Large Eddy Simulation Analysis of Fluid Temperature Fluctuations at a T-junction for Prediction of Thermal Loading

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Shaoxiang Qian ◽  
Naoto Kasahara
Keyword(s):  
Temperature Fluctuation ◽  
Turbulence Models ◽  
Temperature Fluctuations ◽  
Fluid Temperature ◽  
Numerical Schemes ◽  
Smagorinsky Model ◽  
Coupling Analysis ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results

T-junctions are widely used for fluid mixing in power and process plants. Temperature fluctuations generated by the mixing of hot and cold fluids at a T-junction can cause high cycle thermal fatigue (HCTF) failure. The existing Japanese guideline for evaluating HCTF provides margin that varies greatly depending on the case for the evaluation result. Computational fluid dynamics (CFD)/finite element analysis (FEA) coupling analysis is expected to be a useful tool for the more accurate evaluation of HCTF. Precise temperature fluctuation histories are necessary to determine the thermal loads because fatigue damage prediction requires temperature fluctuation amplitudes and their cycle numbers. The present investigation was intended to discover the accurate prediction methods of fluid temperature fluctuations, prior to performing CFD/FEA coupling analysis. Large eddy simulation (LES) turbulence models suitable for the simulation of unsteady phenomena were investigated. The LES subgrid scale (SGS) models used included the standard Smagorinsky model (SSM) and the dynamic Smagorinsky model (DSM). The effects of numerical schemes for calculating the convective term in the energy equation on the simulation results were also investigated. LES analyses of the flow and temperature fields at a T-junction were carried out using these numerical methods. For comparison, the simulation conditions were the same as the experiment in literature. All of the simulation results show the flow pattern of a wall jet with strong flow and temperature fluctuations, as observed in the experiment. The simulation results indicate the numerical schemes have a great effect on the temperature distribution and the temperature fluctuation intensity (TFI). The first-order upwind difference scheme (1UD) significantly underestimates the TFI for each LES SGS model, although it exhibits good numerical stability. However, the hybrid scheme (HS), which is mainly the second-order central difference scheme (2CD) blended with a small fraction of 1UD, can better predict the TFI for each LES SGS model. Furthermore, the DSM model gives a prediction closer to the experimental results than the SSM model, while using the same numerical scheme. As a result, it was found through the systematic investigations of various turbulence models and numerical schemes that the approach using the DSM model and the HS with a large blending factor could provide accurate predictions of the fluid temperature fluctuations. Furthermore, it is considered that this approach is also applicable to the accurate prediction of any other scalar (e.g., concentration), based on the analogy of scalar transport phenomena.

LES Analysis of Temperature Fluctuations at T-Junctions for Prediction of Thermal Loading

2011 ◽  
Author(s):  
Shaoxiang Qian ◽  
Naoto Kasahara
Keyword(s):  
Thermal Loading ◽  
Turbulence Models ◽  
Temperature Fluctuations ◽  
Temperature Fields ◽  
Hybrid Scheme ◽  
Smagorinsky Model ◽  
Coupling Analysis ◽  
Simulation Results ◽  
Les Model ◽  
High Cycle Thermal Fatigue

