Enhancement of Air Cavities for Ship Drag Reduction

船舶是全球货物贸易的主要运输工具，也是化石燃料的主要消费者。减少船舶的水动力阻力可以大大减少能源消耗和排放。一种有前途的减阻技术涉及在水面船体水下部分形成的通风空腔。这些空腔可以减小船体浸湿面积，从而减小船舶阻力。然而，在真实的船体上，在广泛的使用条件下，很难产生和维持稳定的大面积空气腔。拟议的研究将探讨应用流体动力执行器，以提高空气通风腔，并保持其有效性，在不利的制度。该计划的教育活动将导致改进工程课程，开发关于减阻和流动控制的新课程，让本科生参与研究，并为K-12夏令营组织研讨会。通过将空气供应到完全或部分浸没的固体物体周围的水流中，可以形成通风腔。受固体表面约束的气腔流动特性取决于许多因素，包括船体几何形状、速度、重力、空气供应和流体性质。空腔内的波浪和空腔中气穴的脱落增加了这种复杂性。空气腔的减阻潜力通常受到非最佳操作条件的损害，从而导致短腔或不稳定腔。研究了紧凑型作动器对气腔特性和船体阻力的影响。有前途的驱动器候选者包括拦截器，水翼，变形表面，和可变的空气供应。调查将涉及与模型规模的船体和计算模拟与国家的最先进的建模工具的实验研究。这些工作的重点将是了解和控制产生有效的流动状态的条件，从而在小的空气供应率下形成稳定的大面积空腔。研究结果将指导实用空气空腔减阻系统的开发，并将促进多相流和流控方面的知识。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.