Comparison Of Turbulence Models Research Articles

A validated numerical methodology for flow-induced vibration of a semi-spherical end cantilever rod in axial flow

This study presents a simulation method for turbulent flow-induced vibrations of cantilever rods with a semi-spherical end exposed to axial flow, a configuration investigated for the first time. This simulation strategy has been developed using solids4Foam, a toolkit for the open-source package OpenFOAM, which uses the finite-volume approach. The fluid and solid domain equations are solved separately. Coupling is achieved with the Interface Quasi-Newton Inverse Least-Squares (IQN-ILS) algorithm. The mean flow is described by the unsteady Reynolds-averaged Navier–Stokes equations. Turbulence is modeled through either the stress-transport model of Launder, Reece, and Rodi or the effective-viscosity k–ω shear stress transport model, both with the wall-function approach accounting for near-wall turbulence. The methodology is validated using experimental data produced during this study. The simulations show good agreement with the measured values of the oscillation amplitude and frequency for both flow directions (toward rod free-end and away from it). Turbulence model comparisons show that (a) Reynolds stress transport models are necessary to reproduce the vibration amplitude and (b) wall functions enable the simulations to be completed in realistic time scales. The significance to the fluid–solid-interaction (FSI) process of a so far overlooked (with the exception of a couple of recent studies) dimensionless number, the ratio of the flow dynamic pressure to the rod's Young's modulus of elasticity, is also explored. Simulations, which decouple the variation of this dimensionless number from that of the Reynolds number, demonstrate this number's strong effect on the vibration amplitude. This finding is important to the contact of further FSI studies and the scaling of FSI data.

Comparison of turbulence models for the axisymmetrical separated boundary layer problem

Comparison of turbulence models for the axisymmetrical separated boundary layer problem

IKA-FLOW : A Flexible Body Overset Mesh Implementation for Fish Swimming

Simulation of inertial aquatic swimmers requires fluid structure interactions with temporal body geometry deformation. In practice, his results in a change of the computational domain boundaries that represent the ”swimmer.” These simulations are traditionally done sing body-fitted mesh and mesh morphing methods, but have drawbacks of negative cell volumes and small time-steps to account for the complex swimming motion. In contrast, the overset mesh method, also provided by OpenFOAM®, overcomes most of the drawbacks of the mesh morphing method at the expense of interpolation error. The current OpenFOAM® overset motion library only supports rigid body motion and cannot be used to resolve a body undergoing undulation. A modified motion solver is presented that allows for the complex mesh motion of an overset mesh for four body-caudal fin (BCF) virtual swimmers. The results of this solver are compared with published data of body-fitted meshes. The effect of different simulation parameters (including number of solving iterations, time delay, and temporal resolution) is investigated. Additionally, a novel simulation and comparison of the Ostraciiform locomotion mode with Anguilliform, Carangiform, and Thunniform modes are made investigating the wake, drag and lift. It is concluded that fish undulation has a marked effect on reducing lift generation. Lastly, a comparison of turbulence models (Spalart-Allmaras, k − ω SST, and k − kL − ω) at multiple Reynolds numbers shows that all three models have similar performance at lower Reynolds numbers but diverge at higher numbers.

Comparison of Turbulence Models in Simulation of Plane Jet Flow

Plane turbulent jets are widely used in a variety of applications. Such as jets in drying processes, air curtains for room conditioning, heating, mixing, ventilating applications etc., therefore, jet flow is a very important research topic in both experimental and analytical research.
 Depending upon the position and forces acts on the jet, jets are broadly classified as turbulent free jet and turbulent wall jet. The studies conducted herein provide the comparison between various turbulence model present Computational Fluid Dynamics(CFD). Numerical approaches were used in the present investigation. CFD technique helped to understand better the hydrodynamics of the jet flow and correlate the numerical result.
 Among the all turbulence model studied, the k-ε turbulence model performed the best. Performance of k-ω model was found to be somewhat superior to Spalart-Allmaras and Reynolds stress model.

Analysis and comparison of turbulence models on wind turbine performance using SCADA data and machine learning technique

Wind energy has grown significantly over the last decade. With this, various improvements in the design of the wind turbine are geared towards increasing the reliability of several components. Wind turbulence has a huge effect on the fatigue loading of wind turbines considered in the design. Several monitoring methodologies, such as turbulence intensity analysis, are used to identify wind turbulence. In this paper, a method based on machine learning techniques and data from Supervisory Control and Data Acquisition (SCADA) systems is described. Five machine learning models are generated and compared in this study with the use of the operational data from the SCADA of wind turbines in a single wind farm. Results showed that the model based on Linear Regression in terms of a quadratic hyperparameter has lesser errors compared to the other models that were generated. Each parameter used in the creation of the model affects its performance. Observations in the nacelle system also showed higher errors due to the relationship between rotor speed and the blade angle. The rotor performance is mostly influenced by wind turbulence as the variation in wind speeds and rotational speeds have a certain correlation. Based on the results, it can be concluded that the use of SCADA data in generating turbulence models provides key insights into the relation of the turbulence intensity to the various components. It can be used as the basis for developing turbulence monitoring models that could help improve the design and operation of wind turbines.

