CFD Simulation Of Flow Research Articles

CFD Simulation of Flow around External Vehicle: Ahmed Body

CFD Simulation of Flow around External Vehicle: Ahmed Body

CFD simulation of horizontal oil-water flow with matched density and medium viscosity ratio in different flow regimes

Simulation of horizontal oil-water flow with matched density and medium viscosity ratio (μo/μw=18.8) in several different flow regimes (core annular flow, oil plugs/bubbles in water and dispersed flow) was performed with the CFD package FLUENT in this study. The volume of fluid (VOF) multiphase flow modeling method in conjunction with the SST k-ω scheme was applied to simulate the oil-water flow. The influences of the turbulence schemes and wall contact angles on the simulation results were investigated for a core annular flow (CAF) case. The SST k-ω turbulence scheme with turbulence damping at the interface gives better predictions than the standard k-ε and RNG k-ε models for the case under consideration. The flow regime of density-matched oil-water flow with medium viscosity ratio, or more generally speaking, the flow regime of fluids where the surface tension is playing a prevailing role is sensitive to the wall contact angle. Simulation results were compared with experimental counterparts. Satisfactory agreement in the prediction of flow patterns were obtained for CAF and oil plugs/bubbles in water. The simulation results also demonstrated some detailed flow characteristics of CAF with relatively low-viscosity oil (oil viscosity one order higher than the water viscosity in the present study compared to the extensively studied CAF with oil viscosity being two to three orders higher than the water viscosity). Different from the velocity profiles of high-viscosity oil CAF where there is sharp change in the velocity gradient at the phase interface with velocity across the oil core being roughly flat, there is no sharp change in the velocity gradient at the phase interface for CAF with relatively low-viscosity oil.

Numerička simulacija izvedena na modulu višestepene rakete pri različitim vrednostima Mahovog broja

Simulations have been carried out for a multi-body launch vehicle configuration using CFD code 'PARAS-3D'. PARAS-3D is a Reynolds Averaged Navier Stokes equations (RANS) solver with k-e turbulence model. The transonic regime is a critical regime for any launch vehicle configuration because of its typical aerodynamic characteristics such as shock wave disturbances. CFD flow simulations are done at zero degree angle of attack for various strap-on nose cone angle, nose radius and Mach numbers 0.8, 0.9, 0.95, 1.05. For different positions of strap-on obtained through forward and backward shift from its original position, the influence of strap-on on fore body of the core of launch vehicle is investigated. In this article, the results pertaining to the pressure distribution and Mach contour over launch vehicle configuration is presented.

Numerical and Experimental Investigations on Vertical Axis Wind Turbines of Different Models

Wind is a free and abundant energy source and conversion of wind energy to electrical energy has no negative impact to the environment. Though the harvest of energy using a horizontal axis turbine (HAWT) is extremely common worldwide, the wind speed requirement is relatively high for power generation. On the contrary, a vertical axis wind turbine (VAWT) can produce power at low wind speeds as compared to the HAWT counterpart. In addition, a VAWT can produce power regardless of the wind direction and the installation of a VAWT is simple and more cost effective than a HAWT. The purpose of the current study is to compare performances among different VAWT models using both numerical and experimental methods and find the one with the optimum performance. Standard aero-foil blade designs were considered in the current study because of their good aerodynamic characteristics. The study was performed using both computational and experimental methods. The 2D CAD design of five different VAWT models including three aero-foil blades (NACA5510, NACA7510, and NACA9510) were performed using Solid Works. CFD simulation of wind flow around these models was performed using a popular software FLUENT using the moving mesh technique. The pressure and velocity contours as well as different coefficients such as lift coefficient, drag coefficient, torque coefficient, and power coefficient were obtained from this simulation for all VAWT models. In addition, the physical models of NACA 7510, NACA 5510, and semicircular VAWTs were fabricated and tested in a subsonic wind tunnel. At three different speeds, dynamic torques were measured for all models experimentally. The current study showed that the VAWT model with NACA 7510 blade yielded the best result among all the models at a relatively high tip speed ratio (TSR).

CFD-simulation of the air flows in the maxillary sinus

This article summarizes the results of computer simulation of the air flows in the nasal cavity and the maxillary sinus by the computational fluid dynamics (CFD) method. The objective of the study was to apply the method of computational aerodynamics to simulate the air flows in the nasal cavity and the maxillary sinus under the normal conditions and after the surgical interventions on the middle nasal meatus. The normal air space of the nasal cavity and paranasal sinuses was simulated and the computer modeling of the main options for the surgical approach to the maxillary sinus through the middle nasal meatus was performed including balloon sinuplasty, functional endoscopic sinus surgery, and uncinate process mobilization. The study has demonstrated the increase of the air flow velocity in the maxillary sinus after computer-assisted balloon sinuplasty. The computer simulation of functional endoscopic sinus surgery including the removal of the uncinated process revealed the mass exchange between the maxillary sinus and the nasal cavity.

