Active Clearance Control in High-Pressure Compressors

As a consequence of the strive for higher efficiencies, pressure ratios in modern civil aircraft engines have steadily increased over the decades. Higher fluid densities translate into narrower and narrower flow channels, which in turn require shorter rotor and stator blades. This leads to a percentual increase in the tip clearance, defined as blade over gap height. Such gaps are unavoidable to avoid collisions (rubbing) between blade tips and casing during engine service. However, they also have a first-order impact on overall engine performance and operational stability. Traditionally, (cold) clearances are designed to ensure that no rubbing occurs during the most extreme transient manouvers, such as aircraft take-off and engine hot reslam. This leads to sub-optimal (hot or running) clearances during the most part of engine operation. Therefore, robust and efficient ways to actively influence the running clearances have become a matter of interest.

Within this context, this project aims to establish the feasibility of different concepts to influence rotor and casing displacements, so as to keep clerances to a minimum while ensuring safe operation. The core of the project consists of the numerical modelling of a representative high-pressure compressor which will be used to assess and optimize several active control techniques, such as casing cooling through bleed-air and/or heat pipes, and electric casing heating. As a second major step, the main aspects of the model will be identified aiming at robust simplification and surrogate modelling. Such tools can then be used in optimization runs and eventually be coupled with existing preliminary design algorithms.

Aim / Objective:

  • Construction of a robust numerical model able to simulate transient compressor clearances
  • Assessment of clearance control concepts, such as casing cooling/heating techniques
  • Model simplification to enable fast optimization and coupling with preliminary design tools

Project Partner

MTU Aero Engines AG