Commercial Computational Fluid Dynamics Code Research Articles

Investigation of opening position and shape on the natural cross ventilation

A three dimensional computational fluid dynamics (CFD) model is presented to investigate effective parameters on cross ventilation and air flow pattern inside a building. The numerical methodology is based on the finite volume numerical solution of the Navier–Stokes equations, using the CFD commercial code FLUENT. Numerical results are validated with available experimental data. Different opening position and shape configurations are used to investigate effect of position and shape of openings on the flow pattern inside the building. It is shown that openings can determine behavior of flow stream inside the building and designers can use them to increase natural ventilation efficiency of the building and control the recirculation zones which are formed in different rooms.

Numerical investigation of incompressible fluid flow and heat transfer across a bluff body in a channel flow

The Lattice Boltzmann Method is applied to computationally investigate the laminar flow and heat transfer of an incompressible fluid with constant material properties in a two-dimensional channel with a built-in bluff body. In this study, a triangular prism is taken as the bluff body. Not only the momentum transport, but also the energy transport is modeled by the Lattice Boltzmann Method. A uniform lattice structure with a single time relaxation rule is used. For obtaining a higher flexibility on the computational grid, interpolation methods are applied, where the information is transferred from the lattice structure to the computational grid by Lagrange interpolation. The flow is investigated for different Reynolds numbers, while keeping the Prandtl number at the constant value of 0.7. The results show how the presence of a triangular prism effects the flow and heat transfer patterns for the steady-state and unsteady-periodic flow regimes. As an assessment of the accuracy of the developed Lattice Boltzmann code, the results are compared with those obtained by a commercial Computational Fluid Dynamics code. It is observed that the present Lattice Boltzmann code delivers results that are of similar accuracy to the well-established Computational Fluid Dynamics code, with much smaller computational time for the prediction of the unsteady phenomena.

High performance hydraulic design techniques of mixed-flow pump impeller and diffuser

In this paper, we describe a numerical study about the performance improvement of a mixed-flow pump by optimizing the design of the impeller and diffuser using a commercial computational fluid dynamics (CFD) code and design-of-experiments (DOE). The design variables of impeller and diffuser in the vane plane development were defined with a fixed meridional plane. The design variables were defined by the vane plane development, which indicates the blade-angle distributions and length of the impeller and diffuser. The vane plane development was controlled using the blade-angle in a fixed meridional plane. The blade shape of the impeller and diffuser were designed using a traditional method in which the inlet and exit angles are connected smoothly. First, the impeller optimum design was performed with impeller design variables. The diffuser optimum design was performed with diffuser design variables while the optimally designed impeller shape was fixed. The importance of the impeller and diffuser design variables was analyzed using 2k factorial designs, and the design optimization of the impeller and diffuser design variables was determined using the response surface method (RSM). The objective functions were defined as the total head (Ht) and the total efficiency (?t) at the design flow rate. The optimally designed model was verified using numerical analysis, and the numerical analysis results for both the optimum model and the reference model were compared to determine the reasons for the improved pump performance. A pump performance test was carried out for the optimum model, and its reliability was proved by a comparative analysis of the results of the numerical analysis and an experiment using the optimum model.

Heat Storage Performance of a Honeycomb Ceramic Monolith

Honeycomb ceramic is the key component of the regenerative system. The three-dimensional numerical model has been established for 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 regenerative process of a honeycomb ceramic regenerator was simulated under different conditions. The results under different flow rates, different flowing time, different materials and different wall thickness were investigated. The work in this paper 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.

Predictions of Flow Separation at the Valve Seat for Steady-State Port-Flow Simulation

Steady-state port-flow simulations with static valve lift are often utilized to optimize the performance of intake system of an internal combustion engine. Generally, increase in valve lift results in higher mass flow rate through the valve. But in certain cases, mass flow rate can actually decrease with increased valve lift, caused by separation of turbulent flow at the valve seat. Prediction of this phenomenon using computational fluid dynamics (CFD) models is not trivial. It is found that the computational mesh significantly influences the simulation results. A series of steady-state port-flow simulations are carried out using a commercial CFD code. Several mesh topologies are applied for the simulations. The predicted results are compared with available experimental data from flow bench measurements. It is found that the flow separation and reduction in mass flow rate with increased valve lift can be predicted when high mesh density is used in the proximity of the valve seat and the walls of the intake port. Higher mesh density also gives better predictions of mass flow rate compared to the experiments, but only for high valve lifts. For low valve lifts, the error in predicted flow rate is close to 13%.

