Disk cavity purge air outflow into the main gas path of a model turbine stage

Purge (or secondary) air is supplied to rotor–stator disk cavities of gas turbine stages in order to reduce ingestion of hot main gas into the cavities and cool the disks. The air eventually flows out into the main gas path through gap between the disk rim seals, in the process altering the main gas path velocity field and its thermal signature on the airfoils and endwalls. The main gas flow possesses high circumferential velocity downstream of vanes and upstream of blades. This requires fast imaging of the outflowing purge air as it mixes with the main gas. In this work, particle image velocimetry was used to visualize the purge air outflow from the rim cavity into the main gas path of a model single-stage turbine; the rim cavity geometry was a simplification of an actual turbine rim cavity. The low-speed main gas flow had a Mach number of 0.11. The outflow trajectory and velocity field were found to depend on the rim seal geometry, the purge and main gas flow rates, as well as the circumferential position within a vane pitch.