Investigation on Core Penetration Flow in a Turbine Rotor-Stator Disc Cavity

Abstract

(8) Annulus flow coefficient and rotational Reynolds number do not affect the core penetration flow

(9) As purge air rate increases, core penetration flow disappears

(10) The magnitude of negative radial velocity is proportional to the magnitude of the variation of the radial static pressure gradient.

and to examine the effects of annulus flow coefficient, rotational Reynolds number and non-dimensional purge air on core penetration flow. For the experiments, the open loop low speed single-stage turbine test facility in Seoul National University was modified. The axial clearance rim seal and the rotor-stator disc cavity were designed and installed in the test section. Artificial non-axisymmetry in a rotor disc was made with the attachment of a polyethylene terephthalate sheet on the rotor disc to examine the effects of geometric non-axisymmetry on the core penetration flow. Time-resolved tangential and radial velocities and time-resolved static pressures inside the cavity were measured to confirm the existence of core penetration flow and to find its causes with hot-wire anemometers and fast response pressure transducers. Mass flow rates of the annulus and the purge air, rotor angular velocity (RPM), time-averaged static pressures and temperature were measured to calculate the experimental conditions. Velocity field in the cavity was measured with Particle Image Velocimetry (PIV) technique to remove ambiguities associated with point velocity measurement. Experiments were conducted under non-dimensional purge air rates of 1000, 3200, 4000 and 5226

rotational Reynolds number of 7.9ⅹ105 and 9.0ⅹ105

and annulus flow coefficient of 0.26 and 0.23. Experimental results showed that: (1) Core penetration flow does occur, and it increases the angular velocity of an invicid core

(2) Core penetration flow revolves at the disc rotating speed, and occurs at three angular locations of the rotor disc

(3) Core penetration flow is caused by the unsteady radial static pressure gradient in the absolute frame caused by the non-axisymmetry in the rotor disc geometry

(4) When the radial static pressure gradient is suddenly increased by the rotating non-axisymmetric geometry, core penetration flow occurs due to the time lag in the tangential velocity response (Cause 1)

(5) Core penetration flow also occurs due to the time lag in the tangential velocity response to the flow induced increase in the radial static pressure gradient (Cause 2-A)

(6) Core penetration flow occurs due to the time lag in the tangential velocity response to the flow induced increase in the radial static pressure gradient following non-axisymmetric geometry induced reduction in the radial static pressure gradient (Cause 2-B)

(7) Core penetration flow occurs when the temporal variation in the radial static pressure gradient has low frequencies

An experimental investigation has been conducted to confirm the existence of core penetration flow

to find the causes of the core penetration flow occurrence