scholarly journals An assessment of k–ε and k–l turbulence models for a wide range of oscillatory rough bed flows

2000 ◽  
Vol 2 (4) ◽  
pp. 221-234 ◽  
Author(s):  
S. B. Letherman ◽  
M. A. Cotton ◽  
P. K. Stansby ◽  
C. Chen ◽  
D. Chen
Keyword(s):  
Eddy Viscosity ◽  
Reynolds Shear Stress ◽  
Laboratory Data ◽  
Turbulence Models ◽  
Field Measurements ◽  
Mean Flow ◽  
Wide Range ◽  
Rough Bed ◽  
Experimental Resolution ◽  
First Time

The k–ε and k–l eddy viscosity turbulence models are now used extensively in environmental flow modelling. In the present work computations for oscillatory flows are examined over a broader range of experimental parameters than considered previously. Comparisons are made with field measurements and laboratory data, including new measurements reported here for the first time. It is confirmed that the bed friction velocity and mean flow profiles are, in general, adequately predicted by both models (the k–ε model is, however, somewhat more accurate than the k–l formulation). Reynolds shear stress, turbulent kinetic energy, and eddy viscosity are less well predicted, although the k–ε model again gives more accurate results than the k–l model. An attempt has been made to assess the uncertainty in the experimental data for Reynolds stress and eddy viscosity: it is found that the k–ε model computations for both quantities more frequently lie within the estimated uncertainty bounds. Those bounds are nonetheless wide, emphasizing the need for improved experimental resolution of rough bed flows. Such an improvement would assist in the evaluation of proposed refinements to commonly used turbulence models such as those under investigation here and, indeed, to greater reliability in the development and assessment of more sophisticated schemes.

Assessment of Certainty of Ventilation Processes Mathematical Modeling

2015 ◽  
Vol 725-726 ◽  
pp. 1255-1260
Author(s):  
Tamara Daciuk ◽  
Vera Ulyasheva
Keyword(s):  
Mathematical Modeling ◽  
Turbulent Flows ◽  
Turbulence Models ◽  
Field Measurements ◽  
Heat Emission ◽  
Emission Sources ◽  
Wide Range ◽  
Calculation Results ◽  
Definition Of ◽  
Semiempirical Models

Numerical experiment has been successfully used during recent 10-15 years to solve a wide range of thermal and hydrogasodynamic tasks. Application of mathematical modeling used to design the ventilation systems for production premises characterized by heat emission may be considered to be an effective method to obtain reasonable solutions. Results of calculation performed with numerical solution of ventilation tasks depend on turbulence model selection. Currently a large number of different turbulence models used to calculate turbulent flows are known. Testing and definition of applicability limits for semiempirical models of turbulence should be considered to be a preliminary stage of calculation. This article presents results of test calculations pertaining to thermal air process modeling in premises characterized by presence of heat emission sources performed with employment of different models of turbulence. Besides, analysis of calculation results and comparison with field measurements data are presented.

A Turbulent Boundary Layer Flow Over an Open Shallow Cavity

2016 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Vector Fields ◽  
Turbulence Models ◽  
Leading Edge ◽  
Field Measurements ◽  
Recirculation Region ◽  
Mean Flow ◽  
Trailing Edge ◽  
Cavity Depth

Particle Image Velocimetry (PIV) was used to study the flow structure and turbulence, upstream, over, and downstream a shallow open cavity. Three sets of PIV measurements, corresponding to a turbulent incoming boundary layer and a cavity length-to-depth ratio of four, are reported. The cavity depth based Reynolds numbers were 21,000; 42,000; and 54,000. The selected flow configuration and well characterized inflow conditions allow for straightforward assessment of turbulence models and numerical schemes. All mean flow field measurements display a large flow recirculation region, spanning most of the cavity and a smaller, counter-rotating, secondary vortex, immediately downstream of the cavity leading edge. The Galilean decomposed instantaneous velocity vector fields, clearly demonstrate two distinct modes of interaction between the free shear and the cavity trailing edge. The first corresponds to a cascade of vortical structures emanating from the tip of the leading edge of the cavity that grow in size as they travel downstream and directly interact with the trailing edge, i.e., impinging vortices. The second represents vortices that travel above the trailing edge of the cavity, i.e., non-impinging vortices. In the case of impinging vortices, a strong, large scale region of recirculation forms inside the cavity and carries the flow disturbances, arising from the impingement of vortices on the trailing edge of the cavity, upstream in a manner that interacts with and influences the flow as it separates from the cavity leading edge.

