Experimental Measurements of Ingress in a Turbine Stator-Rotor Cavity

The ingress of air from the main annulus into the first stage stator-rotor cavity of high-pressure turbines usually results in the development of complex flow fields that may have a significant impact on the turbine performance. Additionally, the amount of ingested flow can vary significantly during engine operation, particularly under transient or off-design conditions, thus affecting the resulting values of sealing effectiveness. Therefore, the hot gas ingestion experimental facility of the University of Florence has been employed to investigate the sealing performance of a single radial rim seal at both design and off-design conditions. The obtained experimental results indicate that reducing the main annulus flow coefficient from its design value significantly improves sealing performance. On the contrary, increasing the main annulus flow coefficient results in very similar sealing effectiveness curves across the entire investigated range of purge flow. Hence, the obtained results suggest that there are specific operating conditions where the sealing performance is unaffected by the swirl difference between the annulus and the cavity, even though this parameter has been recently suggested as the primary factor influencing the amount of ingested flow. Therefore, the aim of this work is to provide further insights into the link between sealing effectiveness and annulus-cavity swirl difference. Moreover, a recently developed theoretical model, named Ingress Wave Model (IWM), has been used to fit all the measured data. Despite the general good agreement between experimental and predicted values, the model shows slightly worse performance when the main annulus flow coefficient is reduced and at high cavity radius. The former issue may be due to the fact that the model neglects the impact of disk pumping, while the latter could be attributed to increased shear gradients and unsteadiness near the entrance of the rim seal.