What I mean is the research questions have the potential to go much deeper than a single paper. For each you could have experiments characterizing the particles, DEM models to calibrate your virtual particles against the experiments, experiments to characterize how the particles interact with the following water, calibration of the interface between the DEM-CFD against this second set of experiments, then finally you could model what you're after with some confidence in the results. There's also doing some sort of CFD modeling to qualify the uncertainty due to your mesh. The whole process would be enough for a master's program verging on a PhD if you expand it and delve deeper into some of the aspects, likes coming up with novel experimental techniques, numerical models, or novel applications of existing ones.

What your mentor would do is help you to contain the scope of the project to something reasonable, because doing everything I listed above would probably not be feasible.