Neutrally buoyant particle dynamics in fluid flows: Comparison of experiments with Lagrangian stochastic models

We study the validity of various models for the dynamics of finite-sized particles in fluids by means of a direct comparison between theory and experimentally measured trajectories and velocities of large numbers of particles in chaotic two-dimensional flow. Our analysis indicates that finite-sized particles follow the predicted particle dynamics given by the Maxey-Riley equation, except for random correlated fluctuations that are not captured by deterministic terms in the equations of motion, such as the Basset-Boussinesq term or the lift force. We describe the fluctuations via spectral methods and we propose three different Lagrangian stochastic models to account for them. These Lagrangian models are stochastic generalizations of the Maxey-Riley equation with coefficients calibrated to the experimental data. We find that one of them is capable of describing the observed fluctuations fairly well, while it also predicts a drag coefficient in near agreement with the theoretical Stokes drag. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3632100]