General Purpose Computational Fluid Dynamics Research Articles

로켓 노즐의 열전달계수 비교 연구

The goal of heat transfer studies is the accurate prediction of temperature and heat flux distribution on material boundaries. To this purpose, general-purpose computational fluid dynamics(CFD) code is used : FLUENT. Mass fluxes and pressure ratio are calculated for two types of nozzle. The comparative studies reveal that the computational results are in agreement with the experimental data. Also, heat transfer coefficients from FLUENT for one type of nozzle are very similar and agree well with the experimental data in the diverging part of the nozzle, but the calculated results are large in the converging part. The heat transfer coefficients from Bartz equation are over-predicted. We can consider various reasons for these differences, i.e., laminarization by the highly accelerated flow in the nozzle, turbulent flow model and grid generation.

The Numerical Investigation on Vortex Flow Behavior Using FLOW-3D

In this paper a numerical investigation is given for a Rankine type vortex flow inside the cylindrical vortex chamber using FLOW-3D. The FLOW-3D is a general purpose computational fluid dynamics (CFD) package. The fluid motion is described with non-linear, transient, second-order differential equations. Additionally the free surface also exists in many simulations carried out with FLOW-3D because flow parameters and materials properties, such as density, velocity and pressure experience a discontinuity at it. After analysis of the vortex by mentioned details, the finding of time-averaged velocity components, turbulent components, turbulence dissipation, in the 2D briefed sections of chamber were depicted. It was found that there are different flow patterns like clockwise/anticlockwise vortices and some sink points combined with each other in different time intervals, decaying and generating along the time. Also the turbulence intensity and dissipations around the boundary conditions of chamber like central flushing discharge are higher than the flow body. It was also found that this CFD package was not able to simulate thoroughly the central air core of chamber after filling of chamber. This analysis is validated by comparison with previous experimental data that was measured in vortex settling basin.

Modeling and simulation of dense cloud dispersion in urban areas by means of computational fluid dynamics

The formation of toxic heavy clouds as a result of sudden accidental releases from mobile containers, such as road tankers or railway tank cars, may occur inside urban areas so the problem arises of their consequences evaluation.Due to the semi-confined nature of the dispersion site simplified models may often be inappropriate.As an alternative, computational fluid dynamics (CFD) has the potential to provide realistic simulations even for geometrically complex scenarios since the heavy gas dispersion process is described by basic conservation equations with a reduced number of approximations.In the present work a commercial general purpose CFD code (CFX 4.4 by Ansys®) is employed for the simulation of dense cloud dispersion in urban areas. The simulation strategy proposed involves a stationary pre-release flow field simulation followed by a dynamic after-release flow and concentration field simulations.In order to try a generalization of results, the computational domain is modeled as a simple network of straight roads with regularly distributed blocks mimicking the buildings. Results show that the presence of buildings lower concentration maxima and enlarge the side spread of the cloud. Dispersion dynamics is also found to be strongly affected by the quantity of heavy-gas released.

Simulation of natural circulation in a rectangular loop using CFD code PHOENICS

Abstract Single phase natural circulation in a rectangular loop is simulated using the PHOENICS code, a general purpose Computational Fluid Dynamics (CFD) code. The rectangular loop, having different operating power levels, has been modeled with the help of the Multiple Block Fine Grid Embedment (MBFGE) technique. The Co-located Co-variant Method (CCM) is used to simulate this loop in PHOENICS. Extensive experimental and CFD studies have been conducted on single phase natural circulation in a rectangular loop. The paper presents the results of three-dimensional CFD analysis for the prediction of steady state behavior in a rectangular loop and its comparison with experimental data. The results of code prediction and readily available experimental data show good agreement.

Blast response comparison of multiple steel frame connections

When a structural steel frame is subjected to blast, the beam-to-column connections, which are responsible for load transfer between different members within the frame, play a major role in structural response. This paper presents results of a comparative finite element analysis of a steel frame subjected to a blast loading from a vehicular threat. The study compared three connection systems referred as standard, TA and SidePlate TM. Connection plate thickness variations were also considered. Strain rate effects were included in the material constitutive model. The pressure–time histories were determined using FEFLO, a general purpose computational fluid dynamics program developed by the Center for Computational Fluid Dynamics at George Mason University. The numerical results were used to compare both the structural response and the constructability of frames with the studied connection types. Three structural response evaluation criteria and three such constructability criteria were used to determine comparative advantages and disadvantages of the TA and SidePlate TM connection types with respect to the standard connection.

