Study Of Velocity And Turbulence Intensity Distribution Within Ship Twin-propeller Jet

The research of twin-propeller jet is of great significance for calculating the impact load at the marine structure caused by propeller jet and studying the propeller performance.In this paper,the twin-propeller jet model is built based on Lam's(2008)classical single propeller experiment.Standard k-? model is used to simulate the flow field of twin-propeller jet.The distribution of the flow field of twin-propeller jet is studied by comparing the CFD results,Lam's single propeller experimental results and the semi-empirical equations of single propeller jet proposed by previous researchers.The non-interference zone,interference zone,zone of flow establishment,zone of flow establishment with four peak values,zone of flow establishment with two peak values and zone of established flow are divided based on the axial velocity distribution within the twin-propeller.The effects of rotation direction,distance between two propellers,rotating speed,blade area ratio and type of propeller on the efflux velocity and velocity distribution are studied.The 3D CFD numerical simulation is used to simulate the twin-propeller jet.This paper proves that two propellers' jets do not interfere with each other at the efflux plane based on theory.Based on this conclusion,the numerical simulation results of twinpropeller jet are verified by using experimental results at the efflux plane of the single propeller.The effects of grid density and turbulence model on the numerical results are studied.The numerical simulation method which is suitable for predicting twinpropeller jet is proposed.Structured and unstructured mesh,rotating reference frame method and standard k-? model is used in numerical simulation.The axial,tangential and radial velocity components of the twin-propeller jet are studied by comparing the CFD results,Lam's single propeller experimental results and the semi-empirical equations of single propeller jet proposed by previous researchers.The equations to describe the twin-propeller jet are proposed based on the numerical results.The axial velocity component is the largest component of the twin-propeller jet.With the development of the jet,the axial velocity distribution of the two propellers shows a trend of mixing.The tangential velocity component is the second largest velocity component of propeller jet and the radial velocity component accounts for only a small proportion.Maximum turbulence intensity of twin-propeller jet decays firstly,then increases and decays at last as the jet develop downstream.By comparing the similarities and differences between the single-propeller jet and the twin-propeller jet,considering the distance between two propellers and the rotation direction of propeller,the equations of axial velocity distribution of twin-propeller jet is proposed.The influence of rotating speed and blade area ratio on thrust coefficient and efflux velocity are studied.At last,the tangential velocity,radial velocity,axial velocity and turbulence intensity distribution of twin-propeller jet are analysed qualitatively.