Experimental study of main gas ingestion in a subscale 1.5-stage axial flow air turbine

Gas turbine efficiency has improved over the years due to increases in compressor

pressure ratio and turbine entry temperature (TET) of main combustion gas, made viable

through advancements in material science and cooling techniques. Ingestion of main

combustion gas into the turbine rotor-stator disk cavities can cause major damage to the

gas turbine. To counter this ingestion, rim seals are installed at the periphery of turbine

disks, and purge air extracted from the compressor discharge is supplied to the disk

cavities. Optimum usage of purge air is essential as purge air extraction imparts a penalty on turbine efficiency and specific fuel consumption.

In the present work, experiments were conducted in a newly constructed 1.5-stage

axial flow air turbine featuring vanes and blades to study main gas ingestion. The disk

cavity upstream of the rotor, the 'front cavity', features a double seal with radial clearance

and axial overlap at its rim. The disk cavity downstream of the rotor, the 'aft cavity', features a double seal at its rim but with axial gap. Both cavities contain a labyrinth seal radially inboard; this divides each disk cavity into an 'inner cavity' and a 'rim cavity'.

Time-averaged static pressure at various locations in the main gas path and disk

cavities, and tracer gas (CO2) concentration at different locations in the cavities were

measured. Three sets of experiments were carried out; each set is defined by the main air flow rate and rotor speed. Each of the three sets comprises of four different purge air flow rates, low to high.

The mass flow rate of ingested main gas into the front and aft rim cavities is

reported at the different purge air flow rates, for the three experiment sets. For the present stage configuration, it appears that some ingestion persisted into both the front and aft rim cavities even at high purge air flow rates. On the other hand, the front and aft inner cavity were completely sealed at all purge flows.