Commercial Computational Fluid Dynamics Code Research Articles

Nuclear spent fuel cask full scope simulation using coupled Computational Fluid Dynamics models

The interest in medium to long-term nuclear spent fuel storage is growing worldwide. After being cooled during several years in the spent fuel pool, the fuel can be stored in dry casks in a second phase, being moved to a temporary repository for the mid-term and/or into a deep storage facility for the long-term. To ensure the fuel integrity, the peak cladding temperature (PCT) is a common safety parameter. The PCT can be estimated by performing simulations, and Computational Fluid Dynamics (CFD) codes have been widely used for this purpose. In this paper, the commercial CFD code ANSYS CFX 2019 R3 has been used to estimate the PCT in a generic spent fuel dry cask of 32 fuel elements.Although CFD codes are useful tools for that purpose, they also have drawbacks, mainly their computational cost to perform complex simulations. To overcome this issue, a methodology which splits the simulation in two separated but coupled models has been used, significantly reducing the required hardware. The results shown an adequate behavior of the fluid flow together with a best estimate estimation of the PCT for the most conservative thermal load of the cask.

Investigation on entropy generation and flow characteristics of 7-pin sodium cooled wrapped-wire fuel bundle

The fuel assembly of sodium-cooled fast reactor (SFR) is considered a compact heat interchanger with the intricate flow. The wire-wrapped make a great difference on the secondary flow and transverse momentum mixing. The investigations on fully developed convective heat transfer in a 7-pin fuel bundle with wrapped-wire are conducted for particular Reynolds number from 2 × 104 to 2 × 105, and heat flux at 500 to 1500 kW/m2 employing commercial computational fluid dynamic (CFD) code based on the finite volume method (FVM). The SST k-ω turbulent model and periodic boundary conditions are adopted at the inlet and outlet to obtain the fully developed fluid field and capture the detailed information in the near-wall region. The model validation and mesh independence verification are conducted, and the maximum error is 10.3%. The results are analyzed in view of sensitivities of secondary flow and thermodynamic irreversibility to mass flow rate and heat flux from the local and systemic scales by means of the entropy generation analysis approach. The axial profiles of secondary flow and entropy generation rate under different working conditions are studied. The results indicate that due to the helical structure of the wrapped-wire, the secondary flow, and entropy generation present similar periodical fluctuation and symmetric distributions in axial direction. Also, the secondary flow enhance has an impact on the heat transfer. The thermal irreversibility is also analyzed, and the result shows that heat conduction is the leading cause of the irreversible losses. Ep decreases with the Reynolds number, and increases with heat flux, which means the better thermal economic performance occurs at lower velocity and higher heat flux.

Validation of the gamma text{-Re }_{theta } Transition Model for Airfoils Operating in the Very Low Reynolds Number Regime

Micro Aerial Vehicles (MAVs) are state of the art in the aerospace industry and are involved in many operations. The reduced dimensions of these vehicles generate very low Reynolds number conditions in which separation-induced transition typically occurs. The extremely large computational cost of scale resolving simulations, which are capable of capturing laminar to turbulent transition, is prohibitive for most engineering and design applications. Therefore, it becomes very interesting to couple transition models with conventional Reynolds Averaged Navier–Stokes (RANS) simulations to allow the prediction of transition to turbulence at a reduced computational cost. This paper performs an investigation of the application of the gamma text{-Re }_{theta } transition model analysing different empirical correlations available in literature and studying the influence of the relevant model parameters using the commercial Computational Fluid Dynamics (CFD) code STAR-CCM+. The flow around the Eppler 387, Selig/Donovan 7003 and Ishii airfoils has been studied for different Reynolds numbers and angles of attack comparing the drag and lift forces and separation bubble characteristics with experimental and numerical results reported in literature.

