A coupled Eulerian and Lagrangian Mixing Model for Intermittent Concentration Time Series

The time series of scalar concentration at fixed points in space is modeled by a system of Eulerian stochastic differential equations for velocity and concentration using statistics obtained from a Lagrangian micromixing model. The interaction by exchange with the conditional mean model is used in both the Eulerian and Lagrangian frameworks allowing the natural representation of the external, large scale, scalar intermittency due to meandering. The calculated time series includes both the meandering and the relative dispersion time scales. The model is compared to experimental data in decaying grid turbulence and to Lagrangian simulations in stationary homogeneous turbulence. Scalar probability density functions conditioned on the velocity are calculated at two downwind distances from the source along with the corresponding time series to illustrate the separate effects of meandering and relative dispersion. © 2009 American Institute of Physics.