Unsteady hot gas ingestion through the double rim-seals of an axial gas turbine

Abstract

Rim-seals are exposed to one of the most complex flows in modern high-efficiency gas turbines. The flow physics in the vicinity of rim-seals should be understood before predicting the hot gas ingestion that may cause a rise in disc temperature and a catastrophic failure. To investigate the seal performance of rim-seals, experiments were performed using a high-speed rotating test-rig and followed up that the unsteady flow analysis approach was proposed. The rotating rig consisted of 1.5-stage axial turbines with a double rim-seal. Local pressures and CO2 concentrations were measured to evaluate flow characteristics and sealing performance. At a rotational Reynolds number of 1.0 × 106, the circumferential pressure distribution on the vane endwall platform and corresponding distribution of the circumferential sealing effectiveness of the rim-seal were measured. The results of the unsteady Reynolds-averaged Navier–Stokes (URANS) model were in a good agreement with the experimental results. Time-averaged, time-resolved flow observations under various conditions revealed unsteadiness of rim-seal flow; ingress and egress occurred repeatedly over time at all circumferential locations. The results validated unsteady ingestion from a reduction in sealing effectiveness of up to 30% at any instant compared to the time-averaged sealing effectiveness. As the rotational speed increased, the asymmetric pressure distribution of the main flow increased, and the average sealing effectiveness decreased up to 50%. The novelty of this study is that instantaneous hot gas-ingestions reached to a location significantly deeper into the disc cavity than that obtained from time-averaged predictions. It is concluded that understanding the nature of unsteady flow and its effects to hot gas-ingestion is vital to the reliable design of turbine rim-seals.