Entrainment effects on combustion characteristics of various syngases using a perforated burner

This study concentrates on entrainment effects to achieve distributed regime for different syngas compositions (coke oven gas, biogas, and blast-furnace gas). For this purpose, numerical modeling has been performed through a computational fluid dynamics commercial code. In the modeling, The PDF/Mixture Fraction combustion model, standard k-ℇ turbulence model, and P-1 radiation model have been selected to be used. Entrainment without decreasing oxygen concentration in air was provided from the flame holder wall of the newly generated burner at 10%, 20%, and 30% entrainment rates. For only coke oven gas, oxygen concentration was reduced to 15% O2 with the entrainment in order to achieve ultra-low pollutant emissions level. The results showed that the temperature distributions were achieved more uniform for all cases. The flame zones became more thinner for all cases studied. This provided more invisible or colorless flame appearance, and as a result of this, more uniform thermal field was achieved without substantial decrease in combustion performance. Namely, the temperature values between the outlet temperatures for all entrainments have been close to each other (about 1200–1300 K). In terms of evaluation of distributed regime achievement on NOX and CO pollutant emission levels, one can say that ultra-low emission levels (less than 1 ppm) were achieved with entrainment effects without decrease in oxygen concenration in air excluding coke oven gas. Distributed regime could be achieved at lower oxygen concentration with entrainment for coke oven gas combustion.

Hydrothermal performance of humid air flow in a rectangular solar air heater equipped with V‐shaped ribs

AbstractIn this numerical work, heat transfer characteristics of humid air in a rectangular channel as solar air heater equipped with V‐shaped ribs has been investigated. The impacts of geometrical parameters of proposed ribs such as height, pitch, and angle relative to air flow direction, as well as relative humidity and Reynolds number of inlet humid air on thermal performance of proposed solar air heater have been evaluated. The numerical results have been achieved using commercial Computational Fluid Dynamics (CFD) code, ANSYS FLUENT 18.2, which works based on finite volume method. Outcomes shows that, over a wide range of operating conditions, utilizing ribs cause thermal boundary layer to separate and reattach, and eventually enhance heat transfer rate. Increasing the rib angle produces stronger secondary flows, leading to higher local velocities and greater heat transfer rate. Moreover, increasing the relative humidity of inlet air from 0% to 50% leads to improve heat transfer by up to 6%. As Reynolds number increases from 4000 to 12,000, average Nusselt number rises by 7.3% and 31.4% for rib pitches of 6 and 16 mm, respectively. The results demonstrate how thermal performance of a solar air heater can be improved by utilizing V‐shaped ribs.

Design Optimization of a Cross-Flow Air Turbine for an Oscillating Water Column Wave Energy Converter

A cross-flow air turbine, which is a self-rectifying, air-driven turbine, was designed and proposed for the power take-off (PTO) system of an oscillating water column (OWC) wave energy converter (WEC). To predict the complicated non-linear behavior of the air turbine in the OWC, numerical and experimental investigations were accomplished. The geometries of the nozzle and the rotor of the turbine were optimized under steady-flow conditions, and the performance analysis of the model in bi-directional flows was conducted by commercial computational fluid dynamics (CFD) code ANSYS CFX. Experimentation on the full-scale turbine was then undertaken in a cylindrical-type wave simulator that generated reciprocating air flows, to validate the numerical model. The optimized model had a peak cycle-averaged efficiency of 0.611, which is 1.7% larger than that of the reference model, and a significantly improved band width with an increase in flow coefficients. Under reciprocating-flow conditions, the optimized model had a more improved operating range with high efficiency compared to the performance derived from the steady-flow analysis, but the peak cycle-averaged efficiency was decreased by 4.3%. The numerical model was well matched to the experimental results with an averaged difference of 3.5%. The proposed optimal design having structural simplicity with high performance can be a good option to efficiently generate electricity.

