Numerical Study of Different Closure Approaches for Prediction of Forced Convective Turbulent Cylindrical Cavity Flows

2016 ◽  
Vol 366 ◽  
pp. 166-181
Author(s):  
Elizaldo Domingues dos Santos ◽  
Marco Paulsen Rodrigues ◽  
Thiago Smith V.C. de Andrade ◽  
Liércio André Isoldi ◽  
Francis Henrique Ramos França ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Cylindrical Cavity ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Thermal Fields ◽  
Convective Fluxes

The present work exhibits a numerical study comparing the fluid dynamic and thermal fields of turbulent, three-dimensional forced convective cylindrical cavity flows obtained with Large Eddy Simulation (LES) and Reynolds-Averaged Navier Stokes (RANS). In the latter approach, three different closure models are employed: Reynolds Stress Model (RSM), standard k – ε and standard k - ω. It is considered a three-dimensional, incompressible, turbulent fluid flow at the steady state with ReD = 22,000 and Pr = 0.71. The main purpose is to investigate whether discrepancies are noticed in time-averaged and statistics of turbulent flows between LES and RANS predictions. Differences in time-averaged and statistical fields can be important for evaluation of convective fluxes in turbulent flows and combined convective and radiative transfer in participant media, i.e., for study of Turbulence-Radiation Interactions (TRI). The spatially-filtered and time-averaged conservation equations of mass, momentum and energy are solved with the Finite Volume Method (FVM). Results showed that time-averaged and RMS thermal fields obtained with LES and RANS presented reasonable discrepancies in regions near the cavity surfaces, which affects the convective fluxes in this region. For the highest temperature region of the cavity (near its inlet) the predictions obtained with LES and RANS are similar, which can led to similar predictions in heat exchange when thermal radiation is taken into account in optically thin participant media. For optically thick media, where local differences increase their importance, the employment of RANS is not recommended.

Numerical Investigation of Contribution of Three Flow Conditioners in the Development and Establishment of Turbulent Flows

2010 ◽  
Author(s):  
Boualem Laribi ◽  
Pierre Wauters ◽  
Abdelkader Youcefi
Keyword(s):  
Turbulent Flows ◽  
Stokes Equations ◽  
Numerical Study ◽  
Tube Bundle ◽  
Three Dimensional ◽  
Perforated Plate ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Out Of Plane

This numerical study is a comparative study of the development and establishment of turbulent flows through three flow conditioners namely Laws perforated plate, the Etoile and the tube bundle. They are installed in a circular pipe with a disturbance generated by a 90° double bend out of plane which causes a very strong swirl of the fluid. The analysis is done with the code Fluent in which the Navier-Stokes equations describe a three-dimensional incompressible flow with the Reynolds stress model (RSM) as a closure system. This article focuses on the effectiveness of the three packers to produce the condition of fully developed velocity profile. The results are compared to references profiles cited in the literature and experimental results. The flow is simulated with air at Reynolds number of 105 in 100mm pipe diameter. The velocity profiles are compared with the profile obtained by the universal law of power 1/7th.

Calculations of three-dimensional viscous flow in a multiblade centrifugal fan by modelling blade forces

2003 ◽  
Vol 217 (3) ◽  
pp. 287-297 ◽  
Author(s):  
S-J Seo ◽  
K-Y Kim ◽  
S-H Kang
Keyword(s):  
Mathematical Model ◽  
Turbulent Flows ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Centrifugal Fan ◽  
Complex Flows ◽  
Flow Through ◽  
Volume Method ◽  
The Mathematical Model

A numerical study is presented for Reynolds-averaged Navier-Stokes analysis of three-dimensional turbulent flows in a multiblade centrifugal fan. Present work aims at development of a relatively simple analysis method for these complex flows. A mathematical model of impeller forces is obtained from the integral analysis of the flow through the impeller. A finite volume method for discretization of governing equations and a standard k-ɛ model as turbulence closure are employed. For the validation of the mathematical model, the computational results for velocity components, static pressure, and flow angles at the exit of the impeller were compared with experimental data. The comparisons show generally good agreement, especially at higher flow coefficients.

scholarly journals Experimental and Numerical Study of Flow Structures Associated With Low Aspect Ratio Elliptical Cavities

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Taravat Khadivi ◽  
Eric Savory
Keyword(s):  
Aspect Ratio ◽  
Particle Image ◽  
Numerical Study ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Cavity Flows ◽  
Low Aspect Ratio ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

The flow regimes associated with 2:1 aspect ratio elliptical planform cavities of varying depth immersed in a turbulent boundary layer at a Reynolds number of 8.7 × 104, based on the minor axis of the cavity, have been quantified from particle image velocimetry measurements and three-dimensional steady computational fluid dynamics simulations (Reynolds stress model closure). Although these elliptical cavity flows have some similarities with nominally two-dimensional and rectangular cases, three-dimensional effects due to the low aspect ratio and curvature of the walls give rise to features exclusive to low aspect ratio elliptical cavities, including formation of cellular structures at intermediate depths and vortex structures within and downstream of the cavity.

