Modeling the Air-Cooled Gas Turbine: Part 2—Coolant Flows and Losses

Abstract

This paper is Part II of a study concerned with developing a formal framework for modeling air-cooled gas turbine cycles. It deals with the detailed specification of coolant flowrates and losses. For accurate performance assessment, it is necessary to divide the turbine expansion into individual stages with stator and rotor rows being treated separately. Particular care is needed when deriving the equations for the rotor, and it is shown how all required flow variables can be estimated from minimal data if design values are unavailable. Specification of the cooling flowrates is based on a modified Holland and Thake procedure, which can be formalized in terms of averaged parameters. Thermal barrier coatings can be included if present. The importance of allowing for fluctuations in combustor outlet temperature is stressed and procedures for dealing with end-wall and disk cooling are suggested. There is confusion in the literature concerning cooling losses, and it is shown how these may be defined and subdivided in a consistent way. The importance of representing losses in terms of irreversible entropy creation rather than total pressure loss is stressed. A set of models for the components of the cooling loss are presented and sample calculations are used to illustrate the division and magnitude of the loss.