碩士 / 國立中興大學 / 機械工程學系所 / 101 / This study, based on numerical analysis by Fluent, investigates the downstream flow characteristics, propulsive efficiency, the contributions from the pressure difference and the net momentum efflux through control volume analysis while the flexible fin undergoes the coupled oscillating-heaving motion. The inflow velocity is 5cm/s and the corresponding Reynolds number is 5000. By changing the Strouhal number (St) and the phase angle (φ) between two motions, the thrust, the input power coefficient and the propulsion efficiency are evaluated.
Based on the variations of flow patterns and control volume analysis, some results are summarized as follows. For Strouhal number St = 0.08, the flow patterns around the fin and in downstream region is wavy and Tai-Chi shape in nature for the phase angles of 90° and 180°. Both create drag force on the fin and the drag force is mainly caused by the pressure difference. When St = 0.16, the phase angles of 90° and 180°, the downstream flow patterns begin to show reverse vortex street. For 90° and 180° phase angles, the net momentum efflux is positive with 146% and 190%, respectively. However, the pressure difference is negative and takes -46%, -90%, respectively. Both create thrust on the fin. At Strouhal number of 0.32, optimum propulsive efficiency is attained and the net momentum efflux take about 60%, 70%; while the pressure difference takes 40%, 30%, for the phase angles of 90° and 180°. In such cases, both the net momentum efflux and pressure difference are positive and the former has larger contribution that the latter. When St>0.32, the contributions of both the net momentum efflux and the pressure difference are about equal.
For the thrust, the input power coefficient and the propulsive efficiency, while St>0.16, the thrust generated and input power is larger for phase angle 180° than those of 90°. At all Strouhal number, the flow patterns create only drag force on the fin and the magnitudes of drag are larger for the phase angle 0° than those of 270°. For the Strouhal number within 0.16~0.8 and the phase angles of 90° and 180°, the propulsion efficiency is better than those at 0° and 270°. At St=0.32, the propulsive efficiencies attain their maximum values about 31%, 15% for the phase angles of 90° and 180°.
| Identifer | oai:union.ndltd.org:TW/101NCHU5311070 |
| Date | January 2013 |
| Creators | Jhe-Ruei Hu, 胡哲睿 |
| Contributors | 郭正雄 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 96 |
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