Three-Dimensional Laminar Wall Jet Flows

2009 ◽  
Author(s):  
Kofi K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Jet Flows ◽  
Wall Jet ◽  
Navier Stokes Equation ◽  
Flow Geometry

The present article reports on both experimental and numerical study of three-dimensional laminar wall jet flows. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open channel. The Reynolds numbers based on the pipe diameter and jet exit velocity were varied from 310 to 1300. A particle image velocimetry (PIV) was used to conduct detailed velocity measurements at various streamwise-transverse and streamwise-spanwise planes. A complete nonlinear incompressible Navier-Stokes equation was also solved using a co-located finite volume based in-house computational fluid dynamic (CFD) code. This code was used to compute the experimental flow geometry. From the PIV measurements and CFD results, velocities profiles and jet-half-widths were extracted at selected locations. It was observed that the numerical results are in reasonable agreement with the experimental data. The distributions of the velocities, jet-half-widths and visualisation of the secondary flows were used to provide insight into the characteristics of three-dimensional wall jet flows.

A Navier-Stokes Analysis of Three-Dimensional Turbulent Flows Inside Turbine Blade Rows at Design and Off-Design Conditions

1984 ◽  
Vol 106 (2) ◽  
pp. 421-429 ◽  
Author(s):  
C. Hah
Keyword(s):  
Turbulent Flows ◽  
Turbine Blade ◽  
Numerical Scheme ◽  
Control Volume ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Governing Equations ◽  
Navier Stokes Equation

A numerical scheme based on the compressible Navier-Stokes equation has been developed for three-dimensional turbulent flows inside turbine blade rows. The numerical scheme is based on a fully conservative control volume formulation and solves the governing equations in fully elliptic form. Higher order discretizations are used for the convection term to reduce the numerical diffusion. An algebraic Reynolds stress model modified for the effects of the streamline curvature and the rotation is used for the closure of the governing equations. General coordinate transformations are used to represent the complex blade geometry accurately, and a grid generation technique based on elliptic partial differential equations is employed. Comparisons with the experimental data show that various complex three-dimensional viscous flow phenomena (three-dimensional flow separation near the leading edge, formation of the horseshoe vortex, etc.) are well predicted with the present method.

Computational and Analytical Study of Multiphase Rotary Separator Turbine Liquid Outlet

2007 ◽  
Author(s):  
Gocha Chochua ◽  
William C. Maier
Keyword(s):  
Turbulent Flows ◽  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Navier Stokes ◽  
Offshore Platforms ◽  
Centrifugal Forces ◽  
Navier Stokes Equations ◽  
Multiple Frames ◽  
Cfd Analyses

Gas-liquid separation is typically performed in settling tanks using gravitational force, or in cyclones generating higher centrifugal forces by swirl generators. However, in some applications such as offshore platforms or subsea compression stations, further compactness of the separating units is important. The Rotary Separator Turbine, a special type of cyclonic separator, generates even higher centrifugal forces, which allows the design of very compact separators. Due to the complexity of the flow fields in this type of machine, Computational Fluid Dynamic (CFD) analyses were used in the recent design of such a rotary separator. Reynolds Averaged Navier-Stokes equations are solved for multiphase turbulent flows in multiple frames of reference. This paper describes basic functionality of the RST and concentrates on one particular analysis of the lip discharge geometry. In addition to the numerical study, an analytical model is presented for this particular flow.

scholarly journals Three-Dimensional Simulation of High Reynolds Turbulent Flows in a Rectangular Open Channel with the Presence of a Disruptive Element (Obstacles) Transversely

2015 ◽  
Vol 23 (1) ◽  
pp. 1-7
Author(s):  
H’ssine Boudiaf ◽  
Ali Fourar ◽  
Fawaz Massouh
Keyword(s):  
Turbulent Flows ◽  
Reynolds Stress ◽  
Open Channel ◽  
Numerical Study ◽  
Numerical Models ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Dimensional Simulation ◽  
High Reynolds

Abstract This study aims at describing a three-dimensional simulation of a turbulent flow with a high Reynolds number in a rectangular open channel with the presence of a disruptive element (obstacles) transversely. The numerical study is based on measuring the flow velocity in two directions, i.e., horizontal and vertical, in four planes located near the obstacle built across a simulated channel. For the modeling of the free surface, a Volume Of Fluid (VOF) multiphase flow model is used. In the present case, namely a study of turbulence, three numerical models are compared, a k-ε standard, a k-w standard and a Reynolds Stress Model (RSM). The verification of the simulation results has allowed us to show the advantages of the Reynolds stress model. This model is more representative of the phenomena of an intense vortex flow in the presence of obstacles, especially in drainage systems.

