微泡技術在船舶流體動力之應用研究

Abstract

本研究使用透氣材噴氣方式產生微泡，在空化水槽與拖曳水槽使用0.7公尺的平板進行有無噴氣的平板阻力量測，研究發現在空化水槽中平板微泡減阻，減阻效果隨著空氣流量增加而增加，最高有80%的減阻效果，但於推曳水槽中減阻效果只剩下約30%，而且每個速度有一個最佳的空氣流量對應最佳減阻效果。本研究並發展一邊界層混合液模型(Boundary Layer Mixture Model)，預估平板在有噴氣下的減阻效果，其預估結果與在空化水槽中之實驗結果相符合，但是高估了在拖曳水槽中之減阻效果。在空化水槽中平板微泡減阻實驗之減阻效果僅與 有關，但在拖曳水槽中，其減阻效果不僅與 有關且些微與速度有相關。在空化水槽與拖曳水槽的不同減阻效果與微泡在兩個水槽中所遭受的不同速度梯度有關。 將微泡減阻技術應用於不同設計速度域的三種船模上，以期能發現應用於實船減阻之重要參數，在船模減阻實驗中，透氣材的孔徑大小(1微米、10微米與100微米)對減阻效果影響不明顯，實驗結果發現微泡減阻較適合用於平底船且其摩擦阻力為主要的阻力分量，在低速的HSVA油輪上有15%的減阻效果。在圓泌型(Round Bilge)排水型船與橫斜角(Deadrise Angle)的高速艇，皆不適合使用微泡減阻技術。 將透氣材產生微泡的方式應用於二相氣液衝壓系統(Two-Phase Water-Gas Ramjet System)，設計製作一個二相流噴嘴(Two Phase Water-Gas Nozzle)，以泵抽水當作入流，利用高壓氣體經過透氣材產生微泡，在混合段與水均勻混合，並在最後出口段加裝不同角度噴嘴，測試不同角度之影響。在陸上之噴水推進系統實驗以量測純水推力與噴氣後之推力變化，由實驗結果發現，量測的推力隨著空氣含量的增加而遞增，半錐角22.5度的噴嘴，產生的推力效果最高，約為噴水推力值的3倍。當噴流速度超過氣液混合液的聲速時，其推力的增量會明顯增加。 以此二相流噴嘴為基礎，設計一流線形外型，在拖曳水槽中進行實驗，如同水下衝壓引擎實驗，以確認其是否有相同之效果，但由實驗結果發現，氣體少量時，並無明顯推力產生，噴入大量氣體時，氣體會由入流處噴出，無法產生預期之推力結果，利用水下衝壓引擎產生推力為不可行。最後以水上摩托車為載具，修改噴嘴設計，裝設於噴水推進器之後，試驗其是否有相同推力增加的現象。實驗結果顯示，噴氣後，有推力增加的現象， 且推力增加量與噴流動量相符合。以現有的實驗結果推論， 在 =0.5時，有最大的推力增加值，且前進速度(車速)愈快，推力增加的比例也愈高，約可增加90%的推力值。

A porous plate microbubble injecting system and a flat plate drag measuring system were designed to conduct the resistance test in the water tunnel and in the towing tank. A boundary layer mixture model was proposed to predict the drag reduction effect of microbubble drag reduction technique applied in the flat plate. The drag reduction effect predicted by boundary layer mixture model is almost directly proportional to the density ratio of the air water mixture. The test results show that the drag reduction effect increases as air flow rate increases in the water tunnel. However, an optimal air flow rate exists for each velocity in the towing tank. The maximum drag reduction effect of microbubble in the water tunnel is about 80%, and the drag reduction effect is in good agreement with the value predicted by boundary layer mixture model. The maximum drag reduction effect in the towing tank is only about 30% which is much smaller than that predicted by the boundary layer mixture model. The different drag reduction effect in the water tunnel and in the towing tank may be due to the different bubble behaviors produced by the different velocity gradient. The microbubble drag reduction technique was applied in ship model with three different ship types for different design speed range. The test results show that the void size of porous material has no significant effect on drag reduction. The microbubble drag reduction technique has significant drag reduction effect for a ship model with large flat bottom and the frictional resistance is the major component. A ship with round bilge and a high speed craft with deadrise angle have no drag reduction effect when applying the microbubble drag reduction technique. The porous plate microbubble injecting method was applied to a two phase gas-water ramjet system. A two phase gas-water nozzle with a pump, which was used to drive the water into the nozzle, was designed to study the effect of injecting compressed air into the waterjet system. The speed of the nozzle’s exit can reach the sound speed of gas-water mixture in the design two phase gas-water nozzle. Three nozzles with different exit angles were designed to study the effect of nozzle expansion on the thrust produced by the two phase jet. The test results show that the two phase nozzle with injecting compressed air does increase the thrust. The nozzle with half exit angle 22.5 is the best nozzle shown from the test results. The measured maximum thrust with injecting compressed air is three times the thrust produced by the waterjet without injecting compressed air. A two phase nozzle system inside a streamline body was designed to study the effect of injecting compressed air in the towing tank. The experiment is like the underwater ramjet engine. The test results show that the two phase nozzle produced no thrust when the injected compressed air flow rate was low. And the air escaped from the inlet when the air flow rate was high and no thrust produced. Thrust produced by underwater ramjet engine is not feasible. A two phase nozzle was designed to be installed at the exit of the waterjet system of a jet ski. The resistance or thrust of the jet ski with the two phase nozzle was measured in the towing tank. The test results show that the thrust produced by two phase nozzle is increased when the air flow rate or the inflow velocity is increased. The thrust is increased about 90% , which is the maximum increase in the test results, when the non-dimensional air flow rate is 0.5.