This experimental study considered the performance of a chute rim seal downstream of turbine nozzle guide vanes (but without rotor blades). The experimental setup reproduced rotationally-driven ingestion without vanes and conditions of pressure-driven ingestion with vanes. The maximum rotor speed was 9000 rpm corresponding to a rotational Reynolds number of 3.3 × 10⁶ with a flow coefficient of 0.45. Measurements of mean pressures in the annulus and the disk rim cavity as well as values of sealing effectiveness deduced from gas concentration data are presented. At high values of flow coefficient (low rotational speeds), the circumferential pressure variation generated by the vanes drove relatively high levels of ingestion into the disk rim cavity. For a given purge flow rate, increasing the disk rotational speed led to a reduction in ingestion, shown by higher values of sealing effectiveness, despite the presence of upstream vanes. At $Uax/(Ωb)=0.45$⁠, the sealing effectiveness approached that associated with purely rotationally-driven ingestion. A map of sealing effectiveness against non-dimensional purge flow summarizes the results and illustrates the combined rotational and pressure-driven effects on the ingestion mechanism. The results imply that flow coefficient is a relevant parameter in rim sealing and that rotational effects are important in many applications, especially turbines with low flow coefficient.

A chute rim seal cavity has been instrumented with time-resolved and time-averaged pressure transducers as well as a gas concentration measurement system at the Oxford Rotor Facility. The unsteady pressure transducers were unevenly distributed along the circumference generating 15 combinations of angular spacing to conduct a phase analysis. The test operating conditions were modified through different configurations of mainstream flow, a range of rotational speeds and several rates of purge flow to obtain test data in the regimes of rotationally-driven, pressure-driven, and combined ingestion. The rotating unsteady flow structures within the rim seal cavity were studied through a combination of phase analysis of dynamic pressure signals and inspection of the frequency domain. The introduction of mainstream flow (axial and swirled) increased the overall unsteadiness exciting an additional band of lower frequencies. The phase analysis revealed these were associated with acoustic waves, providing the first experimental evidence of the presence and coexistence of inertial and acoustic waves in the rim seal cavity. The interaction of the inertial and acoustic waves strongly depends on the operating conditions, and may be linked to changes in sealing effectiveness.

An investigation of hot gas ingestion driven by the disc pumping effect in a chute seal was conducted at the Oxford Rotor Facility. Measurements of mean pressure, unsteady pressure and gas concentration have been logged and analysed under different operating conditions. The sensitivity of mean cavity pressure coefficient, frequency spectra of the unsteady pressures and sealing effectiveness to changing conditions of purge flow, annulus flow, rotor disc speed and seal clearance have been studied. The steady pressures revealed the development of two vortices in the cavity, induced by the sharp change in geometry of the stator wall. The increased shear at the interface between these two vortices strengthened the unsteady activity at this location. The addition of mainstream flow improved the sealing capability of the chute seal under certain operating conditions. The excitation of further frequencies when an axisymmetric annulus flow was introduced suggests a complex interaction between annulus and purge flows.