T-junctions are widely used for fluid mixing in nuclear power and chemical and refinery plants. Temperature fluctuations generated by the mixing of hot and cold fluids at a T-junction can cause high cycle thermal fatigue (HCTF) failure. Japan Society of Mechanical Engineers (JSME) published ‘Guideline for Evaluation of High Cycle Thermal Fatigue of a Pipe (JSME S017, 2003)’ which results in a very conservative evaluation. CFD/FEM coupling analysis is considered as a useful tool for the more rational evaluation of HCTF. The present paper aims at the validation of CFD simulations to establish a more rational method of evaluating thermal loading, prior to performing CFD/FEM coupling analysis. It is very important to choose the proper turbulence model for the analysis of unsteady phenomena such as the highly fluctuating flow and temperature fields at a T-junction. Here, large eddy simulation (LES) turbulence models suitable for the simulation of the unsteady phenomena were investigated. LES sub-grid scale (SGS) models used include standard Smagorinsky model (SM) and dynamic Smagorinsky model (DSM). The effects of numerical schemes for the calculation of the convective term in the energy equation on the simulation results were also investigated. LES analyses of the flow and temperature fields at a T-junction were carried out using the above SGS turbulence models. For the sake of comparison, the simulation conditions are the same as those of the WATLON experiments conducted at Japan Atomic Energy Agency (JAEA) in the literature. All of the simulation results show the flow pattern of the wall jet with the strong flow and temperature fluctuations, which is the same as that observed in the experiment. The simulation results indicate the numerical schemes have great effect on the temperature distribution and the temperature fluctuation intensity (TFI). The 1st-order upwind differencing (1UD) significantly underestimates the TFI for each LES model, although it exhibits a good numerical stability. On the other hand, the hybrid scheme, which is mainly the 2nd-order central differencing (2CD) blended with a small fraction of 1UD, can better predict the TFI for each LES model. Furthermore, the DSM model gives a prediction closer to the experimental results than the SM model while using the same numerical scheme. In this study, an important finding is that a combination of the DSM model and the hybrid scheme with a large blending factor can provide a prediction agreeing very well with the experimental results.

Very Large Eddy Simulation (VLES) of a Squealer Tipped Axial Turbine Stage

2017 ◽  
Author(s):  
Ryan Kelly ◽  
Aleksandar Jemcov ◽  
Joshua D. Cameron ◽  
Scott C. Morris ◽  
Jesse Coffman ◽  
...  
Keyword(s):  
Performance Prediction ◽  
Turbulence Models ◽  
Aerodynamic Design ◽  
Turbine Stage ◽  
Axial Turbine ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results ◽  
Improved Performance ◽  
The University

This work presents numerical simulation results of a single stage axial turbine consisting of a nozzle and squealer tipped rotor. The VLES method is a hybrid URANS/LES method based on the standard k-ω SST and Coherent Structure LES turbulence models. The simulations were performed at the stage aerodynamic design point (ADP) and the results were validated against high-quality steady experimental data acquired at the University of Notre Dame’s axial transonic research turbine (TRT) facility. Along with the experimental validation, the VLES simulation results were further compared to those predicted using URANS highlighting the benefits of VLES compared to traditional predictive methods. All simulations were performed using a RANS-type grid density to highlight the efficiency of the VLES method and improved performance prediction.

Development of a Partial Blockage Detection Algorithm through Temperature Fluctuation Analyses in a Liquid Metal Reactor

2006 ◽  
Vol 321-323 ◽  
pp. 1758-1761
Author(s):  
Seung Hwan Seong ◽  
Won Dae Jeon ◽  
Seop Hur ◽  
Seong O Kim
Keyword(s):  
Temperature Fluctuation ◽  
Early Stage ◽  
Temperature Fluctuations ◽  
Detection Algorithm ◽  
Significant Parameter ◽  
Eddy Simulation ◽  
Liquid Metal Reactor ◽  
Commercial Code ◽  
Large Eddy ◽  
Significant Temperature

If an assembly is partially blocked, the temperature in the upper plenum fluctuates at an early stage without a significant temperature increase. Therefore, the temperature fluctuation in the upper plenum can detect a partial blockage of an assembly. For developing the detection algorithm for a partial blockage, we numerically analyzed the temperature fluctuation in the upper plenum due to a partial blockage in an assembly. For analyzing the time dependent turbulence variables, the LES (Large Eddy Simulation) turbulence model in a commercial code was used. After analyzing the temperature fluctuations in the upper plenum, we studied the change of its characteristics according to the blocked conditions through some FFT analyses and statistical analyses. We found that the change of the skewness of the temperature fluctuation was the most significant parameter to detect a partial blockage and that its highest frequency is about 15Hz at 10cm beyond the exit of the assembly. Also, we have suggested that the resolution of the thermocouple should be less than 2 K in order to measure the fluctuated values of the temperature and that the response time of the thermocouple was less than 30ms.

