Study On Scale Effect Of Wake Field And Researchofit In Regular Short Waves

Among ship navigation performance,ship powering performance is closely related to its operational efficiency,economy and EEDI energy requirements.The propulsive efficiency of propeller is one of the key factors affecting the speed of the ship in actual sea conditions.In the actual navigation process,the stern wake flow field has an important influence on propeller propulsion efficiency.However,the difference in wake flow field between full scale and model scaleresult in changes of propeller performance under the actual sea conditions,such as the propeller propulsion efficiency andcavitation,vibration,noise,which is called scale effect of wake flow field.Therefore,based on the composition of wake flow field,the factors influencing the change of wake flow field were analyzed and discussed under the condition of the difference in Reynolds number between full scale and model scale and micro wave amplitude.The main research are as follows:Firstly,the development of EFD and CFD methods for scale effects of wake flow field are described in detail.The shortcomings of different theoretical methods and the limitations of the existing experimental research methods and experimental devices in studying the unsteady variation of wake flow field were analyzed.The research direction of ship navigation performance in regular wave was discussed and the shortcomings and related problems of current wake flow field research were put forward.And then we focus on the research of the nominal wake in the flow field around ship,which is essential to the ship around the flow field.In the second chapter,the KCS standard ship model is used as the research object.Based on the RANS method,the wake flow field is calculated underfixed body without considering the free surface.The numerical model?including the method of grid division and the selection of turbulence model?were mainly discussed.The accuracy of the numerical model was verified by comparing with the internationally accepted experimental data.In the third chapter,the wake flow field is calculated with and without viscidity under the condition of ignoring free surface and posture.Coupling results of the potential and frictional flow field were obtained and separated.Its impact on the propeller were discussed.Frictional flow field was analyzed in scale effect including the distribution of axial wake fraction and the variation of wake peak.In the fourth chapter,the numerical simulation of the ship flow field in the short wave was performed with fixed body.The influence of the incident wave height and wavelength on time curve of axial wake fraction was discussed.The reason of change of average wake fraction was analyzed.The formula of the time curve of axial wake fraction is proposed under the condition of?/L_pp and wave steepness being small.Finally,the variation pattern of the flow field in a wave encounter cycle is discussedunder different working conditions.It has laid a foundation for the prediction of unsteady wake flow under the actual sea conditions and real scale.