scholarly journals Direct Numerical Simulation of Fluid Flow in a 5x5 Square Rod Bundle Using Nek5000

2020 ◽  
Author(s):  
Adam Kraus ◽  
Elia Merzari ◽  
Thomas Norddine ◽  
Oana Marin ◽  
Sofiane Benhamadouche
Keyword(s):  
Spectral Element ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Reynolds Stresses ◽  
Complex Flow ◽  
Local Conditions ◽  
Rod Bundle ◽  
Flow Phenomena ◽  
Resolution Analysis ◽  
Water Reactors

Abstract Rod bundle flows are commonplace in nuclear engineering, and are present in light water reactors (LWRs) as well as other more advanced concepts. Inhomogeneities in the bundle cross section can lead to complex flow phenomena, including varying local conditions of turbulence. Despite the decades of numerical and experimental investigations regarding this topic, and the importance of elucidating the physics of the flow field, to date there are few publicly available direct numerical simulations (DNS) of the flow in multiple-pin rod bundles. Thus a multiple-pin DNS study can provide significant value toward reaching a deeper understanding of the flow physics, as well as a reference simulation for development of various reduced-resolution analysis techniques. To this end, DNS of the flow in a square 5 × 5 rod bundle at Reynolds number of 19,000 has been performed using the highly-parallel spectral element code Nek5000. The geometrical dimensions were representative of typical LWR fuel designs. The DNS was designed using microscales estimated from an advanced Reynolds-Averaged Navier-Stokes (RANS) model. Characteristics of the velocity field, Reynolds stresses, and anisotropy are presented in detail for various regions of the bundle. The turbulent kinetic energy budget is also presented and discussed.

CFD Study on Mixing in VVER-440 Fuel Rod Bundle With Guiding Vanes in Spacer Grids

2009 ◽  
Author(s):  
Tellervo Brandt ◽  
Timo Toppila
Keyword(s):  
Turbulence Models ◽  
Heat Fluxes ◽  
Normal Operation ◽  
Navier Stokes ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Fuel Rod ◽  
Rod Bundle ◽  
Computational Fluid Dynamics Cfd ◽  
Water Reactors

In this article, we study mixing in a fuel rod bundle geometry used in VVER-440 type pressurized water reactors. The flow inside the fuel assembly under normal operation is simulated using the FLUENT 6.3 computational fluid dynamics (CFD) solver. Steady state one phase Reynolds-averaged Navier-Stokes modeling is applied with two-equation turbulence models. In the first part of the article, grid independence is studied using a small submodel of the fuel rod bundle. In the second part, flow across a full-length fuel rod bundle is simulated both with constant temperature and with prescribed heat fluxes at the rod walls. Finally, in the third part of the article, we study how guiding vanes included in the spacer grids would enhance mixing in the hottest subchannels. We propose that having four guiding vanes on each side of the hexagonal spacer grid would produce most mixing in the desired locations of the fuel rod bundle.

Application of Large-Eddy Simulation to Pressurized Thermal Shock Problem

2009 ◽  
Author(s):  
M. S. Loginov ◽  
E. M. J. Komen ◽  
A. K. Kuczaj
Keyword(s):  
Large Eddy Simulation ◽  
Life Span ◽  
Thermal Shock ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Pressurized Thermal Shock ◽  
Large Eddy ◽  
Flow Phenomena

Life span assessment is a very important issue for the nuclear community. A serious threat to the life span of a Reactor Pressure Vessel (RPV) is an occurrence of the Pressurized Thermal Shock (PTS) during an Emergency Core Coolant (ECC) injection in a loss-of-coolant accident. Traditional system codes fail to predict the complex three-dimensional flow phenomena resulting from such an ECC injection. Improved results have been obtained using Computational Fluid Dynamics (CFD) analysis based on the Reynolds-Averaged Navier-Stokes (RANS) equations. However, it has been shown also that current transient RANS approaches are less capable to predict complex flow features in the downcomer of the RPV. More advanced CFD methods like Large-Eddy Simulation (LES) are required for modeling of these complex flow phenomena in the downcomer. The current paper addresses the feasibility of the application of LES for single-phase PTS. Furthermore, the required grid resolution for such LES analyses is identified by evaluation of solutions on different meshes. A buoyancy-driven PTS experiment has been considered. This experiment has been performed in the 1:5 linear scale Rossendorf Coolant Mixing Model (ROCOM) facility. In the applied numerical model, the incompressible Navier-Stokes equations are solved in the LES formulation, with an additional transport equation for a scalar, which is responsible for driving the embedded buoyancy term in the momentum equations. Instantaneous mixing characteristics are investigated based on evaluation of the scalar concentration. The analysis presented in this paper indicates that the application of LES is feasible nowadays. It is demonstrated that the mixing in the downcomer is quite sensitive to small turbulent disturbances at the ECC inlet, i.e., two simulations performed with slightly different fluctuations at inlet result in substantially different flow in the downcomer. This complicates the analysis of the data from simulations and suggests that validation against experimental data should not be performed using single physical experiment.