Comparison of turbulence models for solving problems of swirling jet flows

There are several turbulence models that can be used to solve the swirling jet problems, which are typical turbulence problems. A comparison of these models allows us to determine which one is better suited for a given task. When comparing turbulence models for the swirling jet problem, the most important criteria are the accuracy and stability of the solution. Accuracy is assessed by comparison with experimental data or other numerical methods, and stability is assessed by the absence of oscillations and convergence of the solution. In addition, it is also important to consider the computational complexity of each model and its applicability to a specific problem. The swirling flow in a nozzle is studied in the article using various turbulence models (SA, k-ε, k-ω, L-VEL, v2-f, yPlus, SST). To evaluate the performance of different CFD (Computational Fluid Dynamics) turbulence models, their numerical results for velocity profiles are compared with known experimental data.

Comparison of Turbulence Models in the Numerical Simulation of the Model Ducted Propeller

Comparison of Turbulence Models in the Numerical Simulation of the Model Ducted Propeller

Comparison of Turbulence Models and Wall Layer Mesh in a Solar Air Heater

Comparison of Turbulence Models and Wall Layer Mesh in a Solar Air Heater

An overview of the effect of stirrer design on the mechanical properties of Aluminium Alloy Matrix Composites fabricated by stir casting

An overview of the effect of stirrer design on the mechanical properties of Aluminium Alloy Matrix Composites fabricated by stir casting

Validation and comparison of turbulence models for predicting wakes of vertical axis wind turbines

Vertical axis wind turbine (VAWT) array design requires adequate modelling of the turbine wakes to model the flow throughout the array and, therefore, the power output of turbines in the array. This paper investigates how accurately different turbulence models using 2D computational fluid dynamics (CFD) simulations can estimate near and far wakes of VAWTs to determine an approach towards accurate modelling for array design. Three experiments from the literature are chosen as baselines for validation, with these experiments representing the near to far wake of the turbine. Five URANS turbulence models were chosen due to their common and potential usage for VAWT CFD: models k–ω SST, k–ω SST LRN, k–ω SSTI, transition SST, and k–kl–ω. In addition, the lifting line-free vortex wake (LLFWV) model was tested as an alternative to CFD for the far turbine wake where it was appropriate for use. The results for turbulent kinetic energy and vorticity were compared for the first experiment, whilst streamwise and cross-stream velocity were used for the other two experiments. It was found that none of the turbulence models tested or LLFVW produced adequate estimations within the methodology tested, however, transition SST produced the closest estimations. Further adjustments to the methodology are required to improve accuracy due to their large impact on results including use of 3D CFD, adjustment of surface roughness, and inlet flow characteristics.

Comparison of turbulence models for two-phase flow in a centrifugal separator

The numerical results of mathematical modeling of a two-phase, axisymmetric swirling turbulent flow in the separation zone of a centrifugal separator are presented. The movement of the carrier gas flow was modeled using RANS, which were closed using the SARC turbulence models, the SST-RC model, and the SSG/LRR-RSM-w2012 model. For the numerical solution of the problem, the SIMPLE algorithm was used. The article compares the results of numerical calculation of turbulence models. The results of a comparison of numerical calculations with allowance for the effect of the solid phase on the dynamics of the air medium and without taking it into account with experimental data are presented.

CFD simulations of single-phase flow in settling tanks: comparison of turbulence models

ABSTRACT In the present work, single-phase CFD simulations are performed to study flows in the rectangular and circular settling tank. The three-dimensional flow was studied for the predictions of the velocity profiles in the settling tank. The performance of seven different types of turbulence models, standard k-ε model, low Re k-ε models such as AKN model, CHC model and Abid Model, k-ω model, low Re k-ω model and RSM model has been evaluated for the prediction of flow fields. The CFD model is validated with previously published experimental data. The comparison of velocity profiles, turbulent kinetic energy, turbulent Reynolds number and vorticity are presented. The predictive ability of Abid model is better than other models for prediction of the flow field for both rectangular and circular settling tank. The absolute error for the velocity predictions in the case of the low Re k-ε model is around 30% less as compared to the other models. The better prediction using the low Re k-ε models is attributed to the damping functions used in the model.

