Numerical Investigation of Complex Flow Field in Ship Self-Propulsion and Zigzag Maneuverability

Abstract

During the last decades, there are many proposed vortex identification methods, including Q, Δ, λ2 and λci criteria. However, these methods are based on the Cauchy-Stokes decomposition and/or eigenvalues of the velocity gradient. And these methods are not able to capture both strong and weak vortices simultaneously. In the present study, the third generation of vortex identification, liutex, is adopted to capture the vortex structure in the flow field of ship self-propulsion. The method can capture both strong vortices and weak vortices, and the six core issues for vortex definition and identification has been raised. At the same time, the second generation of vortex identification method, Q criterion, is applicated, and the results are compared with that obtained by using the liutex method. In the numerical simulations, the self-propulsion and zigzag manoeuvrability of KCS with a Lpp length of 6.0702 m are carried out, couping with KP505 propeller and the rudder with NACA0018 section. And the Froude number is 0.26. The vortex structure in both cases are present. Firstly, the vortex structure in the self-propulsion is analyzed. Both resluts obtained by liutex method and Q criterion are compared. And the same comparison of calcluted results is carried out in zz10/10 manoeuvrability. The results show that the liutex method better presents the size and direction of the vortex structure.