Characterizing most irregular small-scale structures in turbulence using local Hölder exponents

Area of Science:

• Fluid dynamics
• Turbulence theory
• Computational physics

Background:

• Understanding the topology and dynamics of velocity fields in regions of low regularity is crucial in fluid dynamics.
• Scalar fields can characterize pseudo-Hölder exponents and local energy transfers, offering insights into complex flow behaviors.

Purpose of the Study:

• To analyze the topology and dynamics of velocity fields in areas of lesser regularity using scalar fields.
• To investigate the nature of irregular structures in turbulent flows and their relation to vortex dynamics.

Main Methods:

• Utilized velocity fields from two direct numerical simulations of the Navier-Stokes equations in a triply periodic domain.
• Averaged over 213 irregular events to obtain a typical irregular structure.
• Performed a time-resolved analysis of the birth and death of irregular structures.

Main Results:

• Identified irregular structures similar to a Burgers vortex, exhibiting nonaxisymmetric corrections.
• The asymmetry is potentially explained by vortex interactions, including vortex reconnection.
• Detailed analysis revealed connections between irregular structures and vortex dynamics.

Conclusions:

• Scalar fields effectively capture the topology and dynamics of velocity fields in less regular areas.
• Irregular structures in turbulent flows are closely related to vortex interactions and reconnection events.
• The study provides a deeper understanding of the complex dynamics within turbulent flows.