| WANG Han,LING Zhiyuan,ZENG Zhixiang,HU Hongyi,GENG Jiadong.Effect of Liquid-like Slippery Coating on Drag Reduction and Hydrodynamic Performance of Propeller[J],54(4):242-250 |
| Effect of Liquid-like Slippery Coating on Drag Reduction and Hydrodynamic Performance of Propeller |
| Received:April 07, 2024 Revised:July 01, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.04.020 |
| KeyWord:liquid-like slippery coating drag reduction propeller hydrodynamic performance molecular brush boundary slip |
| Author | Institution |
| WANG Han |
COSCO SHIPPING Energy Transportation Co., Ltd, Shanghai , China |
| LING Zhiyuan |
COSCO SHIPPING Energy Transportation Co., Ltd, Shanghai , China |
| ZENG Zhixiang |
Key Laboratory of Marine Materials and Related Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Zhejiang Ningbo , China |
| HU Hongyi |
Key Laboratory of Marine Materials and Related Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Zhejiang Ningbo , China |
| GENG Jiadong |
COSCO SHIPPING Energy Transportation Co., Ltd, Shanghai , China |
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| Abstract: |
| Drag reduction on marine vehicles like ships and other vessels can greatly reduce carbon emissions and fuel consumption, which is of great social and economic significance. Compared to large areas such as the hull, which can only realize drag reduction by reducing frictional resistance, propeller drag reduction can be achieved through two methods of reducing torque and increasing thrust. Boundary slip is one of the important design principles for achieving drag reduction, but common methods of lubrication through sealing gas or liquid media have the problem of medium escape. Moreover, these methods require high preparation requirements and are difficult to apply on the surface of propellers. The work aims to propose an innovative method, which does not rely on lubricating media, but directly generates boundary slip on the solid-liquid surface through surface grafting to construct a liquid-like slippery surface. The drag reduction performance is characterized by measuring and calculating changes in parameters such as torque, speed, thrust, and power during propeller operation, and finally quantified and compared through propeller efficiency (thrust torque ratio). The specific method is to select two long-chain molecules, dodecyltrimethoxysilane (DTMS) and tetramethoxyisilane (TMOS), as the target monomers. Firstly, a certain amount of DTMS molecules are dissolved in isopropanol, and the pH value of the solution is adjusted to 3 by hydrochloric acid. Then, TMOS molecules are mixed and stirred to obtain a modification solution. Finally, the coating is prepared by the spraying method, which is based on the condensation reaction between siloxane and the surface hydroxyl groups of the material. Both types of silane monomers have extremely low glass transition temperatures, and this highly flexible molecular brush can rotate freely on the surface, exhibiting liquid-like properties. DTMS is responsible for transferring water droplets to achieve surface slip, while TMOS plays a spacing role to increase the transferability. However, if the spacing is too large, it can easily exceed the maximum transmission distance and reduce the transmission capacity. A comprehensive evaluation of the drag reduction performance of slippery coating is conducted by various test methods such as water tunnel test, rotational resistance test, fast boat test, and cavitation tunnel experiment. The test includes linear and rotational flow fields, four types of samples such as flat plates, discs, three bladed propeller, and four bladed propeller, horizontal and vertical rotation axes and three methods of laboratory test, outdoor test, and third-party test, to ensure the authenticity and reliability of the results to the greatest extent possible. The optimal ratio of the two molecular brushes is TMOS∶DTMS=3∶1. At this ratio, the coating surface is smooth and flat, with a roughness of only 0.184 nm and a sliding angle of 6.17°. Water droplets can easily slide on the surface, indicating that the surface has excellent slippery performance and self-cleaning performance. The infrared spectrum confirms that the surface methylene is in a flexible liquid-like conformation (trans-gauche conformation). The drag test results show that the slippery coating can significantly improve the hydrodynamic performance of the propeller at different inlet coefficients, which is manifested as an average 1%-2% torque reduction, 1%-2% speed increase, 4%-7% power reduction, 3%-5% thrust increase, and 5%-6% propeller efficiency improvement. |
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