The aerostatic bearing-rotor system plays a critical role in ensuring the stable operation of highspeed, high-precision rotating machinery. Despite its importance, the system is often affected by nonlinear sub-synchronous vibration instabilities, which limit its performance and development. To address this issue, this study proposes a novel tangentially supplied (TS) bearing. Modified gas lubrication Reynolds equations are derived, and a fluid-structure interaction model for the gas bearing-rotor system is established. By predicting gas film thickness distribution, the bearing lubrication equations and rotor motion equations are solved simultaneously. The nonlinear dynamics of the system are analyzed using bifurcation diagrams, rotor center orbits, and frequency spectrum plots, with comparisons to conventional radially supplied (RS) bearing. The results reveal differences in gas film pressure distribution, where the tangentially supplied bearing demonstrates slightly reduced load capacity but significantly suppresses sub-synchronous vibrations. Additionally, it raises both the bifurcation onset speed and the instability threshold speed, thereby improving system stability. Finally, theoretical predictions are validated through speedup and coast-down experiments.

A common issue associated with gas bearing-rotor systems is the tendency to generate self-excited vibrations, leading to instability. To address this problem, the fluid-structure coupling model of an aerostatic bearing-rotor system is established in this paper. Then, a hybrid method combining the finite difference method (FDM) and direct integration method is employed to solve the bearing lubrication equation and rotor motion equation simultaneously. Furthermore, based on the orbits of rotor center, frequency spectrum diagrams, Poincare maps, waterfall diagrams, and bifurcation diagrams, the effects of rotational speed, rotor mass, orifice diameter, and nominal clearance on the nonlinear dynamic behaviors of the bearing-rotor system are investigated. The results indicate that the system exhibits rich nonlinear behaviors with increasing rotational speed and rotor mass, including the occurrence of typical half-speed whirl. However, the nonlinear vibrations of the system can be restricted by selecting appropriate bearing structural parameters, providing theoretical guidance for the design of aerostatic bearing-rotor systems.

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An experimental helium liquefier/refrigerator, using ultra high speed cryogenic turbo-expanders is designed and developed in Technical Institute of Physics and Chemistry (TIPC), and liquefaction rate of around 42 L/hr and refrigeration capacity of around 130 W @ 4.5 K is achieved. The turbo-expander constitutes the most critical component of a helium liquefier/refrigerator causing that the turbine efficiency has a great influence on the performance of the whole cryogenic process plant. Inlet Flow Radial (IFR) turbine design is dictated by criteria like velocity ratios. For small flow rate plants the size of the turbine impeller needs to be reduced. In order to reach a high efficiency, the rotational speed must be increased to complete a large specific enthalpy drop. The present article describes the latest technical developments at TIPC, including results obtained during field trials with the TIPC helium liquefier and refrigerator. The motivation of these developments is to improve the efficiency of the machines, and also to widen the range of operation.

This study delves into the dynamic behavior of ultra-high-speed rotor systems underpinned by helium hydrostatic gas bearings, with a focus on the impact of rotational velocity on system performance. We have formulated an integrative dynamic model that harmonizes the rotor motion equation with the transient Reynolds equation. This model has been meticulously resolved via the Finite Difference Method (FDM) and the Wilson-Θ technique. Our findings unveil intricate nonlinear dynamics, including 2T-periodic and multi-periodic oscillations, and underscore the pivotal role of first-order temporal fluctuations, which account for over 20% of the transient pressure at rotational speeds exceeding 95.0 krpm. Further, we have executed empirical studies to evaluate the system’s performance in practical settings. It is observed that when the ratio of low-frequency to fundamental frequency approaches 0.3 and the amplitude ratio exceeds 3, the vigilant monitoring of system stability and reliability is imperative. Collective insights from both computational simulations and experimental studies have enriched our understanding of the dynamic attributes of ultra-high-speed rotor systems. These revelations are crucial for the advancement of more efficacious and resilient rotor systems designed for high-speed applications.

At present, the world is in the period of developing large cryogenic system, and the power of turbo expander is increasing continuously. There are several limitations in the traditional braking mode, the direct drive high-speed turbo expander generator braking is becoming the trend. Taking a turbo expander with the power of 30 kW and the speed of 100,000 rpm as an example, the electromagnetic design of high-speed permanent magnet synchronous generator is carried out, and the main structural parameters of the generator are obtained. Furthermore, considering the influence of centrifugal force and interference fit pressure, a two-dimensional stress analytical model was established, and the stress distribution of sleeve and permanent magnet are analyzed by theoretical and finite element analysis method. Then the critical speed and modal shape of the rotor were calculated by transfer matrix method, all the critical speed are far away from the rated speed. The results show that the rotor can meet the requirements of the turbo expander generator brake.

High-speed hydrogen turbo-expander is widely employed in hydrogen liquefaction systems due to its high efficiency. The hydrogen bearings in high-speed turbo-expander are usually applied for low viscosity and pollution-free advantages. Nevertheless, the load capacity of hydrogen bearing is low and the research on maximizing the load capacity is limited by the complicated solution process and danger hydrogen experiment. The purpose of the paper is to easily and quickly acquire the load capacity of high-speed orifice externally pressurized hydrogen journal bearing for optimization of bearing performance. A new simple load capacity predicted model, that is universal for various working fluids involving hydrogen, helium and air, was proposed through the hydrostatic and hydrodynamic analysis. In the model, the evaluation indicators of hydrodynamic and hydrostatic effects were proposed. Based on the model, no numerical analysis and computer programming are needed to calculate the load capacity of journal bearing and numerous key design variables are considered. The results from the predicted model agree very well with those obtained from the finite difference method (FDM) technique. In view of the danger of hydrogen bearing experiment, the load capacity predicted model can be used to design the equivalent experiment of load capacity through substituting air for hydrogen working fluid.

In order to make a detailed understanding of the cryogenic turbo-expander off-design performance at cool-down procedure, an extensive experimental and numerical program have been carried out on a mixed and inward flow radial turbine. According to the design and cooling process condition, just like pressure at stator inlet or brake power of the turbo-expander, a series of CFD simulations were carried out in order to guide design and off-design iterations towards achieving a matched flow capacity for each situation. The analyses also include the study of the effect of different gas models on the CFD calculations. Through the results analysis it was concluded that the direct use of the Hepak database for the real gas properties in the CFD solver improve the prediction of the thermodynamic properties and so the performance of the turbo-expander. With experimental comparison, the cryogenic turbo-expander off-design performance at cooling process can be better known.

In order to make direct performance comparisons of varying the vaneless space in high-speed micro turbo machinery, an extensive experimental and numerical program have been carried out on a 22 mm leading-edge diameter mixed and inward flow radial turbine using a variety of stator designs. The stator was designed using commercial design software, having 9 vanes and the radial clearance (vaneless space) between stator and rotor was 0.5 mm single side, that means the ratio of the stator trailing edge radius to the rotor leading edge radius R-te/r(le) is 1.0455. Two additional stators (R-te/r(le) is 1.0182 and 1.0727) were also designed and manufactured. According to the design condition, just like pressure at stator inlet or mass flow rate for all passages, a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each stator. In this way the variations in the measured stage efficiency could be attributed to the stator passages only, thus allowing direct comparisons to be made. The losses for different radial clearances have been quantified and the variations in the measured and computed efficiency were used to recommend optimum values of R-te/r(le).