High-resolution atmospheric boundary layer simulations using WRF-LES

2020 ◽  
Author(s):  
Gokhan Kirkil
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Cross Sections ◽  
Wrf Model ◽  
Field Measurements ◽  
Mean Flow ◽  
Spatial And Temporal Scales ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy

<p>WRF model provides a potentially powerful framework for coupled simulations of flow covering a wide range of<br>spatial and temporal scales via a successive grid nesting capability. Nesting can be repeated down to turbulence<br>solving large eddy simulation (LES) scales, providing a means for significant improvements of simulation of<br>turbulent atmospheric boundary layers. We will present the recent progress on our WRF-LES simulations of<br>the Perdigao Experiment performed over mountainous terrain. We performed multi-scale simulations using<br>WRF’s different Planetary Boundary Layer (PBL) parameterizations as well as Large Eddy Simulation (LES)<br>and compared the results with the detailed field measurements. WRF-LES model improved the mean flow field<br>as well as second-order flow statistics. Mean fluctuations and turbulent kinetic energy fields from WRF-LES<br>solution are investigated in several cross-sections around the hill which shows good agreement with measurements.</p>

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.

High Resolution Overset Structured Grid RANS Simulations of Flow Past a Surface Mounted Cube Using Eddy Viscosity Closure Models

2018 ◽  
Author(s):  
Marc C. Goldbach ◽  
Mesbah Uddin
Keyword(s):  
Eddy Viscosity ◽  
Complex Structure ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Separated Flow ◽  
Industrial Applications ◽  
Separated Flows ◽  
Transitional Flow ◽  
Stream Velocity ◽  
Mean Flow

While Reynolds-averaged simulatons (RAS) have found success in the evaluation of many canonical shear flows, and moderately separated flows, their application to highly separated flows have shown notable deficiencies. This study aims to investigate these deficiencies in the eddy-viscosity formulation of four commonly used turbulence models under separated flow in an attempt to aid in the improved formulation of such models. Analyses are performed on the flow field around a wall mounted cube at a Reynolds number of 40,000 based on the cube height, h, and free stream velocity, U0. While a common occurrence in industrial applications, this type of flow constitutes a complex structure exhibiting a large separated wake region, high anisotropy, and multiple vortex structures. As well, interactions between vortices developed off of different faces of the cube significantly alter the overall flow characteristics, posing a significant challenge for the commonly used industrial turbulence models. Comparison of mean flow characteristics show remarkable agreement between experimental values and turbulence models which are capable of predicting transitional flow. Evaluation of turbulence parameters show the general underestimation of Reynolds stress for transitional models, while fully turbulent models show this value to be overestimated, resulting in completely disparate representations of mean flow structures between the two classes of models (transitional and fully turbulent).

scholarly journals Assessing theoretical flow velocity profile and resistance in gravel bed rivers by field measurements

2018 ◽  
Vol 49 (4) ◽  
pp. 220-227 ◽  
Author(s):  
Vito Ferro ◽  
Paolo Porto
Keyword(s):  
Velocity Profile ◽  
Flow Velocity ◽  
Froude Number ◽  
Flow Resistance ◽  
Field Measurements ◽  
Mean Flow ◽  
Gravel Bed ◽  
Wide Range ◽  
Gravel Bed Rivers ◽  
Resistance Equation

