An Experimental Investigation on the Dynamic Response Variability of a Turbine Blade With Midspan Dampers

This paper addresses two main subjects. First, a novel test setup is described to experi-mentally study the nonlinear dynamic behavior of a turbine blade coupled with two mid-span dampers (MSDs). To this end, a representative turbine blade and midspan friction dampers are originally designed, and they are assembled to a special test rig which has been previously developed at Politecnico di Torino. Second, the variability of the dynamic response is intensively investigated with a purposely defined loading/unloading strategy. To better understand the inherent kinematics of the blade–damper interaction, contact forces are measured through the novel design of the experimental campaign. It is shown that multiple responses, which are obtained in different tests while keeping all user-controlled inputs nominally same, are due to nonunique contact forces that provide different static force equilibria on the damper. This outcome is further supported by the qualitative illustration of hysteresis cycles. This study contributes to the understanding of the response repeatability linked to the nonuniqueness of friction forces.