Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part I: Simulation of the Vortex Rope

Foroutan, Hosein; Yavuzkurt, Savas

doi:10.1115/1.4026817

Cited by 35 publications

(26 citation statements)

References 11 publications

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“…These pressure pulsations may be explained reasonably when a clear distinction between synchronous (axial) and asynchronous (radial) type pressure pulsations is made [7][8][9][10]. [11][12][13]; however, no study has been reported on the investigation of synchronous-and asynchronous-type pressure pulsations in prototypes. Measurements on the model turbines are not completely representative of the prototype and its dynamic behavior [11,[14][15][16][17].…”

Section: Introductionmentioning

confidence: 91%

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Trivedi

Gogstad

Dahlhaug

2018

Mechanical Systems and Signal Processing

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Hydropower is one of the most reliable renewable sources of electricity generation. With high efficiency and good regulating capacity, hydropower has the ability to meet rapid changes in power demand. Large investments in intermittent renewable energy resources have increased the demand for balancing power. This demand has pushed hydraulic turbines to generate electricity over the operating range from part load to full load. High-amplitude pressure pulsations are developed at off-design conditions, which cause moderate damage to the turbine components. The pressure pulsations may be either synchronous-(axial)-type, asynchronous-(rotating)-type or both. In this study, pressure measurements on low specific-speed prototype Francis turbines were performed; one of them was vertical axis and another was horizontal axis type. Four pressure sensors were mounted on the surface of the draft tube cone. Pressure measurements were performed at five operating points. The investigations showed that, in the vertical axis turbine, amplitudes of asynchronous pressure pulsations were 20 times larger than those of the synchronous component; whereas, in the horizontal axis turbine, amplitudes of asynchronous pressure pulsations were two times smaller than those of the synchronous component.

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Section: Introductionmentioning

confidence: 91%

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Trivedi

Gogstad

Dahlhaug

2018

Mechanical Systems and Signal Processing

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“…13, downward is positive and upward (reverse flow) is negative. As discussed by Foroutan and Yavuzkurt (2014a), the vortex rope forms due to the roll-up of the shear layer at the interface between the low-velocity inner region created by the wake of the crown cone and highly swirling outer flow. This low-velocity inner region (stagnant region) is clearly shown in Fig.…”

Section: Resultsmentioning

confidence: 97%

“…The simulation of a turbulent swirling flow, however, is a challenging task, and accurate numerical calculations of the flow parameters require a careful choice of turbulence closure method. Several previous turbulent swirling flow predictions have been carried out employing the steady Reynolds-averaged NavierStokes (RANS) equations with various turbulence closure models (Yaras and Grosvenor, 2003;Shamami and Birouk, 2008;Foroutan and Yavuzkurt, 2014a). A review of the literature reveals, however, that RANS turbulence models show inadequate performance in simulating highly swirling flows.…”

Section: Introductionmentioning

confidence: 98%

A partially-averaged Navier–Stokes model for the simulation of turbulent swirling flow with vortex breakdown

Foroutan

Yavuzkurt

2014

International Journal of Heat and Fluid Flow

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a b s t r a c tThis paper presents the development and validation of a new partially-averaged Navier-Stokes (PANS) model which can successfully predict turbulent swirling flow with vortex breakdown. The proposed PANS model uses an extended low Reynolds number k-e model as the baseline model. Furthermore, a new formulation for the unresolved-to-total turbulent kinetic energy ratio f k is developed using partial integration of the complete turbulence energy spectrum. Therefore, the present formulation of f k is believed to be superior to the previously used constant or computed values. The newly developed PANS model is used in unsteady numerical simulations of two turbulent swirling flows containing vortex breakdown, namely swirling flow through an abrupt expansion and flow in a draft tube of a hydraulic turbine operating under partial load. The present PANS model accurately predicts time-averaged and root-mean-square (rms) velocities in the case of the abrupt expansion, while it is shown to be superior to the Delayed Detached Eddy Simulation (DDES) and Shear Stress Transport (SST) k-x models. Predictions of the reattachment length using the present model shows at least 14% and 23% improvements compared to the DDES and the SST k-x models respectively. Also, transient features of the flow, e.g. vortex rope formation and precession, is well captured in the case of the complex draft tube flow. The frequency of the vortex rope precession, which causes severe fluctuations and vibrations, is well predicted by only 7% deviations from the experimental data.

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“…This condition may be satisfied in the low-frequency dynamic draft tube surge but not in the wake of the blade [2]. Foroutan and Yavuzkurt [9] studied a simplified draft tube of a model Francis turbine at part load and reported that unsteadiness of the vortex rope cannot be modeled by the URANS approach. Most of the turbulent structures occur in the draft tube for flows in hydro turbines operating at off-design.…”

Section: Introductionmentioning

confidence: 93%

Time-accurate Numerical Simulations of Swirling Flow with Rotor-stator Interaction

Javadi

Nilsson

2015

Flow Turbulence Combust

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A series of numerical simulations is undertaken to study a highly swirling turbulent flow generated by rotor-stator interaction in a swirl generator. The purpose is to assess the applicability of different turbulence models in swirling flow with a high level of unsteadiness and a significant production and dissipation of turbulence in the flow away from the wall. Nine turbulence models are compared: four high-Reynolds URANS, two low-Reynolds URANS and three hybrid URANS-LES. These are the standard k − , SST k − ω, realizable k − , RNG k − , Launder-Sharma k − , Lien-Cubic k − , delayed DES Spalart-Allmaras, DDES SST k − ω and improved DDES-SA. The URANS models are capable of capturing the main unsteady feature of this flow, the so-called helical vortex rope, which is formed by the strong centrifugal force and an on-axis recirculation region. However, the size of the on-axis recirculation region is overestimated by the URANS models. Although the low-Reynolds URANS formulations resolve the boundary layers in the runner and the draft tube more accurately, they still encounter difficulties in predicting the main flow features in the adverse pressure gradient in the draft tube. It is shown that a more detailed resolution, which is provided by the hybrid URANS-LES methods, is necessary to capture the turbulence and the coherent structures. The flow contains a strong disintegration of the vortex rope which is predicted well by the hybrid RANS-LES models. The hybrid methods also capture the blade wakes better than the other models, elucidating the wake interaction with the vortex rope. The frequency of the vortex rope is predicted well and the total turbulence (resolved and modeled), suggested by DDES-SA, corresponds reasonably well to the experimental results.

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Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part I: Simulation of the Vortex Rope

Cited by 35 publications

References 11 publications

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

A partially-averaged Navier–Stokes model for the simulation of turbulent swirling flow with vortex breakdown

Time-accurate Numerical Simulations of Swirling Flow with Rotor-stator Interaction

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