Previous studies showed that integrating a power velocity profile, deduced applying dimensional analysis and the incomplete self-similarity condition, the flow resistance equation for open channel flow can be obtained. At first, in this paper the relationship between the Γ function of the power velocity profile, the channel slope and the Froude number, which was already empirically introduced in a previous paper, is now theoretically deduced. Then this relationship is calibrated using the field measurements of flow velocity, water depth and bed slope carried out in 101 reaches of gravel bed rivers available by literature. The proposed relationship for estimating Γ function and the theoretical flow resistance equation are also tested by an independent dataset of 104 reaches of some gravel bed rivers (Fiumare) in Calabria region. Finally, the theoretically-based relationship for estimating the Γ function is calibrated by the overall available database (205 reaches). In this way the three coefficients of the theoretically based Γ function are estimated for a wide range of slopes (0.1%-6.19%) and hydraulic conditions (Froude number values ranging from 0.08 to 1.25). In conclusion, the analysis shows that the Darcy-Weisbach friction factor for gravel bed rivers can be accurately estimated by the approach based on a power-velocity profile and the theoretically-based relationship proposed for estimating Γ function. The analysis also points out a performance in estimating mean flow velocity better than that obtained in a previous study carried out by the authors.

scholarly journals The Development of the Mean Flow and Turbulence Structure in an Annular S-Shaped Duct

1994 ◽  
Author(s):  
K. M. Britchford ◽  
J. F. Carrotte ◽  
S. J. Stevens ◽  
J. J. McGuirk
Keyword(s):  
Reynolds Stress ◽  
Laser Doppler Anemometry ◽  
Reynolds Shear Stress ◽  
Turbulence Models ◽  
Test Facility ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Mean Velocity ◽  
Curvature Effects ◽  
The Mean

This paper describes an investigation of the mean and fluctuating flow field within an annular S-shaped duct which is representative of that used to connect the compressor spools of aircraft gas turbine engines. Data was obtained from a fully annular test facility using a 3-component Laser Doppler Anemometry (LDA) system. The measurements indicate that development of the flow within the duct is complex and significantly influenced by the combined effects of streamwise pressure gradients and flow curvature. In addition CFD predictions of the flow, using both the k-ε and Reynolds stress transport equation turbulence models, are compared with the experimental data. Whereas curvature effects are not described properly by the k-ε model, such effects are captured more accurately by the Reynolds stress model leading to a better prediction of the Reynolds shear stress distribution. This, in turn, leads to a more accurate prediction of the mean velocity profiles, as reflected by the boundary layer shape parameters, particularly in the critical regions of the duct where flow separation is most likely to occur.

Numerical Benchmark of Nonconventional RANS Turbulence Models for Film and Effusion Cooling

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Cosimo Bianchini ◽  
Luca Andrei ◽  
Antonio Andreini ◽  
Bruno Facchini
Keyword(s):  
Film Cooling ◽  
Eddy Viscosity ◽  
Computational Study ◽  
Turbine Blades ◽  
Density Ratio ◽  
Turbulence Models ◽  
Single Row ◽  
Turbulent Reynolds Number ◽  
Wide Range ◽  
Asme Turbo Expo

