Gas foil bearings with radial injection: Multi-domain stability analysis and unbalance response

Abstract

Gas Foil Bearings (GFBs) possess significant potential for oil-free and environmentally friendly support of high-speed rotating machinery in a wide range of applications. Advances in GFB design and solid lubricants have significantly improved the capabilities of GFBs, but application in heavier machinery still leaves many technical limitations to be overcome. A possible path is through hybridization with radial gas injection as commonly applied in rigid gas journal bearings. From a modelling perspective, modifications of the well-documented Reynolds Equation have previously been proposed to include injection, but the mass flow itself is difficult to predict. In the literature, this is often described using idealized analytical expressions with carefully defined/calculated/identified correction factors. In the present work, a parameter-map approach is presented where the injection flow is interpolated from a five-dimensional pre-generated map of mass flows calculated using a CFD sub-model for the injector valve. This allows injection to be added into a fully coupled simultaneous GFB simulation framework. Non-controlled hybrid mode simulations are presented for a yet-to-be-built version of an existing industrial scale GFB test rig augmented with an existing injection system. The presented results comprise multi-domain mode shape visualizations, Campbell diagrams, and unbalance responses indicating significant improvements attainable already from the hybrid mode. The addition of actively controlled injection is thus considered feasible and may allow hybrid GFBs to support heavier rotors than permissible using the currently available passive variants.