Multi-rotor aircraft experience very complex rotor-to-rotor aerodynamic interactions which affect the rotor forces and moments and vibratory loads (relative to an isolated rotor operating at the same RPM, pitch attitude and cruise speed). This is particularly true for the aft-rotors on a multi-rotor aircraft. This project conducts high fidelity computational fluid dynamics simulations of these complex flows to obtain a detailed understanding of the flow physics and the underlying phenomena that produce the observed changes in rotor performance metrics. The project also provides high-fidelity data to be used as a point of reference for lower-fidelity models. CFD simulations are carried out to understand the effect of changes in rotor separation parameters on performance metrics and to identify optimal configuration designs, with future simulations extending to rotor-rotor-wing systems.