Assessment of RVACS performance for small size lead-cooled fast reactor

Reactor Vessel Air Cooling System (RVACS), adopted by China Lead-based Research Reactor (CLEAR-I), was considered as a promising solution to passively remove the decay heat under accident conditions. In order to assess CLEAR-I RVACS performance, the investigation of CLEAR-I RVACS performance has been conducted by using the RELAP5 code. The RELAP5 model of CLEAR-I RVACS was established and verified by comparison with three-dimensional computational fluid dynamics commercial code CFX calculation. The maximum heat removal capability of CLEAR-I RVACS was investigated. Several design parameters, such as presence of air cool tubes, vessel size and chimney height, have been studied to evaluate their effect on the heat removal capability. It is suggested that CLEAR-I RVACS had the capability to remove the CLEAR-I decay heat and could apply for the 25MW pool type fast reactors as an independent decay heat removal system. The heat removal capability of the RVACS with air channel was 7.5% bigger than that of the RVACS with air tubes for the same main vessel and air thermal cycle. A 10m increase in chimney height resulted in a 5°C decrease in the main and safety vessel temperatures. A 10% increase in the whole size of CLEAR-I RVACS resulted in a 20°C decrease in the main and safety vessel temperatures.

DESIGN AND FLOW SIMULATION OF TRUNCATED AEROSPIKE NOZZLE

Aerospike nozzles are being considered in the development of the Single Stage to Orbit launching vehicles because of their prominent features and altitude compensating characteristics. This paper presents the design of aerospike nozzles using characteristic method in conjunction with streamline function, and performance study through numerical simulation using commercial Computational Fluid Dynamics (CFD) code ANSYS FLUENT. For this purpose nozzles with truncation lengths of 25%, 40%, 50% are choosen, because of the thermal and structural complications in the ideal aerospike nozzle. Simulation of the flow is carried out at three different altitude conditions representing Under-expansion, Ideal, and over-expansion conditions of the flow. FLUENT predictions were used to verify the isentropic flow assumption and that the working fluid reached the design exit Mach number. The flow-fields obtained through the numerical simulation are analysed to know the effect of truncation on the performance of aerospike nozzle. Optimum percentage of the truncation is selected by the comparison of nozzles with different lengths of truncation under various altitude parameters. The results show that the flow pattern of the nozzles under different altitude conditions are almost similar. The 40 % truncated nozzle is found to give optimum performance and it has achieved the desired exit Mach number in all the three altitude conditions.

Surface Texturing한 평행 스러스트 베어링의 열유체윤활 해석: 딤플 반경과 깊이의 영향

School of Mechanical Engineering, ERI, Gyeongsang National University(Received July 19, 2014 ; Revised August 20, 2014 ; Accepted August 22, 2014)Abstract − In order to reduce friction and improve reliability, researchers have applied various surface texturingmethods to highly sliding machine elements such as mechanical seals and piston rings. Despite extensive the-oretical research on surface texturing, previous numerical results are only applicable to isothermal and iso-vis-cous conditions. Because the lubricant flow pattern of textured bearing surfaces is much more complicated thanthat for non-textured bearings, the Navier?Stokes equation is more suitable than the Reynolds equation for theformer. This study carries out a thermohydrodynamic (THD) lubrication analysis to investigate the lubricationcharacteristics of a single micro-dimpled parallel thrust bearing cell. The analysis involves using the continuity,Navier?Stokes, energy, temperature?viscosity relation, and heat conduction equations with the commercial com-putational fluid dynamics (CFD) code FLUENT. This study discretizes these equations using the finite volumemethod and solves them using the SIMPLE algorithm. The results include finding the streamlines, pressure andtemperature distributions, and variations in the friction force and leakage for various dimple radii and depths.Increasing the dimple radius and decreasing the depth causes a recirculation flow to form because of a strongvortex, and the oil temperature greatly increases compared with the non-textured case. The present numericalscheme and results are applicable to THD analysis of various surface-textured sliding bearings and can lead tofurther study. Keywords − dimple (딤플), friction reduction (마찰저감 ), parallel thrust bearing (평행 스러스트 베어링 ), surfacetexturing (표면조직가공), thermohydrodynamic lubrication (열유체윤활)

