15th European Conference on Turbomachinery Fluid dynamics & Thermodynamics

Paper ID:


Main Topic:




Katharina Brinkmann - Institute of Dynamics and Vibration Research, Leibniz University Hannover, 30823 Garbsen, Germany
Thomas Hoffmann - Institute of Dynamics and Vibration Research, Leibniz University Hannover, 30823 Garbsen, Germany
Lars Panning-von Scheidt - Institute of Dynamics and Vibration Research, Leibniz University Hannover, 30823 Garbsen, Germany
Heinrich Stüer - Siemens Energy AG, 45473 Mülheim a. d. Ruhr, Germany


Due to the global power generations ongoing need for flexibilization, turbine blades are more frequently subject to transient resonance crossings. In contrast, academic turbine blade measurements often consider only the steady-state behaviour, which can differ notably from transient responses.In this work, the vibration response of a large-scale academic free-standing turbine bladed disk is analysed regarding the effect of transient run-ups and coast-downs. The measurement data is recorded using both strain gauges at each blade root and tip timing, allowing conclusions to be drawn about the vibration mode. With these evaluations, the blades first bending mode (1F) is considered and tested both linearly and with two different types of nonlinear underplatform friction dampers. Both the excitation forces and the speed gradients were varied for each run-up and subsequent coast-down through two different engine orders (EO). The utilized rotation test rig offers the option of performing tests under vacuum conditions, preventing aerodynamic excitation of the turbine blades so that only one dominant synchronous engine order is present at each resonance crossing.An initial comparison of results from these tests with already existing steady-state responses is used to validate the measurement setup and testing sequence after a previous relocation of the test rig. These results show very good agreement in the considered frequency response functions, so that individual blades could be identified by their respective strain responses. Likewise the effects expected from the transient resonance passage, such as ring-down and a frequency shift of the maximum amplitude, were observed.In order to examine these effects and additionally the influence of friction damping by the underplatform dampers on them, the frequency response functions for tests with several speed gradients are evaluated both with and without the dampers. It is shown that this amount of friction damping is able to inhibit any appearance of ring-down, almost regardless of the speed gradient. Intending to further support these results and to be able to evaluate the transient effects more precisely, a minimal model of a multi-mass oscillator with optional frictional contacts has been created and analysed.Throughout all measurements, each individual blade exhibited a slightly dissimilar dynamic behavior, which is due to geometric mistuning. In the case of transient passages, this can lead to an amplitude amplification, the so called TAMS effect, which could be observed during the measurements on individual blades. Since a possible amplification can have a major impact on the operational reliability of a turbine blade, exemplary results were considered regarding this phenomenon. Analogously to the previous analyses, the TAMS effect is prevented by friction damping from the underplatform dampers.

Download it! Paper is available from journal web site