Commercial Computational Fluid Dynamics Package FLUENT Research Articles

Computational analyses of tail fin configurations for a sounding rocket

Missiles and sounding rockets usually deviate from the trajectory due to unstable roll. Fins with cant angles are generally used to provide a rolling moment in sounding rockets and missiles to minimize the instability. Inducing a rolling moment also leads to an increase in the rocket motor’s power consumption due to the rise in drag, so inducing an optimal rolling moment with a minimal increase in drag is a crucial design criterion. It is crucial to maintain the similarity parameters while testing a scaled-down model in a wind tunnel. Therefore, computational fluid dynamics (CFD) is more efficient than extensive wind tunnel tests. In this paper, three-dimensional, incompressible simulations were performed on different models of sounding rockets using commercial CFD package fluent. The simulations were performed with the help of k-epsilon standard turbulence model. The results obtained were tabulated and graphically represented, and the trends of aerodynamic coefficients like C_{text {d}} and C_{text {m}} were analyzed. The purpose of this study is to analyze the dependency of aerodynamic coefficients on different fin configurations with emphasis on the cant angle. This study will be helpful to researchers designing a sounding rocket and help in maximizing apogee. The experimental and computational results show a favourable comparison. The results will show a particular configuration of fin having greater C_{text {m}}/C_{text {d}} which yields in a greater rolling moment and least amount of drag.

Hydrodynamic and thermal analysis of water, ethylene glycol and water-ethylene glycol as base fluids dispersed by aluminum oxide nano-sized solid particles

PurposeThe purpose of this paper is to carry out a hydrodynamic and thermal analysis of turbulent forced-convection flows of pure water, pure ethylene glycol and water-ethylene glycol mixture, as base fluids dispersed by Al2O3 nano-sized solid particles, through a constant temperature-surfaced rectangular cross-section channel with detached and attached obstacles, using a computational fluid dynamics (CFD) technique. Effects of various base fluids and different Al2O3 nano-sized solid particle solid volume fractions with Reynolds numbers ranging from 5,000 to 50,000 were analyzed. The contour plots of dynamic pressure, stream-function, velocity-magnitude, axial velocity, transverse velocity, turbulent intensity, turbulent kinetic energy, turbulent viscosity and temperature fields, the axial velocity profiles, the local and average Nusselt numbers, as well as the local and average coefficients of skin friction, were obtained and investigated numerically.Design/methodology/approachThe fluid flow and temperature fields were simulated using the Commercial CFD Software FLUENT. The same package included a preprocessor GAMBIT which was used to create the mesh needed for the solver. The RANS equations, along with the standard k-epsilon turbulence model and the energy equation were used to control the channel flow model. All the equations were discretized by the finite volume method using a two-dimensional formulation, using the semi-implicit method for pressure-linked equations pressure-velocity coupling algorithm. With regard to the flow characteristics, the interpolation QUICK scheme was applied, and a second-order upwind scheme was used for the pressure terms. The under-relaxation was changed between the values 0.3 and 1.0 to control the update of the computed variables at each iteration. Moreover, various grid systems were tested to analyze the effect of the grid size on the numerical solution. Then, the solutions are said to be converging when the normalized residuals are smaller than 10-12 and 10-9 for the energy equation and the other variables, respectively. The equations were iterated by the solver till it reached the needed residuals or when it stabilized at a fixed value.FindingsThe result analysis showed that the pure ethylene glycol with Al2O3 nanoparticles showed a significant heat transfer enhancement, in terms of local and average Nusselt numbers, compared with other pure or mixed fluid-based nanofluids, with low-pressure losses in terms of local and average skin friction coefficients.Originality/valueThe present research ended up at interesting results which constitute a valuable contribution to the improvement of the knowledge basis of professional work through research related to turbulent flow forced-convection within channels supplied with obstacles, and especially inside heat exchangers and solar flat plate collectors.