CFD simulation of flow in a long street canyon under a perpendicular wind direction: Evaluation of three computational settings

A street canyon is an important platform for the understanding of local atmospheric flow and other related processes in the built environment. Many previous studies focused on long street canyons under a perpendicular wind direction, as they represent the worst street canyon microclimate, such as stagnation of wind and accumulation of pollutants. While CFD simulations were widely applied to investigate atmospheric processes in street canyons, appropriate computational settings are important factors influencing the predictive reliability. A non-exhaustive literature review of CFD studies on atmospheric processes in long street canyons indicates an arbitrary selection of three important computational settings, namely computational domain configuration, domain dimensions and inflow boundary conditions. Based on previous water tunnel experimental data for street canyons with aspect ratio equal to 0.5, 1.0 and 2.0, this study evaluates the influence of the three computational settings on CFD prediction of isothermal flow field inside the street canyons. Flow field inside an urban street canyon cannot be reasonably predicted using an isolated street canyon included in a conventional computational domain, which, however, can be well predicted using a T-shape computational domain where a street canyon is connected to a free flow layer above the canyon. A T-shape domain with the upstream length, downstream length and height above a street canyon all equal to the height of the street canyon is appropriate when considering both computational cost and predictive accuracy. It is reasonable to use uniform inflow boundary conditions to represent the free layer above street canyons.

CFD SIMULATION OF UPWARD SUBCOOLED BOILING FLOW OF FREON R12

Subcooled flow boiling under forced convection occurs in many industrial applications of purpose to maximize heat removal from the heat source by the very large heat transfer coefficient. This work deals with CFD simulations of the subcooled flow boiling of refrigerant R12 solved by code ANSYS FLUENT r16. The main objective of this paper is verification of used numerical settings on relevant experiments performed on DEBORA test facility. Also comparisons with previously provided simulation on NRI Rez are presented. Data outputs from this work are basis to subsequent calculations of steam-water mixture cooling of Pb-Li eutectic.

CFD Simulation of Air Flow Over an Object with Gable Roof, Revised with Y+ Approach

Abstract Aim of this contribution is to provide insight view into analysis focused on obtaining external pressure coefficients on isolated two storey low-rise building with 15° elevation gable roof using Computer Fluid Dynamics simulation and these are compared to values that offering Eurocodes. Final Volume Model consisting of polyhedral mesh will be used for analysis with two different turbulence models. Mesh was created with respect to y+ parameter, where desired value was below one which leads us to fine mesh type. Secondary aim of this contribution is to compare performance of selected turbulence models. For this purpose were chosen Detached Eddy Simulation and Large Eddy Simulation which are part of the Scale Resolving Simulation turbulence models.

CFD simulation of two-phase gas-particle flow in the Midrex shaft furnace: The effect of twin gas injection system on the performance of the reactor

In the present study a mathematical model is developed to examine the effect of dual gas injection system on the distribution of process variables and energy consumption in the Midrex shaft furnace. The developed model was constructed by considering the major chemical reactions and physical structures within the furnace and describes a counter-current moving bed reactor in which hematite pellets are reduced to sponge iron by pure hydrogen gas. Governing equations containing overall continuity, momentum, energy and mass equations are developed for both gas and solid phases in cylindrical coordinate system. Unreacted shrinking core model is implemented to simulate gas–solid reactions in the reactor. The complicated equations are solved by applying finite volume technique. The model is applied to simulate multiphase flow inside the reactor when it is equipped with one and two hydrogen gas intake ports to examine the impact of gas injection arrangement on the process variables. The radial and axial distributions of operational parameters including gas and solid temperature, fractional reduction of iron oxides and hydrogen and water vapor concentration are obtained for both cases. The results indicate that reduction degree and energy consumption are improved by utilizing dual gas injection system.

