Time-Dependent Diffusion Coefficients for Chaotic Advection due to Fluctuations of Convective Rolls

• Main Authors: Kazuma Yamanaka, Takayuki Narumi, Megumi Hashiguchi, Hirotaka Okabe, Kazuhiro Hara, Yoshiki Hidaka
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Fluids
• Subjects: weak turbulence; chaotic advection; Lagrangian chaos; time-dependent diffusion coefficient; nematic electroconvection; defect turbulence
• Online Access: https://www.mdpi.com/2311-5521/3/4/99

The properties of chaotic advection arising from defect turbulence, that is, weak turbulence in the electroconvection of nematic liquid crystals, were experimentally investigated. Defect turbulence is a phenomenon in which fluctuations of convective rolls arise and are globally disturbed while maintaining convective rolls locally. The time-dependent diffusion coefficient, as measured from the motion of a tagged particle driven by the turbulence, was used to clarify the dependence of the type of diffusion on coarse-graining time. The results showed that, as coarse-graining time increases, the type of diffusion changes from superdiffusion → subdiffusion → normal diffusion. The change in diffusive properties over the observed timescale reflects the coexistence of local order and global disorder in the defect turbulence.