Modeling and Experimental Investigation of Solar Stills for Enhancing Water Desalination Process

Despite the importance of the desalination process in removal of water salinity to produce fresh drinking water, it is an energy-consuming process. Therefore, the use of solar energy as an alternative and free energy source has an important role in enhancing the efficiency of the desalination process. This paper presents an experimental investigation using solar chimney to enhance the desalination process, where a modification to the conventional solar stills has been made. A mathematical model describing air flow inside the solar chimney has been constructed using Computational Fluid Dynamics (CFD). The commercial CFD package fluent release 6.3 has been used in this paper to express the air flow and temperature distribution inside solar chimney. Furthermore, the process parameters such as seasonal temperature, salt concentration, water depth and type of solar desalination unit have been examined to find the best operating conditions. The desalination process has been recommended to be carried out under permissible operating conditions in sunny days, with water depths ranging from (1–2 cm) and low salt concentration ranging from (3.5–8%). The modeled data has been verified with experimental data and the verification results have been estimated at 14%. Simulation results showed that water desalination has been improved by 30%.

Baffle orientation and geometry effects on turbulent heat transfer of a constant property incompressible fluid flow inside a rectangular channel

Purpose A computational fluid dynamics (CFD) analysis has been carried out on the aerodynamic and thermal behavior of an incompressible Newtonian fluid having a constant property and flowing turbulently through a two-dimensional horizontal high-performance heat transfer channel with a rectangular cross section. The top surface of the channel was kept at a constant temperature, while it was made sure to maintain the adiabatic condition of the bottom surface. Two obstacles, with different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel; they were fixed to the top and bottom surfaces of the channel in a periodically staggered manner to force vortices to improve the mixing and consequently the heat transfer. The first fin-type obstacle is placed on the heated top channel surface, and the second baffle-type one is placed on the insulated bottom surface. Five different obstacle situations were considered in this study, which are referred as cases FF (flat fin and flat baffle), FVD (flat fin and V-downstream baffle), FVU (flat fin and V-upstream baffle), VVD (V-downstream fin and V-downstream baffle) and VVU (V-Upstream fin and V-upstream baffle). Design/methodology/approach The flow model is governed by Reynolds-averaged Navier–Stokes equations with the k-epsilon turbulence model and the energy equation. These governing equations are discretized by the finite volume method, in two dimensions, using the commercial CFD software FLUENT software with the Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm for handling the pressure-velocity coupling. Air is the test fluid with the flow rate in terms of Reynolds numbers ranging from 12,000 to 32,000. Findings Important deformations and large recirculation regions were observed in the flow field. A vortex causes a rotary motion inside the flow field, which enhances the mixing by bringing the packets of fluid from the near-wall region of the channel to the bulk and the other way around. The largest value of the axial variations of the Nusselt number and skin friction coefficient is found in the region facing the baffle, while the smallest value is in the region near the fin, for all cases. The thermal enhancement factor (TEF) was also introduced and discussed to assess the performance of the channel for various obstacle situations. It is found that the TEF values are 1.273-1.368, 1.377-1.573, 1.444-1.833, 1.398-1.565 and 1.348-1.592 for FF, FVD, FVU, VVD and VVU respectively, depending on the Re values. In all cases, the TEF was found to be much larger than unity; its maximum value was around 1.833 for FVU at the highest Reynolds number. Therefore, the FVU may be considered as the best geometrical configuration when using the obstacles to improve the heat transfer efficiency inside the channel. Originality/value This study can be a real application in the field of shell-and-tube heat exchangers and flat plate solar air collectors.

CFD investigation on thermal hydraulics of the passive residual heat removal heat exchanger (PRHR HX)

Passive residual heat removal (PRHR) system is a very important component of the passive safety systems in advanced passive safety pressurizer water reactors (PWRs) such as AP1000. The passive residual heat removal heat exchanger (PRHR HX) is a C-shape tube bundle heat exchanger immerged in the In-containment refueling water storage tank (IRWST) which removes the core decay heat during the accident transients. The performance of the PRHR HX is significant for the safety of the nuclear power plant (NPP). In this paper, the thermal hydraulics characteristics of the PRHR HX in the IRWST is analyzed using computational fluid dynamics (CFD). The tube region is modeled by the porous media approach along with the distributed resistance method. Heat transfer from the primary side fluid inside the tube to the secondary side fluid in the IRWST is considered. The simulation is carried out by the commercial CFD package FLUENT. The calculation of the flow resistance and heat transfer in the tube region is implemented using the User Defined Functions (UDF) in FLUENT based on the local flow conditions. Three dimensional distributions of the fluid velocity and temperature in the IRWST are obtained and thermal stratification is observed. The PRHR HX heat transfer capacity and the primary side fluid temperature distribution inside tubes are analyzed.