Multi-point Optimization of Lean and Sweep Angles for Stator and Rotor Blades of an Axial Turbine

In this research, numerical optimization of the rear part of a gas turbine, consisting of a single-stage axial turbine, is carried out. Automated aerodynamic shape optimization is performed by coupling a CFD flow simulation code with the genetic algorithm. An effective multi-point optimization method to improve efficiency and/or pressure ratio of the axial turbine is performed. Some variations of optimization parameters such as lean and sweep angels of stator and rotor blades are accomplished. Furthermore, during the optimization process, three-dimensional and turbulent flow field is numerically investigated using a compressible Navier–Stokes solver. The gas turbine experimental investigations are used for choosing optimization points, specifying the boundary conditions and validation of the simulations. Two operating speeds of the gas turbine are selected for the optimization. Using verified numerical simulation models and the genetic algorithm, the effects of stator and rotor lean and sweep angles on the turbine performance are studied. The present optimization method successfully obtains a result that improves 1.31 and 1.17 % in the turbine stage total-to-total efficiency in its design and off-design speeds, respectively. The modified turbine mass parameter at choke condition increases 2.40 %.

CFD Simulations of Flow Around Octagonal Shaped Structures

CFD Simulations of Flow Around Octagonal Shaped Structures

CFD simulation of two-phase flow in pulsed sieve-plate column – Identification of a suitable drag model to predict dispersed phase hold up

ABSTRACTComputational Fluid Dynamics (CFD) simulations of two-phase flow to predict dispersed phase hold up in a pulsed sieve-plate column have been performed and validated with reported experimental data. Suitability of different drag models for predicting dispersed phase hold up has been evaluated. Drag models applicable for concentrated dispersions are found to be better than the drag models applicable for lean dispersions. Kumar–Hartland drag model is found to be the best among the reported drag models with average error between predicted and experimental hold up being about 15%. Parameters of the Kumar–Hartland drag model are modified to further reduce the error to about 10%.

Baseline Model for Bubbly Flows: Simulation of Monodisperse Flow in Pipes of Different Diameters

CFD simulations of the multiphase flow in technical equipment are feasible within the framework of interpenetrating continua, the so-called two-fluid modelling. Predictions with multiphase CFD are only possible if a fixed set of closures for the interfacial exchange terms is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems. To this end, a baseline model, which is applicable for adiabatic bubbly flow, has been specified recently and has been implemented in OpenFOAM. In this work, we compare simulation results obtained using the baseline model with three different sets of experimental data for dispersed gas-liquid pipe flow. Air and water under similar flow conditions have been used in the different experiments, so that the main difference between the experiments is the variation of the pipe diameter from 25 mm to 200 mm. Gas fraction and liquid velocity are reasonably well reproduced, in particular in the bulk of the flow. Discrepancies can be seen in the turbulent kinetic energy, the gas velocity and in the wall peaks of the gas fraction. These can partly be explained by the simplified modelling, but to some extent must be attributed to uncertainty in the experimental data. The need for improved near-wall modelling, turbulence modelling and modelling of the bubble size distribution is highlighted.

Experimental and CFD simulations of fluid flow and temperature distribution in a natural circulation driven Passive Moderator Cooling System of an advanced nuclear reactor

The Passive Moderator Cooling System (PMCS) of the Advanced Heavy Water Reactor is designed to remove heat from the moderator passively in case of an extended station black out condition (SBO). The hot heavy-water moderator inside the Calandria rises upward due to buoyancy, cooled in a shell and tube heat exchanger (located within the loop) and returns back to the Calandria, completing a natural circulation loop. The heat exchanger, in turn, is cooled by water from a Gravity Driven Water Pool (GDWP); forming a second loop. This coupled natural circulation loop system provides sufficient cooling to prevent the increase of moderator temperature inside the Calandria vessel beyond safe limits during SBO.The feasibility of such a system should be assessed before it is implemented in the reactor. Thus, a scaled test facility was set up to simulate the thermal hydraulic characteristics of the PMCS. A set of time varying power experiments were performed, which capture the flow initiation from rest phenomena and the multidimensional natural convection flow in a coupled natural circulation system. Next, the experimental geometry was simulated using the three-dimensional computational fluid dynamics code (OpenFoam 2.2.0), which predicted temperature and flow distribution inside the system. The CFD results agree well with the experimental data within ±6%. The flow initiation phenomena shows that the initial flow generated recirculates within the Calandria, after ~900s the flow is able to come out of the Calandria. The experiments show a time lag between the starting of the primary and secondary loop circulation. This work demonstrates the experimental and computational capability to understand and design an effective Passive Moderator Cooling System.