Numerical Simulation of Cavities Flow

2010 ◽  
Author(s):  
Jing Hu ◽  
Zhiguo Zhang ◽  
Dakui Feng
Keyword(s):  
Numerical Simulation ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Simple Algorithm ◽  
Navier Stokes ◽  
Complex Flow ◽  
Navier Stokes Equations ◽  
Simple Geometry ◽  
Flow Phenomena ◽  
The Mathematical Model

Flow across the cavity represents a simple geometry complex flow phenomena for many industry field. This paper presents a series of simulation results of both laminar and turbulent flows over cavities. Several important results and conclusions are reported. The mathematical model corresponds to the incompressible, Reynolds-averaged, Navier-Stokes equations plus a turbulence model, and the numerical simulation is performed using the SIMPLE algorithm.

A Numerical Simulation of Combined Radiation and Natural Convection in a Differential Heated Cubic Cavity

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
P. Kumar ◽  
V. Eswaran
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Natural Convection ◽  
Optical Thickness ◽  
Three Dimensional ◽  
Variable Density ◽  
Navier Stokes ◽  
Complex Flow ◽  
Fluid Properties ◽  
Flow Phenomena

This article presents a numerical simulation of combined radiation and natural convection in a three-dimensional differentially heated rectangular cavity with two opposite side walls kept at a temperature ratio Th/Tc=2.0 and Tc=500 K, with others walls insulated. A non-Boussinesq variable density approach is used to incorporate density changes due to temperature variation. The Navier–Stokes (NSE), temperature, as well as the radiative transfer (RTE) equations are solved numerically by a finite volume method, with constant thermophysical fluid properties (except density) for Rayleigh number Ra=105 and Prandtl number Pr=0.71. The convective, radiative, and total heat transfer on the isothermal and adiabatic walls is studied along with the flow phenomena. The results reveal an extraordinarily complex flow field, wherein, along with the main flow, many secondary flow regions and singular points exist at the different planes and are affected by the optical properties of the fluid. The heat transfer decreases with increase in optical thickness and the pure convection Nusselt number is approached as the optical thickness τ>100, but with substantially different velocity field. The wall emissivity has a strong influence on the heat transfer but the scattering albedo does not.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Computational Fluid Dynamic Applications for Jet Propulsion System Integration

1991 ◽  
Vol 113 (1) ◽  
pp. 40-50 ◽  
Author(s):  
R. H. Tindell
Keyword(s):  
System Integration ◽  
Fluid Dynamic ◽  
Low Cost ◽  
Separated Flow ◽  
Propulsion System ◽  
Navier Stokes ◽  
Aerospace Vehicles ◽  
Design Engineers ◽  
Flow Phenomena ◽  
The Impact

The impact of computational fluid dynamics (CFD) methods on the development of advanced aerospace vehicles is growing stronger year by year. Design engineers are now becoming familiar with CFD tools and are developing productive methods and techniques for their applications. This paper presents and discusses applications of CFD methods used at Grumman to design and predict the performance of propulsion system elements such as inlets and nozzles. The paper demonstrates techniques for applying various CFD codes and shows several interesting and unique results. A novel application of a supersonic Euler analysis of an inlet approach flow field, to clarify a wind tunnel-to-flight data conflict, is presented. In another example, calculations and measurements of low-speed inlet performance at angle of attack are compared. This is highlighted by employing a simplistic and low-cost computational model. More complex inlet flow phenomena at high angles of attack, calculated using an approach that combines a panel method with a Navier-Stokes (N-S) code, is also reviewed. The inlet fluid mechanics picture is rounded out by describing an N-S calculation and a comparison with test data of an offset diffuser having massively separated flow on one wall. Finally, the propulsion integration picture is completed by a discussion of the results of nozzle-afterbody calculations, using both a complete aircraft simulation in a N-S code, and a more economical calculation using an equivalent body of revolution technique.

