COMPARISON OF RIM SEALING EFFECTIVENESS IN DIFFERENT GEOMETRICAL CONFIGURATIONS

The flow field developing inside the stator-rotor cavities of gas turbines is characterized by a complex unsteady behaviour which still requires expensive and time consuming CFD simulations to be accurately modelled. Hence, the experimental characterization of the rim sealing effectiveness by means of scaled down geometries that replicate the rim seals found in actual engines still represent a widely used approach in literature. However, the obtained results can greatly depend on the specific geometry of the tested rim seal. Moreover, different geometrical parameters can vary during the operation of the engine, especially under transient or off-design conditions, thus influencing the resulting effectiveness values. For this reason, the sealing performance of seven different configurations of radial rim seals has been investigated and the obtained dataset has been correlated by using the Orifice Model. Hence, a detailed comparison of the results allowed the evaluation of the impact of different values of axial overlap, different distances between the vanes trailing edge and the blades leading edge and different values of radial gap. In particular, a three times greater axial overlap and a modest increase in the distance between the trailing edge of the vanes and the leading edge of the blades were both found to provide a limited improvement in the sealing performance, with a respective average reduction in Fmin of approximately 5% and 6%. A radial gap 2.4 times greater was instead found to lead to an average increase in the required quantity of sealing flow rate of approximately 44%. Hence, the amount of purge flow required to fully seal a cavity was not found to exhibit a linear increase with the radial gap.