SEARCH FOR THE ORIGIN OF SUBSONIC FLUTTER ON THE UHBR ECL5 FAN AT PARTIAL SPEED

The aeroelastic stability mechanism occurring in the UltraHigh Bypass Ratio fan ECL5 at 80% of nominal speed is analysedusing results from 3D time-linearised Reynolds-AveragedNavier-Stokes simulations. At the maximal pressure ratio, thesecond mechanical vibration mode at nodal diameter 5 inducesa negative damping coefficient, meaning the fan can possiblyenter into flutter. For other nodal diameters the damping coefficientis positive. The paper explores different classic aeroelasticmechanisms occurring at the second mechanical vibrationmode for different nodal diameters and operating pointsclose to the point of negative damping coefficient. At the end,analysis points out the link between this instability and the interactionbetween the blade and the adjacent blade tip-leakageflow.