Numerical investigations of wall-bounded turbulence

2011 ◽  
Vol 225 (5) ◽  
pp. 1163-1174 ◽  
Author(s):  
H A Daud ◽  
Q Li ◽  
O A Bég ◽  
S A A AbdulGhani
Keyword(s):  
Experimental Data ◽  
Channel Flow ◽  
Numerical Solutions ◽  
Turbulence Models ◽  
Sensitivity Study ◽  
Computational Fluid Dynamics Cfd ◽  
Solution Accuracy ◽  
Rng Turbulence Model ◽  
High Degree ◽  
Naca 0012

This article investigates numerically the effects on turbulence in two important flow regimes – fully developed channel flow and flow past a NACA 0012 airfoil, using the commercial software – FLUENT 6.3. The solution accuracy is explored via a sensitivity study of mesh type and quality effects, employing different element types (e.g. quadrilateral and triangular). The significance of this article is to elucidate the effects of enhancement wall treatment and standard wall function on the turbulent boundary layer. Furthermore, three different turbulence models have been utilized in this study ( k−ε, re-normalization group (RNG), and shear stress transport (SST) k−ω). The numerical solutions have been compared with available direct numerical simulation (DNS) and experimental data and very good correlation has been achieved. In addition, the statistical turbulence results related to the RNG turbulence model are shown to yield much closer correlation with DNS and experimental data. The effect of Reynolds number ( Reτ = 590 and Reτ = 2320) is studied for the channel flow regime. The near wall resolution is examined in detail by controlling in the y+ value. A particularly important objective in this study is to highlight the importance of validation in computational fluid dynamics (CFD) turbulence simulations and sustaining a high degree of accuracy, aspects which are often grossly neglected with industrial CFD software. The authors therefore hope to provide some guidance to applied aerodynamicists utilizing CFD in future studies.

scholarly journals Impact of Turbulence Models on the Air Flow in a Confined Rectangular Space

2020 ◽  
pp. 46-53
Author(s):  
Jakub Mularski ◽  
Amit Arora ◽  
Muhammad Azam Saeed ◽  
Łukasz Niedźwiecki ◽  
Samrand Saeidi
Keyword(s):  
Experimental Data ◽  
Air Flow ◽  
Turbulence Models ◽  
The Other ◽  
Experimental Measurements ◽  
Wall Region ◽  
Sst Model ◽  
Computational Fluid Dynamics Cfd ◽  
The Impact ◽  
The Given

The paper regards the impact of four different turbulence models on the air flow pattern in a confined rectangular space. The following approaches are analyzed. The Baseline (BSL) Reynolds model, the Speziale-Sarkar-Gatzki (SSG) Reynolds model, the Menter's shear-stress transport (SST) model and the basic k-ε model. Computational fluid dynamics (CFD) results are compared with the experimental measurements in four different planes. The Reynolds number for the given conditions is equal to 5000. The k-ε model yielded the most accurate results with regard to the experimental data but its reliability decreased near the wall region. With respect to the other models, it was also found that the k-ε approach generated the least circulating flow.

On the Validation of Turbulence Models for Wheel and Wheelhouse Aerodynamics

2021 ◽  
Author(s):  
Kaloki Nabutola ◽  
Sandra Boetcher
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Vehicle Body ◽  
Flow Structures ◽  
Time Resolved ◽  
Flow Control Devices ◽  
Vehicle Aerodynamics ◽  
Computational Fluid Dynamics Cfd ◽  
Drag And Lift

Abstract Vehicle aerodynamics plays an important role in reducing fuel consumption. The underbody contributes to around 50% of the overall drag of a vehicle. As part of the underbody, the wheels and wheelhouses contribute to approximately 25-30% of the overall drag of a vehicle. As a result, wheel aerodynamics studies have been gaining popularity. However, a consensus of an appropriate turbulence model has not been reached, partially due to the lack of experiments appropriate for turbulence model validation studies for this type of flow. Seven turbulence models were used to simulate the flow within the wheelhouse of a simplified vehicle body, and results were shown to be incongruous with commonly used experimental data. The performance of each model was evaluated by comparing the aerodynamic coefficients obtained using computational fluid dynamics (CFD) to data collected from the Fabijanic wind tunnel experiments. The various turbulence models generally agreed with each other when determining average values, such a mean drag and lift coefficients, even if the particular values did not fall within the uncertainty of the experiment; however, they exhibited differences in the level of resolution in the flow structures within the wheelhouse. These flow structures are not able to be validated with currently available experimental data. Properly resolving flow structures is important when implementing flow control devices to reduce drag. Results from this study emphasize the need for spatially and time-resolved experiments, especially for validating LES and DES for flow within a wheelhouse.

