Sensitivity Studies of Shear Stress Transport Turbulence Model Parameters on the Prediction of Seven-Rod Bundle Benchmark Experiments

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Cale Bergmann ◽  
S. Ormiston ◽  
V. Chatoorgoon
Keyword(s):  
Shear Stress ◽  
Turbulence Model ◽  
Turbulence Modeling ◽  
Sensitivity Study ◽  
Model Parameters ◽  
Rod Bundle ◽  
Shear Stress Transport ◽  
Sst Turbulence Model ◽  
Sensitivity Studies ◽  
Two Parameters

This paper reports the findings of a sensitivity study of parameters in the shear stress transport (SST) turbulence model in a commercial computational fluid dynamics (CFD) code to predict an experiment from the Generation IV International Forum Supercritical-Water-Cooled Reactor (GIF SCWR) 2013–2014 seven-rod subchannel benchmark exercise. This study was motivated by the result of the benchmark exercise that all the CFD codes gave similar results to a subchannel code, which does not possess any sophisticated turbulence modeling. Initial findings were that the CFD codes generally underpredicted the wall temperatures on the B2 case in the region where the flow was supercritical. Therefore, it was decided to examine the effect of various turbulence model parameters to determine if a CFD code using the SST turbulence model could do a better job overall in predicting the wall temperatures of the benchmark experiments. A sensitivity study of seven parameters was done, and changes to two parameters were found to make an improvement.

scholarly journals Pengaruh Silinder Downstream terhadap Karakteristik Aliran Silinder Upstream Menggunakan Square Disturbance Body Tersusun Tandem

2018 ◽  
Vol 11 (2) ◽  
pp. 58
Author(s):  
Rina Rina ◽  
Sanny Ardhy
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Drag Force ◽  
Turbulence Model ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Model Parameters ◽  
Square Cylinder ◽  
Shear Stress Transport ◽  
Unsteady Rans

Fluida yang mengalir di sekitar bluff body silinder sirkular, akan menimbulkan gaya-gaya aerodinamika salah satunya gaya drag. Drag sangat tidak diinginkan untuk keselamatan struktur body. Reduksi gaya drag dilakukan dengan mengontrol medan aliran seperti meningkatkan kekasaran permukaan, mengiris silinder dengan sudut iris tertentu, dan menempatkan pengganggu di sisi upstream silinder. Penelitian ini bertujuan untuk melihat pengaruh silinder downstream terhadap karakteristik aliran silinder upstream menggunakan square disturbance body yang disusun tandem pada saluran sempit. Geometri yang digunakan adalah dua silinder sirkular yang disusun tandem berdiameter (D) 25 mm dengan variasi jarak antar silinder (L/D) 1,5; 2; 2,5; 3; 3,5; 4. Square Cylinder sebagai body pengganggu ditempatkan pada sisi upstream silinder utama berdiamensi 4 mm. Posisi sudut pengganggu (?) 30°, dan jarak gap (d=0.4mm). Reynolds number berdasarkan diameter silinder, yaitu ReD 2,32x104. Penelitian iini dilakukan secara numerik 2D Unsteady-RANS menggunakan CFD software FLUENT 6.3.26 dengan model viscous Turbulence Model Shear-Stress-Transport (SST) k-?. Parameter yang diamati adalah koefisien pressure (Cp), Koefisien drag pressure (Cdp) dan visualisasi aliran berupa velocity pathline. Hasilnya menunjukkan bahwa Penambahan silinder downstream memberikan kontribusi dalam pengurangan gaya drag pada silinder upstream menggunakan square disturbance body. Pengaruh wake silinder upstream terhadap silinder downstream berkurang dengan meningkatnya rasio L/D. Interaksi wake silinder upstream terhadap silinder downstream terjadi pada konfigurasi L/D 1,5 – 3. Pengurangan gaya drag optimum terjadi pada konfigurasi L/D 3. The fluid flows around the circular cylinder bluff body will produce aerodynamic forces, one of which is the drag force. Drag is very undesirable for the safety of the body structure. Reduction of drag force is carried out by controlling the flow field such as increasing the surface roughness, slicing the cylinder with a certain iris angle, and placing the disturbance on the upstream side of the cylinder. This purpose of the study is to see the effect of downstream cylinders on the flow characteristics of upstream cylinders using a square disturbance body arranged tandem in a narrow channel. The geometry used is two circular cylinders arranged in tandem diameter (D) 25 mm with a variation of distance between cylinders (L / D) 1.5; 2; 2.5; 3; 3.5; 4. Square Cylinder as a disturbing body is placed on the side of the main cylinder upstream with a diameter of 4 mm. The position of the disturbing angle (?) is 30 °, and the gap distance (d = 0.4mm). Reynolds number is based on cylinder diameter, ie ReD 2.32x104. This research was carried out numerical 2D Unsteady-RANS using a FLUENT 6.3.26 CFD software with viscous Turbulence model Shear-Stress-Transport (SST) k-? model. Parameters observed were pressure coefficient (Cp), drag pressure coefficient (Cdp) and flow visualization in the form of velocity pathline. The results show that the addition of a downstream cylinder contributes to the reduction of the drag force on the upstream cylinder using a square disturbance body. The wake influence of upstream cylinder to downstream cylinder decreasing with increasing the ratio of L/D. The interaction of wake cylinder upstream to downstream cylinder occurs at L/D 1.5 - 3. The optimum for the drag force reduction occurs at L/D 3.

