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Experimental Analysis on Wake Characteristics behind Two Cylinders in Tandem and Staggered Arrangements
|關鍵字:||tandem;縱列;staggered;cavity mode;narrow wake;wide wake;錯列;雙圓柱;空穴剪力層||出版社:||機械工程學系||摘要:||
The wake characteristics between two cylinders in tandem and staggered arrangements are investigated at a Reynolds number of 1000 by the flow visualization and the velocity measurement. Quantitative velocity measurement and quantitative flow visualization were performed by ways of LDA system and laser sheet technique. Some important results are concluded as follows:
(1) In case of tandem arrangement(Yc/D=0), the flow are classified into three different characteristics. They are: (a) smooth shear layers between two cylinders as the streamwise spacing (Xc/D) is between 1.5~3.5. (b) when the streamwise spacing (Xc/D) is around 4.0~5.5, the flow characteristic between two cylinders becomes the cavity mode. (c) as the streamwise spacing (Xc/D) is larger than 6.0, the flow structure between two cylinders becomes an alternate shedding vortex street.
(2) In staggered arrangement (Yc/D=0.5), three kinds of flow characteristics are found as follows: (a) as the streamwise spacing (Xc/D) ranges between 1.0 and 3.0, the impinging shear layer is stably deflected downward, interacting with the lower shear layer and shedding downstream. (b) as the streamwise spacing (Xc/D) is around 3.5~5.0, the impinging shear layer becomes cavity mode and the other free shear layer rolls up and sheds downstream. (c) as the streamwise spacing (Xc/D) is larger than 5.5, the flow structure between two cylinders becomes an alternate shedding vortex street.
(3) In staggered arrangement (Yc/D=1.0), two different flow characterics are concluded as follows: (a) as the streamwise spacing (Xc/D) is around 1.0~4.0, the deflected gap flow between two cylinders leads to the narrow wake behind the main cylinder and wide wake behind the control cylinder. (b) as the streamwise spacing (Xc/D) is larger than 4.5, the flow structures behind two cylinders become two independent vortex streets.
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