This work presents a calculation routine for the prediction of the aerodyna
mic loss of axial flow turbines with coolant injection, which can be easily
incorporated into throughflow calculation programs. The concept of the mix
ing layer is introduced and the one-dimensional method is used to estimate
the local mixing pressure loss. For a real annular nozzle guide vane, calcu
lations are performed with the aid of the mixing model and viscous loss cor
relations in order to predict loss at the blade mid-height. Predictions for
various single-row configurations show favourable agreement with experimen
tal results. Losses are also calculated for the multi-row configuration wit
h a consideration of flow recirculation among cooling holes. It is found th
at the coolant recirculation may cause a considerable increase in the press
ure loss when the amount of net coolant supplied is relatively small. The e
ffect of coolant temperature is also examined for both single-row and multi
-row cases.