Unsteady vortical flow simulation in a Francis turbine with special emphasis on vortex rope behavior and pressure fluctuation alleviation

Luo, Xianwu; Yu, An; Ji, Bin; Wu, Yulin; Tsujimoto, Yoshinobu

doi:10.1177/0957650917692153

Cited by 35 publications

(16 citation statements)

References 26 publications

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“…According to Hidalgo et al [4], the C p can be equal to −σ when p s achieves values of p v , which is observed in Figure 7 for ξ values among 0.2 and 0.8. However, the experimental study presents differences at (d) 0.9c due to the fact that C p is higher than −σ with more pulses than numerical results, which are related to the cavity collapse process [3]. For that, the k − ω SST SAS approach matched better the trend of the experimental results than ILES approach.…”

Section: Resultsmentioning

confidence: 76%

“…Studies of unsteady cavitating flow around hydrofoils are important to understand the cavitation dynamic behavior and its impact in hydraulic machinery [1,2]. Experimental studies have shown limitations such as: equipment uncertainty, costs and experiments calibration [3]. Therefore, CFD is an alternative way to study the aforementioned phenomenon based on numerical models [4].…”

Section: Introductionmentioning

confidence: 99%

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Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil

et al. 2019

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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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Section: Resultsmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil

et al. 2019

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“…Gao et al 23 and Gu et al 24 carried out experiments of pressure fluctuation measurements to get further insight into dynamic properties of the vortex in different cyclone separators. Luo et al 25 studied the variation of pressure fluctuation caused by vortex rope under different gas injection, and the air occupation at the draft tube center for the stable operation was proposed. However, certain unusual characteristics of pressure fluctuation induced by vortices are still to be solved urgently in the ultra-low specific-speed centrifugal pump with a complex vorticity field.…”

Section: Introductionmentioning

confidence: 99%

Pressure fluctuation–vortex interaction in an ultra-low specific-speed centrifugal pump

Wang

Zhang

et al. 2018

Journal of Low Frequency Noise, Vibration and Active Control

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To provide a comprehensive understanding of the pressure fluctuation-vortex interaction in non-cavitation and cavitation flow, in this article, the unsteady flow in an ultra-low specific-speed centrifugal pump was investigated by numerical simulation. The uncertainty of the numerical framework with three sets of successively refined mesh was verified and validated by a level of 1% of the experimental results. Then, the unsteady results indicate that the features of the internal flow and the pressure fluctuation were accurately captured in accordance with the closed-loop experimental results. The detailed pressure fluctuation at 16 monitoring points and the monitoring of the vorticity suggest that some inconsistent transient phenomena in frequency spectrums show strong correlation with the evolution of vortex, such as abnormal increasing amplitudes at the monitoring points near to the leading edge on the suction surface and the trailing edge on the pressure surface in the case of lower pressurization capacity of impeller after cavitation. Further analysis applies the relative vortex transport equation to intuitionally illustrate the pressure fluctuation-vortex interaction by the contribution of baroclinic torque, viscous diffusion and vortex convection terms. It reveals that the effect of viscous diffusion is weak when the Reynolds number is much greater than 1. Pressure fluctuation amplitude enlarges on the suction side of blade near to the leading edge due to the baroclinic torque in cavitation regions, whereas the abnormal increase of pressure fluctuation after cavitation on the pressure surface of blade approaching the trailing edge results from the vortex convection during vortices moving downstream with the decrease of available net positive suction head at the same instance.

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“…Cm is a coefficient related to the difference between the smallest and the averaged grid dimension depends on the ratio of grid dimension generated in each case of analysis. Table 1 shows a comparison with different Cm value for predicting hydraulic performance of a Francis turbine, whose geometry and performance are explained in the literature [14]. The data for numerical simulation are marked with "Num", and the tested data are marked with "Exp.".…”

Section: Turbulence Modelmentioning

confidence: 99%

“…Therefore, it is evident that PANS is suitable for predicting complex turbulence behavior of large scale unsteadiness. Though PANS shows excellent improvements to predict cavitating turbulent flows [14,15,16], there is no information regarding the prediction of liquid-solid two phase flow and sediment erosion by applying this method.…”

Section: Introductionmentioning

confidence: 99%

Sediment Erosion Prediction for a Francis Turbine Based on Liquid-Solid Flow Simulation Using Modified PANS

Cando¹,

Huang²,

Valencia³

et al. 2018

World Congress on Mechanical, Chemical, and Material Engineering

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A challenge in the prediction of the sediment erosion is the proper estimation of the motion and velocity of the solid particles, where Reynolds average Navier-Stokes (RANS) methods show limited resolution to determine the motion of solid phase affected by flow fluctuations. The present study adopts a modified partially averaged-Navier Stokes (PANS) method to analyse the sediment erosion prediction for Francis turbines. Numerical simulations were carried out to obtain liquid-solid two-phase flow information in entire flow passage of a Francis turbine using Eulerian-Lagrangrian approach. The hydraulic performance such as efficiency and discharge of the turbine achieved experimentally, are used to validate the present simulation method. The results show that the modified PANS model can improve the prediction accuracy and the smallest unresolved-to-total ratio of turbulence kinetic energy, fk, decided with the consideration of the difference between local average grid size and smallest grid size shows a slight accuracy improvement. Based on the two-phase flow field, sediment erosion was predicted in stay vane, guide vane and runner using a semi-empirical equation obtained from an erosion experiment of liquid-solid flow. It is noted that higher physical resolution captured by the turbulence model causes a diminution of the sediment erosion predicted. Further, the numerical simulation reveals that sediment erosion in stay vane is lower than guide vane and runner, whereas the highest values of the erosion intensity occurs in the runner. The sediment erosion due to fine solid particles in the turbine is mainly resulted from cutting. However, high sediment erosion due to deformation is also produced at the leading edges of stay vane and guide vane.

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Unsteady vortical flow simulation in a Francis turbine with special emphasis on vortex rope behavior and pressure fluctuation alleviation

Cited by 35 publications

References 26 publications

Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil

Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil

Pressure fluctuation–vortex interaction in an ultra-low specific-speed centrifugal pump

Sediment Erosion Prediction for a Francis Turbine Based on Liquid-Solid Flow Simulation Using Modified PANS

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