Session: 05-05: Vibration Monitoring Analysis

Paper Number: 151191

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

Emergency gas turbine generators are designed to supply large volumes of electric power instantaneously in the event of power outages. They are installed in data centers, public facilities, waterworks systems, and other critical infrastructure, where they play key roles in ensuring the safety and security of people and society. In response to the increasing demand for higher capacity generators in recent years, it is required to enhance the output of a 2MW-class gas turbine engine by 25%.

The target gas turbine comprises a single-shaft, two-stage centrifugal compressor, a single-can combustor, and a three-stage axial turbine. Enhancing the output of the gas turbine is anticipated to affect the tip clearance of the compressor. It is well known that impeller performance is affected by tip leakage flow, and its pressure ratio and efficiency deteriorate significantly when the amount of tip leakage increases. This leakage flow occurs through the clearance between the impeller blade tip and the stationary casing surface, and its amount depends on this clearance area and the pressure difference between the pressure and suction surfaces of the impeller blades. The impeller performance deteriorates due to the pressure loss caused by the vortex of tip leakage flow and its mixing with the impeller’s main flow. On the other hand, the amount of tip clearance varies due to changes in compressor operating conditions, such as blade and/or disk deformation due to high centrifugal force and thermal expansion, aerodynamic thrust force on the impeller disk, and so on. Therefore, to enhance the output while maintaining the efficiency of the gas turbine, it is crucial to accurately determine the extent of tip clearance under actual centrifugal compressor operating conditions.

Given these circumstances, the authors installed rub pins and capacitive clearance sensors on both the low-pressure and high-pressure compressors and conducted clearance measurement tests under various operating conditions, including startup, steady states at different outputs, and load rejection. The results revealed that the tip clearance in the low-pressure compressor remained unchanged despite variations in output, whereas the tip clearance in the high-pressure compressor decreased as the gas turbine output increased. Additionally, it was found that the tip clearance in the high-pressure compressor exhibited circumferential distribution due to the temperature distribution caused by the single-can combustor. During engine startup, it was observed that the impeller deformed due to centrifugal stress as the rotational speed increased, leading to a reduction in tip clearance, which further decreased due to subsequent temperature changes.

Presenting Author: Fumiya Kurita IHI Corporation

Presenting Author Biography: Affiliation: Turbo Machinery & Machine Element Department, Corporate Research and Development Division, IHI Corporation
Research Area:He specializes in the development of measurement technologies for turbomachinery. His research focuses on enhancing product performance and reliability through precise measurement.

Authors:

Fumiya Kurita IHI Corporation
Wataru Sato IHI Corporation
Yusuke Yamagishi IHI Corporation
Hisashi Asai IHI Power Systems