Effect of Sinusoidal and Non-sinusoidal Periodic Forces on the Stability of Gas Foil Bearing

The effect of unidirectional sinusoidal and non-sinusoidal external periodic forces on the stability of gas foil bearing has been investigated using the nonlinear transient analysis. In the case of sinusoidal forces, the loading is considered to follow a sine wave. In the case of non-sinusoidal forces, the periodic forces are assumed to follow square and triangular wave. The spatial domain and time domain terms of the governing Reynolds equation have been discretized using the finite difference method and the Crank–Nicholson method, respectively. The Reynolds equation and the equation of film thickness have been coupled with the elastic deformation of the bump foil structure as the deformation of the bump foil structure is a function of hydrodynamic pressure. The stability of the bearing has been investigated for different loading frequency ratio and loading amplitude. Trajectories are obtained for different values of journal speed to ascertain if the rotor-bearing system is in the stable, unstable, or in critically stable condition. The effect of loading frequency ratio and loading amplitude on the minimum film thickness is also presented.