Effects of eccentricity and vibration response on high-speed rigid rotor supported by hybrid foil-magnetic bearing

Abstract

A hybrid foil-magnetic bearing (HFMB) consists of an air foil bearing (AFB) and an active magnetic bearing (AMB). The HFMB, inherently proposed as a backup bearing for an AMB, has many advantages, such as good controllability and the ability to exhibit preload sharing with the two types of bearings (i.e., the AFB and AMB) in high-speed turbomachinery. However, because the bearing has a limited clearance, the eccentric position of the rotor affects its stability and the reliability parameters of the AFBs such as the initial preload rub. In this study, a rigid rotor supported by an HFMB was operated at speeds of up to 18 kr/min and was tested using a proportional-derivative control algorithm, in order to reduce the vibration amplitude. In addition, to elucidate the effect of the initial eccentric position of the rotor, the control algorithm was started from the initial position of the rotor (X: from –100 to 100 µm and Y: from –80 to 200 µm) using a constant gain value. When the HFMB was active, the magnetic control force was remarkably effective in reducing the subsynchronous vibration of the rotor supported by the HFMB. Eccentricities of 0.2–0.5 corresponded to appropriate rotor positions for the hybrid bearing, and the corresponding load distribution of the AFB was found to be the optimal one. In addition, the proportional-derivative control gain was not very high. The performance of the bearing could be improved further by controlling the eccentricity. An HFMB was tested experimentally, and it was verified that it is possible to determine the effective load carrying capacity for a specific load distribution of the AFB.

Stability analysis of rigid rotors supported by gas foil bearings coupled with electromagnetic actuators

“…The hybrid bearing assembly in the current investigation is similar to the hybrid bearing developed by Jeong and Lee. 18 The top foil and the bump foil are inserted in between the actuator and rotor. The cross section of the journal at the bearing location along with the co-ordinates is shown in Figure 1.…”

“…17 conducted experiments on hybrid foil magnetic bearing and demonstrated that in the range of 12,000–15,000 r/min, hybrid bearings had better stability for unbalance vibration and aerodynamic instability. Following which Jeong and Lee 18 investigated the effects of eccentricity on the load sharing of hybrid foil magnetic bearing. The analysis showed that for the proper load sharing, the eccentricity ratio has to be kept between 0.3 and 0.5.…”

Performance of the hybryd bearing with air-lubricated foil bearing and active control

“…[ ℎ 3 • ] + [ ℎ 3 • ] = 6 ( ℎ) + 12 (2) Where: U, Vcircumferential and radial velocities of the surface points of the shaft; μ and ρ are the viscosity and density of the fluid accordingly; hradial gap; KX and KZthe turbulence coefficients in the directions of turbulence, namely, in the X-and Z-directions, correspondingly, that determine the effective viscosity when the flow is turbulent considering the Reynolds stress.…”

“…However, with frequent start-up and shutdowns of the machines, the foils of the gas-dynamic foilbearings are subject to increased wear. This problem is solved by combination of a rolling-element bearing and the gasdynamic foil bearing, which allows to separate their work functions and achieve an optimal combination of useful properties of each type of bearings [1][2][3][4][5][6].The inclusion in the design of the hybrid bearing of various control and switching elements allows to control its characteristics [7][8][9]. One of the most important characteristics of the bearing unit is the load capacity [10][11][12].…”

Theoretical investigation of hybrid foil-magnetic bearings on operation mode and load sharing strategy

“…Yang et al [27] presented a theoretical method to calculate the load capacity, dynamic stiffness and damping coefficients of HFMBs under a specified load sharing factor λ with the predetermined operational state. Jeong and Lee [28] tested a rigid rotor supported by HFMBs to elucidate the effect of initial eccentric position on the vibration response of rotor. Jeong et al [29] developed a 225 kW class turbo blower by including hybrid foil-magnetic bearings.…”