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 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.
Highlights
The Oxford Rotor Facility has been modified to investigate rim sealing flows with more extensive instrumentation installed in the stator-rotor cavity to measure pressure and gas concentration
Steady pressure measurements have revealed the presence of different vortex strengths in the outer and inner sections of the cavity, implying that the change in geometry in the stator wall is inducing two different, coexisting vortices
The frequency spectra of the unsteady pressure signals present a maximum amplitude peak at r/b = 0.95, which is close to the change in stator wall geometry
Summary
Power 2021, Decades of research in the topic of hot gas ingestion point towards disc pumping, circumferential annulus pressure asymmetries and, more recently, rim seal flow instabilities as the main drivers for hot gas ingestion. The sealing performance is assessed based on pressure measurements and values of sealing effectiveness derived from readings of gas concentration in the absence of external flow and with an axial axisymmetric annulus flow The sensitivity of these variables to changes in purge flow, annulus flow, rotor disc speed and seal clearance are discussed. A summary of the main findings of the study is given in the concluding section
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