Abstract
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 has 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 suggested a complex interaction between annulus and purge flows. INTRODUCTION Decades of research in the topic of hot gas ingestion pointed towards disc pumping, circumferential annulus pressure asymmetries and, more recently, unstable rim seal flows as the main drivers for hot gas ingestion. These three mechanisms are depicted in Figure 1. Ingress of high temperature flow from the main gas path is undesired. Rotor discs are not thermally insulated and ingestion of hot gas from the mainstream can significantly reduce the operating life and damage the mechanical integrity of these highly stressed components. To prevent this from occurring, cool air is injected between the stator and rotor discs to purge and pressurise the cavity, however, this comes at the detriment of engine efficiency. The intrinsically convoluted flow field in the turbine rim region creates a complex environment in which fundamental understanding of the basic flow physics becomes paramount to comprehend the synergetic effect of each of the mechanisms mentioned above. This investigation focuses on the performance of a chute rim seal with no blades and vanes in the annulus, such that ingestion is expected to be driven by the effects of rotation. Bru Revert et al. (2021) showed that this scenario is relevant for high pressure turbines at low flow coefficients.