The Role of Turbulence Models for Predicting a Thermal Stratification

2006 ◽  
Vol 128 (4) ◽  
pp. 656-662 ◽  
Author(s):  
Seok-Ki Choi ◽  
Seong-O Kim
Keyword(s):  
Liquid Metal ◽  
Thermal Stratification ◽  
Transport Model ◽  
Numerical Study ◽  
Turbulence Models ◽  
Liquid Metal Reactor ◽  
Temporal Oscillation ◽  
Elliptic Relaxation ◽  
Shear Stress Transport Model

A numerical study of the evaluation of turbulence models for predicting the thermal stratification phenomenon is presented. The tested models are the elliptic blending turbulence model (EBM), the two-layer model, the shear stress transport model (SST), and the elliptic relaxation model (V2-f). These four turbulence models are applied to the prediction of a thermal stratification in an upper plenum of a liquid metal reactor experimented at the Japan Nuclear Cooperation (JNC). The EBM and V2-f models predict properly the steep gradient of the temperature at the interface of the cold and hot regions that is observed in the experimental data, and the EBM and V2-f models have the capability of predicting the temporal oscillation of the temperature. The two-layer and SST models predict the diffusive temperature gradient at the interface of a thermal stratification and fail to predict a temporal oscillation of the temperature. In general, the EBM predicts best the thermal stratification phenomenon in the upper plenum of the liquid metal reactor.

The Role of Turbulence Models for Predicting Thermal Stratification

2006 ◽  
Author(s):  
Seok-Ki Choi ◽  
Seong-O. Kim ◽  
Hoon-Ki Choi
Keyword(s):  
Liquid Metal ◽  
Thermal Stratification ◽  
Transport Model ◽  
Numerical Study ◽  
Turbulence Models ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Liquid Metal Reactor ◽  
Temporal Oscillation ◽  
Shear Stress Transport Model

A numerical study of evaluation of turbulence models for predicting the thermal stratification phenomenon is presented. The tested models are the elliptic blending model (EBM), the two-layer model, the shear stress transport model (SST) and the elliptic relaxation model (V2-f). These four turbulence models are applied to the prediction of a thermal stratification in an upper plenum of a liquid metal reactor experimented at the Japan Nuclear Cooperation (JNC). The algebraic flux model is used for treating the turbulent heat fluxes for all the models. The EBM and V2-f models predict properly the steep gradient of the temperature at the interface of the cold and hot regions which is observed in the experimental data, and the EBM and V2-f models have the capability of predicting the temporal oscillation of the temperature. The two-layer and SST models predict the diffusive temperature gradient at the interface of a thermal stratification and fail to predict a temporal oscillation of the temperature. In general the EBM predicts best the thermal stratification phenomenon in the upper plenum of the liquid metal reactor.

The Effect of an Upstream Dune-Shaped Shells on Forward and Backward Injection Hole Film Cooling

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Fatima Ben Ali Kouchih ◽  
Khadidja Boualem ◽  
Mustapha Grine ◽  
Abbes Azzi
Keyword(s):  
Film Cooling ◽  
Transport Model ◽  
Weighted Average ◽  
Turbulence Models ◽  
Injection Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Barchan Dune ◽  
Shear Stress Transport Model ◽  
Cooling Design

Abstract This article presents the numerical results of a new film cooling design that combines the backward injection hole with Barchan-dune-shaped shells (BH-BDS).The performance of this novel design in improving the film cooling effectiveness is compared to other configurations, forward injection hole (FH), backward injection hole (BH), and the configuration that combines the forward injection with Barchan-dune-shaped shells (FH-BDS). Three blowing ratios are considered in this article, M = 0.5, 1.0, and 1.5. The air coolant was injected through holes inclined at 35 and 155 deg for forward and backward cases, respectively. The lateral-averaged film cooling effectiveness and the distribution of adiabatic film cooling efficiency are studied using commercial software ansys-cfx. Three turbulence models, including the k–ω shear stress transport model, standard k–ε, and renormalization group theory (RNG) k–ε are examined in this investigation. The RNG k–ε model is adopted for the present simulation. The main result of this study reveals that the presence of upstream dune-shaped shells with backward hole yield a better film cooling effectiveness especially at higher blowing ratios (M ≥ 1). At M = 1.5, the FH-BDS and BH-BS cases provide an improvement in the area weighted average film cooling approximately about 24.79% and 10.56%, respectively. The BH-BDS design reduces the pressure loss as compared to BH.

