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1
Shen, De Zhang, He Zhang und Hao Jie Li. „Comparison of Two Two-Equation Turbulence Model Used for the Numerical Simulation of Underwater Ammunition Fuze Turbine Flow Field“. Advanced Materials Research 591-593 (November 2012): 1968–72. http://dx.doi.org/10.4028/www.scientific.net/amr.591-593.1968.
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To figure out the problem of turbulence simulation of underwater ammunition fuze turbine numerical simulation, respectively, realizable k-ε turbulence model and SST k-ω turbulence model are used for two-phase flow numerical simulation of the turbine rotation. The analysis compared the calculation results of the two turbulence models. The results showed that: the cavitation scale obtained from realizable k-ε turbulence model is shorter than that of SST k-ω turbulence model; turbine surface pressure distribution trends are similar of this two model, the results of realizable k-ε turbulence model are bigger than SST k-ω turbulence model; the turbine axial pressure coefficients using realizable k-ε turbulence model are also bigger than that of SST k-ω turbulence model, and the deviation increases with the speed increase.
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Genç, M. S. „Numerical Simulation of Flow over a Thin Aerofoil at a High Reynolds Number Using a Transition Model“. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, Nr. 10 (12.02.2010): 2155–64. http://dx.doi.org/10.1243/09544062jmes2121.
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In this study, a prediction of the transition and stall characteristics of an NACA64A006 thin-aerofoil was numerically simulated by FLUENT using k— kL—ω and k—ω shear-stress transport (SST) transition models, recently developed, and k—ω SST and k—ε turbulence models. Subsonic flow with free stream Mach number ( M∞) of 0.17 and the high Reynolds number ( Re) of 5.8×106 was considered at an angle of attack varying from 2° to 11°. However, the computed results were compared with the experiments of McCollough and Gault. Lift and pressure curves were accurately predicted using the k— kL—ω transition model, while the k—ω SST transition model and the k—ω SST and k—ε turbulence models did not have a good agreement with the experimental results. The k— kL—ω transition model showed that the laminar separation and turbulent reattachment occurred near the leading edge of the NACA64A006 thin aerofoil, which caused the formation of the laminar separation bubble on the suction surface as in the experiments. Consequently, the transition and stalling characteristics of this aerofoil were successfully predicted using FLUENT with the k— kL—ω transition model at high Re number flow.
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Teodosiu, Cătălin, Viorel Ilie und Raluca Teodosiu. „Appropriate CFD Turbulence Model for Improving Indoor Air Quality of Ventilated Spaces“. Mathematical Modelling in Civil Engineering 10, Nr. 4 (01.12.2014): 28–42. http://dx.doi.org/10.2478/mmce-2014-0020.
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Abstract Accurate assessment of air-flow in ventilated spaces is of major importance for achieving healthy and comfortable indoor environment conditions. The CFD (Computational Fluid Dynamics) technique is nowadays one of the most used approaches in order to improve the indoor air quality in ventilated environments. Nevertheless, CFD has still two main challenges: turbulence modeling and experimental validation. As a result, the objective of this study is to evaluate the performance of different turbulence models potentially appropriate for the prediction of indoor airflow. Accordingly, results obtained with 6 turbulence models (standard k-ε model, RNG k-ε model, realizable k-ε model, LRN SST k-ω model, transition SST k-ω model and low Reynolds Stress-ω model) are thoroughly validated based on detailed experimental data. The configuration taken into account in this work corresponds to isothermal and anisothermal airflows produced by mixing ventilation systems in small enclosures at low room air changes per hour. In general, the transition SST k-ω model shows the better overall behavior in comparison with measurement values. Consequently, the application of this turbulence model is appropriate for air flows in ventilated spaces, being an interesting option to more sophisticated LES (Large Eddy Simulation) models as it requires less computational resources.
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Barnes, Andrew, Daniel Marshall-Cross und Ben Richard Hughes. „Validation and comparison of turbulence models for predicting wakes of vertical axis wind turbines“. Journal of Ocean Engineering and Marine Energy 7, Nr. 4 (23.07.2021): 339–62. http://dx.doi.org/10.1007/s40722-021-00204-z.
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AbstractVertical 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.
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Boertz, Hendrik, Albert Baars, Janusz T. Cieśliński und Sławomir Smoleń. „Turbulence Model Evaluation for Numerical Modelling of Turbulent Flow and Heat Transfer of Nanofluids“. Applied Mechanics and Materials 831 (April 2016): 165–80. http://dx.doi.org/10.4028/www.scientific.net/amm.831.165.
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In this work, Nusselt number and friction factor are calculated numerically for turbulent pipe flow (Reynolds number between 6000 and 12000) with constant heat flux boundary condition using nanofluids. The nanofluid is modelled with the single-phase approach and the simulation results are compared with experimental data. Ethylene glycol and water, 60:40 EG/W mass ratio, as base fluid and SiO2 nanoparticles are used as nanofluid with particle volume concentrations ranging from 0% to 10%. A prior turbulence model evaluation of k-ε-, k-ω- and k-ω-SST-model revealed substantial deviations between the tested models and resulted in applying the k-ω-SST-model for the simulation. Nusselt number predictions for the nanofluid are in agreement with experimental results and a conventional single-phase correlation. The mean deviation is in the range of 5%. Friction factor values show a mean deviation of 1.5% to a conventional single-phase correlation, however, they differ considerably from the nanofluid experimental data.
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Matyushenko, A. A., und A. V. Garbaruk. „Non-linear correction for the k-ω SST turbulence model“. Journal of Physics: Conference Series 929 (November 2017): 012102. http://dx.doi.org/10.1088/1742-6596/929/1/012102.
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Engdar, Ulf, Per Nilsson und Jens Klingmann. „Investigation of Turbulence Models Applied to Premixed Combustion Using a Level-Set Flamelet Library Approach“. Journal of Engineering for Gas Turbines and Power 126, Nr. 4 (01.10.2004): 701–7. http://dx.doi.org/10.1115/1.1771687.
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Most of the common modeling approaches to premixed combustion in engineering applications are either based on the assumption of infinitely fast chemistry or the flamelet assumption with simple chemistry. The level-set flamelet library approach (FLA) has shown great potential in predicting major species and heat release, as well as intermediate and minor species, where more simple models often fail. In this approach, the mean flame surface is tracked by a level-set equation. The flamelet libraries are generated by an external code, which employs a detailed chemical mechanism. However, a model for the turbulent flame speed is required, which, among other considerations, depends on the turbulence intensity, i.e., these models may show sensitivity to turbulence modeling. In this paper, the FLA model was implemented in the commercial CFD program Star-Cd, and applied to a lean premixed flame stabilized by a triangular prism (bluff body). The objective of this paper has been to investigate the impact on the mean flame position, and hence on the temperature and species distribution, using three different turbulent flame speed models in combination with four different turbulence models. The turbulence models investigated are: the standard k-ε model, a cubic nonlinear k-ε model, the standard k-ω model and the shear stress transport (SST) k-ω model. In general, the computed results agree well with experimental data for all computed cases, although the turbulence intensity is strongly underestimated at the downstream position. The use of the nonlinear k-ε model offers no advantage over the standard model, regardless of flame speed model. The k-ω based turbulence models predict the highest turbulence intensity with the shortest flame lengths as a consequence. The Mu¨ller flame speed model shows the least sensitivity to the choice of turbulence model.
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Deng, Yilin, Jian Feng, Fulai Wan, Xi Shen und Bin Xu. „Evaluation of the Turbulence Model Influence on the Numerical Simulation of Cavitating Flow with Emphasis on Temperature Effect“. Processes 8, Nr. 8 (17.08.2020): 997. http://dx.doi.org/10.3390/pr8080997.
