Abrasive waterjet machining is a manufacturing process that is used to machine high-performance materials. The internal dynamics of the mixing chamber, where abrasive particles are introduced into the water jet, remain largely unexplored and have primarily been studied through only CFD simulations. When the jet diameter is reduced, additional non-scalable effects emerge, increasing the sensitivity of the mixing process and negatively affecting overall productivity. This article presents a CFD simulation of the processes within the mixing chamber, with the results compared to high-speed imagery of particles in the mixing chamber. Through particle observation, several aspects of the simulation were validated. However, new effects were observed that had not been accounted for in previous CFD simulations. For instance, particle clusters were seen being drawn towards the water nozzle.