Numerical flow simulation and efficiency prediction for axial turbines by advanced turbulence models

Jošt, Dragica; Škerlavaj, A; Lipej, Andrej

doi:10.1088/1755-1315/15/6/062016

Cited by 12 publications

(11 citation statements)

References 5 publications

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“…The kε turbulence models are appropriate for flows characterized by high adverse pressure and intensive separation. This model allows for a more accurate near wall treatment with an automatic switch from wall function to low-Reynolds number formulation, based on grid spacing see [125][126][127][128].…”

Section: An Example Of Modeling Of Turbine Stage With Twisted Rotor Bmentioning

confidence: 99%

On Turbulence and its Effects on Aerodynamics of Flow through Turbine Stages

Ilieva¹

2017

Turbulence Modelling Approaches - Current State, Development Prospects, Applications

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In reality, the flows encountered in turbines are highly three-dimensional, viscous, turbulent, and often transonic. These complex flows will not yield to understanding or prediction of their behavior without the application of contemporary and strong modeling techniques, together with an adequate turbulence model, to reveal effects of turbulence phenomenon and its impact on flow past turbine blades. The discussion primarily targets the turbulence features and their impact on fluid dynamics; streaming of blades, and efficiency performance. Turbulence as a phenomenon, turbulence effects and the transition onset in turbine stages are discussed. Flow parameters distribution past turbine stages, approaches to turbulence modeling, and how turbulent effects change efficiency and require an innovative design, among others are presented. Furthermore, a comparison study regarding the application and availability of various turbulence models is fulfilled, showing that every aerodynamic effect, encountered of flow pass turbine blades can be predicted via different model. This work could be very helpful for researchers and engineers working on prediction of transition onset, turbulence effects, and their impact on the overall turbine performance.

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Section: An Example Of Modeling Of Turbine Stage With Twisted Rotor Bmentioning

confidence: 99%

On Turbulence and its Effects on Aerodynamics of Flow through Turbine Stages

Ilieva¹

2017

Turbulence Modelling Approaches - Current State, Development Prospects, Applications

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“…In [4] steady state analysis was done with several RANS turbulence models, such as the standard k-ε turbulence model, the Wilcox k-ω model, the Baseline (BSL) k-ω model, the SST model and the ε-based SSG RSM [6]. The best results, which were still rather poor at large discharge values, were obtained with SST and SSG RSM.…”

Section: Turbulence Models and Discretisation Schemesmentioning

confidence: 99%

“…For transient simulations besides SST, two scale-resolving simulation models (SAS SST and ZLES) were used. In [4] positive effects of curvature correction (CC) and Kato-Launder limiter of production term (KL) on accuracy of results were found, therefore both, CC and KL, were used in all simulations presented in this paper.…”

Section: Turbulence Models and Discretisation Schemesmentioning

confidence: 99%

“…Up to some point, the results were improved by mesh refinement in guide vane cascade and runner, because the original mesh was rather coarse with large values of y + . In a recent paper [4] about numerical simulations of a Kaplan turbine it was reported that steady state results obtained by various turbulence models (k-ε, k-ω, BSL, SST, SSG RSM) were very poor, while unsteady simulations considerably improved the accuracy of efficiency prediction. The best results were achieved using the zonal LES model, but even the prediction with the transient SST simulation was much better than the steady-state SST simulation.…”

Section: Introductionmentioning

confidence: 99%

“…At low head the inaccuracy is larger, especially at large runner blade angles and large discharge values. The purpose of this paper is to extend the conclusions for Kaplan turbines presented in [4] to bulb turbines and to check the influence of mesh refinement and the effect of the advection scheme on the results. The accuracy of numerical prediction is most critical at low head and therefore a 3-blade bulb turbine which operates at extremely low head was chosen as a test case.…”

Section: Introductionmentioning

confidence: 99%

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Efficiency prediction for a low head bulb turbine with SAS SST and zonal LES turbulence models

Jošt¹,

Škerlavaj²

2014

IOP Conf. Ser.: Earth Environ. Sci.

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View the article online for updates and enhancements. Abstract A comparison between results of numerical simulations and measurements for a 3-blade bulb turbine is presented in order to determine an appropriate numerical setup for accurate and reliable simulations of flow in low head turbines. Numerical analysis was done for three angles of runner blades at two values of head. For the smallest blade angle the efficiency was quite accurately predicted, but for the optimal and maximal blade angles steady state analysis entirely failed to predict the efficiency due to underestimated torque on the shaft and incorrect results in the draft tube. Transient simulation with SST did not give satisfactory results, but with SAS and zonal LES models the prediction of efficiency was significantly improved. From the results obtained by SAS and zonal LES the interdependence between turbulence models, vortex structures in the flow, values of eddy viscosity and flow energy losses in the draft tube can be seen. Also the effect of using the bounded central differential scheme instead of the high resolution scheme was evident. To test the effect of grid density, simulations were performed on four grids. While a difference between results obtained on the basic grid and on the fine grid was small, the results obtained on the coarse grids were not satisfactory. IntroductionFor turbines with small pressure head, such as Kaplan and especially bulb turbines, an accurate simulation of flow in a draft tube is more important for accuracy of efficiency prediction than for Francis turbines. In years 1999, 2001 and 2005 three workshops "Turbine-99" were performed with the aim to gain the knowledge how to perform trustworthy simulations of Kaplan draft tubes. The experimental data was provided for a local best efficiency point, which was close to the best efficiency of the system. The inlet conditions were provided from experimental measurements by the laser Doppler velocimetry (LDV) method. For all tested RANS models, including the SST model, the predicted secondary flow was too weak [1]. The best results were obtained by Kurosawa and Nakamura [2] using the dynamic Smagorinsky LES model. Apart from the Turbine-99 workshops, some other published results outlined the problem of accurate predictions in Kaplan and bulb turbines. In a review paper [3] a steady-state prediction of efficiency of an axial turbine with the SST model was presented. The discrepancy between numerical and experimental values was increasing with rise of runner blade angle. Up to some point, the results were improved by mesh refinement in guide vane cascade and runner, because the original mesh was rather coarse with large values of y + . In a recent paper [4] about numerical simulations of a Kaplan turbine it was reported that steady state results obtained by various turbulence models (k-ε, k-ω, BSL, SST, SSG RSM) were very poor, while unsteady simulations considerably improved the accuracy of efficiency prediction. The best results were achieved using the zonal LES model, b...

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