A Simple Daily Cycle Temperature Boundary Condition for Ground Surfaces in CFD Predictions of Urban Wind Flows

AbstractThe atmospheric boundary exhibits an obvious diurnal cycle. The daily cycle of climate variation has a significant effect on urban airflow, and an understanding of it is very important for city-scale environmental control. A new and simple daily cycle temperature boundary condition for simulations of urban airflows with computational fluid dynamics (CFD) is described herein. An analytical surface temperature formula was obtained after simplifying longwave radiation and sensible heat flux terms. The formula provides a reasonably good prediction of ground surface temperatures on sunny days without adding much complexity. The accuracy of the prediction of daily surface temperature variations in homogeneous soils was evaluated with a benchmark experiment and with weather station data. The new boundary condition was implemented in the commercial CFD software Fluent for a city-scale model. The implementation demonstrates the importance of including diurnal temperature profiles and atmospheric boundary conditions in CFD simulations of urban plumes in which an ideal urban heat island circulation occurs.

Hydrodynamic Study Using CFD Simulations in a Horizontal Two-Phase Flow Through Sudden Contraction

Two-phase flows are encountered in a wide range of industrial application. In the present work, two-phase computational fluid dynamics (CFD) calculations, using Eulerian–Eulerian model and commercial CFD package FLUENT 6.3, were employed to calculate pressure drops caused by abrupt flow area contraction in small circular pipes for two-phase flow of air and water mixtures at room temperature and near atmospheric pressure. The pressure drop is determined by extrapolating the computed pressure profiles upstream and downstream of the contraction. Variables studied include: gas and liquid velocities, and pipe contraction ratio. The numerical results were validated against experimental data from the literature and are found to be in good agreement. Our findings could be useful in designing pipeline.

Effect of Fish Wedge on the Hydrodynamic Characteristics of a Marine Rudder

In this paper, the effects of fish-wedge on the hydrodynamic characteristics of a marine rudder have been studied using computational fluid dynamics (CFD). In this case, NACA0012 airfoil section has been used as the rudder section. The computed results of lift and drag coefficient at different angles of attack for NACA0012 have been validated with the experimental results and then the effects of fish-wedges with different lengths with constant width have been studied using different turbulence models and finally the use of fish wedge section as a flap to increase its efficiency is studied. For model development of the rudder section Rhinoceros 5 has been used and for meshing ANSYS workbench is used. The analysis of flow past rudder with fish-wedge has been done using a commercial CFD software Fluent which is based on Finite Volume Method (FVM). In every case, water is used as the fluid medium and the flow has been simulated at Reynolds number 6×106, which is equivalent to the flow of water having velocity of 6.03 m/s. This type of rudder with fish edge can produce higher lift force in a comparatively low angle of attack, which is suitable for special type of vessels, e.g., tug boat.

CFD Simulation of Liquid–Liquid Two-Phase Hydrodynamics and Axial Dispersion Analysis for a Non-Pulsed Disc and Doughnut Solvent Extraction Column

ABSTRACTA two-phase computational fluid dynamics (CFD) simulation for a non-pulsed disc and doughnut solvent extraction column has been developed with commercial CFD software FLUENT. Simulated hydrodynamic results including phase distribution, velocity fields, and holdup are given, which enables predicted holdup to be compared with experimental data. Average absolute relative deviation (AARD) of experimental data and CFD prediction in this study is found to be 10.8%, which is comparable to the estimated error in the experimental data and the predictions from traditional correlations in the literature. To estimate the extent of axial dispersion, a species transport model is used for the continuous phase with a small amount of tracer introduced in the continuous phase, when Sauter mean diameter of the dispersed phase is set to be 3.5 mm. A two-point monitoring method is used to estimate a Peclet number. The tracer concentration distribution in the two-dimensional distance–time space is interpreted with MATLAB along with the experimental measurement. The simulated Peclet numbers are compared with column experiments, and in general the simulation underestimates the experimental data by 60%. Introducing a modified drag law improves the predictions. This work shows that CFD can successfully model the performance of a non-pulsed disc and doughnut solvent extraction column.

