Handbook of Turbomachinery Second Edition Revised - Ventech!

Two major practical requirements exist when the turbine rotor–stator
system is developed:
1. Define turbine disc local heat-transfer coefficients for specified
rotational speed, geometry, and disc-cooling configuration.
2. Provide a system that prevents hot gas ingress into the disc
plenum.
Disc heat-transfer prediction based on flow visualization (Pincombe, 1989)
and measured angular velocity of the flow core in the plenum between disc
and stator was a traditional method along with complicated direct
measurements of the local disc temperatures or heat fluxes.
Some of the early flow visualization methods for the air in the plenum
were based on application of TiCl4 reacting chemically with the humid air to
produce high-density white smoke. This method of flow visualization is
practically obsolete at the present time because of product toxicity. It was
noticed (Glezer, 1969) [131] and Phadke and Owen, 1988 [132] that
nonaxisimmetric pressure distribution in the main-stream flow over disc–
stator gap can produce a standing wave pattern of ‘‘hot gas’’ ingress into the
plenum even when outward supply of ‘‘cooling’’ air flow exceeded disc
pumping flow. (Turbine nozzle vane wakes present a typical example of
nonaxisimmetric pressure distribution.) This phenomenon has to be
addressed when an actual rotor–stator system is developed.
A very promising experimental technique to study both ‘‘hot gas’’
ingress and local convective heat transfer distribution along turbine disc and
stator, based on application of liquid-crystal coating in a thermal transient
test, was described by Metzger et al. [133]. More recent results performed at
ASU for some practical rotor–stator geometries were referred earlier [105].
An additional study of effect of rotation on the accuracy of the liquidcrystal
experiment was performed by Camci et al. [134] who replaced an
acrylic disc with high-strength aluminum disc dressed with a balsa layer that
was required to meet one-dimensional transient response of ‘‘semi-infinite
solid.’’ Balsa face surface was painted black and coated with thin liquid
crystal. Coating of the disc face and acrylic stator with liquid crystals, which
have significant difference in transitional temperature, allows performing
heat-transfer thermal imagining for both disc and stator during one test.
This approach was used and tested in a full-scale industrial turbine rotor–
stator system rig (Fig. 33). Significant design features required for this rig
included
Full-scale turbine disc with rim seal and preswirler air delivery system
(feeding air into angular disc holes that represent blade-cooling
passages)
Copyright © 2003 Marcel Dekker, Inc.