# Finite scale local Lyapunov exponents distribution in fully developed homogeneous isotropic turbulence

## TL;DR

This paper investigates the distribution of finite scale local Lyapunov exponents in fully developed isotropic turbulence, deriving relationships that support energy cascade modeling and linking Lyapunov exponents to velocity correlations.

## Contribution

It proposes a uniform distribution model for local Lyapunov exponents based on entropy maximization, linking them to turbulence energy cascade equations.

## Key findings

- Distribution of local Lyapunov exponents is uniform within a certain interval.
- Derived relationships support the closure of turbulence equations.
- Established link between Lyapunov exponents and velocity correlation functions.

## Abstract

The present work analyzes the distribution function of the finite scale local Lyapunov exponent of a pair fluid particles trajectories in fully developed incompressible homogeneous isotropic turbulence. According to the hypothesis of fully developed chaos, this PDF is reasonably estimated by maximizing the entropy associated to such distribution, resulting to be an uniform distribution function in a proper interval of variation of the local Lyapunov exponents. From this PDF, we determine the relationship between the average and maximum Lyapunov exponents and the longitudinal velocity correlation function. This link, which leads to the closure of von K\`arm\`an--Howarth and Corrsin equations, agrees with the relation obtained in the previous work, supporting the proposed PDF calculation, at least for the purposes of the energy cascade effect estimation. Furthermore, through the property that the Lyapunov vectors tend to align to the direction of the maximum growth rate of trajectories distance, we obtain the link between maximum and average Lyapunov exponents in line with the previous result.