Numerical Investigation on Thermal Striping Phenomena in a T-Junction Piping System

2014 ◽  
Author(s):  
Masaaki Tanaka ◽  
Yasuhiro Miyake
Keyword(s):  
Numerical Simulation ◽  
Thermal Fatigue ◽  
Large Scale ◽  
Structural Integrity ◽  
Piping System ◽  
Simulation Code ◽  
Fine Mesh ◽  
Large Eddy ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue

Thermal striping phenomena caused by mixing of fluids at different temperature is one of the most important issues in design of Fast Breeder Reactors (FBRs), because it may cause high-cycle thermal fatigue in structure and affect the structural integrity. A numerical simulation code MUGTHES has been developed to investigate thermal striping phenomena and to estimate high cycle thermal fatigue in FBRs. In this study, numerical simulation for the WATLON experiment which was the water experiment of a T-junction piping system (T-pipe) conducted in JAEA was carried out to validate the MUGTHES and to investigate the relation between the mechanism of temperature fluctuation generation and the unsteady motion of large eddy structures. In the numerical simulation, the large eddy simulation (LES) approach with standard Smagorinsky model was employed as eddy viscosity model to simulate large-scale eddy motion in the T-pipe. The mesh as the same with the previous study as reference, the finer mesh and the coarser mesh arrangements were employed to estimate the Grid Convergence Index (GCI) for uncertainty quantification in the validation process. The modified method of the GCI estimation based on the least squire version could successfully quantify uncertainty. Through the numerical simulations, it was indicated that the fine mesh arrangement could improve the temperature distribution in the wake. It could be found that the thermal mixing phenomena in the T-pipe were caused by the mutual interaction of the necklace-shaped vortex around the wake from in the front of the branch jet, the horseshoe-shaped vortex and the Karman’s vortex motions in the wake.

Numerical Simulations of Thermal-Mixing in T-Junction Piping System Using Large Eddy Simulation Approach

2011 ◽  
Author(s):  
Masaaki Tanaka ◽  
Satoshi Murakami ◽  
Yasuhiro Miyake ◽  
Hiroyuki Ohshima
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Branch Pipe ◽  
Three Dimensional ◽  
Piping System ◽  
Thermal Mixing ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue

Thermal striping phenomenon caused by mixing of fluids at different temperatures is one of the most important issues in design of fast breeder reactors (FBRs), because it may cause high-cycle thermal fatigue in structure. Authors have been developed a numerical simulation code MUGTHES to investigate thermal striping phenomena in FBRs and to give transient data of temperature in the fluid and the structure for an evaluation method of the high-cycle thermal fatigue problem. MUGTHES employs the boundary fitted coordinate (BFC) system and deals with three-dimensional transient thermal-hydraulic problems by using the large eddy simulation (LES) approach and artificial wall conditions derived by a wall function law. In this paper, numerical simulations of MUGTHES in T-junction piping system appear. Boundary conditions for the simulations are chosen from an existing water experiment in JAEA, named as WATLON experiment. The wall jet condition in which the branch pipe jet flows away touching main pipe wall on the branch pipe side and the impinging jet condition in which the branch pipe jet impinges on the wall surface on the opposite side of the branch pipe are selected, because significant temperature fluctuation may be induced on the wall surfaces by the branch pipe jet behavior. Numerical results by MUGTHES are validated by comparisons with measured velocity and temperature profiles. Three dimensional large-scale eddies are identified behind of the branch pipe jet in the wall jet case and in front of the branch pipe jet in the impinging jet case, respectively. Through these numerical simulations in the T-pipe, generation mechanism of temperature fluctuation in thermal mixing process is revealed in the relation with the large-scale eddy motion.

Numerical Simulation of Thermal Striping Phenomena in T-Junction Piping System Using Large Eddy Simulation

2008 ◽  
Author(s):  
Masa-Aki Tanaka ◽  
Hiroyuki Ohshima ◽  
Hideaki Monji
Keyword(s):  
Numerical Simulation ◽  
Heat Conduction ◽  
Three Dimensional ◽  
Piping System ◽  
Fluid Temperature ◽  
Numerical Schemes ◽  
Simulation Code ◽  
Simple Method ◽  
Thermal Striping ◽  
Les Model

In Japan Atomic Energy Agency (JAEA), simulation code “MUGTHES (MUlti Geometry simulation code for THErmal-hydraulic and Structure heat conduction analysis in boundary fitted coordinate)” has been developed to evaluate thermal striping phenomena that are caused by turbulence mixing of fluids in different temperature. MUGTHES employs Boundary Fitted Coordinate (BFC) system to treat complex geometries in power plants. And MUGTHES can deal with three-dimensional transient thermal-hydraulic problem coupled with three-dimensional transient heat conduction in the surrounding structure in consideration of conjugated heat transfer. In this paper, numerical schemes for thermal-hydraulic simulation employed in MUGTHES are described including LES model. A simple method to limit numerical oscillation is adopted in energy equation solving process. A new iterative method to solve Poisson equation in BFC system is developed for effective transient calculations. This method is based on BiCGSTAB method and SOR technique. As the code validation of MUGTHES, a numerical simulation in a T-junction piping system with LES approach was conducted. Numerical results related to velocity and fluid temperature distributions were compared with an existing water experimental data and the applicability of numerical schemes with LES model in MUGTHES to the thermal striping phenomenon was confirmed.

