Session: 40-02: Axial Compressor Instabilities and Stall

Paper Number: 151945

Analysis of Unsteady Flow Features in a Multi-Stage Compressor Operating Near the Stability Boundary 

When multi-stage compressors are operating close to the stall boundary, local flow separations and shear layer fluctuations create an inherently unsteady flow. Often, this unsteadiness can be described as a circumferentially travelling disturbance with characteristic frequencies and wave numbers. The nature of the unsteadiness is of interest as it can serve as a precursor to stall and also cause vibrations of the rotor blades. The paper uses full-annulus URANS computational fluid dynamic (CFD) simulations to investigate the unsteady flow features in a multi-stage compressor, for which this present study will be using a one-and-a-half-stage compressor domain. Representative of the front stages found in modern high-speed core compressors. In experiments, the first rotor row experienced vibration in the second torsional vibration mode when operating at part-speed conditions close to the stall boundary, which was caused by part-span stall cells local to the tip of the rotor. The present study concentrates on this part-speed operating condition and, in particular, investigates the evolution of stall features by comparing two different operating points on the compressor characteristic before part-span stall is fully established. Several sources of unsteadiness are identified at the hub and casing of the compressor and linked to characteristic time and length scales.

Presenting Author: Connor McLeod Imperial College London

Presenting Author Biography: Connor is a PhD Student at the Rolls-Royce Vibration University Technology Centre, Dynamics Group, Department of Mechanical Engineering, Imperial College London. His current research focuses on Turbomachinery Aeroelasticity, investigating the origins of non-synchronous vibrations in high-speed multi-stage compressors due to part-span rotating stall.

He obtained an MSc in Thermal Power (Aerospace Propulsion) at Cranfield University in 2022, carrying out his research within the Rolls-Royce UTC which specialises in Performance. He was also investigating low-order modeling for sub-idle turbine performance representative of turbines found in modern aero-engines.

Authors:

Connor McLeod Imperial College London
John Dodds Rolls-Royce plc
Giorgio Occhioni Rolls-Royce plc
Sina Stapelfeldt Imperial College London