Comparison of Pressure Distribution of Naca 0012 Between CFD Code and Experimental

Computational Fluid Dynamics (CFD) is a tool to solve engineering problem. Commercial CFD code are being used most engineering problem but rarely for external aerodynamic problem due some limitation of features. Compare to in house CFD code that able to written in certain area of interest and also implement specific discretization scheme to increase accuracy. In this work, the CFD code are developed by using high resolution scheme (ROE scheme and TVD scheme) for flow past through airfoil NACA 0012. Experimental result of wind tunnel is obtained from literature which are from Gregory and O’Reilly at Mach number M = 0.13 for different values of angle of attack at α= 0° and α = 10°. Another wind tunnel result from Haris at Mach number = 0.8 for different angles of attack α= 0° and α= 3.86°. Comparison results from the both codes indicate that developed CFD code by using TVD scheme able to give the closest result for both experimental.

A Comparison of Computational and Experimental Fluid Dynamics Studies between Scaled and Original Wing Sections, in Single-Phase and Two-Phase Flows, and Evaluation of the Suggested Method

The correlation between computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) is crucial for the behavior prediction of aerodynamic bodies. This paper’s objective is twofold: (1) to develop a method that approaches commercial CFD codes and their link with EFD in a more efficient way, using a downscaled model, and (2) to investigate the effect of rain on the aerodynamic behavior of a wing. More specifically, we investigate the one-phase and two-phase flow over a typical wing section NACA 641-212 airfoil, in the commercial code Ansys Fluent. Two computational models were developed; the first model represents the original dimensions of the wing, while the second is downscaled to 23% of the original. The response of the models in air and air–water flow were primarily studied, as well as the impact on aerodynamic efficiency due to the existence of the second phase. For the computational fluid dynamics simulations, a pressure-based solver with a second-order upwind scheme for the spatial discretization and the Spalart–Allmaras (SA) turbulence model were utilized. Meanwhile, for the two-phase flow of air–water, the discrete phase model (DPM) with wall–film boundary conditions on the surface of the wing and two-way coupling between continuous and discrete phase was considered. The second phase was simulated as water droplets injected in the continuous phase, in a Euler–Lagrange approach. The experimental model was constructed in accordance with the downscaled model and tested in a subsonic wind tunnel, using 3D printing technology which reduced the experiment expenses. The presence of water in two-phase flow was proven to deteriorate the aerodynamic factors of the wing compared to one-phase flow, as expected. The three-stage comparison of CFD and EFD results showed a very good convergence, in both single and two-phase flow. This can lead to the conclusion that a rapid and low-cost study for the estimation of the aerodynamic performance of objects with high accuracy is feasible with the suggested method.

Atmospheric Flow at Alcantara Launch Center

The Alcantara Launch Center (ALC) is the main Brazilian access to space. It is positioned over a complex terrain, and it has some important buildings for assembling, integration and launching activities, such as the Mobile Integration Tower. Being in a region of prevalent trade winds, the flow interaction between the complex terrain and the buildings can affect the safety of operations on the platform, and the dispersion of toxic gases emitted during the launching. The main objective of this work was to study the influence of topography and buildings on the atmospheric flow of ALC using computational fluid dynamics (CFD) techniques. Three geometries were considered: simplified terrain (case 1), smooth complex terrain (case 2), and roughness complex terrain (case 3). The flow conditions over ALC were simulated using the ANSYS Fluent 19.0 CFD commercial code. The numerical simulations used a realizable ?-? to model turbulence effects and the results presented a good agreement with the in-situ field measurements for the most complex geometry (case 3). The topography clearly influences the flow pattern at ALC, with the cliff influence over the wind being the major cause for establishing the flow patterns.

CFD Simulation of Solid and Non-Newtonian Fluid Two-Phase Flow in Anaerobic Digesters