Design and Analysis of Airfoil-Shaped Impeller Blades of Centrifugal Pump

2016 ◽  
Vol 852 ◽  
pp. 539-544
Author(s):  
Parth Shah ◽  
M. Ashwin Ganesh ◽  
Thundil Kuruppa Raj
Keyword(s):  
Centrifugal Pump ◽  
Transport Model ◽  
Turbulence Models ◽  
Suction Side ◽  
3D Analysis ◽  
Centrifugal Pumps ◽  
Pump Impeller ◽  
Outlet Pressure ◽  
Shear Stress Transport Model ◽  
Centrifugal Pump Impeller

This paper deals with a comparative study of the outlet pressure-energy between a conventional and normal blade impeller and an airfoil-shaped blade impeller of a centrifugal pump. Although the volute casing is an important component along with an impeller [1], the present comparative analysis makes the volute casing redundant to the study, hence neglected. All centrifugal pumps are usually designed and manufactured using backward swept blades with equal camber on the top and bottom sides. An increased camber on the top side is an ideal trait for a lift generating airfoil. The purpose is to implement the principle of lift generation of airfoil for centrifugal pumps. As a result, a local suction side and pressure side can be visualized using CFX-post processor. The 3D analysis of such a centrifugal pump impeller is designed in SOLIDWORKS® and analyzed using ANSYS® CFX. The SST (Menter’s Shear Stress Transport) model is used as it combines both the k-ω and k-ε turbulence models.

Evaluation of Turbulence Models for Thermal Striping in a Triple-Jet

2005 ◽  
Author(s):  
Seok-Ki Choi ◽  
Ho-Yun Nam ◽  
Myung-Hwan Wi ◽  
Seong-O Kim ◽  
Jong-Chull Jo ◽  
...  
Keyword(s):  
Experimental Data ◽  
Root Mean Square ◽  
Transport Model ◽  
Computational Study ◽  
Turbulence Models ◽  
Oscillatory Behavior ◽  
Mean Square ◽  
Relaxation Model ◽  
Elliptic Relaxation ◽  
Thermal Striping

A computational study for the evaluation of the current turbulence models for the prediction of a thermal striping in a triple-jet is performed. The tested turbulence models are the two-layer model, the shear stress transport model and the elliptic relaxation model. These three turbulence models are applied to the prediction of the thermal striping in a triple-jet in which detailed experimental data are available. The performances of the tested turbulence models are evaluated through comparisons with the experimental data. The predicted mean and root-mean-square values of the temperature are compared with the experimental data, and the capability of predicting the oscillatory behavior of the ensemble-averaged temperature is investigated. From these works it is shown that only the elliptic relaxation model is capable of predicting the oscillatory behavior of the ensemble-averaged temperature. It is also shown that the elliptic relaxation model predicts best the time-averaged and root-mean-square of the temperature fluctuation. However, this model predicts a slower mixing at the far downstream of the jet.

