ABSTRACT

Vortex dislocations generated in wake-type flows with spanwise nonuniformity are numerically studied. A clear identification of scenario of the formation of vortex dislocations and the basic features of the complex vortex linkages in vortex dislocations are shown by analyzing the substantial modification of vorticity field and vortex line tracks. The influences of the different spanwise nonuniformity on the generation of the vortex dislocations and the flow transition are studied. By these investigations a thorough understanding is gained on how wake flow behaviors accommodate the differences in phase, frequency and strength of vortices between shedding cells via vortex dislocations.

INTRODUCTION

Vortex dislocations generated between spanwise vortex shedding cells out of phase have been shown in the cylinder wake, mixing layer and some other nonlinear waves. The reader is referred to the works of Williamson (1992), Dallard and Browand (1993), among others. The vortex dislocations play an important role in the flow transition to turbulence and are considered of a new mechanism of the transition. Concerning the cylinder wakes, experimental visualization and measurement have provided much information about the generation, and development of the vortex dislocations. Their effects on wake velocity, fluctuation energy and frequency modification are also reported (Williamson 1992, 1996). There are few numerical studies about vortex dislocations. Recently Ling (2001) and Braza (2001) have first made numerical exploration on the vortex dislocations in waketype flow and cylinder wake. The generation of forced vortex dislocations and natural vortex dislocations are confirmed and their influences on the flow are evaluated. However how to describe and understand deeply the generation, the structure and the dynamics of such kind complex phenomena are still challenging problems. The structure of the vortex dislocations, particularly, the real information of the vortex reconnections in vortex dislocations is still not yet known thoroughly.

This content is only available via PDF.
You can access this article if you purchase or spend a download.