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The aim of this paper is to investigate the influence of different turbulence models (k−ε, RNG k−ε, and SST k−ω) on the numerical simulation of cavitating flow in thermosensitive fluid. The filter-based model and density correction method were employed to correct the turbulent viscosity of the three turbulence models. Numerical results obtained were compared to experimental ones which were conducted on the NACA0015 hydrofoil at different temperatures. The applicability of the numerical solutions of different turbulence model was studied in detail. The modified RNG k−ε model has higher accuracy in the calculation of cavitating flow at different temperatures.
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Povilaitis, Mantas, und Justina Jaseliūnaitė. „Simulation of Hydrogen-Air-Diluents Mixture Combustion in an Acceleration Tube with FlameFoam Solver“. Energies 14, Nr. 17 (03.09.2021): 5504. http://dx.doi.org/10.3390/en14175504.
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During a severe accident in a nuclear power plant, hydrogen can be generated, leading to risks of possible deflagration and containment integrity failure. To manage severe accidents, great experimental, analytical, and benchmarking efforts are being made to understand combustible gas distribution, deflagration, and detonation processes. In one of the benchmarks—SARNET H2—flame acceleration due to obstacle-induced turbulence was investigated in the ENACCEF facility. The turbulent combustion problem is overly complex because it involves coupling between fluid dynamics, mass/heat transfer, and chemistry. There are still unknowns in understanding the mechanisms of turbulent flame propagation, therefore many methods in interpreting combustion and turbulent speed are present. Based on SARNET H2 benchmark results, a two-dimensional computational fluid dynamics simulation of turbulent hydrogen flame propagation in the ENACCEF facility was performed. Four combustible mixtures with different diluents concentrations were considered—13% H2 and 0%/10%/20%/30% of diluents in air. The aim of this numerical simulation was to validate the custom-built turbulent combustion OpenFOAM solver based on the progress variable model—flameFoam. Furthermore, another objective was to perform parametric analysis in relation to turbulent speed correlations and turbulence models and interpret the k-ω SST model blending function F1 behavior during the combustion process. The obtained results show that in the simulated case all three turbulent speed correlations behave similarly and can be used to reproduce observable flame speed; also, the k-ε model provides more accurate results than the k-ω SST turbulence model. It is shown in the paper that the k-ω SST model misinterprets the sudden parameter gradients resulting from turbulent combustion.
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Amorim, Felipe Grossi L., Jean Helder M. Ribeiro, Marília Gabriela J. Vaz und Ramon Molina Valle. „Sensitivity Analysis of the Air Flow inside a Single Cylinder Engine for Different Turbulence Models Using CFD“. Advanced Materials Research 1016 (August 2014): 624–29. http://dx.doi.org/10.4028/www.scientific.net/amr.1016.624.
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Theincrease of greenhouse gases emissions makes necessary to improve the comprehension of the Internal Combustion Engines operation. One of the factors that affect the combustion in these engines is the turbulence, since it can raise the quality of the fuel-air mixture inside the combustion chamber. However, when modeling internal combustion engines using CFD, the turbulence model choice is always a relevant problem. The present paper analyzes the results for three different turbulence models (k-ε Realizable, RNG k-ε and Menter k-ω SST) ina single-cylinder engine geometry, comparing numerical and experimental pressure data. For this experiment, the k-ε models obtained more trustable results than the k-ω SST, using less computational resources. The models achieved good results for eddy recirculation inside de cylinder and in regions of free shear flow at the valve openings, which makes possible to observe the correlation between parameters such as tumble and turbulent kinetic energy.
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ZHANG, XIANG-HONG, YI-ZAO WU und JIANG-FENG WANG. „TURBULENCE MODELS FOR ACCURATE AEROTHERMAL PREDICTION IN HYPERSONIC FLOWS“. Modern Physics Letters B 24, Nr. 13 (30.05.2010): 1345–48. http://dx.doi.org/10.1142/s021798491002358x.
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Accurate description of the aerodynamic and aerothermal environment is crucial to the integrated design and optimization for high performance hypersonic vehicles. In the simulation of aerothermal environment, the effect of viscosity is crucial. The turbulence modeling remains a major source of uncertainty in the computational prediction of aerodynamic forces and heating. In this paper, three turbulent models were studied: the one-equation eddy viscosity transport model of Spalart-Allmaras, the Wilcox k -ω model and the Menter SST model. For the k -ω model and SST model, the compressibility correction, press dilatation and low Reynolds number correction were considered. The influence of these corrections for flow properties were discussed by comparing with the results without corrections. In this paper the emphasis is on the assessment and evaluation of the turbulence models in prediction of heat transfer as applied to a range of hypersonic flows with comparison to experimental data. This will enable establishing factor of safety for the design of thermal protection systems of hypersonic vehicle.
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Zhao, Minsheng, Decheng Wan und Yangyang Gao. „Comparative Study of Different Turbulence Models for Cavitational Flows around NACA0012 Hydrofoil“. Journal of Marine Science and Engineering 9, Nr. 7 (05.07.2021): 742. http://dx.doi.org/10.3390/jmse9070742.
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The present work focuses on the comparison of the numerical simulation of sheet/cloud cavitation with the Reynolds Average Navier-Stokes and Large Eddy Simulation(RANS and LES) methods around NACA0012 hydrofoil in water flow. Three kinds of turbulence models—SST k-ω, modified SST k-ω, and Smagorinsky’s model—were used in this paper. The unstable sheet cavity and periodic shedding of the sheet/cloud cavitation were predicted, and the simulation results, namelycavitation shape, shedding frequency, and the lift and the drag coefficients of those three turbulence models, were analyzed and compared with each other. The numerical results above were basically in accordance with experimental ones. It was found that the modified SST k-ω and Smagorinsky turbulence models performed better in the aspects of cavitation shape, shedding frequency, and capturing the unsteady cavitation vortex cluster in the developing and shedding period of the cavitation at the cavitation number σ = 0.8. At a small angle of attack, the modified SST k-ω model was more accurate and practical than the other two models. However, at a large angle of attack, the Smagorinsky model of the LES method was able to give specific information in the cavitation flow field, which RANS method could not give. Further study showed that the vortex structure of the wing is the main cause of cavitation shedding.
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Tahani, Mojtaba, Mehran Masdari, Hamidreza Eivazi und Massoud Tatar. „Assessment of turbulence models for transonic oscillating airfoil“. International Journal of Numerical Methods for Heat & Fluid Flow 27, Nr. 11 (06.11.2017): 2603–28. http://dx.doi.org/10.1108/hff-04-2016-0142.
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Purpose This paper aims to investigate numerical solution of transonic flow around NACA0012 airfoil under sinusoidal pitch oscillation. Accordingly, effects of the amplitude and frequency of oscillations on aerodynamic coefficients are evaluated and the efficiency of the turbulent models, K-ω shear-stress transport (SST), scale adaptive simulation (SAS) and delayed detached eddy simulation (DDES), in simulation of the nonlinear phenomena – i.e. the interaction between shock and boundary layer and the shock oscillations – is studied. Design/methodology/approach K-ω SST, SAS and DDES models are used as turbulence approaches. The numerical results are compared with available experimental and numerical information. Findings According to the results inside the buffet boundaries, the DDES turbulent model expresses results that are more appropriate; however, SAS and SST models are not efficient enough in evaluating the characteristics of nonlinear flow. Originality/value In this research study, hybrid RANS-LES turbulence model is engaged to simulate transonic flow around pitching NACA0012 airfoil, and results are compared to the SAS and Reynolds Average Navier–Stocks simulations as well as available numerical and experimental data. In addition, effects of the amplitude and frequency of oscillations on aerodynamic coefficients are evaluated in buffet regions.
