Computer Simulations of Airflow Field Around a Cube: Comparisons of LES and RANS Models

2010 ◽  
Author(s):  
Behtash Tavakoli ◽  
Goodarz Ahmadi
Keyword(s):  
Experimental Data ◽  
Computational Models ◽  
Transport Model ◽  
Separated Flow ◽  
Realistic Model ◽  
Navier Stokes ◽  
Reynolds Stress Transport Model ◽  
Rans Models ◽  
Airflow Field ◽  
Computationally Intensive

Simulations of flow field around wall mounted square cylinders have been used extensively for validation of computational models in the literature. In this paper the airflow fields around a square cylinder were simulated using the Reynolds Averaged Navier-Stokes (RANS) models as well as the Large Eddy Simulations (LES). Particular attention was given to the case with Reynolds number of 80,000 for which the experimental data of Hussein and Matinuzzi [1] are available. The nature of the 3D wakes behind the cube as well as the vortices in front and at the back of the cube were investigated. The simulation results were compared with the experimental data and the accuracy of different models were studied. While the LES better captured the features of this separated flow, it is computationally intensive. The Reynolds Stress Transport Model (RSTM) did not properly predict some features of this separated flow, but is comparatively more economical. The accuracy of RSTM for predicting the turbulence features of separated flows was discussed, and its application for the flow around a realistic model of a building was pointed out.

Numerical Simulation of Separation Control in Backward Facing Step Turbulent Flow

2002 ◽  
Author(s):  
Emmanuel Guilmineau ◽  
Patrick Queutey
Keyword(s):  
Experimental Data ◽  
Reynolds Stress ◽  
Transport Model ◽  
Turbulence Models ◽  
Separated Flow ◽  
Separation Control ◽  
Local Perturbation ◽  
Backward Facing Step ◽  
Reynolds Stress Transport Model ◽  
Turbulent Separated Flow

The control of turbulent separated flow over the backward-facing step is numerically investigated with various turbulence models ranging from one equation Spalart & Allmaras (1992), two-equation K-ω closures (Wilcox, 1988; Menter, 1993) to a full Reynolds stress transport model based on the Reynolds stress transport Rij-ω model (Deng & Visonneau, 1999). Results are compared with experimental data of Yoshioka et al. (1999) where the flow control was monitoring with alternating suction/injection at the step height. It is shown that the effect of that local perturbation is better represented using the Rij-ω turbulence model.

A Comparison of Unsteady RANS Simulations With PIV Data in an Axial Turbomachine

2005 ◽  
Author(s):  
Daniel Brzozowski ◽  
Oguz Uzol ◽  
Yi-Chih Chow ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Experimental Data ◽  
Transport Model ◽  
Energy Levels ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Piv Measurements ◽  
Flow Solver ◽  
Reynolds Stress Transport Model ◽  
Flow Features ◽  
Rans Simulations

This paper presents a comparison of 2D unsteady Reynolds Averaged Navier-Stokes (RANS) simulations using two standard turbulence models, i.e. RNG k-ε and a Reynolds Stress Transport Model, with experimental data, obtained using two-dimensional Particle Image Velocimetry (PIV) measurements within an entire stage of an axial turbomachine. The computations are performed using the commercial flow solver FLUENT™. A sliding mesh interface between the rotor and stator domains is used. The PIV measurements are performed in a refractive-index-matched facility that provides unobstructed view, and cover the entire 2nd stage of a two-stage axial pump. The inlet velocity and turbulence boundary conditions are provided from the experimental data. Detailed side-by-side comparisons of computed and measured phase-averaged velocity as well as turbulence fields within the entire stage are presented. Quantitative comparisons between the experiments and the computations are also included in terms of line distributions within the rotor-stator gap and the stator wake regions. The results show that, although there is reasonable agreement in general between the experimental results and the computational simulations, some critical flow features are not correctly predicted. The turbulent kinetic energy levels are generally too high in the simulations, with substantial amount of unphysical turbulence generation near the blade leading edges, especially in the case of RNG k-ε model.

