Ships with ventilated cavitation in seaways and active flow control |
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| Institution: | 1. School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China;2. Department of Thermal Engineering, Tsinghua University, Beijing 100084, China;3. Beijing Institute of Astronautical System Engineering, Beijing 100076, China;1. Institute of Ship Technology, Ocean Engineering and Transport Systems, University of Duisburg-Essen, Duisburg 47057, Germany;2. Flow Control Research Lab, Aerospace Engineering Department, Sharif University of Technology, Tehran, Iran;1. Institute of Process Equipment, College of Energy Engineering, Zhejiang University, Hangzhou 310027, China;2. Saint Anthony Falls Laboratory, 2 3rd AVE SE, University of Minnesota, Minneapolis, MN 55414, USA;3. Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA |
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| Abstract: | Bottom ventilated cavitation has been proven as a very effective drag reduction technology for river ships and planning boats. The ability of this technology to withstand the sea wave impact usual for seagoing ships depends on the ship bottom shape and could be enhanced by some active flow control devices. Therefore, there is the need in numerical tools to estimate the effects of bottom changes and to design such devices. The fundamentals of active flow control for the ship bottom ventilated cavitation are considered here on the basis of a special model of cavitating flows. This model takes into account the air compressibility in the cavity, as well as the multi-frequency nature of the incoming flow in wavy seas and of the cavity response on perturbations by incoming flow. The numerical method corresponding to this model was developed and widely manifested with an example of a ship model tested in a towing tank at Froude numbers between 0.4 and 0.7.The impact of waves in head seas and following seas on cavities has been studied in the range of wavelengths from 0.45 to 1.2 of the model (or ship) length. An oscillating cavitator-spoiler was considered as the flow controlling devices in this study. The oscillation magnitude and the phase shift between cavitator oscillation and the incoming waves have been varied to determine the best flow control parameters. The main results of the provided computational analysis include oscillations of cavity surface, of the pressure in cavity and of the moment of hydrodynamic load on the cavitator. The major part of computations has been carried out for the flap oscillating at the frequency coinciding with the wave frequency, but the effect of a frequency shift is also analyzed. |
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| Keywords: | Hydrodynamics Waves Ship drag reduction Active flow control |
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