Underplatform dampers (UPD) are commonly used in aircraft engines to mitigate the risk of high-cycle fatigue
failure of turbine blades. The energy dissipated at the friction contact interface of the damper reduces the vibration
amplitude significantly, and the couplings of the blades can also lead to significant shifts of the resonance frequencies
of the bladed disk. The highly nonlinear behaviour of bladed disks constrained by UPDs requires an advanced
modelling approach to ensure that the correct damper geometry is selected during the design of the turbine, and that
no unexpected resonance frequencies and amplitudes will occur in operation. Approaches based on an explicit model
of the damper in combination with multi-harmonic balance solvers have emerged as a promising way to predict the
nonlinear behaviour of UPDs correctly, however rigorous experimental validations are required before approaches of
this type can be used with confidence.
In this study, a nonlinear analysis based on an updated explicit damper model having different levels of detail is
performed, and the results are evaluated against a newly-developed UPD test rig. Detailed linear finite element models
are used as input for the nonlinear analysis, allowing the inclusion of damper flexibility and inertia effects. The nonlinear
friction interface between the blades and the damper is described with a dense grid of 3D friction contact elements
which allow accurate capturing of the underlying nonlinear mechanism that drives the global nonlinear behaviour. The
introduced explicit damper model showed a great dependence on the correct contact pressure distribution. The use of
an accurate, measurement based, distribution, better matched the nonlinear dynamic behaviour of the test rig. Good
agreement with the measured frequency response data could only be reached when the zero harmonic term (constant
term) was included in the multi-harmonic expansion of the nonlinear problem, highlighting its importance when the
contact interface experiences large normal load variation. The resulting numerical damper kinematics with strong
translational and rotational motion, and the global blades frequency response were fully validated experimentally,
showing the accuracy of the suggested high detailed explicit UPD modelling approach.