Basic Study on the Wind- assisted Propulsion Support System

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For the purpose of energy saving of large vessels, basic study on the wind- assisted propulsion support system was conducted, and following conclusions were obtained.1) The concept is a column-type circular cylinder propulsion assistance system which utilize the existing dodger-support structure and air suction power. Flow field around the column is sucked into the engine room through the intake located in the after part of the cylinder. Boundary layer in the near field is controlled and separation free flow field is generated to exert hydrodynamic lift. Model test in a large wind tunnel test indicated that the maximum lift coefficient is about 7.5, lift drag ratio about 1.3, implying a possibility for obtaining useful propulsion thrust for ships.2) Two types of air intake system were investigated, namely, 'punched metal type' and 'slits type'. In terms of the maximum lift and consistency for wind direction, 'slits type' was concluded to be superior to 'punched metal type' for actual ship applications.3) Air volume used for main engine etc. was surveyed on some actual existing ships, and the analysis showed a relation between the possible lift by the sail and required air volume. This implies a possibility of development of circular cylinder sail.4) The flow around the circular cylinder sail was investigated by flow visualization method and hot wire methods. The effect of air suction was clearly indicated to diminish the flow separation region and generate circulation around the cylinder. It is also found that controlling the slit size may contribute to optimize the sail performance at various wind velocity and direction.5) For practical application of the circular cylinder sail, further improvements of sail performance are necessary. To meet this requirement, dynamic control of slit size can be a possible measure introducing louver control system.