Performance Evaluation in a Fully Purged High-Pressure Turbine Stage Using Seed Gas Concentration Measurements

The efficiency assessment of a high-pressure turbine (HPT) stage is complicated by the presence of upstream and downstream purge flows. In fact, the efficiency calculation is often based on massflow-averaged values of total temperature at the stage inlet and outlet planes. Moreover, the purge flow distribution in the annulus is usually unknown and therefore assumed as uniform. This paper presents and applies an alternative method to calculate the efficiency of a fully purged HPT stage. Such definition relies on seed gas concentration measurements at the HPT stage outlet plane, to determine the outlet purge flow distribution. After comparing the alternative method to the standard definition (based on the assumption of uniform purge) for the nominal purge case, the efficiency variation between the case with nominal purge and the case without purge is investigated.