Turbulence Modeling in a Model Combustor

2005 ◽  
Author(s):  
Lei-Yong Jiang ◽  
Ian Campbell
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Moment Closure ◽  
Superior Performance ◽  
Combustion Model ◽  
Discrete Ordinates ◽  
Viscosity Models

The flow field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically investigated. Solutions obtained from four turbulence models together with a laminar flamelet combustion model, discrete ordinates radiation model and enhanced wall treatment are presented and discussed. The numerical results are compared, in detail, with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, illustrates superior performance over three popular two-equation eddy-viscosity models. Although the main flow features are captured by all four turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and the turbulence kinetic energy distribution in the combustor chamber. In addition, it provides fairly good predictions for all Reynolds stress components, except for the circumferential normal stress at downstream sections. However, the superiority of the RSM is not so obvious for the temperature and species predictions in comparison with eddy-viscosity models, except for the standard k-ε model. This suggests that coupling between the RSM and combustion models needs to be further improved in order to enhance its applications in practical combustion systems.

On the Application of the Full Reynolds Stress Model for Unsteady CFD in Hydraulic Turbomachines

2020 ◽  
Author(s):  
Ernesto Casartelli ◽  
Luca Mangani ◽  
David Roos ◽  
Armando Del Rio
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Reynolds Stress Model ◽  
Moment Closure ◽  
Flow Structures ◽  
Stress Model ◽  
Cfd Simulations ◽  
Viscosity Models ◽  
Hydraulic Machines ◽  
Fully Coupled

Abstract The computation of the characteristic of hydraulic machines, both in pump and turbine mode, needs, when performed over a wide operating range, to take into account turbulence anisotropy. This because highly separated flows largely deviate from isotropic turbulence structures as assumed in RANS eddy viscosity models with the Boussinesq approximation. In this paper CFD computations were performed with anisotropic turbulence models in order to capture the characteristic and investigate flow structures phenomena. Experimental results are compared against the CFD simulations in order to validate the results. Specific occurring phenomena are highlighted and more complex flow structures are evident compared to those computed with standard eddy viscosity models. A in-house pressure based coupled solver was used for the CFD simulations. The code is a finite volume polyhedral CFD solver implemented in a C++ framework with the possibility to implement implicit and coupled algorithms. Second moment closure turbulence model have been successfully implemented with a standard and novel fully coupled algorithm. In the paper the advantage of the novel algorithm is presented for industrial applications. The fully coupled approach for the Reynolds Stress model allows stable simulations of transient and steady state hydraulic machines at any operating point, opening also new opportunities in obtaining high accurate results for anisotropic turbulent flows without the usage of hybrid LES/RANS models and without the model limitation of standard eddy viscosity models.

A Critical Evaluation of Turbulence Modeling in a Model Combustor

2012 ◽  
Author(s):  
Leiyong Jiang
Keyword(s):  
Turbulence Modeling ◽  
Critical Evaluation ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Operating Conditions ◽  
Moment Closure ◽  
Mean Velocity ◽  
Second Moment Closure ◽  
Heat Transfers ◽  
Air Diffusion

Based on the previous benchmark studies on combustion, scalar transfer and radiation models, a critical evaluation of turbulence models in a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers has been performed. Results obtained from six turbulence models are presented and compared in detail with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, is superior over the five popular eddy-viscosity two-equation models. Although the main flow patterns are captured by all six turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and give fairly accurate predictions for mean velocity, temperature, CO2 and CO mole fractions, as well as turbulence kinetic energy in the combustor chamber. In addition, the realizable k-ε (Rk-ε) model illustrates better performance than four other two-equation models and can provide comparable results to those from the RSM for the configuration and operating conditions considered in the present study.

On Application of Nonlinear k-ε Models for Internal Combustion Engine Flows

2002 ◽  
Vol 124 (3) ◽  
pp. 668-677 ◽  
Author(s):  
G. M. Bianchi ◽  
G. Cantore ◽  
P. Parmeggiani ◽  
V. Michelassi
Keyword(s):  
Internal Combustion Engine ◽  
Eddy Viscosity ◽  
Combustion Engine ◽  
Turbulence Models ◽  
Internal Combustion ◽  
Moment Closure ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Numerical Predictions ◽  
Viscosity Models

