Spatial resolution effects on unsteady turbulent flow computations for the rectangular cylinders byκ-ε turbulence models

1997 ◽  
Vol 11 (3) ◽  
pp. 339-347 ◽  
Author(s):  
Sangsan Lee
Keyword(s):  
Turbulent Flow ◽  
Spatial Resolution ◽  
Turbulence Models ◽  
Rectangular Cylinders

Numerical and Experimental Analysis of Turbulent Flow in Corrugated Pipes

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Henrique Stel ◽  
Rigoberto E. M. Morales ◽  
Admilson T. Franco ◽  
Silvio L. M. Junqueira ◽  
Raul H. Erthal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Geometric Configurations ◽  
Corrugated Surfaces ◽  
Friction Factors

This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic “d-type” corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen–Kim k-ε turbulence model, for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model, used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general, the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen–Kim k-ε and LVEL turbulence models show good agreement with the experimental measurements.

Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models

2002 ◽  
Author(s):  
Wang Kee In ◽  
Dong Seok Oh ◽  
Tae Hyun Chun
Keyword(s):  
Turbulent Flow ◽  
Nuclear Fuel ◽  
Turbulence Models ◽  
Convective Transport ◽  
Stress Model ◽  
Convergence Criteria ◽  
Mean Flow ◽  
Numerical Predictions ◽  
Viscosity Models ◽  
Fuel Bundle

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.

Assessment of Different Turbulence Models in Helically Coiled Pipes Through Comparison With Experimental Data

2012 ◽  
Author(s):  
Marco Colombo ◽  
Antonio Cammi ◽  
Marco E. Ricotti
Keyword(s):  
Turbulent Flow ◽  
Great Influence ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Test Facility ◽  
Wall Functions ◽  
Pressure Drops ◽  
Fully Developed Turbulent Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Helical Geometry

This paper deals with a comprehensive study of fully developed single-phase turbulent flow and pressure drops in helically coiled channels. To the aim, experimental pressure drops were measured in an experimental campaign conducted at SIET labs, in Piacenza, Italy, in a test facility simulating the Steam Generator (SG) of a Generation III+ integral reactor. Very good agreement is found between data and some of the most common correlations available in literature. Also more data available in literature are considered for comparison. Experimental results are used to assess the results of Computational Fluid Dynamics (CFD) simulations. By means of the commercial CFD package FLUENT, different turbulence models are tested, in particular the Standard, RNG and realizable k-ε models, Shear Stress Transport (SST) k-ω model and second order Reynolds Stress Model (RSM). Moreover, particular attention is placed on the different types of wall functions utilized through the simulations, since they seem to have a great influence on the calculated results. The results aim to be a contribution to the assessment of the capability of turbulence models to simulate fully developed turbulent flow and pressure drops in helical geometry.

scholarly journals Numerical investigation of unsteady flow past a circular cylinder using 2-D finite volume method

1970 ◽  
Vol 4 (1) ◽  
pp. 27-42 ◽  
Author(s):  
Md Mahbubar Rahman ◽  
Md. Mashud Karim ◽  
Md Abdul Alim
Keyword(s):  
Circular Cylinder ◽  
Unsteady Flow ◽  
Turbulent Flow ◽  
Finite Volume Method ◽  
Finite Volume ◽  
Turbulence Models ◽  
Drag Coefficients ◽  
Pressure Formulation ◽  
Lift And Drag ◽  
Volume Method

The dynamic characteristics of the pressure and velocity fields of unsteady incompressible laminar and turbulent wakes behind a circular cylinder are investigated numerically and analyzed physically. The governing equations, written in the velocity pressure formulation are solved using 2-D finite volume method. The initial mechanism for vortex shedding is demonstrated and unsteady body forces are evaluated. The turbulent flow for Re = 1000 & 3900 are simulated using k-? standard, k-? Realizable and k-? SST turbulence models. The capabilities of these turbulence models to compute lift and drag coefficients are also verified. The frequencies of the drag and lift oscillations obtained theoretically agree well with the experimental results. The pressure and drag coefficients for different Reynolds numbers were also computed and compared with experimental and other numerical results. Due to faster convergence, 2-D finite volume method is found very much prospective for turbulent flow as well as laminar flow.Keywords: Viscous unsteady flow, laminar & turbulent flow, finite volume method, circular cylinder.DOI: 10.3329/jname.v4i1.914Journal of Naval Architecture and Marine Engineering 4(2007) 27-42