On the Numerical Behavior of RANS-Based Transition Models

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Rui Lopes ◽  
Luís Eça ◽  
Guilherme Vaz
Keyword(s):  
Boundary Conditions ◽  
Numerical Solutions ◽  
Turbulence Models ◽  
Discretization Error ◽  
Navier Stokes ◽  
Laminar Separation ◽  
Aft Model ◽  
Transition Models ◽  
Distinct Features ◽  
Naca 0012

Abstract A comparison of several Reynolds-averaged Navier–Stokes (RANS) based transition models is presented. Four of the most widespread models are selected: the γ−Reθ, γ, amplification factor transport (AFT), and kT−kL−ω models, representative of different modeling approaches. The calculations are performed on several geometries: a flat plate, the Eppler 387 and NACA 0012 two-dimensional (2D) airfoils at two angles of attack, and the SD7003 wing. Distinct features such as the influence of the inlet boundary conditions, discretization error, and modeling error are discussed. It is found that all models present a strong sensitivity to the turbulence quantities inlet boundary conditions, and with the exception of the AFT model, are severely influenced by the decay of turbulence predicted by the underlying turbulence model. This makes the estimation of modeling errors troublesome because these quantities are rarely reported in experiments. Despite not having specific terms in their formulation to deal with separation-induced transition, both the AFT and kT−kL−ω models manage to predict it for the Eppler 387 foil, although presenting higher numerical uncertainty than the remaining models. However, both models show difficulties in the simulation of flows at Reynolds numbers under 105. The γ−Reθ and γ models are the most robust alternatives in terms of iterative and discretization error. The use of RANS compatible transition models allows for laminar flow and features such as laminar separation bubbles to be reproduced and can lead to greatly improved numerical solutions when compared to simulations performed with standard turbulence models.

scholarly journals Numerical Simulation of Flow in Parshall Flume Using Selected Nonlinear Turbulence Models

Hydrology ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 151
Author(s):  
Mehdi Heyrani ◽  
Abdolmajid Mohammadian ◽  
Ioan Nistor
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Numerical Simulation ◽  
Computational Fluid Dynamics ◽  
Standard Error ◽  
Physical Modeling ◽  
Hydraulic Structure ◽  
Turbulence Models ◽  
Computational Fluid Dynamics Cfd ◽  
The Right

This study uses a computational fluid dynamics (CFD) approach to simulate flows in Parshall flumes, which are used to measure flowrates in channels. The numerical results are compared with the experimental data, which show that choosing the right turbulence model, e.g., v2−f and LC, is the key element in accurately simulating Parshall flumes. The Standard Error of Estimate (SEE) values were very low, i.e., 0.76% and 1.00%, respectively, for the two models mentioned above. The Parshall flume used for this experiment is a good example of a hydraulic structure for which the design can be more improved by implementing a CFD approach compared with a laboratory (physical) modeling approach, which is often costly and time-consuming.

NUMERICAL AND EXPERIMENTAL ANALYSES OF THE FLOW AROUND A HORIZONTAL WALL-MOUNTED CIRCULAR CYLINDER

2009 ◽  
Vol 33 (2) ◽  
pp. 189-215 ◽  
Author(s):  
M. Sami Akoz ◽  
M. Salih Kirkgoz
Keyword(s):  
Numerical Modeling ◽  
Circular Cylinder ◽  
Numerical Solutions ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Sensitivity Study ◽  
Cylinder Surface ◽  
Image Velocimetry ◽  
Horizontal Wall ◽  
Drag And Lift

The numerical modeling of two-dimensional turbulent flow around a horizontal wall-mounted circular cylinder at Reynolds numbers in the range of 1000≤ReD≤7000 is investigated. Ansys® 10.0-FLOTRAN program package is used to solve the governing equations by finite element method, and the performance of the standard k-ε, standard k-ω and SST turbulence models are examined. A sensitivity study for the three turbulence models is carried out on eight computational meshes with different densities and structures. The computational velocity fields from the present simulations are compared with the experimental results obtained from particle image velocimetry (PIV) measurements for validation purposes. The point of the boundary layer detachment from the cylinder surface and the lengths of primary and secondary separation regions occurring around the cylinder are determined numerically and compared with those obtained experimentally. From these comparisons it is found that the numerical modeling using either of k-ω and SST turbulence models is reasonably successful. Using the results of numerical solutions, the drag and lift coefficients, Cd and Cl, are also calculated and compared with the measured values.

Large eddy simulation of shock train in a convergent–divergent nozzle

2014 ◽  
Vol 25 (04) ◽  
pp. 1450003 ◽  
Author(s):  
Seyed Mahmood Mousavi ◽  
Ehsan Roohi
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Numerical Solutions ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Shock Train ◽  
Eddy Simulation ◽  
Starting Point ◽  
Large Eddy

This paper discusses the suitability of the Large Eddy Simulation (LES) turbulence modeling for the accurate simulation of the shock train phenomena in a convergent-divergent nozzle. To this aim, we selected an experimentally tested geometry and performed LES simulation for the same geometry. The structure and pressure recovery inside the shock train in the nozzle captured by LES model are compared with the experimental data, analytical expressions and numerical solutions obtained using various alternative turbulence models, including k–ε RNG, k–ω SST, and Reynolds stress model (RSM). Comparing with the experimental data, we observed that the LES solution not only predicts the "locations of the first shock" precisely, but also its results are quite accurate before and after the shock train. After validating the LES solution, we investigate the effects of the inlet total pressure on the shock train starting point and length. The effects of changes in the back pressure, nozzle inlet angle (NIA) and wall temperature on the behavior of the shock train are investigated by details.

