An investigation of the hot gas ingestion phenomenon in the Oxford Rotor Facility ex- amined rotor disc rotation, mainstream pressure asymmetries and unsteady structures in the cavity as main drivers. The facility underwent major modifications to allow different annulus flow configurations, higher resolution in the low and high bandwidth pressure instrumentation and the installation of a new system to quantify the sealing effective- ness using the tracer gas technique (±0.0068 uncertainty). Rotationally-driven ingestion was simulated with a bladeless annulus and conditions of pressure-driven ingestion with nozzle guide vanes. By decoupling each contribution, the fundamentals of hot gas ingestion are addressed. A chute rim seal arrangement has been studied with two gap sizes. The influence of non-dimensional purge flow, Cw, rotational Reynolds number, Reφ, axial Reynolds number, Reax, and seal clearance, sc, has been examined through the mean cavity pressure coefficient, Cp, sealing effectiveness, ε, and frequency spectra of the unsteady pressure signals. The maximum Reφ was 3.3 × 106 with a flow coefficient of 0.45 with NGVs. The mean pressure field in the cavity revealed the existence of two vortices. Values of sealing effectiveness showed good agreement with the disc pumping orifice model at low flow coefficients, suggesting operation in the rotationally-induced regime. This finding challenges the extended assumption that pressure-driven ingestion dominates when asymmetries exist in the annulus. However, this hypothesis matched the experimental data at high flow coefficients. The frequency spectra of the high bandwidth pressure signals revealed two sources of unsteadiness in the rim seal region: the large-scale flow features due to rotation of the disc and the interaction between the annulus and purge flows.