Aerodynamic characteristic of small-scale and hyper-rotated plane Couette flow with contracted cross section

Aerodynamic gas bearings, which leverage their hyper-rotational speed and lightweight attributes, have emerged as pivotal components in turbines and compressor turbomachinery. The gas film flow field of aerodynamic gas thrust bearings (AGTBs) is characterized by a small-scale, hyper-rotated plane Couette flow with a contracted cross section. However, the flow dynamics under rotor motion, variable clearance cross sections, and ambient leakage remain unclear. This study investigates the aerodynamic characteristics of plane Couette flow with clearance heights ranging from 30 to 200 μm through numerical simulations and experimental measurements. The key findings reveal that the circumferential contraction and sudden expansion of the gas film channel lead to an alternating distribution of high- and low-pressure zones. A large-scale recirculation zone forms near the backward-facing step owing to flow channel expansion. The hyper-rotated flow is predominantly governed by the interaction between the self-acting pressure difference force and centrifugal force, driven by rotor motion. The pressure difference force induces secondary flow deflection from the inner to outer diameter, whereas the centrifugal force causes fluid inhalation near low-pressure zones and exhalation near high-pressure zones. In addition, the dynamic compression effect of the plane Couette flow correlates positively with the rotational speed and negatively with the clearance height. The centrifugal force, which is amplified by higher rotational speeds, strengthens the secondary flow deflection. The dynamic compression effect diminishes and becomes negligible when the clearance height exceeds 100 μm. An optimal pitch ratio of 0.5 maximizes the dynamic compression effect. This study elucidates the mechanism of a high-speed, small-scale plane Couette flow and offers theoretical insights into AGTB design and optimization.