Numerical simulation of steady cavitating flow of viscous fluid in a Francis hydroturbine

Panov, L. V.; Чирков, Д. В.; Cherny, S. G.; Pylev, I. M.; Sotnikov, Artem

doi:10.1134/s0869864312030079

Cited by 15 publications

(7 citation statements)

References 4 publications

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“…The same blade cavitation also governs the breathing motion of the cavitation vortex rope through a variation of the flow swirl. The corresponding cavities on the blades start developing at stable conditions and are growing with a decreasing cavitation number, which is confirmed numerically and experimentally in other machines for similar operating conditions [5]. Several efforts have been undertaken to simulate full-load pressure surge analytically and numerically.…”

Section: Introductionsupporting

confidence: 54%

U-RANS Simulations and PIV Measurements of a Self-excited Cavitation Vortex Rope in a Francis Turbine

Decaix

Müller

Favrel

et al. 2018

Advances in Hydroinformatics

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In the course of the massive penetration of alternative renewable energies, the stabilization of the electrical power network significantly relies on the off-design operation of turbines and pump-turbines in hydropower plants. The occurrence of cavitation is however a common phenomenon at such operating conditions, often leading to critical flow instabilities, which undercut the grid stabilizing capacity of the power plant. In order to predict and extend the stable operating range of hydraulic machines, a better understanding of the cavitating flows and mainly of the transition between stable and unstable flow regimes is required. In the case of Francis turbines operating at full load, an axisymmetric cavitating vortex rope develops at the outlet runner in the draft tube. The cavity may enter self-oscillation, with violent periodic pressure pulsations propagating throughout the entire hydraulic system. The flow fluctuations lead to dangerous electrical power swings and mechanical vibrations through a fluid-structure coupling across the runner, imposing an inconvenient and costly restriction of the operating range.The paper deals with a numerical and experimental investigation of the transition from a stable to an unstable operating point on a reduced scale model of a Francis turbine at full load. Unsteady homogeneous two-phase RANS simulations are carried out using the ANSYS CFX solver. Cavitation is modelled using the Zwart's model that required solving an additional transport equation for the void fraction. Turbulence is solved using the SST k-ω model. Simulations are compared with the experimental measurements and some insights are provided for a first comprehensive analysis of the transition between the stable and unstable states.

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Section: Introductionsupporting

confidence: 54%

U-RANS Simulations and PIV Measurements of a Self-excited Cavitation Vortex Rope in a Francis Turbine

Decaix

Müller

Favrel

et al. 2018

Advances in Hydroinformatics

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“…Numerical method for the solution of 1D-3D governing equations is described in detail in [8,10]. As in [8], periodic stage approach is used for distributor and runner domains.…”

Section: Figure 3 Mesh For the Turbine Domainmentioning

confidence: 99%

Towards numerical simulation of high part load pulsations in Francis turbines

Чирков

Shcherbakov

Skorospelov

et al. 2022

IOP Conf. Ser.: Earth Environ. Sci.

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One of the most interesting operating points of Francis turbines is the high part load point, which is characterized by synchronous pressure pulsations of large amplitude. Physical mechanisms of these pulsations are not well understood. Experimental observations show that the frequency of the pulsations is 1.5 to 4 times higher than the runner rotation frequency and there exists a 180 degree phase shift of pressure signal measured in the spiral casing and in the draft tube. Numerical modeling this operating point is challenging as it has to account several complex phenomena: cavitation, rotating vortex rope and interaction of the turbine flow with the whole water system of the test rig. In the present paper we carried out a series of 1D-3D calculations of a model turbine in an attempt to simulate the high part load pulsations. 1D hydro-acoustic equations were used for the upstream waterways, while 3D Reynolds averaged Navier-Stokes model of two-phase mixture was used for the turbine. Although the main factors were taken into account, these computations were not able to capture the high part load pulsations. Namely, the frequency and amplitude of the pressure pulsations were significantly lower than those in the experiment, and there was no phase shift in turbine domain. In order to investigate the shortcomings of the present model, we considered a problem of propagation of disturbances in two-phase “liquid-gas” flows. Several 2D test cases were numerically investigated using both incompressible and compressible gaseous phase model. It was shown that in the absence of phase transfer the compressible model correctly represents the speed of sound in both homogeneous and stratified flow regimes. From the other hand, in case of phase transfer the model damps out propagation of pressure disturbances in upstream direction. This behavior explains the failure of the present 1D-3D model to correctly describe the acoustic properties of the two-phase flow in the draft tube, playing a crucial role in the development of high part load pulsations.

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“…In the first approach, the flow in the turbine was simulated using 3D steady-state incompressible RANS equations with k-ε turbulence model. In the second approach cavitation phenomena were simulated using homogeneous "liquid-vapor" mixture model [1]. As such a model Favre averaged Navier-Stokes equations governing the motion of isothermal compressible mixture are used.…”

Section: Problem Setup and Computational Approachmentioning

confidence: 99%

“…A priory, the discharge is not known and is determined in the course of solution. Such an approach was used by the authors for simulation of the single-phase incompressible and two-phase cavitating flows in turbine flow passages [1,4,5,6]. In the inlet of the distributor total flow energy Ein (equivalent to total pressure) and flow angle are kept constant.…”

Section: Boundary Conditionsmentioning

confidence: 99%

Prediction of Runaway Characteristics of Kaplan Turbines Using CFD Analysis

Semenova¹,

Чирков

Ustimenko³

2021

E3S Web Conf.

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In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. Prediction of the runaway speed at the stage of runner design would allow to select a runner considering this characteristic. Given in this paper is the numerical prediction of the runaway speed for a Kaplan turbine. Two approaches for numerical simulation were discussed. In the first one, the flow in the turbine flow passage was simulated using 3-D RANS equations of incompressible fluid using k-ε turbulence model. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. CFD calculations were carried out with using CADRUN flow solver. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.

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Numerical simulation of steady cavitating flow of viscous fluid in a Francis hydroturbine

Cited by 15 publications

References 4 publications

U-RANS Simulations and PIV Measurements of a Self-excited Cavitation Vortex Rope in a Francis Turbine

U-RANS Simulations and PIV Measurements of a Self-excited Cavitation Vortex Rope in a Francis Turbine

Towards numerical simulation of high part load pulsations in Francis turbines

Prediction of Runaway Characteristics of Kaplan Turbines Using CFD Analysis

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