Numerical investigation of aero-elastic coupling in multi-leaf wave foil type dynamic pressure gas radial bearings

To reveal the fluid structure coupling mechanism of multi-leaf wavy foil type dynamic pressure gas bearings, a coupling analysis method was established for the shear flow and elastic foil combination deformation in the rotating-static multi-wedge channel of this type of bearing. The parameter distribution of the unsteady flow field of the rotating-static gap gas film and the unsteady deformation of the elastic foil combination were numerically studied. The research results confirm that there was a strong aero-elastic coupling effect in dynamic pressure gas bearings of the multi-leaf wave foil type. When multiple wedge-shaped channels were coupled with eccentricity, different elastic foils correspond to multiple discrete high/low pressure zones in the gas film. The high pressure zone was located in the convergence area of the channel, while the low pressure zone was located at the sudden expansion step connected to adjacent foils. The local expansion of flow channels in the high-pressure zone induced flow separation and increases shear flow instability. The fluid-elastic coupling weakened the pulsation amplitude in the high-pressure region of the gas film, and strengthened the pressure pulsation amplitude in the low-pressure region. The 1st and 2nd elastic foils deformed in the direction of the bearing sleeve, while the 4th and 5th elastic foils deformed in the direction of the rotating shaft, which corresponds to the distribution of the high-pressure and low-pressure areas of the rotating-static air film. The low-pressure zone of the static gas film induced separation between the top foil and its adjacent overlapping foil. The influence of rotational speed, eccentricity, clearance scale, and elastic foil stiffness on the fluid-elastic coupling performance of bearings was obtained. The gas film pressure in the fluid domain is positively correlated with the bearing capacity, speed, and eccentricity, while negatively correlated with the clearance scale. High rotational speed and large eccentricity induced an increase in the peak value of the low-pressure region in the gas film. In aero-elastic coupling, there was a certain lag in the vibration frequency of the top foil compared to pressure pulsation. And the amplitude of foil vibration and gas film pressure pulsation in the high-pressure region of the fluid domain were greater than that in the low-pressure region of the fluid domain. The results in this study provide theoretical basis and technical quidance for the design of airborne multi-leaf wave foil dynamic pressure gas.