scholarly journals Reynolds Stress Perturbation for Epistemic Uncertainty Quantification of RANS Models Implemented in OpenFOAM

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 113 ◽  
Author(s):  
Luis F. Cremades Rey ◽  
Denis F. Hinz ◽  
Mahdi Abkar
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Reynolds Stress ◽  
Epistemic Uncertainty ◽  
Turbulent Viscosity ◽  
Navier Stokes ◽  
Simulation Data ◽  
Direct Numerical Simulation Data ◽  
Engineering Problems ◽  
Rans Models

Reynolds-averaged Navier-Stokes (RANS) models are widely used for the simulation of engineering problems. The turbulent-viscosity hypothesis is a central assumption to achieve closures in this class of models. This assumption introduces structural or so-called epistemic uncertainty. Estimating that epistemic uncertainty is a promising approach towards improving the reliability of RANS simulations. In this study, we adopt a methodology to estimate the epistemic uncertainty by perturbing the Reynolds stress tensor. We focus on the perturbation of the turbulent kinetic energy and the eigenvalues separately. We first implement this methodology in the open source package OpenFOAM. Then, we apply this framework to the backward-facing step benchmark case and compare the results with the unperturbed RANS model, available direct numerical simulation data and available experimental data. It is shown that the perturbation of both parameters successfully estimate the region bounding the most accurate results.

CFD Modeling of Non-Premixed Combustion in a Gas Turbine Combustor

2002 ◽  
Author(s):  
Kitano Majidi
Keyword(s):  
Gas Turbine ◽  
Transport Model ◽  
Direct Injection ◽  
Turbulence Models ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Reacting Flow ◽  
Gas Temperature ◽  
Gas Turbine Combustor ◽  
Reynolds Stress Transport Model

In the present study numerical calculations are used to solve reacting flow in a gas turbine combustor. A 3-D Favre-Averaged Navier-Stokes solver for a mixture of chemically reacting gases is applied to predict the flow pattern, gas temperature and fuel and species concentrations in the entire combustor. The complete combustor geometry with all important details such as air swirler vane passages and secondary holes are modeled. The calculations are carried out using three different turbulence models. Comparisons are made between the standard k-ε model, RNG k-ε model and a Reynolds stress transport model. To provide a closure for the chemical source term the Eddy Dissipation model is used. A lean direct injection of a liquid fuel is employed. Furthermore the influence of radiation will be investigated.

Prediction of the Flow Around an Airfoil Using a Reynolds Stress Transport Model

1995 ◽  
Vol 117 (1) ◽  
pp. 50-57 ◽  
Author(s):  
Lars Davidson
Keyword(s):  
Experimental Data ◽  
Reynolds Stress ◽  
Transport Model ◽  
Suction Side ◽  
Equation Model ◽  
Staggered Grid ◽  
Poor Agreement ◽  
Third Order ◽  
Reynolds Stress Transport Model ◽  
Quick Scheme

A second-moment Reynolds Stress Transport Model (RSTM) is used in the present work for computing the flow around a two-dimensional airfoil. An incompressible SIMPLEC code is used, employing a non-staggered grid arrangement. A third-order QUICK scheme is used for the momentum equations, and a second-order, bounded MUSCL scheme is used for the turbulent quantities. As the RSTM is valid only for fully turbulent flow, an eddy viscosity, one-equation model is used near the wall. The two models are matched along a preselected grid line in the fully turbulent region. Detailed comparisons between calculations and experiments are presented for an angle of attack of α = 13.3 deg. The RSTM predictions agree well with the experiments, and approaching stall is predicted for α = 17 deg, which agrees well with experimental data. The results obtained with a two-layer κ – ∈ model show poor agreement with experimental data; the velocity profiles on the suction side of the airfoil show no tendency of separation, and no tendency of stall is predicted.

scholarly journals Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays

2021 ◽  
Vol 11 (6) ◽  
pp. 2496
Author(s):  
Alejandro Güemes ◽  
Pablo Fajardo ◽  
Marco Raiola
Keyword(s):  
Separated Flow ◽  
Wind Load ◽  
Solar Panel ◽  
Navier Stokes ◽  
Large Reynolds Number ◽  
Pressure Measurements ◽  
Mean Flow ◽  
Shear Model ◽  
Rans Models ◽  
Reynolds Averaged Navier Stokes

