Published on August 27, 2025
–
Updated on August 27, 2025
Dates
on the September 2, 2025
11h00
Location
Institut de Physique de Nice
Main seminar room
Main seminar room
Double feature! 1) "Forgetful" turbulent energy cascade 2) How universal are Lagrangian statistics of turbulence? Insights from the hierarchy of coherent vortices
Fluid seminars
"Forgetful" Abstract (Ryo Araki):
"Forgetful" Abstract (Ryo Araki):
Turbulence is a ubiquitous phenomenon which appears in our daily lives. In fully developed turbulence, i.e. at high Reynolds numbers, the small-scale statistics are believed to be universal. This characteristic is often associated with an intuitive picture that the small scales become universal by "forgetting" about the large-scale features during the energy cascade process. In our recent work (Araki, Vela-Martin, and Lozano-Duran, J. Phys. Conf. Ser., 2024), we investigated this scenario in an information-theoretic manner. More specifically, we evaluated a quantity called information flux to quantify the level of causal in developed turbulence. Furthermore, we analysed different energy cascade mechanisms and how they contribute to the information transfer in turbulence.
"Lagrangian" Abstract (Yusuke Koide):
"Lagrangian" Abstract (Yusuke Koide):
How universal are the Lagrangian properties of turbulence? From the Eulerian viewpoint, the energy spectrum, once normalized by the kinematic viscosity and the energy dissipation rate, collapses onto a single curve regardless of the method used to drive turbulence. The power spectral density of the Lagrangian velocity has also been reported to follow the Kolmogorov scaling within the Lagrangian inertial range. However, its universality and formation mechanism remain unclear.
To answer this question, we investigate the Lagrangian spectrum for turbulent flows with different Reynolds numbers and forcing methods using direct numerical simulations. This systematic comparison demonstrates that universal behavior is confined to a narrow high-frequency regime, whereas nonuniversality depending on the forcing method appears broadly in a low-frequency regime.
To identify the physical origin of these features, we propose a scale-decomposition method for the Lagrangian velocity that relates the hierarchy of coherent vortices to the Lagrangian properties of turbulence. Our scale-decomposition analysis reveals how vortices at different scales form the power spectral density of the Lagrangian velocity: small-scale vortices in the inertial range contribute to the spectrum in a self-similar manner, whereas the contribution from the largest-scale flows exhibits nonuniversal behavior and can contaminate the Kolmogorov scaling. These findings provide a perspective for interpreting experimental and numerical data on Lagrangian statistics based on the hierarchy of coherent vortices with different length scales.
To answer this question, we investigate the Lagrangian spectrum for turbulent flows with different Reynolds numbers and forcing methods using direct numerical simulations. This systematic comparison demonstrates that universal behavior is confined to a narrow high-frequency regime, whereas nonuniversality depending on the forcing method appears broadly in a low-frequency regime.
To identify the physical origin of these features, we propose a scale-decomposition method for the Lagrangian velocity that relates the hierarchy of coherent vortices to the Lagrangian properties of turbulence. Our scale-decomposition analysis reveals how vortices at different scales form the power spectral density of the Lagrangian velocity: small-scale vortices in the inertial range contribute to the spectrum in a self-similar manner, whereas the contribution from the largest-scale flows exhibits nonuniversal behavior and can contaminate the Kolmogorov scaling. These findings provide a perspective for interpreting experimental and numerical data on Lagrangian statistics based on the hierarchy of coherent vortices with different length scales.