Changlin Li

Bump foil gas bearings (BFGBs) play an important role in high-speed turbomachinery. However, most studies on the dynamic characteristics of BFGBs focus on a one-pad structure composed of a bump foil and a top foil. This paper considers the multi-pad foil structure in BFGBs by developing the finite element model of bump and top foils and introducing nonlinear contact constraints between bearing components. In addition, a transient dynamic model of a rotor and multi-pad bump foil gas bearing (MP-BFGB) system is established through sufficient considerations of coupling effects among rotor, gas film, and foil structures. Nonlinear rotor dynamic responses, including stability and vibration characteristics, are obtained through integrating the transient state variables in the time domain. The results show that the rotor stability can be enhanced by increasing the number of top foil pads, which, however, tends to reduce the bearing load capacity and gas film stiffness. In addition, rotor sub-synchronous vibrations are more prone to appear under greater gas film stiffness.

Gas foil bearings have important and wide applications in high-speed turbomachinery, generating low frictional lubricating gas film in series with underlying elastic foil structures to support the rotor system. Their dynamic performance is of vital significance in maintaining the rotor stability as well as in depressing rotor vibrations. This paper conducts a comprehensive review on dynamic performance studies conducted on gas foil bearings, including research on the dynamic stiffness and damping coefficients, bearing stability, nonlinear vibrations of the rotor–bearing system, and active methods for controlling rotor dynamic motions. This review provides clear observations towards the developments and iterations of the models, methods, and experiments of these studies.

Traditional bump foil bearing, though widely used, is considered to have the problem of inadequate load capacity due to the effect of foil sag between adjacent bumps. In this paper, the thick top foil is applied to cope with the heavy load conditions, which has one order of magnitude larger top foil thickness than traditional top foil. Thick plate and curve shell models are developed to calculate the load-carrying performance of thick top foil bearing based on contact mechanics, and the sag ratio is introduced to describe the degree of foil sag and estimate the bearing load capacity. The impacts of top foil thickness on the stiffness of bearings in different sizes as well as on the adaptability to rotor tilt are discussed. The results indicate that the thick top foil (tt = 2 mm) bearing performs a nearly 100% enhanced load capacity at small gas film thickness whether rotor tilts or not. Thick top foil will increase the bearing stiffness of small size (d = 35 mm) and tends to have little influence on large-size bearing stiffness (d = 70 mm).

Understanding the responses of tribosystems to multiscale roughness is fundamental for the identification of the relevant roughness scales. This work used a point-contact elastohydrodynamic lubrication (EHL) problem as a representative tribosystem and artificially generated waviness with different amplitudes, frequencies, and directions to mimic the multiscale roughness. The amplitudes and frequencies are related to the feature geometry of smooth EHL problems. This work consists of Part I (this paper), focusing on the full-film condition, and Part II, focusing on the partial-film condition. Generated waviness is input to a transient thermal EHL model. The simulation is conducted 1600 times for different waviness parameters, loads, and speeds. Seven performance parameters are extracted: the minimum film thickness, maximum pressure, central film thickness, central pressure, mean film thickness, coefficient of friction (COF), and maximum temperature rise. The ratios of these parameters with and without waviness are plotted on the frequency–amplitude coordinate plane as contour maps. The influences of the amplitude, frequency, wave direction, load, and speed on the seven performance parameters are analyzed and summarized. The simulated data and plotted contour maps are provided to the readers in the Supplementary Material.

This paper presents a detailed three-dimensional (3D) thermo-elastic-hydrodynamic (TEHD) multi-physics model of the bump-type gas foil thrust bearing based on computational fluid dynamics (CFD). In this model, the moving mesh technology is applied in the fluid flow domain, and the new boundary condition of fully developed flow is applied at the inlet and outlet boundaries, which is consistent with the continuous property of fluid flow and has better convergence performance in CFD. The groove between pads is set as the symmetry boundary. The contact pairs with Coulomb friction and contact/separation behaviors are considered in the structure deformation and heat transfer. The simulation results indicated that the boundary pressure has a significant influence on the foil deformation. It also revealed the heat flux transfer path and temperature distribution in the gas foil thrust-bearing (GFTB) system.

The multilayer gas foil thrust bearing (MLFTB) has four layers of foil structures with each having unique configuration and function. In this article, an updated complete model of the overlapped foil layers of MLFTB is established to calculate more accurate foil deformations and bearing performance by considering sufficient possibilities of separations between adjacent foil layers. The accuracy of the model is validated through the load capacity tests of MLFTB, which is presented for the first time in open publications. Based on the complete model, influences of individual and combined key foil structural factors on bearing load-carrying performance and top foil deformations are studied, revealing the function mechanism of each foil layer and obtaining the method of adjusting two-dimensional stiffness distributions. Furthermore, parametric optimizations toward improving the load capacity of this type of foil thrust bearing are conducted based on a developed algorithm. This study provides sufficient theoretical knowledge and designing methods for further investigations of MLFTB.

Multi-leaf journal foil bearing (MLJFB) is well known for its applications in the air cycle machines (ACMs) of airplanes. However, its frictional energy dissipation mechanism of overlapped foils has not been theoretically studied and is still not clear to researchers. This paper models the frictional sliding/sticking behaviors between adjacent foil leaves based on the tangent gap, applying the penalty method of contact mechanics. Large foil deformations are calculated to simulate the processes of foil assembly and rotor insertion using nonlinear curve beam elements. Predictions of the frictional hysteresis characteristics of MLJFB are obtained, influenced by foil boundary conditions, leaf number, bearing radial clearance and other foil structural parameters, which correlate well with the test results. This study lays solid theoretical foundations for the static and dynamic research of MLJFB.