Effect of Shape-Memory-Alloy Activation on the Rub-Impact Risk of a Rotor in a Foil Gas Bearing: An Operating-Point Thermo-Elasto-Hydrodynamic Analysis

Heating shape-memory-alloy (SMA) supports can change the stiffness and preload of a foil gas bearing, but the effect on rotor–foil contact is unknown. We examine whether thermal activation of the supports reduces the rub-impact risk of a rotor, and for which inertias and speeds. A steady thermo-elasto-hydrodynamic (TEHD) model gives the gas-film, temperature and foil fields at a prescribed operating point; first-order pressure perturbations give the film stiffness and damping; and a two-degree-of-freedom rotor model with a unilateral clearance-contact law gives the response. At 100 krpm, heating from 24 to 42 °C raises the direct stiffness 4.8-fold and removes clearance contact for equivalent masses of about 1.4–2.6 kg. At the representative mass of 2.54 kg, the peak orbit ratio falls from 2.02 to 0.30 and the contact-active fraction from 0.58 to zero; all 10 201 sampled initial conditions converge to the non-contacting orbit, whereas 92% of them end in sustained contact in the soft state. The subsynchronous energy ratio is negligible in both states below 120 krpm and near zero in the activated state above it. Above about 13.5 kg, the activated state loses linear stability and contact returns, so activation helps only over an intermediate range of rotor inertia.