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Ramadhan Al-Obaidi, Ahmed. „Effects of Different Turbulence Models on Three-Dimensional Unsteady Cavitating Flows in the Centrifugal Pump and Performance Prediction“. International Journal of Nonlinear Sciences and Numerical Simulation 20, Nr. 3-4 (26.05.2019): 487–509. http://dx.doi.org/10.1515/ijnsns-2018-0336.
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AbstractIn centrifugal pumps, it is important to select appropriate turbulence model for the numerical simulation in order to obtain reliable and accurate results. In this work, ten turbulence models in 3-D transient simulation for the centrifugal pump are chosen and compared. The pump performance is validated with experimental results. The numerical results reveal that the SST turbulence model was closer to the experimental results in predicting head. In addition, the pressure variation trend for the ten models is very similar which increases and then decreases from the inlet to outlet of the pump along the streamline. The SST k-ω model predicts the performance of the pump was more accurately than other turbulent models. Furthermore, the results also found that the error is the least at design operation condition 300(l/min), which is around 1.98 % for the SST model and 2.14 % and 2.38 % for the LES and transition omega model. Within 7.61 %, the errors at higher flow rate 350(l/min) for SST. The error for SST model is smaller as compared to different turbulent models. For the Realizable k-ɛ model, the errors fluctuate were more high than other models.
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Wu, Jian Feng, Cai Hua Wang und Yan Chao Zhao. „The Turbulent Flow Model Selection for Numerical Wind Tunnel Simulation of the Low Layer Double Slope Roof“. Applied Mechanics and Materials 204-208 (Oktober 2012): 4892–95. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.4892.
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Using the FLUENT software, this paper taking the current code for the design of building structures as the comparison standard, have numerical wind tunnel simulation of the wind the surface wind pressure on low layer double slope roof. It focuses on the analysis of the effects of turbulence model selection on the numerical simulation results, such as Spalart-Allmaras、Standard k −ε、RNG k −ε、Realizable k −ε、Standard k −ω、SST k −ω and RSM, to provide a basis for the reasonable selection of turbulence models.
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Mohamed, M. Arif, Y. Wu und Martin Skote. „Assessment of Simple RANS Turbulence Models for Stall Delay Applications at Low Reynolds Number“. Applied Mechanics and Materials 863 (Februar 2017): 260–65. http://dx.doi.org/10.4028/www.scientific.net/amm.863.260.
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This paper assesses the performance of three two-equation turbulence models viz. the SST k-ω, the RNG and realizable k-εfor the simulations of a rotating blade in a wind tunnel experiment where k, ε and ω are turbulent kinetic energy, dissipation rate and specific dissipation respectively. The experiments showed the stall-delay phenomenon at the inboard of the rotating blade at a Reynolds number of 4800. This trend of suction peaks was captured by all three turbulence models albeit not matching the experimental coefficient of pressure accurately. All three models also showed radial flow at the inboard which is consistent with the experiments while the SST predicted the least k at low wall values.
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LIU, JINTAO, SHUHONG LIU, YULIN WU, YUEKUN SUN und ZHIGANG ZUO. „PREDICTION OF "S" CHARACTERISTICS OF A PUMP-TURBINE WITH SMALL OPENING BASED ON V2F MODEL“. International Journal of Modern Physics: Conference Series 19 (Januar 2012): 417–23. http://dx.doi.org/10.1142/s2010194512009014.
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The characteristic of a pump-turbine during the whole starting or stopping period couldn't be calculated accurately by CFD method and most of turbulence models were found inaccurate in the calculation of small opening condition, so a proper turbulence model was needed for the further study of pump-turbine. V2F model which was valid to the solid wall and SST k-ω model were used to calculate the pump-turbine with two openings that one was a small opening and the other was large opening. Results showed that V2F model can be used to simulate characteristics of pump-turbine in the whole opening range and the SST k-ω model can be used only for large openings. Results of V2F model are accuracy and it realizes the real flow in the near wall region. Results of V2F model can obtain small vortexes and some complex flow phenomenon and they are much different from results of SST k-ω model. The V2F model might be used to simulate the starting or stopping period of a pump-turbine.
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Kim, Jun Song, Donghae Baek und Inhwan Park. „Evaluating the Impact of Turbulence Closure Models on Solute Transport Simulations in Meandering Open Channels“. Applied Sciences 10, Nr. 8 (16.04.2020): 2769. http://dx.doi.org/10.3390/app10082769.
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River meanders form complex 3D flow patterns, including secondary flows and flow separation. In particular, the flow separation traps solutes and delays their transport via storage effects associated with recirculating flows. The simulation of the separated flows highly relies in the performance of turbulence models. Thus, these closure schemes can control dispersion behaviors simulated in rivers. This study performs 3D simulations to quantify the impact of the turbulence models on solute transport simulations in channels under different sinuosity conditions. The 3D Reynolds-averaged Navier-Stokes equations coupled with the k − ε , k − ω and SST k − ω models are adopted for flow simulations. The 3D Lagrangian particle-tracking model simulates solute transport. An increase in sinuosity causes strong transverse gradients of mean velocity, thereby driving the onset of the separated flow recirculation along the outer bank. Here, the onset and extent of the flow separation are strongly influenced by the turbulence models. The k − ε model fails to reproduce the flow separation or underestimates its size. As a result, the k − ε model yields residence times shorter than those of other models. In contrast, the SST k − ω model exhibits a strong tailing of breakthrough curves by generating more pronounced flow separation.
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Wu, Guohong, Xiangyu Duan, Jianghui Zhu, Xiaoqin Li, Xuelin Tang und Hui Gao. „Investigations of hydraulic transient flows in pressurized pipeline based on 1D traditional and 3D weakly compressible models“. Journal of Hydroinformatics 23, Nr. 2 (02.02.2021): 231–48. http://dx.doi.org/10.2166/hydro.2021.134.
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Abstract Transient flow characteristics and dissipation mechanism in pressurized pipeline were investigated based on 1D friction models and 3D turbulence models, where the pressure–density model was combined into the 3D continuity equation allowing for the elasticity of the fluid and the pipes. The applicability of 3D realizable k–ε and 3D SST (shear stress transport) k–ω turbulence models was verified with comparison to 1D traditional water hammer models and the experimental data for fast closing of the valve in the reservoir–pipe–valve system. The valve closure rule was instantaneously carried out using the grid slip CFD (computational fluid dynamics) technique. The SST k–ω turbulence model has the highest accuracy in predicting the pressure attenuation of transient flows. The 3D detailed flow field confirms that the asymmetric flows induced by the change of valve opening within approximately three-fourths of the pipe inner diameter before the valve are captured. In the pressure wave cycles, the unsteady inertia, axial pressure gradient, viscous shear stress and turbulent shear stress mainly influence the velocity variations. During the pressure wave propagation, the viscous and turbulent dissipation are critical in the pressure attenuation in the wall region; the viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation increases to the maximum values at y+ = 13–23.
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Kang, Qi, Jiapeng Gu, Xueyu Qi, Ting Wu, Shengjie Wang, Sihang Chen, Wei Wang und Jing Gong. „Hydrodynamic Modeling of Oil–Water Stratified Smooth Two-Phase Turbulent Flow in Horizontal Circular Pipes“. Energies 14, Nr. 16 (23.08.2021): 5201. http://dx.doi.org/10.3390/en14165201.
