以微泡減低物體於流場中的阻力已被證實是一種有效的減阻方法，雖然已有一些數值模擬的結果被提出並與實驗結果有定性上的吻合，但氣泡減阻實際的運作機制仍然是尚未被了解的部份，尤其是氣泡在流場中分佈的情形與尺寸的變化，被指出是影響減阻效果的關鍵。

　　本文以PIV對一圓形噴流流場及空蝕水槽測試段的流速與實驗架構之平板邊界層進行量測，並比較其特性與文獻中的描述，確定儀器及使用技巧之正確性。

　　再對已知可產生明顯減阻效果之含氣泡流場觀察氣泡位置分佈及尺寸變化，並以人工進行資料的統計，得到相關的機率分佈函數，發現有超過一半以上的氣泡會分佈在邊界層外，因此無法確定氣泡分佈與緩衝層之間的關係;流速較高時，氣泡會往壁面集中靠近，氣泡之尺寸則會在下游處成長為剛產生時的2~4倍不等。

　　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.

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