Identification of Vortex Around High-Speed Ship Based on Liutex Method

Abstract

Vortex is ubiquitous in ship navigation. The first-generation vortex identification method is based on vorticity, which is understood as twice the rotational angular velocity around the center. The isosurface is used to explore the vortex structure of the flow field when it comes to second-generation Q, ∆ and other methods. The third-generation Liutex vector defines the local rigid body rotation of the fluid, including the local rotation axis and the rotation strength. The vorticity can be decomposed into the rigid body rotation and the pure shear, and the rigid rotation part can be accurately extracted from the fluid motion. The vortex identification method overcomes the need to adjust the threshold for specific flows and can capture both strong and weak vortices at the same time; Based on the idea of Liutex, the various characteristics of vortices can be quantitatively described, such as the absolute strength of vortices, relative strength, local axis of rotation, vortex core center, vortex core size, and vortex boundary. As a prototype of a destroyer, many engineers use the DTMB model to do a lot of numerical calculations. In this paper, the third-generation Liutex method is used to identify the vortex around the DTMB, and the vortex structure is analyzed in detail and compared with the Q criterion and so on. The calculation results show that the Liutex method has better accuracy.