Evaluation of RANS Approach in Predicting the Physics of Incompressible Turbulent Jets-Into-Crossflows

2007 ◽  
Author(s):  
Khodyar Javadi ◽  
Mohammad Taeibi-Rahni ◽  
Masoud Darbandi
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Simple Algorithm ◽  
Numerical Data ◽  
Turbulent Jets ◽  
Reynolds Stress Model ◽  
Shear Stress Transport Model ◽  
Near Wall

This work is conducted with evaluation of different turbulence models capabilities in predicting three dimensional jet-into-crossflow (JICF) interactions. For this purpose, first of all, comprehensive discussions on the near wall flow complexities due to discharge of a jet into a crossflow are presented. In this regards, large scale coherent structures such as: counter rotating vortex pairs (CRVP’s), near wall secondary motions, horseshoe vortices, and wall jets like are discussed. Secondly, the abilities of different turbulence models in predicting such flows (JICF) are evaluated. Our evaluation is based on three points of view including: 1) JICF characteristics, 2) computed location, and 3) sensitivity to different flow variables. In this regard, the turbulence models such as k-ε, k-ω, shear stress transport model (SST), and Reynolds stress model (RSM) are employed. Their related results are compared to credential available experimental/numerical data as well themselves. Since the same basic code with the same grid density as well as numerical discretization scheme is used, it is save to conclude that, any differences in the results are due to the abilities of turbulence models. The flow field computation was governed by Reynolds Averaged Navier-Stokes (RANS) equations performing finite volume method with SIMPLE algorithm over a non-uniform structured grid.

A Comparative Analysis of Turbulence Models Utilised for the Prediction of Turbulent Airflow through a Sudden Expansion

2015 ◽  
Vol 16 ◽  
pp. 64-78 ◽  
Author(s):  
Karinate Valentine Okiy
Keyword(s):  
Shear Stress ◽  
Convergence Rate ◽  
Transport Model ◽  
Turbulence Models ◽  
Sudden Expansion ◽  
Circular Duct ◽  
Shear Stress Transport ◽  
Shear Stress Transport Model ◽  
Turbulent Airflow ◽  
Recirculation Length

The turbulent airflow in a circular duct with sudden expansion was investigated utilizing three turbulence models. The turbulence models chosen are: the k-epsilon model, the shear stress transport model and the Reynolds-stress model. The performance of the models was investigated with respect to the flow parameter-recirculation length. The turbulent kinetic energy and velocity predictions were compared between the turbulence models and with experimental data, then interpreted on the basis of the recirculation length. From the results, the shear stress transport model predictions of recirculation length had the closest agreement with the experimental result compared to the other model. Likewise, the convergence rate for the shear stress transport model was reasonable compared to that of the Reynolds model which has the slowest convergence rate. In light of these findings, the shear stress transport model was discovered to be the most appropriate for the investigation of turbulent air flow in a circular duct with sudden expansion. Keywords: Turbulence, recirculation length, sudden expansion, Turbulence models.

scholarly journals Several Cases for the Validation of Turbulence Models Implementation

2021 ◽  
Vol 11 (8) ◽  
pp. 3377
Author(s):  
Michael D. Polewski ◽  
Paul G. A. Cizmas
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Transport Model ◽  
Turbulence Models ◽  
Numerical Results ◽  
Test Cases ◽  
Turbine Cascade ◽  
Near Wake ◽  
Shear Stress Transport Model ◽  
Standard Configuration

This paper presents several test cases that were used to validate the implementation of two turbulence models in the UNS3D code, an in-house code. The two turbulence models used were the Shear Stress Transport model and the Spalart–Allmaras model. These turbulence models were explored using the numerical results generated by three computational fluid dynamics codes: NASA’s FUN3D and CFL3D, and UNS3D. Four cases were considered: a flat plate case, an airfoil near-wake, a backward-facing step, and a turbine cascade known as the Eleventh Standard Configuration. The numerical results were compared among themselves and against experimental data.

