Eddy Current Damping: A Concept Study for Steam Turbine Blading

Abstract

In gas and steam turbine applications a common approach to prevent the blades from high cycle fatigue failures due to high vibration amplitudes is the usage of friction damping elements. Besides the intended amplitude reduction this procedure also features some possibly unwanted side effects like a shift in resonance frequencies due to stiffening effects caused by the contact. Thus, as an alternative an eddy current based noncontacting damping concept for the application in turbomachinery is investigated. In this paper two different types of eddy current dampers are considered. Theoretical models for both are established by applying electromagnetic-mechanical theory. The theoretical models are compared with forced response measurements that are performed at a stationary test rig.

Eddy Current Damper for Turbine Blading: Electromagnetic Finite Element Analysis and Measurement Results

“…Magnetic fiux density of a cylindrical permanent magnet (length L, radius r^^g, magnetization MQ) in cylindrical coordinates, coordinate systems' origin coinciding with the magnets center (see Ref. [18] for details) Mechanical Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.…”

“…[18], an analytical model of the damping device was already presented. However, for the sake of completeness and to allow referencing to those equations, the model shall be summarized briefly.…”

“…[18], an eddy current based damping device for last stage steam turbine blades was presented. In this noncontacting approach, permanent magnets and copper plates are embedded into the blades facing each other between adjacent blades (see Fig.…”

“…[18] is restricted to some assumptions regarding geometry and boundary conditions, in this paper, an extended analysis of the eddy current damper is conducted. A transient electromagnetic finite element analysis of the eddy current damping device is performed, and the resulting damping forces are compared to their analytical solution.…”

“…Forced response measurements and simulations of the test rig presented in Ref. [18] are used to demonstrate its dynamic performance and predictability.…”