微泡減阻技術在船舶上的應用研究

Study on the Application of Microbubble Drag Reduction Technique at the Ship Model

本研究採用船模試驗的方法，透過多孔透氣材產生微氣泡，噴入船摸底部的邊界層中，以研究微泡減阻技術在船摸上的減阻效應。由實驗結果顯示微泡減阻技術可以降低船模的摩擦阻力，最大可降低18%的摩擦阻力；同時由研究顯示，若採用空氣流量與邊界層內的水的流量及空氣流量和的比值Cv當參數時，船模速度的效應不明顯。實驗結果也顯示，空氣流量有一最佳值存在，過多的空氣流量反而會降低減阻的效果。本研究並發現在船模上減阻效果（18%）遠低於水洞中平板的減阻效果（降低80%的阻力）的原因是：在拖曳水槽中連續噴出的微氣泡會在船模底部堆積，造成氣泡碰撞而結合成大的氣泡而造成減阻效應下降，甚至會增加阻力。 The model tests were conducted with injecting microbubble into the boundary layer of the ship model's bottom by porous plate in this study. A 18% reduction of frictional resistance was obtained from the tested results. The parameter Cv, defined by the ratio of air flow rate to the sum of air flow rate and water flow rate in the boundary layer, is a good non-dimensional parameter to include the effect of the model speed. The tested results also show that there exists optimum air flow rate. The effect of drag reduction will be reduced by injecting too much air. The 18% drag reduction of the ship model is far smaller than that of the flat plate in water tunnel (80%). The reason is that the microbubbles injecting from the ship model have the same speed as the ship model and microbubbles will be accumulated and coalesced into big bubbles. The big bubbles attached on the bottom of ship model increase the drag and destroy the effect of drag reduction produced by microbubbles.