I'm new to star-cd and it's Lagrangian particle tracking capabilities. Can I (1) compute two-way coupled flow; (2) include Brownian motion; (3) include user defined force terms for wall intertactions?

Thanks

You can definitely compute two-way coupled flow - it's what prostar calls "coupled". And user-defined wall interaction can be done through the drowbc user subroutine. There is no built-in brownian motion model - the closest thing is turbulent dispersion - but you could define your own forces on the droplets using the dromom user subroutine, and this would allow a brownian motion model to be implemented.