fluid dynamics (CFD) code. Sum of three aggregation kernels, such as turbulent, Brownian, and Stokes aggregation, is considered for the calculation. [1] Breakage kernel is a combination of power-law kernel and various daughter distribution functions. Collision efficiency is assumed to be equal and the precursor is considered as spherical particle. Three-dimensional analysis is implemented and the simulation results are compared with experimental data. [1] L. Claudotte, N. Rimbert, P. Gardin, M. Simonnet, J. Lehmann, and B. Oesterle, AIChE J., Vol.56, No.9, pp. 2347-2355 (2010)

Simulation-based determination of systematic errors of flow meters due to uncertain inflow conditions

Computational fluid dynamics (CFD) provides well-established tools for the prediction of the velocity profiles in turbulent pipe flows. As far as industrial pipe and district heating systems are concerned, combinations of elbows are the most common pipe assemblies. Among the different pipe combinations, double elbows out-of-plane are of special interest, since they introduce strong disturbances into the flow profile and have a strong influence on many common types of flow meters. In front of a double elbow there is often another flow-disturbing installation. As a result the upstream conditions are unknown and an investigation of the resulting systematic bias on the measurement of the flow rate and the associated contribution to its measurement uncertainty is necessary. We demonstrate here that this can be achieved by a variation of the inlet profile in terms of swirls and asymmetry components. In particular, an ultrasonic and an electromagnetic flow meter are modeled in order to quantify the systematic errors stemming from uncertain inflow conditions. For this purpose, a generalized non-intrusive polynomial chaos method has been used in conjunction with a commercial CFD code. As the most influential parameters on the measured volume flow, the distance between the double elbow and the flow meter as well as the orientation of the flow meter are considered as random variables in the polynomial chaos approach. This approach allowed us to obtain accurate prediction of the systematic error for the ultrasonic and electromagnetic meter as functions of the distance to the double elbow. The resulting bias in the flow rate has been found to be in the range of 1.5–4.5% (0.1–0.5%) with a systematic uncertainty contribution of 2–2.4% (0.6–0.7%) for the ultrasonic (electromagnetic) flow meter if the distance to the double elbow is smaller than 40 pipe diameters. Moreover, it is demonstrated that placing the flow meters in a Venturi constriction leads to substantial decrease of the bias and the contribution to the measurement uncertainty stemming from the uncertain inflow condition.

Development of the loss coefficient correlation for cross flow between graphite fuel blocks in the core of prismatic very high temperature reactor-PMR200

The core of the very high temperature reactor (VHTR) PMR200 (a prismatic modular reactor rated at 200MW of thermal power) consists of hexagonal prismatic fuel blocks and reflector blocks made of graphite. If the core bypass flow ratio increases, the coolant channel flow is decreased and can then lower the heat removal efficiency, resulting in a locally increased fuel block temperature. The coolant channels in the fuel blocks are connected to bypass gaps by the cross gap, complicating flow distribution in the VHTR core. Therefore, reliable estimation of the bypass flow is highly important for the design and safety analysis of the VHTR core. Because of the complexity of the core geometry and gap configuration, it is challenging to predict the flow distribution in the VHTR core. To analyze this flow distribution accurately, it is necessary to determine the cross flow phenomena, and the loss coefficient across the cross gap has to be evaluated to determine the flow distribution in the VHTR core when a lumped parameter code or a flow network analysis code that uses the correlation of the loss coefficient is employed. The purpose of this paper is to develop a loss coefficient correlation applicable to the cross gap in the PMR200 core. The cross flow was evaluated experimentally using the difference between the measured inlet and outlet mass flow rates. Next, the applicability of a commercial computational fluid dynamics (CFD) code, CFX 15, was confirmed by comparing the experimental data and CFD analysis results. To understand the cross flow phenomena, the loss coefficient was evaluated; in the high Reynolds number region, the cross flow loss coefficient on Reynolds number is nearly constant regardless of the Reynolds number, whereas it varies with the gap size in the low Reynolds number region. Finally, the loss coefficient correlation was proposed on the basis of experiments and the CFD analysis. The developed correlation was compared with existing correlations, and the developed one shows better agreement with the experimental results than the existing ones. Hence, the developed correlation will be applied to the flow network code to analyze flow distribution in the PMR200 core.

