Study On The Scale Effect Of Nominal Wake Field Based On Numerical Simulation Method

The characteristic of stern flow is one of the main factors of studying on ship propulsion performance. The viscous flow field around ship is very complex, and its complexity is fully embodied in stern flow and wake field. Therefore, accurately prediction and evaluation of stern flow field is very important at the ship design stage. Common model test can only meet the requirement of Froude number similarity, and the difference of Reynolds number between model scale and full scale is very large, so there is the problem of scale effect. At present,there still are short of scale correction methods that aiming at the characteristics of different ship types. In this paper, the stern flow is simulated and the influence on flow field of the stern with scale effect is studied. In the process, ANSYS ICEM CFD, STAR-CCM+, AUTO CAD, CATIA, TECPLOT and ORIGIN have been used.In this paper, CFD method is adopted to simulate the wake field of stern. The standard ship type of KRISO 3600TEU container ship KCS is taken as the research object, and SST k-co turbulence model is used in the STAR-CCM+ calculation. Compared with the test results,the error of calculation results is within the acceptable level and good reliability of theoretic calculation method adopted in this paper is proved. Nine KCS models in different scales including the full scale are calculated, the distribution of velocity field at stern and the wake distribution of propeller disc are obtained. The wake distribution at propeller disc, wake fraction at each radius, average value and wake gradient of circumferential wake distribution,the distribution of velocity field at stern, streamline distribution of ship hull in different scales are analyzed, and the influence of scale effect on stern wake field (mainly considering the axial wake fraction) is discussed.In the end of this paper, an unconventional method is provided to predict the wake field of real ship. A model with incomplete geometrical similarity is designed, and only shape of the ship tail is modified, and the rest of the hull remains the same. The numerical calculation of the model is carried on, and then the result is obtained and compared with the data of the real ship. The non-geosim scale model of a container vessel generates a wake field more closely resembling the ship scale target wake field than does the geometrically similar('geosim') hull model. This method will provide a new direction to our train of thought.