CFD analysis of solar tower Hybrid Pressurized Air Receiver (HPAR) using a dual-banded radiation model

Solar receivers used for central tower Concentrated Solar Power (CSP) plants 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). For a solarized gas-turbine application, pressurized air from the compressor is used as heat transfer fluid (HTF) in order to increase both the density and heat capacity of the HTF. If a volumetric receiver is used, it 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. A tubular-type volumetric receiver (named a Hybrid Pressurized Air Receiver (HPAR)) is studied here. The HPAR provides the challenge of enabling maximum heat transfer without causing hot spots on the side of the solar irradiation source. Heat transfer in the HPAR would not be as effective as for a true volumetric receiver because the heat transfer area is limited by the tube wall. The heat transfer to the HTF is however enhanced through mixing generated by external forced convection caused by suction due to a downstream fan in the receiver cavity. In addition, the aperture of the cavity contains a glass windowed louver system, to limit re-radiation losses. 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. A numerical validation is performed to illustrate mesh dependency and the choice of turbulence model. The incoming solar irradiation and its absorption, reflection and transmission are modeled using the Discrete Ordinates (DO) radiation model in ANSYS Fluent. An idealized and a solar flux map based on the PS10 field are used as source. For comparison, both a gray (without a glass louver) and a semi-gray two-banded DO approach are used when modeling the absorption of high-wavelength re-radiation by the glass in front of the aperture. This two-banded approach is also applied to investigate the influence of a band-selective absorber tube and cavity surfaces. The DO model also predicts the emission of thermal re-radiation from all surfaces. The geometry is parameterized in order to allow for various cavity layouts to be automatically generated. 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 for single and dual-band radiation.

Quantitative Computational Fluid Dynamic Analyses of Particle Deposition on a Transonic Axial Compressor Blade—Part II: Impact Kinematics and Particle Sticking Analysis

In heavy-duty gas turbines, the microparticles that are not captured by the air filtration system can cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic (CFD) code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase model were previously validated by the authors in the first part of this work. The kinematic characteristics (velocity and angle) of the impact of micrometric and submicrometric particles with the blade surface of an axial transonic compressor are shown. The blade zones affected by particle impact were extensively analyzed and reported in the first part of this work, forming the starting point for the analyses shown in this paper. The kinematic analysis showed a high tendency of particle adhesion on the suction side (SS), especially for the particles with a diameter equal to 0.25 μm. Fluid dynamic phenomena and airfoil shape play a key role regarding particle impact velocity and angle. This work has the goal of combining, for the first time, the kinematic characteristics of particle impact on the blade with fouling phenomenon by the use of a quantity called sticking probability (SP) adopted from literature. From these analyses, some guidelines for a proper management of the power plant (in terms of filtration and washing strategies) are highlighted.

Quantitative Computational Fluid Dynamics Analyses of Particle Deposition on a Transonic Axial Compressor Blade—Part I: Particle Zones Impact

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the microparticles that are not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side (PS). The suction side (SS) is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, stagnation point, and tip leakage vortex, strongly influence the impact location of the particles.

Towards a more sustainable transport sector by numerically simulating fuel spray and pollutant formation in diesel engines

Diesel engines account for approximately 50% of new passenger-car sales in the European market and are the major contributor to pollutants that adversely affect human health and the environment. The most adverse pollutants emitted by the combustion of diesel fuel are NOx, soot, CO and HC. Numerous studies have been carried out to determine the influence of engine design, fuel injection, fuel-air mixing and combustion on pollutant emissions. Information gained through experimental research of in–cylinder processes is limited, and the body of knowledge can be improved by the use of numerical modelling and computer simulations. Computational Fluid Dynamics (CFD) has become a valuable tool that decreases the time and the cost of experimental research. Therefore, CFD is being increasingly used in development of combustion systems. This paper presents how the development of CFD models is the proper approach towards achieving a cleaner and more sustainable transportation sector. The physical models for the liquid fuel disintegration, evaporation and pollutant formation are used and implemented into the commercial CFD code FIRE. The models are capable of predicting complex in–cylinder processes and, ultimately, the formation of pollutant emissions. The results from numerical simulations, such as NOx and soot concentrations, in–cylinder pressure and temperature are found to be in good agreement with the existing experimental data.

