Investigations of wake flow of a circular cylinder in the critical regime by MEMS film sensors array

• Main Authors: Wei-ting Hsu, 許瑋婷
• Other Authors: Jiun-jih Miau
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/15000169017029822366

碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 96 === 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.