Critical assessment of hybrid and zonal wall functions for missile aerodynamics simulations

A state-of-the-art wall function near-wall modelling capability was implemented into a general-purpose computational fluid dynamics solver to assess its performance in viscous missile aerodynamics simulations. Test cases included a simple two-dimensional boundary layer, a complex missile configuration with fixed control surfaces, and a spinning missile with dithering canards. Results indicate that judicious use of wall functions may provide a useful compromise between economy and accuracy for viscous missile aerodynamics simulations. However, the results do not indicate a substantial advantage to using any particular version of the wall functions, at least for the test cases addressed in this study.

ICONE19-43536 Development of CFD Analysis Method Based on Droplet Tracking Model for BWR Fuel Assemblies

It is well known that the minimum critical power ratio (MCPR) of the boiling water reactor (BWR) fuel assembly depends on the spacer grid type. Recently, improvement of the critical power is being studied by using a spacer grid with mixing devices attaching various types of flow deflectors. In order to predict the critical power of the improved BWR fuel assembly, we have developed an analysis method based on the consideration of detailed thermal-hydraulic mechanism of annular mist flow regime in the subchannels for an arbitrary spacer type. The proposed method is based on a computational fluid dynamics (CFD) model with a droplet tracking model for analyzing the vapor-phase turbulent flow in which droplets are transported in the subchannels of the BWR fuel assembly. We adopted the general-purpose CFD software Advance/FrontFlow/red (AFFr) as the base code, which is a commercial software package created as a part of Japanese national project. AFFr employs a three-dimensional (3D) unstructured grid system for application to complex geometries. First, AFFr was applied to single-phase flows of gas in the present paper. The calculated results were compared with experiments using a round cellular spacer in one subchannel to investigate the influence of the choice of turbulence model. The analyses using the large eddy simulation (LES) and re-normalisation group (RNG) k-ε models were carried out. The results of both the LES and RNG k-ε models show that calculations of velocity distribution and velocity fluctuation distribution in the spacer downstream reproduce the experimental results qualitatively. However, the velocity distribution analyzed by the LES model is better than that by the RNG k-ε model. The velocity fluctuation near the fuel rod, which is important for droplet deposition to the rod, is also simulated well by the LES model. Then, to examine the effect of the spacer shape on the analytical result, the gas flow analyses with the RNG k-ε model were performed for three kinds of spacers of actual fuel assemblies: a lattice type spacer, a round cell type spacer, and a grid spacer with mixing vanes, respectively. The results indicate that the swirling flow is generated by the mixing vane, and the turbulence energy increases near the surface of fuel rod. The Lagrangian method was applied to droplet behavior in turbulent gas flow around the round cell type spacer and that around a mixing vane spacer as trial analyses. It was confirmed that liquid droplet deposition is promoted in downstream from the mixing vane spacer because of swirling flow.

Learning hydraulic turbomachinery with computational fluid dynamics (CFD) codes

In fluid mechanics courses of engineering curricula, theoretical performance curves of hydraulic turbines are obtained by means of simple analytical expressions that tend to overestimate experimental data. As we show here in the analysis of a laboratory-scale Pelton wheel, a much deeper physical insight can be achieved by means of general-purpose commercial computational fluid dynamics (CFD) software programs, becoming a suitable tool for academic activities. © 2010 Wiley Periodicals, Inc. Comput Appl Eng Educ 21: 684–690, 2013

Numerical and Experimental Fluid-Dynamic Analysis To Improve the Mass Transfer Performances of Pd−Ag Membrane Modules for Hydrogen Purification

This work is aimed at investigating the impact of the fluid flow features on the behavior of gas separation membrane modules. The investigation is carried out by particle image velocimetry (PIV) experiments and computational fluid dynamics (CFD) simulations. The experimental velocity data collected in a laboratory scale membrane module confirm the reliability of the gas velocity field calculated numerically solving the Navier−Stokes equations by a general-purpose finite volume CFD code, and the effect of the observed nonideal flow distribution on the module separation performances is discussed. Afterward, the case of a pilot scale module equipped with three Pd−Ag membranes, which are well-suited for the separation of H2 from methane steam reforming gas mixtures, is considered. The appropriateness of the selected CFD method for the design and the geometric optimization of membrane modules of pilot size is demonstrated.

