Aerodynamic Interaction Between Main Annulus Flow and Injected Secondary Air in Transonic High-Pressure Turbine Stage

Abstract This study explored the effects of secondary air blowing on the main annulus flow field and the performance of a transonic high-pressure turbine (HPT) experimentally and numerically. The test section featured a single-stage, unshrouded turbine with a blading consistent with modern low aspect ratio HPTs. The full annular, rotating, continuous turbine test rig was used for the whole testing campaign. This resulted in the most accurate and unparalleled matching of the similarity parameters to reality for both the primary and secondary air streams. An elaborate secondary air system built into the hardware enabled it to simulate all the critical coolant/purge air streams typically found in advanced hot sections. Detailed three-dimensional flow field and efficiency measurements for various secondary air flowrates were conducted. A complete set of numerical simulations was conducted in parallel with testing to assess how effectively they capture the flow physics, particularly the interaction between the mainflow and ejected secondary air streams. The rotor exit survey in the experiment suggests that film-coolant ejection from stator vanes intensifies passage vortices in the cascade, especially at the hub. Rotor blade film-cooling and rotor forward purge air appear to have the same enhancing effect on rotor-induced passage vortices. However, the vortex intensity in the region of stator–rotor vortex interaction is not enhanced further or even suppressed. Blade coolant also appears to enhance tip leakage flow, which then reduces work extraction. The enhanced tip leakage discharges into the mainstream, boosting the tip clearance vortices. Coolant blown from the over-tip casing also appears to enhance the passage vortices at the tip; however, it also has a positive effect, diminishing the tip leakage vortices.