Pulsation effects on pollutant and sediment transport in free-surface flow

A series of numerical simulations are performed to study the pollutant and sediment transport in free surface channel flow. The present paper examines the dispersion of passive contaminants injected from a time periodic source in a fully developed turbulent flow. More precisely, the pulsation effects on the distribution behaviors of dissolved and particulate pollutants are analyzed and discussed. Simulations are carried out using a commercial Computational Fluid Dynamic (CFD) code, Fluent 6.3, which is based on the finite volume approach. The standard k−ε turbulence closure model is selected to simulate the turbulence generation and the Volume of Fluid (VOF) method is used to accurately capture the time varying free surface. The Discrete Phase Model (DPM) is used for capturing the movement of particles. Numerical results show that increasing pulsation amplitude and decreasing frequency generates higher dispersive effects in the concentration profiles of a dissolved pollutant. It is also concluded that, unlike dissolved substances, the particle transportation can be enhanced only for certain combinations of the pulsation amplitude and frequency due to the synchronization of the particle’s movement with the oscillating potential.•Increasing pulsation amplitude and decreasing frequency generates higher dispersive effects.•Particle transportation can be enhanced only for certain amplitude-frequency combinations.

Conceptual design of helium cooling circuit for irradiation target

Small metal specimens of about 20 mm × 20 mm and 0.4 mm thick are irradiated in cyclotron facilities for radiation damage studies. Cooling of these specimens is an important factor which decides the intensity of irradiation. In this paper helium is used for the cooling of irradiation target specimen. In order to have enhanced heat removal from the specimen jet cooling is employed. The cooling scheme and the conceptual helium cooling circuit has been arrived at based on the empirical correlation available in the literature. The heat removal rate has been estimated for various jet velocities. Experiments with impinging air jets have been carried out to compare the empirical predictions. Numerical predictions have also been carried out using commercial Computational Fluid Dynamic (CFD) code. Experimental predictions are 35%–55% higher compare to empirical correlation. The empirical correlation is 30% higher compare to CFD predictions.

Numerical investigation of in-cylinder flow characteristics of hydrogen-fuelled internal combustion engine

This paper addresses the computational fluid dynamics (CFD) simulation to investigate the in-cylinder flow characteristics of 2D combustion chamber for a hydrogen-fuelled four-stroke internal combustion engine. CFD simulation has been carried out using commercial CFD codes. The engine speed was varied from 1000 to 3000 rpm, the range of equivalent ratio from 0.6 to 1.0 and the crank angle from 0 to 720 degrees in this study. The effect of the engine speed and equivalence ratio on the flow-field characteristics and volumetric efficiency are investigated in the motoring condition. The increase of engine speed gives a more efficient diffusion process for hydrogen and gives a more homogeneous air–fuel mixture structure. The characteristics of the flow-field are represented by the in-cylinder pressure and temperature distribution as well as the contours of the hydrogen mass fraction for different engine speeds. The acquired results show the maximum in-cylinder temperature and pressure obtained of 650 K and 1.143 MPa at the engine speed of 3000 rpm respectively. It can be seen that the engine speed and equivalence ratio are strongly related to the volumetric efficiency. The results show that the volumetric efficiency increases linearly with increase of the engine speed, but decreases with increase of the equivalence ratio. The results obtained from the simulation can be employed to examine the homogeneity of the air–fuel mixture structure for a better combustion process and engine performance.

화염전달함수의 위상차를 이용한 시간지연 분석

Main purpose of the current paper is to show results of time lag analysis using phase information of flame transfer function in order to predict combustion instabilities in a gas turbine combustor. The flame transfer function (FTF) is modeled using a commercial Computational Fluid Dynamics (CFD) code (Fluent). Comparisons of the modeled flame shapes with the measured ones were made using the optimized heat transfer conditions and combustion models. The FTF modeling results show a quite good agreement with the measurement data in predicting the phase delay (i.e. time lag). Time lag analysis results using the phase of FTF shows better combustion instability prediction accuracy than using time lag calculated from the steady state flame length.

그루브의 Trap 효과에 대한 CFD 해석: 제 1부 − 그루브 단면 형상의 변화

Trap effect of groove is evaluated in a lubricating system using computational fluid dynamics (CFD) analysis. The simulation is based on the standard k-ε turbulence model and the discrete phase model (DPM) using a commercial CFD code FLUENT. The simulation results are also capable of showing the particle trajectories in flow field. Computational domain is meshed using the GAMBIT pre-processor. The various grooves are applied in order to improve lubrication characteristics such as reduction of friction loss, increase in load carrying capacity, and trapping of the wear particles. Trap effect of groove is investigated with variations in cross-sectional shape and Reynolds number in this research. Various cross-sectional shapes of groove (rectangular, triangle, U shaped, trapezoid, elliptical shapes) are considered to evaluate the trap effect in simplified two-dimensional sliding bearing. The particles are assumed to steel, and defined a single particle injection condition in various positions. The “reflect” boundary condition for discrete phase is applied to the wall boundary, and the “escape” boundary condition to “pressure inlet” and “pressure outlet” conditions. The streamlines are compared with particles trajectories in the groove. From the results of numerical analysis in the study, it is found that the cross-sectional shapes favorable to the creation of vortex and small eddy current are effective in terms of particle trapping effect. Moreover, it is found that the Reynolds number has a strong influence on the pattern of vortex or small eddy current in the groove, and that the pattern of the vortex or small eddy current affects the trap effect of the groove.

