Numerical Study of Pump-Turbine Instabilities Under Pumping Mode Off-Design Conditions

Ješe, Uroš; Patella, Régiane Fortes; Dular, Matevž

doi:10.1115/ajkfluids2015-33501

Cited by 19 publications

(15 citation statements)

References 11 publications

(14 reference statements)

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“…Detailed information about the main parameters is listed in Table 1. In 2015, Ješe also talked about the existence of a hysteresis phenomenon in pump-turbines in his doctoral thesis [13], however he did not carry out any related studies on formation mechanism of the hysteresis characteristic.…”

Section: Pump-turbine Specificationmentioning

confidence: 99%

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

Wang

Chen

et al. 2016

Energies

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Abstract:The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (n q = 36.1 min´1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04-0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

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Section: Pump-turbine Specificationmentioning

confidence: 99%

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

Wang

Chen

et al. 2016

Energies

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“…Euler momentum (Δcu·u) is a function of incidence angle (cu1) at the inlet and the deviation angle at the exit (cu2). (Δcu·u) can be determined by Equations (4) and (5). For the experimental method, Equation (4) gives an approximate value of Euler torque [16].…”

Section: Analysis Of Energy Dropmentioning

confidence: 99%

“…As a consequence, more and more researchers have focused on studies of the hump instability characteristic using experimental and numerical methods. The hump characteristic is mainly caused by the prerotation, recirculation [1], and suction surface cavitation [2] at the runner inlet, backflow and vortex motion [3], rotating stall [4,5], and secondary flow pattern [6] in the diffuser channels. Lots of achievements have been obtained, which provide a deep understanding of the hump characteristic.…”

Section: Introductionmentioning

confidence: 99%

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Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

Li¹,

Wang²,

Chen³

et al. 2016

Preprint

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The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

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“…However, these parameters are unknown before the pump-turbine is selected or the runner model test is carried out, and they are varying from hub to shroud when the operating point changes [38][39][40]. There are two solutions: first, collect the geometric dimensions of the runner of different specific speed pump-turbines and the flow angle with different operation conditions, including the guide vane height, runner diameter, blade angle, absolute flow angle and relative flow angle.…”

Section: Mathematical Modelmentioning

confidence: 99%

Prediction Method for the Complete Characteristic Curves of a Francis Pump-Turbine

Huang

Yang

Guo

et al. 2018

Water

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Abstract:Complete characteristic curves of a pump-turbine are essential for simulating the hydraulic transients and designing pumped storage power plants but are often unavailable in the preliminary design stage. To solve this issue, a prediction method for the complete characteristics of a Francis pump-turbine was proposed. First, based on Euler equations and the velocity triangles at the runners, a mathematical model describing the complete characteristics of a Francis pump-turbine was derived. According to multiple sets of measured complete characteristic curves, explicit expressions for the characteristic parameters of characteristic operating point sets (COPs), as functions of a specific speed and guide vane opening, were then developed to determine the undetermined coefficients in the mathematical model. Ultimately, by combining the mathematical model with the regression analysis of COPs, the complete characteristic curves for an arbitrary specific speed were predicted. Moreover, a case study shows that the predicted characteristic curves are in good agreement with the measured data. The results obtained by 1D numerical simulation of the hydraulic transient process using the predicted characteristics deviate little from the measured characteristics. This method is effective and sufficient for a priori simulations before obtaining the measured characteristics and provides important support for the preliminary design of pumped storage power plants.

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Numerical Study of Pump-Turbine Instabilities Under Pumping Mode Off-Design Conditions

Cited by 19 publications

References 11 publications

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

Prediction Method for the Complete Characteristic Curves of a Francis Pump-Turbine

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