Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

Radial Flow Gas Turbines 281
FIG. 8.18. Pressure ratio limit function for a turbine (Wood 1963) (By courtesy of the
American Society of Mechanical Engineers).
FIG. 8.19. Cross-section of film-cooled radial turbine.
of the turbine exposed to the high temperature gas. Following the successful application
of blade cooling techniques to axial flow turbines (see, for example, Horlock
1966 or Fullagar 1973), methods of cooling small radial gas turbines have been
developed.
According to Rodgers (1969) the most practical method of cooling small radial
turbines is by film (or veil) cooling, Figure 8.19, where cooling air is impinged on
the rotor and vane tips. The main problem with this method of cooling being its
relatively low cooling effectiveness, defined by
where T m is the rotor metal temperature,
(8.56)