Multiple blade shedding in aviation gas turbine engines: FE modeling and characterization

In this paper, we extend our earlier single blade shedding studies by examining the dynamics of multiple blade shedding in a fan disc of an aviation gas turbine engine experimentally using a scaled-down test rig with improved instrumentation and numerically using nonlinear finite element simulations. The newly improved scaled-down rig is designed using dimensional analysis to maintain its dynamic equivalency with a fan disc in a medium size engine. The improved instrumentation includes additional strain gauges, accelerometer, temperature and speed sensors for improved characterisation of the shedding dynamics. High speed photography was also used to capture the time history of the multiply released blades. The shedding experiments were compared with high resolution finite element simulations of a fully bladed fan disc of a realistic gas turbine engine. We took account of blade airfoil, strain rate effects, and multiple contacts between the blades and the containment ring in our finite element simulations. The results of the current investigations reveal that (i) the released multiple blades interact with the trailing blades causing maximum damage to the trailing blades, (ii) large strains develop in the containment ring due to the multiple blade shedding and (iii) the predicted transient response of the finite element simulations of multiple blade interactions are in agreement with the findings of the scaled-down experiments, confirming the validity of our scaled-down test rig as a possible alternative or a compliment to full engine shedding tests.