A CFD model is used to study solid suspension in anaerobic digesters.Simulations of solid and non-Newtonian fluid two-phase flow are performed.Minimum impeller speed for avoiding solid accumulation in the digester is proposed.Major issues arising from the simulation results are discussed.Abstract. A principal goal of solid-liquid flow modelling is to predict the minimum power consumption for avoiding solid accumulation in stirred reactors. In this study, a computational fluid dynamics (CFD) technique was used to characterize solid suspension in anaerobic digesters with mechanical mixers where the liquid phase exhibited non-Newtonian fluid behavior. The commercial CFD code Fluent 16.0 was utilized to solve the multiphase flow. The impeller torque and cloud height as a function of impeller speed in a small tank were validated against the experimental data from the literature. The simulation results demonstrate that the impeller torques from CFD modeling match perfectly with those from measurements, and that the predicted cloud heights agree reasonably well with the measured ones. The solid-liquid flow in a large egg-shaped digester with a mechanical draft tube mixer was modeled where the impeller speed ranged from 400 to 750 rpm at 50 rpm increments. A combination of tangent line and uniformity index methods was used to predict the minimum impeller speed to maintain solid suspension in the digester. Moreover, the major issues arising from results were discussed. Keywords: Anaerobic digester, Computational fluid dynamics, Multiphase flow, Non-Newtonian fluid, Solid suspension.

CFD Analysis of the removal process of residual carbon

Recently, the need of renewable energy is significantly increasing by carbon neutral, the demand of silicon wafers is also increasing as a result of growth of the solar energy industry. However, the recycling technology of silicon sludge is needed because a large amount of waste silicon sludge is generated from the silicon wafer manufacturing process. Many researches have been studied to convert the silicon component contained in the silicon sludge to silicon carbide (SiC). SiC powder can be synthesized using silicon sludge by heat treatment with carbon addition. Therefore, the removal process of residual carbon is required because the excess carbon is generally used to maximize the SiC conversion rate. In this work, computational fluid dynamic (CFD) analysis of the removal process of residual carbon has been studied by using the commercial CFD code ANSYS FLUENT.

Experimental and Numerical Investigation of Flow Field and Soot Particle Size Distribution of Methane-Containing Gas Mixtures in a Swirling Burner.

The formation of soot in a swirling flow is investigated experimentally and numerically in the context of biogas combustion using a CO2-diluted methane/oxygen flame. Visualization of the swirling flow field and characterization of the burner geometry is obtained through PIV measurements. The soot particle size distributions under different fuel concentrations and swirling conditions are measured, revealing an overall reduction of soot concentration and smaller particle sizes with increasing swirling intensities and leaner flames. An axisymmetric two-dimensional CFD model, including a detailed combustion reaction mechanism and soot formation submodel, was implemented using a commercial computational fluid dynamics (CFD) code (Ansys Fluent). The results are compared with the experiments, with similar trends observed for the soot size distribution under fuel-lean conditions. However, the model is not accurate enough to capture soot formation in fuel-rich combustion cases. In general, soot particle sizes from the model are much smaller than those observed in the experiments, with possible reasons being the inappropriate modeling in Fluent of governing mechanisms for soot agglomeration, growth, and oxidation for CH4-CO2 mixtures.

DETERMINATION OF DRAG AND LIFT RELATED COEFFICIENTS OF AN AUV USING COMPUTATIONAL AND EXPERIMENTAL FLUID DYNAMICS METHODS

Determination of hydrodynamic coefficients is a vital part of predicting the dynamic behavior of an Autonomous Underwater Vehicle (AUV). The aim of the present study was to determine the drag and lift related hydrodynamic coefficients of a research AUV, using Computational and Experimental Fluid Dynamics methods. Experimental tests were carried out at AUV speed of 1.5 m s-1 for two general cases: I. AUV without control surfaces (Hull) at various angles of attack in order to calculate Hull related hydrodynamic coefficients and II. AUV with control surfaces at zero angle of attack but in different stern angles to calculate hydrodynamic coefficients related to control surfaces. All the experiments carried out in a towing tank were also simulated by a commercial computational fluid dynamics (CFD) code. The hydrodynamic coefficients obtained from the numerical simulations were in close agreement with those obtained from the experiments.

