Study on the Application of Microbubble Technique in Ship Hydrodynamics
Date Issued
2011
Date
2011
Author(s)
Chen, Chi-Chuan
Abstract
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.
Subjects
Microbubble
Drag Reduction
Boundary Layer Mixture Model
Ship Model Test
Ramjet Engine
Two Pahse Nozzle
Type
thesis
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