I am trying to perform a particle simulation through the human lung bifurcation geometry. I have created a idealistic geometry for three bifurcations and then I am trying to perform analysis in Openfoam using DPMFOAM because it involves Multiphase fluid particles as a Lagrangian and air as continous phase and trying to simulate the flow of the particle behaviour with a particle size of 0.0001 - 0.01 microns. The case is only a Laminar case , but the DPMFOAM by default has a PISO solver So can I change it to SIMPLE and one other big problem is that I have to incorporate two conditions i.e, one is inhalation where inlet is given from one inlet and outlet is obtained from eight outlets and after 2 seconds of the inhalation is done the same outlets has to act as inlets and flow has to come back but the particles will be carried away forward but only air is obtained back. So how can I perform this type of analysis using DPMFOAM. Please help me with this problem. The geometry is attached below?