Cooling turbine blade rows

In the second approach, a value for is not assumed but a relationship for dip/dT is determined from semi-empirical expressions for the amount of cooling air that is required in an (elementary) turbine blade row. One such relationship, derived in Ref. [5], gives... 

Open cooling of turbine blade rows—detailed fluid mechanics and thermodynamics... 

In Chapter 5 (and Appendix A), the detailed fluid mechanics and thermodynamics involved in cooling an individual turbine blade row are discussed, enabling if/ to be... 

We concentrate here on open loop cooling in which compressor air mixes with the mainstream after cooling the blade row, the system most widely used in gas turbine plants (but note that a brief reference to closed loop. steam cooling in combined cycles is made later, in Chapter 7). For a gas turbine blade row, such as the stationary entry nozzle guide vane row where most of the cooling is required, the approach first described here (called the simple approach) involves the following ... 

Hart.sel, J.E. (1972). Prediction of effects of ma.s.s-transfer cooling on the blade-row efficiency of turbine airfoils. AIAA paper 72-11. 

At very high combustion temperatures, it is not sufficient that the first blade row alone needs to be cooled. In practice, up to half a dozen rows may be cooled in an industrial gas turbine, if the combustion temperature is high and the allowable blade metal temperature is low. The cooling fractions for each of the cooled rows must be estimated and u.sed in the cycle calculations, which now become complex. 

The results of calculations for the cooling air flow fractions in the first (nozzle guide vane) row of the turbine, ba.sed on the assumptions outlined in Section 5.2 for film cooled blading, are illustrated in Fig. 5.1. The entry gas temperature Tgi was taken as the combustion temperature Tcoi = Ty and the cooling air temperature as the compressor delivery temperature T2. The cooling air required is. shown here as a fraction of the exhaust gas flow, i.e. as ip/( 1 + ip), plotted against compressor pressure ratio and combustion temperature for an allowable blade metal temperature, Tpi = 800°C. Also shown are... 

---