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In the petrochemical industry, multiphase flow, including oil–water two-phase stratified laminar flow, is more common and can be easily obtained through mathematical analysis. However, there is limited mathematical analytical model for the simulation of oil–water flow under turbulent flow. This paper introduces a two-dimensional (2D) numerical simulation method to investigate the pressure gradient, flow field, and oil–water interface height of a pipeline cross-section of horizontal tube in an oil–water stratified smooth flow. Three Reynolds average N–S equation models (k−ε, k−ω, SST k−ω) are involved to simulate oil–water stratified smooth flow according to the finite volume method. The pressure gradient and oil–water interface height can be computed according to the given volume flow rate using the iteration method. The predicted result of oil–water interface height and velocity profile by the model fit well with several published experimental data, except that there is a large error in pressure gradient. The SST k−ω turbulence model appears higher accuracy for simulating oil–water two-phase stratified flow in a horizontal pipe.
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Qurooni, Faisal Al, Ali Vakil, Ehab Elsaadawy und Sheldon I. Green. „Numerical simulation of an over-expanded supersonic and subsonic industrial nozzle flow relevant to flaring system“. Transactions of the Canadian Society for Mechanical Engineering 43, Nr. 4 (01.12.2019): 471–80. http://dx.doi.org/10.1139/tcsme-2018-0230.
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Flaring in oil and gas production is the controlled burning of unwanted exhaust gases to enhance safety. To improve flare combustion, gas flares are equipped with air nozzles that introduce extra oxygen and improve mixing in the combustion zone. These nozzles are operated in the subsonic, sonic, or supersonic regimes. In this paper, we are concerned with turbulence modeling of the jet flow exiting from a particular convergent–divergent nozzle used in flare systems. That nozzle has convergent and divergent sections that are connected via a throat section with a finite length and constant diameter. The Realizable k – ε and SST k – ω models are used to study the compressible flow within the nozzle. The velocity profiles, turbulent kinetic energy, Mach number profiles, and entrainment rate coefficients predicted by both turbulence models are compared for nozzle pressure ratios in the range 1.18 ≤ NPR ≤ 1.78. It is shown that both turbulence models predict nearly identical flow evolution along the nozzle. When the flow becomes supersonic, the shock surface, and consequently nozzle outlet velocity profiles, predicted by the SST k – ω model deviates slightly from the other model. The differences, however, become negligible a couple of diameters downstream of the nozzle outlet.
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Afghan Khan, Sher, Mir Owais Ali, Miah Mohammed Riyadh, Zahid Hossen und Nafis Mahdi Arefin. „Assessment of different turbulence models in simulating axisymmetric flow in suddenly expanded nozzles“. International Journal of Engineering & Technology 7, Nr. 3.29 (24.08.2018): 243. http://dx.doi.org/10.14419/ijet.v7i3.29.18804.
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A numerical simulation was carried out to compare various turbulence models simulating axisymmetric nozzle flow past suddenly expanded ducts. The simulations were done for L/D = 10. The convergent-divergent nozzle has been modeled and simulated using the turbulence models: The Standard k-ε model, The Standard k-ω model and The SST k-ω model. Numerical simulations were done for Mach numbers 1.87, 2.2, and 2.58 and the nozzles were operated for NPRs in the range from 3 to 11. From the numerical analysis it is apparent that for a given Mach number and effect of NPR will result in maximum gain or loss of pressure. Numerical results are in good agreement with the experimental results.
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Wang, Liu, Wang, Zhou, Jiang und Li. „Numerical Simulation of the Sound Field of a Five-Stage Centrifugal Pump with Different Turbulence Models“. Water 11, Nr. 9 (26.08.2019): 1777. http://dx.doi.org/10.3390/w11091777.
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To study the influence of the turbulence model on the sound field of pumps, the standard k-ε, Re-normalization Group (RNG) k-ε and Shear Stress Transfer (SST) k-ω models were employed to simulate flow and sound fields of a five-stage centrifugal pump with a vaned-diffuser. The vibration characteristics of the pump were simulated with the modal response method. A vibration experiment in the pump was carried out to verify the feasibility of the numerical simulation of the hydrodynamic noise in the pump. Results show that in the spectrum of internal and external noise, the peak value appears at axial passing frequency (APF) and its harmonic frequency. Compared with the standard k-ε model, the RNG k-ε and SST k-ω models show good consistence with the noise characteristics of experimental results, indicating the characteristic frequency and revealing the approximate behavior of the sound field in the pump. In general, the simulation of the sound field based on the RNG k-ε model is most appropriate for the multistage centrifugal pump with a vaned-diffuser.
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Benahmed, Lamia, und Khaled Aliane. „Simulation and Analysis of a Turbulent Flow Around a Three-Dimensional Obstacle“. Acta Mechanica et Automatica 13, Nr. 3 (01.09.2019): 173–80. http://dx.doi.org/10.2478/ama-2019-0023.
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Abstract The study of flow around obstacles is devised into three different positions: above the obstacle, upstream of the obstacle, and downstream of the latter. The behaviour of the fluid downstream of the obstacle is less known, and the physical and numerical modelling is being given the existence of recirculation zones with their complex behaviour. The purpose of the work presented below is to study the influence of the inclined form of the two upper peaks of a rectangular cube. A three-dimensional study was carried out using the ANSYS CFX calculation code. Turbulence models have been used to study the flow characteristics around the inclined obstacle. The time-averaged results of contours of velocity vectors <V>, cross-stream <v> and stream wise velocity <u> and streamlines were obtained by using K-ω shear -stress transport (SST), RANG K-ε and K-ε to model the turbulence, and the governing equations were solved using the finite volume method. The turbulence model K-ω SST has presented the best prediction of the flow characteristics for the obstacle among the investigated turbulence models in this work.
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Zhang, Ying, Longtao Wang, Angui Li und Pengfei Tao. „Performance evaluation by computational fluid dynamics modelling of the heavy gas dispersion with a low Froude number in a built environment“. Indoor and Built Environment 29, Nr. 5 (19.06.2019): 656–70. http://dx.doi.org/10.1177/1420326x19856041.
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To evaluate the dispersion of a heavy gas, such as sulphur hexafluoride, with a low Froude number in a built environment, an experimental and numerical simulation study was conducted. The experiment was carried out using seven different injection inlet configurations in an experimental chamber. The release rate was found to have a great effect on the concentration in the lower part of the chamber. The obstacle in the middle of the chamber could cause a non-uniform distribution of concentration, particularly due to variations in locations and angles of the release outlets. Additionally, numerical simulations were carried out to evaluate four turbulence models: the standard k- ε model, the realizable k- ε model, the re-normalization group (RNG) k- ε model and the shear stress transport (SST) k-ω model. Four indicators were used to evaluate the turbulent model performance. In general, the SST k-ω model performed the best, with geometric mean bias ( MG) = 0.968 and geometric variance ( VG) = 1.09 at 0.055 m height, and with MG = 0.384 and VG = 2.80 at 0.6 m height. The standard k- ε model was the next best in performance, followed by the realizable k- ε and the RNG k- ε model.
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Newir, Ahmed E., und Mohamed Ibrahim. „Experimental and Numerical Investigation for Mechanical Ventilated Greenhouse (Comparison between Different Turbulence Models)“. European Journal of Engineering and Formal Sciences 2, Nr. 3 (29.12.2018): 107. http://dx.doi.org/10.26417/ejef.v2i3.p107-115.
