An Advanced Microturbine System with Water‐Lubricated Bearings

Nakano, Susumu; Kishibe, Tadaharu; Inoue, Tomoaki; Shiraiwa, Hiroyuki

doi:10.1155/2009/718107

Cited by 15 publications

(10 citation statements)

References 6 publications

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“…The performance of micro thrust and journal bearings is important for the overall performance and dynamic behavior of rotating microengines [1][2][3]. For micro thrust bearing applications, recent research has demonstrated that properly designed texture patterns may substantially increase bearing performance.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Stiffness and Damping in Textured Sector Pad Micro Thrust Bearings Using Computational Fluid Dynamics

Papadopoulos

Nikolakopoulos

Kaiktsis

2012

Journal of Engineering for Gas Turbines and Power

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In the present paper, a study of stiffness and damping in sector-pad micro thrust bearings with artificial surface texturing is presented, based on computational fluid dynamics (CFD) simulations. The bearing pads are modeled as consecutive three-dimensional independent microchannels, each consisting of a smooth rotating wall (rotor) and a partially textured stationary wall (stator). CFD simulations are petformed, consisting in the numerical solution of the Navier-Stokes equations for incompressible isothermal flow. The goal of the present study is to characterize the dynamic behavior of favorable designs, identified in previous optimization studies, comprising parallel and convergent thrust bearings with rectangular texture patterns. To this end, a translational degree of freedom (DOF) along the thrust direction and a rotational (tilting) DOF of the rotor are considered. By implementing appropriate small perturbations around the equilibrium (steady-state) position and processing the simulation results, the stiffness and damping coefficients of the bearing are obtained for each DOF. The computed dynamic coefficients of textured thrust bearings are compared to those of conventional (smooth slider) designs. It is found that the dependence of bearing stiffness and damping on geometrical parameters exhibits the same trends for both DOFs. Both stiffness and damping are found to increase with bearing width. In general, increasing the bearing convergence ratio results in iticreased bearing stiffness and decreased damping. Finally, the present results demonstrate that properly textured parallel sliders are characterized by an overall dynamic performance that is superior to that of smooth converging sliders.

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Section: Introductionmentioning

confidence: 99%

Characterization of Stiffness and Damping in Textured Sector Pad Micro Thrust Bearings Using Computational Fluid Dynamics

Papadopoulos

Nikolakopoulos

Kaiktsis

2012

Journal of Engineering for Gas Turbines and Power

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“…Efficient and reliable bearing systems are essential for microrotating machinery, such as micro-motors and micro-turbines [1][2][3]. In micro-thrust bearing applications, liquid lubricants provide increased rotor stability and reduce the probability of solid contact between rotating and stationary parts.…”

Section: Introductionmentioning

confidence: 99%

Geometry Optimization of Textured Three-Dimensional Micro- Thrust Bearings

Papadopoulos

Efstathiou

Nikolakopoulos

et al. 2011

Journal of Tribology

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This paper presents an optimization study of the geometry of three-dimensional microthrust bearings in a wide range of convergence ratios. The optimization goal is the maximization of the bearing load carrying capacity. The bearings are modeled as microchannels, consisting of a smooth moving wall (rotor), and a stationary wall (stator) with partial periodic rectangular texturing. The flow field is calculated from the numerical solution of the Navier-Stokes equations for incompressible isothermal flow; processing of the results yields the bearing load capacity and friction coefficient. The geometry of the textured channel is defined parametrically for several width-to-length ratios. Optimal texturing geometries are obtained by utilizing an optimization tool based on genetic algorithms, which is coupled to the CFD code. Here, the design variables define the bearing geometry and convergence ratio. To minimize the computational cost, a multi-objective approach is proposed, consisting in the simultaneous maximization of the load carrying capacity and minimization of the bearing convergence ratio. The optimal solutions, identified based on the concept of Pareto dominance, are equivalent to those of singleobjective optimization problems for different convergence ratio values. The present results demonstrate that the characteristics of the optimal texturing patterns depend strongly on both the convergence ratio and the width-to-length ratio. Further, the optimal load carrying capacity increases at increasing convergence ratio, up to an optimal value, identified by the optimization procedure. Finally, proper surface texturing provides substantial load carrying capacity even for parallel or slightly diverging bearings. Based on the present results, we propose simple formulas for the design of textured micro-thrust bearings.

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“…Figure 14 shows rotational speed and temperature rises of lubricant water of the combined bearing. (26), where the distribution ratio of lubricant water and the iron loss are assumed to be 0.45 and 0.2 kW which were deduced from the same kind of generator test [7]. As increasing rotational speed at load rejection brings about an increase of journal bearing loss and churning loss, which depend on rotational speed, the temperature of lubricant water on the antiload side of the thrust bearing increases slightly.…”

Section: Comparison Of Simulation and Measured Resultsmentioning

confidence: 99%

“…Bearing losses are calculated by the governing equations of the water film which are composed of a Reynolds equation for the pressure distribution and an energy equation for the temperature distribution of the water film [7]. The generator rotor is supported by two kinds of bearings.…”

Section: Fig 6 Caicuiation Resuits Of Thrust Bearing and Ciiurning Imentioning

confidence: 99%

Load Rejection Tests and Their Dynamic Simulations With a 150 kW Class Microsteam Turbine

Nakano

Tsubouchi

Shiraiwa

et al. 2013

Journal of Engineering for Gas Turbines and Power

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A simulation method for load rejection with a 150 kW class radial inflow steam turhine system was proposed to determine over rotational speed at load rejection. Simulations were carried out for several parameters of valves which are operated in an emergency. In addition, load rejection tests were carried out to confirm the machine reliability and to obtain results for comparison with the simulation results. Simulation results show that operation delay times of the steam release and vacuum break valves greatly affect over rotational speed at load rejection. Load rejection tests were done for generator outputs from 69 kW to 113 kW. Maximum over rotational speed of 54,160 rpm was measured at the generator output of 113 kW. Over rotational speed calculated by the dynamic simulation has relatively good agreement with the result for the operation delay time of 0.21 s. If the operation delay time of the steam release valves are kept as 0.21 s at the load rejection for the rated load of 150kW, the over rotational speed is suppressed within 55,200 rpm which is less than the allowed rotational speed of 56,100 rpm.

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An Advanced Microturbine System with Water‐Lubricated Bearings

Cited by 15 publications

References 6 publications

Characterization of Stiffness and Damping in Textured Sector Pad Micro Thrust Bearings Using Computational Fluid Dynamics

Characterization of Stiffness and Damping in Textured Sector Pad Micro Thrust Bearings Using Computational Fluid Dynamics

Geometry Optimization of Textured Three-Dimensional Micro- Thrust Bearings

Load Rejection Tests and Their Dynamic Simulations With a 150 kW Class Microsteam Turbine

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