The rims of high pressure turbines in aeroengines are sealed with air via the internal air system. This sealing is required to avoid occurrence of hot gas ingestion into the rotor-stator cavities. Due to a rapid decrease of turbine disc life at higher temperatures, such ingestion would present a hazard to the integrity of the discs and subsequently to the safety of the aircraft. One of the driving factors for ingestion is the circumferential pressure variation downstream of vanes and blades due to the aerodynamic wakes. Small ingestion cavities close to the annulus are commonly used to damp down this pressure variation. Substantial ingestion into these cavities is permitted. The actual sealing of the rotor-stator cavity itself is accomplished with a secondary seal.
A numerical simulation of the flow in an engine type rotor-stator cavity was carried out using a commercial CFD code. The cases studied comprise relevant features as rotor-stator and ingestion cavities, leakage across rotor blade shanks and circumferential pressure variation downstream of an NGV. The simulation was carried out at relevant engine temperatures and pressures.
The paper will firstly present the effects of a variation of the rim sealing mass flow on the flow field, ingestion and temperature increase in the cavity. These results were solely gained by computational means. For validation of a new air system design, engine tests on the BR715 jet engine have been performed. The data measured in these tests not only serve for certification purposes, but also may be used as input for CFD calculations. Thus, the experimental data was the baseline for comparison with the results from the present study.