Experimental aerodynamic and aeroelastic investigation of a transonic compressor rotor with reduced blade count

Authors

Daniel Franke - Technical University of Darmstadt, Institute of Gas Turbines and Aerospace Propulsion
Daniel Möller - Technical University of Darmstadt, Institute of Gas Turbines and Aerospace Propulsion
Maximilian Jüngst - Technical University of Darmstadt, Institute of Gas Turbines and Aerospace Propulsion
Heinz-Peter Schiffer - Technical University of Darmstadt, Institute of Gas Turbines and Aerospace Propulsion
Thomas Giersch - Rolls-Royce Deutschland Ltd & Co KG
Bernd Becker - Rolls-Royce Deutschland Ltd & Co KG

Abstract

Environmental challenges and related regulations regarding reduced emissions of exhaust gases and noise require novel technological approaches for future aero engines. Therefore, developments aim for opportunities to increase efficiency in conjunction with reduced weight and size. The axial compressor as a major component offers great potential by increasing the overall pressure ratio with a minimum number of compressor stages as well as combining a reduced blade count with a BLISK rotor design. However, these measures result in increased aerodynamic blade loading associated with a vulnerability to blade vibration, especially for front stage rotors during part speed operating conditions.Therefore, this paper investigates the aerodynamic and aeroelastic characteristics of a transonic axial compressor, focusing on blade count reduced rotor behavior. The analysis is based on several experimental investigations, conducted at the transonic compressor test rig at Technical University of Darmstadt. Two BLISK rotors with similar aerodynamic designs and a variation in blade count were tested in combination with an equal inlet guide vane and stator configuration. In order to obtain measurement data for the detailed aerodynamic and aeroelastic analysis, extensive steady and unsteady instrumentation was applied, including strain gauges on the rotor blades as well as blade tip timing and unsteady wall pressure transducers in the casing.Besides the transient measurements at the stability limit to determine the operating range and limiting phenomena, performance measurements were carried out, presenting promising results with respect to the capabilities of rotors with reduced blade count. For steady and transient operation close to the stability limit, low-pressure spots, indicating disturbances like radial vortices, were detected. Those disturbances vary in count, size, speed and trajectory, depending on rotor configuration, speed line and pre-swirl. In order to determine the aeroelastic behavior, unsteady aerodynamics and non-synchronous blade vibration during stall inception were analyzed. Comparing the rotor configurations results in different stability limits along the compressor map as well as changes in the aeromechanical behavior. Those effects can partially be traced back to the variation in blade pitch and associated aerodynamics within the passage.