Impact of the Purge Flow Density Ratio on the Rim Sealing Effectiveness in Hot Gas Ingestion Measurements

Abstract

Predicting the correct quantity of purge flow necessary to prevent excessive ingestion of hot gases while, at the same time, minimizing the penalties in terms of engine efficiency and aerodynamics represents a great challenge for the engine designers. Since CFD approaches are still expensive and time-consuming, especially if 3D domains and unsteady conditions have to be simulated, fundamental test cases, replicating actual engines geometries, are still a valid approach to calibrate correlations or simplified models such as the Orifice Model. However, most of the experimental studies deal with test rigs at room temperature and do not consider the effect of the density ratio between purge and main flows. To fill this gap, the present paper investigates the impact of the density ratio on the rim sealing effectiveness by performing a non-intrusive diagnostic based on the PSP technique. The analysis was performed on a cold test rig where two different values of density ratio were tested by using N2 (DR = 1) and CO2 (DR = 1.52) as purge flow. The PSP effectiveness maps allowed to calibrate the Orifice Model for the stator side and to fit the coefficients of the Buffer Ratio model for the rotor surface at different flow conditions in the Externally-Induced ingress regime. In conclusion, it is shown that the obtained results can be used to scale experimental data, generally collected at DR close to one, towards more representative engine values where the difference between the density of purge and main flows cannot be neglected.