Abstract
Today’s aircraft turbine engines are exposed to higher temperatures, higher pressure with the need of increased rotor life to meet customer demand with higher thrust and better fuel efficiency. The case structure and rotating parts have different thermal and mechanical expansion and contraction which drive clearances to be excessive. In most of commercial engines, interstage seals (ISS) and mid-seals connected to tip clearance control system are designed to schedule seal clearances to maintain cavity pressures and balance purge flow. The system is designed to manage the gap for efficiency but prevent hot gas ingestion from overheating during engine operation.
Measurement of seal clearances would be a crucial way to understand seal clearance changes and to design purge flow for secondary flow and thermal design. For example, real time measurement would provide a way to adjust seal gaps to maintain turbine efficiency in new and deteriorated conditions. However, there is no promising method or an apparatus to sense and measure seal clearances in actual engine test or operation because ISS and mid-seals are located at inner flow path, such as buffer cavities through vane or nozzle, which are not favorable to directly install clearance probes and sensors.
This study is to review flight test data of turbine mid-seal clearance and radial tip clearances measurement and demonstrate its linear correlation between pressure and temperature against clearance changes during test of different operating conditions such as power calibration test at low and high altitudes and Active Clearance Control (ACC) valve swing test at high power. As a result, the study proposes new methods to assess seal clearances using conventional pressure sensors at forward and aft cavities with the linear conversion curves. The conversion method was developed for new engines tests, but it can be applicable for deteriorated conditions of production engines to improve efficiency and operability if independent seal clearance control system is developed and adapted.