Design optimization of a novel vertical augmentation channel housing a cross-flow turbine and performance evaluation as a wave energy converter

A novel vertical augmentation channel housing a direct-drive cross-flow turbine, with nozzles on both the sides of the turbine, was designed and an optimized configuration was obtained. The geometries of the guide nozzle and the front nozzle were optimized under steady flow conditions. The performance of the cross-flow turbine was analyzed using commercial computational fluid dynamics (CFD) code ANSYS-CFX. The optimized design was then evaluated as a wave energy converter both experimentally and computationally. The waves in the numerical wave tank (NWT) were generated using a piston type wave-maker. The optimized design gave a maximum output power of 13.2 W and an efficiency of 48.31% at a wave height of 0.2 m and wave period of 2.75 s for a rotational speed of 35 rpm. The difference between numerical and experimental efficiencies was within 3.5%. In addition to this, particle image velocimetry was used to study the flow characteristics in the augmentation channel and the turbine. The results show that the CFD code captures the flow in the augmentation channel and around the turbine accurately. The optimized design, which occupies less space than other wave energy converters, can be used to efficiently harness energy from the waves.

CFD-PBE coupled model for size-driven segregation in polydisperse granular flows

Mixtures of granular materials made of different-sized particles may segregate when subjected to vibration or shear rate and in the presence of a gravitational field. This leads to highly inhomogeneous mixtures, which are undesirable in many industrial processes. This work focuses on size-driven segregation in polydisperse mixtures. We described the evolution of the particle size distribution through a Population Balance Equation (PBE), which we solved numerically with the Direct Quadrature Method of Moments. To allow segregation and micromixing to occur, we closed the size-conditioned velocity of the particles with a segregation-remixing model. The PBE was then included in an Eulerian-Eulerian model and solved in a commercial Computational Fluid Dynamics (CFD) code. We used the model to study granular flows down inclined planes. The numerical results were then compared with those obtained from Discrete Element Method simulations. The CFD-PBE model predicts well segregation and micromixing in packed beds of polydisperse powders.

Combining CFD, ASE, and HEKF approaches to derive all of the hydrodynamic coefficients of an axisymmetric AUV

In this proposed method, which is based on combination of the nonlinear Hybrid Extended Kalman Filter (HEKF) observer, Analytical and Semi-Empirical (ASE) formulas, and Computational Fluid Dynamics (CFD) simulations, all of the hydrodynamic coefficients of a REMUS AUV are estimated to simulate its motions in 6 Degrees of Freedom (6-DoF). First, Using ASE formulas along with necessary static simulations of the AUV using commercial CFD code of ANSYS CFX software, some hydrodynamic derivatives like drag, lift, and fin coefficients are obtained. Then, utilizing the dynamic simulation of the Straight-Line Test (SLT), the longitudinal added mass coefficient is derived. Finally, benefiting from the HEKF code based on the parameter identification, other unknown coefficients like added mass and damping are estimated in the MATLAB software environment. In HEKF, positions and velocities of the vehicle, which are the system output vector, are obtained from a 6-DoF dynamic maneuver in CFX. It is worth mentioning that, in the present study, the remeshing algorithm in the dynamic mesh approach is used to simulate the dynamic maneuvers of the vehicle. Results, obtained from the proposed combined method, indicate a good agreement for estimated coefficients in comparison with the available analytical and experimental values.

Effect of inlet/outlet on thermal performance of naturally ventilated building

Abstract Ventilation is a way of improving the air quality of rooms by circulation. The position of the inlet and outlet greatly influences the thermal comfort. This attempt proposes to analyse the effect of the position of window openings for a room building with natural ventilation and the air flow and temperature distribution numerically using a commercial computational fluid dynamics (CFD) code. This proposed study consists of (i) approving the numerical model against experimental data gathered in an environment similar to the one used in simulations and (ii) applying the CFD model to explore the results of four varying configurations of ventilator on the natural ventilation system and thermal comfort. For the varying arrangements, the wind speed is 0.2 m⋅s−1 perpendicular to the openings for a wind, (iii) evaluating the comfort level utilizing the Air Diffusion Performance Index (ADPI) on the basis of ASHRAE 55-210 criteria. The obtained results show that the positions of outlet and inlet openings highly affect the performance in the thermal comfort while they have a trivial effect on the occupied zone mean velocity. The computational results showed that the two cases (a) and (b) present results very close to each other with a slight difference at the center of the chamber. Most of the calculated values (effective draft temperature, EDT) are between (−1.7 and 1.1). Then ADPI is over 70% for case (a) and over 75% for case (b), so all points they are located in the comfort zone. The results affirmed also that configuration with inlet openings set at 1.022 m above ground and an outlet opening set at 0.52 m brings about the most applicable solution ventilation efficiency and give the best EDT that fulfills the criteria of ASHRAE 55-210 with an ADPI of ~90%.