CFD Simulation of Round Impinging Jet and Comparison With Experimental Data

2016 ◽  
Author(s):  
H. Arabnejad ◽  
A. Mansouri ◽  
S. A. Shirazi ◽  
B. S. McLaury
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Reynolds Stress Model ◽  
Ansys Fluent ◽  
Target Wall ◽  
Computational Fluid Dynamics Cfd ◽  
Better Than

In this work, fluid dynamics of a turbulent round impinging jet has been studied using Computational Fluid Dynamics (CFD) and the results have been compared with experimental data from the literature. The fluid was water with density of 1000 kg/m3 and the average velocity of the submerged jet was kept constant at 10.7 m/s while the liquid viscosity varied from 1 cP to 100 cP. Different turbulence models including k-ε, k-ω and Reynolds Stress Model (RSM) have been employed in ANSYS FLUENT and the predicted axial and radial velocity profiles at various distances from the wall are compared with LDV data. It was observed that at locations away from the target wall, predicted velocities are comparable to the measured velocities for all the viscosities. However, near the wall, the deviation between the CFD predictions and experimental measurements become noticeable. The performance of k-ω model and RSM are found to be better than the k-ε model especially for the highest viscous fluid, but no model was found to be superior for all conditions and at all locations.

Effects of Over Fire Air on the Combustion and NOx Emission Characteristics of a 600 MW Opposed Swirling Fired Boiler

2012 ◽  
Vol 512-515 ◽  
pp. 2135-2142 ◽  
Author(s):  
Yu Peng Wu ◽  
Zhi Yong Wen ◽  
Yue Liang Shen ◽  
Qing Yan Fang ◽  
Cheng Zhang ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Empirical Method ◽  
Nox Emission ◽  
Emission Characteristics ◽  
Cfd Model ◽  
Nitrogen Release ◽  
Computational Fluid Dynamics Cfd ◽  
Low Nox Emission

A computational fluid dynamics (CFD) model of a 600 MW opposed swirling coal-fired utility boiler has been established. The chemical percolation devolatilization (CPD) model, instead of an empirical method, has been adapted to predict the nitrogen release during the devolatilization. The current CFD model has been validated by comparing the simulated results with the experimental data obtained from the boiler for case study. The validated CFD model is then applied to study the effects of ratio of over fire air (OFA) on the combustion and nitrogen oxides (NOx) emission characteristics. It is found that, with increasing the ratio of OFA, the carbon content in fly ash increases linearly, and the NOx emission reduces largely. The OFA ratio of 30% is optimal for both high burnout of pulverized coal and low NOx emission. The present study provides helpful information for understanding and optimizing the combustion of the studied boiler

Wear of a Tool in Double-Disk Lapping of Silicon Wafers

2010 ◽  
Author(s):  
Adam Barylski ◽  
Mariusz Deja
Keyword(s):  
Experimental Data ◽  
Integrated Circuits ◽  
Tool Wear ◽  
Silicon Wafers ◽  
Silicon Ingot ◽  
Proposed Model ◽  
Tool Wear Prediction ◽  
Simulation Results ◽  
High Degree ◽  
Kinematical Parameters

Silicon wafers are the most widely used substrates for fabricating integrated circuits. A sequence of processes is needed to turn a silicon ingot into silicon wafers. One of the processes is flattening by lapping or by grinding to achieve a high degree of flatness and parallelism of the wafer [1, 2, 3]. Lapping can effectively remove or reduce the waviness induced by preceding operations [2, 4]. The main aim of this paper is to compare the simulation results with lapping experimental data obtained from the Polish producer of silicon wafers, the company Cemat Silicon from Warsaw (www.cematsil.com). Proposed model is going to be implemented by this company for the tool wear prediction. Proposed model can be applied for lapping or grinding with single or double-disc lapping kinematics [5, 6, 7]. Geometrical and kinematical relations with the simulations are presented in the work. Generated results for given workpiece diameter and for different kinematical parameters are studied using models programmed in the Matlab environment.

Numerical Simulation of Indoor Thermal Environment of a Double-Skin Facade Office with Different Shutter Angles

2014 ◽  
Vol 694 ◽  
pp. 256-259
Author(s):  
Xin Zhan ◽  
Hua Yang ◽  
Feng Yun Jin
Keyword(s):  
Heat Transfer ◽  
Thermal Environment ◽  
Ventilation Rate ◽  
Air Distribution ◽  
Indoor Thermal Environment ◽  
Double Skin ◽  
Computational Fluid Dynamics Cfd ◽  
Heat Transfer Simulation ◽  
Shading Devices ◽  
Rng Turbulence Model

Airflow and heat transfer simulation was conducted for a double-skin façade (DSF) system equipped with shading devices in the cavity, using computational fluid dynamics (CFD) with RNG turbulence model and PISO algorithm, for five conditions of slat angles (θ=0°, 30°, 45°, 60°, 90°). The present study indicates that the presence of shading devices influences the temperatures, the ventilation rate and the air distribution in the DSF system. Besides, the different angles will make different influences.

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