Modeling Transition to Turbulence in Eccentric Stenotic Flows

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Sonu S. Varghese ◽  
Steven H. Frankel ◽  
Paul F. Fischer
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Turbulence Models ◽  
Transition To Turbulence ◽  
Mean Flow ◽  
Poor Agreement ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results

Mean flow predictions obtained from a host of turbulence models were found to be in poor agreement with recent direct numerical simulation results for turbulent flow distal to an idealized eccentric stenosis. Many of the widely used turbulence models, including a large eddy simulation model, were unable to accurately capture the poststenotic transition to turbulence. The results suggest that efforts toward developing more accurate turbulence models for low-Reynolds number, separated transitional flows are necessary before such models can be used confidently under hemodynamic conditions where turbulence may develop.

Large-Eddy Simulation for Temperature Fluctuation of Mixing Hot and Cold Fluids in a Tee Junction

2010 ◽  
Author(s):  
T. Lu ◽  
W. Y. Zhu ◽  
K. S. Wang
Keyword(s):  
Large Eddy Simulation ◽  
Temperature Fluctuation ◽  
Flow Simulation ◽  
Temperature Fluctuations ◽  
Numerical Results ◽  
Piping System ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Tee Junction ◽  
Fluctuating Temperatures

In the present work the temperature fluctuations in a mixing tee were simulated on FLUENT platform using the Large-eddy simulation (LES) turbulent flow model with the sub-grid scale (SGS) model of Smagorinsky-Lilly (SL). The temperature and velocity fields, the normalized mean and fluctuating temperatures and velocities were predicted and analyzed with consideration of buoyancy. The normalized mean and fluctuating temperatures were defined to describe the time-averaged temperature and the time-averaged temperature fluctuation intensity. The numerical results of the normalized mean and fluctuating temperatures were compared with those of the experimental ones published in previous literature, which shows that numerical results have good agreement with the experimental data. The temperature fluctuations and power spectrum densities (PSD) at the locations having the strongest temperature fluctuations both in tee junction and on the walls were analyzed to evaluate the potential of thermal fatigue. The LES flow simulation and power spectral analysis are helpful for the Integrity evaluation of the structures such as the tee junction, elbow, piping system to predict the temperature fluctuation and thermal stripping in a tee junction of mixing hot and cold fluids.

Large Eddy Simulation with Three Kinds of Sub-Grid Scale Model on Temperature Fluctuation of Hot and Cold Fluids Mixing in a Tee

2012 ◽  
Vol 152-154 ◽  
pp. 1307-1312 ◽  
Author(s):  
Tao Lu ◽  
Yong Wei Wang ◽  
Ping Wang
Keyword(s):  
Large Eddy Simulation ◽  
Temperature Fluctuation ◽  
Eddy Viscosity ◽  
Energy Transport ◽  
Flow Model ◽  
Temperature Fluctuations ◽  
Scale Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Thermal Striping

In the present work the temperature fluctuations in a mixing tee were simulated on FLUENT platform using the large-eddy simulation (LES) turbulent flow model with three kinds of sub-grid scale (SGS) models such as Smagorinsky-Lilly (SL) model, Wall-adapted Local Eddy-viscosity (WALE) model, and Kinetic-energy transport (KET) model. The normalized mean and root mean square temperatures were predicted and analyzed with consideration of buoyancy. The numerical results showed that buoyancy greatly influences the mixing flow and the thermal striping phenomena were quite obvious. These three SGS models have somewhat similar accuracies for prediction of the temperature fluctuation and thermal stripping in a tee of mixing hot and cold fluids.

scholarly journals Large Eddy Simulation of gravity currents with a high order DG method

2017 ◽  
Vol 8 (1) ◽  
pp. 128-148 ◽  
Author(s):  
Caterina Bassi ◽  
Antonella Abbà ◽  
Luca Bonaventura ◽  
Lorenzo Valdettaro
Keyword(s):  
Numerical Simulations ◽  
Gravity Current ◽  
Turbulence Models ◽  
Variable Density ◽  
Large Eddy Simulations ◽  
Benchmark Problems ◽  
Smagorinsky Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Dg Method

