Experimental Nonlinear Vibration Analysis of a Shrouded Bladed Disk Model on a Rotating Test Rig
The optimization of the mechanical design process of turbomachinery has already been subject of research for decades. In this context, many researchers developed efficient numerical methods to calculate the vibration response of bladed disks. In particula
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Experimental Nonlinear Vibration Analysis of a Shrouded Bladed Disk Model on a Rotating Test Rig Ferhat Kaptan, Lars Panning-von Scheidt, and Jörg Wallaschek
Abstract The optimization of the mechanical design process of turbomachinery has already been subject of research for decades. In this context, many researchers developed efficient numerical methods to calculate the vibration response of bladed disks. In particular, shrouded bladed disks with frictional contacts present a major challenge in the design process. Beside efficient simulations, the validation process plays an important role in most recent studies. The quality of the comparison depends directly on the system’s boundary conditions in the simulation as well as in the experiment. For instance, the estimation of the excitation forces should be as precise as possible, because the vibration response, in particular in the nonlinear case, depends strongly on the excitation forces. In this paper, a newly developed rotating test rig for bladed disks is introduced. The test rig consists of a rotating shaft mounted in a vacuum chamber, in order to avoid any aerodynamic loadings and damping, and an excitation with multiple permanent magnets. Here, a large number of permanent magnets is applied to approximate a continuous force distribution along the circumference. To estimate the overall force distribution, magnetic field simulations are performed and compared to the measurements with a very good agreement. Compared to other excitation methods such as a single ac-magnet or air jet excitation, the presented method manages a high energy input at a specific engine order or frequency with modest complexity. The nonlinear vibration response is measured by strain gauges for various numbers of magnets and excitation force amplitudes. The presented results are characterized by an excellent repeatability and precise measurements of resonance passages. Especially, the nonlinear behavior of the structure such as rotational speed and excitation force dependent resonance amplitudes and frequencies as well as jumping phenomena can be shown. The developed rotating test rig proves to be particularly suitable for the vibration analysis of rotating bladed disks considering nonlinearities. Keywords Nonlinear dynamics · Bladed disk · Shroud contact · Rotating test rig
21.1 Introduction During operation of turbomachinery, the streaming unsteady airflow causes dynamic excitation of the rotating turbine blades. Actually, the airflow is a chaotic distributed dynamic pressure field. Due to a certain number of preconnected guide vanes or other parts in the flow channel, the pressure field contains periodic components leading to a stationary harmonic excitation of the rotating system. To avoid High Cycle Fatigue (HCF) failure, a good prediction of the vibration response at the operating range of the system is necessary. Friction damping, e.g. through underplatform dampers or tip shrouds, is commonly used to reduce the vibration amplitudes by energy dissipation. The design process of fri
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