Predicting urban heat island circulation using CFD

Most existing microscale computational fluid dynamics (CFD) models and mesoscale meteorological models cannot consider multi-scale urban wind flows, as neither can completely take into account the mesoscale and microscale physics, and their interactions. Here we suggest a CFD model which has good potential for development of the meso-micro scale models for predicting and designing multi-scale urban airflows. The principal idea is to use CFD numerical methods to solve a set of governing equations with appropriate boundary conditions that can govern both major mesoscale and microscale flow characteristics. Based on the coordinate transformation method proposed by Kristóf, Rácz and Balogh (2009), we derived a similar set of governing equations with some improvements and used an existing porous turbulence model for modeling the urban canopy layer. The approach was then successfully implemented using a commercial CFD package (Fluent) for studying urban heat island circulation (UHIC), which is considered to be one of the most difficult problems in CFD. Our predicted mean quantities agree well with existing data in the literature obtained from large eddy simulations, mesoscale models, and laboratory experiments. Our predicted results also reveal the effects of the different heat fluxes and urban height of a city on UHIC characteristics.

LES and RANS comparison of flow and pollutant dispersion in urban environment

This study investigates air pollution dispersion in urban areas by means of Computational Fluid Dynamics (CFD). The commercial CFD software FLUENT was used to implement two different turbulence simulation methods (RANS and LES), in domains similar to complex urban environments. Particularly, different combinations of roof shapes were studied and simulation results of pollutant (ethane) concentrations were compared against experimental data. The building height (H) to the neighbour building distance (B) ratio was also taken into consideration. Previous studies showed that both RANS and LES models are accurate enough to predict pollutant concentrations fields in B/H = 1. In the present study the incapability of RANS models to predict accurately pollutant concentration in B/H = 0.5 for all roof shapes configurations is revealed.

Steady and transient solutions of neutronics problems based on finite volume method (FVM) with a CFD code

In recent years, Computational Fluid Dynamics (CFD) methodology has been widely used for solving multi-dimensional thermal-hydraulics problems in nuclear science and engineering. As for the neutronics analysis, it mostly depends on the deterministic or probabilistic method codes which are independent of the thermal-hydraulic ones. Usually an extra interface program needs to be developed for the data exchange between the two kinds of codes in the coupled calculation. In this paper, a Temporal And Spatial Neutronics Analysis Module (TASNAM) in commercial CFD package FLUENT was developed based on the User Defined Function (UDF) and User Define Scalar (UDS) to solve the neutronics problems. Neutron diffusion equations and delayed neutron precursors balance equations are discretized by finite volume method (FVM) and can be solved with CFD conservation equations simultaneously. In order to demonstrate the feasibility and accuracy of TASNAM in FLUENT, three neutronics benchmark problems, the 2D-IAEA, 2D-TWIGL, and 2D-LRA benchmark problem are analyzed. The calculation results in the present paper have a good agreement with the reference values, which demonstrates that the TASNAM in FLUENT can solve neutronics problems accurately.

A Computational Fluid Dynamics Method for Resistance Prediction of the Floating Hull of Wave Glider

The wave glider is a surface vehicle with an attached sub-surface wing system which propels the surface component forward, negating the need for a motor. Wave glider could be used for intelligence, surveillance, passive monitoring of marine life, monitoring exclusive economic zones for fishing and other economic resources that are important and useful to coastal countries. Monitoring of coastal waters normally requires large amounts of expensive surveillance. They can be used to find and research resources and fisheries at a fraction of the cost of other methods. Since the wave glider can either be programmed for a journey or to keep station, it is looked at as an alternative for expensive moored buoys. In this paper we present a method focused on the mesh generation to predict calm water resistance for the floating part of the wave glider (the hull). In this study a wigley hull form (4m) used as the floating hull has been investigated in order to predict the fluid flow of the ship using computational fluid dynamics (CFD). Calculations for total resistance are carried out for Froude numbers in the range of 0.10 to 0.40. Commercial CFD software fluent is used to investigate the fluid flow of wigley hull. Three different mesh sizes are used in this study to calculate the mesh effects. The results obtained from CFD calculations for total resistance are compared with the experimental results for accuracy of the solution parameters. The comparison shows a good agreement between experimental and CFD results. The method is evaluated by comparing the numerical predictions for wigley hull form (2m) with wigley hull form (4m) using the same mesh sizes under the same conditions in an attempt to design the floating hull of wave glider . The results obtained from CFD calculations are compared for accuracy of the solution parameters and the method is useful and acceptable.