Numerical Investigations of Quenching Cooling Processes for Different Cast Aluminum Parts

In this paper, discussions of a recently improved Computational Fluid Dynamics (CFD) methodology for virtual experimental investigation of the heat treatment for cast aluminium parts are presented. The immersion quenching process of the heated work piece in a sub-cooled liquid pool is handled by employing the Eulerian multi-fluid modelling approach, which is implemented within the commercial CFD code AVL FIRE®. The applied heat and mass transfer rates are modelled based on the different boiling regime, which is controlled by the Leidenfrost temperature. The objective of the present research is to present an updated quenching model where variable Leidenfrost temperature is applied. Furthermore, simulation results are compared with available measurements for a wide variety of quenching scenarios involving immersion cooling of the step plate and real cylinder head with different solid parts orientations. The temperature histories predicted by the presented model fit very well with the available experimental data at different monitoring locations ©2014 Journal of Mechanical Engineering. All rights reserved.

Solid circulation characteristics of the three-reactor chemical-looping process for hydrogen production

The three-reactor chemical-looping (TRCL) system for high purity hydrogen production and intrinsic CO2 separation is an innovative concept using a circulating oxygen carrier. The process employs iron oxide as an oxygen carrier, via which a redox reaction takes place alternately within three reactors, i.e. a fuel reactor (FR), where the natural gas is combusted to CO2 and H2O, a steam reactor (SR), where the steam is reduced to hydrogen, and an air reactor (AR), where the oxygen carrier returned to its original form by aeration. As it consists of three reactors (AR, FR, and SR) and a riser, the TRCL system has complicated hydrodynamic characteristics.In this study, a cold mode TRCL system with non-mechanical valve was designed and constructed to investigate the solid circulation characteristics. A series of hydrodynamic tests on the system was performed in which zirconia (d¯ρ=181μm, ρs = 3850 kg/m3) was used as a bed material. The solid flow rate increased up to a maximum value with increasing gas velocity into the loop-seal. The gas leakages between AR and FR, and between FR and SR due to solid circulation were negligible. Furthermore, a two-dimensional (2D) computational fluid dynamics (CFD) simulation using a commercial CFD code was carried out in order to better understand the flow behavior of the gas solid mixture inside the TRCL system.

Application of the computational method for predicting NOx reduction within large scale coal-fired boiler

Constantly increase popularity of the reburning process for reduction of NOx emission, forces to investigate the impact of reburning process on the combustion conditions within the large scale industrial pulverized coal (PC) boiler. For that purpose the constantly developed numerical tools, like the Computational Fluid Dynamic (CFD) can be used. Presented paper shows the usability of the combustion of sewage sludge gasification gas within the retrofitted PC boiler for reduction of the NOx emission. In presented level of model complexity no modifications to the boiler construction for reburning process have been introduced. Evaluated results have been compared with specified limitation and requirements posted to the reburning technology in large scale industrial boilers. Presented paper should be seen as a case study where different location of the syngas injection ports and syngas proportion have been investigated. Moreover, the usability of NOx emission model from commercial CFD code has been presented.

CFD analysis of bubble hydrodynamics in a fuel reactor for a hydrogen-fueled chemical looping combustion system

This study investigates the temporal development of bubble hydrodynamics in the fuel reactor of a hydrogen-fueled chemical looping combustion (CLC) system by using a computational model. The model also investigates the molar fraction of products in gas and solid phases. The study assists in developing a better understanding of the CLC process, which has many advantages such as being a potentially promising candidate for an efficient carbon dioxide capture technology.The study employs the kinetic theory of granular flow. The reactive fluid dynamic system of the fuel reactor is customized by incorporating the kinetics of an oxygen carrier reduction into a commercial computational fluid dynamics (CFD) code. An Eulerian multiphase treatment is used to describe the continuum two-fluid model for both gas and solid phases. CaSO4 and H2 are used as an oxygen carrier and a fuel, respectively. The computational results are validated with the experimental and numerical results available in the open literature. The CFD simulations are found to capture the features of the bubble formation, rise and burst in unsteady and quasi-steady states very well. The results show a significant increase in the conversion rate with higher dense bed height, lower bed width, higher free board height and smaller oxygen carrier particles which upsurge an overall performance of the CLC plant.

