Hydrocyclones form an important stage within conveying systems for dewatering or size classification. Over the past few decades they have been subject to significant modeling and experimental investigations. Yet, it is only with modern developments in computational fluid dynamics (CFD) and nonintrusive measurements such as tomography and laser techniques that a proper understanding of the internal flow dynamics is being developed. This paper presents new insight into the mechanisms governing the air-core dynamics and particle separation within the hydrocyclone that have been achieved by means of CFD. In particular, the flow field is identified to be distinctly asymmetric, such that the commonly assumed deterministic and symmetric assumptions of particle separation are inaccurate. In fact, radial particle transport is identified to rely upon the positive correlation of the mean and fluctuating components of radial velocity. The mechanism for air-core development during start-up is also inferred and for the first time related to experimental observation. High-speed video and radiographic measurements have provided validation for the predicted flowfield. In addition, the potential for application of tomographic techniques to the challenging verification of high-solids CFD has been demonstrated.