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).

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

2019 ◽  
Vol 4 (1) ◽  
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 ◽  
Mean Flow ◽  
Freestream Velocity

Abstract While Reynolds-averaged simulations 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 aimed 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 (WMC) at a Reynolds number of 40,000 based on the cube height, h, and freestream 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).

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.

Numerical simulations for swirlmeter on flow fields and metrological performance

2016 ◽  
Vol 40 (4) ◽  
pp. 1072-1081 ◽  
Author(s):  
Desheng Chen ◽  
Baoling Cui ◽  
Zuchao Zhu
Keyword(s):  
Vortex Core ◽  
Reverse Flow ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Internal Flow ◽  
Industrial Applications ◽  
Throat Region ◽  
Vortex Precession ◽  
Metrological Performance

Measurements of flow rates of fluids are important in industrial applications. Swirlmeters (vortex precession meters) are widely used in the natural gas industry because of their advantage in having a large measurement range and strong output signal. In this study, using air as a working medium, computational fluid dynamics (CFD) simulations of a swirlmeter were conducted using the Reynolds-averaged Navier–Stokes (RANS) and renormalization group (RNG) k–ε turbulence models. The internal flow characteristics and the influence of the tube structure (geometric parameter of flow passage) on metrological performance were studied, with a particular focus on the meter factor. Calibration experiments were performed to validate the CFD predictions; the results show good agreement with those from simulations. From the streamline distributions, a clear vortex precession is found in the throat region. At the end of throat, the pressure fluctuation reached a maximum accompanied by the largest shift in the vortex core from the centreline. There exists a large reverse flow zone in the vortex core region in the convergent section. To mitigate the influence of reverse flow on vortex precession, a suitable length of throat is required. For a larger convergent angle, the fluid undergoes higher acceleration leading to an increase in velocity that produces more intensive pressure fluctuations. The minor diameter of the throat also produces a higher velocity and larger meter factor. Compared with both divergent angle and throat length, the convergent angle and throat diameter play a more important role in determining precession frequency.

An improved turbulence model for predicting unsteady cavitating flows in centrifugal pump

2015 ◽  
Vol 25 (5) ◽  
pp. 1198-1213 ◽  
Author(s):  
Jian Wang ◽  
Yong Wang ◽  
Houlin Liu ◽  
Haoqin Huang ◽  
Linglin Jiang
Keyword(s):  
Centrifugal Pump ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulent Viscosity ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Content Type ◽  
Cavitation Inception ◽  
Cavitation Performance ◽  
Unsteady Rans

Purpose – The purpose of this paper is to study the unsteady caivitating flows in centrifugal pump, especially for improving the turbulence model to obtain highly resolution results-capable of predicting the cavitation inception, shedding off and collapse procedures. Design/methodology/approach – Both numerical simulations and experimental visualizations were performed in the present paper. An improved RCD turbulence models was proposed by considering three corrected methods: the rotating corrected method, the compressible corrected method and the turbulent viscosity corrected method. Unsteady RANS computations were conducted to compare with the experiments. Findings – The comparison of pump cavitation performance showed that the RCD turbulence model obtained better performance both in non-cavitation and cavitation conditions. The visualization of the cavitation evolution was recorded to validate the unsteady simulations. Good agreement was noticed between calculations and visualizations. It is indicated the RCD model can successfully capture the bubbles detachment and collapse at the rear of the cavity region, since it effectively reduces the eddy viscosity in the multiphase region of liquid and vapor. Furthermore, the eddy viscosity, the instantaneous pressure and density distribution were investigated. The effectiveness of the compressibility was found. Meanwhile, the influence of the rotating corrected method on prediction was explored. It is found that the RCD model solved more unsteady flow characteristics. Originality/value – The current work presented a turbulence model which was much more suitable for predicting the cavitating flow in centrifugal pump.

Simulation of a 3D Axisymmetric Hill: Comparison of RANS and Hybrid RANS-LES Models

2016 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Experimental Data ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Leeward Side ◽  
Mean Flow ◽  
Rans Model ◽  
Reynolds Number Flow ◽  
Low Dissipation

Computational fluid dynamics (CFD) prediction of high Reynolds number flow over a 3D axisymmetric hill presents a unique set of challenges for turbulence models. The flow on the leeward side of the hill is characterized by the presence of complex vortical structures, unsteady wakes, and regions of boundary layer separation. As a result, traditional eddy-viscosity Reynolds-averaged Navier-Stokes (RANS) models have been found to perform poorly. Recent studies have focused on the use of Large Eddy Simulation (LES) and hybrid RANS-LES (HRL) methods to improve accuracy. In this study, the capability of a dynamic hybrid RANS-LES (DHRL) model to resolve the flow over a 3D axisymmetric hill is investigated and compared to numerical results using a traditional RANS model and a conventional hybrid RANS-LES model, and to experimental data. Results show that the RANS model fails to accurately predict the mean flow features in the wake region, which is in agreement with prior studies. The conventional HRL model provides better prediction of the flow characteristics but suffers from grid sensitivity and delayed transition to LES mode. The DHRL method provides the best agreement with experimental data overall and shows least sensitivity to grid resolution. Results also highlight the importance of using a low dissipation flux formulation for flow simulations in which a portion of the turbulence spectrum is resolved, including hybrid RANS-LES.