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Using computational fluid dynamics (CFD) in agriculture field especially in designing greenhouses is becoming ever more important to reduce the energy consumption, wherefore a comparison between the experimental and numerical results increasing the credibility of theoretical studies and therefore depending on it. Forced ventilation greenhouse has been used in even span greenhouse to study the experimental measurements of temperature distribution in summer rush hours, the experiment has been performed in October 6 University, Giza, Egypt. More than one turbulence models (Standard K-ε, RNG K- ε, Reynolds Stress Model (RSM), Transition Shear-Stress Transport (SST), Standard K-ω and K-KL-ω) are used for the (CFD) numerical study implemented for comparison between the experimental and numerical measurements. After this study can get that SST turbulence model is the most efficient numerical solution for this case, a good qualitative and quantitative agreement found between the numerical results and the experimental measurements.
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Kaewbumrung, Mongkol, und Chalermpol Plengsa-ard. „Relaminarization of a hot air impingement on a flat plate“. E3S Web of Conferences 128 (2019): 10004. http://dx.doi.org/10.1051/e3sconf/201912810004.
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The research mainly focuses on a numerical analysis for heat transfer in the transition flow regimes. The simulation is presented by using ANSYS-FLUENT and Reynolds Averaged Navier Stokes (RANS) technique is employed in order to simulate the complex flow fields. The turbulent jet which impinges on the flat plate with a constant surface heat fluxes is tested. The average Nusselt number predictions are also calculate and compared with existing measurement results. The jet Reynolds number is set to 23,000 which based on jet nozzle diameter, while a jet-toplate spacing of H/D is fixed at 2.0. The turbulence models evaluated in the present study are one equation Spalart Allmaras (SA) model, k-ɛ, shear stress transport (SST) k-ω and SST with transition model. It can be summarized that the SA, k-ɛ, and SST k-ω models fail to calculate the global trend of the instantaneous simulated Nusselt number profiles. Only the simulated results from the SST with transition model provides agree fairly well with experimental results. Moreover, the first highest point of predicted Nusselt number are close to the stagnation point and decrease monotonically in the radial direction within the wall jet region. The second peak of Nusselt number prediction is also observed, and the RANS simulations can capture the relaminarization mechanisms within the boundary layer near walls.
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Singh, Parampreet, Neel Kanth Grover, Vivek Agarwal, Shubham Sharma, Jujhar Singh, Milad Sadeghzadeh und Alibek Issakhov. „Computational Fluid Dynamics Analysis of Impingement Heat Transfer in an Inline Array of Multiple Jets“. Mathematical Problems in Engineering 2021 (12.04.2021): 1–10. http://dx.doi.org/10.1155/2021/6668942.
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Amid all convective heat transfer augmentation methods employing single phase, jet impingement heat transfer delivers significantly higher coefficient of local heat transfer. The arrangement leading to nine jets in square array has been used to cool a plate maintained at constant heat flux. Numerical study has been carried out using RANS-based turbulence modeling in commercial CFD Fluent software. The turbulent models used for the study are three different “k-ε” models (STD, RNG, and realizable) and SST “k-ω” model. The numerical simulation output is equated with the experimental results to find out the most accurate turbulence model. The impact of variation of Reynolds number, inter-jet spacing, and separation distance has been considered for the geometry considered. These parameters affect the coefficient of heat transfer, temperature, and turbulent kinetic energy related to flow. The local “h” values have been noticed to decline with the rise in separation distance “H/D.” The SST “k-ω” model has been noticed to be in maximum agreement with the experimental results. The average value of heat transfer coefficient “h” reduces from 210 to 193 W/m2K with increase in “H/D” from 6 to 10 at “Re” = 9000 and S/D of 3. As per numerical results, inter-jet spacing “S/D” of 3 has been determined to be the most optimum value.
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Hidalgo, Víctor, Xavier Escaler, Esteban Valencia, Xiaoxing Peng, José Erazo, Diana Puga und Xianwu Luo. „Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil“. Applied Sciences 9, Nr. 18 (05.09.2019): 3696. http://dx.doi.org/10.3390/app9183696.
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The present paper focuses on the numerical simulation of unsteady cavitation around a NACA66 hydrofoil to improve the understanding of the cavitation effects on hydraulic machinery. For this aim, the Zwart–Gerber–Belamri cavitation model was updated and uploaded as a library file for OpenFOAM’s solvers using C++ language. Furthermore, the hybrid Reynold average Navier–Stokes (RANS)–large eddy simulation (LES) model k - ω SST scale adaptive simulation (SAS) was implemented as a turbulence model for the present study of scale adaptive simulation. For validation, numerical results were compared with experimental results obtained by Leroux at the Naval Academy Research Institute in France. In order to highlight the benefits in terms of computational consumption and reproduction of the phenomenon the k - ω SST SAS model was compared against implicit large eddy simulation (ILES). Results show that the cavitation evolution including the maximum vapor length, the detachment and the oscillation frequency were reproduced satisfactorily using k - ω SST SAS. Moreover, k - ω SST SAS results predicted a lower total vapor volume on time than ILES, which is related to observed pulses of pressure coefficient, C p , and those match fairly well with the experimental results. To summarize, the k - ω SST SAS model predicts with good accuracy unsteady cavitation behavior around hydrofoils and shows improved versatility over the ILES approach.
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Akoz, M. Sami, und M. Salih Kirkgoz. „NUMERICAL AND EXPERIMENTAL ANALYSES OF THE FLOW AROUND A HORIZONTAL WALL-MOUNTED CIRCULAR CYLINDER“. Transactions of the Canadian Society for Mechanical Engineering 33, Nr. 2 (Juni 2009): 189–215. http://dx.doi.org/10.1139/tcsme-2009-0017.
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The numerical modeling of two-dimensional turbulent flow around a horizontal wall-mounted circular cylinder at Reynolds numbers in the range of 1000≤ReD≤7000 is investigated. Ansys® 10.0-FLOTRAN program package is used to solve the governing equations by finite element method, and the performance of the standard k-ε, standard k-ω and SST turbulence models are examined. A sensitivity study for the three turbulence models is carried out on eight computational meshes with different densities and structures. The computational velocity fields from the present simulations are compared with the experimental results obtained from particle image velocimetry (PIV) measurements for validation purposes. The point of the boundary layer detachment from the cylinder surface and the lengths of primary and secondary separation regions occurring around the cylinder are determined numerically and compared with those obtained experimentally. From these comparisons it is found that the numerical modeling using either of k-ω and SST turbulence models is reasonably successful. Using the results of numerical solutions, the drag and lift coefficients, Cd and Cl, are also calculated and compared with the measured values.
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Mahon, Stephen, und Xin Zhang. „Computational Analysis of Pressure and Wake Characteristics of an Aerofoil in Ground Effect“. Journal of Fluids Engineering 127, Nr. 2 (27.09.2004): 290–98. http://dx.doi.org/10.1115/1.1891152.
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The pressure and wake of an inverted cambered aerofoil in ground effect was studied numerically by solving the Reynolds-averaged Navier-Stokes equations. Efforts were focused on the setting up of an accurate numerical model and assessing the abilities of various turbulence models in capturing major physical features associated with the flow, such as surface pressure distribution, separation, level of downforce, and wake. A number of ride heights were studied covering various force regions. Surface pressures, sectional forces, and wake characteristics were compared to experimental data. The k−ω SST and Realizable k−ε turbulence models were found to offer good overall simulations, with the k−ω SST performing better for the surface pressure and the Realizable k−ε better for the wake. The simulations at various ride heights correctly captured the trends in flow-field variations with ride height. The surface pressures, wake flow field, and region of separation on the suction surface of the aerofoil, at lower ride heights, were all modeled accurately.
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Chaiyanupong, Jaruwan, und Tawit Chitsomboon. „Effects of turbulence models and grid densities on computational accuracy of flows over a vertical axis wind turbine“. International Journal of Renewable Energy Development 7, Nr. 3 (15.12.2018): 213–22. http://dx.doi.org/10.14710/ijred.7.3.213-222.
