Numerical Investigation of Rim Seal Flow in a Single-Stage Axial Compressor

This study conducts experimental and modeling analyses to comprehend the unsteady flow phenomena within cavity gaps, with a specific focus on finding the optimal rim seal flow rate for enhancing turbine efficiency. The rim seal flow phenomenon is investigated and validated against the University of BATH's single-stage turbine experiment rig. The emphasis is on the steady-state computation of rim seal qualities using passive-scalar transport for tracer gas modeling, with limited exploration of unsteady phenomena. The LISA 1.5 stage model from Zurich University serves as a baseline for turbine efficiency studies, incorporating the rim seal configuration. The computational domain's influence, including the turbomachinery Multi-Reference Frame approach, is investigated. While the Frozen Rotor accurately predicts ingression flow fields, the no-interface model poorly predicts ingression, favoring a simplified "thin seal" model. A statistical approach is introduced for the "Orifice" model to implicitly calculate the minimum sealing flow for each rim seal configuration. Pre-swirling the rim seal demonstrates a reduction in shear forces on the rotor wall, consequently lowering friction torque on the rotor disc. However, swirling flow appears ineffective in influencing ingression and egression due to the model's long propagate distance. In addition to steady-state investigations, the harmonic balance method explores unsteady phenomena in Axial turbine configuration. Kelvin-Helmholtz instabilities within the rim seal gap are observed, acting as driving mechanisms for large-scale structures at 98% rotor speed. Incorporating wheel-space cavities in the LISA 1-stage model significantly alters flow phenomena and turbine efficiency. Rotor-stator interaction at specific times can complicate wheel space sealing, contrary to bladeless model predictions. Furthermore, an increase in rim seal flow is associated with reduced turbine isentropic efficiency.