The linear k-ε model, in its different formulations, still remains the most widely used turbulence model for the solutions of internal combustion engine (ICE) flows thanks to the use of only two scale-determining transport variables and the simple constitutive relation. This paper discusses the application of nonlinear k-ε turbulence models for internal combustion engine flows. Motivations to nonlinear eddy viscosity models use arise from the consideration that such models combine the simplicity of linear eddy-viscosity models with the predictive properties of second moment closure. In this research the nonlinear k-ε models developed by Speziale in quadratic expansion, and Craft et al. in cubic expansion, have been applied to a practical tumble flow. Comparisons between calculated and measured mean velocity components and turbulence intensity were performed for simple flow structure case. The effects of quadratic and cubic formulations on numerical predictions were investigated too, with particular emphasis on anisotropy and influence of streamline curvature on Reynolds stresses.

scholarly journals Rotating Flow and Heat Transfer in Cylindrical Cavities With Radial Inflow

2012 ◽  
Author(s):  
B. G. Vinod Kumar ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Stress ◽  
Integral Method ◽  
Eddy Viscosity ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Rotating Disc ◽  
Flow And Heat Transfer ◽  
Viscosity Models

Design and optimization of an efficient internal air system of a gas turbine requires thorough understanding of the flow and heat transfer in rotating disc cavities. The present study is devoted to numerical modelling of flow and heat transfer in a cylindrical cavity with radial inflow and comparison with the available experimental data. The simulations are carried out with axi-symmetric and 3-D sector models for various inlet swirl and rotational Reynolds numbers upto 2.1×106. The pressure coefficients and Nusselt numbers are compared with the available experimental data and integral method solutions. Two popular eddy viscosity models, the Spalart-Allmaras and the k-ε, and a Reynolds stress model have been used. For cases with particularly strong vortex behaviour the eddy viscosity models show some shortcomings with the Spalart-Allmaras model giving slightly better results than the k-ε model. Use of the Reynolds stress model improved the agreement with measurements for such cases. The integral method results are also found to agree well with the measurements.

Applications of EARSM Turbulence Models to Internal Flows

2012 ◽  
Author(s):  
O. Z. Mehdizadeh ◽  
L. Temmerman ◽  
B. Tartinville ◽  
Ch. Hirsch
Keyword(s):  
Reynolds Stress ◽  
High Performance ◽  
Eddy Viscosity ◽  
Computational Cost ◽  
Turbulence Models ◽  
Industrial Applications ◽  
Mean Flow ◽  
Viscosity Models ◽  
Stress Models ◽  
Corner Flows

Turbulence modeling remains an active CFD development front for turbomachinery as well as for general industrial applications. While DNS and even LES still seem out of reach within the typical industrial design cycle due to their high computational cost, RANS-based models remain the workhorse of CFD. Currently, the most widely used models are Linear Eddy-Viscosity Models (LEVM), despite their known limitations for certain flow complexities. Therefore, extending the reliability of eddy-viscosity models to more complex flows without significantly increasing the computational cost can immediately contribute to more reliable CFD results for wider range of applications. This, in turn, can further reduce the need for costly tests and consequently can reduce the product development cost. A promising approach to achieve this goal is using Explicit Algebraic Reynolds Stress Models (EARSM), obtained through a simplification of the full Differential Reynolds Stress Models (DRSM), and can be perceived as an extension of LEVMs by including the non-linear relation between the turbulence stress tensor, the mean-flow gradient and the turbulence scales. These models are thus less demanding than DRSM, yet capable of capturing more complex turbulence features, compared to LEVM, such as anisotropy in the normal stresses. This may be particularly important in corner flows, for instance, in the hub-blade regions or in diffusers. This work explores the application of EARSM models to a double diffuser and a high-performance centrifugal compressor stage (HPCC). The results are compared to available experimental data [1,2] showing the importance of including the anisotropy of turbulence in the model, particularly in presence of turbulent corner flows in a diffuser. Furthermore, the EARSM results are also compared to results from the commonly used SST turbulence model. The CFD comparison includes details of the flow structure in the diffuser, where the most noticeable impact from the use of EARSM turbulence models is expected.

scholarly journals Rotating Flow and Heat Transfer in Cylindrical Cavities With Radial Inflow

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
B. G. Vinod Kumar ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Stress ◽  
Integral Method ◽  
Eddy Viscosity ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Rotating Disc ◽  
Flow And Heat Transfer ◽  
Viscosity Models

The design and optimization of an efficient internal air system of a gas turbine requires a thorough understanding of the flow and heat transfer in rotating disc cavities. The present study is devoted to the numerical modeling of flow and heat transfer in a cylindrical cavity with radial inflow and a comparison with the available experimental data. The simulations are carried out with axisymmetric and 3-D sector models for various inlet swirl and rotational Reynolds numbers up to 1.2 × 106. The pressure coefficients and Nusselt numbers are compared with the available experimental data and integral method solutions. Two popular eddy viscosity models, the Spalart–Allmaras and the k-ɛ, and a Reynolds stress model have been used. For cases with particularly strong vortex behavior the eddy viscosity models show some shortcomings, with the Spalart–Allmaras model giving slightly better results than the k-ɛ model. Use of the Reynolds stress model improved the agreement with measurements for such cases. The integral method results are also found to agree well with the measurements.

