Fast Prediction Method of Instability Limit of Steam Turbine Rotor System Based on Shroud Zero Damping

Abstract

This disclosure discloses a fast prediction method for the instability limit of a steam turbine rotor system based on shroud zero damping. By establishing a three-dimensional geometric model of the steam turbine rotor system, the modal analysis module and the transient response analysis module of the finite element software are used to obtain the maximum vibration of the system. The adjacent peak value of the transient displacement response of the blade is read from the displacement response curve (A 1 、A 2 ), calculate the logarithmic damping δ and damping ratio ξ of the rotor system considering the shroud friction under the rotational speed and harmonic excitation loads of each order, and quantitatively calculate the shroud damping C at different speeds s . The present invention uses the FFT multi-harmonic balance method to extend the existing modeling of the surrounding band damping considering the influence of the simple harmonic excitation and the quantitative solution method based on the envelope of the transient response to the multi-frequency excitation. The operation process is clear and the calculation is simple. It has high efficiency, provides theoretical basis and methods for the design and manufacture of steam turbine rotor system, and has important theoretical significance and engineering application value for ensuring the safe operation of steam turbines.

Description

technical field [0001] The disclosure relates to the field of steam turbine rotor stability prediction, in particular to a fast prediction method for instability limit of a steam turbine rotor system based on shroud zero damping. Background technique [0002] The statements in this section merely mention background art related to the present disclosure and do not necessarily constitute prior art. [0003] The large steam turbine rotor system has complex structural features such as heavy duty, long shafting, large-size flexible blades and shrouds. The operating speed is usually above the critical speed of the first to second order. During operation, the large flexible blades are prone to bending and torsional vibration and casing Rubbing will seriously endanger the safe and stable operation and service life of the entire unit. There are many cases in domestic and foreign power plants that the unit shut down due to blade vibration failure and caused huge losses. At present, ...

AI Technical Summary

Problems solved by technology

However, the inventors of this patent have found through in-depth research that the final stage blades of the low-pressure rotor of large-scale nuclear / thermal power steam turbines in actual operation are in wet steam, and they are subjected to more complex fluid multi-frequency excitations in addition to the simple harmonic excitation related to the rotor speed. However, the vibration of the shroud driven by blades under multi-frequency excitation is far more complex than that of single harmonic excitation. According to the generation of friction damping and vibration suppression mechanism of the shroud: the vibration of the blade under the multi-frequency excitation of fluid such as wet steam drives the movement of the shroud to make adjacent The friction of the shroud contact surface produces energy consumption and vibration suppression, that is, the shroud damping mainly depends on the vibration response of the blade under the excitation of the actual operation, which has a significant excitation-dependent nonlinearity. Under the multi-frequency excitation of fluid such as wet steam The impact of the vibration response on the shroud damping cannot be ignored, and the design of the shroud structure of the blade shroud of a large steam turbine unit using the existing technology such as the quantitative calculation method of the shroud damping induced by a single harmonic excitation will lead to excessive errors due to serious deviations from the actual working conditions , but at present, due to the limitation of the technical level of the test, neither the field test nor the laboratory test can accurately obtain the damping of the shroud and the entire rotor system (including rotating parts such as shafts, blades, shrouds, and bearing supports, hereinafter referred to as the rotor system). characteristics, the lack of shroud damping calculation methods and instability limit prediction methods that can consider the influence of multi-frequency excitation of fluids such as wet steam has become a bottleneck that seriously affects the design quality of steam turbines and their key components, resulting in safety hazards such as operational instability. In the first stage, it is possible to accurately design the shroud structure and its damping characteristics, predict whether the shroud can play the expected role of damping, suppressing vibration and increasing stability under multi-frequency excitation in actual operation, and establish a rotor system instability suitable for the characteristics of large steam turbine units with shrouds The limit rapid prediction method has important theoretical significance and engineering application value

Images