A Study of Continuous Flow Gas Lift System Using CFD

Gas lift optimization has been a point of interest for some decades in order to increase production in oil fields. Despite that there are still lacks of user friendly software in gas lift optimization. The ultimate goal of this study is to develop user friendly program using commercial Computational Fluid Dynamics (CFD) software for optimization of continuous flow gas lift for single well. GAMBIT 2.3.16 was used for modelling the tubing string prior the simulation process. Two-phase CFD calculations using Eulerian–Eulerian model and commercial CFD package FLUENT 6.0 were employed to calculate the gas-liquid flow in the string. The depth and the rate of gas injection were the main parameter tested. The simulation results showed that the highest velocity of flowing fluid was observed when the gas was injected at the lowest point, which is at 5 m from the casing shoe in this study. The velocity of flowing fluid was increased by 1.7% when the gas injection rate increased 20%. This interrelationship was observed with regard of the decrease in liquid column density. CFD is capable in aiding faster continuous flow gas lift optimization process.

Numerical investigations of the heating distribution effect on the boiling flow in bubble pumps

Numerical simulations of the heating repartition effect on the boiling flow in vertical tube are performed using the commercial CFD (Computational Fluid Dynamics) package FLUENT. The Eulerian multiphase flow framework model was applied to describe the phase interactions. User-Defined Functions (UDFs) are provided to compute the wall heat transfer and the inter-phase heat and mass transfer. Two different configurations of the bubble pump are considered: Total and partial heating of the pump tube.Preliminary calculations are performed with pure water as working fluid. The results presented and discussed in this paper concern the void fraction distribution, flow regime repartition, liquid–vapor velocities arrangement and temperature profiles.

CFD Simulation of Deep-Bed Paddy Drying Process and Performance

Computational Fluid Dynamics (CFD) was applied three-dimensionally to simulate the drying behavior of paddy in a deep-bed dryer. The commercial CFD software Fluent 6.3.26 was used. The deep-bed paddy drying process and performance were studied by incorporating user-defined function (UDF) in Fluent written in C language. The predicted drying parameters were compared with experimental data of deep-bed drying of paddy. The values of mean relative deviation (MRD), standard error of prediction (SEP), and maximum error of prediction (MEP) for prediction of grain moisture content, air temperature, and absolute humidity were less than 6, 10, and 9%; 0.33% (d.b), 1.24°C, and 0.06% (kg/kg of dry air); and 2.25% (d.b), 6.8°C, and 0.37% (kg/kg of dry air), respectively, which reflect reasonable accuracy. Moreover, the energetic and exergetic performance of deep-bed paddy drying were simulated and analyzed. The effects of inlet air temperature and mass flow rate on the performance parameters were investigated. It was shown that the application of higher levels of inlet air temperature and lower mass flow rates yielded higher exergy efficiencies of deep-bed paddy drying.

Prediction of Separation Length of Turbulent Multiphase Flow Using Radiotracer and Computational Fluid Dynamics Simulation

Multiphase flow modeling presents great challenges due to its extreme importance in various industrial and environmental applications. In the present study, prediction of separation length of multiphase flow is examined experimentally by injection of two kinds of iodine-based radiotracer solutions into a hydrocarbon transport pipeline (HCT) having an inner diameter of 24 in (60,96 m). The main components of fluids in the pipeline are water 95%, crude oil 3% and gas 2%. A radiotracing experiment was carried out at the segment of pipe which is located far from branch points with assumptions that stratified flows in such segment were achieved. Two radiation detectors located at 80 and 100 m from injection point were used to generate residence time distribution (RTD) curve resulting from injection of radiotracer solutions. Multiphase computational fluid dynamics (CFD) simulations using Eulerian-Eulerian control volume and commercial CFD package Fluent 6.2 were employed to simulate separation length of multiphase flow. The results of study shows that the flow velocity of water is higher than the flow rate of crude oil in water-dominated system despite the higher density of water than the density of the crude oil. The separation length in multiphase flow predicted by Fluent mixture model is approximately 20 m, measured from injection point. This result confirms that the placement of the first radiation detector at the distance 80 m from the injection point was correct. Received: 04 December 2012; Revised: 29 January 2013; Accepted: 09 March 2013

