Development and application of multiphysics simulation tools for foil thrust bearings operating with carbon dioxide

Abstract

Foil bearings can enable different turbomachinery architecture. The use of the cycle's working fluid within the bearings results in an oil-free and compact turbomachinery system. Using CO 2 as the operating fluid for a foil bearing creates new operating and new modelling challenges. These include turbulent flow within the film, non-negligible inertia forces, high windage losses, non-ideal gas behaviour and reduced rotordynamic damping. Since the flow phenomena within foil bearings are complex, involving fluid flow, structural deformation and heat transfer, use of the conventional Reynolds equation is not proven to be suitable for foil bearings with CO 2 as the operating fluid. To address these modelling issues, a multi-physics multi-timescale simulation tool including fluid, structure and thermal solvers was developed to predict the performance of foil bearings and to create insight on their operations with CO 2. New flow physics and operation challenges for foil thrust bearings with

Compressible high-pressure lubrication flows in thrust bearings

“…The boundary conditions for the fluid are (2.4a,b) where v r , v θ and v z are the r-, θ -and z-components of the fluid velocity. We follow the previous investigations of Conboy et al (2012), Conboy (2013), Qin (2017) by requiring that the pressures all have the same value at θ = 0, θ = θ end , r = R i and r = R o . Thermal boundary conditions include the isothermal-wall condition where the surfaces of the rotor and stator have fixed known temperatures, and the adiabatic-wall condition where one of the walls is taken to be adiabatic and another wall has a fixed known temperature.…”

“…Most of these studies evaluated the thermodynamic properties of pressurized gases using digital table lookups. Examples include the NIST REFPROP database (Lemmon, Huber & McLinden 2002) used by Conboy (2013), Kim (2016) and Qin (2017), and the CoolProp database (Bell et al 2014) used by Guenat & Schiffmann (2018). While table lookups can be useful in detailed numerical simulations of specific configurations, it is difficult to identify key physical and thermodynamic parameters governing the flow; the present study identifies these key factors.…”

“…Recently, research has focused on lubrication with pressurized gases, i.e.gases corresponding to pressures and temperatures of the order of that of the thermodynamic critical point. These studies include those of Conboy (2013), Kim (2016), Dousti & Allaire (2016), Qin (2017), Heshmat, Walton & Cordova (2018 and Guenat & Schiffmann (2018) who employed numerical schemes to solve different versions of their Reynolds equation. Most of these studies evaluated the thermodynamic properties of pressurized gases using digital table lookups.…”

Virial Approximation for Load and Loss in High-Speed Journal Bearings Using Pressurized Gases

“…When the pressures are on the order of those of the thermodynamic critical point, the gas can no longer be regarded as ideal, and more complex gas models must be employed. In order to investigate the effects of pressurized gases on bearing performance, previous studies [17][18][19][20] have numerically solved the Reynolds equation along with digital table look-ups to capture the real gas behavior. Conboy [17], Kim [18] and Qin [19] used the NIST REFPROPdatabase [21], while Guenat and Schiffmann [20] employed the COOLPROPdatabase [22].…”