Adaptability of turbulence models to predict the performance and blade surface pressure prediction of a Francis turbine

2016 ◽  
Vol 33 (1) ◽  
pp. 238-251 ◽  
Author(s):  
WenRuo Zhu ◽  
ZhongXin Gao ◽  
YongJun Tang ◽  
JianGuang Zhang ◽  
Li Lu
Keyword(s):  
Flow Field ◽  
Turbulence Model ◽  
Prediction Accuracy ◽  
Turbulence Models ◽  
Francis Turbine ◽  
Blade Surface ◽  
Complex Flow ◽  
Content Type ◽  
Cfd Models ◽  
Turbine Performance

Purpose – The purpose of this paper is to analyze the ability of turbulence models to model the flow field in the runner of a Francis turbine. Although the complex flow in the turbine can be simulated by CFD models, the prediction accuracy still needs to be improved. The choice of the turbulence model is one key tool that affects the prediction accuracy of numerical simulations. Design/methodology/approach – This study used the SST k-w and RNG k-e turbulence models, which can both accurately predict complex flow fields in numerical simulations, to simulate the flow in the entire flow passage of a Francis turbine with the results compared against experimental data for the performance and blade pressure distribution in the turbine to evaluate the applicability of the turbulence models. Findings – The results show that the SST k-w turbulence model more accurately predicts the turbine performance than the RNG turbulence model. However, the blade surface pressures predicted by the SST k-w turbulence model were basically identical to those predicted by the RNG k-e turbulence model, with both accurately predicting the experimental data. Research limitations/implications – Due to the lack of space, the method used to measure the blade surface pressure distributions is not introduced in this paper. Practical implications – Turbine performance and flow field pressure in the runner, which are the basis of turbine preliminary performance judgment and optimization through CFD, can be used to judge the rationality of the turbine runner design. The paper provides an evidence for the turbulence selection in numerical simulation to predict turbine performance and flow field pressure in the runner and improves the CFD prediction accuracy. Originality/value – This paper fulfils a test of the flow field pressure in the runner, which provide an evidence for judge the adaptability of turbulence model on the flow field in runner. And this paper also provides important evaluations of two turbulence models for modeling the flow field pressure distribution in the runner of a Francis turbine to improve the accuracy of CFD models for predicting turbine performance.

Numerical analysis for wake flow field of Ahmed model based on a nonlinear-LRN/DES turbulence model

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Le Dian Zheng ◽  
Yi Yang ◽  
Guang Lin Qiang ◽  
Zhengqi Gu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Wake Flow ◽  
Field Analysis ◽  
Content Type ◽  
Des Model

Purpose This paper aims to propose a precise turbulence model for automobile aerodynamics simulation, which can predict flow separation and reattachment phenomena more accurately. Design/methodology/approach As the results of wake flow simulation with commonly used turbulence models are unsatisfactory, by introducing a nonlinear Reynolds stress term and combining the detached Eddy simulation (DES) model, this paper proposes a nonlinear-low-Reynolds number (LRN)/DES turbulence model. The turbulence model is verified in a backward-facing step case and applied in the flow field analysis of the Ahmed model. Several widely applied turbulence models are compared with the nonlinear-LRN/DES model and the experimental data of the above cases. Findings Compared with the experimental data and several turbulence models, the nonlinear-LRN/DES model gives better agreement with the experiment and can predict the automobile wake flow structures and aerodynamic characteristics more accurately. Research limitations/implications The nonlinear-LRN/DES model proposed in this paper suffers from separation delays when simulating the separation flows above the rear slant of the Ahmed body. Therefore, more factors need to be considered to further improve the accuracy of the model. Practical implications This paper proposes a turbulence model that can more accurately simulate the wake flow field structure of automobiles, which is valuable for improving the calculation accuracy of the aerodynamic characteristics of automobiles. Originality/value Based on the nonlinear eddy viscosity method and the scale resolved simulation, a nonlinear-LRN/DES turbulence model including the nonlinear Reynolds stress terms for separation and reattachment prediction, as well as the wake vortex structure prediction is first proposed.

Computational analysis of convective heat transfer properties of turbulent slot jet impingement

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Anuj Kumar Shukla ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
High Efficiency ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Complex Flow ◽  
Content Type

Purpose Convective heat transfer features of a turbulent slot jet impingement are comprehensively studied using two different computational approaches, namely, URANS (unsteady Reynolds-averaged Navier–Stokes equations) and SAS (scale-adaptive simulation). Turbulent slot jet impingement heat transfer is used where a considerable heat transfer enhancement is required, and computationally, it is a quite challenging flow configuration. Design/methodology/approach Customized OpenFOAM 4.1, an open-access computational fluid dynamics (CFD) code, is used for SAS (SST-SAS k-ω) and URANS (standard k-ε and SST k-ω) computations. A low-Re version of the standard k-ε model is used, and other models are formulated for good wall-refined calculations. Three turbulence models are formulated in OpenFOAM 4.1 with second-order accurate discretization schemes. Findings It is observed that the profiles of the streamwise turbulence are under-predicted at all the streamwise locations by SST k-ω and SST SAS k-ω models, but follow similar trends as in the reported results. The standard k-ε model shows improvements in the predictions of the streamwise turbulence and mean streamwise velocity profiles in the zone of outer wall jet. Computed profiles of Nusselt number by SST k-ω and SST-SAS k-ω models are nearly identical and match well with the reported experimental results. However, the standard k-ε model does not provide a reasonable profile or quantification of the local Nusselt number. Originality/value Hybrid turbulence model is suitable for efficient CFD computations for the complex flow problems. This paper deals with a detailed comparison of the SAS model with URANS and LES for the first time in the literature. A thorough assessment of the computations is performed against the results reported using experimental and large eddy simulations techniques followed by a detailed discussion on flow physics. The present results are beneficial for scientists working with hybrid turbulence models and in industries working with high-efficiency cooling/heating system computations.

