Application of a BEM time stepping algorithm in understanding complex unsteady propulsion hydrodynamic phenomena |
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| Authors: | Gerasimos K Politis |
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| Institution: | Department of Ship and Marine Hydrodynamics, School of Naval Architecture and Marine Engineering, National Technical University of Athens, Heroon Politechniou 9, Zografos, Athens, Greece |
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| Abstract: | We solve the problem of unsteady potential flow around a system of arbitrarily moving rigid or flexible, lifting or non-lifting bodies, in an infinite fluid free of distributed vorticity. For the solution we use a time stepping algorithm and a potential based formulation of the corresponding free BVP. Nonlinear free shear layer dynamics are included in our modeling. This is a major innovation in treating complex unsteady propulsion problems since no simplifying assumptions (like that of a helicoidal wake) are used regarding the wake model. Bilinear quadrilateral elements are used to describe body and shear layer geometry at each time t. Three types of Kutta conditions can be alternatively applied for the determination of the shed vorticity from lifting bodies. The theoretical and numerical aspects of the method are presented followed by a number of applications, elucidating the qualitative and quantitative physical characteristics of a number of complex unsteady propulsion problems. |
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| Keywords: | Boundary element method Incompressible non-viscous unsteady lifting flows Unsteady shear layer dynamics Unsteady wake rollup Unsteady propulsor hydrodynamics |
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