Integrated Design and Optimization of Gas Bearing Supported Rotors

Abstract

The design of direct driven turbomachinery is an interdisciplinary task. Standard design procedures propose to split such systems into subcomponents and to design each one individually. This common procedure, however, tends to neglect the interactions between the different components leading to suboptimal solutions. The authors propose an approach based on the integrated philosophy for designing and optimizing gas bearing supported rotors. Based on the choice for herringbone grooved journal and spiral groove thrust bearings, the modeling procedure for predicting their properties and the linking to the rotordynamic behavior of a generic rotor supported on gas lubricated bearings is provided. The global model for gas bearing supported rotors is linked to a multiobjective optimizer for maximizing the dynamic stability and for minimizing the windage losses of the rotor and of the bearings. Two typical rotor layouts have been included in the optimization. The geometry of a proof of concept system, that has been designed previously using the fragmented component view, is represented as a comparison to the proposed integrated approach. It is shown that the integrated solution allows to reduce the windage losses by 25% or to increase the stability margin by 35%, emphasizing the advantage of the proposed integrated design tool.

Design and Optimization of an Innovative Solid Oxide Fuel Cell–Gas Turbine Hybrid Cycle for Small Scale Distributed Generation

“…Schiffmann and Favrat [23,24] has experimentally demonstrated the technical feasibility of a small scale, oil-free, and direct driven turbocompressor for domestic heat pump applications. High rotational speed introduces bearing and rotor dynamic challenges.…”

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

“…The approach here is based on Pan's spectral analysis method [9] extended by Schiffmann and Favrat [7,8]. An important feature of gas-lubricated bearings is that the bearing properties are not only a function of rotor speed but also depend on excitation frequency.…”

“…An important feature of gas-lubricated bearings is that the bearing properties are not only a function of rotor speed but also depend on excitation frequency. Equation (7) yields an eigenvalue problem with eigenvalues (8) where the imaginary part cu, = fi/CORot represents the damped natural frequency of the whirl motion and A, is the corresponding damping coefficient. The approach here is based on Pan's spectral analysis method [9] extended by Schiffmann and Favrat [7,8].…”

“…The maximum bearing DN value is set to 2.7 x 10*. The optimization process is performed by coupling the integrated rotor-bearing system to an evolutionary algorithm [19], which has been successfully used in similar optimization problems [8,16]. Hence, laminar fiow can be considered and the modified Reynolds equation is applicable.…”

“…Hence, providing gas-lubricated bearing technology with reduced windage losses not only yields beneficial effect on overall efficiency but also facilitates the implementation of small-scale turbomachinery with regards to thermal management. Trading off rotordynamic stability and windage losses by using advanced multiobjective optimization tools the bearing diameter of this demonstrator was set to 10 mm, operating at a nominal clearance of 3 ßm [8]. 1 Scaling effect on impeller, motor, and bearing diameters, on rotor speed and on heat fluxes as a function of shaft power a converging fluid film generates a pressure increase yielding load capacity.…”