Experimental Investigation of Swirl and Flow Structure Inside a Rotor-Stator Cavity

In order to ensure safety, predictable and acceptable life of gas turbine engines an important task is the design of the secondary air system (SAS). To avoid hot gas path ingestion, one of the most critical concerns in a well-performing SAS is the understanding of the air motion within of the stator-rotor cavity systems. The state of the art of the fluid solver tools used to predict the flow behaviour inside cavities is generally based on codes with correlative approaches, in order to reduce calculation times and computational resources. In order to improve the precision of correlations, by means of data with reduced associated uncertainty, experimentalists performed an experimental campaign selecting a simple test case composed by a rotating disc facing a flat stator. Imposing several working conditions, the rotational speed was varied in order to gain a rotational Reynolds number up to 1:2 X 10 ^ 6 which is one order of magnitude less than eal seals working conditions. The analysis of the swirl rate as well as the frictional moment exerted by the rotor on the fluid was carried out based on different sealing mass flows. Pressure probes were used to obtain radial distribution of static and total pressure on the stator side. In order to deepen the analysis on the flow behaviour inside cavity, flow field measurements using a 2D PIV system was performed on two different planes: velocity contours were used to help the detection of the core region. Finally, the wide database of the experimental results were used to improve a simple model able to predict the behaviour of rotorstator cavities including the effect of the inlet geometry of the cavity.