An integrated numerical simulator for thermal performance assessments of firefighters’ protective clothing

Research and development of firefighters’ protective clothing relies on a large number of fire disaster experiments in order to assess the thermal performance. It would be substantially advantageous to substitute a virtual numerical experiment for a real one in terms of time, cost and safety. The present article reports the development of an integrated numerical simulator that makes possible the estimation of burn injuries originating from fire disasters. In the simulator, a general-purpose computational fluid dynamics program computes the fluid flow and heat transfer in an in situ fire event, while a one-dimensional program calculates the radiative–conductive heat transfer through the clothing and human skin. A data interface combines the two simulations by loose coupling so as to give the real-time burn injury progress output. The predicted surface heat fluxes and burn degrees agree with experimental measurements reasonably well. Possible numerical error sources are discussed that call for potential improvements in the future.

Implementation of a Pressure Drop Model for the CFD Simulation of Clogged Containment Sump Strainers

The present study aims at modeling the pressure drop of flows through growing cakes of compressible fibrous materials, which may form on the upstream side of containment sump strainers after a loss-of-coolant accident. The model developed is based on the coupled solution of a differential equation for the change of the pressure drop in terms of superficial liquid velocity and local porosity of the fiber cake and a material equation that accounts for the compaction pressure dependent cake porosity. Details of its implementation into a general-purpose three-dimensional computational fluid dynamics code are given. An extension to this basic model is presented, which simulates the time dependent clogging of the fiber cake due to capturing of suspended particles as they pass trough the cake. The extended model relies on empirical relations, which model the change of pressure drop and removal efficiency in terms of particle deposit in the fiber cake.

Studies on Fanning Friction (f) and Colburn (j) Factors of Offset and Wavy Fins Compact Plate Fin Heat Exchanger–A CFD Approach

The objective of this work is to address the uncertainties in the estimation of the Fanning friction (f) and Colburn (j) factors in a compact offset plate fin heat exchanger, and the generation of flow friction and heat transfer correlations in the form of f and j for compact wavy plate fin heat exchangers. A typical offset fin has been analyzed using FLUENT software (a general purpose computational fluid dynamics (CFD) simulation tool) for estimation of f and j data. These results are compared with the results of the available correlations in the literature and in-house experimental results. Uncertainties in estimation of f and j data are reviewed and the variations in the results are highlighted. In the case of wavy fin configuration, very limited correlations are available in the literature. Hence, with the objective of developing correlations, 18 different types of wavy fins geometries have been analyzed using a CFD tool to find out the f and j data in the laminar and turbulent regions. Multiple regression analysis has been carried out on the set of data to generate the correlations for f and j. These correlations have been compared with the experimental results of wavy fin reported in the literature.

Correlation-Based Transition Modeling for Unstructured Parallelized Computational Fluid Dynamics Codes

A new correlation-based transition model has been developed, which is built strictly on local variables. As a result, the transition model is compatible with modern computational fluid dynamics techniques such as unstructured grids and massively parallel execution. The model is based on two transport equations, one for intermittency and one for a transition onset criterion in terms of momentum-thickness Reynolds number. A number of validation papers have been published on the basic formulation of the model. However, until now the full model correlations have not been published. The main goal of the present paper is to publish the full model and release it to the research community so that it can continue to be further validated and possibly extended or improved. Included in this paper are a number of test cases that can be used to validate the implementation of the model in a given computational fluid dynamics code. The authors believe that the current formulation is a significant step forward in engineering transition modeling, as it allows the combination of transition correlations with general-purpose computational fluid dynamics codes. There is a strong potential that the model will allow the first-order effects of transition to be included in everyday industrial computational fluid dynamics simulations.

Computation of the viscous hydrodynamic forces on a KVLCC2 model moving obliquely in shallow water

The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety. In the paper, the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag, lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics (CFD) package FLUENT with shear-stress transport (SST) k-ω turbulence model. The numerical computation is performed at different drift angels and water depths. The numerical results are compared with experimental results, and a good agreement is demonstrated.

EFFICIENT CALCULATION OF RADIATION HEAT TRANSFER IN ANISOTROPICALLY SCATTERING MEDIA USING THE QL METHOD

In the general-purpose computational fluid dynamics codes, radiation heat transfer is often computed using the P1 model, which can be inaccurate, or the Finite Volume or Discrete Ordinates method, which can be computationally very expensive. The present research objective was to develop a solution method, called the QL method, which permits both the accuracy and cost to be controlled. The method has been previously shown to work well for radiation-only problems involving emission/absorption and isotropic scattering in a gray medium. This paper demonstrates the method on problems involving anisotropic scattering. It is shown that any scattering phase function can be handled in the QL method, and that accurate results are obtained at reasonable cost.

