覆環式蒸汽渦輪機葉片之顫振分析

Flutter Analysis of Shrouded Steam Turbine Blades

張琳雅(Lin-Ya Chang)

指導教授 ： 蔣小偉

國立清華大學/工學院/動力機械工程學系/碩士(2009年)

摘要

渦輪機之轉子葉片可能有葉片振動的問題。通常由於顫振(flutter)，或是強制響應(forced response)所引起的過度振動，會造成葉片的損壞(failure)。葉片之設計通常採用覆環式(shrouded)，以提升轉子葉片的結構阻尼(structural damping)與強度。
本研究主要針對電廠渦輪機葉片之顫振現象進行分析。有鑑於日本濱岡與志賀機組發生疑似顫振現象，而台電龍門電廠之機組又與其同為先進沸水反應爐型(ABWR，Advanced Boiling Water Reactor)之核電廠，故針對此機組之葉片進行分析，並建立一套完整系統之研究方法，探討覆環式動葉片產生顫振之主要機制。首先要取得葉片的結構動態特性，估算葉片表面之流場，以計算出由於結構運動所產生的非穩定氣動力負載。由於覆環式的動葉片設計造成整體轉子呈現系統模態(system mode)運動，必須採用週期對稱方法(cyclic symmetry method)，再結合顫振分析系統，才能計算出整個覆環式動葉片系統之氣動力阻尼(aero damping)，以決定其顫振特性。
本研究分析的實例為電廠汽渦輪機之覆環式動葉片，其結構阻尼較日本濱岡與志賀機組為高。考慮不同參數之流場等對系統穩定性之影響。對於較複雜之模態，相較於單一葉片法，在某些情況下無法提供足夠判斷的依據之缺點，週期對稱方法可提供一個客觀且省時的結果，為一個有效的分析工具。而分析結果顯示葉片的振動模態、氣流特性與結構阻尼皆為影響顫振特性之重要因素，其中超音速流場系統出現不穩定之情形，葉片有斷裂之可能，操作時須避免此情況，以提高系統之安全性。

關鍵字

覆環葉片 ； 顫振 ； 複數模態 ； 氣彈力學 ； 週期對稱法

並列摘要

All the rotor blades in turbo-machinery, including turbojet engines and turbo-generators, have vibration problems. The blades are damaged because of vibrations caused by flutter or forced response. Generally, the shrouded design of the turbine blades is used to raise the structural damping and strength of the rotor blades. This research is primarily focused on vibration phenomenon of steam turbine’s shrouded rotor blades. Because the Hamoaka Nuclear Power Station No. 5 occurred some phenomenon like flutter, and the low pressure steam turbines of Hamoaka Nuclear Power Station No. 5 and Taipower’s Lung-Men Nuclear Power Plant Units 1&2 are both the Advanced Boiling Water Reactors, the research begin to analysis the rotor blades of the low pressure steam turbine. A complete system approach has been set up to study the main mechanism of shrouded rotor blade vibration. The research starts with the dynamic structural properties of the blades, the properties along with flow fields were used to calculate the unsteady steam load caused by structural movement. Because the design of shrouded rotor blades will cause the entire rotor into system mode shapes, it is necessary to use cyclic symmetry along with the modal flutter analysis system to calculate the aero damping of the shrouded dynamic blade system and to determine its flutter instability of the low pressure steam turbine of Taipower’s Lung-Men Nuclear Power Plant. This study will be based on a Taipower plant case to investigate the flutter boundary of steam turbine rotor blades under different operating conditions. However, for the bending and torsion combined system modes, the single mode analysis can be misleading. From the complex mode analyzed results, it was demonstrated that the mode shape, the characteristic of flow field, and the structural damping play an important role in determining the blade flutter stability. And there is flutter phenomenon in supersonic flow field, it may result in blades failure. So, it’s necessary to prevent this condition to improve the system safety.

並列關鍵字

shrouded rotor ； blade flutter ； complex mode ； turbo-machinery ； cyclic symmetry

參考文獻

[1] Srinivasan, A. V., 1997, “Flutter and Resonant Vibration Characteristics of Engine Blades,” ASME J. of Engineering for Gas Turbines and Power, Vol. 119, pp.742-775

[3] Kielb, R. E., 1998,“Unsteady Flows - An Aeroelastic Blade Design Perspective,” ERCOFTAC Turbomachinery Seminar and Workshop, Aussois, France

[5] Hodges, D. H., Pierce, G. A., 2002, “Introduction to Structural Dynamics and Aeroelasticity,” Cambridge University Press

[6] Chiang, H. D., Kielb, R. E., 1993, “An Analysis System for Blade Forced Response,” ASME Journal of Turbomachinery, Vol. 115, pp. 762-770.

[9] Armstrong, E.K., Stevenson, R.E., 1960, “Some practical aspects of compressor blade vibration,” Journal Royal Aeronautic Society, Vol. 64, p. 117f.