Enhancement of Air Cavities for Ship Drag Reduction

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Marine vessels are the dominant transportation means in the global trade of goods, as well as a major consumer of fossil fuels. Reducing the hydrodynamic resistance of ships can substantially decrease energy consumption and emissions. A promising technique for drag reduction in water involves air-ventilated cavities formed on the underwater portion of surface ship hulls. These cavities can decrease the hull wetted area and therefore ship drag. However, it is difficult to create and sustain stable large-area air cavities on real ship hulls in broad operational conditions. The proposed research will investigate the application of hydrodynamic actuators for enhancing air-ventilated cavities and maintaining their effectiveness in adverse regimes. Educational activities of this program will result in improving engineering curriculum, developing a new course on drag reduction and flow control, involving undergraduate students in research, and organizing workshops for K-12 summer camps. Air-ventilated cavities can be formed by supplying air into water flow around completely or partially immersed solid objects. Characteristics of the flow with air cavities restricted by solid surfaces depend on many factors, including hull geometry, speed, gravity, air supply, and fluid properties. Waves inside the cavities and shedding of air pockets from the cavities add to this complexity. The drag reduction potential of the air cavities is often compromised by non-optimal operating conditions, resulting in short or unstable cavities. The influence of compact actuators on the air-cavity properties and hull resistance will be investigated in a range of important factors. Promising actuator candidates include interceptors, hydrofoils, morphing surfaces, and variable air supply. The investigation will involve experimental studies with model-scale hulls and computational simulations with the state-of-the-art modeling tools. The focus of these efforts will be on understanding and controlling the conditions that produce efficient flow regimes, resulting in formation of stable large-area cavities at small air supply rates. The results will guide the development of practical air-cavity drag reduction systems and will advance knowledge on multi-phase flows and flow control.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.