Dynamics of multiscale vortex core filaments in electromagnetically driven two-dimensional turbulence

Chen-Yu Siao^1*, Wei-Shuo Lo¹, Lin I¹

¹Department of Physics, National Central University, Taoyuan City, Taiwan

* Presenter:Chen-Yu Siao, email:chenyusiao@g.ncu.edu.tw

Hydrodynamic turbulence, composed of interacting multiscale vortices, widely exists in various systems, such as water, smoke, stellar atmospheres, and blood flow, etc. The scale-by-scale cascade leads to continuous power spectrum with power-law decay. Previous works have mainly focused on some statistical properties, like scaling of power-law decay, velocity structure function and dynamics of tracers. Nevertheless, the spatiotemporal evolution of multiscale vortices and their interactions remain unsolved. In this work, the above issues are experimentally investigated using electromagnetically driven two-dimensional (2D) turbulence in the water solution with low concentration CuSO₄. Multiscale vortices are generated by the Lorentz force, from the DC horizontal electric field by two electrodes on the tank sides and the spatially alternating polarized magnetic field by a 2D square lattice array of magnets under the tank. The flow field and vortices are spatially decomposed into different modes by band-pass filtering. The cores of the multiscale vortices are tracked and used as singular objects to characterize vortex dynamics. It is found that vortex cores appear in the form of chaotic filaments in the xyt space with multiscale life times. Their averaged lifetimes decrease with increasing mode number. The Lagrangian velocity distributions of vortex cores exhibit non-Gaussian tails. The radial correlation function of vortex pairs shows that adjacent scales vortices with same helicity are more likely to entangle together.

Keywords: 2D turbulence, Vortex interaction, Mode decomposition