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Flows through a vertical axis wind turbine (VAWT) are very complex due to their inherent unsteadiness caused by large variations of the angle of attacks as the turbine is rotating and changing its azimuth angles simultaneously. In addition, a turbine must go through a wide range of operating conditions especially the change in blade speed ratio (BSR). Accurate prediction of flows over VAWT using Reynolds-Averaged Navier-Stokes (RANS) model needs a well-tested turbulence model as well as a careful grid control around the airfoil. This paper aimed to compare various turbulence models and seek the most accurate one. Furthermore, grid convergence was studied using the Roache method to determine the sufficient number of grid elements around the blade section. The three-dimensional grid was generated by extrution from the two-dimensional grid along with the appropriate y+ controlling. Comparisons were made among the three turbulence models that are widely used namely: the RNG model, the shear stress transport k-ω model (SST) and the Menter’s shear stress transport k-ω model (transition SST). Results obtained clearly showed that turbulence models significantly affected computational accuracy. The SST turbulence model showed best agreement with reported experimental data at BSR lower than 2.35, while the transition SST model showed better results when BSR is higher than 2.35. In addition, grid extruding technique with y+ control could reduce total grid requirement while maintaining acceptable prediction accuracy.Article History: Received April 15th 2018; Received in revised form June 16th 2018; Accepted September 17th 2018; Available onlineHow to Cite This Article: Chaiyanupong,J and Chitsomboon, T. (2018) Effects of Turbulence Models and Grid Densities on Computational Accuracy of Flows Over a Vertical Axis Wind Turbine. Int. Journal of Renewable Energy Development, 7(3), 213-222.http://dx.doi.org/10.14710/ijred.7.3.213-222
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Wang, Cai Hua, Jian Feng Wu und Wei Ling Wang. „The Effect of the Numerical Wind Tunnel Simulation Results of Arched Roof for Different Turbulence Models“. Advanced Materials Research 711 (Juni 2013): 348–51. http://dx.doi.org/10.4028/www.scientific.net/amr.711.348.
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Using the FLUENT software, this paper taking the wind load shape coefficient in the current code for the design of building structures as the comparison standard, have numerical wind tunnel simulation of the wind the surface wind pressure on arch roof. It focused on the effect of the different turbulence models on the numerical simulation, such as Spalart-Allmaras, Standard k ε, RNGk ε, Realizablek ε, Standard k ω, SST k ωand RSM. It provided reasonable reference for selection of turbulence model.
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Adanta, Dendy, I. M. Rizwanul Fattah und Nura Musa Muhammad. „COMPARISON OF STANDARD k-epsilon AND SST k-omega TURBULENCE MODEL FOR BREASTSHOT WATERWHEEL SIMULATION“. Journal of Mechanical Science and Engineering 7, Nr. 2 (09.10.2020): 039–44. http://dx.doi.org/10.36706/jmse.v7i2.44.
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Currently, Computational Fluid Dynamics (CFD) was utilized to predict the performance, geometry optimization or physical phenomena of a breastshot waterwheel. The CFD method requires the turbulent model to predict the turbulent flow. However, until now there is special attention on the effective turbulent model used in the analysis of breastshot waterwheel. This study is to identify the suitable turbulence model for a breatshot waterwheel. The two turbulence models investigated are: standard k-epsilon model and shear stress transport (SST) k-omega. Pressure based and one degrees of freedom (one-DoF) feature was used in this case with 75 Nm, 150 Nm, 225 Nm and 300 Nm as preloads. Based on the results, the standard k-epsilon model gave similar result with the SST k-omega model. Therefore, the simulation for breastshot waterwheel will be efficient if using the standard k-epsilon model because it requires lower computational power than the SST k-omega model. However, to study about physical phenomenon, the SST k-omega model is recommend.
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Tachos, N. S., A. E. Filios und D. P. Margaris. „A comparative numerical study of four turbulence models for the prediction of horizontal axis wind turbine flow“. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, Nr. 9 (01.09.2010): 1973–79. http://dx.doi.org/10.1243/09544062jmes1901.
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The analysis of the near and far flow fields of an experimental National Renewable Energy Laboratory (NREL) rotor, which has been used as the reference rotor for the Viscous and Aeroelastic Effects on Wind Turbine Blades (VISCEL) research program of the European Union, is described. The horizontal axis wind turbine (HAWT) flow is obtained by solving the steady-state Reynolds-averaged Navier—Stokes (RANS) equations, which are combined with one of four turbulence models (Spalart—Allmaras, k—∊, k—∊ renormalization group, and k—ω shear stress transport (SST)) aiming at validation of these models through a comparison of the predictions and the free field experimental measurements for the selected rotor. The computational domain is composed of 4.2×106 cells merged in a structured way, taking care of refinement of the grid near the rotor blade in order to enclose the boundary layer approach. The constant wind condition 7.2 m/s, which is the velocity of the selected experimental data, is considered in all calculations, and only the turbulence model is altered. It is confirmed that it is possible to analyse a HAWT rotor flow field with the RANS equations and that there is good agreement with experimental results, especially when they are combined with the k—ω SST turbulence model.
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Rogowski, Krzysztof, Grzegorz Królak und Galih Bangga. „Numerical Study on the Aerodynamic Characteristics of the NACA 0018 Airfoil at Low Reynolds Number for Darrieus Wind Turbines Using the Transition SST Model“. Processes 9, Nr. 3 (07.03.2021): 477. http://dx.doi.org/10.3390/pr9030477.
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A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model.
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Chýlek, Radomír, Ladislav Šnajdárek und Jiří Pospíšil. „Vortex Tube: A Comparison of Experimental and CFD Analysis Featuring Different RANS Models“. MATEC Web of Conferences 168 (2018): 02012. http://dx.doi.org/10.1051/matecconf/201816802012.
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The Ranque–Hilsch vortex tube represents a device for both cooling and heating applications. It uses compressed gas as drive medium. The temperature separation is affected by fluid flow behaviour inside the tube. It has not been sufficiently examined in detail yet and has the potential for further investigation. The aim of this paper is to compare results of numerical simulations of the vortex tube with obtained experimental data. The numerical study was using computational fluid dynamics (CFD), namely computational code STAR-CCM+. For the numerical study, a three-dimensional geometry model, and various turbulence physics models were used. For the validation of carried out calculations, an experimental device of the vortex tube of identical geometrical and operating conditions was created and tested. The numerical simulation results have been obtained for five different turbulence models, namely Standard k-ε, Realizable k-ε, Standard k-ω, SST k-ω and Reynolds stress model (RSM), were compared with experimental results. The most important evaluation factor was the temperature field in the vortex tube. All named models of turbulence were able to predict the general flow behaviour in the vortex tube with satisfactory precision. Standard k-ε turbulence model predicted temperature distribution in the best accordance with the obtained experimental data.
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Araya, Guillermo. „Turbulence Model Assessment in Compressible Flows around Complex Geometries with Unstructured Grids“. Fluids 4, Nr. 2 (28.04.2019): 81. http://dx.doi.org/10.3390/fluids4020081.
