Summary:
UCLA researchers in the Department of Mechanical and Aerospace Engineering have developed a design of microstructured surfaces capable of retaining air pockets under water at flow speeds above 10 knots so that watercraft can travel with a reduced drag.
Background:
A major challenge limiting efficiency and speed of watercraft is the friction watercraft experience while traveling over the surface of the water. These forces slow down all traveling watercraft, leading to decreased efficiencies and increased fuel requirements. To overcome this, the undersides of watercraft are often coated with a superhydrophobic layer which may trap microscopic gas pockets (referred to as a plastron) in between the hull and water. Plastrons are effective at reducing drag and increasing efficiency, but at realistic speeds (10 knots or above) are unstable and lost. Previous innovations have presented drag reduction achieved on superhydrophobic surfaces that have plastron, but few have addressed the surface structure necessary to retain the plastron in turbulent flow. There is a clear need for methods to sustain plastrons and increase efficiency of watercraft.
Innovation:
UCLA researchers led by Prof. CJ Kim have developed a design of microtrenches that enable the plastron to retain its shape and integrity when traveling under water. The geometric and dimensional design of the trenches address common failure points of plastrons and earlier attempts to overcome these. A prototype on a motorboat effectively pinned plastrons on trenches at cruising speeds. This design results in a plastron-retaining surface for watercraft at standard operational velocities, which could prove valuable for both private and commercial watercraft operations.
Potential Applications:
• Watercraft manufacturing
• Water sports
• Naval/maritime applications
• Shipping/logistics
Advantages:
• Improve fuel efficiencies.
• Increased speed
• Reduction of drag in turbulent and flowing conditions
• Can be fitted to existing watercraft
Development-To-Date:
Components of the innovation have been published in peer-reviewed journals.
Related Papers:
H. Park, C.-H. Choi, and C.-J. Kim, " Superhydrophobic Drag Reduction in Turbulent flows: a Critical Review", Experiments in Fluids, Vol. 62, Issue 11, November 2021, 229(29). (doi: 10.1007/s00348-021-03322-4)
M. Xu, N. Yu, J. Kim, and C.-J. Kim, "Superhydrophobic drag reduction in high-speed towing tank", Journal of Fluid Mechanics, Vol. 908, No. 10, February 2021, A6. (doi:10.1017/jfm.2020.872)
M. Xu, A. Grabowski, N. Yu, G. Kerezyte, J.-W. Lee, B. R. Pfeifer, and C.-J. Kim, “Superhydrophobic Drag Reduction for Turbulent Flows in Open Water,” Physical Review Applied, Vol. 13, Issue 3, March 2020, 034056(10). (doi: 10.1103/PhysRevApplied.13.034056)
Reference: UCLA Case No. 2023-204
Lead Inventor: Chang-Jin Kim