Numerical study of a swirl gas turbine combustor for turbulent air and oxy-combustion of ammonia/kerosene fuels

Since ammonia has a carbon-free substance and involves hydrogen atoms per volume unit, many scientists think it could be used as an alternative fuel instead of natural gas or kerosene-based fuels in gas turbine combustors. The main goal of this study is to investigate turbulent swirl combustion ammonia-assisted kerosene fuels with air and pure oxygen combustion conditions in a model gas turbine combustor. For this purpose, numerical modelings have been performed by using a commercial computational fluid dynamics (CFD) code. Ammonia was introduced into the combustor from the different inlets. The ammonia composition was determined until 70% kerosene-30% ammonia mixture in an interval of 10% by heat fraction. During this addition, the total heat load provided was kept constant. The results showed that there was no considerable change over the combustion performance of kerosene. However, the maximum temperature levels and its locations changed somewhat in the combustor with ammonia addition. In addition to temperature distributions of kerosene and ammonia-assisted kerosene fuels, NOX emission levels have been addressed by performing post-processing of the CFD code used in this study. According to the predicted NOX levels, it was seen that the predicted NOX emissions levels increased significantly in the high temperature flame zone due to bound-nitrogen in ammonia (fuel-NOX mechanism). But, the predicted NOx emission levels were not too high at the exit of the combustion chamber. Therefore, it can be concluded that ammonia-assisted kerosene fuels have considerable potential in terms of combustion performance as a new and renewable fuel.

Effect of Rain on the Aerodynamic Performance of a Horizontal Axis Wind Turbine – A Computational Study

This paper analyzes numerically the impact of rainfall on the aerodynamic performance of a three-bladed Horizontal Axis Wind Turbine, with blades constructed by NACA 4418 airfoil. The simulations were conducted by the help of the commercial Computational Fluid Dynamics code, ANSYS Fluent. Firstly, the optimum geometry of the blade was designed with an application based on Blade Element Momentum theory. The Moving Reference Frame Model was applicated to simulate the rotation of the blades and the k-ω shear-stress transport turbulence model was added as well. The simulation of rain was accomplished by the Discrete Phase Model and the Taylor Analogy Breakup model was enabled to simulate droplets breakup. Three different rainfall conditions were studied, corresponding to Liquid Water Contents of 10g/m³, 30g/m³ and 60g/m³. The influence of droplet diameter on the aerodynamic performance of the blade was also examined. The results showed that the aerodynamic performance of the wind turbine is degraded in rain conditions, and the degradation is greater for higher values of Liquid Water Content and for larger diameter of water droplets.

CFD investigation of a JAEA 7-pin fuel assembly experiment with local blockage for SFR

Three-dimensional structures of a vortical flow field and heat transfer characteristics in a partially blocked 7-pin fuel assembly mock-up of sodium-cooled fast reactor have been investigated through a numerical analysis using a commercial computational fluid dynamics code, ANSYS CFX. The simulation with the SST turbulence model agrees well with the experimental data of outlet and cladding wall temperatures. From the analysis on the limiting streamline at the wall, multi-scale vortexes developed in axial direction were found around the blockage. The vortex core has a high cladding wall temperature, and the attachment line has a low cladding wall temperature. The small-scale vortex structures significantly enhance the convective heat transfer because it increases the turbulent mixing and the turbulence kinetic energy. The large-scale vortex structures supply thermal energy near the heated cladding wall surface. It is expected that control of the vortex structures in the fuel assembly plays a significant role in the convective heat transfer enhancement. Furthermore, the blockage plate and grid spacer increase the pressure drop to about 36% compared to the bare case.