This paper reports a comparison between wind-tunnel measurements and numerical simulations to assess the capabilities of Reynolds-Averaged Navier-Stokes models to estimate the wind load over solar-panel arrays. The free airstream impinging on solar-panel arrays creates a complex separated flow at large Reynolds number, which is severely challenging for the current Reynolds-Averaged Navier-Stokes models. The Reynolds-Averaged Navier-Stokes models compared in this article are k-ϵ, Shear-Stress Transport k-ω, transition and Reynolds Shear Model. Particle Image Velocimetry measurements are performed to investigate the mean flow-velocity and turbulent-kinetic-energy fields. Pressure taps are located in the surface of the solar panel model in order to obtain static pressure measurements. All the Reynolds-Averaged Navier-Stokes models predict accurate average velocity fields when compared with the experimental ones. One of the challenging factor is to predict correctly the thickness of the turbulent wake. In this aspect, Reynolds Shear provides the best results, reproducing the wake shrink observed on the 3rd panel in the experiment. On the other hand, some other features, most notably the blockage encountered by the flow below the panels, are not correctly reproduced by any of the models. The pressure distributions over the 1st panel obtained from the different Reynolds-Averaged Navier-Stokes models show good agreement with the pressure measurements. However, for the rest of the panels Reynolds-Averaged Navier-Stokes fidelity is severely challenged. Overall, the Reynolds Shear model provides the best pressure estimation in terms of pressure difference between the front and back sides of the panels.

scholarly journals Mixing in Axial-Flow Compressors: Conclusions Drawn From 3-D Navier-Stokes Analyses and Experiments

1990 ◽  
Author(s):  
J. H. Leylek ◽  
D. C. Wisler
Keyword(s):  
Experimental Data ◽  
Numerical Solutions ◽  
Turbulence Modeling ◽  
Axial Flow ◽  
Separated Flow ◽  
Navier Stokes ◽  
Tracer Gas ◽  
Flow Through ◽  
First Time ◽  
Axial Flow Compressors

Extensive numerical analyses and experiments have been conducted to understand mixing phenomena in multistage, axial-flow compressors. For the first time in the literature the following are documented: detailed 3-D Navier-Stokes solutions, with high-order turbulence modeling, are presented for flow through a compressor vane row at both design and off-design (increased) loading; comparison of these computations with detailed experimental data show excellent agreement at both loading levels; the results are then used to explain important aspects of mixing in compressors. The 3-D analyses show the development of spanwise and cross-passage flows in the stator and the change in location and extent of separated flow regions as loading increases. The numerical solutions support previous interpretations of experimental data obtained on the same blading using the ethylene tracer-gas technique and hot-wire anemometry. These results, plus new tracer-gas data, show that both secondary flow and turbulent diffusion are mechanisms responsible for both spanwise and cross-passage mixing in axial-flow compressors. The relative importance of the two mechanisms depends upon the configuration and loading levels. It appears that using the correct spanwise distributions of time-averaged inlet boundary conditions for 3-D Navier-Stokes computations enables one to explain much of the flow physics for this stator.

scholarly journals A Volumetric Approach to Wake Reduction: Design, Optimization, and Experimental Verification

2016 ◽  
Vol 2016 ◽  
pp. 1-15 ◽  
Author(s):  
Dean R. Culver ◽  
Earl Dowell ◽  
David Smith ◽  
Yaroslav Urzhumov ◽  
Abraham Varghese
Keyword(s):  
Computational Models ◽  
Fused Deposition Modeling ◽  
Stationary Flow ◽  
Optimization Methods ◽  
Navier Stokes ◽  
Fused Deposition ◽  
Gradient Based ◽  
Rans Models ◽  
Field Disturbance ◽  
Local Gradient