Direct numerical simulation of separated flow in a three-dimensional diffuser

2010 ◽  
Vol 650 ◽  
pp. 307-318 ◽  
Author(s):  
JOHAN OHLSSON ◽  
PHILIPP SCHLATTER ◽  
PAUL F. FISCHER ◽  
DAN S. HENNINGSON
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Separated Flow ◽  
Spectral Element ◽  
Mean Flow ◽  
Development Section ◽  
Inflow Condition

A direct numerical simulation (DNS) of turbulent flow in a three-dimensional diffuser at Re = 10000 (based on bulk velocity and inflow-duct height) was performed with a massively parallel high-order spectral element method running on up to 32768 processors. Accurate inflow condition is ensured through unsteady trip forcing and a long development section. Mean flow results are in good agreement with experimental data by Cherry et al. (Intl J. Heat Fluid Flow, vol. 29, 2008, pp. 803–811), in particular the separated region starting from one corner and gradually spreading to the top expanding diffuser wall. It is found that the corner vortices induced by the secondary flow in the duct persist into the diffuser, where they give rise to a dominant low-speed streak, due to a similar mechanism as the ‘lift-up effect’ in transitional shear flows, thus governing the separation behaviour. Well-resolved simulations of complex turbulent flows are thus possible even at realistic Reynolds numbers, providing accurate and detailed information about the flow physics. The available Reynolds stress budgets provide valuable references for future development of turbulence models.

scholarly journals Standard and Modified SST Models with the Consideration of the Streamline Curvature for Separated Flow Calculation in a Narrow Channel with a Conical Dimple on the Heated Wall

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5038
Author(s):  
Sergey Isaev ◽  
Dmitry Nikushchenko ◽  
Alexandr Sudakov ◽  
Nikita Tryaskin ◽  
Ann Egorova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Slope Angle ◽  
Separated Flow ◽  
Narrow Channel ◽  
Separated Flows ◽  
Heated Wall ◽  
Return Flow ◽  
Shear Stresses ◽  
Streamline Curvature

The testing of the standard and modified SST models of the transfer of shear stresses was carried out on an example of calculating the heat transfer with an intense detached flow around a conical dimple with a slope angle of 45° on the heated wall of a narrow channel. It was shown that the standard turbulence model by Menter SST (MSST) of 2003, widely used in the packages Fluent, CFX, StarCCM+, etc., significantly underestimated the intensity of the return flow. A correction of this model was presented that took into account the influence of the curvature of streamlines within the framework of the Rodi-Leshziner-Isaev (RLI) approach for spatial separated flows. It was found that the predictions for the RLI MSST 2003 were close to the predictions for the original standard MSST 1993, in which the eddy viscosity was calculated using the vorticity modulus. At the same time, the predictions based on the modified one, following Smirnov-Menter (SM) MSST 2003, included in the ANSYS model catalog did not differ too much from the standard MSST 2003. The preference of the MSST modified within the RLI 2003 for calculating the heat transfer in intense separated flows was substantiated.

scholarly journals Assessment of Computational Fluid Dynamics Capabilities for the Prediction of Three-Dimensional Separated Flows: The DELFT 372 Catamaran in Static Drift Conditions

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
R. Broglia ◽  
S. Zaghi ◽  
E. F. Campana ◽  
T. Dogan ◽  
H. Sadat-Hosseini ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Separated Flow ◽  
Lateral Force ◽  
Separated Flows ◽  
Overlapping Grids ◽  
Wave Induced

In this paper, capabilities of state-of-the-art computational fluid dynamics (CFD) tools in the prediction of the flow-field around a multihull catamaran advancing in straight ahead motion at nonzero drift angles are investigated. CFD estimations have been provided by three research institutes by using their in-house codes: CNR-INM using Xnavis, IIHR using CFDShip-Iowa, and CNRS/ECN using ISIS. These allowed an in-depth comparison between different methodologies, such as structured overlapping grids versus unstructured grid, different turbulence models and detached eddy simulations (DES) approaches, and level-set (LS) versus volume of fluid (VoF). The activities were pursued within the NATO AVT-183 group “reliable prediction of separated flow onset and progression for air and sea vehicles,” aimed at the assessment of CFD predictions of large three-dimensional separated flows. Comparison between estimations is provided for both integral and local quantities, and for wave-induced vortices. Validation is reported by comparison against the available experimental fluid dynamics (EFD) data. Generally, all the simulations are able to capture the main features of the flow field; grid resolution effects are dominant in the onset phase of coherent structures and turbulence model affects the dynamic of the vortices. Hydrodynamic loads are in agreement between the submissions with standard deviation of about 3.5% for the resistance prediction and about 7% for lateral force and yaw moment estimation. Wave-induced vortices are correctly captured by both LS and VoF approaches, even if some differences have been highlighted, LS showing well-defined and long life vortices.

Evaluation of transition-sensitive eddy-viscosity turbulence models for separated flow in OpenFOAM

2017 ◽  
Author(s):  
H. Fadhila ◽  
H. Medina ◽  
A. Beechook ◽  
S. Aleksandrova ◽  
S. Benjamin
Keyword(s):  
Eddy Viscosity ◽  
Turbulence Models ◽  
Separated Flow
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