Study on Wake and Lock on Characteristics behind Staggered Cylinders of Diameter Ratio Two at Large Gap Ratio
| Autor: | Fei-Long Song, 宋飛龍 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 This study investigates the wake and lock-on characters behind two staggered cylinders of diameter ratio 2 at large gap ratios. All the experiments are performed in a low-speed recirculation water channel at Reynolds number 1000. Qualitative flow structures and quantitative velocity measurements were obtained by dye flow visualization, the LDV system and the PIV system. From the fluctuating energy viewpoint, some important results are summarized as follows. For Mode 1 flow structures: The spectral energy at vortex shedding frequency behind small cylinder in staggered arrangement is higher than that of a single small cylinder; and the maximum energy is about 5.5% of inflow energy. The spectral energy distribution at vortex shedding frequency behind large cylinder is similar to that of a single large cylinder; but the magnitude on the free stream side is large. The maximum spectral is about 14% of inflow energy. Both the spectral energy become weak as the horizontal spacing reduces. In transition region between modes 1 and 2, the spectral energy behind both staggered cylinders attains the local minimal. For Mode 2 flow structures: The spectral energy distribution at vortex shedding frequency behind large cylinder is still similar to those in Mode 1. While the horizontal spacing increases, the magnitudes of the spectral energy distribution behind large cylinder gradually recover to that behind a single large cylinder (about 9.8% of inflow energy). However, that behind the small cylinder decreases monotonously as the horizontal spacing increases. While the wake of large cylinder experiences the primary and 1/3 sub-harmonic lock-on, the wake of small cylinder is not locked on. The frequency bands of both lock on range didn’t change too much; but the phase shift between the flow structures across the lock-on frequency band indeed varies. The spectral energy behind large cylinder at exciting frequency is higher than that of a single cylinder. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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