Alternative Approach for Modeling Transients in Smooth Pipe With Low Turbulent Flow

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
David A. Hullender
Keyword(s):  
Differential Equations ◽  
Turbulent Flow ◽  
Ordinary Differential Equations ◽  
Steady Flow ◽  
Flow Resistance ◽  
Turbulence Models ◽  
Engineering System ◽  
Partial Differential ◽  
Simplified Approach ◽  
Linear Ordinary Differential Equations

A new simplified approach for modeling and simulating pressure transients resulting from the rapid acceleration or deceleration of turbulent flow in smooth-walled fluid lines is introduced. In contrast to previous approaches for modeling turbulence by modifying the head loss terms in the momentum partial differential equation, this approach is achieved by coupling the frequency domain analytical solution to the laminar flow version of the partial differential equations in series with a lumped resistance that has been sized so that the steady flow resistance for the line is equivalent to an empirical turbulent steady flow resistance. The model provides normalized pressure and flow transients that have good agreement with experimental data and with method-of-characteristics (MOC) solutions associated with previously validated turbulence models. The motivation for this research is based on the need for a practical means to simulate the effects of fluid transients in lines that are internal components within a total engineering system without the need to understand the different unsteady turbulence one- and two-dimensional (1D/2D) friction models and also be proficient with the complexities of nonlinear interaction of friction and interpolation errors encountered using MOC. This modeling approach utilizes a preprogramed inverse frequency algorithm, commonly used for system identification, which generates “equivalent” high-order normalized linear ordinary differential equations that can be coupled with models for other fluid power components and easily solved in the time domain using preprogramed numerical algorithms for ordinary differential equations.

Heat Transfer and Hydraulic Resistance in Turbulent Flow in Vertical Round Tubes At Supercritical Pressures. Part 1. Results From Numerical Simulations Using Algebraic Turbulent Viscosity Models

2020 ◽  
Author(s):  
Georgii Glebovich Yankov ◽  
Vladimir Kurganov ◽  
Yury Zeigarnik ◽  
Irina Maslakova
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulent Flow ◽  
Hydraulic Resistance ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Heating And Cooling ◽  
Prediction Techniques ◽  
Vertical Tubes

Abstract The review of numerical studies on supercritical pressure (SCP) coolants heat transfer and hydraulic resistance in turbulent flow in vertical round tubes based on Reynolds-averaged Navier-Stokes (RANS) equations and different models for turbulent viscosity is presented. The paper is the first part of the general analysis, the works based on using algebraic turbulence models of different complexity are considered in it. The main attention is paid to Petukhov-Medvetskaya and Popov et al. models. They were developed especially for simulating heat transfer in tubes of the coolants with significantly variable properties (droplet liquids, gases, SCP fluids) under heating and cooling conditions. These predictions were verified on the entire reliable experimental data base. It is shown that in the case of turbulent flow in vertical round tubes these models make it possible predicting heat transfer and hydraulic resistance characteristics of SCP flows that agree well with the existed reliable experimental data on normal and certain modes of deteriorated heat transfer, if significant influence of buoyancy and radical flow restructuring are absent. For the more complicated cases than a flow in round vertical tubes, as well as for the case of rather strong buoyancy effect, more sophisticated prediction techniques must be applied. The state-of-the-art of these methods and the problems of their application are considered in the Part II of the analysis.

Application of Non-Linear k–ω Model to the Turbulent Flow Inside a Sharp U-Bend

2000 ◽  
Author(s):  
B. Song ◽  
R. S. Amano
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Higher Order ◽  
Shear Stresses ◽  
Complex Flow ◽  
Streamline Curvature ◽  
Non Linear ◽  
Low Reynolds

Simulation of the complex flow inside a sharp U-bend needs both refined turbulence models and higher order numerical discretization schemes. In the present study, a nonlinear low-Reynolds number (low-Re) k–ω model including the cubic terms was employed to predict the turbulent flow through a square cross-sectioned U-bend with a sharp curvature, Rc/D = 0.65. In the turbulence model employed for the present study, the cubic terms are incorporated to represent the effect of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. In order to accurately predict such complex flowfields, a higher-order bounded interpolation scheme (Song, et al., 1999) has been used to discretize all the transport equations. The calculated results by using both the non-linear k–ω model and the linear low-Reynolds number k–ε model (Launder and Sharma, 1974) have been compared with experimental data. It is shown that the present model produces satisfactory predictions of the flow development inside the sharp U-bend and well captures the characteristics of the turbulence anisotropy within the duct core region and wall sub-layer.

