臺灣博碩士論文加值系統

本研究是探討流場流經一個平滑的圓柱表面時的分離現象，雷諾數範圍介於4.1x105~5.67x105，利用可饒式熱膜感測器平貼於圓柱表面進行流場量測，在運用快速傅立葉轉換以及希伯特黃轉換來進行分析。由於本實驗在穿音速風洞中進行，所以同時考慮可壓縮流場所造成的壓縮效應。利用熱膜感測器的特性，量測在流線方向上，圓柱表面上的流場分離現象。研究結果可以清楚地發現，在分離點發生前以及分離流場中，會有倍頻產生，此時渦流溢放訊號也會較強。流場分離的不定常現象亦可在本研究中發現。

An experimental investigation of flow around a smooth circular cylinder was carried out in a transonic wind tunnel,at Reynolds numbers 4.1x105~5.67x105,corresponding the Mach numbers in a range of 0.4 to 0.7. Unsteady characteristics of flow separation were studied with an
array of self-made micro-electrical-mechanical-system (MEMS) film sensors, which were flushed with the cylinder surface, aligned in the circumferential direction. By correlation analysis of the signals obtained by two neighboring sensors, it is found that the location of flow
separation can be identified by comparing the correlation coefficients obtained, which falls in the region where the correlation coefficients drops pronouncedly along the circumferential direction. By FFT analysis of the signals of each MEMS sensor, an interesting feature noted
is that in the neighborhood of the flow separation pioint, the signal fluctuations contain a harmonic component of the vortex shedding frequency. Further, the results obtained by Hilbert-Huang Transformation of the signals measured indicate that downstream of the flow separation point, the fluctuating energy contained in the vortex
shedding frequency component was reduced greatly. Since the
experiments were made in a transonic wind tunnel, the effect of flow compressibility was discussed. As noted, through the present Reynolds numbers studied, the Strouhal numbers corresponding to the vortex shedding frequencies reduced remained about 0.2, distinguished different
from those reported by the studies made in the low-speed wind tunnels, in the regime of the critical Reynolds numbers.

中文摘要………………………………………………………………………I
英文摘要……………………………………………………………………II
誌謝…………………………………………………………………………IV
目錄…………………………………………………………………………VI
表目錄………………………………………………………………………X
圖目錄………………………………………………………………………XI
符號說明…………………………………………………………………XIV
第一章 序論…………………………………………………………………1
1.1 研究動機與目的………………………………………………………1
1.2 文獻回顧………………………………………………………………2
1.2.1 圓柱流場…………………………………………………………2
1.2.2 壓縮效應…………………………………………………………5
第二章 實驗設備與模型……………………………………………………7
2.1 穿音速風洞……………………………………………………………7
2.2 圓柱模型………………………………………………………………7
2.3 DC訊號放大電路……………………………………………………8
2.4 AC訊號放大電路……………………………………………………9
2.5 資料擷取系統…………………………………………………………9
2.5.1搭配DC訊號放大電路的資料擷取系統…………………………9
2.5.2搭配AC訊號放大電路的資料擷取系統…………………………9
2.6 壓力轉換器…………………………………………………………10
2.7 可饒式熱膜感測器…………………………………………………10
2.7.1 可饒式熱膜感測器之特………………………………………10
2.7.2 可饒式熱膜感測器與環境溫度之關係………………………12
第三章 實驗方法與步驟…………………………………………………14
3.1 風洞實驗參數分析…………………………………………………14
3.1.1 雷諾數…………………………………………………………14
3.1.2 無因次頻率……………………………………………………15
3.1.3 壓力係數………………………………………………………15
3.2 圓柱基部壓力量測…………………………………………………16
3.3 訊號處理……………………………………………………………17
3.3.1 相關性係數…………………………………………………17
3.3.2 希伯特黃轉換………………………………………………18
第四章 實驗結果與討論…………………………………………………20
4.1 Re=4.1x105……………………………………………………………20
4.1.1 表面相關性分析………………………………………………20
4.1.2 瞬時溢放率……………………………………………………22
4.2 Re=4.99x105…………………………………………………………24
4.2.1 表面相關性分析………………………………………………24
4.2.2 瞬時溢放頻率…………………………………………………25
4.3 Re=5.67x105…………………………………………………………27
4.3.1 表面相關性分析………………………………………………27
4.3.2 瞬時溢放頻率…………………………………………………27
4.4 壓縮效應對無因次頻率的影響……………………………………29
第五章 結論與建議………………………………………………………32
5.1 可壓縮臨界圓柱流場………………………………………………32
5.2 未來建議…………………………………………………………35
參考文獻……………………………………………………………………36

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