Wake reduction is a crucial link in the chain leading to undetectable watercraft. Here, we explore a volumetric approach to controlling the wake in a stationary flow past cylindrical and spherical objects. In this approach, these objects are coupled with rigid, fluid-permeable structures prescribed by a macroscopic design approach where all solid boundaries are parameterized and modeled explicitly. Local, gradient-based optimization is employed which permits topological changes in the manifold describing the composite solid component(s) while still allowing the use of adjoint optimization methods. This formalism works below small Reynolds number (Re) turbulent flow (Re≈100–10,000) when simulated using small Reynolds-averaged Navier-Stokes (RANS) models. The output of this topology optimization yields geometries that can be fabricated immediately using fused deposition modeling (FDM). Our prototypes have been verified in an experimental water tunnel facility, where the use of Particle Image Velocimetry (PIV) described the velocity profile. Comparisons with our computational models show excellent agreement for the spherical shapes and reasonable match for cylindrical shapes, with well-understood sources of error. Two important figures of merit are considered: domain-wide wake (DWW) and maximum local wake (MLW), metrics of the flow field disturbance whose definitions are described.

Flow and Particle Deposition in Asymmetric Human Airways

2006 ◽  
Author(s):  
L. Tian ◽  
G. Ahmadi ◽  
P. K. Hopke ◽  
Y.-S. Cheng
Keyword(s):  
Particle Transport ◽  
Particle Deposition ◽  
Transport Model ◽  
Tracheobronchial Tree ◽  
Upper Airways ◽  
Reynolds Stress Transport Model ◽  
Airflow Field ◽  
Human Airways ◽  
Upper Thoracic ◽  
Drug Delivery Devices

Transport and deposition of particles in human upper thoracic airways is important to understand their toxicology and the effect of exposure to environmental particulate matter as well as in the design of inhalation drug delivery devices. In the past, limited studies have employed 3-D asymmetric models to study the airflow through human lung, although tracheobronchial branching is generally asymmetric. Also limited work has been devoted to the study of particle deposition in upper airways where turbulence is important to particle depositions. It is also known that the asymmetry of the airways has a profound effect on the airflow fields and particle transport and deposition. The present study is concerned with providing a more accurate computational model for lung deposition. A realistic 3-D asymmetric bifurcation representation of human upper tracheobronchial tree has been developed to simulate the airflow field characterizing the inspiratory flow conditions using a turbulence Reynolds stress transport model. A Lagrangian particle trajectory analysis was also used for analyzing particle transport and deposition patterns in the upper tracheobronchial tree.

Mixing in Axial-Flow Compressors: Conclusions Drawn From Three-Dimensional Navier–Stokes Analyses and Experiments

1991 ◽  
Vol 113 (2) ◽  
pp. 139-156 ◽  
Author(s):  
J. H. Leylek ◽  
D. C. Wisler
Keyword(s):  
Experimental Data ◽  
Numerical Solutions ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Axial Flow ◽  
Separated Flow ◽  
Navier Stokes ◽  
Tracer Gas ◽  
Flow Through ◽  
Axial Flow Compressors

Extensive numerical analyses and experiments have been conducted to understand mixing phenomena in multistage, axial-flow compressors. For the first time in the literature the following are documented: Detailed three-dimensional Navier–Stokes solutions, with high order turbulence modeling, are presented for flow through a compressor vane row at both design and off-design (increased) loading; comparison of these computations with detailed experimental data show excellent agreement at both loading levels; the results are then used to explain important aspects of mixing in compressors. The three-dimensional analyses show the development of spanwise (radial) and circumferential flows in the stator and the change in location and extent of separated flow regions as loading increases. The numerical solutions support previous interpretations of experimental data obtained on the same blading using the ethylene tracer-gas technique and hot-wire anemometry. These results, plus new tracer-gas data, show that both secondary flow and turbulent diffusion are mechanisms responsible for both spanwise and circumferential mixing in axial-flow compressors. The relative importance of the two mechanisms depends upon the configuration and loading levels. It appears that using the correct spanwise distributions of time-averaged inlet boundary conditions for three-dimensional Navier–Stokes computations enables one to explain much of the flow physics for this stator.

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