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One of the key factors in simulating realistic wall-bounded flows at high Reynolds numbers is the selection of an appropriate turbulence model for the steady Reynolds Averaged Navier–Stokes equations (RANS) equations. In this investigation, the performance of several turbulence models was explored for the simulation of steady, compressible, turbulent flow on complex geometries (concave and convex surface curvatures) and unstructured grids. The turbulence models considered were the Spalart–Allmaras model, the Wilcox k- ω model and the Menter shear stress transport (SST) model. The FLITE3D flow solver was employed, which utilizes a stabilized finite volume method with discontinuity capturing. A numerical benchmarking of the different models was performed for classical Computational Fluid Dynamic (CFD) cases, such as supersonic flow over an isothermal flat plate, transonic flow over the RAE2822 airfoil, the ONERA M6 wing and a generic F15 aircraft configuration. Validation was performed by means of available experimental data from the literature as well as high spatial/temporal resolution Direct Numerical Simulation (DNS). For attached or mildly separated flows, the performance of all turbulence models was consistent. However, the contrary was observed in separated flows with recirculation zones. Particularly, the Menter SST model showed the best compromise between accurately describing the physics of the flow and numerical stability.
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Karbasian, H. R., S. A. Moshizi und M. J. Maghrebi. „Dynamic Stall Analysis of S809 Pitching Airfoil in Unsteady Free Stream Velocity“. Journal of Mechanics 32, Nr. 2 (18.09.2015): 227–35. http://dx.doi.org/10.1017/jmech.2015.72.
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AbstractIn this paper, the dynamic stall of S809 airfoil that widely used in horizontal axis wind turbine, in different reduced frequencies is investigated. The simulation was carried out numerically handling Navier-Stokes equations. For this purpose, the segregated solver with SIMPLE algorithm was chosen to solve the momentum equations. The effect of turbulence on the flow field is taken into account using Shear Stress Transport (SST) K-ω turbulence model. The obtained numerical results are compared with experimental and a few numerical results. The results indicate that the K-ω SST model is in good agreement with experimental results for both steady and unsteady conditions. Furthermore, a non-dimensional parameter, relating the acceleration of unsteady free stream velocity and acceleration of pitch motion (known as reduced frequency), is also investigated. In addition, the results show that any increase in the reduced frequency increases the instantaneous aerodynamic characteristics of oscillating airfoil.
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Kamran, Ahmad, Zhi Gang Wu und Muhammad Amjad Sohail. „CFD Analysis of Oscillating Airfoil during Pitch Cycle“. Applied Mechanics and Materials 152-154 (Januar 2012): 906–11. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.906.
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This research paper presents the CFD analysis of oscillating airfoil during pitch cycle. Unsteady subsonic flow is simulated for pitching airfoil at Mach number 0.283 and Reynolds number 3.45 millions. Turbulent effects are also considered for this study by using K-ω SST turbulent model. Two-dimensional unsteady compressible Navier-Stokes code including two-equation turbulence model and PISO pressure velocity coupling is used. Pressure based implicit solver with first order implicit unsteady formulation is used. The simulated pitch cycle results are compared with the available experimental data.
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Gopalakrishnan, Raj, und Peter Disimile. „CFD Analysis of Twin Turbulent Impinging Round Jets at Different Impingement Angles“. Fluids 3, Nr. 4 (23.10.2018): 79. http://dx.doi.org/10.3390/fluids3040079.
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Round jets impinging at multiple impingement angles were considered for this study to gain better understanding of the parameters affecting resultant jet growth and velocity distribution. Work done by the authors previously on single jet has helped to establish that the SST (Shear Stress Transport) k-ω model is the ideal turbulence model for predicting flow characteristics of jets exiting a fully developed pipe at low Reynolds number. Hence, for the study of impinging jets, SST k-ω turbulence model was used to study the velocity and jet growth characteristics. Based on the mesh obtained from the grid sensitivity study, jets impinging at 30, 45 and 60 degrees at Reynolds number of 7500 were numerically analyzed. It was observed that the profile of the resultant jet closely matched with the prediction of elliptical profile predicted by past researchers. In addition, it was seen that higher jet growth was predicted in the case of jets impinging at a higher impingement angle.
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Hamdani, Ari, Satoshi Abe, Masahiro Ishigaki, Yasuteru Sibamoto und Taisuke Yonomoto. „Unsteady Natural Convection in a Cylindrical Containment Vessel (CIGMA) With External Wall Cooling: Numerical CFD Simulation“. Energies 13, Nr. 14 (15.07.2020): 3652. http://dx.doi.org/10.3390/en13143652.
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In the case of a severe accident, natural convection plays an important role in the atmosphere mixing of nuclear reactor containments. In this case, the natural convection might not in the steady-state condition. Hence, instead of steady-state simulation, the transient simulation should be performed to understand natural convection in the accident scenario within a nuclear reactor containment. The present study, therefore, was aimed at the transient 3-D numerical simulations of natural convection of air around a cylindrical containment with unsteady thermal boundary conditions (BCs) at the vessel wall. For this purpose, the experiment series was done in the CIGMA facility at Japan Atomic Energy Agency (JAEA). The upper vessel or both the upper vessel and the middle jacket was cooled by subcooled water, while the lower vessel was thermally insulated. A 3-D model was simulated with OpenFOAM®, applying the unsteady Reynolds-averaged Navier–Stokes equations (URANS) model. Different turbulence models were studied, such as the standard k-ε, standard k-ω, k-ω shear stress transport (SST), and low-Reynolds-k-ε Launder–Sharma. The results of the four turbulence models were compared versus the results of experimental data. The k-ω SST showed a better prediction compared to other turbulence models. Additionally, the accuracy of the predicted temperature and pressure were improved when the heat conduction on the internal structure, i.e., flat bar, was considered in the simulation. Otherwise, the predictions on both temperature and pressure were underestimated compared with the experimental results. Hence, the conjugate heat transfer in the internal structure inside the containment vessel must be modeled accurately.
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Weaver, Dustin Steven, und Sanja Mišković. „A Study of RANS Turbulence Models in Fully Turbulent Jets: A Perspective for CFD-DEM Simulations“. Fluids 6, Nr. 8 (31.07.2021): 271. http://dx.doi.org/10.3390/fluids6080271.
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This paper presents an analysis of linear viscous stress Favre averaged turbulence models for computational fluid dynamics (CFD) of fully turbulent round jets with a long straight tube geometry in the near field. Although similar work has been performed in the past with very relevant solutions, considerations were not given for the issues and limitations involved with coupling between an Eulerian and Lagrangian phase, such as in fully two-way coupled CFD-DEM. These issues include limitations on solution domain, mesh cell size, wall modelling, and momentum coupling between the two phases in relation to the particles size. Therefore, within these considerations, solutions are provided to the Navier–Stokes equations with various turbulence models using a three-dimensional wedge long straight tube geometry for fully developed turbulence flow. Simulations are performed with a Reynolds number of 13,000 and 51,000 using two different tube diameters. It is found that a modified k-ε turbulence model achieved the most agreeable results for both the velocity and turbulent flow fields between these two flow regimes, while a modified k-ω SST/BSL also provided suitable results.
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Algieri, Angelo, Sergio Bova, Carmine De Bartolo und Alessandra Nigro. „Numerical and Experimental Analysis of the Intake Flow in a High Performance Four-Stroke Motorcycle Engine: Influence of the Two-Equation Turbulence Models“. Journal of Engineering for Gas Turbines and Power 129, Nr. 4 (24.01.2007): 1095–105. http://dx.doi.org/10.1115/1.2719265.
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An experimental and numerical analysis of the intake system of a production high performance four-stroke motorcycle engine was carried out. The aim of the work was to characterize the fluid dynamic behavior of the engine during the intake phase and to evaluate the capability of the most commonly used two-equation turbulence models to reproduce the in-cylinder flow field for a very complex engine head. Pressure and mass flow rates were measured on a steady-flow rig. Furthermore, velocity measurements were obtained within the combustion chamber using laser Doppler anemometry (LDA). The experimental data were compared to the numerical results using four two-equation turbulence models (standard k-ε, realizable k-ε, Wilcox k-ω, and SST k-ω models). All the investigated turbulence models well predicted the global performances of the intake system and the mean flow structure inside the cylinder. Some differences between measurements and computations were found close to the cylinder head while an improving agreement was evident moving away from the engine head. Furthermore, the Wilcox k-ω model permitted the flow field inside the combustion chamber of the engine to be reproduced and the overall angular momentum of the flux with respect to the cylinder axis to be quantified more properly.
