Abstract
With foil bearings, rotors achieve high rotational speeds with less friction and wear. In addition, here the required space is small and no peripheral components like liquid tanks or pumps are needed. The drawback is a more complex prediction of the real behavior in rotordynamic systems. Impedance test rigs are suitable for investigating the structural-dynamic bearing properties and for validating the theoretical models. This article presents and discusses the measurement of dynamic behavior, i.e., stiffness and damping coefficients, of the structure of a leaf type bearing with undersprings. These measurements include variations in static load due to the relative displacement of the bearing and shaft as well as an attempt to explain the noticed anisotropic behavior of the bearing. This article also shows how much a controlled excitation improves the comparability across the frequency band. For this purpose, a test rig is presented that has been further developed in comparison to known literature approaches. The results show, that the loss factors of the examined bearing structure are up to 4 times bigger below lift-off compared to the operation at 60,000 rpm. Furthermore, the movement amplitudes and the static loads have a great influence on the stiffness and the damping.
Highlights
Aerodynamic foil bearings are increasingly becoming the focus of mobile applications.Drives with fuel cells require high-speed compressors for the intake air
This paper presents and discusses stiffness and damping coefficients of a leaf-type bearing structure with undersprings
The test rig developed and used for our investigations is limited to the essentials: A compact and non-rotating journal mounted on a vibration isolated table (Figure 1)
Summary
Aerodynamic foil bearings are increasingly becoming the focus of mobile applications.Drives with fuel cells require high-speed compressors for the intake air. There is no need of fluids and additional devices like oil pumps or tanks. This results in low weights and low costs. One concept is the (multi) leaf type bearing, initially developed by Garrett Corporation (USA) [4]. It consists of circular arranged foils, each one bracing direct neighbors. To improve the load-bearing capacity researchers like Heshmat [5], Arakere [6], Silver and Wenban [7], Du et al [8] or Duan et al [9] increased the foil stiffness by adding a backing structure below the “leafs”. The design varies from nearly undeformed foils [7] to bumps [9] or jagged stripes [5,8]
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