scholarly journals ASHEE-1.0: a compressible, equilibrium–Eulerian model for volcanic ash plumes

2016 ◽  
Vol 9 (2) ◽  
pp. 697-730 ◽  
Author(s):  
M. Cerminara ◽  
T. Esposti Ongaro ◽  
L. C. Berselli
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Volume Fraction ◽  
Radial Profile ◽  
Air Entrainment ◽  
Compressible Turbulence ◽  
Eulerian Model ◽  
Volcanic Plumes ◽  
Large Eddy ◽  
Non Equilibrium

Abstract. A new fluid-dynamic model is developed to numerically simulate the non-equilibrium dynamics of polydisperse gas–particle mixtures forming volcanic plumes. Starting from the three-dimensional N-phase Eulerian transport equations for a mixture of gases and solid dispersed particles, we adopt an asymptotic expansion strategy to derive a compressible version of the first-order non-equilibrium model, valid for low-concentration regimes (particle volume fraction less than 10−3) and particle Stokes number (St – i.e., the ratio between relaxation time and flow characteristic time) not exceeding about 0.2. The new model, which is called ASHEE (ASH Equilibrium Eulerian), is significantly faster than the N-phase Eulerian model while retaining the capability to describe gas–particle non-equilibrium effects. Direct Numerical Simulation accurately reproduces the dynamics of isotropic, compressible turbulence in subsonic regimes. For gas–particle mixtures, it describes the main features of density fluctuations and the preferential concentration and clustering of particles by turbulence, thus verifying the model reliability and suitability for the numerical simulation of high-Reynolds number and high-temperature regimes in the presence of a dispersed phase. On the other hand, Large-Eddy Numerical Simulations of forced plumes are able to reproduce the averaged and instantaneous flow properties. In particular, the self-similar Gaussian radial profile and the development of large-scale coherent structures are reproduced, including the rate of turbulent mixing and entrainment of atmospheric air. Application to the Large-Eddy Simulation of the injection of the eruptive mixture in a stratified atmosphere describes some of the important features of turbulent volcanic plumes, including air entrainment, buoyancy reversal and maximum plume height. For very fine particles (St → 0, when non-equilibrium effects are negligible) the model reduces to the so-called dusty-gas model. However, coarse particles partially decouple from the gas phase within eddies (thus modifying the turbulent structure) and preferentially concentrate at the eddy periphery, eventually being lost from the plume margins due to the concurrent effect of gravity. By these mechanisms, gas–particle non-equilibrium processes are able to influence the large-scale behavior of volcanic plumes.

Numerical analysis of thermal striping induced high cycle thermal fatigue in a mixing tee

2009 ◽  
Vol 239 (5) ◽  
pp. 833-839 ◽  
Author(s):  
Jeong Ik Lee ◽  
Lin-wen Hu ◽  
Pradip Saha ◽  
Mujid S. Kazimi
Keyword(s):  
Numerical Analysis ◽  
Thermal Fatigue ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue

scholarly journals Numerical simulation of 2D real large scale floods on GPU: the Ebro River

2018 ◽  
Vol 40 ◽  
pp. 06007
Author(s):  
Isabel Echeverribar ◽  
Mario Morales-Hernández ◽  
Pilar Brufau ◽  
Pilar García-Navarro
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Numerical Models ◽  
Water System ◽  
Free Surface Flow ◽  
Middle Part ◽  
Surface Flow ◽  
Ebro River ◽  
Model Free ◽  
Fine Mesh

Modern flood risk management and mitigation plans incorporate the presence of numerical models that are able to assess the response of the system and to help in the decision-making processes. The shallow water system of equations (SWE) is widely used to model free surface flow evolution in river flooding. Although 1D models are usually adopted when simulating long rivers due to their computational efficiency, 2D models approximate better the behaviour in floodplains of meandering rivers using a fine mesh which implies unaffordable computations in real-world applications. However, the advances on parallelization methods accelerate computation making 2D models competitive. In particular, GPU technology offers important speed-ups which allow fast simulations of large scale scenarios. In this work, an example of the scope of this technology is presented. Several past flood events have been modelled using GPU. The physical domain (middle part of the Ebro River in Spain) has a extent of 477 km2, which gives rise to a large computational grid. The steps followed to carry out the numerical simulation are detailed, as well as the comparison between numerical results and observed flooded areas reaching coincidences up to 87.25 % and speed enhancements of 1-h of simulation time for 1-day flood event. These results lead to the feasible application of this numerical model in real-time simulation tools with accurate and fast predictions useful for flood management.

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