Second-Moment Closure Model for IC Engine Flow Simulation Using Kiva Code1

1999 ◽  
Vol 122 (2) ◽  
pp. 355-363 ◽  
Author(s):  
S. L. Yang ◽  
B. D. Peschke ◽  
K. Hanjalic
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Flow Simulation ◽  
Reynolds Stress Model ◽  
Tensor Component ◽  
Moment Closure ◽  
Stress Model ◽  
Closure Model ◽  
Ic Engine ◽  
Second Moment

The flow and turbulence in an IC engine cylinder were studied using the SSG variant of the Reynolds stress turbulence closure model. In-cylinder turbulence is characterized by strong turbulence anisotropy and flow rotation, which aid in air-fuel mixing. It is argued that solving the differential transport equations for each turbulent stress tensor component, as implied by second-moment closures, can better reproduce stress anisotropy and effects of rotation, than with eddy-viscosity models. Therefore, a Reynolds stress model that can meet the demands of in-cylinder flows was incorporated into an engine flow solver. The solver and SSG turbulence model were first successfully tested with two different validation cases. Finally, simulations were applied to IC-engine like geometries. The results showed that the Reynolds stress model predicted additional flow structures and yielded less diffusive profiles than those predicted by an eddy-viscosity model. [S0742-4795(00)00101-0]

Assessment of a Reynolds Stress Closure Model for Appendage-Hull Junction Flows

1995 ◽  
Vol 117 (4) ◽  
pp. 557-563 ◽  
Author(s):  
Hamn-Ching Chen
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Moment Closure ◽  
Superior Performance ◽  
Navier Stokes ◽  
Second Moment ◽  
Eddy Viscosity Model ◽  
Second Moment Closure

A multiblock numerical method, for the solution of the Reynolds-Averaged Navier-Stokes equations, has been used in conjunction with a near-wall Reynolds stress closure and a two-layer isotropic eddy viscosity model for the study of turbulent flow around a simple appendage-hull junction. Comparisons of calculations with experimental data clearly demonstrate the superior performance of the present second-order Reynolds stress (second-moment) closure over simpler isotropic eddy viscosity models. The second-moment solutions are shown to capture the most important features of appendage-hull juncture flows, including the formation and evolution of the primary and secondary horseshoe vortices, the complex three-dimensional separations, and interaction among the hull boundary layer, the appendage wake and the root vortex system.

Turbulence Modeling for the Numerical Simulation of Film and Effusion Cooling Flows

2007 ◽  
Author(s):  
Alessandro Bacci ◽  
Bruno Facchini
Keyword(s):  
Numerical Simulation ◽  
Film Cooling ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Cooling Flows ◽  
Eddy Simulation ◽  
Viscosity Models ◽  
Rans Turbulence Models ◽  
Computationally Intensive

RANS simulations are known to suffer from serious deficiencies in the prediction of jet in a crossflow (JCF) because of the high complexity of this kind of flow. Particularly, the coherent structures resulting from the interaction of the two flow streams are characterized by a highly unsteady and anisotropic behavior which hardly stresses the hypotheses underling common eddy viscosity models (EVMs). Direct numerical simulation (DNS) and large eddy simulation (LES) methodologies are still excessively computationally intensive to be used as ordinary design tools. Therefore, the development of reliable RANS turbulence models for film cooling flows deserved a great deal of attention from the gas turbine community. Computations presented in this work were carried out using a modified k-ε turbulence model specifically designed for film cooling flows. The model, due to Lakehal et al., is based on the usage of an anisotropic eddy viscosity. The model has been implemented in the framework of a CFD commercial package through the user subroutine features. Computational model is developed following the suggestions of Walters and Leylek concerning the correct representation of the problem geometry and the location of the boundary conditions. The predictive capabilities of the model concerning the ability to capture the main flow structures as well as heat transfer features are investigated. Comparison of computed adiabatic effectiveness profiles with experimental measurements is provided in order to quantitatively validate the model. Results obtained with standard EVMs, particularly a two layer standard k-ε model, are also shown in order to reveal the improvements in the predictive capabilities resulting from the modified models.

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