Implementation of vibration and stability evaluation criteria for rotating machineries equipped with active magnetic bearings

Imbalance vibration is the main factor affecting the stability of rotating machineries equipped with active magnetic bearings (AMB). Accordingly, for safe and reliable operation, ISO 14839 standard sets out guidelines for measuring and evaluating the vibration and stability. However, technical approaches to realize fulfillment of the evaluation criteria have never been studied in theory. This paper presents insights of these criteria and proposes effective methods to simultaneously implement these evaluation criteria. Based on imbalance vibration model of AMB-rotor system, the theoretical connections between these evaluation indices are revealed. In order to obtain accurate vibration model of single-input single-output (SISO) AMB-rotor system, modal analysis is carried out and equivalent mass of SISO system is figured out. Afterwards, with the analysis of sensitivity function in theory, new indices of the evaluation criteria are proposed, which helps establish requirements of controller design and rotor balance quality. Finally, through experimental verification on a test rig, the limitations on the evaluation criteria can be negligible, and the proposed methods to simultaneously implement the evaluation criteria are validated.

Uncertainty Analysis for Static Balance Measurement of Hollow Be Rotor

The hollow Be rotor is grinded by the four-shaft-ball lapping machine, it has been repeated grinded to reach the accuracy requirement. The eccentric distance of rotor is measured by gas floating method. Actual measurements found that repeated measurement of the balancing cycle change a little during the rough finish and semi finishing stage while it changes a lot in the finish machining stage. This paper established the rotor balance equation of gas floating that is solved by Matlab software, and draw the curve of motion of the rotor changing along with time, analyze the motion curve to draw a conclusion that the starting conditions of finish machining stage have large influence on balancing cycle.

The Rotor System Balance Design of Scroll Fluid Machinery

The rotor system balance design is always one of the main concerns in scroll fluid machinery dynamics, as it affects the scroll mechanical reliability, safety and life. According to the scroll fluid machinery working principle and structure, combined with the dynamic balance theory, four kinds of balance weight design philosophy were proposed in this paper and verified by a specific example, in which the bearding loads were calculated using four design methods and compared. The results show that the balance design philosophy will have a significant effect on fluid dynamic characteristics. The result is helpful for optimizing the rotor balance design of scroll fluid machinery and improving the mechanical properties.

An Improvement to Holospectrum Based Field Balancing Method by Reselection of Balancing Object

In this paper, the holospectrum technique based balancing method has been improved by reselection of the balancing object. Current holospectrum based balancing technique uses the initial phase vector (IPV) as the balancing object. Theoretical analysis of the precession behavior of an unbalanced rotor with anisotropic stiffness shows that, compared with the IPV, its forward precession component vector is much better in describing the rotor balance state and is more suitable to be used as the measurement of unbalance response. After the backward precession component is removed, the impact of probe orientation on the balancing analysis and calculation is completely eliminated and the computational procedure is greatly simplified without sacrificing the balancing precision. The experiments and field application cases verify the accuracy and effectiveness of this method.

Blade Vibration Phenomena of HPC Bliscs Considering Manufacturing Effects and Strain Gauge Application

Compared to conventional bladed disc assemblies with heavy blade-disc connections, the integrated design (blisc) of modern aero engine compressors results in reduced rotor masses, facilitates higher maximum rotational velocities and improved pressure ratios (increased efficiency factors). Apart from these advantages a number of disadvantages occur. Some of them are for example a very low structural damping and a higher sensitivity to manufacturing- and material tolerances (mistuning). This results in localized vibration modes, higher displacement amplitudes, critical stress levels and reduced high cycle fatigue (HCF) of several blades due to inauspicious aerodynamic excitations. From this, an optimum choice of blades to be instrumented with strain gauges (s/g) is the basis of a convincing vibration monitoring system during rig tests. Based on an extensive measurement campaign and numerical investigations an overview of all major manufacturing effects (blisc milling, rotor tip grinding, welding the single bliscs together, compressor assembly) and also the strain gauge application itself on the vibration behavior of real mistuned bliscs will be presented for a multi-stage high pressure research compressor (HPC) in detail (see Fig. 1). The investigations show, that the original blade mistuning deviations resulting from the initial blisc milling procedure remain until the last manufacturing process of the aero engine and still dominate the blisc forced response behavior during aerodynamic excitation. In contrast to this effect, rotor tip grinding procedures as well as the assembly of the rotor drum only cause an even frequency shift of every blade, which does not significantly change the blisc behavior. Complementary to the influence of manufacturing-caused blade mistuning on the whole rotor balance, the effects of an application of high-temperature strain gauges on HPC-blades will be discussed regarding the modification of the blisc vibration modes. Finally different methods will be introduced aiming at a compensation of the strain gauge induced blade stiffening depending on the blade dimensions to ensure the best possible vibration monitoring results.