Wind tunnel testing and numerical simulation on aerodynamic performance of a three-bladed Savonius wind turbine

Abstract The purpose of this research work is to investigate experimentally and computationally the feasibility of improving the performance of the vertical-axis Savonius wind turbine. The authors first performed a series of wind tunnel investigations on semi-cylindrical three-bladed Savonius rotor scale models with different overlap ratios and without overlap. These experiments were conducted in front of a low-speed subsonic wind tunnel at different Reynolds numbers. Pressures around the concave and convex surfaces of each blade, as well as the static torque for the rotor models, were measured. Using these experimental data, the authors calculated aerodynamic characteristics such as drag coefficients, static torque coefficients, and power coefficients. The authors then performed computational fluid dynamics (CFD) simulations using the commercial CFD software FLUENT and GAMBIT to analyze the static rotor aerodynamics of those models. The experimental and computational results were then compared for verification. Three different models with different overlap ratios were designed and fabricated for the current study to find the effect of overlap ratios. The results from the experimental part of the research show a significant effect of overlap ratio and Reynolds number on the improvement of aerodynamic performance of the Savonius wind turbine. At higher Reynolds number, the turbine model without overlap ratio gives better aerodynamic coefficients, and at lower Reynolds number, the model with moderate overlap ratio gives better results.

Computational Fluid Dynamics (CFD) modelling of transfer chutes: A study of the influence of model parameters

Transfer chutes are essential components in almost all bulk material handling plants. Belt conveyors utilize transfer chutes to load and redirect bulk materials from one conveyor to another, with their reliability and performance being critical to the overall operation of the plant. While reliability and operational performance is typically measured by availability and throughput, transfer chutes must also operate with minimal environmental impact. Consequently, the design of transfer chutes in relation to entrained air flow, with the aim of minimizing fugitive dust emissions, is an area of ongoing research and investigation requiring the analysis of complex multiphase systems. Computational Fluid Dynamics (CFD) has been successfully applied to evaluate potential dust emissions from transfer chutes, with the implementation of appropriate models and modelling parameters shown to be critical to the overall accuracy of the simulation results. A notable shortcoming in the current research is the lack of systematic guidelines available to appropriately select model parameters. The aim of this paper is to offer guidance in this regard, and provide a better understanding of the influence of the maximum fractional packing limit and evaluate the most appropriate model parameters for simulations, including particle–particle restitution coefficient values and solid slip conditions. For this purpose, the two-phase three-dimensional Euler–Euler model of commercial CFD software Fluent has been selected to model the granular and air flow in the transfer chute. Air velocities were measured experimentally by Particle Image Velocimetry (PIV) with the simulated velocity profiles being in good overall agreement with the experimental data.

Enhanced Transient Heat Transfer From Arrays of Jets Impinging on a Moving Plate

This article addresses the numerical analysis of single and multiple circular jets impinging perpendicularly on a flat plate for heating and cooling purposes. Computational fluid dynamics (CFD) is used to evaluate heat transfer calculations for different configurations and different flow boundary conditions. The commercial CFD package FLUENT is employed with various turbulence models. Results for a single jet are validated against experimental data. The SST k − ω turbulence model is compared with the elliptic V2F model, and both were validated against experimental data. Results were obtained for a range of jet Reynolds numbers and jet-to-target distances. Optimization results for the single jet case are validated against experimental data. The SST k − ω and V2F turbulence models succeeded with a reasonable accuracy (within 20% error) in reproducing experimental results. The heat transfer rates from the use of multijet configurations are discussed in the article. Transient heat transfer between multiple jets and a moving plate is more difficult to study due to the changing boundaries but is also very relevant in engineering applications. This article presents full CFD calculations of the transient heat transfer between a bank of circular jets and a moving plate. Design optimization has also been achieved for the single- and multiple-jet configurations.