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Et.al, Ki-Hyuk Yang. „Numerical Simulation Of Supersonic Compression Ramp Flow“. Turkish Journal of Computer and Mathematics Education (TURCOMAT) 12, Nr. 6 (11.04.2021): 812–21. http://dx.doi.org/10.17762/turcomat.v12i6.2101.
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Shock wave/boundary layer interaction (SWBLI) is a highly critical problem that occurs in aircraft in transonic or supersonic flow. This study performed CFD analysis of the supersonic ramp flow of freestream Mach number 2.79. To secure reliability of the CFD analysis, adaptive mesh refinement using a gradient p sensor was used. Through this, a grid of sufficient resolution was obtained for the region of shock wave, expansion wave, and flow separation. The prediction performance of 7 turbulence models that are widely used in engineering application were compared. The baseline k–ω two-equation model showed the best prediction performance, while the SST k–ω model, which is one of the most widely used two-equation models, and the 2 Reynolds stress models showed relatively poor prediction performance. In the SWBLI problem, the use of adaptive mesh refinement made it possible to secure sufficient grid resolution; meanwhile, comparison of the prediction performance of the various turbulence models confirmed that for the SWBLI problem, the generally used turbulence model was somewhat inappropriate.
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Domfeh, Martin Kyereh, Samuel Gyamfi, Mark Amo-Boateng, Robert Andoh, Eric Antwi Ofosu und Gavin Tabor. „Numerical Simulation of an Air-Core Vortex and Its Suppression at an Intake Using OpenFOAM“. Fluids 5, Nr. 4 (26.11.2020): 221. http://dx.doi.org/10.3390/fluids5040221.
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A common challenge faced by engineers in the hydraulic industry is the formation of free surface vortices at pump and power intakes. This undesirable phenomenon which sometimes entrains air could result in several operational problems: noise, vibration, cavitation, surging, structural damage to turbines and pumps, energy losses, efficiency losses, etc. This paper investigates the numerical simulation of an experimentally observed air-core vortex at an intake using the LTSInterFoam solver in OpenFOAM. The solver uses local time-stepping integration. In simulating the air-core vortex, the standard k − ε, realizable k − ε, renormalization group (RNG) k − ε and the shear stress transport (SST) k − ω models were used. The free surface was modelled using the volume of fluid (VOF) model. The simulation was validated using a set of analytical models and experimental data. The SST k − ω model provided the best results compared to the other turbulence models. The study was extended to simulate the effect of installing an anti-vortex device on the formation of a free surface vortex. The LTSInterFoam solver proved to be a reliable solver for the steady state simulation of a free surface vortex in OpenFOAM.
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Matyushenko, A. A., und A. V. Garbaruk. „Adjustment of the k-ω SST turbulence model for prediction of airfoil characteristics near stall“. Journal of Physics: Conference Series 769 (November 2016): 012082. http://dx.doi.org/10.1088/1742-6596/769/1/012082.
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Li, Yuan, Zengjin Xu, Zuoxia Xing, Bowen Zhou, Haoqian Cui, Bowen Liu und Bo Hu. „A Modified Reynolds-Averaged Navier–Stokes-Based Wind Turbine Wake Model Considering Correction Modules“. Energies 13, Nr. 17 (27.08.2020): 4430. http://dx.doi.org/10.3390/en13174430.
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Increasing wind power generation has been introduced into power systems to meet the renewable energy targets in power generation. The output efficiency and output power stability are of great importance for wind turbines to be integrated into power systems. The wake effect influences the power generation efficiency and stability of wind turbines. However, few studies consider comprehensive corrections in an aerodynamic model and a turbulence model, which challenges the calculation accuracy of the velocity field and turbulence field in the wind turbine wake model, thus affecting wind power integration into power systems. To tackle this challenge, this paper proposes a modified Reynolds-averaged Navier–Stokes (MRANS)-based wind turbine wake model to simulate the wake effects. Our main aim is to add correction modules in a 3D aerodynamic model and a shear-stress transport (SST) k-ω turbulence model, which are converted into a volume source term and a Reynolds stress term for the MRANS-based wake model, respectively. A correction module including blade tip loss, hub loss, and attack angle deviation is considered in the 3D aerodynamic model, which is established by blade element momentum aerodynamic theory and an improved Cauchy fuzzy distribution. Meanwhile, another correction module, including a hold source term, regulating parameters and reducing the dissipation term, is added into the SST k-ω turbulence model. Furthermore, a structured hexahedron mesh with variable size is developed to significantly improve computational efficiency and make results smoother. Simulation results of the velocity field and turbulent field with the proposed approach are consistent with the data of real wind turbines, which verifies the effectiveness of the proposed approach. The variation law of the expansion effect and the double-hump effect are also given.
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Richardson, G., und N. Qin. „An eddy-viscosity limited algebraic stress model for shock-boundary-layer interaction“. Aeronautical Journal 105, Nr. 1045 (März 2001): 105–18. http://dx.doi.org/10.1017/s0001924000092022.
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Abstract This paper presents a μt-limited explicit algebraic stress model for shock-wave-turbulent boundary-layer interactions based on an investigation of various two-equation turbulence models. The results of the κ-ω model, the shear stress transport (SST) model, and a quadratic explicit algebraic stress model are presented and analysed for the Delery channel bump, and the Bachalo and Johnson axisym-metric bump test cases. While the κ-ω model failed to give good predictions, the SST model proved reasonably successful in predicting strong interaction problems. The non-linear quadratic explicit algebraic stress model gave improved results (when compared with the original κ-ω model) for the channel bump test cases, but was not as good as the SST model. Inspired by this investigation, a model formulation is proposed in which Bradshaw's assumption for eddy-viscosity limiting (as used in the SST model) is applied to a quadratic explicit algebraic stress model. The QSST model further improves the SST model for strong shock-boundary-layer interactions.
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Lin, Jinghua, You-Lin Xu, Yong Xia und Chao Li. „Structural Analysis of Large-Scale Vertical-Axis Wind Turbines, Part I: Wind Load Simulation“. Energies 12, Nr. 13 (04.07.2019): 2573. http://dx.doi.org/10.3390/en12132573.
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When compared with horizontal-axis wind turbines, vertical-axis wind turbines (VAWTs) have the primary advantages of insensitivity to wind direction and turbulent wind, simple structural configuration, less fatigue loading, and easy maintenance. In recent years, large-scale VAWTs have attracted considerable attention. Wind loads on a VAWT must be determined prior to structural analyses. However, traditional blade element momentum theory cannot consider the effects of turbulence and other structural components. Moreover, a large VAWT cannot simply be regarded as a planar structure, and 3D computational fluid dynamics (CFD) simulation is computationally prohibitive. In this regard, a practical wind load simulation method for VAWTs based on the strip analysis method and 2D shear stress transport (SST) k-ω model is proposed. A comparison shows that the wind pressure and aerodynamic forces simulated by the 2D SST k-ω model match well with those obtained by 2.5D large eddy simulation (LES). The influences of mean wind speed profile, turbulence, and interaction of all structural components are considered. A large straight-bladed VAWT is taken as a case study. Wind loads obtained in this study will be applied to the fatigue and ultimate strength analyses of the VAWT in the companion paper.