Modification of Shear Stress Transport Turbulence Model Using Helicity for Predicting Corner Separation Flow in a Linear Compressor Cascade

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Yangwei Liu ◽  
Yumeng Tang ◽  
Ashley D. Scillitoe ◽  
Paul G. Tucker
Keyword(s):  
Shear Stress ◽  
Turbulence Model ◽  
Incidence Angle ◽  
Computational Cost ◽  
Separation Flow ◽  
Compressor Cascade ◽  
Production Term ◽  
Corner Separation ◽  
Shear Stress Transport ◽  
Sst Model

Abstract Three-dimensional corner separation significantly affects compressor performance, but turbulence models struggle to predict it accurately. This paper assesses the capability of the original shear stress transport (SST) turbulence model to predict the corner separation in a linear highly loaded prescribed velocity distribution (PVD) compressor cascade. Modifications for streamline curvature, Menter’s production limiter, and the Kato-Launder production term are examined. Comparisons with experimental data show that the original SST model and the SST model with different modifications can predict the corner flow well at an incidence angle of −7 deg, where the corner separation is small. However, all the models overpredict the extent of the flow separation when the corner separation is larger, at an incidence angle of 0 deg. The SST model is then modified using the helicity to take account of the energy backscatter, which previous studies have shown to be important in the corner separation regions of compressors. A Reynolds stress model (RSM) is also used for comparison. By comparing the numerical results with experiments and RSM results, it can be concluded that sensitizing the SST model to helicity can greatly improve the predictive accuracy for simulating the corner separation flow. The accuracy is quite competitive with the RSM, whereas in terms of computational cost and robustness it is superior to the RSM.

How well do we know our models?

2020 ◽  
Author(s):  
Denise Degen ◽  
Karen Veroy ◽  
Mauro Cacace ◽  
Magdalena Scheck-Wenderoth ◽  
Florian Wellmann
Keyword(s):  
Finite Element ◽  
Surrogate Model ◽  
Sensitivity Study ◽  
Reduced Basis Method ◽  
Sensitivity Analyses ◽  
Model Parameters ◽  
Reduced Basis ◽  
Global Sensitivity ◽  
Sensitivity Studies ◽  
Basis Method

<p>In Geosciences, we face the challenge of characterizing uncertainties to provide reliable predictions of the earth surface to allow, for instance, a sustainable and renewable energy management. In order, to address the uncertainties we need a good understanding of our geological models and their associated subsurface processes.</p><p>Therefore, the essential pre-step for uncertainty analyses are sensitivity studies. Sensitivity studies aim at determining the most influencing model parameters. Hence, we require them to significantly reduce the parameter space to avoid unfeasibly large compute times.</p><p>We distinguish two types of sensitivity analyses: local and global studies. In contrast, to the local sensitivity study, the global one accounts for parameter correlations. That is the reason, why we employ in this work a global sensitivity study. Unfortunately, global sensitivity studies have the disadvantage that they are computationally extremely demanding. Hence, they are prohibitive even for state-of-the-art finite element simulations.</p><p>For this reason, we construct a surrogate model by employing the reduced basis method. The reduced basis method is a model order reduction technique that aims at significantly reducing the spatial and temporal degrees of freedom of, for instance, finite element solves. In contrast to other surrogate models, we obtain a surrogate model that preserves the physics and is not restricted to the observation space. As we will show, the reduced basis method leads to a speed-up of five to six orders of magnitude with respect to our original problem while retaining an accuracy higher than the measurement accuracy.</p><p>In this work, we elaborate on the advantages of global sensitivity studies in comparison to local ones. We use several case studies, from large-scale European sedimentary basins to demonstrate how the global sensitivity studies are used to learn about the influence of transient, such as paleoclimate effects, and stationary effects. We also demonstrate how the results can be used in further analyses, such as deterministic and stochastic model calibrations. Furthermore, we show how we can use the analyses to learn about the subsurface processes and to identify model short comes.</p>

A case study on the calibration of the k–ω SST (shear stress transport) turbulence model for small scale wind turbines designed with cambered and symmetrical airfoils

Energy ◽  
2016 ◽  
Vol 97 ◽  
pp. 144-150 ◽  
Author(s):  
P. A. Costa Rocha ◽  
H. H. Barbosa Rocha ◽  
F. O. Moura Carneiro ◽  
M. E. Vieira da Silva ◽  
C. Freitas de Andrade
Keyword(s):  
Shear Stress ◽  
Turbulence Model ◽  
Wind Turbines ◽  
Small Scale ◽  
Shear Stress Transport

An Improved Shear Stress Transport(SST) Model for High Speed Flows

2012 ◽  
Vol 229-231 ◽  
pp. 625-629
Author(s):  
Jing Yuan Liu ◽  
Wen Qiang Cheng
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulence Model ◽  
High Speed ◽  
Correction Term ◽  
Plate Boundary ◽  
Experimental Results ◽  
Tvd Scheme ◽  
Shear Stress Transport ◽  
Sst Model

An improved Shear Stress Transport(SST) model, which allows for the compressible corrections, is proposed in this study. Numerical scheme was established by taking advantage of the improved Total Variation Diminishing (TVD) scheme and by applying implicit scheme to the negative source terms of the turbulence model. Hypersonic flat-plate boundary-layer flows and hypersonic compression ramp flows marked with separation, reattachment and shock/boundary-layer interactions are then computed. The comparisons between the computational results, the experimental results and the semi-empirical formulations show that the compressible correction term of the SST turbulence model is the scalar product of the weighted density average of the turbulent fluctuating velocity and the pressure gradients of the average flow field correlation quantities. In addition, for flow with separation and without separation, calculation results of wall pressures, friction coefficients and wall heat transfer rate distributions using the improved model and established scheme agree better with the experimental results than that using the original SST model.

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