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研究生:余培華
研究生(外文):Per-Wha Yih
論文名稱:Francis水輪機尾管穴蝕特性之研究
論文名稱(外文):Study on Cavitation Characteristics in Francis Turbine Draft-Tube
指導教授:郭正雄郭正雄引用關係
學位類別:碩士
校院名稱:國立中興大學
系所名稱:機械工程學系所
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2010
畢業學年度:98
語文別:中文
論文頁數:92
中文關鍵詞:水輪機穴蝕頻譜
外文關鍵詞:hydraulic turbinecavitationspectra
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摘要
本文主要是研究水輪機組尾管穴蝕的現象。安裝加速度規在一部出力67MW及另一部105MW的原型Francis水輪機組尾管人孔上方,分別在10個特定負載量進行振動訊號的量測,振動訊號均以FFT轉換頻譜;另以小波變換解析馬鞍機組時頻訊號,研究尾管穴蝕特性。另整理、分析水輪機峻工試驗、模型試驗、尾管水壓及電力脈動等測試報告,輔助說明量測結果。
研究結論為:(1)尾管穴蝕是由動輪葉尾流區的3個特徵結構產生,分別是:在低負載是大量的氣泡、在中負載是卡氏渦漩、在高負載時無明顯穴蝕現象,3者的頻率特徵均集中於3KHz,頻寬分佈在1KHz~5KHz之間;(2)在300Hz~500Hz有明顯且集中的訊號,推論是由動輪葉出口壓力脈動產生的週期訊號。(3)在40%~80%負載出力時,尾管渦帶的壓力脈動最嚴重;(4)經由中空軸的補氣機構,改變進氣量及補氣管長度可以降低渦帶的強度,但也因進氣量及補氣位置改變使低載穴蝕的強度增加。動輪冠下方安裝補氣管可以改善低載穴蝕,但會造成尾管流場紊亂,而且補氣管的尾流區產生嚴重的渦流及穴蝕。
關鍵字:水輪機、穴蝕、頻譜


Abstract
This study focuses on the cavitation detection in the draft tube of hydraulic turbines. One seismic transducers is installed on the 67MW and the other on the draft tube of a 105MW prototype Francis turbine to measure the structural vibration for ten varying loads. The signal is proceses via FFT and wavelet to analyze the spectra and the time-frequency characteristics. In additions, sorting the data from new Tienlun、Maan and Shihlin hydropower test records of Taiwan power company can help to illustrate the experimental results.
The experimental results show that:(1)The cavitation detected in the draft tube is caused by three different flow conditions from the runner impeller outlet. While the machine operates at low load , massive bubbles are produced. The Karman vortex cavitation is formed when operated at the middle load the middle load.And at high load, no obvious cavitation is observed. Their characteristic frequencies are concentrated around 3KHz with a frequency band ranging within 1 KHz ~5 KHz.(2)The signal frequency ranged within 300Hz~500 Hz is probably caused by the period pressure pulse induced at the runner outlets.(3)when operating around 40%~80% full load ,the period pressure pulse is significantly induced by the swirl at draft tube.(4)Not only the amount of purged air and the length of air-supply pipe can leviate the strength of swirl at the draft tube.Meanwhile but they will also lead to series cavitation at low loads, .On the other hand, if the air-supply pipe is stalled below the runner cone, the cavitation at the low load will be largely improved.However this will also induce the more turbulent flow in draft tube,which may cause serious vortex and cavitation in the wake of the air- supply pipe.

Keywords:hydraulic turbine , cavitation , spectra

目錄
中文摘要 Ⅰ
英文摘要 Ⅱ
目錄 Ⅳ
圖表目錄 Ⅵ
符號說明 Ⅹ
第一章 緒論 1
1.1研究動機 1
1.2文獻回顧 3
第二章 理論方法 8
2.1穴蝕機理 8
2.2一般穴蝕的分類 9
2.3 水輪機穴蝕的分類 11
2.4 穴蝕產生的噪音 14
2.5訊號分析的理論基礎 17
2.6小波分析 17
2.7水輪機特性說明 19
第三章 量測實驗設施 24
3.1馬鞍機組穴蝕量測系統簡介 24
3.2天輪#5機訊號量測設備 25
3.3天輪#5量測過程 25
3.4馬鞍及天輪#5機組Francis水輪機特性參數說明 25
第四章 結果與討論 26
4.1尾管穴蝕訊號量測結果 26
4.2由水輪機穴蝕的類別特性區分尾管的振動訊號源 28
4.3 尾管壓力脈動與機組出力關係的探討 33
4.4馬鞍與天輪#5兩部機組穴蝕特性差異的探討 33
4.5總結 35
第五章 建議與未來發展方向 36


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