CFD Analysis of Aerostatic Bearing for Cryogenic Turbo-Expander

Expansion turbine plays the major role in any cryogenic plants like helium and hydrogen liquefier,air separation plants and low temperature refrigerator.These turbines run at speed around 50,000 to 5,00,000 rpm.At such a high speed no bearing is feasible to support the load except gas bearing.In gas bearing there is no physical contact between stator and rotor takes place so the friction between the stator and rotor is negligible.Because of this the rotor can move smoothly inside the stator.Hence aerostatic bearing used for achieving high accuracy and precession. Due to cleanness of aerostatic bearing it is also used in electronic and food processing industry.In order to avoid complexities at the time of formulation analytical studies has been carried out.Governing variables are kept limited that helps in dynamic and performance conduct of aerostatic bearing.Finally a three dimensional model of aerostatic bearing was built in Solidworks and a two dimensional cross-section model of aerostatic bearing in ANSYS workbench 15. After doing rectangular meshing to the geometry made in workbench Computational fluid dynamics(CFD)analysis was done in ANSYS Fluent. The pressure and velocity distribution at the bearing clearance and at orifice had shown.It is found that there is rapid change in pressure and velocity at the exit of the orifice.Variation of Load carrying capacity with the change of inlet pressure was studied and compared with numerical valu

Gas Bearings: Modelling, Design and Applications

This book focuses on the modelling and the design process of gas bearings, on the experimental validation of such models, and on their applications. In particular, recent developments about foil bearings, aerostatic bearings, porous bearings, and non-contact precision positioning systems are shown

An mechatronics coupling design approach for aerostatic bearing spindles

In this paper, a new design approach for aerostatic bearing spindles (ABS) is firstly proposed which takes into account of the interactions between the mechanical and the servo subsystems, including the integration of electromagnetic effects, static pressure characteristics, servo control and mechanical characteristics. According to the air bearing design principle, the geometry of the spindle rotor is designed. The fluid software is used to analyze the influence of the bearing capacity and stiffness on the stability of the spindle. The simulation shows when the air film thickness is 12 μm, the bearing has good load carrying capacity and rigidity. In addition, the influence of motor harmonics on the spindle shaft modes is considered to avoid the resonance of ABS, and to ensure ABS anti-interference capability, proper inertia of ABS is calculated and analyzed. Finally, ABS has a good follow-up effect on the servo control and machining performance through the experimental prototype. The electromechanical coupling design approach for ABS proposed in this paper, can achieve a peak value better than 0.8 μm (surface size: 9 mm × 9 mm) and a surface roughness better than 8 nm in end face turning experiments

Modelling and Simulation of Aerostatic Thrust Bearings

This paper demonstrates the modelling and simulation comparison of the static characteristics of a porous, orifice, and multiple type aerostatic thrust bearings on the basis of load-carrying capacity(LCC) and stiffness. The equations Navier-Stokes (N-S) are used to solve the internal distribution of pressure in computational fluid dynamics(CFD) simulation environment. An axisymmetric model, which minimizes the computational time and increases efficiency, is used to evaluate the static characteristics of a porous, orifice, and multiple restrictors of aerostatic bearings. Our numerical analysis and empirical results show the agreement with the significant effect of material and geometrical parameters on the LCC and stiffness. The thickness of the air film is less than 10\mu \text{m} , the multiple orifice restrictors have more LCC than porous and orifice restrictor. The porous restrictor's stiffness is larger than orifice and multiple restrictors. The LCC of porous and orifice is notably smaller than multiple orifice restrictors. Additionally, it is analyzed that LCC of porous, orifice, and multiple orifice restrictors can be improved with an increase in the supply of air pressure

Running characteristics of aerodynamic bearing with self-lifting capability at low rotational speed

This article has been made available through the Brunel Open Access Publishing Fund - Copyright @ 2011 Tadeusz Adam Stolarski.An aerodynamic journal bearing that is capable of self-generating squeeze-film pressure is presented and its dynamic characteristics investigated numerically and experimentally. A numerical method based on a time-marching static model was applied to assess the orbit trajectory path of the rotor upon a perturbation. Experimental results were obtained to validate the effect of the self-generated squeeze-film pressure on the stability of the rotor. Analyzing the Fast Fourier Transform (FFT) responses of the rotor orbits enabled identification of self-excited whirling instabilities. Both numerical and experimental results showed that increasing the squeeze-film effect of the bearing could raise the threshold speed of instability

Aerodynamic analysis of compliant journal foil bearings

This thesis provides a detailed study about the aerodynamic analysis of compliant journal foil bearings. In high speed turbomachinery elements, conventional bearings can’t be used since at such a high speed (50000-80000) rpm these bearings get worn and thus they fail. In this project the analysis of a compliant bearing, which has bump foils to enhance the load carrying capacity, has been done. The thin air film between the rotating shaft and the bearing creates the pressure to support the load. Reynolds Equation was first devised for the given compliance system. Due to its nonlinear nature iterative methods are required to solve it. For calculating the pressure distribution and hence the load carrying capacity of the bearings Finite Difference Approximations were used and a unique method, method of quadratic equations was used to find out several parameters. Using MATLAB several codes have been written to find out the pressure profile and the minimum film thickness whose 3 dimensional graphs have been plotted. After the pressure profile has been generated the load carrying capacity has been evaluated for the bearing under the given input parameters. Thereafter several comparisons have been made between the foil and the rigid bearing on the basis of the plots. Finally two different materials, one used for high temperature applications-Inconel X-750 and another used for low temperature applications Aluminium Bronze have been compared to find out their compatibility in different commercial applications based on their load carrying capacity

Design and Shape Optimisation of Nozzles for a Flat Air Bearing Device

This study offers a numerical and experimental study in the design and further shape optimisation of nozzles for a flat type air-bearing device which is supposed to be used for handling a certain magnitude of loads. Making use of pressurised air allows for the design of mechanical systems requiring handling heavy loads or extreme precision in positioning. In a design of flat type air-bearings, particularly when carrying heavy loads is considered, the shape of nozzles becomes very important. In order to analyse and further optimisation of the dimensions of a nozzle in this study, Computational Fluid Dynamic (CFD) analysis with k-ω turbulence modelling has been performed to simulate the supersonic fluid flow behaviour inside the chamber and divergent nozzle of the bearing device. Three different geometries with fixed inlet diameter of 2 mm and outlet diameters of 3, 6 and 12 mm were studied. An experimental investigation was conducted with the same nozzle geometries and also different nozzle numbers (and arrangements) to find the best option with respect to the performance in handling loads. Results from experimental study are in accordance with results of CFD analysis, making the numerical modeling a useful tool for a comparative study in this research to determine the optimum size and shape of nozzles as well as optimum pressure for a particular load

Physical Modeling of Process-Machine-Interactions in Micro Machining

Increasing demands for smaller and smarter devices in a variety of applications requires the investigation of process-machine-interactions in micro manufacturing to ensure process results that guarantee part functionality. One approach is the use of simulation-based physical models. In this contribution, methods for the physical modeling of high-precision air bearing and magnetic bearing spindles are presented in addition to a kinematic model of the micro milling process. Both models are superimposed in order to carry out investigations of the slot bottom surface roughness in micro end milling. The results show that process-machine-interactions in micro manufacturing can be modeled by the superposition of a physical model of the machine tool spindle taking cutting forces into consideration and a purely kinematic model of the machining process, providing the necessary tools for a variety of further investigations into process-machine-interactions in micro manufacturing