Self-Excited Blade Vibration Experimentally Investigated in Transonic Compressors: Rotating Instabilities and Flutter

Abstract

This paper investigates the vibrations that occurred on the blisk rotor of a 1.5-stage transonic research compressor designed for aerodynamic performance validation and tested in various configurations at Technische Universität Darmstadt. During the experimental test campaign self-excited blade vibrations were found near the aerodynamic stability limit of the compressor. The vibration was identified as flutter of the first torsion mode and occurred at design speed as well as in the part-speed region. Numerical investigations of the flutter event at design speed confirmed negative aerodynamic damping for the first torsion mode, but showed a strong dependency of aerodynamic damping on blade tip clearance. In order to experimentally validate the relation between blade tip clearance and aerodynamic damping, the compressor tests were repeated with enlarged blade tip clearance for which stability of the torsion mode was predicted. During this second experimental campaign, strong vibrations of a different mode limited compressor operation. An investigation of this second type of vibration found rotating instabilities to be the source of the vibration. The rotating instabilities first occur as an aerodynamic phenomenon and then develop into self-excited vibration of critical amplitude. In a third experimental campaign, the same compressor was tested with reference blade tip clearance and a non-axisymmetric casing treatment. Performance evaluation of this configuration repeatedly showed a significant gain in operating range and pressure ratio. The gain in operating range means that the casing treatment successfully suppresses the previously encountered flutter onset. The aeroelastic potential of the non-axisymmetric casing treatment is validated by means of the unsteady compressor data. By giving a description of all of above configurations and the corresponding vibratory behavior, this paper contains a comprehensive summary of the different types of blade vibration encountered with a single transonic compressor rotor. By investigating the mechanisms behind the vibrations, this paper contributes to the understanding of flow induced blade vibration. It also gives evidence to the dominant role of the tip clearance vortex in the fluid-structure-interaction of tip critical transonic compressors. The aeroelastic evaluation of the non-axisymmetric casing treatment is beneficial for the design of next generation casing treatments for vibration control.

Influence of blade vibration on part-span rotating stall

“…This type of interaction has been reported in recent experimental and computational investigations such as Kielb et al (2003), Dodds (2016) and Holzinger et al (2016). As blades in multi-stage compressors become more loaded, the occurrence of such events is expected to be frequent.…”

Influence of Gap Detailing on Calculated Unsteady Non-Adjacent Blade Row Aero-Forcing in a Transonic Compressor Stage

“…1. The geometry as commissioned in the FUTURE project was designed to encounter flutter in the operating range, and non-synchronous excitations were observed [2]. The here presented focus is on the encountered resonance crossing of the first rotor torsion mode (1T) in the operating range of the compressor.…”

The impact of circumferential casing grooves on rotating instability in a transonic axial compressor

“…Their study suggests that the RIs are due to synchronized tip clearance vortex oscillation across the blade passages. Holzinger et al 12 conducted experimental investigations on a 1.5-stage transonic research compressor. They found that RIs occur as the tip clearance is enlarged, and then develop into self-excited vibration of critical amplitude.…”