Numerical Study of the Influence of Combustion Models and Kinetic Schemes When Predicting the Diffusion Flames

2012 ◽  
Vol 28 (4) ◽  
pp. 701-713
Author(s):  
A. Khelil ◽  
S. Nechad ◽  
H. Naji ◽  
L. Loukarfi ◽  
M. Braikia ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Combustion Process ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Flamelet Model ◽  
Number Of Factors ◽  
Energy Equations

ABSTRACTThis article aims to study numerically three-dimensional (3D) reactive turbulent flow in a combustion chamber of a gas turbine by solving a steady Reynolds-Averaged Navier-Stokes (RANS) )and energy equations. The Reynolds stress model (RSM) is coupled with the probability density function (PDF), laminar flamelet and Chemistry models to describe the turbulent flow and turbulence–chemistry interaction. Numerical computations are conducted to exhibit thermal and concentration behaviour under a quite number of factors, which influence the combustion process. Their influence are examined and compared favourably with available experimental results. Concentration of some radicals as O and OH are obtained assuming the partial-equilibrium assumption and using a PDF in terms of temperature. The 3D simulations demonstrate that the use of RSM, PDF and flamelet model allow simulating velocity and thermochemical fields.

scholarly journals Dynamics of Single Droplet Splashing on Liquid Film by Coupling FVM with VOF

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 841
Author(s):  
Yuzhen Jin ◽  
Huang Zhou ◽  
Linhang Zhu ◽  
Zeqing Li
Keyword(s):  
Liquid Film ◽  
Weber Number ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Single Droplet ◽  
Navier Stokes Equations ◽  
Volume Method ◽  
The Relationship

A three-dimensional numerical study of a single droplet splashing vertically on a liquid film is presented. The numerical method is based on the finite volume method (FVM) of Navier–Stokes equations coupled with the volume of fluid (VOF) method, and the adaptive local mesh refinement technology is adopted. It enables the liquid–gas interface to be tracked more accurately, and to be less computationally expensive. The relationship between the diameter of the free rim, the height of the crown with different numbers of collision Weber, and the thickness of the liquid film is explored. The results indicate that the crown height increases as the Weber number increases, and the diameter of the crown rim is inversely proportional to the collision Weber number. It can also be concluded that the dimensionless height of the crown decreases with the increase in the thickness of the dimensionless liquid film, which has little effect on the diameter of the crown rim during its growth.

scholarly journals Numerical Study of Three-Dimensional Surface Jets Emerging from a Fishway Entrance Slot

Water ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1079
Author(s):  
Lena Mahl ◽  
Patrick Heneka ◽  
Martin Henning ◽  
Roman B. Weichert
Keyword(s):  
Boundary Conditions ◽  
Turbulent Flows ◽  
Numerical Study ◽  
Three Dimensional ◽  
Free Water ◽  
Lateral Wall ◽  
Lateral Spreading ◽  
Propagation Length ◽  
Vertical Slot ◽  
Surface Jets

The efficiency of a fishway is determined by the ability of immigrating fish to follow its attraction flow (i.e., its jet) to locate and enter the fishway entrance. The hydraulic characteristics of fishway entrance jets can be simplified using findings from widely investigated surface jets produced by shaped nozzles. However, the effect of the different boundary conditions of fishway entrance jets (characterized by vertical entrance slots) compared to nozzle jets must be considered. We investigate the downstream propagation of attraction jets from the vertical slot of a fishway entrance into a quiescent tailrace, considering the following boundary conditions not considered for nozzle jets: (1) slot geometry, (2) turbulence characteristics of the approach flow to the slot, and (3) presence of a lateral wall downstream of the slot. We quantify the effect of these boundary conditions using three-dimensional hydrodynamic-numeric flow simulations with DES and RANS turbulence models and a volume-of-fluid method (VoF) to simulate the free water surface. In addition, we compare jet propagation with existing analytical methods for describing jet propagations from nozzles. We show that a turbulent and inhomogeneous approach flow towards a vertical slot reduces the propagation length of the slot jet in the tailrace due to increased lateral spreading compared to that of a jet produced by a shaped nozzle. An additional lateral wall in the tailrace reduces lateral spreading and significantly increases the propagation length. For highly turbulent flows at fishway entrances, the RANS model tends to overestimate the jet propagation compared to the transient DES model.

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