The Investigation of Turbulence Models Based on Numerical Simulation

2014 ◽  
Vol 590 ◽  
pp. 91-95
Author(s):  
Rui Li ◽  
Chang Hong Tang
Keyword(s):  
Transport Model ◽  
Turbulence Models ◽  
Algebraic Model ◽  
Equation Model ◽  
Turbulent Model ◽  
Stress Equation ◽  
Advantages And Disadvantages ◽  
Development Direction ◽  
Shear Stress Transport Model ◽  
Improvement Measures

The algebraic model, one-equation model, two equation models are Analyzed in the paper. Focusing on the k-ε turbulent model contains (the standardk-εturbulence model, RNGk-εmodel, Realizablek-ε model), and the origin of the shear stress transport model, Reynolds stress equation model on mathematical and physical model is discussed.the advantages and disadvantages of each model is Pointed out ,And the future development direction of turbulent model and improvement measures are proposed on the paper.

Numerical investigation of V-shaped riblets and an improved model of riblet effects

2017 ◽  
Vol 232 (9) ◽  
pp. 1622-1631 ◽  
Author(s):  
Yu Yang ◽  
Zhang Ming-Ming ◽  
Li Xue-Song
Keyword(s):  
Shear Stress ◽  
Transport Model ◽  
Fluid Dynamic ◽  
Turbulence Models ◽  
Friction Reduction ◽  
Group Model ◽  
Shear Stress Transport ◽  
Shear Stress Transport Model ◽  
Skin Friction Reduction ◽  
Improved Model

Symmetric V-shaped riblets are simulated by using the computational fluid dynamic method to understand the riblet effects on the turbulent boundary layer and the skin friction reduction. Three classical turbulence models, namely Spalart–Allmaras, shear stress transport, and re-normalization group k-epsilon models, are investigated under different grid densities. The re-normalization group model produces good results consistent with the experiment, as compared with the existing theoretical and experimental drag results of the flat plate and the V-shaped riblets with different sizes. Simulating V-shaped riblets yield the unexpected discovery that the shear stress transport model produces large errors, and the Spalart–Allmaras model even produces results of qualitative errors. Another finding is that von Kármán’s constants can no longer meet the requirement of describing velocity profiles in the logarithmic law layer. Aside from the traditional shift of the logarithmic law’s intercept, the slope is also changed by riblet height and spacing. Therefore, an improved model of riblet effects is proposed by redefining von Kármán’s constants.

scholarly journals Numerical Study of the Lift Enhancement Mechanism of Circulation Control in Transonic Flow

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 311
Author(s):  
Ye Chen ◽  
Zhongxi Hou ◽  
Xiaolong Deng ◽  
Zheng Guo ◽  
Shuai Shao ◽  
...  
Keyword(s):  
Transonic Flow ◽  
Rational Design ◽  
Transport Model ◽  
Numerical Study ◽  
Underlying Mechanism ◽  
Circulation Control ◽  
Trailing Edge ◽  
Airfoil Surface ◽  
Shear Stress Transport Model ◽  
Lift Enhancement

The lift of an aircraft can be effectively enhanced by circulation control (CC) technology at subsonic speeds, but the efficiency at transonic speeds is greatly decreased. The underlying mechanism of this phenomenon is not fully understood. In this study, Reynolds averaged Navier—Stokes simulation with k−ω shear stress transport model was utilized to investigate the mechanism of lift enhancement by CC in transonic flow. For validation, the numerical CC results were compared with the NASA experimental data obtained for transonic CC airfoil. Thereafter, the RAE2822 airfoil was modified with a Coanda surface. The lift enhancement effects of CC via steady blowing with different momentum coefficients were tested at Ma=0.3 and 0.8 at α=3∘, and various fluid mechanics phenomena were investigated. The results indicate that the flow structure of the CC jet is insensitive to the incoming flow conditions because of the similarity to the local static pressure field around the trailing edge of the airfoil. Owing to the appearance of shockwaves on the airfoil surface in the transonic regime, the performance of the CC jet is restricted to the trailing edge of the airfoil. Transonic CC achieved a slight improvement in aerodynamic performance owing to a favorable shift in the shockwave pattern and accelerated flow in the separation region on the airfoil surfaces. Revealing the mechanism of lift enhancement of CC in the transonic regime can facilitate the rational design of new fluidic actuators with high activity and expand the potential applications of CC technology.

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