Particle Collision Effect on Turbulent Prandtl Number in Gas-Solid Flows

2006 ◽  
Author(s):  
Zohreh Mansoori ◽  
Majid Saffar-Avval ◽  
Hasan Basirat-Tabrizi ◽  
Goodarz Ahmadi ◽  
Payam Ramezani
Keyword(s):  
Prandtl Number ◽  
Turbulent Flow ◽  
Time Scale ◽  
Turbulence Models ◽  
Flow Region ◽  
Eddy Diffusivity ◽  
Particle Collision ◽  
Turbulent Prandtl Number ◽  
Particle Collisions ◽  
Particle Properties

Traditional gas-solid turbulence models using constant or the single-phase gas turbulent Prandtl number cause error in the thermal eddy diffusivity and thermal turbulent intensity fields calculation. The thermo-mechanical turbulence model is based on solving the hydrodynamic transport equations of the turbulent kinetic energy and turbulent time scale, beside the thermal turbulent equations of temperature variance and thermal turbulence time scale. This model has the ability to calculate the turbulent Prandtl number directly by computing the eddy viscosity and the thermal eddy diffusivity through the values of turbulence fluctuation velocity and thermal variances and time scales. A four way Eulerian/Lagrangian formulation was used to study the effect of particle properties on the turbulent flow and thermal fields, as well as on turbulent Prandtl number in a gas-solid developing pipe flow. Inter-particle collisions were included and the Lagrangian trajectory analysis was used. The earlier results showed that turbulent Prandtl number is influenced by the variations of gas and particle properties and also inter-particle collisions in a fully-developed riser. In the current study, the developing gas-solid flow region in a pipe was considered and the variation of turbulent flow field due to inter-particle collision was evaluated.

Comparative Studies of Turbulence Models Application in Thermal Hydraulic Analysis of Nuclear Reactor Core

2010 ◽  
Author(s):  
Heyi Zeng ◽  
Yun Guo
Keyword(s):  
Fluid Dynamics ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Nuclear Reactor ◽  
Nuclear Reactors ◽  
Reactor Core ◽  
Turbulence Models ◽  
Flow Phenomena ◽  
Nuclear Reactor Core ◽  
Complicated Geometry

Rod bundles are essential elements of pressurized water nuclear reactors. They consist of tightly packed arrays of rods, which contain the nuclear fuel and are surrounded by flowing liquid coolant. Flow phenomena in the subchannels bounded by adjacent rods are quite complex and exhibit patterns not present in pipe flows. Development of nuclear reactors and of fuel assemblies requires fluid dynamics analysis activities. The detailed prediction of velocity and temperature distributions inside a rod bundle is one of the main objectives of the current research in reactor thermal hydraulics. Computational fluid dynamics (CFD) simulation is of great interest for the design and safety analysis of nuclear reactors since it has recently achieved considerable advancements. In the present studies, numerical simulation were performed on developed turbulent flow through core subchannels with configurations of triangle and square lattice, and impact of different turbulence models built-in software package FLUENT upon simulation results of velocity distribution and hydraulic characteristics in channels with complicated geometry were compared and analyzed. Results show that simulation result greatly depends on turbulence models. Due to the complicated geometric construction, the complicated three-dimensional turbulent flow shows highly anisotropic characteristics. Turbulence models assuming isotropic turbulent viscosity failed to predict secondary flow phenomena during turbulent flow in fuel assembly channel. By solving Reynolds stresses transport equations, more elaborate Reynolds stress model (RSM) can catch secondary flow accurately. The present studies have provided valuable references and guidelines for further investigation on convective heat transfer simulation in complicated geometry and thermalhydrulic analysis of nuclear reactor core.

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