Thermohydrodynamic Analysis of a Controllable Stiffness Foil Bearing with Shape Memory Alloy Springs: Experimental Tests and Theoretical Predictions

Shape memory alloy (SMA)-gas foil bearings (SMA-GFBs) are novel gas bearings comprising top foil, SMA springs, and housing. The radial clearance, stiffness, and damping coefficients of SMA-GFBs can be regulated by the bearing temperature which is determined by the electric heating of SMA springs and the cooling flow. A 3D thermohydrodynamic model (THD) considering the conduction and convection of the top foil, bearing housing, and hollow rotor, and the heat energy of heated SMA springs is presented to simulate the temperature distribution of SMA-GFBs at different rotational speeds, heating powers, and cooling flows. Centrifugal growth of the rotor and thermal expansions of the rotor, SMA springs, and bearing housing are also considered. A test rig is built to measure the bearing temperature and to validate the effectiveness of the theoretical model and circumferential cooling mode. Parametric studies are conducted with different speeds, heating powers, and cooling flows. The heat transfer ratios of the rotor and substructure are also compared. Compared to the temperature differences of the bearing temperature in the circumferential or axial directions, the effects of rotational speed and cooling flow on the bearing temperature are more apparent. The phase transition process of SMA spring can be controlled by adjusting the rotor speed and the cooling flow reasonably, and then the temperature characteristics of SMA-GFB can be changed. The temperature depending on the compressed gas film and heated SMA springs and cooling flow can be adjusted to confirm the feasibility of actively altering the performance of the bearing-rotor system.