Comparison of different turbulence models in a high pressure fuel jet

Comparison of different turbulence models in a high pressure fuel jet

Particle-resolved simulations of catalytic fixed bed reactors: Comparison of turbulence models, LES and PIV measurements

Particle-resolved CFD simulations are widely used for the predictions of particle-scale flow, transport processes and chemical reactions. However, the effect of turbulence models used in such simulations is not quantitatively established. In the present work, particle-resolved simulations are performed to understand the influence of different turbulence models (standard k − ε (KE), SST k − ω (SST), SSG Reynolds-stress (SSG), BSL Reynolds-stress (BSL) and LES WALE (LES)) on the particle-scale predictions of the flow, heat transfer and reactions. A comparison of the PIV measurements and particle-resolved simulations of a square column containing 72 spherical particles with a tube-to-particle diameter ratio (TPDR) of ∼3.6 and Rebed of 9765 was performed. The ε−based models (KE and SSG) under-predicted the velocity (Vx and Vy) profiles due to the over-estimation of the turbulence parameters (k and ε) and an opposite behaviour was observed for the ω−based models (SST and BSL). The LES model showed a better agreement with the measurements. In addition, numerical investigations of methane steam reforming reactions were performed in a packed bed containing 30 randomly packed 7-hole cylindrical particles with a TPDR of 5, and Ret of 50,000. The ε−based models predicted lower values of velocities, temperature and species concentration in the bulk region (and higher values on the particle surfaces) resulting into higher CH4 conversion compared to the ω−based models, whereas the LES model showed the highest ΔP and CH4 conversion. Overall, the predictions of the LES model were found to be closer to the experiments. The predictions of the RSM (SSG and BSL) models did not show any improvements over the eddy-viscosity (KE and SST) models.

A comparison of turbulence models and two and three dimensional meshes for unsteady CFD ash deposition tools

This work aims to assess the adequacy of the often made two dimensional mesh simplification in ash deposition models. Little information is available regarding its validity due to the heavy computational costs that a proper three-dimensional grid model would entail. We have implemented a case study (a deposition probe in a kraft recovery furnace) with 2D and 3D mesh models in order to compare their results regarding the ash deposition and the fluid flow. An additional simulation has been carried out to compare the results between URANS and DES turbulence models.For the particular case studied in this article, the two-dimensional simplification is justified as the results did not vary notably whereas entailing remarkably smaller computational costs. Nonetheless, the usage of DES turbulence model yielded moderately different results, qualitatively closer to deposit observations, justifying perhaps the three-dimensional approach when accuracy is needed for the deposition of fine particles on the lee edges of the tubes.

Comparison of turbulence models and CFD solution options for a plain pipe

Present paper is partly a declaration of state of a currently ongoing PhD work about turbulent flow in a thick walled pipe in order to analyze conjugate heat transfer. An ongoing effort on CFD investigation of this problem using cylindrical coordinates and dimensionless governing equations is identified alongside a literature review. The mentioned PhD work will be conducted using an in-house developed code. However it needs preliminary evaluation by means of commercial codes available in the field. Accordingly ANSYS CFD was utilized in order to evaluate mesh structure needs and asses the turbulence models and solution options in terms of computational power versus difference signification. Present work contains a literature survey, an arrangement of governing equations of the PhD work, CFD essentials of the preliminary analysis and findings about the mesh structure and solution options. Mesh element number was changed between 5,000 and 320,000. k-ϵ, k-ω, Spalart-Allmaras and Viscous-Laminar models were compared. Reynolds number was changed between 1,000 and 50,000. As it may be expected due to the literature, k-ϵ yields more favorable results near the pipe axis and k-ωyields more convenient results near the wall. However k-ϵ is found sufficient to give turbulent structures for a conjugate heat transfer problem in a thick walled plain pipe.

Comparison of Turbulence Models in the Flow over a Backward Facing Step

This work presents the numerical simulation and analysis of the turbulent flow over a two-dimensional channel with a backward-facing step. The computational simulation performed in this study is based on the Reynolds equations using a technique denominated Reynolds Average Navier-Stokes (RANS). The main objective of the present work is the comparison of different models of turbulence applied to the turbulent flow over a backward-facing step. The performance of each RANS model used will be discussed and compared with the results obtained through a direct numerical simulation present in the literature. The RANS turbulence models used are k-ω, k-e, Shear Stress Transport k-ω (SST k-ω) and the second-order closure model called Reynolds Stress Model (RSM). The Reynolds number used in all the numerical simulations constructed in this study is equal to 9000, based on the height of the step h and the inlet velocity Ub. The results are the reattachment length, the mean velocity profiles and the turbulence intensities profiles. The k-e model obtained poor results in most of the analyzed variables in this study. Among the RANS turbulence models, the SST k-ω model presented the best results of reattachment length, mean velocity profile and contour when compared to results obtained in the literature. The RSM model found the best results of turbulence intensity profile, when compared to the models of two partial differential equations that use the Boussines hypothesis.