Over the course of the years, several turbulence models specifically developed to improve the predicting capabilities of conventional two-equations Reynolds-averaged Navier–Stokes (RANS) models have been proposed. They have, however, been mainly tested against experiments only comparing with standard isotropic models, in single hole configuration and for very low blowing ratio. A systematic benchmark of the various nonconventional models exploring a wider range of application is hence missing. This paper performs a comparison of three recently proposed models over three different test cases of increasing computational complexity. The chosen test matrix covers a wide range of blowing ratios (0.5–3.0) including both single row and multi-row cases for which experimental data of reference are available. In particular the well-known test by Sinha et al. (1991, “Film-Cooling Effectiveness Downstream of a Single Row of Holes with Variable Density Ratio,” J. Turbomach., 113, pp. 442–449) at BR = 0.5 is used in conjunction with two in-house carried out experiments: a single row film-cooling test at BR = 1.5 and a 15 rows test plate designed to study the interaction between slot and effusion cooling at BR = 3.0. The first two considered models are based on a tensorial definition of the eddy viscosity in which the stream-span position is augmented to overcome the main drawback connected with standard isotropic turbulence models that is the lower lateral spreading of the jet downwards the injection. An anisotropic factor to multiply the off diagonal position is indeed calculated from an algebraic expression of the turbulent Reynolds number developed by Bergeles et al. (1978, “The Turbulent Jet in a Cross Stream at Low Injection Rates: A Three-Dimensional Numerical Treatment,” Numer. Heat Transfer, 1, pp. 217–242) from DNS statistics over a flat plate. This correction could be potentially implemented in the framework of any eddy viscosity model. It was chosen to compare the predictions of such modification applied to two among the most common two-equation turbulence models for film-cooling tests, namely the two-layer (TL) model and the k–ω shear stress transport (SST), firstly proposed and tested in the past respectively by Azzi and Lakeal (2002, “Perspectives in Modeling Film Cooling of Turbine Blades by Transcending Conventional Two-Equation Turbulence Models,” J. Turbomach., 124, pp. 472–484) and Cottin et al. (2011, “Modeling of the Heat Flux For Multi-Hole Cooling Applications,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46330). The third model, proposed by Holloway et al. (2005, “Computational Study of Jet-in-Crossflow and Film Cooling Using a New Unsteady-Based Turbulence Model,” Proceedings of the ASME Turbo Expo, Paper No. GT2005-68155), involves the unsteady solution of the flow and thermal field to include the short-time response of the stress tensor to rapid strain rates. This model takes advantage of the solution of an additional transport equation for the local effective total stress to trace the strain rate history. The results are presented in terms of adiabatic effectiveness distribution over the plate as well as spanwise averaged profiles.

Numerical Benchmark of Non-Conventional RANS Turbulence Models for Film and Effusion Cooling

2012 ◽  
Author(s):  
L. Andrei ◽  
A. Andreini ◽  
C. Bianchini ◽  
B. Facchini
Keyword(s):  
Film Cooling ◽  
Eddy Viscosity ◽  
Isotropic Turbulence ◽  
Turbulence Models ◽  
Lateral Spreading ◽  
Algebraic Expression ◽  
Test Plate ◽  
Single Row ◽  
Turbulent Reynolds Number ◽  
Wide Range

In the course of the years several turbulence models specifically developed to improve the predicting capabilities of conventional two-equations RANS models have been proposed. However they have been mainly tested against experiments only comparing with standard isotropic models, in single hole configuration and for very low blowing ratio. A systematic benchmark of the various non-conventional models exploring a wider range of application is hence missing. This paper performs a comparison of 3 recently proposed models over three different test cases of increasing computational complexity. The chosen test matrix covers a wide range of blowing ratios (0.5–3.0)including both single row and multi-row cases for which experimental data of reference are available. In particular the well known test by Sinha and Bogard [1] at BR = 0.5 is used in conjuction with two in-house carried out experiments: a single row film-cooling test at BR = 1.5 and a 15 rows test plate designed to study the interaction between slot and effusion cooling at BR = 3.0. The first two considered models are based on a tensorial definition of the eddy viscosity in which the stream-span position is augmented to overcome the main drawback connected with standard isotropic turbulence models that is the lower lateral spreading of the jet downwards the injection. An anisotropic factor to multiply the off-diagonal position is indeed calculated from an algebraic expression of the turbulent Reynolds number developed by Bergeles [2] from DNS statistics over a flat plate. This correction could be potentially implemented in the framework of any eddy viscosity model. It was chosen to compare the predictions of such modification applied to two among the most common two-equation turbulence models for film-cooling tests, namely the Two-Layer (TL) model and the k–ω Shear Stress Transport (SST), firstly proposed and tested in the past respectively by Azzi and Lakeal [3] and Cottin at al. [4]. The third model, proposed by Holloway et al. [5], involves the unsteady solution of the flow and thermal field to include the short-time response of the stress tensor to rapid strain rates. This model takes advantage of the solution of an additional transport equation for the local effective total stress to trace the strain rate history. The results are presented in terms of adiabatic effectiveness distribution over the plate as well as spanwise averaged profiles.

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