Turbulence models assessment for separated flows in a rectangular asymmetric three-dimensional diffuser

Purpose – The purpose of this paper is to present a full three-dimensional (3D) computational fluid dynamics (CFD) analysis of a rectangular asymmetric 3D diffuser utilizing seven turbulence models frequently used in engineering to assess the predictive capabilities of the turbulence models for separated flows in internal flows. Design/methodology/approach – The structured computational grids are generated by means of the mesh generation tool IGG software package. The computational grids are imported into the commercial CFD code Fluent. The performance of the different turbulence models adopted has been systematically assessed by comparing the numerical results with the available experimental and direct numerical simulation/large eddy simulations data. Findings – The comparisons show that the Reynolds stress model (RSM) evidently performs better than the other turbulence models for predicting wall pressure, velocity, and vorticity fields. Moreover, only the RSM can predict the separation bubble region around the top right corner, which is consistent with the experiment. It is found that the RSM can well predict Prandtl’s secondary flow of the second kind for considering turbulence anisotropy, whereas the other models cannot. Originality/value – The paper utilizes seven turbulence models frequently used in engineering in detailed numerical investigations of a real 3D diffuser to expand the scope of application for various turbulence models. The studies are valuable for the proper use of the turbulence models, allowing the designers to understand the numerical results further and contributing to the modification of the turbulence models for 3D flows.

Performance and Aerodynamic Attitude of KIONAS, a New Configuration of a Vertical Axis Wind Turbine

The aim of this work is to show the performance and the aerodynamic attitude of KIONAS, a new configuration of a vertical axis wind turbine. KIONAS has a stator over the rotor and the special feature that is able to consist of several stages. The stator is shaped in such a way to increase the velocity of the air which impacts the rotor blades and the performance of each stage increases with the increase of number of stages. The effects of wind velocity, the various numbers of blades of the rotor, the inclination of these blades, the rotor diameter, the stator’s shape and the number of stages on the performance on the vertical axis wind turbine were studied. A FORTRAN code was developed to solve the equations of continuity and momentum in order to predict the power on several cases. A commercial Computational Fluid Dynamics code was used to gain further knowledge on the flow field. It was concluded that for higher wind velocities and greater number of blades, more power is produced. The performance was found to be higher for a stator with curved guide vanes and for KIONAS configuration with more stages.

Effect of engine parameters on in-cylinder flows in a two-stroke gasoline direct injection engine

This paper deals with the in-cylinder flow field analysis in a two-stroke engine under motoring conditions by particle image velocimetry (PIV) and computational fluid dynamics (CFD). The main objective is to analyze the effect of engine parameters viz., engine speed, compression ratio (CR) and port orientation on the in-cylinder flows in a loop-scavenged two-stroke gasoline direct injection (GDI) engine, with an aim to help researchers to design fuel efficient and less polluting two-stroke engines. In this study, a single-cylinder 70cm3 two-stroke engine which is very commonly used for the two-wheeler application, is considered. The engine cylinder is modified to provide optical access into the in-cylinder region. The PIV experiments are conducted at various engine speeds viz., 500, 1000 and 1500rev/min, and the plane averaged velocity vector fields obtained, are analyzed to understand the in-cylinder flow behavior. The CFD study is also carried out using the commercial CFD code, STARCD, to study and compare the in-cylinder flow parameters at various engine operating conditions. The CFD results are compared with the experimental results to the extent possible. The CFD predictions are found to be in good agreement with the experimental results. Therefore, the CFD analysis has been extended further to understand the effect of various engine parameters on the in-cylinder flows. We found that the turbulent kinetic energy and tumble ratio increased by about 25% and 20% respectively, when the engine speed was increased from 1000 to 1500rev/min. Also, we found that the turbulent kinetic energy and tumble ratio decreased by about 13% and 26% when the compression ratio was increased from 7 to 8. In addition, we found that the port orientation, rather than port areas had a greater influence on the in-cylinder flow parameters.