On the Use of Pressure-Sensitive Paint to Determine the Rim Sealing Effectiveness

The control of cavities sealing has been a challenging problem since early gas turbine development stages and several aspects regarding the flow physics and the modeling of rim seal flows, especially in terms of unsteady phenomena, still represent an open question. Fundamental test cases have been extensively used in the open literature to characterize the level of ingestion by varying the main flow parameters and the geometrical features. In most of them, the seal effectiveness is measured by using taps connected to a gas analyzer used to sample the concentration on the stator surface of a reference foreign gas (generally CO2) used to seed the purge flow. Consequently, the results are usually single-point measurements, and unsteady effects are inevitably neglected. Moreover, the intrusiveness of the approach must be carefully checked, and the application on the rotor side demands for complex slip-rings or telemetry. To overcome these limitations, the current work presents the application of the pressure-sensitive paint (PSP) technique to the study of hot gas ingestion phenomena on a single-stage rotating cold rig. By using an oxygen-free gas such as N-2 as purge flow, the PSP was used to measure the partial pressure of oxygen at the wall through the wide optical accesses present in the rig. Then, the collected 2D distributions of pressure were related to the seal effectiveness inside the wheel space. The proposed methodology was first validated through a comparison with the data obtained from standard gas sampling and then applied as main experimental technique to characterize the seal ingestion. The analysis of the results highlighted the capabilities of the PSP technique to fast collect data on both stator and rotor sides, including the tip of the seal tooth where nonuniform efficiency distributions in the circumferential direction have been detected.