CFD Simulation of In-Cylinder Flow on Different Piston Bowl Geometries in a DI Diesel Engine

CFD Simulation of In-Cylinder Flow on Different Piston Bowl Geometries in a DI Diesel Engine

Investigation of the Optimal Omni-Direction-Guide-Vane Design for Vertical Axis Wind Turbines Based on Unsteady Flow CFD Simulation

With soaring energy demands, the desire to explore alternate and renewable energy resources has become the focal point of various active research fronts. Therefore, the scientific community is revisiting the notion to tap wind resources in more rigorous and novel ways. In this study, a two-dimensional computational investigation of the vertical axis wind turbine (VAWT) with omni-direction-guide-vane (ODGV) is proposed to determine the effects of this guide vane. In addition, the mesh and time step (dt) size dependency test, as well as the effect of the different turbulence models on results accuracy are investigated. Eight different shape ratios (R) of the omni-direction-guide-vane were also examined in this study. Further, the CFD model is validated by comparing the numerical results with the experimental data. Validation results show a good agreement in terms of shape and trend in CFD simulation. Based on these results, all the shape ratios, except two ratios including 0.3 and 0.4 at TSR of 1.3 to 3, have a positive effect on the power and torque coefficient improvement. Moreover, results show that the best case has a shape ratio of 0.55, which improves the power coefficient by 48% and the torque coefficient up to 58%.

Characterization of the velocity fields generated by flow initialization in the CFD simulation of multiphase flows

Recent improvements in numerical algorithms for Eulerian-based CFD simulations of multiphase flows can now recover the exact balance between the pressure and surface tension terms within the momentum equation. This has led to the minimization of the so called “spurious velocities”: unphysical flows appearing at interfaces when using implementations of the Continuum Surface Force technique to model surface tension forces. Nevertheless, non-null velocity fields are still observed in the proximity of interfaces despite the absence of external forces, and it will be shown here that they can still considerably influence the accuracy of two-phase flow simulations. This study demonstrates that the evolution of these velocity fields is due to the generation of a capillary wave at the beginning of the simulation. This arises from the inability of the surface tension algorithm to evaluate a constant interface curvature from the initial color function field, although this is obtained by mapping an exact circumference on the computational grid, which then generates an initial perturbation that evolves as a capillary wave. A linear stability analysis of a two-dimensional circular static droplet subjected to initial small amplitude perturbations is here developed and compared with the results of CFD simulations to corroborate this thesis. This methodology provides a novel insight on the nature and behavior of spurious currents and their influential parameters, and it yields results which are not only in line with previous observations but also unify some contrasting trends reported in the literature. It is observed that the velocity magnitude induced by the capillary wave scales with the surface tension coefficient and the inverse of the fluid density and droplet radius. Furthermore, it decreases when refining the computational mesh only if the interface curvature estimations converge to the exact value, while otherwise showing the opposite trend.

CFD simulations of shell-side flow in a shell-and-tube type heat exchanger with and without baffles

Shell-and-tube heat exchanger has been extensively used in industrial and research fronts for more than a century. However, most of its design procedures are based on empirical correlations extracted from experimental data of long length shell and tube heat exchanger. In this paper, an attempt has been made to investigate the complex flow and temperature pattern in such a short shell and tube type heat exchanger, with and without baffles in the shell side. Heat exchangers of length by hydraulic diameter ratio between 7<L/Dh<21(0.15m<DS<0.6m) for unbaffled and L/Dh<7(DS=0.09m) for baffled heat exchangers are analysed using CFD code OpenFOAM-2.2.0 for different mass flow rates. It was observed that the cross flow near the nozzle region has a significant contribution towards the heat transfer, hence the conventional heat transfer correlations do not apply to these short heat exchangers. Furthermore, a sensitivity study of turbulence models was performed and it was observed that the standard k–ε model gives best results for the velocity profile as well as heat transfer, provided average y+ of the first node adjacent to the heat transfer surface is maintained greater than 15. The commonly used boundary conditions at the exit are not realistic, as it tends to give either incorrect flow and temperature fields, or the solution was found to diverge. Through a sensitivity study of the exit length, it was found that exit length to shell side velocity ratio of 2.5 is required for proper convergence. Finally the effect of flow field on shell side heat transfer coefficient and a comparison with analytical methods are presented.

CFD Simulation of Turbulent Air Flow in Diffuser and it's Effect on Fluid Properties

CFD Simulation of Turbulent Air Flow in Diffuser and it's Effect on Fluid Properties

ドラッグデリバリーに係るミクロ管内極低ReながれのCFD解析

ドラッグデリバリーに係るミクロ管内極低ReながれのCFD解析