Adaptation of Pressure Based CFD Solvers for Mesoscale Atmospheric Problems

General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes, such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface energy balance are important further steps towards the practical application of the method.

Thermal stratification studies in a side heated water pool for advanced heavy water reactor applications

Strong heat source at the isolation condenser wall of an Advanced Heavy Water Reactor, results in natural convection in gravity driven water pool, which leads to a thermally stratified pool. Governing equations simulating fluid flow and heat distribution are solved numerically by a general purpose Computational Fluid Dynamics solver developed at Indian Institute of Technology, Kanpur. Incompressible finite volume method with non-staggered grid arrangement is used in this exercise. This algorithm is fully implicit and semi-coupled. Turbulent natural convection in a boundary layer for high Rayleigh numbers is analyzed by the Lam–Bremhorst k − e turbulence model. Analysis of unsteady laminar natural convection in a side-heated water cavity is also done for different values of Rayleigh number. Results show a warm fluid layer floating on the top of gradually colder layer (along the vertical direction) that indicates the presence of thermal stratification phenomenon. This fact necessitates additional safety features in such a system so that the detrimental effect such as stratification is minimized.

Noise computation of an axisymmetric free jet using general purpose CFD code

The increasing interest in the noise prediction of the turbulent flows is leading the general purpose Computational Fluid Dynamics (CFD) software developers to integrate noise predicting methods into their code. However the aeroacoustic simulation of free shear flows, where the mean source of noise is the turbulent fluctuations in the free space is challenging with a general purpose CFD application. The aim of this work is to investigate the capabilities of commercial CFD software in the field of noise prediction of free shear flows. The important acoustical properties of a low Reynolds number, low Mach number axisymmetric (2D) jet is computed by means of hybrid Computational Aeroacoustic method using Fluent. The noise source is computed without modeling instantaneously using the compressible solver of the code, and the far field acoustical data is evaluated by the Ffowcs‐Williams‐Hawkings acoustical analogy. The results is compared to the Direct Numerical Simulation of [Jiang2004 J. Sound Vib.] in terms of frequency spectra in the far field and directivity pattern of the jet.

On the Dynamics of Environmental Pollution: Simulation of the near Field of a Jet in Crossflow

This paper investigates numerically the complex flow in the near field of a rectangular jet discharging vertically downward into a uniform crossflow. This flow situation exists when pollutants generated from many industrial processes are released into the environment. Examples include those released from petrochemical plants, power plants, and desalination units. A thorough understating of turbulent dispersion of such pollutants is a first step towards the development of appropriate control methods. Using general purpose Computational Fluid Dynamics (CFD) software, the turbulent Navier-Stokes equations for unsteady, three-dimensional, incompressible flows are numerically solved in this study. The accuracy of this computational software is assessed by comparing the computed results with Laser Doppler Anemometry (LDA) measurements for two flow cases. Both cases (jet-to-crossflow velocity ratios 3 and 5) yield favorable agreement for the turbulence characteristics of the flow. The present computational methodology not only allows us to capture the coherent structures of the flowfield which include tornado-like vortices, counter-rotating vortices, and a horseshoe-type vortex, but also helps in understanding the mixing processes of pollutants with the ambient. This, in turn, may help in the utilization, enhancement, or suppression of selected vortices in many environmental pollution problems.

Reynolds-Averaged Navier-Stokes Simulations for High-Speed Wigley Hull in Deep and Shallow Water

Reynolds-averaged Navier-Stokes simulations and verification and validation studies for a high-speed Wigley hull in deep and shallow water are presented using CFD-SHIP-IOWA Version 4.00, which is a general-purpose ship hydrodynamics computational fluid dynamics code: single-phase level set free surface and k-w turbulence modeling; higher-order conservative discretization, embedded overset grids, advanced iterative solvers, and implicit coupling flow field and predicted motions numerical methods; and high-performance computing for message-passing interface (MPI)-based domain decomposition. The results are presented for low to high speed and deep to shallow water. The investigation is exploratory in nature using an idealized geometry and relatively coarse grids. Based on the verification and validation results, modifications for increased grid resolution at the bow for high speed and improved grid orthogonality for shallow water are made to obtain better solutions. The flow physics observations provide both integral and differential views of the highspeed and shallow-water flow fields, including resistance, pressure variation, wave pattern, boundary layer, and vortices.