Fluid Flow Structure in Arterial Bypass Anastomosis

2005 ◽  
Vol 127 (4) ◽  
pp. 611-618 ◽  
Author(s):  
C. M. Su ◽  
D. Lee ◽  
R. Tran-Son-Tay ◽  
W. Shyy
Keyword(s):  
Fluid Flow ◽  
Flow Structure ◽  
Bypass Graft ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Arterial Bypass ◽  
Flow Recirculation ◽  
Area Reduction ◽  
Complex Flow Structure

The fluid flow through a stenosed artery and its bypass graft in an anastomosis can substantially influence the outcome of bypass surgery. To help improve our understanding of this and related issues, the steady Navier-Stokes flows are computed in an idealized arterial bypass system with partially occluded host artery. Both the residual flow issued from the stenosis—which is potentially important at an earlier stage after grafting—and the complex flow structure induced by the bypass graft are investigated. Seven geometric models, including symmetric and asymmetric stenoses in the host artery, and two major aspects of the bypass system, namely, the effects of area reduction and stenosis asymmetry, are considered. By analyzing the flow characteristics in these configurations, it is found that (1) substantial area reduction leads to flow recirculation in both upstream and downstream of the stenosis and in the host artery near the toe, while diminishes the recirculation zone in the bypass graft near the bifurcation junction, (2) the asymmetry and position of the stenosis can affect the location and size of these recirculation zones, and (3) the curvature of the bypass graft can modify the fluid flow structure in the entire bypass system.

Numerical Investigation of Flow Around Bluff Bodies

1998 ◽  
Vol 14 (3) ◽  
pp. 153-159 ◽  
Author(s):  
Chou-Jiu Tsai ◽  
Ger-Jyh Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Near Wake ◽  
Navier Stokes Equations ◽  
Physical Description ◽  
Geometrical Shapes ◽  
Flow Phenomena ◽  
Volume Method

ABSTRACTIn this study, fluid flow around bluff bodies are studied to examine the vortex shedding phenomenon in conjuction with the geometrical shapes of these vortex shedders. These flow phenomena are numerically simulated. A finite volume method is employed to solve the incompressible two-dimensional Navier-Stokes equations. Thus, quantitative descriptions of the vortex shedding phenomenon in the near wake were made, which lead to a detailed description of the vortex shedding mechanism. Streamline contours, figures of lift coefficent, and figures of drag coefficent in various time, are presented, respectively, for a physical description.

Investigation of Mathematical Model of Turbulent Flow for Marine Propeller

2015 ◽  
Author(s):  
Nilima C. Joshi ◽  
Ayaz J. Khan
Keyword(s):  
Modern Technology ◽  
Hydrodynamic Performance ◽  
Marine Propeller ◽  
Turbulent Model ◽  
Complex Flow ◽  
Ansys Fluent ◽  
Flow Phenomena ◽  
Fluent Software ◽  
Effective Design ◽  
Mathematical And Numerical Modeling

ost of the flow phenomena important to modern technology involve turbulence. Propellers generally operate in the very complex flow field that may be highly turbulent and spatially non-uniform. Propeller skew is the single most effective design parameter which has significant influence on reducing propeller induced vibration. Up to date applications of propeller skew does not has a specified criteria for any turbulent model. This paper deals with the model which explains the effect of propeller skewness on hydrodynamic performance related to study of turbulent model via mathematical and numerical modeling. The simulation work is carried out using ANSYS-FLUENT software.

Computation of Discrete-Hole Film Cooling by a Near-Wall Second-Moment Turbulence Closure

1999 ◽  
Author(s):  
Hamn-Ching Chen ◽  
Gengsheng Wei ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Moment Closure ◽  
Navier Stokes ◽  
Closure Model ◽  
Complex Flow ◽  
Second Moment ◽  
Finite Analytic Method ◽  
Second Moment Closure ◽  
Effectiveness Prediction ◽  
Near Wall

Abstract A multiblock Favre-Averaged Navier-Stokes (FANS) method has been developed in conjunction with a chimera domain decomposition technique for investigation of flat surface, discrete-hole film cooling performance. The finite-analytic method solves the FANS equations in conjunction with a near-wall second-order Reynolds stress (second-moment) closure model and a two-layer k-ε model. Comparisons of flow fields and turbulence quantities with experimental data clearly demonstrate the capability of the near-wall second-moment closure model for accurate resolution of the complex flow interaction bewteen the coolant jet and the mainstream. The near-wall second-moment anisotropic model provides better agreement in adiabatic film effectiveness prediction than the two-layer k-ε model.

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