Experimental and Numerical Analysis of Rotational Speed Influence on the Nonlinear Dynamics of Turbine Blades with Shroud Coupling

The structural mechanical properties of blades in turbomachinery depend on the operating speed. In addition to effects such as stress stiffening and spin softening, the rotational speed influences the nonlinear contact properties in shroud-coupled turbine blades. A change in operating point consequently leads to changes in natural frequencies, vibration modes and effective damping. For the design of new turbine blades, the correct modeling of all combined speed-variable properties is necessary to protect the blades against high cycle fatigue failures at any operating point. A nonlinear computational model with a variable-speed formulation of the structural properties is developed and the dynamics of a medium-pressure turbine blading with shroud coupling is analyzed at several operating points. In a rotational test rig, the disk and blade assembly is excited with higher-harmonic excitation force components at different rotational speeds. The comparison of the amplitude responses shows the influence of the rotational speed on the damping and the resonant frequency and confirms the validity of the developed computational model. Copyright ©2024 Florian Jäger, Lars Panning-von Scheidt and Jörg Wallaschek.