博士 / 中原大學 / 機械工程研究所 / 94 / Currently, the vehicles are some of the major sources for the Earth energy consumption. It might decrease the energy loss in case it is available to reduce the drag of various vehicles. In the study, the drag reduction by coatings and micro bubbles which are applied to marine vehicles may result in an increase of the operating capability.
The experiment is proceeded with two kinds of drag reducing techniques. The drag reduction by coatings on the surface is the simplest way since it has no need to change the original design. The micro bubbles drag reduction methodology can not only be used for an extended period of time but it also has high efficacy. The micro bubble generation system for vehicle structure is very complicated as far as the system’s design and fabrication are concerned.
In the drag reduction by coatings study, the range of Reynolds number for the submerged body model is 0.74E6~2.81E6. The feature of drag reduction of hydrophobic coatings is better than hydrophilic coatings for the range of Reynolds number measured. Drag reduction for hydrophilic coatings is enhanced as the speed of submerged body is increased very fast.
Whenever the micro bubbles are over by supplied, there will pile-up effect happened which makes micro bubbles to coagulate each other as a large size air film. Although they still has the drag reduction effect, but the efficiency of drag reduction drops at this transition period. In the experiment of vertical type circulating water tunnel, when 1μm porous medium is at 7m/s flow speed, the CV value defined as the ratio of the air injection rate to the sum of the air injection rate and the liquid injection rate at 0.056 has the best drag reduction efficiency of 26%. While 10μm porous medium is at the same flow speed, the drag reduction efficiency is only around 23%.
When the CV value is around 0.16 during surface ship mode experiment, it can be treated as a critical condition. When CV value is larger than 0.16, its drag reduction efficiency stays relatively flat. Even it will increase the resistance whenever there has over by massive air injection. In the present study, we have found that the larger the area of region covered with micro bubbles, the higher the efficacy of drag reduction. Of the air is injected simultaneously from both the front and rear ends, then the best drag reduction efficiency is around 30%.
Identifer | oai:union.ndltd.org:TW/094CYCU5489016 |
Date | January 2006 |
Creators | Tsung-Te Lin, 林聰得 |
Contributors | Cheng-Hsing Hsu, 許政行 |
Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
Language | zh-TW |
Detected Language | English |
Type | 學位論文 ; thesis |
Format | 115 |
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