Non-equilibrium formulation for inertial particles in turbulent swirling flows
We study the dynamics of inertial particles in turbulence using datasets obtained from both direct numerical simulations and laboratory experiments of turbulent swirling flows. By analyzing time series of particle velocity increments at different scales, we show that their evolution is consistent with a Markov process across the inertial range. This Markovian character enables a coarse-grained description of particle dynamics through a Fokker-Planck equation, from which we can extract drift and diffusion coefficients directly from the data. The inferred coefficients reveal scale-dependent relaxation and noise amplitudes, indicative of inertial filtering and intermittency effects. Beyond the kinematic description, we analyze the thermodynamic properties of particle trajectories by computing the trajectory-dependent entropy production. We show that the statistics of entropy fluctuations satisfy both the Integral Fluctuation Theorem and, under certain conditions, the Detailed Fluctuation Theorem. These results establish a quantitative bridge between stochastic thermodynamics and particle-laden flows, and open the door to modeling turbulent transport using effective stochastic theories constrained by data and physical consistency.