The Characteristics of Drag-Reducing Air Bubbles near Boundary Layer

• Main Authors: Chung-Ming Lin, 林俊明
• Other Authors: Jeng-Horng Chen
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/75295470749035712715

碩士 === 國立成功大學 === 系統及船舶機電工程學系碩博士班 === 92 === 　　Microbubbles has been proven to be a successful drag-reducing techniquefor a body in fluids. Although some numerical simulations have qualitativeagreements with experimental results, the mechanism of the microbubble drag reduction still remains unidentified. Generally, the spatial distribution in flow field and size change of gas bubbles are considered to be the key of drag reduction. 　　First we measure the flow field of a circular jet flow, the velocity distri-bution of the testsection of a cavitaion channel and the boundary layer of aflat-plate in testsection, and then compare the measurements with referencesto prove the equipments and experiment skills. 　　Then, we check the bubbles’ spatial distribution and size change of the flow with bubbles at known drag reduction conditions, and obtain the probabilitydistribution functions. Because over-half of bubbles distribute outside theboundary layer, we cannot confirm the relationship between the bubble distribution near buffer layer and drag reduction effect. When the flow velocitygets higher, bubbles will concentrate closer to the wall. Also, the size ofbubbles will grow 2~4 times in the downstream than those just generated.