Session: 22-01 Fan and LPT Flutter

Paper Number: 152836

The INFRa-Rig: Synchronous and Non-Synchronous Vibrations of an UHBR Fan at Clean and Crosswind Conditions 

Due to ecological requirements, the bypass-ratio of future civil turbofan engines will be increased. To counteract the increasing weight and aerodynamic drag of the enlarged ultra-high bypass (UHBR) engines, the intake length will be shortened. This leads to a stronger coupling between intake and rotor blades that can increase the risk of the aeroelastic instabilities and a forcing due to inlet distortions.

The Institute of Jet Propulsion and Turbomachinery (IFAS) build the Integrated Fan Rig Assembly (INFRa) to experimentally investigate fans under variably and highly critical operating conditions. The rig is built in the Propulsion Test Facility (PTF) that allows to set different head and cross wind conditions.

In the presented paper, the blade forcing at different operating conditions and cross wind amplitudes are experimentally investigated. The fan speed is varied between low-speed subsonic to transonic flow at different throttle conditions. The inlet distortions are experimentally determined and blade vibrations are measured with strain gauges on the rotor blade, blade tip timing, and high-speed digital image correlation.  Significant blade vibrations are present at resonance and off-resonance excitation and compared to inlet distortion based on the cross-wind condition.  At off-resonance, in addition to the forced engine order (EO) a significant vibration at mode frequency is observed, which is dependent on the cross-wind amplitude.  Additionally, rotating instabilities are present at throttled fan condition leading to convective non-synchronous vibrations under clean and cross-wind conditions. The results show the importance of considering cross-winds for the aeroelastic assessment of UHBR fans. The INFRa-Rig allows detailed measurements of such critical conditions.

Presenting Author: Jan Goessling Leibniz University Hannover - TFD

Presenting Author Biography: 2015-2018: Student Assistant: Institute of Turbomachinery and Fluid Dynamics Research, Hannover

2017: Internship: German Aerospace Center (DLR), Institute for aerodynamic and flow technology, Göttingen

2018-2019: Student Assistant: Institute of Dynamics and Vibration Research, Hannover

2020-present: Research Assistant: Institute of Turbomachinery and Fluid Dynamics, Hannover

Authors:

Jan Goessling Leibniz University Hannover - TFD
Jonas Grubert TU Braunschweig - IFAS
Patrick Brunow TU Braunschweig - IFAS
Nick Gottschalk TU Braunschweig - IFAS
Maximilian Mennicken Institute of Propulsion Technology, German Aerospace Center (DLR)
Niklas Maroldt Leibniz University Hannover - TFD
Jens Friedrichs TU Braunschweig - IFAS