Abstract

In the more aggressive architectures of future high-bypass aero engines, outlet guide vanes (OGVs) will be deployed even closer to the fan. Under certain circumstances this can lead to OGV buffeting. Buffeting is an aeroelastic instability, characterized as the structural response to aerodynamic excitations caused by self-sustaining flow instabilities. Buffeting of OGVs can cause structural fatigue within the low pressure system. This study aims to identify indications of buffet on an engine’s operating map, before assessing how the flow field interacts with the relevant vibrational mode. Steady simulations of the whole low pressure system were used to produce characteristics for three fan speeds and the operating points suspected of buffet were then subject to time-accurate simulations. The steady simulations were used to detect buffet symptoms and examine the change in shock formation, separation patterns and simulation residuals with changing conditions. The time-accurate CFD predicted the highest excitation of the first bow mode at the engine speed where high vibration levels were detected during static off-design engine tests. Time-averaged results of the time-accurate simulations were used to look for trends linking buffeting behaviour with aerodynamic parameters. The time-accurate data also gave indications of a transonic buffet phenomenon.

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