Calculation method of efficiency factor in Alford's force

The steam exciting force has been proved to be great threat to the operation safety of steam turbines. The mechanism of steam exciting vibration cannot be profoundly revealed by simply analyzing the steam exciting force, especially in simplified models. Therefore, a full-circle stage of steam turbine with shroud and labyrinth seals was investigated by numerical simulator CFX. The instability of leakage flow and the pressure fluctuation were analyzed on the eccentric condition. The effects of leakage vortexes, the depth-width ratio of seal cavity, and the eccentricity on the steam exciting force were studied. Results show that the leakage flow is nonuniform in the circumferential direction with the change of front teeth vortexes, which causes the steam exciting force. The tangential and radial steam exciting force both increase with the eccentricity increasing. The effects of the depth-width ratio of seal cavity on the two forces are different. In addition, the pressure fluctuation caused by the leakage vortexes on the shroud surfaces is a main factor inducing the steam exciting force. This research provides a theoretical guidance for the operation safety and optimization of steam turbines.

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“…Based on Alford's force formula in literature [24], can be written in the following generic equation:…”

Section: Resultsmentioning

confidence: 99%

Numerical Analysis on Steam Exciting Force Caused by Rotor Eccentricity

Cao

Wang

et al. 2017

Shock and Vibration

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“…The static eccentricity of a rotor model is calculated with a steady-state solver, in which the rotor only has rotational motion. The results show that the radial and tangential steam flow exciting forces on rotor increase with the increase of eccentricity [9] and [10]. The rotor dynamic coefficients have a nonlinear relationship with the eccentricity.…”

Section: Introductionmentioning

confidence: 92%

Dynamic Characteristics and Stability Prediction of Steam Turbine Rotor Based on Mesh Deformation

Cao

2020

SV-JME

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In order to study the steam flow excited vibration caused by the eccentricity of a rotor, three-dimensional rotor whirl motion is simulated based on mesh deformation. The mechanism of steam flow excited vibration and its influence on the dynamic characteristics of the rotor are investigated. The results show that the exciting forces change with the displacement of the rotor’s centre. Rotor dynamic coefficients are nonlinear when the rotor whirls pass the mesh deformation. The rotor dynamic coefficients and effective damping increase with the increase of whirl frequency. When the whirl frequency is 24.41 Hz, the rotor dynamic coefficients are strongly affected by rotational velocity. The maximum fluctuations of average direct stiffness, cross-coupling stiffness, direct damping and cross-coupling damping are 8.1 %, 113.2 %, 45.8 %, and 121.0 %, respectively. Effective damping fluctuates greatly when both whirl and rotational frequency are 24.41 Hz. The direct stiffness, direct damping, and effective damping increase with the increase of pressure ratio, which can improve rotor stability. The pressure fluctuation on the rotor’s surface is a primary reason for steam flow excited vibration. The stability margin of the rotor can be estimated precisely via effective damping.

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“…Chai turbine governing stage with partial admission [9]. Ding corrected the Alford equation and derived the efflciency coefficient equation in Alford force [10,11]. In the research on force performance of steam-flow-excited vibration, Li studied the resonance vibration of turbine caused by steam-flow-excited vibration in rotor system with labyrinth seal, and obtained the empirical parameters of Muszynska model and the system's dynamic sub-harmonic resonance response [12].…”

Section: Introductionmentioning

confidence: 99%

Catastrophe Performance Analysis of Steam-Flow-Excited Vibration in the Governing Stage of Large Steam Turbines With Partial Admission

Li¹,

Guo²,

Yu³

et al. 2013

Journal of Energy Resources Technology

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Steam-flow-excited vibration is one of the main faults of large steam turbines. The catastrophe caused by steam-flow-excited vibration brings danger to the operation of units. Therefore, it is signiflcant to Identify the impact factors of^ catastrophe, and master the rules of catastrophe. In this paper, the quantitative analysis of catastrophe performance induced by steam exciting force in the steam turbine governing stage is conducted based on the catastrophe theory, nonlinear vibration theory, and fluid dynamics. The model of steam exciting force in the condition of partial admission in the governing stage is derived. The nonlinear kinetic model of the governing stage with steam exciting force is proposed as well. The cusp catastrophe and bifurcation set of steam-flow-excited vibration are deduced. The rotational angular frequency, the eccentric distance and the opening degrees of the governing valves are identifled as the main impact factors to induce catastrophe. Then, the catastrophe performance analysis is conducted for a 300 MW subcritical steam turbine. The rules of catastrophe are discussed, and the system's catastrophe areas are divided. It is discovered that the system catastrophe will not occur until the impact factors satisfy given conditions. Finally, the numerical calculation method is employed to analyze the amplitude response of steam-flow-excited vibration. The results verify the correctness of the proposed analysis method based on the catastrophe theory. This study provides a new way for the catastrophe performance research of steam-flowexcited vibration in large steam turbines.

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Calculation method of efficiency factor in Alford's force

Cited by 8 publications

References 5 publications

Numerical Analysis on Steam Exciting Force Caused by Rotor Eccentricity

Numerical Analysis on Steam Exciting Force Caused by Rotor Eccentricity

Dynamic Characteristics and Stability Prediction of Steam Turbine Rotor Based on Mesh Deformation

Catastrophe Performance Analysis of Steam-Flow-Excited Vibration in the Governing Stage of Large Steam Turbines With Partial Admission

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