Comparison of Turbulence Models for Single Sphere Simulation Study Under Supercritical Fluid Condition

Abstract In this paper, the comparison of turbulence models for fluid flow past single sphere under supercritical conditions is reported. Firstly, Dixon et al.’s models [1], which are under non-supercritical conditions, were used as benchmarks to validate the simulated results. Two turbulence models namely RNG k-ε and SST k-ω models parameters were fine-tuned accordingly in order to obtain almost comparable results generated by Dixon et al.’s models [1]. The simulation works were then extended to simulate flow of supercritical carbon dioxide. The second part of this paper, therefore, presents a comparative study of the turbulence models i. e. standard k-ε, RNG k-ε, realizable k-ε and SST k-ω models. This study emphasises on the predictions and evaluations of the velocity profiles at different flow regimes namely recirculation, recovery and near-wake. Simulations were carried out to determine the velocity profiles at subcritical and supercritical conditions by varying Reynolds numbers (2000 and 20,000), pressures (65 and 80 bar) and temperatures (283.15 and 308.15K). Simulation results indicate that the predicted results are consistent with the literature data. Interesting flow features were identified for all the simulations. The results of this study also reveal that the SST k-ω turbulence model was able to better capture the flow characteristics near-wake of the sphere.

The effect of meshing and comparing different turbulence models in predicting the topography of Bed and flow field in the 90 degree bend with moving Bed

Centrifugal force at the bend causes the terrain slope at water surface that increases water surface in outer arc and reduces in internal arc. This phenomenon creates adverse pressure gradient inside the arc of cross. As a result, a flow in the transverse direction within the cross is shaped that is called secondary flow. Secondary flow and its interaction with the inertia of the flow, which leads to create a spiral flow causes changes in the topography of the Bed. Understanding the topography of Bed in arcs is essential for specifying scour positions and sediments to determine the best location for the construction of hydraulic structures such as the groin, pond and rivers organizing management. Also in numerical models, one of the most important steps is meshing optimization to achieve the most accurate results and also the least time of analysis of model. Since investigating the numerical sediment transport has been very difficult and research in this area is little; In this study, the most optimal meshing in numerical model is investigated and then tried to be stimulated scouring in the channel bend 90°. For this purpose, the results of the topography of Bed within the arc of channel are obtained using the software FLOW3D and with different turbulence models and compared with experimental results. It should be noted that due to inability of software in the results in perpendicular sections and in direction of flow in the arc, neural network and genetic pattern was used for extracting numerical results in points matching laboratory results. Then flow field in arc is compared with experimental results. The results show the high ability of numerical model FLOW3D in simulating channel with moving Bed. The comparison of turbulence models indicates superiority of turbulence model of LES in investigating changes of Bed in arc channel to other turbulence models.

Comparison of turbulence models for bubble column reactors

Though bubble column reactors are widely used in industry, the present design practice is still closer to an art than a desired state of science because of the complexity of its fluid mechanics. The empiricism can be reduced by understanding detailed flow pattern, turbulence characteristics and turbulent structures and their effects on the performance such as mixing and axial mixing in both the phases and rate of heat and mass transfer. For this purpose, in the present work, CFD simulations have been undertaken by using standard k-ε, RSM and LES turbulence models. The cylindrical column having a computational height of HD=900mm with inside diameter of D=150mm was employed as a bubble column operated at three superficial gas velocities (20, 40 and 100mm/s). The instantaneous three dimensional velocity field is obtained by means of two phase Eulerian-Eulerian Large Eddy Simulations (LES). The conservation equations for turbulent kinetic energy (k) and the turbulent energy dissipation rate (ε) have been derived from the two fluid governing equations using the Reynolds averaging procedure. This enabled accurate estimation of convective transport, diffusive transport, turbulent transport, production and dissipation of k and ε. These estimations have been compared with the modelled terms of the standard k-ε and Reynolds stress models. The difference in values gives an idea about the severity of assumptions made in these models. An attempt has been made to bring out the implications of simplifying assumptions.