Numerical and Experimental Damping Assessment of a Thin-Walled Friction Damper in the Rotating Setup With High Pressure Turbine Blades

Abstract

Underplatform friction dampers are possible solutions for minimizing vibrations of rotating turbine blades. Solid dampers, characterized by their compact dimensions, are frequently used in real applications and often appear in patents in different forms. A different type of the friction damper is a thin-walled structure, which has larger dimensions and smaller contact stresses on a wider contact area in relation to the solid damper. The damping performance of a thin-walled damper, mounted under the platforms of two rotating, freestanding high pressure turbine blades, is investigated numerically and experimentally in this paper. The tangential and normal contact stiffness that are crucial parameters in optimal design of any friction damper are determined from three-dimensional finite element computations of the contact behavior of the damper on the platform including friction and centrifugal effects. The computed contact stiffness values are applied to nonlinear dynamic simulations of the analyzed blades coupled by the friction damper of a specified mass. These numerical analyses are performed in the modal frequency domain, which is based on the harmonic balance method for the complex linearization of friction forces. The numerical dynamic results are in good agreement with the measured data of the real mistuned system. In the analyzed excitation range, the numerical performance curve of the thin-walled damper is obtained within the scatter band of the experimental results. For the known friction coefficients and available finite element and harmonic balance tools, the described numerical process confirms its usability in the design process of turbine blades with underplatform dampers.

A novel test rig to investigate under-platform damper dynamics

“…The pressure distribution on conforming contact surface was deduced by tables and graphs given in [32]. The blade is inserted in an adapter (14) in which a bucket groove was machined to match the blade root geometry. The blade adapter is pushed against the shoulders on the central block.…”

“…Dampers are loaded in a more realistic way when tests are performed with a rotating disks. In this regard, in [14] an experimental and numerical study was carried out on a thin-walled damper in a rotating disk with blades excited with piezoelectric actuators. The test rig described in [15,16] was used to measure the effect of wedge shaped dampers on the dynamic response of a simple bladed disk.…”

Measuring the performance of underplatform dampers for turbine blades by rotating laser Doppler Vibrometer

“…An important step has been made in [13], where the damping of thin-walled underplatform dampers is measured experimentally by using a rotating rig, where the test structure included two pairs of turbine blades mounted symmetrically on the disk and the excitation was produced by using piezoelectric devices connected to the blades. In order to test the effect of underplatform dampers on a full 3601 bladed disk, a static rig [14] has been designed where the bladed disk is excited by a rotating travelling wave excitation generated by a set of non-contact electromagnets and measured using a Scanning Laser Doppler Vibrometer (SLDV).…”

Gas Turbine Blade Damper Optimization Methodology

“…The latest and most advanced contact models make use of three parameters to characterize the contact behavior, namely, friction coefficient, tangential contact stiffness and normal contact stiffness [11][12][13]. Szwedowicz et al [13] investigated numerically and experimentally the performance of a thin-walled damper mounted under the platform of two rotating free-standing high-pressure turbine blades. Characterization of friction contact of nonspherical contact geometries obeying the Coulomb friction law with constant friction coefficient and constant normal load is proposed by [14].…”