Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/1624
標題: 以小波方法分析具跳頻現象的空穴剪力流之鎖定特性
Wavelet Analysis on Lock-on Characteristics of Cavity Shear Layer with Frequency Jump
作者: 楊大慶
Yang, Da-ching
關鍵字: cavity shear layer;空穴剪力層;lock-on;frequency jumps;跳頻現象;鎖定現象
出版社: 機械工程學系所
引用: 參考文獻 1. Ashcroft, G., Zhang, X., “Vortical Structures over Rectangular Cavities at Low Speed”, Physics of Fluids, 2005,Vol. 17, No.1, article No. 015104. 2. Blake, W. K., “Mechanics of Flow-Induced Sound and Vibration”, Chapter 3, Vol. 17-I, Academic Press. Inc., 1986. 3. Gharib, M., “Response of the Cavity Shear Layer Oscillations to External Forcing”, AIAA Journal, 1987, Vol.25, pp.43-47. 4. Gharib, M. and Roshko, A., “The Effect of Flow Oscillations on Cavity Drag”, Journal of Fluid Mechanics, Vol.177, 1987, pp.501-530. 5. Grace, S., Dewar. M. W. G., Donald E. W., “Experimental Investigation of the Flow Characteristics within a Shallow Wall Cavity for Both Laminar and Turbulent Upstream Boundary Layers”, Experiments in Fluids, 2004, Vol. 36, p.p. 791-804. 6. Hall, M. S. and Griffin, O. M., “Vortex Shedding and Lock-on in a Perturbed Flow”, Journal of Fluids Engineering, 1993, Vol. 115, June, pp.283-291. 7. Rockwell, D. and Knisely, C., “Self-Sustained Low FreqUtncy Components in an Impinging Shear Layer”, Journal of Fluid Mechanics, 1982, Vol.116, pp. 157-186. 8. Rockwell, D. and Naudascher, E., “Review of Self-Sustaining Oscillations of Flow Past Cavities”, Transaction. of ASME, Journal of Fluids Engineering, 1978 ,Vol.100, pp. 152-165. 9. Zsoy, E., Rambaud, P., Stitou, A., Riethmuller, M. L., “Vortex Characteristics in Laminar Flow at Low Mach”, Experiments in Fluids, 2005, Vol. 38, p.p. 133-145. 10. 張志偉, “具有上蓋平板之空穴內振盪流場之探討”, 中興大學機械工程研究所碩士論文, 1996。 11. 黃士豪, “空穴中振盪流場之實驗分析與控制”,中興大學機械工程研究所碩士論文, 1998。 12. 林耀宗, “圓柱對空穴中振盪流場影響的研究”, 中興大學機械工程研究所碩士論文, 1999。 13. 楊大葳, “空穴剪力流鎖定現象的實驗研究”, 中興大學機械工程研究所碩士論文, 2000。 14. 鄭文益, “切線擾動對空穴剪力層鎖定現象的實驗研究”, 中興大學機械工程研究所碩士論文, 2001。
摘要: 
本研究係以實驗方法,研究具跳頻現象的空穴剪力層流場的鎖定特性。利用壓克力製作空穴長深比為3的空穴模型,安置於低速循環迴路水槽中進行,並以雷射都普勒測速儀系統,進行空穴流場速度量測,以獲得流場定量分析數據。透過流場量測及小波法分析工具,呈現具有跳頻現象時,空穴流場特徵頻率發生的不穩定現象;並藉外加擾動的方式,探討對具有跳頻現象空穴流場的鎖定特性,進而達成流場控制的目的。
本研究主要對象為空穴跳頻現象及其被鎖定特性。從實驗分析結果顯示:
1、在不具有跳頻現象的空穴流場受到外加擾動時,鎖定現象以空穴原有頻率fo為中心向高低頻擴張,並隨著切線擾動振幅縮小而向兩側縮減。
2、在具有跳頻現象的空穴流場受到外加擾動時,鎖定頻段較為狹窄,且當fe介於fL及fH間時具有較明顯的鎖定現象。
3、發生半頻共振的原因為較大的擾動振幅及其半頻頻率接近fo的鎖定頻段。
4、發生倍頻共振的原因在於2fe或3fe位於fo、fL及fH鎖定頻段內。

The objective of the present investigate is to study the lock-on phenomena of cavity shear layer with the frequency jump by way of the velocity measurement. The quantitative velocity measurement were performed by way of LDA system, and analyzed by the wavelet transformation to present the time varying characteristic frequency of the cavity shear layer. The external perturbation is performed by a small rotational cylinder locatcted near the upstream corner of the cavity. Lenth-to-Depth ratio of the cavity is 3.

It is found that: (1) The lock-on frequency band of the cavity shear layer is found to centered at fe / fo = 1 in the cavity flow for the case without frequency jumps. The lock-on bandwidth will be narrowed when the oscillating amplitude of the external excitation oscillation deceases. (2) The lock-on bandwidth of the cavity shear layer with frequency jumps lies in the frequency band between the low and high natural frequencies. (3) The subharmonic resonance happens when half of the perturbation frequency with a strong oscillation amplitude is closed to the lock-on frequency band for the case without frequency jump (4) The superharmonic resonance happens when two or three times of the perturbation frequency is closed to the lock-on frequency band for cases both with and without frequency jump.
URI: http://hdl.handle.net/11455/1624
其他識別: U0005-1708200610302200
Appears in Collections:機械工程學系所

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