Effect of RANS Method on the Stall Onset Prediction by an Eigenvalue Approach

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Zhe Xie ◽  
Yangwei Liu ◽  
Xiaohua Liu ◽  
Lipeng Lu ◽  
Xiaofeng Sun
Keyword(s):  
Flow Field ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Wake Flow ◽  
Spatial Discretization ◽  
Eigenvalue Approach ◽  
Trailing Edge ◽  
Transonic Compressor ◽  
Rans Simulation ◽  
Grid Independence

The eigenvalue approach is a recently developed compressor stability model used to predict stall onset. In this model, the flow field from a Reynolds-averaged Navier–Stokes (RANS) simulation provides the basic flow. This paper presents the effect of the RANS methods (including the computational grid, the turbulence model, and the spatial discretization scheme) on the eigenvalue and investigates the most influencing flow structures to the eigenvalue. The test compressor was the transonic compressor of NASA Rotor 37. Three individual meshes with different grid densities were used to validate the grid independence, and the results indicated that RANS simulation and eigenvalue calculation obtain grid independence at the same grid density. Then, the effect of four turbulence models (including Spalart–Allmaras (SA) turbulence model, two different k–ε models with the extended wall function model (EWFKE), and the Yang–Shih model (YSKE), and k–ω shear stress transport (SST) model), and three spatial discretization schemes (the central scheme, the flux difference splitting (FDS) scheme, and the symmetric total variation diminishing (STVD)) was also studied. Further investigation showed that the SA turbulence model combined with the STVD scheme provided the best stall point prediction, with a relative error of 0.05%. Detailed exploration of the three-dimensional flow field revealed that there were two flow patterns near the blade tip necessary for precisely predicting stall onset: the flow blockage generated by the shockwave-tip leakage vortex (TLV) interaction, and the trailing edge separation and corresponding wake flow. The effect of the blockage was greater than the effect of the trailing edge flow.

Numerical study of the flow field characteristics over a backward facing step using k-kl-ω turbulence model: comparison with different models

2018 ◽  
Vol 15 (1) ◽  
pp. 173-180 ◽  
Author(s):  
Yasser M. Ahmed ◽  
A.H. Elbatran
Keyword(s):  
Experimental Data ◽  
Fluid Mechanics ◽  
Turbulence Model ◽  
Flow Separation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Numerical Results ◽  
Backward Facing Step ◽  
Content Type ◽  
Case Comparison

Purpose This paper aims to investigate numerically the turbulent flow characteristics over a backward facing step. Different turbulence models with hybrid computational grid have been used to study the detached flow structure in this case. Comparison between the numerical results and the available experiment data is carried out in the present study. The results of the different turbulence models were in a good agreement with the experimental results. The numerical results also concluded that the k-kl-ω turbulence model gave favorable results compared with the experiment. Design/methodology/approach It is very important to study the flow characteristics of detached flows. Therefore, the current study investigates numerically the flow characteristics in backward facing step by using two-, three- and seven-equation turbulence models in the finite volume code ANSYS Fluent. In addition, hybrid grid has been used to improve the capability of the unstructured mesh elements for predicting the flow separation in this case. Comparison between the different turbulence models and the available experimental data was done to find the most suitable turbulence model for simulating such cases of detached flows. Findings The present numerical simulations with the different turbulence models predicted efficiently the flow characteristics over the backward facing step. The transition k-kl-ω gave the best acceptable results compared with experimental data. This is a good concluded remark in the fields of fluid mechanics and hydrodynamics because the phenomenon of flow separation is not easy to be predicted numerically and can affect greatly on the predicted drag of moving bodies in many engineering applications. Originality/value The CFD results of using different turbulence models have been validated with the experimental work, and the results of k-kl-ω proven acceptable with flow characteristics. The results of the current study conclude that the use of k-kl-ω turbulence model will contribute towards a more efficient utilization in the fields of fluid mechanics and hydrodynamics.