Numerical investigation of the three-dimensional dynamic process of sabot discard

The sabot discard process of an armor-piercing, fin-stabilized discarding sabot (APFSDS) is crucial for the flight stability of the projectile. In this paper, the sabot discard behavior after projectile ejection from the muzzle is investigated at Mach number 4.0 and angle of attack of 0°. 3D compressible equations implemented with a dynamic unstructured tetrahedral mesh are numerically solved with a commercial computational fluid dynamics (CFD) code (FLUENT 12.0). Six-degrees-of-freedom (6DOF) rigid-body motion equations is solved with the CFD results through a user-defined function to update the sabot trajectory at every time step. A combination of springbased smoothing and local re-meshing is employed to regenerate the meshes around the sabot and describe its movement at each time step. Computational results show three different separation processes during the sabot discard process. Furthermore, the aerodynamic forces of APFSDS are calculated, and the trajectories of the three sabots are illustrated through the numerical solution of 6DOF equations. The results of the present study agree well with typical experimental results and provide detailed parameters that are important for analyzing the stability of the projectile. The present computations confirm that the numerical solution of the governing equations of aerodynamics and 6DOF rigid-body equations are a feasible method to study the sabot discard processes of APFSDS.

The importance of a full 3D fluid dynamic analysis to evaluate the flow forces in a hydraulic directional proportional valve

Purpose – The purpose of this paper is to present a full 3D Computational Fluid Dynamics (CFD) analysis of the flow field through hydraulic directional proportional valves, in order to accurately predict the flow forces acting on the spool and to overcome the limitations of two-dimensional (2D) and simplified three-dimensional (3D) models. Design/methodology/approach – A full 3D CAD representation is proposed as a general approach to reproduce the geometry of an existing valve in full detail; then, unstructured computational grids, which identify peculiar positions of the spool travel, are generated by means of the mesh generation tool Gambit. The computational grids are imported into the commercial CFD code Fluent, where the flow equations are solved assuming that the flow is steady and incompressible. To validate the proposed computational procedure, the predicted flow rates and flow forces are compared with the corresponding experimental data. Findings – The superposition between numerical and experimental curves demonstrates that the proposed full 3D numerical analysis is more effective than the simplified 3D flow model that was previously proposed by the same authors. Practical implications – The presented full 3D fluid dynamic analysis can be employed for the fluid-dynamic design optimization of the sliding spool and, more generally, of the internal profiles of the valve, with the objective of reducing the flow forces and thus the required control force. Originality/value – The paper proposes a new computational strategy that is capable of recognizing all 3D geometrical details of a hydraulic directional proportional valve and that provides a significant improvement with respect to 2D and partially 3D approaches.

Numerical study of co-firing pulverized coal and biomass inside a cement calciner.

The use of waste wood biomass as fuel is increasingly gaining significance in the cement industry. The combustion of biomass and particularly co-firing of biomass and coal in existing pulverized-fuel burners still faces significant challenges. One possibility for the ex ante control and investigation of the co-firing process are computational fluid dynamics (CFD) simulations. The purpose of this paper is to present a numerical analysis of co-firing pulverized coal and biomass in a cement calciner. Numerical models of pulverized coal and biomass combustion were developed and implemented into a commercial CFD code FIRE, which was then used for the analysis. Three-dimensional geometry of a real industrial cement calciner was used for the analysis. Three different co-firing cases were analysed. The results obtained from this study can be used for assessing different co-firing cases, and for improving the understanding of the co-firing process inside the calculated calciner.

Low-Speed Model Testing Studies for an Exit Stage of High Pressure Compressor

This paper discusses detailed experimental studies of a low-speed large-scale axial compressor, which is typical of an exit stage of HPC. Numerous measuring techniques were performed, and detailed experimental results were obtained, including inlet boundary layer total pressure distributions, overall compressor and model-stage performance, traverse flow field between blade rows and inside the stator for the model stage, static pressure on the stator blade and casing dynamic pressure of the rotor. The objective of the study is to assess the low-speed model compressor design and verify 3D computational fluid dynamics (CFD) code. Results show that inlet endwall blockage requirement of HPC exit stage is achieved; the low-speed model compressor design is fundamentally successful; the flow rate and pressure rise requirements are met at the design operating point, although the flow loss is relatively larger than design values for the lower half span, which can be attributed to a certain hub-corner separation. Furthermore, the reliability of adopted 3D commercial CFD code is validated. It is proved that the low-speed model testing technique is still a prospective way for the design of high performance HPC.