Tip Clearance Behavior in Centrifugal Compressors of High-Powered Emergency Gas Turbines

Emergency gas turbine generators are designed to supply large amounts of electric power instantaneously in the event of power outages. These generators are crucial for ensuring the safety and security of data centers, public facilities, and other critical infrastructure. In response to the increasing demand for higher capacity generators, enhancing the output of a 2MW-class gas turbine engine has become required. This study investigates the impact of output enhancement on the tip clearance of the two-stage centrifugal compressor in a single-shaft gas turbine with a single-can combustor and a three-stage axial turbine. The performance of the centrifugal compressor is sensitive to tip leakage flow, which degrades the pressure ratio and efficiency. Tip clearance is influenced by factors such as centrifugal force, thermal expansion, and aerodynamic thrust. Accurate determination of tip clearance under various operating conditions is therefore essential for improving gas turbine output while maintaining efficiency. To address this, capacitive clearance sensors and rub pins were installed on both the low-pressure and high-pressure compressors. Tip clearance measurements were conducted under different conditions including startup, steady states at varying outputs, and load rejection. Results indicated that tip clearance in the low-pressure compressor remained constant regardless of output variations, while the high-pressure compressor’s tip clearance decreased with increasing gas turbine output. Circumferential distribution of tip clearance in the high-pressure compressor was observed, attributed to heat transfer from the single-can combustor. During startup, centrifugal stress and subsequent temperature changes caused a reduction in tip clearance.