Abstract This work deals with Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of a turbulent gravity current in a gas, performed by means of a Discontinuous Galerkin (DG) Finite Elements method employing, in the LES case, LES-DG turbulence models previously introduced by the authors. Numerical simulations of non-Boussinesq lock-exchange benchmark problems show that, in the DNS case, the proposed method allows to correctly reproduce relevant features of variable density gas ows with gravity. Moreover, the LES results highlight, also in this context, the excessively high dissipation of the Smagorinsky model with respect to the Germano dynamic procedure.

scholarly journals Comparative Study of Different Turbulence Models for Cavitational Flows around NACA0012 Hydrofoil

2021 ◽  
Vol 9 (7) ◽  
pp. 742
Author(s):  
Minsheng Zhao ◽  
Decheng Wan ◽  
Yangyang Gao
Keyword(s):  
Angle Of Attack ◽  
Large Angle ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Specific Information ◽  
Cloud Cavitation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Shedding Frequency ◽  
Reynolds Average

The present work focuses on the comparison of the numerical simulation of sheet/cloud cavitation with the Reynolds Average Navier-Stokes and Large Eddy Simulation(RANS and LES) methods around NACA0012 hydrofoil in water flow. Three kinds of turbulence models—SST k-ω, modified SST k-ω, and Smagorinsky’s model—were used in this paper. The unstable sheet cavity and periodic shedding of the sheet/cloud cavitation were predicted, and the simulation results, namelycavitation shape, shedding frequency, and the lift and the drag coefficients of those three turbulence models, were analyzed and compared with each other. The numerical results above were basically in accordance with experimental ones. It was found that the modified SST k-ω and Smagorinsky turbulence models performed better in the aspects of cavitation shape, shedding frequency, and capturing the unsteady cavitation vortex cluster in the developing and shedding period of the cavitation at the cavitation number σ = 0.8. At a small angle of attack, the modified SST k-ω model was more accurate and practical than the other two models. However, at a large angle of attack, the Smagorinsky model of the LES method was able to give specific information in the cavitation flow field, which RANS method could not give. Further study showed that the vortex structure of the wing is the main cause of cavitation shedding.

scholarly journals Large Eddy Simulation of Film Cooling Involving Compound Angle Holes: Comparative Study of LES and RANS

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 198
Author(s):  
Seung Il Baek ◽  
Joon Ahn
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Orientation Angle ◽  
Turbulence Models ◽  
Film Cooling Effectiveness ◽  
Injection Angle ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Compound Angle

A large eddy simulation (LES) was performed for film cooling in the gas turbine blade involving spanwise injection angles (orientation angles). For a streamwise coolant injection angle (inclination angle) of 35°, the effects of the orientation angle were compared considering a simple angle of 0° and 30°. Two ratios of the coolant to main flow mass flux (blowing ratio) of 0.5 and 1.0 were considered and the experimental conditions of Jung and Lee (2000) were adopted for the geometry and flow conditions. Moreover, a Reynolds averaged Navier–Stokes simulation (RANS) was performed to understand the characteristics of the turbulence models compared to those in the LES and experiments. In the RANS, three turbulence models were compared, namely, the realizable k-ε, k-ω shear stress transport, and Reynolds stress models. The temperature field and flow fields predicted through the RANS were similar to those obtained through the experiment and LES. Nevertheless, at a simple angle, the point at which the counter-rotating vortex pair (CRVP) collided on the wall and rose was different from that in the experiment and LES. Under the compound angle, the point at which the CRVP changed to a single vortex was different from that in the LES. The adiabatic film cooling effectiveness could not be accurately determined through the RANS but was well reflected by the LES, even under the compound angle. The reattachment of the injectant at a blowing ratio of 1.0 was better predicted by the RANS at the compound angle than at the simple angle. The temperature fluctuation was predicted to decrease slightly when the injectant was supplied at a compound angle.

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