Unsteady Measurement of Core Penetration Flow in a Turbine Rotor-Stator Disc Cavity

Abstract

The existence and causes of the deep ingress of the annulus flow into the core region of a turbine rotor-stator disc cavity, or core penetration flow, have been investigated experimentally. In addition, the effects of annulus flow coefficient, rotational Reynolds number, and non-dimensional purge air flow rate on the core penetration flow have been examined. Using the low–speed, low expansion ratio single-stage cold turbine test facility at Seoul National University (SNU), time-resolved tangential and radial velocities in the cavity have been measured with 2-D hot-wire anemometers. In addition, time-resolved static pressures on the stator disc have been measured with fast response pressure transducers, and the unsteady cavity velocity field in the absolute frame has been measured using Particle Image Velocimetry (PIV). Geometric non-axisymmetry (e.g. eccentricity of a rotor disc cover in this study) can change the cavity exit pressure, and thus the radial pressure gradient in the cavity. A time lag in the tangential velocity adjustment to the variation in the radial pressure gradient results in a net radial force, leading to core penetration flow. The core penetration flow occurs twice when the cavity exit pressure increases, and once when the cavity exit pressure decreases. In this study, with a once per revolution geometric non-axisymmetry, the core penetration flow occurs three times per revolution, revolving at the disc’s rotational speed. Variations in the annulus flow coefficient or rotational Reynolds number do not affect the core penetration flow, but increasing the purge air flow rate weakens the core penetration flow.