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

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

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

Experimental and Computational Comparisons of Fan-Shaped Film-Cooling on a Turbine Vane Surface

2005 ◽  
Author(s):  
W. Colban ◽  
K. A. Thole ◽  
M. Haendler
Keyword(s):  
Turbulence Model ◽  
Film Cooling ◽  
Turbulence Models ◽  
Complex Flow ◽  
Ir Camera ◽  
Turbine Engine ◽  
Film Cooling Effectiveness ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Film Cooling Holes

The flow exiting the combustor in a gas turbine engine is considerably hotter than the melting temperature of the turbine section components, of which the turbine nozzle guide vanes see the hottest gas temperatures. One method used to cool the vanes is to use rows of film-cooling holes to inject bleed air that is lower in temperature through an array of discrete holes onto the vane surface. The purpose of this study was to evaluate the row-by-row interaction of fan-shaped holes as compared to the performance of a single row of fan-shaped holes in the same locations. This study presents adiabatic film-cooling effectiveness measurements from a scaled-up, two-passage vane cascade. High resolution film-cooling measurements were made with an infrared (IR) camera at a number of engine representative flow conditions. Computational fluid dynamics (CFD) predictions were also made to evaluate the performance of some of the current turbulence models in predicting a complex flow such as turbine film-cooling. The RNG k-ε turbulence model gave a closer prediction of the overall level of film-effectiveness, while the v2-f turbulence model gave a more accurate representation of the flow physics seen in the experiments.

Research on Numerical Simulation Method for 3D Complex Flow in Rotating Machinery

2012 ◽  
Vol 226-228 ◽  
pp. 52-55
Author(s):  
Guang Yu Du ◽  
Zhen Tan ◽  
Wei An ◽  
De Сhun Ba
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Gas Flow ◽  
Turbulence Models ◽  
Simulation Method ◽  
Rotating Machinery ◽  
Field Analysis ◽  
Complex Flow ◽  
Structure Interaction ◽  
Numerical Simulation Method

A numerical simulation method with gas-structure interaction to analyze 3D complex flow in rotating machinery was presented and the effects with different aerodynamic turbulence model for gas-structure interaction was also presented. The blades are an important component in rotating machinery. Gas flow is unsteady three-dimensional turbulence motion with transient and anisotropic. Then the gas flow and the vibration of rotating blades interfere with each other, resulting in a complex coupling effect. It affects the machine efficiency directly. For discussing the effects on flow field of the coupling field, the blade model was built. And flow around the blades was simulated by gas-structure interaction with three turbulence models respectively. The turbulence models were standard κ-ε, renormalization group κ-ε and Smagorinsky LES. A feasible method was provided for flow field analysis in rotating machinery.

Numerical Investigation of a Transonic Centrifugal Compressor

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Seiichi Ibaraki
Keyword(s):  
Shock Waves ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Tip Clearance ◽  
Complex Flow ◽  
Low Velocity ◽  
Flow Measurements ◽  
Vaned Diffuser

A three-dimensional Navier-Stokes solver is used to investigate the flow field of a high-pressure ratio centrifugal compressor for turbocharger applications. Such a compressor consists of a double-splitter impeller followed by a vaned diffuser. The inlet flow to the open shrouded impeller is transonic, thus giving rise to interactions between shock waves and boundary layers and between shock waves and tip leakage vortices. These interactions generate complex flow structures which are convected and distorted through the impeller blades. Detailed laser Doppler velocimetry flow measurements are available at various cross sections inside the impeller blades highlighting the presence of low-velocity flow regions near the shroud. Particular attention is focused on understanding the physical mechanisms which govern the flow phenomena in the near shroud region. To this end numerical investigations are performed using different tip clearance modelizations and various turbulence models, and their impact on the computed flow field is discussed.

Influence of Turbulence Modelling on Predicting the Round Jet Flow Field: Technical Note

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
D. Hasen ◽  
S. Elangovan ◽  
M. Sundararaj ◽  
K.M. Parammasivam
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Flow Regime ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Technical Note ◽  
The Other ◽  
Round Jets ◽  
Mesh Density ◽  
Better Than

In this study, the effects of different turbulence models on the decay characteristics of round jets were studied. The turbulence models considered for the current study is SST, k-ε, k-ω, RNG kε. For the entire turbulence model mesh density and boundary conditions were mentioned same. By comparing the simulated results with the experiments interesting results were obtained. SST predicts the flow better than the other models in this flow regime.

Numerical Investigation of a Transonic Centrifugal Compressor

2006 ◽  
Author(s):  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Seiichi Ibaraki
Keyword(s):  
Shock Waves ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Tip Clearance ◽  
Complex Flow ◽  
Low Velocity ◽  
Flow Measurements

A three-dimensional Navier-Stokes solver is used to investigate the flow field of a high pressure ratio centrifugal compressor for turbocharger applications. Such a compressor consists of a double-splitter impeller followed by a vane diffuser. The inlet flow to the open shrouded impeller is transonic, thus giving rise to interactions between shock waves and boundary layers and between shock waves and tip leakage vortices. These interactions generate complex flow structures which are convected and distorted through the impeller blades. Detailed Laser Doppler Velocimetry (LDV) flow measurements are available at various cross sections inside the impeller blades highlighting the presence of low velocity flow regions near the shroud. Particular attention is focused on understanding the physical mechanisms which govern the flow phenomena in the near shroud region. To this end numerical investigations are performed using different tip clearance modelizations and various turbulence models, and their impact on the computed flow field is discussed.

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