Measurement of Inertial and Acoustic Waves in a Turbine Chute Rim Seal Cavity

Abstract

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.